Imaging of coronary atherosclerosis using computed tomography: Current status and future directions

High-density lipoprotein and atheroma monitoring

PURPOSE OF REVIEW

To highlight the use of arterial wall imaging to evaluate the impact of therapies that promote high-density lipoproteins.

RECENT FINDINGS

High-density lipoproteins possess a number of biological properties, which have a direct impact on the extent and composition of atherosclerosis. Arterial wall imaging has been employed to demonstrate the beneficial influence on atherosclerosis of a number of therapeutic agents that modify high-density lipoprotein.

SUMMARY

Atheroma imaging has become an integral component of the clinical development of novel therapeutic agents designed to promote the atheroprotective activity of high-density lipoprotein.

Coronary magnetic resonance angiography

Coronary magnetic resonance angiography (MRA) is a powerful noninvasive technique with high soft-tissue contrast for the visualization of the coronary anatomy without X-ray exposure. Due to the small dimensions and tortuous nature of the coronary arteries, a high spatial resolution and sufficient volumetric coverage have to be obtained. However, this necessitates scanning times that are typically much longer than one cardiac cycle. By collecting image data during multiple RR intervals, one can successfully acquire coronary MR angiograms. However, constant cardiac contraction and relaxation, as well as respiratory motion, adversely affect image quality. Therefore, sophisticated motion-compensation strategies are needed. Furthermore, a high contrast between the coronary arteries and the surrounding tissue is mandatory. In the present article, challenges and solutions of coronary imaging are discussed, and results obtained in both healthy and diseased states are reviewed. This includes preliminary data obtained with state-of-the-art techniques such as steady-state free precession (SSFP), whole-heart imaging, intravascular contrast agents, coronary vessel wall imaging, and high-field imaging. Simultaneously, the utility of electron beam computed tomography (EBCT) and multidetector computed tomography (MDCT) for the visualization of the coronary arteries is discussed.

ACR clinical statement on noninvasive cardiac imaging

Coronary artery disease and other acquired and congenital cardiac diseases are major medical and socio-economic problems. Historically, imaging has had a critical role in the diagnosis and evaluation of acquired and congenital cardiac disease. Advances in computed tomography (CT), with multidetector CT and electron beam CT technology, and magnetic resonance (MR) imaging, now make it possible to noninvasively image the coronary arteries, cardiac chambers, valves, myocardium, and pericardium and assess cardiac function, and CT and MR imaging are becoming increasingly important in the evaluation of cardiac disease. Radiologists, because of their extensive experience in CT and MR imaging, have an important role in imaging cardiac patients using these modalities. This clinical statement of the ACR discusses various technical and patient safety issues related to cardiac CT and MR imaging, and it suggests appropriate qualifications for radiologists until such time as ACR practice guidelines for the performance of cardiac CT and cardiac MR imaging are written and approved through the usual ACR process. It stresses that the interpreting physician is responsible for examining not only the cardiac structures of interest but also all the visualized noncardiac structures and must report any clinically relevant abnormalities of these adjacent structures.

Feasibility and Optimization of Aortic Valve Planimetry with MDCT

OBJECTIVE

The aortic valve can be assessed using MDCT; however, measurements of the aortic opening area vary with the cardiac cycle. In this study, we sought to assess the optimal timing for measuring the area of the aortic opening with MDCT.

MATERIALS AND METHODS

Retrospectively gated MDCT was performed in 57 patients with the following parameters: gantry rotation time, 420 milliseconds; tube voltage, 120 kV; tube current, 550 mAs with tube current modulation; and slice collimation, 16 x 0.75 mm. From 72 to 100 mL of contrast agent (320 g/mL3) was injected i.v. at 4-5 mL/s. High-resolution data sets were obtained for planimetry at phase starts of 0, 50, 100, 150, and 200 milliseconds after the R wave peak and were assessed for aortic opening area and the presence of artifacts.

RESULTS

In 41% of patients, the cardiac phase with the largest aortic opening area was at 50 milliseconds after the R wave peak. The area of the aortic opening measured at 0 milliseconds after the R peak was 2.7 +/- 0.8 cm2 (mean +/- SD); at 50 milliseconds, 2.9 +/- 0.2 cm2; at 100 milliseconds, 2.9 +/- 0.7 cm2; at 150 milliseconds, 2.8 +/- 0.7 cm2; and at 200 milliseconds, 2.4 +/- 0.8 cm2. The image quality was best at 50 milliseconds after the R peak in 42% of patients, 100 milliseconds in 29%, 150 milliseconds in 20%, 0 milliseconds in 7%, and 200 milliseconds in 2%. The aortic valve appeared closed in three patients at 0 milliseconds and in four patients at 200 milliseconds. Fewer artifacts were present in the midsystolic phases (i.e., 50-150 milliseconds) ("double-leaflet" artifact, 5-13%; "incomplete contour" artifact, 20-26%) than in the early (0 milliseconds) and late (200 milliseconds) systolic phases (double-leaflet artifact, 38% and 43% of patients; incomplete contour artifact, 76% and 73%, respectively).

CONCLUSION

Aortic valve planimetry is best performed at phase starts of 50-100 milliseconds after the R peak because the area of the aortic opening is widest and image quality is best at that phase.

Multidetector computed tomography for the diagnosis of coronary artery disease: a systematic review

PURPOSE

The study's purpose was to determine the sensitivity and specificity of contrast-enhanced multidetector computed tomography (CT) for the detection of coronary artery disease.

SUBJECTS AND METHODS

A search of the literature in all languages was performed incorporating both electronic and manual components. Manual reference checks of recent reviews and all original investigations supplemented the electronic searches.

RESULTS

Average sensitivity for patient-based detection of significant (>50% or > or =50%) stenosis was 61 of 64 (95%) with 4-slice CT, 276 of 292 (95%) with 16-slice CT, and 47 of 47 (100%) with 64-slice CT. Average specificity was 84% for 4-slice CT, 84% for 16-slice CT, and 100% for 64-slice CT. The sensitivity for a significant stenosis in evaluable segments was 307 of 372 (83%) with 4-slice CT, 1023 of 1160 (88%) with 16-slice CT, and 165 of 176 (94%) with 64-slice CT. Average specificity was 93% or greater with all multidetector CT. Seventy-eight percent of segments were evaluable with 4-slice CT, 91% with 16-slice CT, and 100% with 64-slice CT. Stenoses in proximal and mid-segments were shown with a higher sensitivity than distal segments. Left main stenosis was identified with high sensitivity with all multidetector CT, but sensitivity in other vessels increased with an increasing number of detectors.

CONCLUSION

Multidetector CT has the potential to be used as a screening test in appropriate patients. Contrast-enhanced 16-slice CT seems to be reasonably sensitive and specific for the detection of significant coronary artery disease but has shortcomings. Preliminary data with 64-slice CT suggest that it is more sensitive and specific.

Quantification of Calcification in Atherosclerotic Lesions

Calcification can be deposited throughout the vasculature in several forms of calcium phosphate, including calcium hydroxyapatite (CHA). Calcium accumulation in arteries by mineralization and calcium loss from bone by osteoporosis often coexist, and vascular calcification may share common mechanisms with bone remodeling. Deposition of calcification in valves and arteries diminishes the valvular or arterial wall elasticity, a major cause of aneurysm and stenosis. Obstruction of arteries by calcification and other components can lead to heart attack and stroke. Mineralization in the femoral arteries can cause intermittent claudication in the legs, causing decreased mobility. Accurate measurement of calcification is essential for identifying other factors associated with this process and ultimately for elucidating the mechanism(s) of calcification. A wide range of methods for visualizing and measuring calcification for diagnosis and treatment in vivo and for studying the calcification process ex vivo are available. This review provides a critical comparison of older established methods and newer evolving technologies for quantifying calcification.