Scan Techniques for Cardiac and Coronary Artery Imaging With Multislice CT

Abstract

Cardiac imaging is a demanding application for any noninvasive imaging modality. On the one hand, high temporal resolution is needed to virtually freeze cardiac motion and thus avoid motion artifacts in the images. On the other hand, sufficient spatial resolution—at best submillimeter—is required to adequately visualize small and complex anatomical structures like the coronary arteries. The complete heart volume has to be examined within a single short breath-hold time to avoid breathing artifacts and to limit the amount of contrast agent, if necessary. The motion of the heart is both complex and very fast. Some estimates of the temporal resolution needed to freeze cardiac motion in any phase of the cardiac cycle are as low as 10 ms. In 1984, electron beam computed tomography (EBCT) was introduced as a noninvasive imaging modality for the diagnosis of coronary artery disease (1–4). Its temporal resolution of 100 ms allows for relatively motion-free imaging of the cardiac anatomy in the diastolic phase, even at higher heart rates. Because the EBCT at that time was limited to axial scanning for electrocardiogram (ECG)-synchronized cardiac investigations, a single breath-hold scan of the heart required slice widths of at least 3 mm. The resulting axial resolution was therefore limited and not adequate for 3D visualization of the coronary arteries. With the advent of subsecond rotation, combined with prospective and retrospective ECG-gating, mechanical single-slice helical or spiral CT systems with superior general image quality entered the realm of cardiac imaging (4,5). Since 1999, 4-slice CT systems, which have the potential to overcome some of the limitations of single-slice cardiac CT scanning, have been used to establish ECG-triggered or ECGgated multislice CT (MSCT) examinations of the heart and the coronary arteries in clinical use (6– 10). As a result of the increased scan speed with four simultaneously acquired slices, coverage of the entire heart volume with thin slices within one breath-hold became feasible. The improved axial resolution provided much more accurate CT imaging of the heart and the coronary arteries (11–14). Recent clinical studies have demonstrated the potential of MSCT to differentiate and classify lipid, fibrous, and calcified coronary plaques (15). Despite these promising advances, the 4-slice CT scanner technology still faces some challenges and limitations with respect to motion artifacts in patients with higher heart rates, limited spatial resolution, and long breath-hold times (12). In 2001, a new generation of MSCT systems with simultaneous acquisition of up to 16 slices was introduced (16,17). With submillimeter slice acquisition and gantry rotation times shorter than 0.5 s, both spatial and temporal resolution are improved, while examination times are considerably reduced. KeywordsCoronary Artery CalciumHigh Heart RateSlice WidthCoronary Artery Calcium MeasurementReconstruct Slice WidthThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.