[Effects of heart rate on image quality and radiation dose of "triple rule-out" 320-row-640-slice multidetector computed tomography scan in patients with acute chest pain].

OBJECTIVE: To evaluate the effects of heart rate (HR) on image quality and radiation dose of "triple rule-out" 320-row-640-slice multidetector computed tomography (MDCT) scan in patients with acute chest pain.

METHODS: Retrospective analyses were performed for the clinical and imaging data of 38 cases with acute chest pain. All patients received 320-row-640-slice MDCT. Scanning program was electrocardiography-gated helical scan of full chest (160×0.5 mm). Based upon different heart rates, they were divided into A and B groups (A: n = 18, HR ≤ 65 bpm; B: n = 20, HR > 65 bpm). T he results of image quality and radiation dose of pulmonary artery, aorta and coronary artery between A and B group were evaluated respectively. T he subjective quality indicators of coronary artery were excellent, good, qualified and poor.

RESULTS: (1) Overall quality assessment: the mean CT values of ascending aortic root, main pulmonary artery, right coronary artery and left coronary artery were (412 ± 79) HU, (381 ± 107) HU, (408 ± 79) HU, (406 ± 79) HU respectively; the contrast-noise ratio (CNR) of ascending aorta root was 12 ± 7; excellent stage of subjective quality assessment of coronary artery accounted for 66.13%, good and qualified stage 32.79% and poor stage 1.08%. T he mean radiation dose was 22 ± 3 mSv. (2) The mean CT value between A and B groups of ascending aortic root, main pulmonary artery, right coronary artery and left coronary artery, and CNR of ascending aortic root [(421 ± 62) HU vs (404 ± 93) HU, (402 ± 103) HU vs (362 ± 110) HU, (417 ± 62) HU vs (400 ± 92) HU, (417 ± 63) HU vs (397 ± 92) HU, 10 ± 3 vs 13 ± 8 respectively] were not statistically different (P > 0.05); the number of segments of excellent subjective quality assessment and evaluable (excellent, good and qualified) of coronary artery between A and B groups were statistically significant (P = 0.001, P = 0.019). Group A was better than Group B. But the number of diagnosed segments of Group B still accounted for 97.9%. T he radiation doses of two groups were 18 ± 6 and 26 ± 5 mSv respectively. Group B was significantly higher than Group A and significant difference existed between two values (P = 0.000).

CONCLUSION: The "triple rule-out" 320-row-640-slice MDCT scan may acquire high quality images of aorta, pulmonary arteries and coronary arteries for both high and low HR groups. With a low contrast-medium dosage and patient radiation dose, it is ideal for an etiological diagnosis of acute chest pain. Reducing HR further improves image quality and lowers radiation dose.