Chest computed tomography radiation dose optimization comparison of automatic exposure control strength curves

Purpose: The aim of the study was to compare radiation dose and image quality between the "average" and the "very strong" automatic exposure control (AEC) strength curves. Materials and Methods: Images reconstructed with filtered backprojection techniques and radiation dose data of unenhanced helical chest computed tomography (CT) examinations obtained at 2 hospitals (hospital A, hospital B) using the same scanner devices and acquisition protocols but different AEC strength curves were evaluated over a 3-month period. The selected AEC strength curve applied to "slim" patients (diameter <32cm estimated from the attenuation automatically measured on the topogram) was "average" and "very strong" in hospital A and hospital B, respectively. Two radiologists with 13 and 24 years of experience scored the image quality of the lung parenchyma and the mediastinum on a 5-point scale. The patients' effective diameter, the delivered CT dose index volume, and dose-length products were recorded. Results: A total of 410 patients were included. The average body mass index was 24.0 kg/m2 in hospital A and 24.8 kg/m2 in hospital B. There was no significant difference between hospitals with respect to age, sex ratio, weight, height, body mass index, effective diameters, and image quality scores for each radiologist (P ranging from 0.050 to 1.000). The mean CT dose index volume for the entire population was 2.0mGy and was significantly lower in hospital B with the "very strong" AEC curve as compared with hospital A (-11%, P=0.001). The mean dose-length product delivered in this 70 kg-weight population was 68mGycm, corresponding to an effective dose of 0.95 mSv. Conclusion: Changing the AEC strength curve from "average" to "very strong" for slim patients maintains image quality and reduces the radiation dose to