Bony Landmarks on Computed Tomographic Localizer Radiographs to Prescribe a Reduced Scan Range in Patients Undergoing Multidetector Computed Tomography for Suspected Urolithiasis

Objective: The objective of this study was to determine bony landmarks that can be used on computed tomographic (CT) localizer radiographs to prescribe a reduced scan range for noncontrast CT (NCCT) for suspected urolithiasis. Methods: This retrospective review comprised 243 patients who underwent NCCT for suspected urolithiasis. Scout line mode was used to correlate axial images with the z-axis location on CT localizer radiographs. The most inferior vertebral body end plate (superior or inferior) that was above the superiormost aspect of the highest kidney was recorded. The superior or inferior border of the pubic symphysis was determined to be below the inferiormost aspect of the bladder. The CT studies were then viewed to identify any findings that would be missed above or below the defined bony landmarks. Results: Using the top or bottom of T10 included both kidneys in their entirety in 243 (100%) of 243 cases. Using the top or bottom of T11 included both kidneys in 241 (99%) of the 243 and 189 (78%) of the 243 cases, respectively. Using the top or bottom of the pubic symphysis included the entire bladder in 158 (65%) of the 243 and 243 (100%) of the 243 cases, respectively. The mean reduction in scan length was 5.17 cm (11.3%) above the bottom of T10 and 2.89 cm (6.3%) below the pubic symphysis, for a total reduction of 8.06 cm (17.7%). Conclusions: Reducing the scan length is an effective technique to reduce radiation dose in patients undergoing NCCT for suspected urolithiasis. The bottom of T10 and the bottom of the pubic symphysis should be used as landmarks on the CT localizer radiograph.