Chapter 12: Computed Tomography of the Coronary Arteries

HISTORICAL PERSPECTIVE

Computed tomography (CT) was developed in the early 1970s. The first computed axial tomography (CAT) scanners developed by Sir Geoffrey Hounsfield and colleagues required long acquisition and reconstruction times and were only suited for (small) stationary body parts like the head (Fig. 12-1). However, within the same decade, scanners dedicated to cardiac imaging were developed that were able to acquire images in 100 milliseconds or less, which was sufficient to virtually freeze cardiac motion. Contrary to mechanical CT scanners, these electron-beam CT systems lacked mechanically rotating parts. Instead of a rotating tube-detector unit, a beam of electrons was electromagnetically swept along a stationary tungsten target ring around the patient. As the electrons hit the tungsten ring, a roentgen fan beam was created. On the opposite side of the gantry, attenuated roentgen rays were collected by a stationary ring of roentgen detectors. For over 2 decades, these scanners were in operation, primarily to image coronary calcium,¹ but also to image the coronary lumen after intravenous contrast injection.² Technical and other practical challenges to electron-beam CT, such as difficulties expanding the number of simultaneously acquired slices and expanding the longitudinal scan range, stalled further exploitation.

In the 1990s, the introduction of slip-ring technology for cableless exchange of energy between the rotating and stationary scanner components of mechanical CT scanners allowed for faster, uninterrupted scanner rotation and the development of spiral CT imaging techniques.³ Spiral or helical scan protocols, through continuous table movement and data acquisition, allow for faster longitudinal coverage and propelled the possibilities for contrast-enhanced CT applications, including coronary imaging. Just before the turn of the millennium, the first 4-slice spiral CTs with electrocardiogram (ECG) synchronization for cardiac imaging were introduced.^4,5 Over the next decade, the technical capabilities of cardiac CT improved rapidly, with faster rotating scanners and increasing numbers of detector rows for better and easier coronary imaging (Fig. 12-2). However, concerns about the increasing radiation burden associated with cardiac CT emerged, which motivated technical innovations to reduce the radiation dose while maintaining sufficient diagnostic accuracy.

In addition to noninvasive assessment of coronary stenosis, coronary CT also allows for assessment of the atherosclerotic changes in the vessel wall. Endeavors to noninvasive identify vulnerable plaques are ongoing. As the technologic accuracy of coronary CT angiography (CTA) matured and the radiation exposure reached acceptable ...