[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.