Arm raising at exposure-controlled multidetector trauma CT of thoracoabdominal region: higher image quality, lower radiation dose.

ABSTRACT

PURPOSE: To evaluate the effect of arm position on image quality and effective radiation dose in an automatic exposure-controlled (AEC) multidetector thoracoabdominal computed tomography (CT) protocol in trauma patients. MATERIALS AND METHODS: This retrospective study of the data of 177 trauma patients (117 male; median age, 39 years) was approved by the institutional ethics board, with informed patient consent waived. Patients underwent scanning by using an AEC 16-detector thoracoabdominal CT protocol in which both arms were raised above the shoulder region (standard-position group, 132 patients), one arm was raised and the other was down (one-arm group, 27 patients), or both arms were down (two-arm group, 18 patients). Objective and subjective image quality was assessed. Individual effective radiation dose was calculated from the effective tube current-time product per exposed section. For this purpose, section location-dependent conversion factors were derived by using a CT dosimetry calculator. The effect of arm position on effective dose was quantified by using linear regression analysis with correction for patient volume and attenuation. RESULTS: Compared with the image quality in the standard-position group, the image quality in the one- and two-arm groups was decreased but within acceptable diagnostic limits. The median corrected effective dose in the standard-position group was 18.6 mSv; the dose in the one-arm group was 18% (95% confidence interval 11%, 25%) higher than this, and that in the two-arm group was 45% (95% confidence interval 34%, 57%) higher. CONCLUSION: Omitting arm raising results in lower but acceptable image quality and a substantially higher effective radiation dose. Hence, effort should be made to position the arms above the shoulder when scanning trauma patients. Clinical trial registration no. NCT00228111.