Radiation dose control for CT urography based on different body mass index

Objective To explore the optimization of CT urography imaging parameters and the control measures of radiation dose to patients with different body mass index. Methods A total of 133 patients who were required to undergo CT urography were prospectively selected in terms of three different types of CT urography scan; firstly, conventional parameter scan (120 kV, CARE Dose4D); secondly, low kV scan (BMI ≤ 22.9∶80 kV, 22.9 < BMI < 30∶100 kV, BMI ≥ 30∶120 kV, CARE Dose4D) and thirdly, low mAs scan (120 kV, 40% reduction in mAs on CARE Dose4D). Noise, signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) of all images were measured as objective evaluation indicators of image quality. The subjective evaluation of the images was performed by two radiologists who had been working for more than five years using a double-blind method and a 5-score system evaluation. The effective dose values (CTDIvol, DLP, E) in each group were measured. Results Patients′ effective dose was decreased by 77.7% in 80 kV group and 38.3% in 100 kV group, with a statistical difference between the two groups (Z=-3.330, -5.559, P 0.05). There was a statistically significant difference in renal cortex noise and SNR between the 100 kV scan group and the routine scan group (Z=-5.096, -3.566, P 0.05). The effective dose from low mAs scan in the three types of patients was decreased by 38.3%, 32.0%, and 34.7%, respectively, with a statistical difference between them (P 0.05) besides ureteral CNR in the 22.9 < BMI < 30 group (Z=-2.587, P<0.05). The subjective evaluation scores of all images were greater than 3 points. Conclusions In this study, the scan method for low kV and low mAs used for patients with different body mass index can effectively reduce the radiation dose to patients and meet the requirements of clinical diagnosis. Key words: Body mass index; CT urography; Low-dose scan; Urinary system disease