ReviewMulti-detector row computed tomography: imaging the coronary arteries
Introduction
Coronary artery disease continues to be one of the leading causes of morbidity and mortality in England and Wales; 108,000 deaths from coronary disease were recorded in the year 2000. More than 41,000 of these deaths took place under the age of 75 years. The current prevalence of angina is over 2 million in the UK,1 about 300,000 people experience a myocardial infarction each year and coronary disease accounts for about 3% of all hospital admissions in England.2
Following other non-invasive diagnostic procedures, such as exercise-ECG testing, conventional invasive catheter coronary angiography currently provides the standard of reference for definitive diagnosis.3, 4, 5 Its advantages are high spatial (∼0.15 mm) and temporal resolution and the options of performing percutaneous angioplasty or stent insertion on the same occasion. However, many of these examinations do not lead to revascularization therapy; up to 25% of subjects in the UK are found to have normal coronary arteries,6 and 66% of subjects in the USA3 undergo invasive angiography for the presence and assessment of disease severity alone. In order to prevent unnecessary invasive tests, a reliable and reproducible non-invasive diagnostic test for the detection and grading of coronary artery stenosis is highly desirable. The most promising method at present is multi-detector row computed tomographic (MDCT) coronary angiography.7, 8, 9
Imaging the coronary arteries is a technical challenge, owing to continuous cardiac motion and the small luminal diameter of the vessels. High-performance temporal resolution (time needed to acquire one image) and spatial resolution (ability to distinguish between adjacent structures) is therefore required. There have been recent technical advances which have led to improvements in temporal resolution, fast ECG-gated scanning10 and reconstruction techniques for motion-free cardiac imaging, with improvements in spatial resolution for sub-millimetre imaging and reduction in radiation exposure times, resulting in the generation of images without artefacts.
Cardiac imaging with MDCT acquired with a single breath hold confers additional benefits, providing information about cardiac morphology, volume assessment and ejection fraction.11, 12 MDCT cardiac perfusion application software is under ongoing development for potential use in the clinical setting.13, 14
The ultimate aim of MDCT coronary angiography will be to complement conventional diagnostic invasive coronary angiography15, 16 and other existing imaging methods, avoiding negative invasive coronary angiograms and assisting the planning of any revascularization procedure.
MRI also can assess cardiac morphology, function, perfusion and viability with low temporal resolutions (20 to 50 ms). However, the 3D spatial resolution achievable is marginal for coronary arterial imaging and is therefore not yet reliable, thus limiting this particular application.17
We present this update review of cardiac MDCT, with particular emphasis on coronary artery imaging. Brief historical perspectives and present and future uses are discussed with reference to current clinical experience in our own institution.
Section snippets
Pathology of coronary artery disease
When using and interpreting cardiac MDCT coronary angiography, it is useful to have some understanding of the pathological processes involved in the development of atherosclerosis.
Angina is caused by coronary artery atherosclerosis leading to luminal stenosis. A mature fibrolipid plaque has a core of extracellular lipid, surrounded by smooth muscle cells, and is separated from the arterial lumen by a fibrous cap.18, 19 At the edge of the plaque is a vulnerable zone that is often the site of
Overview of cardiac CT evolution
Coronary arterial CT imaging has been a challenging area of research because of limitations in scanner speed, volume coverage and temporal resolution (Table 1).
Even higher isotropic spatial resolution is now possible with the next generation of CT technology, i.e. the 32-channel and 64-channel MDCT (0.35 mm collimation and 340 ms rotation times). The 64-MDCT is currently being developed, with recent results indicating visual clarity of up to fifth-order coronary arterial branches.22 This should
Technical and practical aspects of cardiac CT
A number of factors must be optimized in order to achieve the highest quality images.
Clinical applications of cardiac CT
The usefulness of cardiac CT is under continual evolution from research to clinical setting. Ultimately, the aim is to establish MDCT as a complementary adjunct to conventional established techniques.
Other clinical uses and future considerations
Coronary artery anomalies are being described with greater frequency because of the increased use of coronary angiography. Myocardial bridging and ectopic aortic origins of the coronary arteries are generally asymptomatic, unless the course is altered to pass between the aorta and the right ventricular outflow tract (Fig. 11) or via a prolonged intramuscular course, both of which may result in vessel impingement and ischaemic symptoms. Anomalous coronary arterial origins from the pulmonary
Conclusion
With the advent and increasing clinical use of 16-detector row machines, and now with the imminent clinical emergence of 64-channel and flat-plate technology, the improvements in spatial and temporal resolution, sophisticated ECG-gating and post-processing software algorithms are allowing motion-free, fast, accurate, detailed, contrast-enhanced cardiac imaging that not only rivals the accuracy of traditional invasive and non-invasive diagnostic techniques, but also provides additional
Acknowledgements
The Royal College of Radiologists Research Fellowship Award 2004/5 funds N. Manghat to study the clinical applications of cardiac CT. Thanks are also due to General Electric Medical Systems for assistance. Figure 13, Figure 14 are used by kind permission of D. Foley. Particular thanks are extended to all the CT radiographers at Derriford Hospital for their continued enthusiasm and support.
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