Very low-dose computerized tomography for confirmation of urinary stone presence

To determine whether a modified non-contrast very low-dose computed tomography (VLD-CT) protocol is applicable for confirmation of known urolithiasis. Consecutive adult patients with a CT scan showing urinary tract stone(s) between 6/2017–12/2018 were included. They were referred to a modified VLD-CT protocol if stone presence was equivocal or if stone location needed reassessment before an endourological interventional procedure. The scanned area was limited to the level of initial stone location caudally. Data on patients' demographics andbody mass index, were collected. The scanned length and radiation dose were calculated. Images were reviewed by two radiologists who assessed stone size and location. Follow-up reference standard included stone passage, surgical removal, and other imaging and clinical information. Sixty-three patients [63 stones, mean BMI 28.7 (range 19–41.9)] were included. VLD-CTs revealed 31 stones in 31 patients, with a mean stone length of 5.5 mm. Fifteen stones remained at the same location, and 16 had migrated, of which two appeared in the bladder. Thirty-two stones were not observed on VLD-CT. The mean span scanned on the VLD-CT was 274 mm (± 80). The average radiation exposure was 1.47 mGy (range 1.09–3.3), and the absorbed dose was 0.77 mSv (range 0.39–1.43), compared to 10.24 mGy (range 1.75–28.9) and 7.87 mSv (range 1.44–18.5) in the previous scan. The mean radiation dose reduction between scans was 89%. On follow-up, all VLD-CT findings were confirmed. A modified imaging protocol is applicable for confirmation of stone presence and location by utilizing very low-dose radiation exposure.