Prospective and Retrospective ECG Gating for Thoracic CT Angiography: A Comparative Study

OBJECTIVE. The objective of our study was to compare radiation dose, contrast load, thoracic aortic attenuation value, and image quality parameters of MDCT thoracic aortography performed with prospective and retrospective cardiac gating. MATERIALS AND METHODS. Studies were performed on 80 patients (prospective ECG gating, n = 40; retrospective ECG gating, n = 40) either being evaluated for thoracic aortic aneurysm ( n = 23) or aortic dissection (n = 36) or undergoing postsurgical or postintervention follow-up (n = 21). Image acquisition parameters and radiation dose (CT dose index volume [CTDIvol] and dose-length product [DLP]) were obtained from image archival data. Contrast load and aortic attenuation values were obtained from a data registry. The comparative degrees of motion artifact and banding artifact were assessed on parasagittal maximum-intensity-projection (MIP) images and reformatted images in the plane of the aortic valve. RESULTS. CTDIvol and DLP in the prospective ECG-gating group was 28.8 +/- 2.12 mGy (mean +/- SD) and 833.7 +/- 115.77 mGy/cm, respectively, which are significantly lower (p < 0.001) than those values in the retrospective ECG-gating group (74.7 +/- 13.42 mGy and 2,547.3 +/- 553.27 mGy/cm). The average contrast load in the prospective gating group was 109.1 +/- 14.74 mL and in the retrospective gating group, 101.3 +/- 10.45 mL (p < 0.05). The average aortic attenuation values (in Hounsfield units) for the prospective and retrospective ECG-gated groups were 447.6 and 350.2 HU, respectively, for the mid ascending aorta, 413.6 and 325.7 HU for the mid aortic arch, 418.2 and 327.6 HU for the mid descending aorta, and 355.0 and 306.2 HU for the supraceliac aorta. Subjective scores of motion artifact and banding artifact were equivalent between the two groups. CONCLUSION. Compared with retrospective ECG-gated thoracic CT angiography, prospective ECG-gated thoracic CT angiography was associated with a lower radiation dose, slightly increased contrast load, increased aortic attenuation values, and equivalent image quality.