ABSTRACT
A CT scanner consists of an X-ray tube that rotates around the patient, with images collected by a row of detectors on the opposite side (Figure 9.1). The patient is continuously moved through the X-ray field while data are digitally recorded from the detectors. The resulting X-ray projection data form a helix or spiral, hence the description ‘spiral-CT’. While CT has been available for clinical use since the early 1970s, it has been poorly suited to cardiac imaging until a few years ago. Indeed, accurate noninvasive assessment of the coronary arteries poses several difficulties. First, high spatial resolution is required for accurate visualization of their small size and tortuous three-dimensional anatomy. Second, sufficient temporal resolution is needed to minimize artifacts related to rapid coronary motion. Third, the scan must be performed within a single short breath hold to avoid respiratory motion artifacts. To obtain motion-free images data are typically obtained
X-ray tube
X-ray beam
DetectorsGantry
Patient
Figure 9.1 Frontal (a) and side (b) view of a CT scanner
a b
during the diastolic phase of the cardiac cycle. Image acquisition must therefore be synchronized to the cardiac cycle using electrocardiogram (ECG) gating. In most instances retrospective ECG gating is used. This means that data are acquired during the whole cardiac cycle. After data acquisition, different reconstruction windows during the diastolic phase of the heart can be explored to obtain images with the lowest number of motion artifacts. Heart-rate-lowering drugs are generally recommended for patients with a resting heart rate above 70 beats/minute7.
