Effect of Low Dose Radiation Computerized Tomography Protocols on Distal Ureteral Calculus Detection

Purpose: Unenhanced multidetector computerized tomography is the imaging modality of choice for urinary calculi but exposes patients to substantial radiation doses with a subsequent risk of radiation induced secondary malignancy. We compared ultra low dose and conventional computerized tomography protocols for detecting distal ureteral calculi in a cadaveric model. Materials and Methods: A total of 85 calcium oxalate stones 3 to 7 mm long were prospectively placed in 14 human cadaveric distal ureters in 56 random configurations. The intact kidneys, ureters and bladders were placed in a human cadaveric vehicle and computerized tomography was performed at 140, 100, 60, 30, 15 and 7.5 mA seconds while keeping other imaging parameters constant. Images were independently reviewed in random order by 2 blinded radiologists to determine the sensitivity and specificity of each mA second setting. Results: Overall sensitivity and specificity were 98% and 83%, respectively. Imaging using 140, 100, 60, 30, 15 and 7.5 mA second settings resulted in 98%, 97%, 97%, 96%, 98% and 97% sensitivity, and 83%, 83%, 83%, 86%, 80% and 84% specificity, respectively. Interobserver agreement was excellent (κ >0.87). There was no significant difference in sensitivity or specificity at any mA second settings. All false-negative results were noted for 3 mm calculi at a similar frequency at each mA second setting. Conclusions: Ultra low dose computerized tomography protocols detected distal ureteral calculi in a fashion similar to that of conventional computerized tomography protocols in a cadaveric model. These protocols may decrease the radiation dose up to 95%, reducing the risk of secondary malignancies.