CHAPTER 17: COMPUTED TOMOGRAPHY OF THE HEART

Amir Ahmadi; Jagat Narula; Jonathon Leipsic

INTRODUCTION

Computed tomography (CT) is a technique that can fully evaluate both cardiac structure and function. Recent advances in imaging allow for evaluation of not only relatively stationary anatomy, such as the thoracic aorta, but also rapidly moving structures, such as the myocardium and coronary arteries. This imparts the ability to noninvasively evaluate for significant coronary artery disease (CAD), myocardial and pericardial abnormalities, and aortic pathology. When combined with electrocardiographic (ECG) gating, freeze-frame images of the heart can be obtained, eliminating most of the motion artifact. This is particularly important in contrast-enhanced CT angiography (CTA) of the coronary arteries and in quantification of coronary artery calcium. Advances in spatial and temporal resolution and image reconstruction software have also helped in the evaluation of cardiac structures such as coronary veins, saphenous vein grafts, atria, ventricles, and pulmonary arteries and veins, helping precisely define their spatial relationships within the cardiovascular system and allowing for a comprehensive assessment of a variety of cardiovascular disease processes. This chapter details the current and future role of cardiac CT for the assessment of cardiovascular physiology and pathology.

TECHNICAL CONSIDERATIONS

Advancements in CT technology have made it possible to noninvasively image the beating heart. Multidetector computed tomography (MDCT) scanners produce images by rotating an x-ray tube around a circular gantry through which the patient advances on a moving table. Improvements in gantry rotation speeds and the development dual source and large detector technologies have reduced effective temporal resolution to less than 100 milliseconds. The coronary arteries move independently throughout the cardiac cycle and even at slow heart rates exhibit significant translational motion of up to 60 mm/s for the right coronary artery (RCA) and 20 to 40 mm/s for the left anterior descending (LAD) and circumflex coronary arteries (Fig. 17–1).^1,2 Image acquisition of less than 50 milliseconds is truly required to completely avoid cardiac motion artifacts.¹

FIGURE 17–1.

Coronary artery velocity varies substantially throughout the cardiac cycle, depending on whether the heart rate is relatively slow (72 beats/min) (A) or fast (89 beats/min) (B). The greatest motion occurs in the right coronary artery (RCA), followed by the left circumflex (LCX) and left anterior descending (LAD) coronary arteries. A. A biphasic pattern of rest is found during end-systole (at 40%-50% of the R-R interval) and mid-diastole (at 70%-80% of the R-R interval). B. A monophasic rest period pattern was found near end-systole (at 40%-60% of the R-R interval). Reproduced with permission from Lu B, Mao SS, Zhuang N et al: Coronary artery motion during the cardiac cycle and optimal ECG triggering for coronary artery imaging. Invest Radiol. 2001 May;36(5):250-256.¹