Evaluation of optimal match between gantry rotation time and cardiac cycle on multislice spiral CT coronary angiography imaging.

OBJECTIVE: To evaluate the relationship between gantry rotation time, heart rate and image quality during multislice spiral CT coronary angiography (MSCTCA). PATIENTS AND METHODS: Data of 83 patients who underwent MSCTCA were reviewed. Based on the ratio between cardiac cycle and gantry rotation time, the patients were divided into two groups. Patients whose heart rates fell in the resonance frequency (the cardiac cycle / gantry rotational time ratio of 1.5, 2 or 2.5) +/- 2 bpm were classified as synchronous (25 cases), while the remaining 58 patients (included a subgroup of 34 cases in whom heart rates were the same as in synchronous group but who had a different gantry rotation time). comprised the asynchronous group. Image qualities were compared between both groups. RESULTS: In the synchronous group, most (199/287; 69.33%) images were poor. When gantry rotation time was changed in the subgroup of the asynchronous group, the majority (423/442 or 95.70%) of images improved. There was a significant difference (p < 0.001) in the image quality among these patients. In 58 patients from asynchronous group, 757 segments of coronary arteries were evaluated, and 716 segments were of best quality (716/757; 94.58%). CONCLUSIONS: When heart rate and gantry rotation time correlate and synchronous, the so-called frequency harmonics, coronary artery image quality is poor. However, by changing gantry rotation time to avoid the harmonic helps to improve the image quality on MSCTCA. Based on the patient's heart rate, appropriate gantry rotation time can be selected in order to avoid resonance and obtain high quality images.