Dual-source computed tomographic temporal resolution provides higher image quality than 64-detector temporal resolution at low heart rates.

In 64–detector row coronary computed tomographic angiography (CTA), a single x-ray source within the gantry rotates 360 degrees in 0.33 to 0.35 seconds (330–350 milliseconds), depending on the manufacturer. By using half-scan reconstruction, an effective temporal resolution of 165 milliseconds can be achieved near isocenter. Sixty-four–detector row scanners, operating with this temporal resolution, produce coronary images with very little motion degradation in patients with low heart rates (≤70 beats per minute [bpm]).1 Furthermore, the sensitivity and specificity for detecting coronary stenoses, as compared with catheter angiography, have been very high in patients with low heart rates,2 heart rates that have usually been achieved by premedicating patients with β-blocking medications. Recently, the temporal resolution of 64–detector row scanners has been improved by mounting a second x-ray source and detector array pair on the gantry. Use of both x-ray sources and a gantry rotation time of 330 milliseconds allow the effective temporal resolution to be cut in half to 83 milliseconds.3 With this scanner type, known as a dual-source CT (DSCT) scanner, high quality images can be acquired in patients with higher heart rates than is possible on single-source 64–detector row scanners,4 and patients can be scanned with no β-blocker premed-ication.5,6 However, it is unknown whether DSCT provides incremental value over single-source 64–detector row CT in patients with low heart rates and, if so, over what portions of the cardiac cycle. Moreover, it would be helpful to make all of these comparisons from images collected at the same time in the same patient, to minimize physiologic variations that would occur from scanning at different times. Therefore, the purpose of this study was to retrospectively compare coronary image quality at typical DSCT (83 milliseconds) and typical 64–detector row temporal resolutions (165 milliseconds) in patients with low heart rates, using data collected from the same patient at the same time. The second purpose was to determine the portion of the cardiac cycle with maximal coronary image quality for both types of images.