Standard vs. reduced-radiation-dose CT in the tracing of the ureter

Purpose To assess the effectiveness of reduced-radiation-dose computed tomography (CT) protocols in the tracing of the ureter in patients with suspected renal colic. Methods The study was approved by our institutional review board, and informed consent was obtained from the participants. From July 2012 to April 2014, 310 consecutive patients with suspected urolithiasis were recruited to undergo unenhanced CT at 280 ( n = 62), 200 ( n = 62), 140 ( n = 62), 100 ( n = 62), and 70 ( n = 62) reference mA seconds (mAs) while keeping other imaging parameters constant. Images were independently and randomly reviewed by two radiologists blinded to the study to determine the tracing rates of the ureter and the acceptable rates of image quality according to different tube charge settings. Results A significant linear association was noted between tube charge settings, the rates for tracing of the ureter, and the acceptability of image quality (linear-by-linear association; p = 0.000 in all rates for both readers). The 140 reference mAs is the point at which the tracing rates deteriorate rapidly, with the tracing rate of 41.5% (95% CI 32.6%–51.0%) in reader 1 and 51.9% (95% CI 42.5%–61.2%) in reader 2, and with the acceptable rate of 82.3% (95% CI 70.8%–90.0%) in reader 1 and 96.8% (95% CI 88.3%–99.8%) in reader 2. Conclusion Decreasing the tube charge settings from 280 to 70 reference mAs resulted in a significant reduction in the tracing rate of the ureter, with 140 reference mAs being the breaking point.