Radiation Exposure to the Sacroiliac Joint From Low-Dose CT Compared With Radiography

The primary objective of this study was to estimate the effective dose delivered to the sacroiliac joint (SIJ) from low-dose (LD) CT compared with that from radiography. Secondary objectives included evaluation of diagnostic quality of LD CT of the SIJ and development of a clinical protocol for LD CT of the SIJ. Data from 36 patients (19 women, 17 men) undergoing LD CT for suspected renal colic were analyzed. Two effective dose estimates were calculated: one for the SIJ and another for an extended region from the iliac crest to 1 cm below the SIJ. Thirty-six anteroposterior pelvic and 36 SIJ view radiographs were age-, sex-, and body width-matched to CT scans. Effective dose from radiography was estimated using the method described in International Commission on Radiologic Protection Publication 60. Maximum effective dose to the SIJ from LD CT was less than 1 mSv in all cases, with a mean ± SD of 0.42 ± 0.18 mSv (range, 0.14-0.83 mSv), whereas mean dose to the extended region was 0.57 ± 0.24 mSv (range, 0.19-1.11 mSv). Mean dose from SIJ radiographs was 0.15 ± 0.10 mSv (range, 0.07-1.38 mSv), and mean dose from a single pelvic radiograph was 0.09 ± 0.06 mSv (range, 0.04-0.37 mSv). All CT studies were of diagnostic quality for assessment of the SIJ. LD CT of the SIJ can be consistently performed with an effective radiation dose of less than 1 mSv. Because reliability and sensitivity of radiography for sacroiliitis is poor, we recommend that LD CT replace radiography for dedicated evaluation of the SIJ.