A technique using dual-energy CT shows promise in gallstone disease imaging and can potentially reduce the need for further gastrointestinal imaging using US or MRI for patients with cholelithiasis or choledocholithiasis.
Soesbe
"Our approach offers faster diagnosis of cholelithiasis or choledocholithiasis without subsequent imaging, thus providing a reduction in imaging costs, shorter time to diagnosis, and lower risk for patients," said Todd C. Soesbe, PhD, an assistant professor in the Department of Radiology at UT Southwestern Medical Center in Dallas.
"Isoattenuating gallstones occur when cholesterol-based gallstones have the same Hounsfield units as the surrounding bile and are therefore difficult to see on CT scans of the gallbladder," Dr. Soesbe said. Motivated by a suggestion from mentor and study co-author John Leyendecker, MD, Dr. Soesbe and colleagues sought to develop a dual-energy CT method to address this challenge.
To test their hypothesis, the team first made a CT phantom containing a pure cholesterol pellet (to simulate an isoattenuating gallstone) and dehydrated ox-bile (in solution, to simulate human bile).
"We were excited to discover that even though the cholesterol pellet and ox-bile were isoattenuating in the conventional CT image, they appeared in different locations within a 2D histogram made from photoelectric effect and Compton scattering attenuation values," Dr. Soesbe said. "Therefore, cholesterol-based gallstones could be easily differentiated and segmented from bile using our custom methods, allowing them to be easily seen in the CT image."
For proof of concept, the researchers first performed an ex vivo study, published in Radiology, using gallstones collected from cholecystectomy patients and ox-bile.
The researchers have since performed a retrospective in vivo study evaluating CT scans from 20 patients with isoattenuating gallstones and 20 gallstone-free patients. All patients were scanned with dual-energy CT between July 2015 and October 2019.
They confirmed positive and negative stone diagnoses using MR cholangiopancreatography (MRCP), endoscopic retrograde cholangiopancreatography (ERCP) or US performed withing 90 days of CT.
Conventional, 40 keV monoenergetic, and effective-Z series were created for each patient, as well as two custom segmented series using either Compton and photoelectric attenuation data, or denoised 200 and 40 keV monoenergetic data.
Four readers evaluated the presence of isoattenuating stones in each of the five series. Out of the gallstone-positive patients, the types of stones identified were gallbladder stones, cystic duct stones and common bile duct stones.
According to Dr. Soesbe, comparing the 2D histogram of all patients who were gallstone-positive patients to that of those who were gallstone-negative revealed that isoattenuating stones appear in a separate and unique 2D location that permitted material differentiation and visual segmentation of isoattenuating stones within the conventional CT series. For all patients, the Compton/photoelectric or denoised monoenergetic series provided the highest agreements and overall diagnostic performance.
"The retrospective in vivo study results, which we present here, required hours and hours of customized image analysis and radiologist readings, but our team efforts were well worth it," Dr. Soesbe said. "The vendor-neutral aspects of our improved in vivo method have the potential to make dual-energy CT the reference standard to evaluate gallstone disease."
Access the presentation, "A Technique to Identify Isoattenuating Gallstones With Dual-Energy CT: An In Vivo Study," (M3-SSGI05-06) on demand at Meeting.RSNA.org
.
