Electrocardiographically Gated 16-Section CT of the Thorax: Cardiac Motion Suppression
Radiology 2004; 233:927-933.
Hofmann LK, Zou KH, Costello P, Schoepf UJ.
Thirty patients underwent 16-section multi-detector row computed tomographic (CT) angiography of the thorax with retrospective electrocar-diographic gating. Institutional review board approval was obtained for retrospective analysis of CT scan data and records; patient informed consent was not required. Images reconstructed at six different time points (0%, 20%, 40%, 50%, 60%, 80%) within the R-R interval on the electrocardiogram were analyzed by two radiologists for diagnostic quality, to identify suitable reconstruction intervals for optimal suppression of cardiac motion. Five regions of interest (left coronary artery, aortic root, ascending and descending aorta, pulmonary arteries) were evaluated. Best image quality was achieved by referencing image reconstruction to middiastole (50%- 60%) for the left coronary artery, aortic root, and ascending aorta. The pulmonary arteries are best displayed during mid- to late diastole (80%).
Cardiac motion artifacts degrade the diagnostic quality of thoracic cardiovascular computed tomographic (CT) images. Some of these artifacts (eg, motion artifacts that mimic aortic dissection) are recognized as important sources of potential diagnostic error (1,2). Synchronization of the CT acquisition with the patient's electrocardiogram (ECG) reduces cardiac motion artifacts and enables non-invasive visualization of the coronary arteries (3,4) and other cardiac anatomy (5,6). ECG synchronization also has been shown to improve image quality at CT imaging of noncardiac thoracic structures (7-9).
Retrospective ECG gating (10) is the most commonly used strategy for ECG synchronization at multi-detector row CT. Substantial effort has been invested in denning suitable time points during the cardiac cycle for reconstruction of CT data to provide optimal depiction of the coronary arteries (11-13). It has been shown that retrospective ECG gating can be beneficially employed for reducing transmitted cardiac pulsation also in more extensive scanning volumes in the thorax (9,14). However, the through-plane spatial resolution that could be achieved with the retrospective ECG gating technique by using the previous generation of four-section multi-detector row CT scanners was limited by the relatively long scanning duration inherent in data oversampling. Thus, high-resolution acquisition could be achieved only for relatively small volumes—for example, the coronary arterial tree—but not for extended coverage of the entire chest. The advent of multi-detector row CT scanners with 16 or more detector rows effectively has eliminated these limitations and enables scanning of the entire thorax with retrospective ECG gating and submillimeter (ie, 0.50-0.75-mm, depending on scanner type) through-plane resolution in a single breath hold (15). Thus, the purpose of our study was to identify ECG-referenced image reconstruction intervals for suppressing cardiac motion at high-resolution 16-section CT angiography in the thorax.