Application of low dosemulti-slice helical CT in orbital trauma patients

：Objective To investigatethe most appropriate low radiation dose in multi-slice CT (MSCT) scans for orbital traumapatients. Methods Thirty trauma patients with suspected orbital fractures who underwenthelical CT scans with a 64-MSCT using regular dose were selected. Noise was artificiallyintroduced to the axial images using an image space noise addition tool to simulate 6 setsof 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 determinedbased on the evaluation of the overall image quality and fracture detection on images atdifferent dose levels. The determined lowest tube current was then validated usingclinical scans. Radiation dose related parameters CTDIvol, DLP, ED were alsorecorded.Image quality was evaluated according to its low-density resolution, noise andstructure clarity and characterized into 5-grades of excellent, good, fair, worse andworst Rank sum test and X2 test were wsed for statistics. Results In 30 trauma patientswith regular dose of 300 mA, there were 30 cases of orbital fracture, 19 cases ofintraorbital emphysema, 12 cases of ocular muscle injury and 1 case of intraorbitalforeign body. These changes could still be clearly observed and correctly diagnosed whenthe tube current was reduced to as low as 70 mA. However, the overall image quality wasmostly fair. At the simulated dose of 100 mA, the majority of images were characterized asexcellent or good, and there was no statistical difference compared with that of regulardose scans (P > 0.05 ) . In the clinical evaluation for 20 orbital trauma patients withthe reduced tube current of 100 mA, the majority of images were judged to be excellent (9cases) or good(17 cases) and fair (4 cases). The radiation dose(0. 29 mSv) was reduced by70% compared with that of regular tube current of 300 mA(0. 86 mSv). Conclusion The tubecurrent of MSCT may be used as low as 100 mA in orbital trauma patients to reduceradiation dose and keep the image quality diagnosable.