Résumé : PURPOSE: To prospectively compare the sensitivity and specificity of unenhanced low-dose multi-detector row computed tomography (CT) with those of contrast material-enhanced standard-dose multi-detector row CT in patients suspected of having acute diverticulitis. MATERIALS AND METHODS: Institutional review board approval and informed consent were obtained. One hundred ten consecutive patients (40 men, 70 women; age range, 30-82 years; mean, 57 years) suspected of having acute diverticulitis underwent unenhanced multi-detector row CT with 4 x 2.5-mm collimation, 120 kVp, and 30 effective mAs, as well as contrast-enhanced standard-dose multi-detector row CT with the same parameters but with 120 mAs. All scans were independently read by four readers. Intra- and interobserver agreements were calculated with the kappa statistic. Contrast-enhanced standard-dose scans read by three other experts and considered together with results from colonoscopy, surgery, and pathologic evaluation were used as reference. Differences in sensitivity and specificity between readers, radiation doses, and reading sessions were investigated. Pearson exact test and logistic regression models were used. RESULTS: Colon diverticulitis was present in 39 patients (34%) and was graded as mild in 22 patients (56%) and severe in 17 (44%). Agreement within and between readers was good to excellent. No significant difference was observed in sensitivity (P ranging from .081 to >.99) or in specificity (P ranging from .326 to >.99) for any sign or overall diagnosis between radiation doses by all readers, except wall thickening, which for one reader had a higher specificity at low dose than at standard dose (P = .025). No significant difference in misclassification was detected between doses, regardless of the reader (P ranging from .481 to >.99). At both doses, the most predictive sign for acute diverticulitis was retroperitoneal fat stranding (P < .001). CONCLUSION: Low-dose unenhanced multi-detector row CT has a diagnostic performance similar to that of contrast-enhanced standard-dose multi-detector row CT in patients suspected of having acute diverticulitis.