Comparison of diagnostic accuracy of ultra low‐dose computed tomography and X‐ray of the kidneys, ureters and bladder for urolithiasis in the follow‐up setting

Abstract

AbstractIntroductionUrolithiasis is frequently followed up with a low‐dose computed tomography of the kidneys ureters and bladder (LD‐CTKUB) with doses typically less than 3 millisieverts. Although X‐ray is a lower dose (0.5–1.1 mSv) alternative for follow up, it has lower diagnostic accuracy and is limited to radiopaque calculi. This study aims to compare the diagnostic accuracy of sub‐millisievert ultra‐low dose CT (ULD‐CTKUB) against X‐ray KUB for the follow up of urolithiasis when both are compared against the standard of care of a low‐dose CT KUB (LD‐CTKUB).MethodsThis prospective study included patients with a known diagnosis of urolithiasis on prior CTKUB presenting for follow up. Each patient underwent a repeat reference LD‐CTKUB, ULD‐CTKUB and X‐ray KUB. All imaging studies were interpreted by three readers. The radiation dose and quantitative noise was calculated for each CT. Both CT and X‐ray were assessed for the presence, number and size of all calculi ≥2 mm.ResultsA total of 58 patients were included in this study. LD‐CTKUB identified 197 calculi. ULD‐CTKUB in our study had a mean effective dose of 0.5 mSv compared to X‐ray KUB where doses range in the literature from 0.5 to 1.1 mSv. Per‐patient pooled analysis for intrarenal calculi when comparing ULD‐CTKUB versus X‐ray KUB against a reference LD‐CTKUB found a sensitivity of 90% versus 67% (P < 0.01) and specificity of 93% versus 98% (P = 0.18) respectively. For ureteric calculi, the sensitivity was 67% versus 33% (P < 0.01) and specificity 94% versus 94% (P = 1.00) respectively. Per‐stone pooled analysis detection rate was 79% for ULD‐CTKUB versus 48% for X‐ray (P < 0.01) when each was compared to the reference LD‐CTKUB. Interobserver agreement was high for intrarenal calculi and moderate for ureteric calculi.ConclusionSub‐millisievert ULD‐CTKUB had lower doses and higher sensitivity than X‐ray in patients requiring follow up of known urolithiasis.