Carbon dioxide (CO2) gas is widely used for luminal insufflation during endoscopic retrograde cholangiopancreatography (ERCP) of the biliary tract. While frequently observed during routine ERCP, there are few data on the topic of "air" or "CO2" cholangiography. Our primary aim is to compare radiographic cholangiograms in patients with biliary tract disease (from stones or strictures) during ERCP obtained by using carbon dioxide as the contrast medium vs. conventional iodinated contrast.

It has been recommended that endoscopic retrograde cholangiopancreatography (ERCP) be performed using carbon dioxide (CO2) instead of room air as the infused "air" or gas for luminal insufflation for reasons of improved patient comfort and in case of procedural adverse events (as CO2 is more quickly absorbed by the body and as it can be exhaled via the lungs). Air cholangiograms are often incidentally visible on fluoroscopy (radiographically) during ERCP prior to injection of iodinated contrast into the biliary tree. Despite the information from an air cholangiogram being readily available in many instances, biliary endoscopists and radiologists who read the fluoroscopic images taken during ERCP do not usually comment or interpret the "air" or "CO2" cholangiograms. Consequently, very little data is available on the topic of "air" or "CO2" cholangiography. As a contrast medium for cholangiography, CO2 might be safer than iodinated contrast, which is the standard contrast medium used during ERCP, as iodinated contrast cannot be easily absorbed by the body and as it can be trapped proximal to obstructing biliary stones or strictures and lead to biliary tract infection.

This is a prospective cohort study that will enroll patients undergoing ERCP for suspected choledocholithiasis and/or biliary stricture(s). If they did not participate in this study, these patients would still require an ERCP with CO2 used as the endoscopically insufflated "air" medium. Enrolled patients will undergo an initial cholangiogram with CO2 (injected into the bile ducts) utilizing both conventional fluoroscopy and digital subtraction fluoroscopic imaging, followed by conventional cholangiography using iodinated contrast (injected into the bile ducts). Digital subtraction fluoroscopic imaging is a commercially available setting on certain fluoroscopy units that optimizes resolution with air or CO2 used as a contrast medium. Findings on CO2 cholangiography will be compared to those obtained from pre-procedural abdominal imaging along with the cholangiogram done using iodinated contrast at the time of the ERCP procedures.

Inclusion Criteria:

• Patients 18 years of age or older
• Patients with choledocholithiasis, benign biliary strictures, malignant biliary strictures
• Biliary pathology suggested or confirmed by imaging with abdominal ultrasonography, CT scan, MRI/MRCP scan, or endoscopic ultrasonography (EUS)

Exclusion Criteria:

• Pregnancy (self reported)
• Presence of cholangitis before ERCP
• Prior history of surgery on the stomach or duodenum that precludes conventional ERCP or prior biliary tree surgery (not including cholecystectomy)
• Failure to selectively cannulate the bile duct
• Life expectancy less than 30 days
• Prisoners
• Patients unable to give consent