Sensitivity of CT scout radiography and abdominal radiography for revealing ureteral calculi on helical CT: Implications for radiologic follow-up

OBJECTIVE. We compared the sensitivity of CT scout radiography with that of abdominal radiography in revealing ureteral calculi on unenhanced helical CT. MATERIALS AND METHODS. Over a 6-month period, patients presenting to the em ergency department with acute flank pain were examined with standard abdomi nal radiography and unenhanced helical CT, which included CT scout radiogra phy. In 60 patients in whom a diagnosis of ureteral calculus was made, CT s cout radiographs and abdominal radiographs were examined by two interpreter s who assessed whether stones could be visualized. Ail CT scout radiographs were viewed on a workstation using optimized window settings. RESULTS. CT scout radiography and abdominal radiography revealed 28 (47%) a nd 36 (60%) of 60 ureteral calculi, respectively. All ureteral calculi that appeared on CT scout radiography also appeared on abdominal radiography. H owever, eight calculi that were visible on abdominal radiography were not v isible on CT scout radiography. CT scout radiography and abdominal radiogra phy revealed 28% and 46% of 39 calculi less than or equal to 3 mm in diamet er, respectively. For 21 calculi larger than 3 mm, the sensitivity of CT sc out radiography and abdominal radiography was 81% and 86%, respectively. CONCLUSION. Abdominal radiography is more sensitive than CT scout radiograp hy in revealing ureteral calculi; however, some calculi revealed on unenhan ced helical CT cannot be seen on either abdominal radiography or CT scout r adiography. Ureteral calculi not visible on either study can only be follow ed, when necessary, with unenhanced helical CT.