February 2, 2011 — NEW YORK (Reuters Health) – Low-dose noncontrast CT isn’t as effective as standard-dose CT in diagnosis of kidney stones, particularly small ones, but this reduced radiation approach may still have advantages over other imaging tools.
“Low-dose protocol CT for kidney stone detection is more sensitive compared to plain abdominal film or ultrasound.” Dr. Dorit E. Zilberman told Reuters Health by e-mail. The study results appear in the March Journal of Urology, available online now.
Dr. Zilberman and colleagues at Duke University Medical Center, Durham, North Carolina, used standard renal stone protocol CT with a tube current of 160 mA to examine 62 patients with suspected urolithiasis.
Next, they added noise to the images to simulate tube currents of 70, 100, and 130 mA. Three independent observers evaluated the original and modified images. A 56% reduction in current, the researchers point out, would lead to a radiation exposure equivalent to that from approximately 4.5 abdominal x-rays.
Only stone size was associated with reviewer agreement on the diagnosis of stone disease. Each 1-mm increase in stone size increased the likelihood of a concordant response by 3.55 times when the tube current was reduced by a simulated 19%, by 2.7-fold when the current was cut by 38%, and by 2-fold when the current was reduced by 56%.
As the current fell, so did the observers’ ratings of their overall confidence, especially in findings in the bony pelvis. Agreement wasn’t associated with multiple stones or with index stone location.
The researchers note that among limitations of the study were that “a single baseline protocol was used and it is unclear whether other stone protocols would have yielded similar results.”
The role of low-dose CT in diagnosis of small stones is problematic, the investigators acknowledge. “On the other hand, it is associated with less radiation exposure compared to standard-dose CT scan, therefore it may serve as a reliable tool for long term follow-up in patients with an established diagnosis of kidney stone disease,” concluded Dr. Zilberman.
The researchers conclude that more prospective trials are needed.
By David Douglas
J Urol 2011.
Last Updated: 2011-02-01 13:00:14 -0400 (Reuters Health)