Radiation dose study of 64-slice spiral CT coronary angiography: a paired design

To compare image noise and radiation dose differences between prospective and retrospective ECG-gated computed tomography (CT) coronary artery imaging with 64-slice spiral CT (64-MSCT) in a paired design. Prospective and retrospective ECG-gated CT coronary angiography was performed among 20 out-patients with suspected coronary artery diseases. If one protocol failed, chose the other instead. The differences in effective dose (ED), image noise, contrast-to-noise ratio (CNR) and signal-to-noise ratio (SNR) between the two scan protocols were compared. Usual causes of failures were analysed for each. The average ED of retrospective and prospective protocol was 21.6±2 and 6.0±1.2 mSv, respectively. There was a significant statistical difference in the two protocols (p < 0.05 and 6.16e(-14)). The image noise and SNR between the two protocols made no differences (p=0.71, 0.26, >0.05). The average image noise and SNR of retrospective and prospective protocol were (27.95±2.82, 28.66±2.9) and (12.15±1.83, 10.9±1.17). The CNR of retrospective and prospective protocol was (14.52±1.59) and (17.3±2.09), respectively. There was a statistical difference (p < 0.05 and 0.045). The prospective protocol can lower the ED of 64-MSCT a lot than the retrospective protocol. The image noise and SNR made no differences, whereas the prospective protocol gave a better CNR result.