Chapter 5. Cardiac Computed Tomography

Introduction

Cardiac computed tomography (CT) has become one of the fast growing areas of cardiovascular imaging since the advent of multidetector scanners in 1998. Early cross-sectional CT imaging of the heart was performed using electron beam CT. Continued advancements in multidetector CT (MDCT) scanners as well as their widespread availability, however, have further increased the utility of cardiac MDCT for evaluation of a variety of cardiovascular diseases.

CT uses rapidly rotating x-ray sources and detectors to create an image. The x-ray sources and detectors are mounted opposite one another on a ring, and the rotating unit is called the gantry. The patient is placed inside the ring, and radiation that is not absorbed by the patient passes into multiple detectors, and, through a process known as filtered back projection, a cross-sectional image is generated (Fig. 5–1). Images are acquired in an axial (transverse) plane in thin sections to yield isotropic voxels, matching that of in-plane spatial resolution. CT angiography (CTA) of the cardiovascular system refers to CT scanning that is performed during the injection of an iodinated contrast agent. Although much information can be obtained from a noncontrast CT, optimal evaluation of cardiac structures, including vascular anatomy, usually requires CTA.

Important aspects of cardiac CT imaging include:

1. High temporal resolution with electrocardiogram (ECG) synchronization of data acquisition to minimize cardiac motion artifacts

2. High spatial resolution with isotropic voxels to allow for oblique reconstructions without loss of resolution

3. Contrast resolution

4. Radiation dose

Image quality optimization mainly consists of elimination of artifacts related to cardiac motion, respiratory motion, and partial volume effects. Different aspects of CT imaging, including collimation, pitch, breath-hold period, field of view, reconstruction interval, rate and volume of intravenous contrast administration, reconstruction algorithm, and radiation dose, affect overall image quality. Unfortunately, no single set of optimal scan parameters currently suffices for all cardiac CT applications on all CT systems. Instead, CT techniques often reflect a combination of personal or institutional preferences coupled with individual manufacturer capabilities and tailored, to a large extent, to the individual patient's specific clinical needs.

Specific Technical Aspects

Scanner Design

The gantry design of all MDCT scanners is similar with only minor variations. Single-source systems consist of a single set of x-ray source and detectors, and dual-source systems have two sets of x-ray sources and detectors mounted on the gantry. Detector geometry and postprocessing algorithms are system specific and somewhat dependent on the number of detectors used in the gantry design and number of slices generated, currently anywhere from 4 to 320 slices. Special three-dimensional (3D) back-projection algorithms are used to correct for artifacts that arise from the cone-beam geometry that results from the oblique ...