Magnetic resonance (MR) cholangiopancreatography has proved a robust and 
noninvasive imaging modality for evaluating the biliary and pancreatic ducts 
without the use of ionizing radiation. Although MR cholangiopancreatography 
reliably depicts the main extrahepatic and intrahepatic bile ducts, it does not 
depict the segmental intrahepatic ducts unless they are dilated. The segmental 
ducts are difficult to visualize with MR cholangiopancreatography because of 
their small caliber and the limited spatial resolution and signal-to-noise ratio 
achievable with standard MR pulse sequences. However, visualization of the 
normal (ie, nondistended) biliary system is necessary for the evaluation of 
donor candidates for living related liver transplantation. Because of the 
prevalence of variant biliary anatomy, MR cholangiopancreatography is often used 
for preoperative evaluation of prospective liver donors. Intravenous morphine 
administered prior to MR cholangiopancreatography can improve image quality by 
causing the sphincter of Oddi to contract, which increases pressure in and 
distention of the biliary and pancreatic ducts. Morphine administration may also 
be particularly helpful for the evaluation of patients with primary sclerosing 
cholangitis, malignant neoplasms such as cholangiocarcinoma, or cystic and 
non-organ-deforming benign pancreatic neoplasms.