Improving Cardiovascular Risk Assessment with CT Coronary Angiography and Myocardial CT Perfusion
Accurate assessments of coronary atherosclerosis, calcification and myocardial perfusion are necessary to determine future cardiovascular risk in various clinical settings. CT coronary angiography (CTCA) and myocardial CT perfusion (CTP) are promising techniques for the assessment of these factors. This thesis is comprised of several projects which explore refinements and new techniques aimed at improving diagnosis and risk stratification by CTCA. In order to improve CT methodology, coronary motion in mid-diastole was examined utilizing both high temporal-resolution tissue Doppler imaging and CT. The period of mid-diastole was found to occur relatively later in the cardiac cycle with increasing heart rate. The study demonstrated the importance of heart rate control and precise timing in cardiac imaging. The coronary calcium score allows quantification of cardiovascular risk in asymptomatic patients. A new method of calculating the coronary calcium score from contrast-enhanced CTCA was developed and assessed. Within the validation cohort, the calculated calcium score was highly correlated with the measured calcium score with minimal bias. Coronary calcium may also affect accurate assessment of the degree and extent of coronary disease at CTCA. We examined CTCA findings in patients with a calcium score of >600. Downstream investigations, cardiovascular events, revascularization and mortality were recorded. It was shown that while CT in this setting has reduced specificity, the sensitivity to clinically significant disease appears to be preserved. CTP may be used to assess the functional significance of coronary disease. Utilizing a validated CT and MRI compatible perfusion phantom, the sensitivity of CTP and magnetic resonance perfusion were directly compared under various conditions. Despite the distinct physical basis of each technique, the sensitivity and signal-to-noise ratios were similar, supporting the further development of CTP techniques. Image noise is a major limitation of current CTP methods. A novel four-dimensional median value filter was developed which selects the most stable voxels over both time and surrounding image space. The technique reduced transient image artifact and improved contrast to noise ratios. As a whole, the thesis provides the basis for ongoing improvements in coronary CT and CT myocardial perfusion and supports an increasing role for these techniques in cardiovascular risk assessment.
Cardiac MRI, Computed tomography, Cardiac CT, Myocardial perfusion, Calcium score
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