ABSTRACT
Objective To investigate the most appropriate low radiation dose in multi-slice CT (MSCT) scans for orbital trauma patients. Methods Thirty trauma patients with suspected orbital fractures who underwent helical CT scans with a 64-MSCT using regular dose were selected. Noise was artificially introduced to the axial images using an image space noise addition tool to simulate 6 sets of lower dose scans with tube current of 30, 70, 100, 140, 170 and 200 mA, respectively. The lowest tube current with adequate image quality for confident diagnosis was determined based on the evaluation of the overall image quality and fracture detection on images at different dose levels. The determined lowest tube current was then validated using clinical scans. Radiation dose related parameters CTDIvol, DLP, ED were also recorded.Image quality was evaluated according to its low-density resolution, noise and structure clarity and characterized into 5-grades of excellent, good, fair, worse and worst Rank sum test and X2 test were wsed for statistics. Results In 30 trauma patients with regular dose of 300 mA, there were 30 cases of orbital fracture, 19 cases of intraorbital emphysema, 12 cases of ocular muscle injury and 1 case of intraorbital foreign body. These changes could still be clearly observed and correctly diagnosed when the tube current was reduced to as low as 70 mA. However, the overall image quality was mostly fair. At the simulated dose of 100 mA, the majority of images were characterized as excellent or good, and there was no statistical difference compared with that of regular dose scans (P > 0.05 ) . In the clinical evaluation for 20 orbital trauma patients with the reduced tube current of 100 mA, the majority of images were judged to be excellent (9 cases) or good(17 cases) and fair (4 cases). The radiation dose(0. 29 mSv) was reduced by 70% compared with that of regular tube current of 300 mA(0. 86 mSv). Conclusion The tube current of MSCT may be used as low as 100 mA in orbital trauma patients to reduce radiation dose and keep the image quality diagnosable.