Objectives: Purpose of this study was to compare the effect of high-pitch spiral data acquisition with prospective electrocardiography (ECG)-triggering on the x-ray induced DNA damages to blood lymphocytes with commonly used low-pitch spiral scans.
Materials and methods: Thirty four patients underwent coronary computed tomography angiography either using high-pitch spiral data acquisition (n = 15; dual-source computed tomography (CT) scanner, 38.4 mm collimation, 100-120 kV, 320-456 mAs/rotation, pitch value 3.2-3.4) or using a low-pitch protocol (n = 19; dual-source CT scanner, 19.2 mm collimation, 120 kV, 330-438 mAs/rotation, pitch 0.2-0.39, ECG-based tube current modulation). Blood samples were obtained before and 30 minutes after CT. Lymphocytes were isolated, stained against the phosphorylated histone variant gammaH2AX, and DNA double-strand breaks (DSBs) were visualized using fluorescence microscopy. Radiation dose to the blood was estimated by relating in vivo DSB levels to values of in vitro irradiated blood samples (50 mGy). Dose length product was registered as provided by the patient protocol.
Results: Total dose length product ranged from 101 to 237 (median 112) mGy cm in high-pitch and from 524 to 1283 (median 1025) mGy cm in low-pitch scans (P < 0.0001). The median CT induced DSB level 30 minutes after exposure was significantly lower after high-pitch (0.04 DSBs/cell, range 0.02-0.10 DSBs/cell) compared with low-pitch scans (0.39 DSBs/cell, 0.22-0.71 DSBs/cell, P < 0.0001). Both DSB levels and radiation dose to the blood showed a significant correlation to the dose length product (r = 0.82, P < 0.0001). The radiation dose to the blood was significantly reduced in the high-pitch (median 3.1, range 2.0-8.1 mGy) compared with the low-pitch group (median 26.9; range 14.2-44.9 mGy, P < 0.0001).
Conclusions: Prospectively ECG-triggered high-pitch spiral data acquisition can considerably reduce the radiation dose to the blood in coronary CT angiography as compared with low pitch protocols.