Whole-Heart 320-Row Computed Tomography: Reduction of Radiation Dose via Prior Coronary Calcium Scanning

Abstract

The whole heart can be scanned in one rotation using 320-row coronary computed tomography angiography (CCTA), which covers up to 16 cm. Since most hearts are smaller, the total radiation dose may be reduced by adjusting the CCTA range to the individual heart size defined on a low-dose calcium scan (CACS). Forty-five patients with suspected coronary artery disease (13 women, 32 men; mean 61 ± 10 years) underwent CCTA preceded by low-dose CACS on a 320-row scanner (Aquilion ONE, Toshiba; 0.35 s gantry rotation, 120 kV, 350 - 450 mA) with 16-cm z-axis coverage (120 kV, 150 mA). The subsequent CCTA was performed over an adjusted scan range calculated as the individual heart size on CACS (+ 1 cm above and below). The total radiation dose of 16-cm CACS and the individually adjusted CCTA was compared with that of a calculated single CCTA using full 16-cm z-axis coverage. CCTA could be performed with a reduced scan length in the z-axis in all patients. None of the scans had to be performed over the whole range of 16 cm. The adjusted scan length was 14 cm in 2 patients, 12.8 cm in 3 patients, and 12 cm in 40 patients. The effective CCTA scan range was 12.1 ± 0.5 cm based on mean individual heart sizes of 9.6 ± 1.1 cm. The mean total effective radiation dose of the entire cardiac CT examination (individually adapted CCTA and CACS) was significantly smaller than the exposure calculated for 16-cm CCTA without CACS (8.5 ± 4.7 vs. 9.1 ± 6.0 mSv, p = 0.006). The dose reduction was most relevant in patients with heart rates above 65 beats/min (n = 10) in whom 2 or 3 heartbeats were necessary for CCTA (17.7 ± 6.5 vs. 21.1 ± 8.4 mSv, p = 0.001). 320-row CCTA with an individually adjusted scan range based on prior CACS significantly reduces the radiation exposure compared with full 16-cm CCTA.