Analysis of X-ray based angiography systems in the interest of cost-effectiveness and patient health - Research Paper Example

? Analysis of X-ray based angiography systems in the interest of cost-effectiveness and patient health. Part The importance of flexible, cost-effective alternatives to surgical catheterization are evaluated and compared via literature meta-analysis. Traditional surgical methods of angiography are compared with X-ray based systems. The 320 detector-row is contrasted with the 64 detector-row systems. Patient factors that can affect the findings of X-ray based angiography are defined and evaluated. The 320-detector row system provides advantages in terms of patient safety, as well as overall cost. OBJECTIVE : Diagnostic comparison between 320 detector-row CT and 64 detector-row scan protocols and dosages to determine image quality, sensitivity, specificity, and accuracy. Research projects focus on literature reviews. KEYWORDS Angiogram, Angiography, Computed Tomography, Coronary Artery Disease, Multi-Slice, X-ray INTRODUCTION Coronary artery disease (CAD) can be counted as the preeminent cause of death in western industrialized countries. In fact, CAD is the single most important cause of death in Australia and New Zealand. (Sun, 2009) To better quantify this risk factor, more than 1 million instances of an invasive diagnostic coronary angiography operation are conducted annually in the United States alone, as part of billions of dollars spent for treatment costs of coronary artery disease, and just under 4 billion in Australia. The basic method for diagnosis of CAD is still an invasive procedure of coronary angiography. This can be described as the reference standard for the evaluation of the coronary arteries. This preference is largely due to apparent advantages of high spatial and temporal resolution, though it is also a relatively costly procedure. Despite this cost and the general inconvenience of such surgeries, it is utilized in part due to a low but noteworthy procedural morbidity of 1.5%, and mortality of 0.2% (Sun, 2009) With these findings underscoring both the clinical necessity of the procedure due to the severity of the disease, and the financial investments that have been poured into the procedures needed to diagnose it; there is a manifest interest in new technologies that would permit either a refinement of the procedure, cuts in cost, or a more efficient alternative. To that end, non-invasive X-ray angiography techniques are being pioneered as a similarly effective alternative without the surgical risks. In most cases, this alternative takes the form of X-ray angiography using selective contrast injection through cardiac catheterization. (de Feyter, 2004) Other methods involving multi-slice, computed tomography scanners (MSCT) have also proven successful. (Nieman et al. 2001) CT is an effective option suited for the evaluation of patients with varying levels of risk for coronary disease, allowing a non-invasive option that minimizes surgical complications, at relatively low cost. (Schuijf et al. 2006) But there are still outstanding issues necessary for the improvement of the process for yet greater gains in efficiency and safety. Radiation exposure and possible poisonings is always a source of concern. The principle issue is a scan high enough to reduce image noise and deliver acceptable quality; yet not so high that there is real risk of radiation damage to the patient, or for that matter the radiologist operators. It will be necessary to assess and contrast this factor also, in delineating between the available methods of CT-scanning. Part 2 Methodology In terms of the options available to clinicians, there are cardiac catheterizations via physical surgery, or these X-ray-based methods described herein. Either the 64 row or the 320 row can provide medically useful data without surgery; but in terms of overall patient health, we must return to radiation once again as an essential consideration. A variety of investigations have compared the benefits of X-ray based tomography systems compared to actual cardiac catheterization, and these methods undergo continuous evalation and analysis for further refinement; both in terms of efficiency and safety. Useful to a diagnosis of coronary aberrations relating to heart disease is the assessment of preoperative small vessels, via computed tomography, as mentioned above. Contrast enhancement can maximize the results from X-rays. Computed Tomography is aided by recent developments that utilize optimized detector geometry and thinner slice collimations along with greater gantry rotation speed. (Kitajima et al. 2010) The available literature contains many examples of experimental studies comparing the data gathered from relatively small patient populations scanned with older systems, and with new CT devices; Specifically, newer designs using 320-detector rows. These devices are popular among the modern arsenal of clinical options, and should be compared with other techniques as a cost-benefit analysis. The 320-row system is also known as an Area Detector CT, or ADCT which improves upon single-row, standard helical CT systems. The ADCT's z-axis rotational acquisition capability avoids 'stitching artifacts' between layer slices due to questionable data interpolations. Not only cardiac, but brain imaging is also a possibility using only a single rotational pass yielding a complete data set for the entire organ. (Steigner et al. 2008) When investigating the heart, ADCT does have highly efficient capabilities; but its potential for scanning the abdomen requires a staggered, stepwise approach; it does not appear possible at present to scan the entire abdomen using ADCT. The other alternative is a helical scan using a 64-detector row system. In terms of the heart exclusively, ADCT represents a technological leap. (Kitajima et al. 2010) Large-Scale Studies When applying the technology on a larger scale, the studies typically range from 27 to just under 50 human subjects; (Dewey et al. 2009), (Luo et al. 2011), (Steigner et al. 2008) but larger investigations have been conducted using hundreds of patients. The largest noted used 252 for an investigation of a 256-row multi-detector. (Law et al. 2011) Studies have analyzed imaging results for a single heart beat, (Steigner et al. 2008), and for differences between beats, in terms of whether there are scanning or processing anomalies based on analytic artifacts between a series of heart beats. (Tomizawa et al. 2010) Of concern to all investigators are issues of overall image quality, and computer processing in terms of the assembly of slices into a coherent, diagnostic picture. Studies must account for quality, while also taking into account possible distortions from the motion of a functional heart. A study by van der Wall proposes a four-point system for the evaluation of image quality during the comparative scans. A series of scans, and partial scans were conducted to test quality, as well as judge the ability of the computer system to accurately reconstruct the images. When the quantified image quality score of at least one of a pair of half-scan image reconstructions was superior to the score of a multiple-segment reconstructed image-scan, the half-scan reconstruction image was deemed to be superior to the multi-segment reconstructed image. In the other instance, image quality of a multisegment reconstructed image was deemed superior to that of the half-scan reconstruction when the image quality score of the multi-segment reconstruction image was superior to the scores of both half-scan reconstruction images. (van der Wall, et al. 2010) It is also necessary to differentiate between the 320 and 64 systems. A study by Einsten has investigated the efficacy of the 64-row system in terms of radiation risk. Patient organs were subjected to doses from 64-slice Computed Tomography Coronary Angiography using a standardized computational model. Female and male patients were analyzed using Monte Carlo simulation methods, with standard spiral CT scanning protocols. Age- and sex-specific Lifetime attributable risk factors for individual cancers were estimated using the approach of BEIR VII and compiled using summation to obtain a quantification of lifetime risk factors for the entire body of the patient. (Einsten et al. 2007) The Monte Carlo simulation system uses the ImpactDose package to estimate radiation dosages to organs through a model of photon transportation from coronary tomography into a standardized selection of mathematical 'phantoms' designed to mimic probable data resulting from a human subject. The subjects' data was then analyzed using numerical findings outlined in the BEIR VII report; which is a risk-modeling theoretical system used for estimating risks associated with carnicogenicity, in this case. (Einstein et al. 2007) Scanning Protocols Kitajima has performed a noteworthy 60-patient investigation comparing the area-detector 360 and 64-row systems on several levels. ADCT examinations were performed using the following protocols: 200–320 row ? 0.5mm detector collimation, 0.35s/gantry rotation, 120kVp ,400mA, and 3 to 5 rotations. Every subject was initially examined using pure, unenhanced CT. Another test was conducted to supplement these findings with 80ml of an iodinated contrast medium that was injected at a rate of 3 ml/ per second followed by a 20 ml dose of saline solution administered at the same rate. Third, a tri-phasic contrast-enhanced CT scan was conducted on each subject using delay periods of 40, 70, and 150 seconds following the initial injection. The 64-detector scan used the settings listed below: 64 row ? 0.5 mm detector collimation, 0.5 per second/ gantry rotation, 120kVp, 350mA, and 0.94 beam pitch. Each subject initially examined under unenhanced CT. Followed by the injection of 90ml of iodinated contrast medium at 3.0 ml/ per second and then of 20ml of saline solution at the same rate. The scanning protocol for 64-detector row CT consisted of unenhanced and tri-phasic contrast-enhanced CT scans during the arterial,corti-comedullary, and nephrographic phases. After which there were delays of 25-30 seconds for the arterial phase with automatic triggering, and 60 seconds for the following corticomedullary phase, and then 120 seconds for the nephrographic phase. The body regions scanned were set for the area between the biacetabular line and the bifurcation of the aorta, starting from the diaphragm. Body weight and body mass index were also recorded for each patient to determine the computed tomographic dose index, as a means of assessing the average radiation dose for each scanning protocol. Body volumes, weight, and the BMI were compared with an unpaired t-test. (Kitajima et al. 2010) This analysis is similar to a process used by Einstein; as both studies employed what they described essentially as mathematical phantom extrapolations of an anthropomorphic subject as part of radiation dosage calculations. (Kitajima et al. 2010) , (Einstein et al. 2007) Results The available studies were typically performed with an eye towards consistency of results, disqualifying subjects in which medical complications, time constraints, or risk factors might have affected the findings. Some challenges included irregularities in the flow of the contrast agent, as a disqualifier. (Dewey et al. 2009) Current technology has determined that the heart beat itself, the motion and rates of motion are essential factors in the quality of the images recorded for later reconstruction. CT systems derives more meaningful findings based on patient health, and its bearing on heart rate. One study found an inverse relationship between heart rate, and the width of the phase window for the scan; resulting in differences in image quality. Using a 320-row system, Cardiac scans were higher quality, and thus more diagnostically useful in patients with lower heart rates, than in those at the higher end of the statistical curve. (Steigner et al. 2008) In addition to heart motion affecting image quality, the ability of the software to interpret the scan-slices is also dependent on motion rations, and thus by size. Smaller coronary artery segments are more susceptible to image degradation due to natural cardiac motion than larger vessels. (van der Wall et al. 2010) Variations are inevitable in scan quality, but radiation exposure is also affected by the condition of the patients' heart. Average radiation exposure was found to be lower in patients with higher heart rates. (Dewey et al. 2009) Where radiation exposure rates were a concern, it was determined in most instances that a lower effective radiation dose (and contrast agent) were possible for the 320-row CT. 4.2 rather than 8.5, in the studies conducted by Dewey. (Dewey et al. 2009) Lifetime attributable risk factors showed highest for women in their 20's, declining noticeably towards age 40 and beyond, a rate of decrease at approximately 50%, ( 0.70% verus 0.35% risk) (Einstein et al. 2010) This is consistent with older results indicating declining sensitivity to carcinogenicity from radiation with advancing age. (Thompson et al. 1994) There is ample evidence supporting a median radiation exposure dosage at approximately 12 mSv using the 320-row system. (Dewey et al. 2009) , (Einstein et al. 2009) which is lower than the rates seen using the 64-row device. There are other lines of evidence where differences between the 360 and 64-row systems are apparent: For the imaging results of epigastric and mesenteric marginal arteries, imaging scores tended to be of higher quality when using the 320-system, but comparisons in terms of body weight, or body mass-index did not produce differences between the systems. (Kitajima et al. 2010) Part 3 Discussion and Conclusion The studies described herein are valuable investigations into the apparent leading cause of death in the industrialized world, as a tool for the diagnosis and treatment of heart disease. Noninvasive analytical tools such as contrast-enhanced CT are growing popular among medical professionals in recent years due to the higher costs of conventional, surgical tools for angiography. The relative expensive, complication risks, and cost in terms of time compel us to seek alternatives. It is not difficult to express and appreciate the advantages of X-ray based scans as opposed to surgical catheterization of the heart; but further improvements are always desirable, both in the interest of cost-minimization, and patient health. It is not a challenge to identify other studies supporting the utility of angiographic images for anatomic data prior to treatment for heart disease. (Brennan et al. 2007) , (Ferrari et al. 2007) , (Sugita et al. 2008) Crucial to any discussion concerning a radiological procedure is the issue of radiation exposure and the necessity of minimizing the risk. While a singular, isolated procedure may seem to carry only a minor risk of carcinogenicity; when such treatments are performed millions of times upon millions of individuals; it behooves medical scientists to investigate the statistical probability of nucleus damage due to radioactivity. Any means by which the same data can be gathered with a minimization of exposure to potentially harmful particles is an option that must be pursued. The helical scanning pattern of the 64-row CT angiography system does yield useful, clinical data. It can perform the job in a similar fashion as the 320; but in terms of overall utility and safety, it is not the most preferable option. In essence, the 320 system with its Z-axis scanning capabilities is able to get the same basic image-slices as the 64, but by capturing more images with each exposure, the same clinical information can be gathered by exposing the patient to less radiation. (Dewey et al. 2009) , (Einstein et al. 2009) Plus, there exists the likelihood that the images that are gathered will result in higher quality resolutions. (Kitajima et al. 2010) A limitation of radiation exposure over the entire patient population reduces cancer risk-factors, and is likely to lower costs to healthcare systems worldwide. 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