Objective To investigate the feasibility of 320 slice CT angiography of coronary artery in patients with heart rate < 75 times per minute in free-breathing state and to evaluate the image quality and radiation dose.

Methods Coronary artery CT imaging was performed in a single cardiac cycle using Lianying 320 slice CT by prospective electrocardiogram gating technique for 94 patients with suspected coronary heart disease and heart rate lower than 75 times per minute. The patients were divided into two groups according to their breathing patterns. There were 47 cases of breath-holding in group A and 47 cases of free-breathing in group B. Signal to noise ratio (SNR) of the aorta, contrast to noise ratios (CNR)of the aorta, left main trunk, proximal anterior descending artery, proximal circumflex artery, proximal and middle right coronary artery, were measured. Two radiologists evaluated 18 segments of the coronary artery of 94 patients by 5-point and double-blind methods, and score ≥ 3 meet the diagnostic requirements.

Results There was no significant difference in CNR, SNR, and CT values between the two groups. In group A and B, percentages of patients scored 5, 4, and 3 were 68.8% and 67.4%, 18.0% and 20.3%, and 10.2% and 10.4%, respectively. The radiation dose received by patients in group B was less that in the group A (P < 0.01).

Conclusions There is no significant difference in image quality between free-breathing and standard breath-holding CCTA. Free-breathing CCTA is an acceptable solution for patients with heart rate lower than 75 times per minute.