The effect of decreasing mAs on image quality and patient dose in sinus CT

The aim of this study was to determine the effect of reducing mAs on the di agnostic quality of images and the radiation dose to the orbits in patients undergoing sinus CT. We studied 40 consecutive patients undergoing paranas al sinus CT for inflammatory disease prior to functional endoscopic sinus s urgery (FESS). Four groups of 10 patients were scanned at 200 mAs, 150 mAs, 100 mAs and 50 mAs, respectively. Orbital radiation dose was measured usin g thermoluminescent dosemeters. Images were reviewed independently by two o bservers who were unaware of the mAs setting used. Image quality was evalua ted using a semi-quantitative scoring system for six anatomical structures. The osteomeatal complex, uncinate process, infundibulum, frontal recess, m iddle turbinate and optic nerve were assessed as: clearly demonstrated (2 p oints); demonstrated but not clearly visualized (1 point); or not seen (0 p oints). No significant difference was shown between any of the four groups in terms of image quality according to the scoring system used in this stud y. Mean radiation dose to the orbit was reduced by 77%, from 13.5 mGy at 20 0 mAs to 3.1 mGy at 50 mAs (p<0.05). CT of the sinuses can be performed in patients prior to FESS at greatly reduced mAs without loss of diagnostic qu ality of the images. This is important in reducing the radiation dose to th e lens.