Iterative Reconstruction Cuts Dose for CT for Urinary Stones

CT radiation doses for imaging for urolithiasis reduced with the use adaptive statistical iterative reconstruction allows for effective evaluation without affecting image quality or diagnostic confidence, show findings of a study published online in the journal Radiology.

Patients with urinary calculi often undergo repeated scanning, which potentially exposes them to high doses of radiation. Researchers from Massachusetts General Hospital investigating lower dose options evaluated the performance of CT scans at 80 kV and 100 kV with tube-current time products 75 to 150 mA and the effect of ASIR.

Twenty-five patients with 33 stones (mean age 35) with urolithiasis participated in the study, which took place between November 2010 and April 2011. Imaging was compared with filtered back projection (FBP) on CT image quality.

The researchers found that the modified-protocol FBP images showed low image quality (score: 2.5) that was improved on the modified-protocol adaptive statistical iterative reconstruction (ASIR) images (score: 3.4). All stones, which were a mean of 6.1 mm, were diagnosed by the two readers with the modified-protocol CT.

ASIR images were also considered to be adequate to diagnose other abdominal diagnosis (score: 2.0), while this was less accurate with the FBP images (score: 1.3).

The modified-protocol CT provided a mean radiation dose of 1.8 mGy, but was as low as 1.3 mGy for patients who weighed less than 100 pounds and as high as 2.3 mGy for those over 200 pounds. This compares with 9.9 mGy for the reference protocol.

The researchers concluded, “Image quality improvements with ASIR at reduced radiation dose of 1.8 mGy enabled effective evaluation of urinary calculi without substantially affecting diagnostic confidence.” They acknowledged that imaging quality will continue to improve as the method is used by more facilities.