50% tube exposure provides comparable diagnosis of urolithiasis

CT images reconstructed from 50 percent tube exposure reconstructed with sinogram-affirmed iterative reconstruction (SAFIRE) are not inferior to images reconstructed with 100 percent exposure in the diagnosis of urolithiasis, according to a study published online May 7 by Radiology.

Given the high ten-year recurrence rate in patients with urolithiasis, many have to undergo numerous CT scans. Due to concern about radiation exposure, reduced exposure exams are a potential solution to this safety risk. Lead author Erick M. Remer, MD, of the Cleveland Clinic, and colleagues compared images acquired with 100 percent tube exposure and reconstructed with filtered back projection (FBP) and images obtained with 50 percent tube exposure and reconstructed with SAFIRE on a dual-source scanner to determine how dose reduction influences reader ability in detecting stones, reader confidence in detection and stone size measurements and abnormal findings outside of the urinary tract.

The researchers assessed 99 patients with urolithiasis in the study. After the data were reconstructed using the aforementioned methods, seven readers evaluated randomized studies for calculi in nine regions. Reader confidence was scored using a five-point scale and ancillary findings were recorded. The area under the receiver operating characteristic curves with 95 percent confidence intervals were estimated to test for noninferiority of 50 percent exposure with SAFIRE.

Calculi were discovered in 113 locations and were not found in 752 locations. The mean area under the operating characteristic curve for FBP was 0.879 and 0.883 for SAFIRE. The SAFIRE images were not significantly inferior to the FBP images, as reader confidence levels for images with stones were similar between the two groups.

There were 52 patients with extraurinary findings and readers correctly reported them in 74.4 percent of cases for FBP and 72 percent for SAFIRE. Nine patients had potentially important findings according to the reference standard and the detection rates were 44 percent for FBP and 33 percent for SAFIRE. Of the 43 patients who had unimportant or likely unimportant findings, the false detection rates were 15 percent and 14 percent, respectively.

“Scanning with 50 percent exposure and iterative reconstruction can be substituted for 100 percent exposure with filtered back projection without substantially decreased detection of urolithiasis or reader confidence; however, potentially important extraurinary findings might be missed,” the authors wrote.