Chapter 6

Over the last decade, advances in computed tomography (CT) technology have revolutionized the diagnosis of cardiovascular disease. As illustrated in this chapter, CT has dramatically reduced, and for some clinical indications eliminated, the need for diagnostic arterial catheterization. In the process, CT has become invaluable in cardiac diagnosis and surgical planning.

CT is based on a source of x-rays and a system to detect those x-rays that pass though the patient. The x-ray source and detector are mounted on the “CT gantry” that rotates around the patient. As detailed below, two major technology advances have enabled CT to image the beating heart. The first is the speed at which the CT gantry rotates. The second is the incorporation of an increasing number of detectors that can resolve small anatomic detail. One of the great promises of modern CT is the ability to noninvasively exclude coronary artery disease in as little as one heartbeat (Fig. 6-1). However, the role of CT extends far beyond the coronary arteries alone. Using the same CT acquisition, native coronary imaging can be extended to coronary bypass grafts, the beating myocardium, valve motion, ventricular outflow tracks, and cardiac lesions.

###### Figure 6-1

Selected coronary computed tomography angiography (CTA) image of the proximal left coronary arterial system in a patient scheduled for isolated mitral valve surgery. Using the protocol detailed in this chapter, CT demonstrated normal coronary arteries in this patient, eliminating the need for arterial catheterization.

In order to understand the clinical contribution of CT and to avoid pitfalls in image interpretation, it is essential for the surgeon to appreciate the basic principles of CT used in cardiac imaging. This chapter is divided into two sections. The first section describes the technical considerations for cardiac CT. By understanding each component, the surgeon will be better able to distinguish image artifacts from pathology. The second section reviews those CT examinations that are most frequently performed in the noninvasive cardiovascular imaging program at Brigham and Women's Hospital (BWH), detailing the strengths and limitations of each exam.

### Cardiac CT Protocols

#### Introduction

Most advances in cardiac CT, for example in coronary CT angiography (CTA), have focused on the development of protocols consistent with the rapid incremental improvements in the technology. One of the major technological advances has been the incorporation of multiple elements into the CT detector system, called Multi-Detector CT (MDCT). MDCT is synonymous with multi-slice CT. Data from each of the detectors is used to reconstruct an axial slice perpendicular to the long axis, or z-axis, of the patient. The width of the detectors determines the slice thickness and thus the ability to resolve small anatomic detail (spatial resolution) of the scanner. Thinner slices yield superior spatial resolution; however, comparing two scanners that produce the same number of slices, ...

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