Scanning protocol optimisation for dual-energy computed tomography angiography (DECTA) in peripheral artery stenting

 

 

 

 

 

 

 

 

 

 

Literature Review

Factors Affecting Radiation Dose and Image Quality

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 LITERATURE REVIEW: FACTORS AFFECTING RADIATION DOSE AND IMAGE QUALITY  

Introduction

The literature review section is intended to provide a basis and background to understanding the subject matter in a given study. In the case of this study, the literature review brings out an understanding of the image quality and the radiation dose of the Multi detector Computed Tomography Angiography (Here in referred to as MDCTA) in peripheral arteries. The same is compared to dual energy Computed Tomography (CT) angiography. During the literature analysis, factors affecting the radiation dose and the image quality will be identified from the literature and applied to propose a new dose saving peripheral DECTA protocol for stent imaging.

   MDCTA is a modern platform which allows quality spatial resolution. As opined by Bae and Heiken [1], the platform is essential in ensuring high quality and non-invasively image. Before engaging in a thorough analysis of these devices, it will be appropriate to first provide a genesis of radiology and radiography development as far as image and radiation exposure is concerned.

General Overview

In the past, peripheral artery and occlusions were treated with angioplasty in different parts of the human anatomy. Stent implantation was also used in the treatment of arterial stenoses. However, this kind of treatment requires a constant follow up of examinations due to potential risk of in-stent restenosis. According to Soto, Munera and Morales[2], three possible threats are eminent. For instance, they assert that apart from arterial wall inflammation, stent thrombosis is set to occur after such treatment. In addition, neointimal proliferation effect is bound to take place after stent implantation.[3]

In the current clinical practice, there is an emergency of new devices to avert and reduce possible threats during peripheral treatment. Imaging devices like Digital Subtraction Angiography (DSA) have been introduced. However, the imaging device is faced with the challenge of invasiveness calling for avenues to explore less invasive device. In the long run, devices like dual energy CT, Computed Tomography Angiography (CTA) and CT scanners equipped with 64-slice has been devised.[4]

These devices use noninvasive ability to analyze peripheral arteries and clear image acquisition with more slices in the shortest possible time. However, these devices have several effects ranging from the image quality and radiation exposure from the x-rays beam. In the same note, the effects are also associated with the tube voltage, tube current and finally the pitch also referred to as table speed. These three aspects contribute heavily on the radiation dose during any peripheral procedure[5]

Image Quality and Radiation Dose in Peripheral Arteries

In terms of image quality, Lin, Huynh and Kougias[6] opine that the use of MDCTA has become a desirable component in not only among the physicians but also the patients. As such, they argue that desirable characteristics like speed and spatial resolution are achieved. In addition, the scholars have also contended that MDCTA has enabled wider volume coverage. Isotropic information can also be acquired using this component. For instance, a three dimensional (3D) is possible in addition to other post-analysis methods like arterial image display.[7]

As far as image quality is concerned, Yanaga and Awai[8] contend that MDCTA is the first priority in assessing and analyzing the aorta. Thus, the MDCTA has a greater advantage since the CT angiography CTA is non-invasive which means that the anticipated complications are minimal. In addition to the detailed image that the CTA offers, the authors also assert that the technique has shortened the number of examinations times.

In the view of expertise in the field of medicine, technical parameters and optimization are taken into account before administering a MDCTA to a patient. As opined by Rubin and Schmidt[9], the considerations include the type of scanner used. In this case, they argue that MDCTA encompasses volumetric data set as opposed to one way detector device which produced single set of data. A single set of data had greater complications on the patient. In addition, the physicians had a challenge in deducing the kind of image due to quality problems. As aforementioned, the MDCTA has multiple detectors which ensure greater volume coverage in one breath hold. [10],[11]

In the peripheral artery, Rubin and Schmidt contend that a contrast bolus is responsible for the shaping of the MDCTA. For this reason, the contrast bolus is affected by various phenomena. According to these authors, the rate and the time taken for the injection is a determinant factor in the contrast bolus. In the same context, the authors also assert that the type and the concentration of the contrast determine the shaping of the MDCTA.

The shape is known to depict the time taken for the contrast to reach the peripheral artery. For image quality acquisition, at least 250 Hounsfield units HU) is required[12]. According to Utsunomiya, Awai and Tamura[13], two methods are used to determine contrast arrival time. A bolus tracing software is used to trigger the CTA device once attenuation of a needed location is achieved. The second method encompasses 10 to 15 mL when the MDCTA is used at higher rate.

Different substances behave differently at different energies. The behavior is very important since it provides different information about the substance. In this regard, a device known as dual-energy CT gives all the information about the substance subjected to different set of energies. In another words, the device has the ability to provide unenhanced datasets which have low energy.

Radiation dose

Due to the health hazard associated with radiation exposures, stakeholders are ever looking for means and ways to ensure the levels are at all time low. One way of minimizing the said levels of exposure involves the adoption of precautionary measures.[14] Radiologists are encouraged to make use of such techniques as the iterative reconstruction of CT images.[15] The said process suppresses the noise emanating from imaging which in turn reduces the exposure to radiation due to imaging.

A study was once conducted to make a comparison of the image characteristics alongside the effective organ dose of a female breast. The same was with regard to the pulmonary multi-detector CT angiography.[16] In this process, the specialists were to make use of two techniques. One was the standard filtered back projection technique (herein referred to as FBP). The other technique to be applied in this process is the aforementioned iterative reconstruction in image space (herein referred to as IRIS). To the best of their knowledge, the researchers of this study are of the opinion that a similar comparative study is yet to be carried out hence their involvement.

The study involved only females between the ages of 18 and 17 who numbered 150.[17] Most of the women involved in the study were suspected to have pulmonary embolism. The scans carried out on the sample group were reconstructed using the standard FBP. The process was followed up by a reconstruction upgrade using IRIS.[18] In both cases it is necessary to have a standard figure of the patient’s body mass index (herein referred to as BMI). In the case of the group that required FBP, the BMI is recorded as 25.3. The IRIS group had a BMI of 27.9. A comparison of the two revels that the difference was almost negligible.[19]

The respective scans were performed on an MDCT scanner of a single source. The span of the scan’s coverage included the regions of the lung apex extending to the posterior costophrenic recesses.[20] The importance of the parameters used in the process should not escape attention. The tube voltage during the process was at 100kV.

Authors like Diehm, Pena and Benenati, [21] opine that the radiation dose is in variant with different procedures used. On the same vein, they assert that in a single procedure, there are different tenfold procedures amounting to different radiation dose. As such, the scholars are of the opinion that the knowledge of radiation dose is paramount for the cardiologist especially when carrying out an invasive process. Studies carried out to show effects of radiation exposure reveal that on a dose- area product (DAP), stochastic risks are eminent.[22] An analysis was carried out on the same where peripheral arteries procedures were conducted to validate the DAP as well as the potential risks of malignancy.

During peripheral artery catheterization, the aforementioned analysis realized that among the sample used in the study, the radiation exposure varied exponentially. The DAP meter was attached on the radiation device to try and come up with an estimation of the dose exposed to the patients during the peripheral catheterization.[23] From this analysis, the paper sought to review on the factors affecting radiation dose and image quality.

Factors Affecting Radiation Dose and Image Quality

Before a review of factors affecting radiation dose and image quality is tackled, it important to firstly define the terms radiation dose as well as radiation exposure.  According to Raman and Napel[24] , radiation exposure is term used to describe the amount of air being released by the X-ray beam. As such, the rays are exposed to a procedural area known as dose area product DAP as aforementioned elsewhere in this study.

On the other hand, radiation dose as defined by Raman and Napel[25] is associated with the part being examined by the physician.  As such, a radiation dose can be measured by depicting the amount of radiation rays falling on the part being examined. Therefore, radiation energy is a term related to human body. From these definitions, the study can freely embark on the factors affecting the radiation dose as well as its image quality.

Scholars in the field of medicine have contended that radiation dose is a process that must be as effective as possible. In this case, less radiation dose will lead to noisy process and as such, the image quality will be degraded.[26] Consequently, radiation dose that is high at some level will not improve image quality either. In most cases, the procedural part being examined will be heavily deposited with radiation dose.[27]

Other than the level of radiation energy, there are other factors that affect the radiation dose and image quality. The amount of voltage mostly referred as kVp has been contended to affect the output x-ray beam. Rankin[28] affirms that radiation dose will be minimal to the patient when low amount of tube voltage are used. This is due to the fact that low tube voltage reduces the x-ray beam exposed to the patient.

Authors in the field of medicine assert that the low tube voltage has an effect that will see a rise in the CT tissue attenuation. In addition, the voltage reduction has an effect on the huge patients whereby the radiation dose will be less exposed to such patients. A large number of scanning as far as CT scanners is concerned, offers limited options during procedural process. Normal body scans provide options that range between 120 and 140kVp.[29] Therefore, from this analysis it is clear that any amount of tube voltage used has some sought of effects to the patients. However, amount of 80 kVp is allowed when attending to pediatric patients. This is an attempt to reduce the radiation dose to this type of people.

Another factor that compromises the radiation dose and image quality is the tube current (mA). As asserted by Brockman and Sadick[30], the effects of mA are not as complicated as it is in the tube voltage. A tube current can be adjusted from a range of 10 mA up to a range of 800 mA. An increase in the mA has a positive effect on the image quality. For instance, an image is clearer with an increased mA. In the same vein, the radiation dose as well as the image quality is directly affected by the time taken to scan the image.[31]

Pitch and radiation dose is another aspect that affects the image quality and the radiation energy. A high pitch as asserted by Koechl, Kanitsar and Lomoschitz[32] will result to a decrease in the radiation dose. In addition, the scan duration is also decreased with an increase in the level of pitch. However, these scholars noted that the effects will be in that nature only when tube voltage and mA are constant.

In the same context, various studies have opined differently as far as the pitch effect is concerned. Lawler and Fishman[33]assert that in the event of multi-detector row, the pitch is not directly proportional to radiation dose. As such, the two scholars opinionate that the effect can be avoided by increasing the amount of mA to compensate the risen noise and also the increased pitch values. In the same note, it is clear that high pitch does not stipulate a reduced radiation. Having discussed and reviewed the effects of radiation dose and image quality, the review shifts its context to dual-energy computed tomography CT.

Dual Energy CT (DECT) Protocol

Before reviewing the Dual-Energy CT, it is important to firstly contextualize the concept of dual energy CT. The use of DECT has reportedly yielded positive results in the clinical arena. Genitourinary imaging has been a successful with the application of DECT. During the process, it has been contended that the use of DECT has not only provided phenomenal morphological information, but also capable of producing specific and quantified information.[34]

The difference between the single-sourced CT scanners and the DECT lies in the image acquisition as well as processing methods. As such, Bae [35] purports that the difference in the two set of scanner is useful in the optimization dual-energy CT protocols. In the advancement in the use of scanning protocols, DECT is the only option since it enhances refined techniques and reduction of image noise.   

In the review of this device however, various short coming are noticed ranging from high radiation dose and distortion of image. During a scanning process with DECT technology, a twined image data is achieved on the same anatomic plane. The two data sets encompass another double rayed spectrum from x-ray beam which makes it possible to analyze material during attenuation. Attenuation is very important since different materials are involved. As such, energy is prone to change under different circumstances. The different materials involved show different and particular change in attenuation from the two image datasets achieved during scanning. More features are seen and analyzed since there is a difference between the high energy spectrum and low energy spectrum.[36]

In this discussion, there is another important aspect that comes into play in regard to scan CT scan- “slice”. The term “slice” as described by Kalra, Maher and Toth [37] asserts that a single horizontal section in tissue is what is referred to as slice. It has been noted that the more the slice is formed during the imaging process, the more it is easy to depict harmful part on human body part being examined. As such, different slicing devices have been into use but the paper focuses on the 64-slice, which is more advanced than any other scan of 16-slice or 32-slice.

 

 

The 64-Slice (64CT) and image quality in peripheral artery imaging

Radiology departments are in the move to acquire newer devices that suits the constant changing environment in the clinical practice. However, it is not certain whether the newer acquired devices are up to the task. In regard to 64-slice CT and image quality, studies embarked on peripheral artery where carried out and various effects where noted. The study centered on two main aspects, image quality and radiation dose implications on the people being examined.

From the studies conducted, it has been revealed that the 64 CT has improved image quality compared to other multi slice devices especially on the peripheral arterial procedures.[38] While using the 64 CT device, Rubin[39] in his study opine that though the image quality are the same with other CT scanners, there is a difference in terms of radiation dose administered. He affirms that a 43% higher dose is used when the 64 CT is used.

The major challenge in clinical approach is to minimize radiation dose as low as possible.[40] The introduction of newer devices still emits more radiation dose than expected. Also to note, different parts of the body require different amount of radiation dose. Due to large presence of mass in the peripheral artery, large amount of radiation is required. Compared to chest cavity where there is a lot of air due to breathing, arterial needs higher radiation dosage and a such, the 64 CT is important in producing more slices to be scanned but the amount of radiation dose is higher and at some times uncontrollable.[41],[42]     

New dose saving peripheral DECTA protocol for stent imaging

From the literature review, the paper now shifts its context to propose new dose saving peripheral DECTA protocol for stent imaging.  Various factors affecting radiation dose exposure has been analyzed. Proposals will be based from these effects. Authors like Gorich, Rilinger and Sokiranski[43] opine that most scanners are devised to reduce radiation dose during imaging process on patients. In this case, they assert that the devices must modify in such a way that the x-rays not contributing to the final imaging process is discarded. This protocol suggests that this can be done by using peripheral artery filters.

It is also contended that multiple data acquisition parameters can be used to lower radiation dose. In this case, Jonker, Schlosser and Moll[44] argue that primary factors for instance those that encompass tube potential and secondary factors like scan length can be accelerated to directly lower radiation. The same authors also argue that the radiation dose can be reduced by altering the image quality. This is achieved through acquisition parameters that proportionally affect radiation exposure.

A study to evaluate the benefit of stent imaging is the iterative reconstruction of peripheral MDCTA in the arteries has been found to reduce radiation dose is greatly. For instance, electrocardiogram (ECG) synchronization can be replaced with helical scanning which use shorter times during stent imaging. [45]

From the review the paper realized that CT scans in the peripheral arteries requires correlation of data acquisition in single phase. This is disadvantageous due to the fact that the data is acquired in a continuous revolution of the gantry. This effect can be controlled by prospectively initiating data acquisition. For prospective or retrospectives to be successful, the ECG of the patient is used to initiate information acquisition.  

Due to its robust and reduced threat to artifacts, retrospective ECG- gated scan is used. In this case, information is acquired through the continuous revolution of the gantry and at the same time, table movement is initiated. During this process, retrospective CT information is retrospectively gated to ECG helical scan where stent imaging is defined at different point during scanning.[46]

 The effect of tube potential has also been analyzed during this review. The effects can be controlled by understanding the fact that radiation exposure is directly proportional to the square of kVp. For instance, a reduction from of 120 kVp causes a reduced dose at around 30%.  In this case, it is assumed that no other changes are initiated on the radiation dose parameters. In the long run, the x-rays energy is reduced considerably lowering their penetration ability and at the same time, noise is increased. [47]

 Noise is another challenge to overcome during stent imaging. From the fact that noise is directly proportion to 1 kVP hence it obvious that a reduction of 120 kVp will trigger a 20% increase in image noise.[48] To reduce radiation exposure on patients, x-ray mA and kVp are adjusted in accordance to the size of people being examined. This reduces unnecessary radiation on the small size people and increasing tube potential for instance, from 120 kVp on larger patients. [49]

Helical scanning works with the application of pitch aspect. Pitch has been conventionally defined as the ratio of the table moved usually calculated in (mm) in every gantry revolution.[50] Pitch varies when different devices are applied. For multi-DECT device, noise is a variant as far as pitch is concerned. However, the latest dual source CT technology allows ECG scanning with higher pitch values.[51]

 Slice thickness is used to determine the amount of x-rays playing a role in the CT imaging process and to an extent, image noise. As such, reconstruction of slice thickness plays an important role in reduction of radiation dose and acquisition of clear images.[52] For instance, the concept of reconstruction slice thickness has been affirmed such that when a radiation dose is kept constant, an image of 3mm thickness produces 72% less noise compared to an image of 1mm thickness.[53]

The use of 64-slice scan is efficient in reconstruction of different slice thickness. From the review, it is evident that slice thickness relationship between different aspects like noise, kVp and mA permits manipulation of radiation dose exposure.[54] However, it should be noted that this dose reduction strategy comes with some limitations. For instance, a lower dose used causes a reduced image resolution. Therefore, this strategy is not effective in smaller structures like coronary arteries but efficient with larger arteries like aorta and pulmonary vein.

Summary and Conclusions

Ensuring whether peripheral stent imaging is successful, a comprehensive study on the effects of various devices of radiology, cardiology and radiography is studied.  However much the latest technology is, the effects are eminent and ranges from minor adjustment of the devices used. For instance, the introduction of the 64-slice CT scans, patients and even physicians have been exposed to radiation dose more than when a 16-slice scan was used.

Moreover, the techniques and equipment introduced to study the reduction of the radiation dose are not only contrary to what is expected results but also confusing. For instance, high-tech devices used to acquire high resolution images and detailed information in area are most cases leading to opposite results which are contrary to the results acquired with the former devices. This calls for a thorough analysis of devices introduced in the clinical practice.

In summary, the paper notes that radiation dose reduction is strategized by suiting the CT imaging protocol based on the nature of the patients. The size of patients matters when using tube potential and tube current. Parameter settings that promote low radiation exposure without compromising imaging resolution are recommendable.

 

 

 

 

 

 

References

  1. Albrecht T, Foert E, Holtkamp R. 16-MDCTangiography of aortoiliac and lower    extremity arteries: comparison with digital subtraction angiography. AJR Am J Roentgenol. 2007; 189(3):702–11.
  2. Bae K, Heiken J. Scan and contrast administration principles of MDCT. Eur Radiol. 2005 Dec;15(l5):46–59.
  3. Bae T. Test-bolus versus bolus-tracking techniques for CT angiographic timing. Radiology. 2005 May; 236(1):369–70.
  4. Brenner J, Hall J. Computed tomography—an increasing source of radiation exposure. N Engl J Med. 2007; 357(22):2277–84.
  5. Brewster C. Clinical and anatomical considerations for surgery in aortoiliac disease and results of surgical treatment. Circulation. 2005;83(2):I42–52.
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  14. Kim JK, Kim JH, Bae SJ, Cho KS. CT angiography for eval­uation of living renal donors: comparison of four reconstruc­tion methods. AJR Am J Roentgenol. 2004; 183: 471–477.
  15. Kirchgeorg A, Prokop M. Increasing spiral CT benefits with post processing applications. Eur J Radiol. 2008; 28: 39–54.
  16. Koechl A, Kanitsar A, Lomoschitz E.Comprehensive assessment of peripheral arteries using multi-path curved planar reformation of CTA datasets. Eur Radiol 2003; 13: 268–269.
  17. Lawler P, Fishman K. Multidetector row computed tom­ography of the aorta and peripheral arteries. Cardiol Clin. 2003; 21: 607–629.
  18. Lawler P, Fishman K. Multi-detector row CT of thoracic disease with emphasis on 3D volume rendering and CT angi­ography. Radiographics. 2001; 21: 1257–1273.
  19. Lin H, Huynh T, Kougias P.  Descending thoracic aortic dissection: evaluation and management in the era of endovascular technology. Vasc Endovascular Surg. 2009 Jan ;43(1):5–24.
  20. Napoli A, Fleischmann D, Chan P, Computed tom­ography angiography. State-of-the-art imaging using multi­detector-row technology. J Comput Assist Tomogr. 2004; 28: 32–45.
  21. Norgren L, Hiatt R, Dormandy A. Inter-Society Consensus for the Management of Peripheral Arterial Disease (TASC II). J Vasc Surg. 2007; 45:5–67.
  22. Ota H, Takase K, Igarashi K,  MDCT compared with dig­ital subtraction angiography for assessment of lower extremity arterial occlusive disease. Importance of reviewing cross-sectional images. AJR Am J Roentgenol. 2004; 182: 201–209.
  23. Raman R, Napel S, Rubin GD. Curved-slab maximum inten­sity projection: method and evaluation. Radiology. 2003; 229: 255–260.
    1. Rankin C. CT Angiography. Eur Radiol. 2009; 9: 297–310.
    2. Rubin D, Schmidt J, Logan J, Sofilos C. Multi-detector row CT angiography of lower extremity arterial inflow and runoff: initial experience. Radiology. 2001; 221: 146–158. 
    3. Rubin D. Data explosion: the challenge of multidetector-row CT. Eur J Radiol.2000; 36: 74 80.
    4. Soto A, Munera F, Morales C. Focal arterial inju­ries of the proximal extremities. Helical CT arteriography as the initial method of diagnosis. Radiology. 2001; 218: 188–194.
    5. Sueyoshi E, Sakamoto I, Hayashi K. Aortic aneurysms in patients with Takayasu’s arteritis: CT evaluation. AJR Am J Roentgenol 2009;175(6):1727–33.
    6. Utsunomiya D, Awai K, Tamura Y,  16-MDCT Aortography with a low-dose contrast material protocol. Am J Roentgenol. 2006; 186: 374–378.
    7. Wintersperger B, Jakobs T, Herzog P. Aortoiliac multi-detector-row CT angiography with low kVp settings: improved vessel enhancement and simultaneous reduction of radiation dose. Eur Radiol. 2005; 15(2):334–41.
    8. Yanaga Y, Awai K, Nakaura T. Effect of contrast injection protocols with dose adjusted to the estimated lean patient body weight on aortic enhancement at CT angiography. AJR Am J Roentgenol 2009 Jan; 192(4):1071–8.

 

 

 


[1] Bae K, Heiken J. Scan and contrast administration principles of MDCT. Eur Radiol. 2005 Dec; 15(l5):46–59.

[2]  Soto A, Munera F, Morales C. Focal arterial inju­ries of the proximal extremities. Helical CT arteriography as the initial method of diagnosis. Radiology. 2001; 218: 188–194

[3]  Kim JK, Kim JH, Bae SJ, Cho KS. CT angiography for eval­uation of living renal donors: comparison of four reconstruc­tion methods. AJR Am J Roentgenol. 2004; 183: 471–477.

[4]Calhoun S, Kuszyk S, Heath G, Carley C, Fishman K. Three-dimensional volume rendering of spiral CT data: theory and method. Radiographics.210; 19: 745–764.

[5]  Wintersperger B, Jakobs T, Herzog P. Aortoiliac multi-detector-row CT angiography with low kVp settings: improved vessel enhancement and simultaneous reduction of radiation dose. Eur

Radiol. 2005; 15(2):334–41

[6]Lin H, Huynh T, Kougias P.  Descending thoracic aortic dissection: evaluation and management in the era of endovascular technology. Vasc Endovascular Surg. 2009 Jan; 43(1):5–24.

 

[7] Rubin D, Schmidt J, Logan J, Sofilos C. Multi-detector row CT angiography of lower extremity arterial inflow and runoff: initial experience. Radiology. 2001; 221: 146–158. 

 

[8]Yanaga Y, Awai K. Effect of contrast injection protocols with dose adjusted to

the estimated lean patient body weight on aortic enhancement at CT angiography. AJR Am J Roentgenol 2009 Jan; 192(4):1071–8.

[9]Rubin D, Schmidt J, Logan J, Sofilos C. Multi-detector row CT angiography of lower extremity arterial inflow and runoff: initial experience. Radiology. 2001; 221: 146–158.   

[10]Brewster DC. Clinical and anatomical considerations for surgery in aortoiliac disease and results of surgical treatment. Circulation. 2005;83(2):I42–52.

[11] Utsunomiya D, Awai K, Tamura Y, et al. 16-MDCT Aortography with a low-dose contrast material protocol. Am J Roentgenol 2006; 186: 374–378

[12]Norgren L, Hiatt R, Dormandy A. Inter-Society Consensus for the Management of Peripheral Arterial Disease (TASC II). J Vasc Surg. 2007; 45(Suppl S):S5–67.

 

[13] Utsunomiya D, Awai K, Tamura Y, et al. 16-MDCT Aortography with a low-dose contrast material protocol. Am J Roentgenol 2006; 186: 374–378.

[14] Sueyoshi E, Sakamoto I, Hayashi K. Aortic aneurysms in patients with Takayasu’s arteritis: CT evaluation. AJR Am J Roentgenol 2009;175(6):1727–33.

[15] ibid

[16] ibid

[17] ibid

[18] Hara K, Paden G, Silva C. Iterative reconstruction technique for reducing body radiation dose at CT: feasibility study. AJR Am J Roentgenol. 2009; 193(3):764–71.

 

[19]Hara K, Paden G, Silva C. Iterative reconstruction technique for reducing body radiation dose at CT: feasibility study. AJR Am J Roentgenol. 2009; 193(3):764–71.

[20] Albrecht T, Foert E, Holtkamp R. 16-MDCTangiography of aortoiliac and lower extremity arteries: comparison with digital subtraction angiography. AJR Am J Roentgenol. 2007; 189(3):702–11.

[21] Diehm N, Pena C, Benenati F, Adequacy of an early arterial phase low-volume contrast

protocol in 64-detector computed tomography angiography for aortoiliac aneurysms. J Vasc

Surg. 2008 Feb;47(3):492–8.

[22] ibid

[23]Diehm N, Pena C, Benenati F, Adequacy of an early arterial phase low-volume contrast

protocol in 64-detector computed tomography angiography for aortoiliac aneurysms. J Vasc

Surg. 2008 Feb;47(3):492–8.

[24] Raman R, Napel S, Rubin GD. Curved-slab maximum inten­sity projection: method and evaluation. Radiology. 2003; 229: 255–260.

[25] ibid

[26]  Napoli A, Fleischmann D, Chan P, Computed tom­ography angiography. State-of-the-art imaging using multi­detector-row technology. J Comput Assist Tomogr. 2004; 28: 32–45.

[27] Napoli A, Fleischmann D, Chan P, Computed tom­ography angiography. State-of-the-art imaging using multi­detector-row technology. J Comput Assist Tomogr. 2004; 28: 32–45.

[28] Rankin S. CT angiography. Eur Radiol. 2009; 9: 297–310.

[29]  Napoli A, Fleischmann D, Chan P, Computed tom­ography angiography. State-of-the-art imaging using multi­detector-row technology. J Comput Assist Tomogr. 2004; 28: 32–45.

[30] Brockmann C, Sadick M. Dual-energy CT angiography in peripheral arterial occlusive disease. Cardiovascular Intervent Radiol. 2009; 32: 630–637.

[31] Rubin D. Data explosion: the challenge of multidetector-row CT. Eur J Radiol.2000; 36: 74–80.

[32] Koechl A, Kanitsar A, Lomoschitz E,  Comprehensive assessment of peripheral arteries using multi-path curved planar reformation of CTA datasets. Eur Radiol 2003; 13: 268–269.

[33]Lawler P, Fishman K. Multidetector row computed tom­ography of the aorta and peripheral arteries. Cardiol Clin. 2003; 21: 607–629.

  

[34] Koechl A, Kanitsar A, Lomoschitz E,  Comprehensive assessment of peripheral arteries using multi-path curved planar reformation of CTA datasets. Eur Radiol 2003; 13: 268–269.

[35] Bae T. Test-bolus versus bolus-tracking techniques for CT angiographic timing. Radiology.

2005 May; 236(1):369–70.

[36]  ibid

[37] Kalra K, Maher M, Toth L. Strategies for CT radiation dose optimization. Radiology. 2004; 230(3):619–28.

 

[38]Brenner J, Hall J. Computed tomography—an increasing source of radiation exposure. N Engl J Med. 2007; 357(22):2277–84.

[39] Rubin D. Data explosion: the challenge of multi detector-row CT. Eur J Radiol.2000; 36: 74–80.

[40] Kirchgeorg A, Prokop M. Increasing spiral CT benefits with post processing applications. Eur J Radiol. 2008; 28: 39–54.

[41]Lawler P, Fishman K. Multi-detector row CT of thoracic disease with emphasis on 3D volume rendering and CT angi­ography. Radiographics. 2001; 21: 1257–1273.

[42] ibid

[43] Gorich J, Rilinger N, Sokiranski R. Leakages after endovascular repair of aortic aneurysms: classification based on findings at CT, angiography, and radiography. Radiology 2009;213(3):767–72.

 

[44] Jonker H, Schlosser J, Moll L, Dissection of  the abdominal aorta. Current evidence and implications for treatment strategies: a review and metaanalysis of 92 patients [comment]. J Endovasc Ther. 2009;16(1):71–80.

 

[45] Kirchgeorg A, Prokop M. Increasing spiral CT benefits with post processing applications. Eur J Radiol. 2008; 28: 39–54

[46] Brenner J, Hall J. Computed tomography—an increasing source of radiation exposure. N Engl J Med. 2007; 357(22):2277–84.

[47] Ota H, Takase K, Igarashi K,  MDCT compared with dig­ital subtraction angiography for assessment of lower extremity arterial occlusive disease. Importance of reviewing cross-sectional images. AJR Am J Roentgenol. 2004; 182: 201–209.

[48] Yanaga Y, Awai K, Nakaura T. Effect of contrast injection protocols with dose adjusted to the estimated lean patient body weight on aortic enhancement at CT angiography. AJR Am J Roentgenol 2009 Jan; 192(4):1071–8.

 

[49] Calhoun S, Kuszyk S, Heath G, Carley C, Fishman K. Three-dimensional volume rendering of spiral CT data: theory and method. Radiographics.210; 19: 745–764.

[50] Bae T. Test-bolus versus bolus-tracking techniques for CT angiographic timing. Radiology. 2005 May; 236(1):369–70.

[51] Brockmann C, Jochum S, Sadick M, Dual-energy CT angiography in peripheral arterial occlusive disease. Cardiovasc Intervent Radiol. 2009; 32: 630–637.

[52] Hara K, Paden G, Silva C. Iterative reconstruction technique for reducing body radiation dose at CT: feasibility study. AJR Am J Roentgenol. 2009; 193(3):764–71.

 

[53] Catalano C, Fraioli F, Laghi A,  Infrarenal aortic and lower-extremity arterial disease: diagnostic performance of multi-detector row CTangiography. Radiology 2004; 231(2):555–63.

[54] Brewster C. Clinical and anatomical considerations for surgery in aortoiliac disease and results of surgical treatment. Circulation. 2005;83(2):I42–52

Scanning protocol optimisation for dual-energy computed tomography angiography (DECTA) in peripheral artery stenting

Introduction

The literature review section is intended to provide a basis and background to understanding the subject matter in a given study. In the case of this study, the literature review brings out an understanding of the image quality and the radiation dose of the Multi detector Computed Tomography Angiography (Here in referred to as MDCTA) in peripheral arteries. The same is compared to dual energy Computed Tomography (CT) angiography. MDCTA is a modern platform which allows quality spatial resolution as far as imaging is concerned. As opined by Bae and Heiken[1], the platform is essential in ensuring high quality and non-invasively image.

 As such, the literature will compare different findings and a comparison of dual energy CT angiography (CTA) will be tackled. There are factors that affect radiation dose in relation to image quality. The review will also put the effects in to perspectives. Some effects have posed a challenge in diagnosing the atherosclerotic illness. A literature that proposes how to overcome the challenges will be also put into perspective for instant, a proposal of a new dose saving peripheral DECTA protocol for stent imaging will be analyzed.

Image Quality

In 1984, morphologic imaging of the arteries was carried out for the first time in the history of radiology. The same was conducted with the aid of scanners referred to as the electron beam computed tomography (EDCT).[2]  During the nineties, the practice of radiology witnessed the entry of the helical multi-detector CT. With this new device, the imaging of blood vessels ike the arteries became improved by a significant extent. The device enabled the coverage of arteries based on their volume to be significantly improved. The same was achieved by acquiring 4 slices for each gantry. The effect of this would be realized by the reduction of the acquisition time to a new low of 40 seconds. With this new devise, the image quality of the said organ would attain a resolution of 250 msec.

In terms of image quality, Lin, Huynh and Kougias[3], opine that the use of MDCTA has become a desirable component in not only among the physicians but also the patients. As such, they argue that desirable characteristics like speed and spatial resolution are achieved. In addition, the scholars have also contended that MDCTA has enabled wider volume coverage. Isotropic information can also be acquired using this component. For instance, a three dimensional (3D) is possible in addition to other post-analysis methods like arterial image display.[4]

As far as image quality is concerned, Yanaga and Awai[5] contend that MDCTA is the first priority in assessing and analyzing the aorta. Thus, the MDCTA has a greater advantage since the CT angiography CTA is non-invasive which means that the anticipated complications are minimal. In addition to the detailed image that the CTA offers, the authors also assert that the technique has shortened the number of examinations times.

In the view of expertise in the field of medicine, technical parameters and optimization are taken into account before administering a MDCTA to a patient. As opined by Rubin and Schmidt[6], the considerations include the type of scanner used. In this case, they argue that MDCTA encompasses volumetric data set as opposed to one way detector device which produced single set of data. A single set of data had greater complications on the patient. In addition, the physicians had a challenge in deducing the kind of image due to quality problems. As aforementioned, the MDCTA has multiple detectors which ensure greater volume coverage in one breath hold. [7],[8]

In the peripheral artery, Rubin and Schmidt contend that a contrast bolus is responsible for the shaping of the MDCTA. For this reason, the contrast bolus is affected by various phenomena. According to these authors, the rate and the time taken for the injection is a determinant factor in the contrast bolus. In the same context, the authors also assert that the type and the concentration of the contrast determine the shaping of the MDCTA.

The shape is known to depict the time taken for the contrast to reach the peripheral artery. For image quality acquisition, at least 250 Hounsfield units HU) is required[9]. According to Utsunomiya, Awai and Tamura[10], two methods are used to determine contrast arrival time. A bolus tracing software is used to trigger the CTA device once attenuation of a needed location is achieved. The second method encompasses 10 to 15 mL when the MDCTA is used at higher rate.

Different substances behave differently at different energies. The behavior is very important since it provides different information about the substance. In this regard, a device known as dual-energy CT gives all the information about the substance subjected to different set of energies. In another words, the device has the ability to provide unenhanced datasets which have low energy

Radiation dose

The practice of radiology often exposes the practitioners to certain amounts of radiation. The successive development and advancement of the machines, notwithstanding, radiation levels among the said medical practitioners is steadily increasing.[11] It is important to appreciate that in some of the more developed nations like the United States, levels of exposure have gotten to extremes that can be at par with those of the natural background radiation. The main source of these levels of exposure is the computed tomography.[12] The process, alone, accounts for more that 65% of the cumulative medical exposure.

Due to the health hazard associated with radiation exposures, stakeholders are ever looking for means and ways to ensure the levels are at an all time low. One way of minimizing the said levels of exposure involves the adoption of precautionary measures.[13] Radiologists are encouraged to make use of such techniques as the iterative reconstruction of CT images.[14] The said process suppresses the noise emanating from imaging which in turn reduces the exposure to radiation due to imaging.

A study was once conducted to make a comparison of the image characteristics alongside the effective organ dose of a female breast. The same was with regard to the pulmonary multi-detector CT angiography.[15] In this process, the specialists were to make use of two techniques. One was the standard filtered back projection technique (herein referred to as FBP). The other technique to be applied in this process is the aforementioned iterative reconstruction in image space (herein referred to as IRIS). To the best of their knowledge, the researchers of this study are of the opinion that a similar comparative study is yet to be carried out hence their involvement.

The study involved only females between the ages of 18 and 17 who numbered 150.[16] Most of the women involved in the study were suspected to have pulmonary embolism. The scans carried out on the sample group were reconstructed using the standard FBP. The process was followed up by a reconstruction upgrade using IRIS.[17] In both cases it is necessary to have a standard figure of the patient’s body mass index (herein referred to as BMI). In the case of the group that required FBP, the BMI is recorded as 25.3. The IRIS group had a BMI of 27.9. A comparison of the two revels that the difference was almost negligible.[18]

The respective scans were performed on an MDCT scanner of a single source. The span of the scan’s coverage included the regions of the lung apex extending to the posterior costophrenic recesses.[19] The importance of the parameters used in the process should not escape attention. The tube voltage during the process was at 100kV.

Authors like Diehm, Pena and Benenati, [20] opine that the radiation dose is in variant with different procedures used. On the same vein, they assert that in one single procedure, there are different tenfold procedures amounting to different radiation dose. As such, the scholars are of the opinion that the knowledge of radiation dose is paramount for the cardiologist especially when carrying out an invasive process. Studies carried out to show effects of radiation exposure reveal that on a dose- area product (DAP), stochastic risks are eminent.[21] An analysis was carried out on the same where peripheral arteries procedures were conducted to validate the DAP as well as the potential risks of malignancy.

During peripheral artery catheterization, the aforementioned analysis realized that among the sample used in the study, the radiation exposure varied exponentially. The DAP meter was attached on the radiation device to try and come up with an estimation of the dose exposed to the patients during the peripheral catheterization.[22]

 

 

 

 

 

 

 

 

 

 

 

 

 


[1]

[2]

[3]

[4]

[5]

[6]

[7]

[8]

[9]

[10] Utsunomiya D, Awai K, Tamura Y, et al. 16-MDCT Aortography with a low-dose contrast material protocol. Am J Roentgenol 2006; 186: 374–378.

 

Scanning protocol optimisation for dual-energy computed tomography angiography (DECTA) in peripheral artery stenting

 

 

 

 

 

 

 

 

 

 

Literature Review

Factors Affecting Radiation Dose and Image Quality

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Name of Institutions

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 LITERATURE REVIEW: FACTORS AFFECTING RADIATION DOSE AND IMAGE QUALITY 

Introduction

The literature review section is intended to provide a basis and background to understanding the subject matter in a given study. In the case of this study, the literature review brings out an understanding of the image quality and the radiation dose of the Multi detector Computed Tomography Angiography (Here in referred to as MDCTA) in peripheral arteries.

 The same is compared to dual energy Computed Tomography (CT) angiography as well as single-detector row CT scanner (SDCT). During the literature analysis, factors affecting the radiation dose and the image quality will be identified from the literature and applied to propose a new dose saving peripheral DECTA protocol for stent imaging.

The surge in the use of MDCT is spreading widely than the decline in dose examination. In addition, technology is continuously growing and dynamic than radiation dose management strategies. Previous findings indicate that the use of MDCT increased radiation dose relative to SDCT. However, recent reports indicate a decrease in radiation dose in MDCT processes. Compared to SDCT, there are numerous influential parameters related to MDCT which increase or decline radiation dose. This calls for a thorough review in the devices used in the radiation dose and image quality. [1]

Before engaging in a thorough analysis of these devices, it will be appropriate to first provide a genesis of radiology and radiography development as far as image and radiation exposure is concerned.

General Overview

In the past, peripheral artery and occlusions were treated with angioplasty in different parts of the human anatomy. Stent implantation was also used in the treatment of arterial stenoses. However, this kind of treatment requires a constant follow up of examinations due to potential risk of in-stent restenosis. According to clinical practice studies, three possible threats are eminent.[2] For instance, they assert that apart from arterial wall inflammation, stent thrombosis is set to occur after such treatment. In addition, neointimal proliferation effect is bound to take place after stent implantation.[3]

In the current clinical practice, there is an emergency of new devices to avert and reduce possible threats during peripheral treatment. Imaging devices like Digital Subtraction Angiography (DSA) have been introduced. However, the imaging device is faced with the challenge of invasiveness calling for avenues to explore less invasive device. In the long run, devices like dual energy CT, Computed Tomography Angiography (CTA) and CT scanners equipped with 64-slice has been devised.[4]

These devices use noninvasive ability to analyze peripheral arteries and clear image acquisition with more slices in the shortest possible time. However, these devices have several effects ranging from image quality and radiation exposure. In addition, scanning parameters and reconstruction parameters have a substantial effect on image quality and radiation dose. In regard to scanning parameters, for instance, x-ray beam, tube potential (kVp), tube current (mA), revolution time, collimation and pitch contribute greatly on both image quality and radiation does. In reconstruction wise, the parameters which encompass slice thickness, reconstruction kernel and Field of view (FOV) and iterative reconstruction (IR) play a big role in depicting image quality and radiation dose.[5]

In this short analysis, the paper has noted two ways for instance, scanning parameters and reconstruction parameters which affect both radiation dose and image quality. The paper will therefore put the two aspects into deeper perspective by engaging each aspect individually.

Factors Affecting Radiation Dose and Image Quality

Before a review of factors affecting radiation dose and image quality is tackled, it is important to firstly define the terms radiation dose as well as radiation exposure. Radiation exposure is term used to describe the amount of air being released by the X-ray beam.[6] The rays are exposed to a procedural area known as dose area products DAP.

On the other hand, radiation dose is associated with the part being examined by the physician.[7] As such, a radiation dose can be measured by depicting the amount of radiation rays falling on the part being examined. Therefore, radiation energy is a term related to human body. From these definitions, the study can freely embark on the factors affecting the radiation dose as well as its image quality.

  1. a.      Scanning Parameters

As aforementioned earlier, scanning parameters encompass, x-ray beam, pitch, and tube potential, tube current, collimation and rotation time. Each of these parameters will be discussed separately to try and depict specific effects in regard to radiation dose and image quality.

Scholars in the field of medicine have contended that radiation dose is a process that must be as effective as possible. In this case, less radiation dose will lead to noisy process and as such, the image quality will be degraded.[8] Consequently, radiation dose that is high at some level will not improve image quality either. In most cases, the procedural part being examined will be heavily deposited with radiation dose.[9]

 

Collimation

Collimation is a process by which x-ray beam is directed towards the needed area. This is achieved through, narrowing of the rays to become more aligned towards a specific area. There are some rays that are scattered to different direction; a collimator device comes in handy to filter unwanted rays and in turn directs parallel rays to the required region. Thus, collimation has effect in determining the amount of radiation exposure and image quality.[10]

There are three levels of collimation in reference to exposed areas which affect the amount of radiation and image quality. These are minimum, medium and maximum collimation with the minimum level also referred to as strict being the smallest area of radiation exposure.[11]

Current studies in reference to collimation aspect assert that collimation reduces the amount of radiation in a number of ways.  The effect is felt by reducing the FOV of the beam and in the long run, a dose area product -DAP will result to less material getting in contact with the primary beam exposure. In the same vein, a potential exposure of secondary beam in the peripheral area is reduced extensively. By reducing the intensity of secondary beam radiation, quality image achieved greatly.[12]

Studies conducted on the same venture postulate that effect of collimation depends on the exposed area.[13] For instance, fixed collimations used in all FOV tend to decrease the amount of radiation used. However, studies conducted noticed a sharp contrast in variable exposure. A constant exit dose used revealed that a higher dose is released on the lens when small irradiated field are used. It is believed that the effect is due to the fact that a smaller field scatters less radiation demanding a bigger exposure to get the same exit dose. Thus, the assumption that strict collimation reduces radiation should be discarded and revised.[14]

Compared to higher levels of collimation, strict collimation tends to produce high resolution image. Studies conducted to determine the effects of collimation on image during peripheral artery procedures deduced that the quality improved significantly regardless of fixed or variable exposure. [15]

X-ray beam

This aspect has taken place by what is referred to as over beaming. This is a situation whereby a-ray beam used on patients extends to non active detector area. As a result, the extended beam is not used for imaging purpose compromising the procedural process in peripheral arteries.[16] This effect takes place in attempts to improve slice sensitivity profile. During the process, slice collimation is placed between the scan and the patient to prevent exposure of unnecessary radiation to the patient.[17]

Different devise use different x-ray beam. For the case of a multi detector CT, the exposure must be uniformly distributed across all the active areas. In contrast, the single detectors use the entire dose profile but the slice profile is affected during the process. A small total beam width results to higher radiation dose. This is more pronounced in single detector CT calling for optimization of CT devices.[18]

Tube voltage

Other than the level of radiation energy, there are other factors that affect the radiation dose and image quality. The amount of tube voltage mostly referred as kVp has been contended to affect the output x-ray beam. It has been affirmed that low amount radiation dose will be used by patient when low amount of tube voltage is applied. This is due to the fact that low tube voltage reduces the x-ray beam exposed to the patient.[19]

Authors in the field of medicine assert that low tube voltage has an effect that will see a rise in the CT tissue attenuation. In addition, the voltage reduction has an effect on the huge patients whereby the radiation dose will be less exposed to such patients. A large number of scanning as far as CT scanners are concerned is that they offer limited options during procedural process. Normal body scans provide options that range between 120 and 140kVp.[20] Therefore, from this analysis it is clear that any amount of tube voltage used has some sought of effects to the patients. However, amount of 80 kVp is allowed when attending to pediatric patients. This is an attempt to reduce the radiation dose to this type of people.

Tube Current

Another factor that compromises the radiation dose and image quality is the tube current (mA). As asserted by clinical authors, [21] the effects of mA are not as complicated as it is in the tube voltage. A tube current can be adjusted from a range of 10 mA up to a range of 800 mA. An increase in the mA has a positive effect on the image quality. For instance, an image is clearer with an increased mA. In the same vein, the radiation dose as well as the image quality is directly affected by the time taken to scan the image.[22]

 

 

 

Pitch

Pitch is another aspect that affects image quality and the radiation dose. A high pitch as asserted by Cook , Zimmerman, Steingall , Boonn and Kim[23] will result to a decrease in the radiation dose. In addition, the scan duration is reduced with an increase in the level of pitch. However, these scholars noted that the effects will be in that nature only when tube voltage and mA are constant.

In the same context, various studies have opined differently as far as the pitch effect is concerned.  Prakash, Kalra and Kambadakone [24] assert that in the event of multi-detector row, the pitch is not directly proportional to radiation dose. As such, the two scholars opinionate that the effect can be avoided by increasing the amount of mA to compensate increased noise and pitch values. In the same note, it is clear that high pitch does not stipulate a reduced radiation. Having discussed and reviewed the effects of radiation dose and image quality, the review shifts its context to dual-energy computed tomography CT. But before then, it will be wise to engage into reconstruction parameters which play a role in image acquisition and radiation dosage.

Summary on Scanning Parameters

The role of kV setting related to image quality in the evaluation of vascular disease has been addressed on few articles. Delesalle at al. investigates spectral optimization of thoracic arteries and found that virtual monochromatic energy at 60keV and 100kev provided similar or better image quality compare to standard chest CTA.

Maturen at al. evaluated endovascular aneurysm for the aorta and demonstrated high sensitivity in the detection of endoleaks using 55 keV MEI compared to standard PEI. Sudarskiet al. suggested that using a 70 kev MEI compared to dual energy PEI, will achieve a high CNR in abdominal arteries. However, for lower extremities they suggested 60 keV provided the best image quality compared to PEI. Pehno et al. in their study compared the subjective and objective image quality of virtual MEI DECTA to PEI in aortoillic arteries demonstrating optimal contrast enhancement and improve image quality using 70 keV MEI compared to single energy CTA.

Yu et al. studied different sizes of phantoms (small, medium, large and X-large) to evaluate the MEI at multiple keV levels for optimization of the image quality in chest. He found that energies were 66,68,70 and 72 keV. The optimal MEI were used for each phantom and the noise level were similar to and the CNR was better than that in single energy at 120 KVp with the same radiation dose.

  1. b.      Reconstruction Parameters

These parameters are mostly dependent on the system software. They encompass slice thickness, reconstruction kernel, reconstruction FOV and iterative reconstruction among others.

Slice thickness has been contended to increase image quality with detailed information. When slice thickness is increased in the peripheral arteries, signal to noise ratio is lowered. This in turn lowers the spatial resolution affecting the image clarity. The vice versa happens when the slice thickness is decreased. Spatial resolution is defined as the capability to see different structures in a single image.[25]

Voxel is another component that affected by slice thickness. An increased slice thickness causes the voxel to increase proportionally. High voxel rate reduces signal related to noise. [26] Therefore, it can be deduced that voxel and slice thickness affects noise as well as a number of components that comprise quality image.

Slice gap is a line in the middle of each slice. This slice gaps can be measured in millimeters a scenario that can permit experts in the clinical practice to regulate the size of the images formed. Hence slice thickness has both positive and negative effects as far as image quality and radiation dose is concerned.[27]

Reconstruction kernel is parameters created to suit certain examination process. There are specific reconstruction kernel meant for peripheral arteries and like other parameters, they have various effects. As opined by most scholars, the effects depend mostly with the lesion detection.[28] Effects range from increased noise, blurring of image and so forth.

During image reconstruction, a total of 1000 projection is achieved from a complete rotation for instance 3600 around the person being examined. Acquisition of FOV demands an enormous beam angle which is realized by process of collimation as well as raising the number of detectors. [29] This is what is referred to as reconstruction FOV. It has the effect of dictating the type of projection needed so as to a specific FOV.

Dual Energy CT (DECT) Protocol 

Before reviewing the Dual-Energy CT, it is important to firstly contextualize the concept of dual energy CT. The use of DECT has reportedly yielded positive results in the clinical arena. Genitourinary imaging has been a successful with the application of DECT. During the process, it has been contended that the use of DECT has not only provided phenomenal morphological information, but also capable of producing specific and quantified information.[30]

The difference between the single-sourced CT scanners and the DECT lies in the image acquisition as well as processing methods. It has been purported that the difference in the two set of scanner is useful in the optimization dual-energy CT protocols.[31] In the advancement in the use of scanning protocols, DECT is the only option since it enhances refined techniques and reduction of image noise.   

In the review of this device however, various short coming are noticed ranging from high radiation dose and distortion of image. During a scanning process with DECT technology, a twined image data is achieved on the same anatomic plane. The two data sets encompass another double rayed spectrum from x-ray beam which makes it possible to analyze material during attenuation. Attenuation is very important since different materials are involved. As such, energy is prone to change under different circumstances leading to either increased or decreased radiation dose acquisition effect.[32]

The different materials involved show different and particular change in attenuation from the two image datasets achieved during scanning. More features are seen and analyzed since there is a difference between the high energy spectrum and low energy spectrum.[33]

There are other important scenarios arising from the image quality as far as DECT is concerned. These are optional bone removal from the images, reduction of metal artifacts in the image, tissue re-composition, CNR and SNR.

           Optional bone removal from the images in Peripheral Arteries

As aforementioned earlier in this study, DECT has numerous advantages over its predecessors. It has the ability for optional bone removal purposes, for instance, it has photoelectric mechanism and Compton distribution capability which depends on the beam rays energy and atoms numerical (z) of the materials used. In this case, materials which exhibit higher z values will result to increased photoelectric effect and in turn, a higher attenuation beam is achieved. [34]

An increased attenuation coefficient is described as K edge of material which is characterized by high photon current greater than the K edge material. The difference acquired between the calcium (bone) and iodine as a result of K edge material is conventionally stated as DECT angiography (DECTA). This is due to the fact that iodine has the capacity to contrast the arterial structure with calcium which is subtracted out leaving the vessels intact for viewing.[35]

Reduction of Metal Artifacts in the Image

Artifacts are metallic implants found in patients recommended for CT scan services. Artifacts have various effects on not only on scanning devices, but also on the patients themselves. The effects range from image acquisition to radiation dose supervision. This calls for reduction of metal artifacts in the image during procedural process in the peripheral artery. [36]

To reduce artifacts for clear images, hardware used is examined thoroughly and it has been contend that hardware made of titanium alloy has less obstruction compared to those made of stainless steel devices. To achieve clear image, the implant is paced in such a way that x-ray beam traverses the implanted region with smallest possible diameter. [37]

Artifacts can also be reduced by increasing high voltage volts usually at the peak. High tube charge is also applicable in reducing artifacts. Conversely, narrow collimation as well as thin slices is significant in reducing artifacts. Image reconstruction has a role to play in artifact reduction. For instance, thick sections decreased kernel figures and increased CT scans helps to reduce artifacts in image acquisition. [38]

However, it should be noted that optimization of DECT protocols is dangerous due to the increased radiation dose. As aforementioned in this paper, increasing tube current leads to an increased radiation dose. As such, increased dose is a threat to the patients hence radiologist should be aware of the threats accompanied to optimization of DECT for clear image acquisition.[39]

Contrast –to –noise Ratio (CNR) and Signal –to –noise- Ratio

Clinical practitioners define CNR as the ability to measure clarity of acquired image. This terminology is synonymous to SNR but a ratio subtraction from CNR prior to final ratio makes the difference. This aspect is significant in acquiring clear image when a bias clarity is noticed for instance, a haze cleans an image but intensity is still at high magnitude leading to a phenomenon referred to as contrast resolution due to low CNR and high SNR. [40]

DECT has the ability to quantify the quality of acquired images but in most cases, clarity depends on how an observer sees it. Contrast can be either positive or negative a disadvantage that face DECT as far as CNR and SNR is concerned leading to misrepresenting of images formed.[41]

The 64-Slice (64CT) and image quality in peripheral artery imaging

  Single horizontal section in tissue is what is referred to as slice. It has been noted that the more the slices formed during imaging process, the more it is easy to depict harmful part being examined on the patient. As such, different slicing devices have been introduced with the ability to form more slices. The paper focuses on the 64-slice, which is more advanced than any other scan of 16-slice or 32-slice but not a new modality of MDCT or DECT.[42]

Radiology departments are in the move to acquire newer devices that suits the constant changing environment in the clinical practice. However, it is not certain whether the newer acquired devices are up to the task. In regard to 64-slice CT and image quality, studies embarked on peripheral artery where carried out and various effects where noted. The study centered on two main aspects, image quality and radiation dose implications on the people being examined.

From the studies conducted, it has been revealed that the 64 CT has improved image quality compared to other multi slice devices especially on the peripheral arterial procedures.[43] While using the 64 CT device, clinical studies agree that though the image quality are the same with other CT scanners, there is a difference in terms of radiation dose administered. The study confirms that a 43% higher dose is used when the 64 CT is used. [44]

The major challenge in clinical approach is to minimize radiation dose as low as possible.[45] The introduction of newer devices still emits more radiation dose than expected. Also to note, different parts of the body require different amount of radiation dose. Due to large presence of mass in the peripheral artery, large amount of radiation is required. Compared to chest cavity where there is a lot of air due to breathing, arterial needs higher radiation dosage and a such, the 64 CT is important in producing more slices to be scanned but the amount of radiation dose is higher and at some times uncontrollable.[46],[47]    

The accuracy of DECT on peripheral CTA compared to DSA

DECT devices produces outstanding intra and inter observer in deducing vessel’s length compared to DSA. DECTS imaging criterion is farfetched since it can be used to capture any peripheral tree. Also to note, DECT is non invasive procedure as opposed to DSA which involve invasive angiogram encompassing artery puncture. [48]

DSA application has been affected by plaque morphological like lesions an aspect that has compromised its accuracy compared to the DECT accuracy. For the case of DECT accuracy, it has been revealed that DECT is sensitive to residual aneurysm detection. At the neck remnant, DECT is not accurate but clinical practitioners contend that remnant inaccuracy is insignificant to clinical procedures compared to DSA devices.[49]Therefore, DECT devices are more accurate compared to DSA devices.

New dose saving peripheral DECTA protocol for stent imaging

From the literature review, the paper now shifts its context to propose new dose saving peripheral DECTA protocol for stent imaging.  Various factors affecting radiation dose exposure has been analyzed. Proposals will be based from these effects.

 Authors in clinical practice have opined that most scanners are devised to reduce radiation dose during imaging process on patients. In this case, they assert that the devices must modify in such a way that the x-rays not contributing to the final imaging process is discarded. This protocol suggests that use of peripheral artery filter is used to subdue unnecessary radiation exposure.[50]

It is also contended that multiple data acquisition parameters can be used to lower radiation dose. In this case, it has been argued that primary factors for instance those that encompass tube potential and secondary factors can reduce radiation directly.[51]The same is also argued that the radiation dose can be reduced by altering the image quality. This is achieved through acquisition parameters that proportionally affect radiation exposure.

From the review the paper realized that CT scans in the peripheral arteries requires correlation of data acquisition in single phase. This is disadvantageous due to the fact that data is acquired in a continuous revolution of the gantry.  

 The effect of tube potential has also been analyzed during this review. The effects can be controlled by understanding the fact that radiation exposure is directly proportional to the square of kVp. For instance, a reduction from of 120 kVp causes a reduced dose at around 30%.  In this case, it is assumed that no other changes are initiated on the radiation dose parameters. In the long run, the x-rays energy is reduced considerably lowering their penetration ability and at the same time, noise is increased. [52]

 Noise is another challenge to overcome during stent imaging. From the fact that noise is directly proportion to 1 kVP, it is obvious that a reduction of 120 kVp will trigger a 20% increase in image noise.[53] To reduce radiation exposure on patients, x-ray, mA and kVp are adjusted in accordance to the size of people being examined. This reduces unnecessary radiation on the small size people and increasing tube potential for instance, from 120 kVp on larger patients. [54]

 Slice thickness is used to determine the amount of x-rays used in the CT imaging process and to an extent, image noise. As such, reconstruction of slice thickness plays an important role in reduction of radiation dose and acquisition of clear images.[55] For instance, the concept of reconstruction slice thickness has been affirmed such that when a radiation dose is kept constant, an image of 3mm thickness produces 72% less noise compared to an image of 1mm thickness.[56]

The use of 64-slice scan is efficient in reconstruction of different slice thickness. From the review, it is evident that slice thickness relationship between different aspects like noise, kVp and mA permits manipulation of radiation dose exposure.[57] However, it should be noted that this dose reduction strategy comes with some limitations. For instance, a lower dose used causes a reduced image resolution. Therefore, this strategy is not effective in smaller structures like coronary arteries but efficient with larger arteries like aorta and pulmonary vein.

Summary and Conclusions

Success in stent imaging requires a comprehensive study on the effects of various devices of radiology, cardiology and radiography.  However much the latest technology provides, the effects are eminent and ranges from minor adjustment of the devices used. For instance, the introduction of the 64-slice CT scans, patients and even physicians have been exposed to radiation dose more than when a 16-slice scan was used.

Moreover, the techniques and equipment introduced to study the reduction of the radiation dose are not only contrary to what is expected results but also confusing. For instance, high-tech devices used to acquire high resolution images and detailed information in area are most cases leading to opposite results which are contrary to the results acquired with the former devices. This calls for a thorough analysis of devices introduced in the clinical practice.

In summary, the paper notes that radiation dose reduction is strategized to suite the CT imaging protocol based on the nature of the patients and not otherwise. The size of patients matters when using tube potential and tube current. Parameter settings that promote low radiation exposure without compromising imaging resolution are recommendable. In the same note, device optimization is paramount to ensure that no unnecessary radiation is exposed to the patients.

 

 

 

 

 

 

 

 

 

 

References

  1. Abujudeh H, Kaewlai R, Asfaw A, Thrall H. Quality initiatives: key performance indicators for measuring and improving radiology department performance. RadioGraphics 2010; 30(3):571–580.
  2. Bogaert E, Bacher K, Lapere R, Thierens H. Does digital flat detector technology tip the scale towards better image quality or reduced patient dose in in­terventional cardiology? Eur J Radiol 2009; 72(2): 348–353.
  3. Boland W. Enhancing CT productivity: strategies for increasing capacity. AJR Am J Roentgenol 2008; 191(1):3–10.
  4. Brenner J, Hall J. Computed tomography: an increasing source of radiation exposure. N Engl J Med 2007; 357(22):2277–2284.
  5. Brenner J, Hall J. Computed tomography—an increasing source of radiation exposure. N Engl J Med. 2007; 357(22):2277–84.
  6. Christner A, Kofler M, McCollough H. Es­timating effective dose for CT using dose-length product compared with using organ doses: con­sequences of adopting International Commission on Radiological Protection publication 103 or dual-energy scanning. AJR Am J Roentgenol 2010; 194(4):881–889.
  7. Cohen D. Optimizing the use of pulsed fluoros­copy to reduce radiation exposure to children. J Am Coll Radiol 2008; 5(3):205–209.
  8. Cook S, Zimmerman L, Steingall S, Boonn W, Kim W. An algorithm for intelligent sorting of CT-related dose parameters. Proc SPIE. 2011; 7961:79612H.
  9. Cook S, Zimmerman S, Maidment D, Kim W, Boonn W. Automated extraction of radiation dose information for CT examinations. J Am Coll Radiol 2010; 7(11):871–877.
    1. Eller A, Wuest W, Scharf M, Brand M, Achenbach S, Uder M, Lell M. attenuation based automatic kilovolt selection in computed tomography of the chest: effects on radiation exposure and image quality. Eur J Radiol. 2013 Aug 30.  23:731–833.
    2. Engel C, Lee M, Seifarth H, Sidhu S, Brady J, Hoffmann U, Ghoshhajra B. Weekly dose report: the effects of continous quality improvements initiative on coronarycomputed tomorgraphy angiography raditiationdoses at tertiary medical centre. Acad Radiol. 2013 Aug;20(8):1015-23.
    3. Eric P, Tamm X. Fitzgerald, and Vikas Kundra .Quality Initiatives: CT Radiation Dose Reduction: How to Implement Change without Sacrificing Diagnostic Quality Radiographics November-December 2011 31:7 1823-1832.
    4. Fleischmann D, Boas E. Computed tomography— old ideas and new technology. Eur Radiol 2011; 21 (3):510–517.
    5. Huda W, Mettler  A. Volume CT dose index and dose-length product displayed during CT: what good are they? Radiology 2011; 258(1):236–242.
    6. Kambadakone R, Prakash P, Hahn F, Sahani V. Low-dose CT examinations in peripheral arteries: impact on image quality, diagnostic perfor­mance, and radiation dose. AJR Am J Roentgenol 2010;195(1):78–88.
    7. Koch M, Brau C, Chen W, Gold E, Hargreaves A, Koff M. Imaging near metal with a MAVRIC-SEMAC hybrid. Magn Reson Med 2011; 65:71–82.
    8. Koch M, Hargreaves A, Pauly B, Chen W, Gold E, King F. Magnetic resonance imaging near metal implants. J Magn Reson Imaging 2010; 32:773–8.
    9. Koch M, Lorbiecki E, Hinks S, King F. A multispectral three-dimensional acquisition technique for imaging near metal implants. Magn Reson Med. 2009; 61:381–90.
    10. Landro L. Radiation risks prompt push to curb CT scans. Wall Street Journal. 2010 March 2; 19(4):871–889.
    11. Lee F, Kim S, Lee A. Overcoming artifacts from metallic orthopedic implants at high-field-strength mr imaging and multidetector CT. Radiographics. 2007; 27:791–803
    12. Martin C. Effective dose: how should it be applied to medical exposures? Br J Radiol. 2007; 80:639–47.
    13. Morsbach F, Frauenfelder T, Alkadhi H. Modern techniques for dose reduction in computed tomography imaging. 2013 Jul 3; 102(14):865-8. 
    14. Mouton A,Megherbi N, Van Slambrouck K, Nuyts J, Breckon TP. J Xray Sci Technol . An experimental survey of metal artifacts reductionin computed tomography. 2013;21(2):193-226. 
      1. Oliveira L, Seren E, Rocha C, Brunetto Q, Ramos D, Button L. Attenuation correction effects on SPECT/CT procedures: Phantoms studies. Conf Proc IEEE Eng Med Biol Soc. 2013 Jul; 2013:2324-2327.
      2. Orth C, Wallace J, Kuo D. Technology Assess­ment Committee of the Society of Interventional Radiology. C-arm cone-beam CT: general principles and technical considerations for use in interven­tional radiology. J Vasc Interv Radiol. 2008; 19(6): 814–820.
      3. Paul  J, Abada T. Strategies for reduction of radiation dose in arteries CT. Eur Radiol 2007; 17:2028.
      4. Prakash P, Kalra K, Kambadakone K.  Re­ducing abdominal CT radiation dose with adaptive statistical iterative reconstruction technique. Invest Radiol 2010; 45(4):202–210.
      5. Reid J, Gamberoni J, Dong F, Davros W. Opti­mization of kVp and mAs for pediatric low-dose simulated abdominal CT: is it best to base param­eter selection on object circumference? AJR Am J Roentgenol 2010; 195(4):1015–1020.
      6. Sohaib S. The effect of decreasing mAs on image quality and patient dose in sinus and peripheral arteries  CT. Br J Radiol 2011; 74:157.
      7. Thomas E, Parnell-Parmley J, Haidar  S. Assessment of radiation dose awareness among pediatricians. Pediatr. Radiol. 2012;36(8):823-832.
      8. Tonkopi E, Ross AA, MacDonald A. CT dose optimization for the whole body PET/CT examinations. AJR Am J Roentgenol. 2013 Aug; 201(2):257-63. 
      9. Van Gompel G, Van K, Defrise M, Batenburg J, de Mey J, Sijbers J, Nuyts J. Med Phys. Iterrative correction of beam hardening artifacts in CT 2011 Jul;38 Suppl 1:S36. 
      10. Van S, Nutyts J. Metal artifact reduction in computed tomography using local models in an image block-iterative scheme. Department of Nuclear Medicine, 2012 Nov;39(11):7080-93. 
      11. Willinek A, Gieseke J, Kukuk M, Nelles M, Morakkabati-Spitz N. Dual-source parallel radiofrequency excitation body MR imaging compared with standard MR imaging at 3.0 T: initial clinical experience. Radiology 2010; 256:966–75.

 

 

 

 

 

 

 

 

 

 


[1]Abujudeh H, Kaewlai R, Asfaw A, Thrall H. Quality initiatives: key performance indicators for measuring and improving radiology department performance. RadioGraphics 2010; 30(3):571–580.

 

[2] Boland W. Enhancing CT productivity: strategies for increasing capacity. AJR Am J Roentgenol 2008; 191(1):3–10.

 

[3] ibid

[4]  Tonkopi E, Ross AA, MacDonald A. CT dose optimization for the whole body PET/CT examinations. AJR Am J Roentgenol. 2013 Aug; 201(2):257-63.  

 

[5]Lee F, Kim S, Lee A. Overcoming artifacts from metallic orthopedic implants at high-field-strength mr imaging and multidetector CT. Radiographics. 2007; 27:791–803.

[6]Martin C. Effective dose: how should it be applied to medical exposures? Br J Radiol. 2007; 80:639–47.

 

[7] Brenner J, Hall J. Computed tomography—an increasing source of radiation exposure. N Engl J Med. 2007; 357(22):2277–84.

[8] Sohaib S. The effect of decreasing mAs on image quality and patient dose in sinus and peripheral arteries  CT. Br J Radiol 2011; 74:157

[9]ibid

  

 

[10]  Van S, Nutyts J. Metal artifact reduction in computed tomography using local models in an image block-iterative scheme. Department of Nuclear Medicine, 2012 Nov;39(11):7080-93.

 

[11]Van Gompel G, Van K, Defrise M, Batenburg J, de Mey J, Sijbers J, Nuyts J. Med Phys. Iterrative correction of beam hardening artifacts in CT 2011 Jul;38 Suppl 1:S36

 

[12] Martin C. Effective dose: how should it be applied to medical exposures? Br J Radiol. 2007; 80:639–47.

 

[13] Van Gompel G, Van K, Defrise M, Batenburg J, de Mey J, Sijbers J, Nuyts J. Med Phys. Iterrative correction of beam hardening artifacts in CT 2011 Jul;38 Suppl 1:S36

 

[14]Cook S, Zimmerman L, Steingall S, Boonn W, Kim W. An algorithm for intelligent sorting of CT-related dose parameters. Proc SPIE. 2011; 7961:79612H.

[15] Reid J, Gamberoni J, Dong F, Davros W. Opti­mization of kVp and mAs for pediatric low-dose simulated abdominal CT: is it best to base param­eter selection on object circumference? AJR Am J Roentgenol 2010; 195(4):1015–102

[16]Van Gompel G, Van K, Defrise M, Batenburg J, de Mey J, Sijbers J, Nuyts J. Med Phys. Iterrative correction of beam hardening artifacts in CT 2011 Jul;38 Suppl 1:S36.  

[17]Cohen D. Optimizing the use of pulsed fluoros­copy to reduce radiation exposure to children. J Am Coll Radiol 2008; 5(3):205–209.

 

 

[18] Orth C, Wallace J, Kuo D. Technology Assess­ment Committee of the Society of Interventional Radiology. C-arm cone-beam CT: general principles and technical considerations for use in interven­tional radiology. J Vasc Interv Radiol. 2008; 19(6): 814–820.

[19] Eller A, Wuest W, Scharf M, Brand M, Achenbach S, Uder M, Lell M. attenuation based automatic kilovolt selection in computed tomography of the chest: effects on radiation exposure and image quality. Eur J Radiol. 2013 Aug 30.  23:731–833.

[20]Bogaert E, Bacher K, Lapere R, Thierens H. Does digital flat detector technology tip the scale towards better image quality or reduced patient dose in in­terventional cardiology? Eur J Radiol 2009; 72(2): 348–353.

 

[21]Cook S, Zimmerman L, Steingall S, Boonn W, Kim W. An algorithm for intelligent sorting of CT-related dose parameters. Proc SPIE. 2011; 7961:79612H.

[22] Bogaert E, Bacher K, Lapere R, Thierens H. Does digital flat detector technology tip the scale towards better image quality or reduced patient dose in in­terventional cardiology? Eur J Radiol 2009; 72(2): 348–353.

[23]Cook S, Zimmerman L, Steingall S, Boonn W, Kim W. An algorithm for intelligent sorting of CT-related dose parameters. Proc SPIE. 2011; 7961:79612H.

[24] Prakash P, Kalra K, Kambadakone K.  Re­ducing abdominal CT radiation dose with adaptive statistical iterative reconstruction technique. Invest Radiol 2010; 45(4):202–210.

[25]Fleischmann D, Boas E. Computed tomography— old ideas and new technology. Eur Radiol 2011;21 (3):510–517.

 

[26] Sohaib S. The effect of decreasing mAs on image quality and patient dose in sinus and peripheral arteries  CT. Br J Radiol 2011; 74:157.

[27]  ibid

[28] Christner A, Kofler M, McCollough H. Es­timating effective dose for CT using dose-length product compared with using organ doses: con­sequences of adopting International Commission on Radiological Protection publication 103 or dual-energy scanning. AJR Am J Roentgenol 2010; 194(4):881–889.

 

[29] Huda W, Mettler  A. Volume CT dose index and dose-length product displayed during CT: what good are they? Radiology 2011; 258(1):236–242.

[30]  Engel C, Lee M, Seifarth H, Sidhu S, Brady J, Hoffmann U, Ghoshhajra B. Weekly dose report: the effects of continous quality improvements initiative on coronarycomputed tomorgraphy angiography raditiationdoses at tertiary medical centre. Acad Radiol. 2013 Aug;20(8):1015-23.

[31] Morsbach F, Frauenfelder T, Alkadhi H. Modern techniques for dose reduction in computed tomography imaging. 2013 Jul 3; 102(14):865-8.  

 

[32] Eric P, Tamm X. Fitzgerald, and Vikas Kundra .Quality Initiatives: CT Radiation Dose Reduction: How to Implement Change without Sacrificing Diagnostic Quality Radiographics November-December 2011 31:7 1823-1832.

[33]  Thomas E, Parnell-Parmley J, Haidar  S. Assessment of radiation dose awareness among pediatricians. Pediatr. Radiol. 2012;36(8):823-832.

[34] Koch M, Brau C, Chen W, Gold E, Hargreaves A, Koff M. Imaging near metal with a MAVRIC-SEMAC hybrid. Magn Reson Med 2011; 65:71–82.

 

[35] Koch M, Hargreaves A, Pauly B, Chen W, Gold E, King F. Magnetic resonance imaging near metal implants. J Magn Reson Imaging 2010; 32:773–8.

 

[36] Brenner J, Hall J. Computed tomography: an increasing source of radiation exposure. N Engl J Med 2007;357(22):2277–2284.

 

[37] Koch M, Hargreaves A, Pauly B, Chen W, Gold E, King F. Magnetic resonance imaging near metal implants. J Magn Reson Imaging 2010; 32:773–8.

 

 

[38] Willinek A, Gieseke J, Kukuk M, Nelles M, Morakkabati-Spitz N. Dual-source parallel radiofrequency excitation body MR imaging compared with standard MR imaging at 3.0 T: initial clinical experience. Radiology 2010; 256:966–75.

 

[39] Koch M, Lorbiecki E, Hinks S, King F. A multispectral three-dimensional acquisition technique for imaging near metal implants. Magn Reson Med. 2009; 61:381–90.

 

 

[40]  Oliveira L, Seren E, Rocha C, Brunetto Q, Ramos D, Button L. Attenuation correction effects on SPECT/CT procedures: Phantoms studies. Conf Proc IEEE Eng Med Biol Soc. 2013 Jul; 2013:2324-2327.

[41] ibid

[42] Cook S, Zimmerman L, Steingall S, Boonn W, Kim W. An algorithm for intelligent sorting of CT-related dose parameters. Proc SPIE. 2011; 7961:79612H.

 

[43]Brenner J, Hall J. Computed tomography—an increasing source of radiation exposure. N Engl J Med. 2007; 357(22):2277–84.

[44] Brenner J, Hall J. Computed tomography: an increasing source of radiation exposure. N Engl J Med 2007; 357(22):2277–2284.

[45] Morsbach F, Frauenfelder T, Alkadhi H. Modern techniques for dose reduction in computed tomography imaging. 2013 Jul 3; 102(14):865-8.  

[46]  Eric P, Tamm X. Fitzgerald, and Vikas Kundra . Quality Initiatives: CT Radiation Dose Reduction: How to Implement Change without Sacrificing Diagnostic Quality Radiographics November-December 2011 31:7 1823-1832.

[47]  Huda W, Mettler  A. Volume CT dose index and dose-length product displayed during CT: what good are they? Radiology 2011; 258(1):236–242.

[48] Fleischmann D, Boas E. Computed tomography— old ideas and new technology. Eur Radiol 2011; 21 (3):510–517.

[49]Fleischmann D, Boas E. Computed tomography— old ideas and new technology. Eur Radiol 2011; 21 (3):510–517.

[50] Sohaib S. The effect of decreasing mAs on image quality and patient dose in sinus and peripheral arteries  CT. Br J Radiol 2011; 74:157.

[51] ibid

[52] Mouton A,Megherbi N, Van Slambrouck K, Nuyts J, Breckon TP. J Xray Sci Technol . An experimental survey of metal artifacts reductionin computed tomography. 2013;21(2):193-226.  

[53] Kambadakone R, Prakash P, Hahn F, Sahani V. Low-dose CT examinations in peripheral arteries: impact on image quality, diagnostic perfor­mance, and radiation dose. AJR Am J Roentgenol 2010;195(1):78–88.

[54] Cook S, Zimmerman S, Maidment D, Kim W, Boonn W. Automated extraction of radiation dose information for CT examinations. J Am Coll Radiol 2010; 7(11):871–877.

[55] Thomas E, Parnell-Parmley J, Haidar  S. Assessment of radiation dose awareness among pediatricians. Pediatr. Radiol. 2012;36(8):823-832.

[56]  Landro L. Radiation risks prompt push to curb CT scans. Wall Street Journal. 2010 March 2; 19(4):871–889.

[57] Landro L. Radiation risks prompt push to curb CT scans. Wall Street Journal. 2010 March 2; 19(4):871–889.

 

Deadly Medicine

 

Deadly Medicine

Name:

Institute:

Tutor:

Course:

Date:

 

 

 

 

.

 

 

The failure by F.D.A. to administer the standard of tests is a major administrative issue. There is a general lack of an effective chain of command, whose responsibility should be in the line of testing drugs. In the beginning most trials where conducted by unqualified researchers, most of whom were from the universities. The standards of the system were generally low. Currently most companies conduct their researches by recruiting potential patients, performing the trials and presenting the results for approval. As they had no following on how research was conducted, F.D.A. approves the results, most of which are doctored in the favor of the company.

Oversight is a major administrative mistake the federation has made. It is charged with an administrative duty of authorizing the locations in which tests are conducted in order to approve drugs. Granting drug companies the authority to conduct tests outside America is an administrative mistake that affects the quality of approved medicine. The Inspector General of the Department of Health indicated that an increase of 2000percent was recorded between 1990 and 2008 when tests carried abroad rose from an average of 271 tests to 6,485 tests. The National Health Institute further noted that in 2000, 58,788 trials were conducted in 173 different countries out of the United States. The inspector general’s report indicated that 80 percent of tests submitted to F.D.A. in 2008 were from overseas. A several reasons may lead to difference in the metabolisms of the drugs from that in America, is it a mistake that the results from other countries are approved by F.D.A.

It is the administrative duty of F.D.A to ensure that drugs are only used for purposes they were initially tested for. The drawback in administration has seen some drugs being used for purpose they are not intended for. An example is Seroquel which was approved to treat schizophrenia. Increase in sales saw the drug being advertised as able to treat a number of other conditions which include aggression, anxiety and anger-management. This saw the wrongful use go 70 percent raising sales by over $ 4 million within a year. The drug finally led to weight gain and diabetes in some patients, an occurrence F.D.A could not control due to insufficient rule making.

F.D.A. have also failed in their administrative activity of inspecting the manufacturing companies. This is another issue of oversight. They should inspect the drug manufacturing plants in other countries to ensure they are set to the required standards. The lack of adequately inspecting the companies has led to the rise of companies whose standards are poor making the final products to adversely affect the lives of the users. An example is the Chinese company making blood thinner heparin whose standard of manufacture were poor, affecting the health of patients using the medicine. The company made heparin from mucous membranes of slaughtered pigs’ intestines. The mixing and cooking were carried out in unregulated work places of families. The drug caused serious allergic reactions to patients in 2007 and 2008 due to contamination.

The lack of knowledge of the location of several companies manufacturing drugs out of America is also a major administrative drawback caused by oversight. As it is its duty to inspect the standards of such companies, it is ironical that the Federation does not know where most of them are located. The federation inspected a wrong company in china to be producing heparin even after the product caused more than 200 deaths in America. That was due to confusion in the names of the companies.

Various political factors have also played a part in the approval of drugs by F.D.A. The cover F.D.A. give to some inadequate tests and wrong results lead to approval of drugs with harmful effect to human population. This is a cause of lack of transparency as the federation gives favors to specific companies. An example is the approval of Celebrex whose research findings were wrongly presented. The F.D.A. with the background information about possible risks the drug could have on human beings went ahead to approve it. Its sales boomed till the effects on patients were seen later. These effects could have been prevented if the Federation refused to approve the drug.The approval of drugs with false findings was also seen in the case ofKetek. Though it had knowledge of possible effects, it allowed the drug in the market and supported it during early stages of realization that it could harm patients.

Political factors have also caused favors towards the approval of drugs of some companies. The F.D.A approve drugs that may be harmful to patients. This is another case of lack of transparency. When the effects of drugs are noticed, the federation only write new warning labels on the drugs instead of removing them from the market. The use of Avandia saw many patients be exposed to more dangerous medical complications but F.D.A could only put labels as black box warning to indicate the danger the medicine may cause. Even the increased deaths caused by the medicine could not convince the federation to remove it from the market.

Political factors always affect the reaction time of F.D.A. even when an issue regarding a drug had become a matter of global concern, the decision made by the federation was almost the last, especially when the effects of a drug had worried everyone in America. This is always a result of insufficient rule making procedure. The case of Avandia had resulted in many deaths and heart attacks but the decision made by F.D.A. came after similar bodies in other countries had pulled the drug from the shelves. Even with the records that showed a lot of heart attacks being caused by the drug, the federation only imposed new restrictions concerning how available the drug would be instead of stopping its use.

The issue of acceptance of bribes by government employees in order to approve drugs is another political factor affecting drug approval. It causes the federation to cover some companies, thus not being transparent. As Senate finance committee estimated, unlawful drug dealings had led to many companies paying fines. An estimate of more than $ 7 billion of fines were estimated since May 2004.

The federation lack of strong regulations is a political issue that affect the approval of drugs. As drugs affect the lives of almost all citizens, they ought to lay down precise rules that would ensure only drugs that are proven to be safe are used by patients. The absence of strict regulations have seen many people, including children, die in drug trials without proper action being taken to avoid such deaths in future. A resent test in 2008 in United States saw seven babies die as result of an adverse event as stated by the clinical community. Insufficient rulemaking procedure has prevented the federation from making rules to control deaths during trials.

 

 

 

 

 

 

 

 

 

 

Reference

Donald L.B and James B.S. (2011), Deadly medicine. Politics. Retrieved from

http://www.vanityfair.com/politics/features/2011/01/deadly-medicine-201101

 

 

 

Math Problem Set: (must use Matlab) Risk and Asset Allocation

Documentation Center

estimate

Class: garch

Estimate GARCH model parameters

expand all in page

Syntax

EstMdl = estimate(Mdl,y)
[EstMdl,EstParamCov,logL,info] = estimate(Mdl,y)
[EstMdl,EstParamCov,logL,info] = estimate(Mdl,y,Name,Value)

Description

EstMdl = estimate(Mdl,y) uses maximum likelihood to estimate the parameters of the GARCH(P,Q) model Mdl given the observed univariate time series y. EstMdl is a new garch model that stores the results.

[EstMdl,EstParamCov,logL,info] = estimate(Mdl,y) additionally returns EstParamCov, the variance-covariance matrix associated with estimated parameters, logL, the optimized loglikelihood objective function, and info, a data structure of summary information.

[EstMdl,EstParamCov,logL,info] = estimate(Mdl,y,Name,Value) estimates the model with additional options specified by one or more Name,Value pair arguments.

Input Arguments

Mdl

GARCH model, as created by garch or estimate.

estimate treats non-Nan elements in Mdl as equality constraints, and does not estimate the corresponding parameters.

y

Response data whose conditional variances are inferred by the software, i.e., the data to which estimate fits the GARCH model. y is a single path of the series in a column vector.

y is usually an innovation series with mean zero and conditional variance characterized by the model specified in Mdl. In this case, y is a continuation of the innovation series E0. y might also represent an innovation series with mean zero plus an offset. A nonzero Offset signals the inclusion of an offset in the garch model, Mdl.

The last observation of y is the most recent.

Name-Value Pair Arguments

Specify optional comma-separated pairs of Name,Value arguments. Name is the argument name and Value is the corresponding value. Name must appear inside single quotes (' '). You can specify several name and value pair arguments in any order as Name1,Value1,...,NameN,ValueN.

'ARCH0'

Initial estimates of the lagged squared innovation coefficients, specified as the comma-separated pair consisting of 'ARCH0' and a vector with nonnegative entries.

The number of coefficients in ARCH0 must equal the number of lags associated with nonzero coefficients in the ARCH polynomial (ARCH), as specified in ARCHLags.

Default: estimate derives initial estimates using standard time series techniques.

'Constant0'

Initial estimate for the GARCH(P,Q) model constant, specified as the comma-separated pair consisting of 'Constant0' and a positive scalar.

Default: estimate derives initial estimates using standard time series techniques.

'Display'

Indicator for what results to display in the Command Window, specified as the comma-separated pair consisting of 'Display' and a string or cell vector of strings.

Set Display to any combination of values in this table.

Value estimate Displays
'diagnostics' Optimization diagnostics
'full' Maximum likelihood parameter estimates, standard errors, t-statistics, iterative optimization information, and optimization diagnostics
'iter' Iterative optimization information
'off' Nothing in the Command Window
'params' Maximum likelihood parameter estimates, standard errors, and t-statistics

For example,

  • To run a simulation where you are fitting many models, and therefore want to suppress all output, use 'Display','off'.

  • To display all estimation results and the optimization diagnostics, use 'Display',{'params','diagnostics'}.

 

Default: 'params'

'DoF0'

Initial estimate of the t-distribution degree-of-freedom parameter, specified as the comma-separated pair consisting of 'DoF0' and a positive scalar. DoF0 must exceed 2.

Default: 10

'E0'

Presample innovations that have mean 0 and provide initial values for the GARCH(P,Q) model, specified as the comma-separated pair consisting of 'E0' and a column vector. E0 must contain at least Mdl.Q rows. If E0 contains more rows than required, then estimate uses the most recent Mdl.Q presample innovations. The last row contains the most recent presample innovation.

Default: estimate sets the necessary observations to the square root of the average squared value of the offset-adjusted response series y.

'GARCH0'

Initial estimates for the lagged conditional variance coefficients, specified as the comma-separated pair consisting of 'GARCH0' and a vector with nonnegative entries. The number of coefficients in GARCH0 must equal the number of lags associated with nonzero coefficients in the GARCH polynomial (GARCH), as specified in GARCHLags.

Default: estimate derives initial estimates using standard time series techniques.

'Offset0'

Initial estimate for the offset in the innovation mean model, specified as the comma-separated pair consisting of 'Offset0' and a scalar.

Default: estimate sets the initial estimate to the sample mean of y.

'Options'

Optimization options, specified as the comma-separated pair consisting of 'Options' and an optimoptions or optimset optimization controller. For details on altering the default values of the optimizer, see optimoptions, optimset, or fmincon in Optimization Toolbox™.

For example, suppose that you want to change the constraint tolerance to 1e-6. Set Options = optimoptions(@fmincon,'TolCon',1e-6,'Algorithm','sqp'), and then pass Options into estimate using 'Options',Options.

Default: estimate uses the same default options as fmincon, except Algorithm = sqp and TolCon = 1e-7.

'V0'

Presample conditional variances providing initial values for the GARCH(P,Q) model, specified as the comma-separated pair consisting of 'V0' and column vector with positive entries.

V0 must have at least Mdl.P rows. If the number of rows in V0 exceeds the number necessary, only the most recent Mdl.P observations are used. The last row contains the most recent observation.

Default: estimate sets the necessary observations to the average squared value of the offset-adjusted response series y.

Notes  

  • NaNs indicate missing values, and estimate removes them. The software merges the presample data (E0 and V0) separately from the effective sample data (y), then uses list-wise deletion to remove any NaNs. The removal of NaNs in the data reduces the sample size. Such removal can also create irregular time series.

  • estimate assumes that you synchronize the presample data such that the most recent observations occur simultaneously.

    • If you specify a value for Display, then it takes precedence over the specifications of the optimization options Diagnostics and Display.

    • If you do not specify a value for Display, then estimate honors all selections related to the display of optimization information in the optimization options.

Output Arguments

EstMdl

Model containing the parameter estimates, returned as a garch model. estimate uses maximum likelihood to calculate all parameter estimates not constrained by Mdl (i.e., all parameters in Mdl that you set to NaN).

EstParamCov

Variance-covariance matrix of maximum likelihood estimates of the model parameters known to the optimizer, returned as a matrix.

The rows and columns associated with any parameters estimated by maximum likelihood contain the covariances of estimation error. The standard errors of the parameter estimates are the square root of the entries along the main diagonal.

The rows and columns associated with any parameters held fixed as equality constraints contain zeros.

estimate uses the outer product of gradients (OPG) method to perform covariance matrix estimation

estimate orders the parameters in EstParamCov as follows:

  • Constant

  • Nonzero GARCH coefficients at positive lags

  • Nonzero ARCH coefficients at positive lags

  • Degrees of freedom (t innovation distribution only)

  • Offset (models with nonzero offset only)

logL

Optimized loglikelihood objective function value.

info

Summary information, returned as a structure.

Field Description
exitflag Optimization exit flag (see fmincon in Optimization Toolbox)
options Optimization options controller (see optimoptions and fmincon in Optimization Toolbox)
X Vector of final parameter estimates
X0 Vector of initial parameter estimates

For example, you can display the vector of final estimates by typing info.X in the Command Window.

Examples

expand all

Estimate GARCH Model Parameters Without Initial Values

Fit a GARCH(1,1) model to simulated data.

Simulate 500 data points from the GARCH(1,1) model

where and

Use the default Gaussian innovation distribution for zt.

Mdl = garch('Constant',0.0001,'GARCH',0.5,...
    'ARCH',0.2);
rng('default');
[v,y] = simulate(Mdl,500);

The output v contains simulated conditional variances. y is a column vector of simulated responses (innovations).

Specify a GARCH(1,1) model with unknown coefficients, and fit it to the series y.

ToEstMdl = garch(1,1);
EstMdl = estimate(ToEstMdl,y)
    GARCH(1,1) Conditional Variance Model:
    ----------------------------------------
    Conditional Probability Distribution: Gaussian

                                  Standard          t     
     Parameter       Value          Error       Statistic 
    -----------   -----------   ------------   -----------
     Constant    9.89111e-05   3.07264e-05        3.21909
     GARCH{1}       0.453934      0.111926        4.05567
      ARCH{1}       0.263739     0.0569312        4.63259

EstMdl = 

    GARCH(1,1) Conditional Variance Model:
    --------------------------------------  
    Distribution: Name = 'Gaussian'
               P: 1
               Q: 1
        Constant: 9.89111e-05
           GARCH: {0.453934} at Lags [1]
            ARCH: {0.263739} at Lags [1]

The result is a new garch model called EstMdl. The parameter estimates in EstMdl resemble the parameter values that generated the simulated data.

Estimate GARCH Model Parameters Using Presample Data

Fit a GARCH(1,1) model to the daily close NASDAQ Composite Index returns.

Load the NASDAQ data included with the toolbox. Convert the index to returns.

load Data_EquityIdx
nasdaq = Dataset.NASDAQ;
y = price2ret(nasdaq);
T = length(y);

figure
plot(y)
xlim([0,T])
title('NASDAQ Returns')

The returns exhibit volatility clustering.

Specify a GARCH(1,1) model, and fit it to the series. One presample innovation is required to initialize this model. Use the first observation of y as the necessary presample innovation.

Mdl = garch(1,1);
[EstMdl,EstParamCov] = estimate(Mdl,y(2:end),'E0',y(1))
    GARCH(1,1) Conditional Variance Model:
    ----------------------------------------
    Conditional Probability Distribution: Gaussian

                                  Standard          t     
     Parameter       Value          Error       Statistic 
    -----------   -----------   ------------   -----------
     Constant    1.99864e-06   5.42273e-07        3.68567
     GARCH{1}       0.883564    0.00843403        104.762
      ARCH{1}       0.109026    0.00764706        14.2573

EstMdl = 

    GARCH(1,1) Conditional Variance Model:
    --------------------------------------  
    Distribution: Name = 'Gaussian'
               P: 1
               Q: 1
        Constant: 1.99864e-06
           GARCH: {0.883564} at Lags [1]
            ARCH: {0.109026} at Lags [1]

EstParamCov =

   1.0e-04 *

    0.0000   -0.0000    0.0000
   -0.0000    0.7113   -0.5343
    0.0000   -0.5343    0.5848

The output EstMdl is a new garch model with estimated parameters.

Use the output variance-covariance matrix to calculate the estimate standard errors.

se = sqrt(diag(EstParamCov))
se =

    0.0000
    0.0084
    0.0076

These are the standard errors shown in the estimation output display. They correspond (in order) to the constant, GARCH coefficient, and ARCH coefficient.

References

[1] Bollerslev, T. “Generalized Autoregressive Conditional Heteroskedasticity.” Journal of Econometrics. Vol. 31, 1986, pp. 307–327.

[2] Bollerslev, T. “A Conditionally Heteroskedastic Time Series Model for Speculative Prices and Rates of Return.” The Review of Economics and Statistics. Vol. 69, 1987, pp. 542–547.

[3] Box, G. E. P., G. M. Jenkins, and G. C. Reinsel. Time Series Analysis: Forecasting and Control. 3rd ed. Englewood Cliffs, NJ: Prentice Hall, 1994.

[4] Enders, W. Applied Econometric Time Series. Hoboken, NJ: John Wiley & Sons, 1995.

[5] Engle, R. F. “Autoregressive Conditional Heteroskedasticity with Estimates of the Variance of United Kingdom Inflation.” Econometrica. Vol. 50, 1982, pp. 987–1007.

[6] Greene, W. H. Econometric Analysis. 3rd ed. Upper Saddle River, NJ: Prentice Hall, 1997.

[7] Hamilton, J. D. Time Series Analysis. Princeton, NJ: Princeton University Press, 1994.

See Also

filter | forecast | garch | infer | print | simulate

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ClOUD cOMPUTING: Storing Confidential Data on internet clouds

Name:

Department:

Institution:

Date:

 

 

Abstract

The concept of cloud computing is continuously evolving as more developments arise and as more and more people become aware of how cloud computing affects their daily lives. The main purpose of this discussion is to give an insight into the concept of cloud computing, exploring its main characteristics, service and deployment models and the technical legal issues related to it. Many organizations are turning on cloud computing to ease the burden on their IT facilities and to increase the value of their resources not to mention improve on their efficiencies. Whilst cloud computing to a larger extent has been more than beneficial to such companies, there are pertinent issues that come with its application and in particular those related to security.

1.       Introduction

The primary conception of cloud computing revolved around moving services and applications into the internet cloud (Rouse, 2010). The growth of cloud computing can be traced back to  remote sharing of computer applications and resources, where individuals and business entities could be able to use classical methods such as the Ethernet to share files and other resources across different computers. Today however, cloud computing has been defined to encompass different types of applications and services being delivered and shared through the internet cloud ((Foster, Hao and Aicu, 2008, p. 7). Further, technical developments have nullified the necessity of special applications for one to get access to cloud computing.

Companies such Microsoft, Google and Salesforce.com among others have increasing made cloud computing services available to consumers. Similarly, many consumers including both individual and businesses have realized the benefits of cloud computing as compared to the traditional method of having an all inclusive IT department. The cloud-based applications have software used for business planning services, training management and engineering design service (Voas and Zhang, 2009, p. 16). Cloud technology has also been adopted by large organizations which opt to rent instead of owning computer resources. This allows cost savings, greater flexibility and safety, trying emerging technologies and resilience during natural disasters and includes applications that allow single sign-on with the use of Active Directory, enabling workers to access cloud services that have been approved, by signing on to a single, federated system.  Google Inc., Amazon and Microsoft Corp allow their computing infrastructure to be leased by third parties via an internet-based connection. Despite the benifts associated with cloud computing, there are certain risks that a company or users must weigh before moving confidential data on internet clouds. The purpose of this paper is to examine the technical and legal issues associated with storing confidential data on internet clouds.

2.      TECHNICAL ISSUES

Despite the fact that data and information stored in the internet cloud can be accessed from anywhere and at any given time, there are some technical challenges associated with cloud computing and which every user should put into consideration when embarking on any project especially when it comes to confidential data.

2.1. Technical hitches

Man-made machines are not always perfect and are often prone to dysfunctions. Unexceptionally, cloud computing is prone to technical hitches and outages that can sometimes lead to inconveniences such as loss of data, technical bleaches and delayed access. While some of the technical hitches can be detected and fixed in time, this may not always be true and setbacks are bound to occur now and then (Vouk, 2008, p. 36).

2.2. Network hacking

As more and more advanced technologies are developed, the knowledge level increases. Computer and network hacking continues to pose a very big threat in the field of information technology. Confidential data or information stored on an internet cloud is prone to network hacking which can subsequently lead to loss or exposure to third parties (Voas and Zhang, 2009, p. 17). Whilst cloud service providers uses secure connections and other security measures, it is not always possible to detect network hacking activities and at times consumers may lose vital data or get exposed to third parties. Cloud computing services are accessed across the internet and can be done from a variety of devices including mobile devices, personal computers, and laptops among others. The deployment of cloud computing services encompasses a lot of things ranging from business applications to smart phones applications among others. It follows therefore that it is possible for a person with the knowhow to use a remote device and hack into the network thus compromising data stored in the clouds.

2.3. Privacy

It has been argued that host companies have the capability of monitoring communication between the end user and the company. It follows therefore that host companies have access to information data stored in the clouds thus posing the risk of exposing confidential data to non-interested/third parties.  Such parties could be the host company itself through its employees or other cloud service users such as advertising agencies. Further, the exception mandate given by communication and security agencies to these companies in regard to monitoring network activities make it even harder for one to rely on cloud computing for storing confidential data/information (Keahey, 2009, p. 47). Cloud computing makes use of a virtualized software model that allows users to share physical services, networking and storage capabilities. Regardless of the model adopted, cloud infrastructure endeavors maximally utilize the available infrastructure across different users. The fact that users share the network makes it all the more vulnerable for privacy invasion. Technical hitches and malicious activities are some of the factors that can result to loss of private data to thirdparties.

3.      LEGAL ISSUES

4.1    Trademark/copyright infringement

One of the major legal challenge of cloud computing revolves around legal ownership of data. Given the fact that host companies are the ones in possession of cloud data, it can be argued that they have some legal rights over such data. However, it must be understood that host companies are not necessarily the legal owners of this data (Keahey, 2009, p. 48). The problem of legal ownership of internet data is prominent within legal discussions mainly due to the silence accorded by the terms of agreement on the matter of ownership.

4.2    Data sharing

Another legal issue relating to cloud computing emancipates from the tendency of host companies to share customers’ information with their affiliates companies. While most of this data is reused for other purposes other than hurting the victims, most customers do not like it when confidential data is made available to other parties. A case example can be drawn from marketing companies which after obtaining data from host companies sends marketing and advertising emails to the affected customers (Vouk, 2008, p. 33). In essence, it is possible to find an email account full of junk or spam emails all sent from unauthorized companies which have illegally secured customer’s information from their affiliates. This leads to the issue of privacy.

4.3    Security and privacy

One of the most debated legal issues relating to cloud computing involves securing and storing data over internet cloud. Included here is the issue of network monitoring. Often, this issue has been associated with slowed deployment of internet cloud services leading to poor accessibility and flexibility. As aforementioned earlier, the issue of network monitoring coupled with the issue of data possession challenges consumers legal ownership of data stored on internet clouds (Foster, Hao and Aicu, 2008, p. 10). To mitigate this challenge, many users have opted to make use of internal storage while allowing it to be used over the cloud. However, there must be clear cut security mechanisms between the host company and the customer for the network system to be robust and fully secure.

4.4    Lack of standard

Despite the fact that clouds possess documented interfaces, they lack standards making them highly none-standardized.  While there are some efforts to establish standards to guide the use and application of these interfaces, it is difficult to keep up with such standards especially given the fact that cloud computing is only a recent concept that is evolving at unprecedented rate.

4.5    Compliance concerns

Many compliance issues relating to cloud computing as of today emancipates from the Sarbanes-Oxley Act (SOX) and EU Data Protection directives. However, it must be understood that compliance issues are dependent on the type of application in use and data in question.   Copyrighted materials are treated differently than other types of data and ISO together with cloud computing service providers are expected to instill measures that protects consumers against unlawful access of their data by a third party.

4.      CONCLUSION

The concept of cloud computing continues to attract the attention of many organizations today. It essence, cloud computing has been seen as a good way of increasing efficiency while at the same time reducing costs as organizations no longer require complex IT infrastructure to dispense their IT obligations. The technology has enabled companies to reassign their software engineers and other IT employees from mundane activities enabling them to enhance business performance, like development of new applications. Some of the gaps in IT capabilities involve the risks posed by external unauthorized intruders into the IT systems but future capabilities continue to be enhanced with development of modern technology.

5.      BIBLIOGRAPHY

[1]    Foster, I., Hao, Y., and Aicu, I.  2008. “Cloud Computing and Grid Computing 360-Degree Compared” In Grid computing Environments Workshop (GCE ’08), Austin, Texas, USA, November 2008, 1-10

[2]    Keahey, K., Tsugawa, M., Matsunaga, A. and Fortes, J. 2009. Sky Computing: Internet Computing, IEEE, Vol. 13, (5): 43-51.

[3]    Rouse M. 2010. Cloud Computing. [Online] http://searchcloudcomputing.techtarget.com/definition/cloud-computing

[4]    Voas, J. and Zhang, J. 2009. Cloud Computing: New Wine or Just a New Bottle? It Professional, Vol. 11(2): 15-17.

[5]    Vouk, M. A. 2008. “Cloud Computing: Issues, Research and Implementations” In Information Technology Interfaces, 2008. Iti 2008. 30th International Conference on, 31-40.

 

 

 

Human Spatial Behavior Presentation

Human Spatial Behavior Presentation

Introduction

Human spatial behavior involves the conduct of human to respond and react to the immediate environment. Notably, a normal human being will be conscious of events happening around him or her. As a result, the human being will behave in a manner that indicates awareness or consciousness of whatever is happening around (Hogh-Olesen, 2008). In this case, we will discuss various factors that influence the response and reaction of a human to the surrounding. We shall consider the immediate surroundings of a human, both inanimate and animate with regard to how they influence the response and reaction of a human being. We will keenly look at the universal aspects related to human spatial behavior.

Discussion

Research indicates that personal space is important in ensuring the comfort of the individual. Personal space will shrink or expand as appropriate based on context and depending on whether an individual occupies or arrives at a territory occupied by someone else. Culture influences human spatial behavior. Different people have different customs, norms, and beliefs, which determine how they view phenomena in their surrounding (Hogh-Olesen, 2008). As a result, human being from different territories will reasons and react different within their territories as well as outside their original territories. For instance, considering people from southern European, Latin America, and Arabian countries, known as contact cultures, these people tend to have shorter interactional distance compared to people from North America, and northern Europe.

Gender is another significant factor that determined human spatial behavior. For instance, comparing men and women, you will find that men tend to prefer more space around them compared to women. Many other factors including age, personality, and relation determine the level required for personal space and distance from the surrounding. Based on research findings, it is clear that humans will mostly be organized based on a spacing principle leaving room between two strangers. On the other hand, objects and animals are organized according to a proximity principle, which leaves no or significantly less room between representatives (Hogh-Olesen, 2008). Children have significantly less space compared to adults but of course more space than both objects and animals. Number influences the spacing of humans.

Generally, people in all contexts will indeed keep a larger distance in situations with more than one stranger. There is usually a home ground advantage. This clearly indicates that there is smaller space between subject and stranger. In social places, personal space is usually smaller than in non-social places. There is a possibility that personal space may ‘rub off’ personal object and animals require more space than neutral representatives of these categories do. Various factors influence these responses by human and objects as indicated in our discussion. As indicates, age, nature, culture and other factors determine the personal space as well as distance to exist between and among individuals and objects from similar or different territories (Hogh-Olesen, 2008).

Conclusion

To sum up, it is evident that personal space depends on the particular human traits determined by age, culture and other significant factors. The distance between and among humans from different territories depends on who is visiting, and who is the host. Culture influences how human respond and react to their surroundings. The attitudes, beliefs, and norms developed determine the actions and reaction that an individual will depict while responding to some form of stimuli, occurrence, or phenomena that has substantial implication for the individual.

 

References

Hogh-Olesen, H. (2008). Human Spatial Behavior: The Spacing of People, Objects and Animals in Six Cross-Cultural Samples. Journal of Cogniti

Nerve injury and vascular necrosis complications management in old people

Nerve injury and vascular necrosis complications management in old people

 

Name:

Institution:

Date:

 

 

 

 

 

 

 

 

 

 

Introduction:

So as to understand femoral nerve injury, it is important to have a clue of how the nervous system works. To begin with, a nerve consists of numerous fibers known as axons which happen to be insulated by a layer of tissue known as the myelin sheath. Having known that, it is significant to recognize that the femoral nerve found in the legs. It aids muscles in mobility activities of the hip as well as straightening the leg. It also provides a feeling sensation of the front part of the thigh and the lower leg. If damage comes to this particular nerve, especially in old people, then a condition results. It is known as mononeuropathy. This condition means that a primary cause within it where other disorders could involve the whole body may result in isolated nerve permanent damage. Some of these causes include; falling or inflicted damage, long term pressure on the nerve, compressed state of the nerves by body parts or tumors among others. When a person is suffering from this condition, the following signs manifest themselves from time to time. They include; changes in sensation around the knee area or region and thigh, numbness, a burning sensation on the upper parts of the legs, buckling of the knees and unfamiliar pain in the thigh and having difficulty when ascending or descending a staircase.

In most cases, diagnosis and treatment of this condition differ from one person to another but in general, the doctor first identifies the condition and then goes ahead to treat its cause beginning with the nerve that is damaged. Other forms of medication include; injection of Corticosteroids into the affected region to take care of the swelling.

 

 

 

 

As elderly people’s population grows, the total number of their hip fractures exceedingly continues to grow as well. This is because the elderly have weaker bones and are much more prone to falling down due to poorer physique balance, medical side effects and difficulty in maneuvering around their surroundings hazards. Medical experts in various fields who take part in taking care of these patients with hip fractures are supposed to be familiar with basic assessment and dealing with these injuries. Statistics suggest that there will be of a total of 6 million hip fractures by the year 2050. There is an estimated number of 500,000 individuals who are hospitalized currently around the globe. Hip fractures gradually increase the chances of dying as well as morbidity among the elderly people in the society. Approximately one-third of these patients have gone ahead for hip replacement in various medical facilities. However, some can’t afford it which leaves them in pain and in a desolate state because the cost is high. The prognosis composition of hip fractures differs by anatomic positioning. The intertrochanteric area has a large number of counselors bones that contains good blood supply hence intertrochanteric fractures heal normally when appropriate medical attention is accorded to such a person. It is very significant to ensure that this rampant condition among the old is given enough attention to prevent it from contributing to loss of life by providing funding and the best medical experts to foundations geared towards making the lives of senior citizens more and more comfortable.

 

 

 

 

 

 

 

Reference

 

Walker K. (2013) Hip fractures in adults

http://www.uptodate.com/contents/hip-fractures-in-adults

 

Jasmin L. (2011) Femoral nerve dysfunction

http://www.nlm.nih.gov/medlineplus/ency/article/000687.htm

 

Uddin R. (2011) Femoral Nerve Damage Symptoms

http://www.livestrong.com/article/116794-femoral-nerve-damage-symptoms/

 

Murugappan S. (2013) Femur Fractures

http://emedicine.medscape.com/article/1246915-overview

 

C. Dugdale (2011) Femoral Nerve Dysfunction

http://health.nytimes.com/health/guides/disease/femoral-nerve-dysfunction/overview.html

 

 

 

 

 

Canterbury (C)

Name

Institution

 

 

 

 

 

 

 

 

 

 

 

Canterbury City, New South Wales, Australia

1-Births (from 2006 to 2011) (compare to NSW)

From 2006 to 2010, the number of births in Canterbury has been increasing but in 2011it decreased. There were 2139 people born in 2006, 2,240 births in 2007, 2,351 in 2008, 2,388 in 2009, 2,509 in 2010 and 2,442 in 2011. In New South Wales the total number of births in 2006 were 87,336, 89,495 in 2007, 94,684 in 2008, 92,783 in 2009, 95,918 in 2010 and in 2011, 95,879 children were born in NSW in general. Compared to NSW, Canterbury had experienced high births in 2006 according to the rate of population increase.

2-Deaths (from 2006 to 2011) (compare to NSW)

Those people who died in Canterbury in 2006 were 732, in 2007 788, 803 in 2008 746 in 2009, 770 in 2010 and 842 in 2011. In 2011, 110 children together with young people died in NSW, in 2010, in 2009, 45,678 people died while as in 2008 41, 908 people died in general. In 2007, 38,675 people died out of many causes like accidents and sicknesses among others. And in 2006, 39,987 people died. It is clear that many people died in NSW compared to those who have been dying in Canterbury in all those years.
3-Country of birth (2006 to 2011)

Canterbury (C) (LGA11550) 33.6 sq Kms

             

e:

                 

Country Of Birth Of Person(A) By Year Of Arrival In Australia (2 Of 2)

       

Count of persons born overseas(b)

               
                 
                 
 

Year of arrival

 
 

 

 

 

 

 

 

 

 

 

2006

2007

2008

2009

2010

2011(c)

 

Total

                 

Bosnia and Herzegovina

0

0

0

4

0

0

 

Cambodia

3

4

0

6

0

0

 

Canada

3

0

0

0

3

0

 

China (excl. SARs and Taiwan)(d)

369

449

475

457

331

164

 

Croatia

0

0

0

3

3

0

 

Egypt

43

75

47

19

37

10

 

Fiji

19

12

25

17

19

17

 

Former Yugoslav Republic of Macedonia (FYROM)

3

3

3

3

4

0

 

Germany

10

3

10

3

3

3

 

Greece

13

6

8

0

6

5

 

Hong Kong (SAR of China)(d)

21

13

11

11

10

3

 

India

261

331

374

227

140

58

 

Indonesia

130

117

115

87

101

31

 

Iraq

32

24

16

23

41

20

 

Ireland

0

3

5

8

13

10

 

Italy

12

4

7

3

10

8

 

Japan

3

12

6

6

0

6

 

Korea, Republic of (South)

69

74

111

79

75

24

 

Lebanon

76

114

95

95

59

46

 

Malaysia

28

22

12

23

22

11

 

Malta

0

0

0

0

0

0

 

Netherlands

3

0

0

0

3

3

 

New Zealand

68

58

63

57

67

55

 

Philippines

82

79

70

74

55

31

 

Poland

8

0

3

3

0

0

 

Singapore

5

4

13

0

0

0

 

South Africa

9

3

6

3

0

0

 

South Eastern Europe, nfd(e)

0

0

0

3

0

0

 

Sri Lanka

6

7

6

10

15

8

 

Thailand

13

15

24

24

14

5

 

Turkey

0

8

0

0

6

0

 

United Kingdom, Channel Islands and Isle of Man(f)

26

19

14

22

13

8

 

United States of America

3

5

3

13

4

0

 

Vietnam

82

87

84

101

75

55

 

Born elsewhere(g)

832

1,180

1,170

1,163

825

442

 

             

 

Total

2,232

2,731

2,776

2,547

1,954

1,023

 

             

 

This table is based on place of usual residence.

           

 

(a) This list of countries consists of the most common Country of Birth responses (excluding Australia) reported in the 2006 Census.

 

 

(b) Excludes persons who did not state their country of birth.

         

 

(c) The year 2011 is the period 1 January 2011 to 9 August 2011.

         

 

(d) Special Administrative Regions (SARs) comprise ‘Hong Kong (SAR of China)’ and ‘Macau (SAR of China)’.

   

 

(e) Includes persons who stated their birthplace as Yugoslavia.

           

 

(f) Comprises ‘United Kingdom, Channel Islands and Isle of Man, nfd’, ‘England’, ‘Isle of Man’, ‘Northern Ireland’, ‘Scotland’, ‘Wales’, ‘Guernsey’ and ‘Jersey’.

   

(g) Includes countries not identified individually, ‘Australian External Territories’, ‘Inadequately described’ and ‘At sea’.

       

              There are many people born in some countries and migrated to Canterbury as compared to others. In Vietnam, China and Hong Kong, they are the countries with very many people compared to countries like Malta, Iraq and South Easter Europe which have very few people born there and migrating to Canterbury.
4-Number of Vehicles (2006 to 2011)

Australian Bureau Of Statistics  2006-2011 Census of Population and Housing

 

 

 

Canterbury (C) (LGA 11550) 33.6 sq. Kms

   

 

 

Number Of Motor Vehicles(A) By Dwellings

 

 

 

     

 

 

 

 

Dwellings 2006-2011

 

 

 Number of motor vehicles per dwelling:

   

 

 

None

 

8,041

7,131

 

 

1 motor vehicle

 

18,750

19,291

 

 

2 motor vehicles

 

11,002

12,716

 

 

3 motor vehicles

 

2,898

3,369

 

 

4 or more motor vehicles

 

1,269

1,467

 

 

Total

 

41,960

43,974

 

 

     

 

 

 

Number of motor vehicles not stated

 

2,299

1,953

 

 

     

 

 

 

Total

 

44,259

45,927

 

 

     

 

 

     

 

 

(a) The entire list of number of vehicles excludes motorbikes/scooters.

   

 

 

(b) It also excludes ‘Visitors only’ and ‘Other not classifiable’ households.

 

 

 

     

 

                                                   

Many people have one vehicle according to the graph above because in 2006 and 2011 statistical records, it is clear that majority of people have one vehicle followed by the number of these people who own two vehicles.

5-Average Tax Income (2006 to 2011)

Australian Bureau Of Statistics  2006-2011 Census of Population and Housing

         

List of tables

Canterbury (C) (LGA 11550) 33.6 sq. Kms

               

Concepts and Definitions

 

 

Average  Individual Income (Weekly) By Age By Sex (1 Of 2)

         

Census Data Quality Statement

 

Count of persons aged 15 years and over

           

© Commonwealth of Australia 2007

 

                 

 

                     

 

 

15-19

20-24

25-34

35-44

45-54

55-64

65-74

75-84

85 years

 

 

 

years

years

years

years

years

years

years

years

and over

Total

 

 

MALES

 

 

                   

 

        Negative/Nil income

1,558

635

683

438

299

329

210

59

16

4,224

 

$1-$149      

942

413

223

235

237

249

286

168

36

2,787

 

$150-$249  

303

493

657

824

843

1,184

1,926

1,200

208

7,638

 

$250-$399

241

524

840

880

894

783

723

562

144

5,593

 

$400-$599

147

787

1,471

1,508

1,303

886

434

237

66

6,840

 

$600-$799

54

566

1,546

1,424

1,217

787

228

98

16

5,935

 

$800-$999

19

275

1,217

1,102

838

557

110

48

18

4,187

 

$1,000-$1,299 

7

139

1,048

1,069

832

480

81

29

7

3,691

 

$1,300-$1,599

4

53

446

660

487

220

36

9

6

1,919

 

$1,600-$1,999

0

4

273

402

310

130

20

11

0

1,147

 

$2,000 or more

5

6

241

461

300

120

22

14

0

1,170

 

                     

 

Individual income not stated

718

504

954

1,032

857

643

486

402

143

5,741

 

                     

 

Total

3,999

4,396

9,596

10,035

8,40

6,369

4,563

2,837

660

50,872

 

 

                   

 

 

FEMALES

 

                     

 

Negative/Nil income

1,475

679

1,355

1,009

948

723

268

124

41

6,623

 

$1-$149      

1,084

442

689

750

539

504

331

175

52

4,566

 

$150-$249  

328

559

1,061

1,355

1,358

1,807

2,166

1,319

349

10,303

 

$250-$399

192

557

1,026

1,283

1,048

852

965

994

377

7,295

 

$400-$599

133

836

1,460

1,720

1,413

795

310

240

68

6,979

 

$600-$799

41

569

1,195

1,093

919

372

105

60

22

4,377

 

$800-$999

4

266

891

691

555

268

54

25

12

2,763

 

$1,000-$1,299 

3

77

780

653

493

179

34

19

6

2,244

 

$1,300-$1,599

3

17

296

400

310

124

13

3

0

1,167

 

$1,600-$1,999

0

5

108

166

127

36

4

8

3

457

 

$2,000 or more

2

6

88

175

84

30

11

12

7

416

 

                     

 

Individual income not stated

567

465

939

906

772

569

484

510

303

5,514

 

                     

 

Total

3,838

4,479

9,887

10,202

8,566

6,259

4,744

3,489

1,240

52,704

 

                   

 

                     
 

15-19

20-24

25-34

35-44

45-54

55-64

65-74

75-84

85 years

 

 

years

Years

years

years

years

Years

years

years

and over

Total

 

PERSONS

 

                   

Negative/Nil income

3,034

1,313

2,038

1,447

1,247

1,055

478

183

57

10,847

$1-$149      

2,024

856

912

985

776

752

616

343

88

7,353

$150-$249  

635

1,051

1,718

2,179

2,201

2,991

4,092

2,519

557

17,941

$250-$399

434

1,083

1,866

2,164

1,941

1,635

1,688

1,556

521

12,888

$400-$599

280

1,624

2,931

3,229

2,716

1,681

746

477

134

13,819

$600-$799

97

1,135

2,740

2,517

2,136

1,159

333

158

38

10,312

$800-$999

24

541

2,108

1,792

1,392

827

164

73

30

6,950

$1,000-$1,299 

10

216

1,828

1,721

1,324

659

115

48

13

5,935

$1,300-$1,599

5

70

742

1,060

798

344

49

12

6

3,086

$1,600-$1,999

1

9

378

568

437

166

24

19

3

1,604

$2,000 or more

7

12

329

636

385

150

30

26

7

1,586

                     

Individual income not stated

1,286

969

1,893

1,938

1,630

1,213

970

912

446

11,255

                     

Total

7,838

8,875

19,483

20,236

16,983

12,628

9,308

6,326

1,900

103,576

                     
                                                                                             

The graph above shows the average amount of tax income from 2006 to 2011 according to statistical records. Many people get low income and very few get high income. Majority of people get less than $ 250 while those who earn more than $2,000 are very few.

 

 

 

 

 

References

McManus, P., & Connor, L. H. (2013). What’s mine is mine (d): Contests over marginalisation of rural life in the Upper Hunter, NSW. Rural Society, 22(2), 166-183.

Reid, M. (2010). Hauora Waitaha i: Health Profile for Māori in Canterbury. Canterbury District Health Board.

Zander, A., Rissel, C., Rogers, K., & Bauman, A. (2013). Walking to Work in Sydney: Analysis of Journey-to-work Census Data from 2001 and 2011.

Haverwood Furniture, Inc. Case Study

Haverwood Furniture, Inc. Case Study

 

Opportunity – The opportunity is to find a balance between Michael Harvey’s proposal (that the expenditure for consumer spending be increased by $225,000 in 2008) and John Bott’s proposal (that an additional sales representative was required to service company accounts since more than 50 new accounts were recently added). Under Michael Harvey’s proposal, consumer spending would be increased by $225,000 and cooperative advertising and trade advertising allowances would remain at 2007 levels. John Bott however maintained that since sales and administration expenses were projected to rise by more than $65,000 in 2008, around $135,000 in additional sales expenses have to be added into the promotional budget for 2008. So, under John Bott’s proposal, consumer spending as well as cooperative advertising and trade advertising allowances would remain at 2007 levels while sales and administration expenses would be raised by $135,000.

Causes – This opportunity presents itself due to the following reasons. Firstly, consumer spending for wood furniture is very cyclical and directly related to the frequency of new housing starts, consumer confidence, and disposable income. Since spending for wood furniture is considered deferrable, Michael Harvey believes that increasing consumer spending by $225,000 will significantly influence consumer confidence in the company’s favor, driving sales up. Secondly, even though industry research suggests that consumers regard the furniture shopping experience to be pleasurable, consumers recognize the fact that they often lack the necessary skills and confidence to evaluate furniture construction, provide judgments about quality, and to objectively assess the price of furniture. Furthermore, most consumers find it really hard to select among the many styles available, fearful that they may not like their choice several years after the purchase. As a consequence, John Bott believes that educating consumers should be the priority and that raising the company’s public relations expenses by $135,000 will serve this purpose.

Recommended Solution – The solution I am recommending is to accommodate both proposals by drawing additional funds from cooperative and trade advertising allowances. The idea is to draw up around $225,000 from the cooperative advertising allowance and $135,000 from the trade advertising allowance (the budget allocated for cooperative advertising expenses is substantially greater than the budget allocated for trade advertising expenses). Professor Bates mentions that the $225,000 increase in promotion will bring the budget up to the 5% percentage of sales policy limit. However, by drawing additional funds from cooperative and trade advertising allowances, such increase can be accommodated without violating the 5% percentage of sales policy limit. And naturally, it is also possible to accommodate John Bott’s proposal without violating the same policy.

Alternative Solution – Another solution considered is to reduce Harvey’s additional cost expense to $90,000 and retain John Bott’s initial proposal of $135,000. As said earlier, consumer spending for wood furniture is very cyclical and directly related to the frequency of new housing starts, consumer confidence, and disposable income. Since spending for wood furniture is considered deferrable, it can also be argued that increasing consumer spending may have little effect on boosting consumer confidence. However, the problem with this solution is that the delay involved in developing consensus among the implementers, particularly Harvey and Bott, may be offset by the speed and quality of implementation in the costing of projected advertising expenses (Rodriguez & Echanis, 2008). Furthermore, the plan may generate no commitment from some implementers, particularly Michael Harvey, who may not understand or accept the proposed plan (Bott’s proposal) designed without their due consent (Daft, 2008).

 

Haverwood Furniture – Promotion Budget

         

Item

2007

Percent of Revenue (2007)

 Proposal 2008

Percent of Revenue (2008)

Direct Sales – Sales Expense and Admin.

995,500

1.30

1,060,000.00

1.35

Advertising

—- 

—Cooperative

1,650,000

2.20

1,580,000.00

2.01

—Trade

467,000

0.62

400,000.00

0.51

—Consumer

562,500

0.75

500,000.00

0.63

Sales Promotion

0

225,000.00

0.29

Public Relations

0

135,000.00

0.17

Total

3,675,000

4.9%

3,900,000

4.95

Revenue

75,000,000

100.0%

78750000 

4.95

         

Note: All green cells (without values) must contain values when you submit with your case.

 

 

 

 

 

 

 

 

 

 

 

References

Daft, R. (2008). Management. New York: Macmillan Publishing Company.

Rodriguez, R.A. & Echanis, E.S. (2008). Fundamentals of Management. Manila: Diwata Publishing, Inc.