RESUMO
OBJECTIVE: To identify the best cardiac phase in different patient's heart rate on 16-slice coronary CT angiography. MATERIAL AND METHOD: The patients who had undergone coronary CT angiography with 16 multi-detector rows CT at Siriraj Hospital between September 2003 and August 2004. For each patient, the image reconstruction based on relative timing was performed placed at center of 35% to 85% of the R-R interval with step increments 10%. The authors created six data sets (35%, 45%, 55%, 65%, 75%, and 85% of R-R interval) throughout the cardiac cycle. The coronary arteries were reviewed based on cross-sectional images and reformat images. The authors inspected all data sets and selected the cardiac phase that contained the best image quality for each coronary artery. RESULTS: Five hundred sixty four vessels were evaluated in the 141 patients (83 men, 58 women). The mean patient age was 63.3 +/- 16.7 years (range 4-89 years). Mean patient heart rate was 65.7 +/- 16.5 beats per minute (bpm), range 46-104 bpm. The most coronary arteries were well demonstrated at center of 75% of R-R interval (66.8%). Ninety-eight patients (69.5%) required one phase that provided best overall image quality and motion free delineation for four coronary arteries. Forty-three patients (30.5%) required combination of data from each phase to achieve motion free images. CONCLUSION: The best cardiac phase of evaluate coronary artery in 16 slices coronary CT angiography in the patient's heart rate below 70 bpm is 75% of cardiac cycle (mid to late diastole). In patients with a heart rate 71-80 bpm, the authors required a combination of images from 45% and 75% of cardiac cycle to completely evaluate all coronary arteries. In patients with a heart rate above 80 bpm, 45% of cardiac cycle (end-systole) is the best phase.