Multi-detector row CT of the heart: methodological evaluation and application in high-risk patients

Abstract

Cardiac imaging with multi-detector row CT has undergone a rapid development since the advent of 4-detector row CT scanners in 1998. This thesis deals with the evaluation of current protocols for CT coronary calcium scoring and contrast-enhanced coronary CT angiography and the potential for optimization of such protocols. Furthermore, non-contrast-enhanced calcium scoring and contrast-enhanced coronary CT angiography were studied as part of a screening protocol for cardiac disease in patients with peripheral arterial disease without cardiac symptoms but at high risk for cardiac morbidity and mortality. The evaluation of current protocols for calcium scoring described in this thesis showed that small variations in scan starting position are an important source of calcium score variability in contiguous 3-mm data sets. The reduction of calcium score variability without application of high patient radiation doses was studied subsequently. To achieve such reduction without high patient doses either prospectively ECG-triggered data sets need to be reconstructed overlapping, or retrospectively ECG-gated calcium scoring scanning should to be combined with application of ECG-based tube current modulation, optimized by adjusting for patient heart rate. The evaluation of contrast injection for contrast-enhanced cardiac CT described in this thesis showed that the use of a high contrast material concentration (370 mgI/ml) at a standard contrast injection rate, does not yield higher enhancement than the use of a moderate concentration contrast medium (300 mgI/ml) while using identical iodine flux and total iodine load for both contrast medium concentrations. We further found that contrast medium throughput can be improved with the use of a dual head contrast medium injector that allows simultaneous infusion of contrast medium and saline. This means that adequate enhancement throughout the heart can be reached with less contrast medium, while homogeneity of contrast enhancement is improved. The last part of this thesis deals with the application of cardiac CT in a comprehensive screening protocol to detect a significant left main coronary artery stenosis. A significant left main stenosis is a severe form of coronary artery disease and has a treatment indication even before the development of symptoms. Comprehensive screening was performed in cardiac asymptomatic peripheral arterial disease patients at high risk for cardiac morbidity and mortality. We showed that calcium scores may be able to select the patients most at risk for a left main stenosis. CT calcium scoring, which is non-invasive and relatively inexpensive, may therefore be used as a gatekeeper for further diagnostic tests in future screening protocols. Before large screening endeavors with cardiac CT will become reality the improvement of patient outcome through this type of screening should be demonstrated. Meanwhile, cardiac CT rapidly develops and continuous improvements of protocols are necessary to obtain optimal results and to contain radiation exposure. When it comes to imaging the heart with CT we have only just started; it will take a further effort to reach the heart of the matter.