Alternatives to the baseline KUB for CTKUB-detected calculi: evaluation of CT scout and average and maximum intensity projection images.

PURPOSE: A CT of the kidneys, ureters, and bladder (CTKUB) is the investigation of choice in suspected renal colic. Plain kidney, ureter, and bladder radiographs (KUB) can be used to monitor the progress of a stone if radiographically visible on a baseline KUB. This study aims to determine if a low-dose CT Scout, thick-slab average intensity projection (AIP), or maximum intensity projection (MIP) images are suitable as substitutes for a baseline KUB.

METHOD: A retrospective review of patients from a tertiary adult institute that had a positive CTKUB and a KUB within 4 h of the CT was performed. Two consultant radiologists independently reviewed the KUB, CT Scout, AIP, and MIP for stone visibility and their sensitivities and agreement values were compared. Stone characteristics (size, location, and peak Hounsfield units) and patient thickness were recorded and examined for any association with discordant results.

RESULTS: 74 stones were evaluated for the study. KUB had a sensitivity of 66.2% (95% CI 54.3-76.8), CT Scout 47.3% (95% CI 35.6-59.3), AIP 55.4% (95% CI 43.4-67.0), and MIP 83.8% (95% CI 73.4-91.3). Fair agreement was found between the KUB and both CT Scout (κ=0.363, 95% CI 0.167-0.558) and AIP (κ=0.384, 95% CI 0.175-0.592). Moderate agreement was found between the KUB and MIP (κ=0.412, 95% CI 0.198-0.625). Neither any stone characteristic nor patient thickness had a significant association with discordant results.

CONCLUSION: None of the possible substitutes for a baseline KUB showed strong agreement with the KUB. Low-dose CT Scouts have a similar sensitivity to the published literature for higher dose CT Scouts.