CT post-processing method reduces radiation exposure to patients with bile duct stones

A team of Korean researchers has found a way to reduce the radiation dose to patients undergoing dual-energy CT (DECT) for bile duct stone detection, reported authors of an April 25 study published in the European Journal of Radiology.

DECT scanners have peaked the interest of clinicians for its ability to evaluate biliary stone disease, wrote Jae Seok Bae, with the department of radiology, Seoul National University Hospital in South Korea, and colleagues. During DECT post-processing virtual non-contrast (VNC) images can be created by subtracting the iodine from the contrast-enhanced images, a potential substitute for true non-contrast (TNC) images.

“If VNC images could provide comparable diagnostic performance in detecting biliary stone disease to TNC, we might replace TNC with VNC, and consequently, reduce the radiation dose,” the authors wrote.

For their study, Bae et al. retrospectively enrolled 75 patients with suspicious biliary disease who underwent dual-source DECT and surgery and/or endoscopic intervention within two months of the CT scan. Forty-five patients had biliary stones. The team compared the sensitivity and specificity of TNC and VNC for detecting gallstone and common bile duct (CBD) stones using the McNemar test.

In total, 37 patients had gallstones, two had CBD stones and six had both. The diagnostic accuracy was similar between TNC and VNC images. For detecting gallstones, TNC scored a 90.7% sensitivity and 87.5% specificity, compared to the 88.4% and 90.6%, respectively for the VNC images.

For CBD stones, sensitivity and specificity were 87.5% and 98.5%, respectively, for TNC images. In comparison, VNC images notched a 75% sensitivity and 100% specificity.

Perhaps more importantly, Bae and colleagues found that using VNC images could result in an expected radiation dose reduction of 22.4%.

“The VNC images could reduce the radiation dose by eliminating the need to acquire the TNC images  because the VNC images provided comparable diagnostic capability in detecting biliary stones compared to the TNC images,” the authors added.

The researchers acknowledged their study had a few limitations, including the fact that results were produced using a DECT scanner from a single vendor and may not be generalized to other protocols or machines.

Bae and colleagued did agree their findings present sufficient evidence for VNC to replace TNC images.

“This is the first study that evaluated the specificity for the detection of CBD stones on the VNC images,” Bae et al. concluded. “Hence, the VNC images may eliminate the need for acquisition of TNC images, especially for the evaluation of biliary stone, thereby reducing the radiation exposure in patients undergoing TNC imaging which accounts for 22.4% of the total radiation dose in the biliary protocol CT.”