Low-dose nonenhanced helical CT of renal colic: Assessment off ureteric stone detection and measurement of effective dose equivalent

PURPOSE: To evaluate a low-dose, nonenhanced helical computed tomographic ( Cf) protocol in the detection of ureteric stones and measure the associated effective dose equivalent (H-E) of radiation. MATERIALS AND METHODS: Sixty patients suspected of having renal colic and r eferred by emergency department physicians underwent nonenhanced helical CT with 7-mm collimation and a 2:1 pitch and then conventional intravenous ur ography (IVU). The two studies were prospectively and independently interpr eted. The diagnostic accuracy of CT for ureteric stone detection was determ ined by comparing the scans with the IVU images and with a combination of c linical, surgical, and other imaging findings. The radiation risk from typi cal Cf and IVU examinations (five images) was measured in terms of HE and c ompared with the estimated risk from two previously reported CT protocols. RESULTS: CT correctly depicted 36 of 37 ureteric stones, and one false-posi tive case was recorded, for a sensitivity of 97%, specificity of 96%, and a ccuracy of 97%. The H-E for our CT protocol was determined to be 2.8 mSv, w hich is about double that for IVU and about 75% and 50% of that for two pre viously reported CT protocols. CONCLUSION: Our low-dose CT protocol is superior to IVU and clinically adeq uate for diagnosis of renal colic.