Effect of altering automatic exposure control settings and quality reference mAs on radiation dose, image quality, and diagnostic efficacy in MDCT enterography of active inflammatory Crohn's disease.

Objective: The purpose of our study was to determine whether the MDCT enterography dose can be reduced by changing automatic exposure control (AEC) setting and quality reference milliampere-seconds (mAs) without altering subjective image quality or efficacy in active inflammatory Crohn's disease.

Subjects And Methods: This is a prospective study of 2,310 MDCT enterography procedures performed using 16- and 64-MDCT in three cohorts (original, intermediate, and final dose levels). For 16-MDCT, the original and intermediate dose level quality reference mAs was 200, and weight-based (1 pound [0.45 kg] = 1 mAs) for the final dose level. For 64-MDCT, the original dose level quality reference mAs was 260; the mAs was 220 for intermediate and weight-based for the final dose level. For the intermediate and final dose levels, AEC was changed from strong to weak increase for obese and weak to strong decrease for slim patients. Demographic data and volume CT dose index (CTDI(vol)) were analyzed. Three readers evaluated the cases for image quality and efficacy differentiating normal from active inflammatory Crohn's disease.

Results: For 16-MDCT, CTDI(vol) decreased from 12.82 to 10.14 mGy and 10.14 to 8.7 mGy between original to intermediate and intermediate to final dose levels. For 64-MDCT, the CTDI(vol) decreased from 15.72 to 11.42 mGy and 11.42 to 9.25 mGy between original to intermediate and intermediate to final dose levels. Images were rated suboptimal or nondiagnostic more often in the intermediate dose level (p < 0.05) but not in the final. There was no reduction in diagnostic efficacy as measured by area under the ROC curve (p > 0.1443 except for one comparison with one reader).

Conclusion: Substantial dose reduction can be achieved using weight-based quality reference mAs and altering AEC settings without affecting diagnostic efficacy in active inflammatory Crohn's disease of the terminal ileum. However, subjective image quality can be compromised at these dose settings, depending on radiologist preference.