Emergency imagers can cut CT radiation dose by more than 85 percent and still produce diagnostic images that reliably identify patients with acute flank pain who, as suspected, need intervention within 90 days for calculi in the urinary system, according to a study posted ahead of print in Radiology.

Led by Yale’s Christopher Moore, MD, the study’s authors describe their application of STONE scoring—the word is an acronym for sex, timing, origin, nausea and erythrocytes—to prospectively qualify for reduced-dose CT all patients with high likelihood of ureteral stones.

Patients with moderate likelihood as assessed by STONE scores underwent either reduced-dose CT or standard CT, the decision being left up to the attending clinician’s discretion.

The team followed a total of 264 study subjects for 90 days after initial imaging, recording clinical courses and primary outcomes of any interventions.

Their key observation was that all patients who underwent reduced-dose CT alone and required a urological intervention had their calculi correctly diagnosed.

Meanwhile, even in patients who had a standard-dose CT after reduced-dose CT—the second exam having been ordered mostly by radiologists who perceived low image quality—blinded rereads of the reduced-dose CT images showed a sensitivity of 85.7 percent and a specificity of 100 percent for ureteral calculi.

As for the depth of the radiation reduction, the average dose-length product for the standard-dose CTs was 857 mGy-cm ± 395 compared with 101 mGy-cm ± 39 for the reduced-dose CTs.

This drop represented an average radiation dose reduction of 88.2 percent.

Also, the average dose-length product actually received by all study patients, including those who had both standard-dose and reduced-dose CT, was 555 mGy-cm.

This was 35 percent lower than the average standard-dose CT radiation dose of 857 mGy-cm.

In their study discussion, Moore et al. acknowledge lack of randomization as a study limitation.

They further note that a case can be made from previous randomized research for not using CT at all, whether at standard or reduced dose, as ultrasound often may suffice.

“However, ultrasonography is often limited by not being able to define stone size and location, which may be considered important for prognosis or therapy,” they write, adding that, in one study that randomized patients to ultrasound, around one-third of the patients who were initially randomized to ultrasound ended up undergoing CT after all.

“A relatively high proportion of patients in our study had urologic procedures, specifically 24 of 79 stones identified on reduced-dose CT,” they write, “which accurately predicted need for intervention.”

A CT protocol with better than 85 percent dose reduction “can be used in patients with moderate to high likelihood of ureteral stone,” the authors conclude, “to safely and effectively identify patients in the ED who will require urologic intervention.”