PURPOSE: To determine whether a very low dose CT protocol can be applied in patients for confirmation of known urolithiasis considered for intervention.
MATERIALS AND METHODS: A consecutive review of adults that underwent a modified protocol of very low dose non-contrast CT (VLD-CT). All patients had a previous CT scan showing a urinary tract stone. The confirmation non-contrast scans were conducted on a 256-slice CT scanner (Revolution, GE Healthcare). The scanned area was limited to the level of initial stone location caudally. Patients` demographics and BMI were reviewed. Length scanned and radiation dose were calculated. Images were assessed in consensus by two radiologists for stone dimensions and location. Reference standard included clinical information including passage, surgical removal, other imaging.
RESULTS: Fifty-five patients with mean BMI of 28.9 were included. The average patient span scanned on the VLD-CT was 276 mm (+/-80). Average radiation exposure was 1.50 mGy (+/-0.35) and absorbed dose 0.78 mSv (+/-0.25), compared to 9.43 mGy (+/-3.89) and 7.62 mSv (+/-3.28) on prior CT. Of 55 diagnosed index stones, confirmation VLD-CT revealed 31 stones in 31 patients with a mean stone length of 5.8 mm. Seventeen stones migrated from their initial location, out of which 3 appeared in the bladder and 24 were not present on the VLD-CT. Radiation dose reduction between scans was 89%. Of 35 patients followed clinically, all VLD findings were confirmed.
CONCLUSION: A non-contrast CT protocol with a significant dose reduction can be used for confirmation of stone presence in patients with urolithiasis diagnosed on CT, thus helping to guide management.
