Radiation dose reduction and coronary assessability of prospective electrocardiogram-gated computed tomography coronary angiography: comparison with retrospective electrocardiogram-gated helical scan.

OBJECTIVES The aim of this study was to evaluate radiation dose and coronary assessability of a prospective electrocardiogram (ECG)-gated scan by 64-slice multidetector (row) computed tomography (MDCT)-coronary angiography (CA) compared with a retrospective ECG-gated helical scan. BACKGROUND The 64-slice MDCT-CA has been widely used; however, a high radiation dose by 64-slice MDCT-CA has been reported. Prospective ECG-gated scan using "step-and-shoot" protocol can reduce radiation exposure effectively. METHODS MDCT-CA was performed in 229 consecutive patients. Fifty-six patients were excluded because of higher heart rates of >65 beats/min; of patients with heart rates <or=65 beats/min, 97 were analyzed by helical scan with tube current modulation and 76 were analyzed by prospective gating. Coronary assessability and diagnostic accuracy were investigated in comparison with selective CA as the gold standard. Radiation doses were evaluated in both protocols. RESULTS Coronary assessability of helical scan was 95.5% (1,303 of 1,364 segments), while that of prospective gating was 96.6% (1,053 of 1,089 segments), showing similar coronary assessability (p = 0.14). Sensitivity and specificity for coronary obstructive and occlusive lesions in the assessable segments were 97.0% (162 of 167) and 97.6% (1,109 of 1,136) by helical scan, while those of prospective gating were 96.4% (81 of 84, p = 0.84) and 98.5% (955 of 969, p = 0.12), respectively. Effective doses of helical scan and prospective gating were 21.1 +/- 6.7 mSv and 4.3 +/- 1.3 mSv, respectively (p < 0.0001), showing that prospective gating decreased radiation dose by 79% compared with that of helical scan. CONCLUSIONS MDCT-CA by prospective gating showed equivalent coronary assessability and diagnostic accuracy with decreased radiation dose in comparison with a retrospective ECG-gated helical scan with tube current modulation.