Abdominal imaging - MRI, including MRA and MRCP

Principle

MRI provides superior soft-tissue contrast for the abdomen without ionising radiation - particularly valuable for hepatobiliary and pancreatic imaging, and via specific sequences (MRA for vasculature, MRCP for the biliary/pancreatic ductal system)
MRCP uses heavily T2-weighted sequences to produce a non-invasive "cholangiogram-like" image of the bile ducts and pancreatic duct, without needing contrast injection into the ducts themselves (unlike ERCP) - excellent for detecting choledocholithiasis, strictures, and ductal anatomy, but diagnostic only, not therapeutic
MRA uses contrast-enhanced or flow-sensitive sequences to image abdominal vasculature (e.g. mesenteric, renal, portal vessels) without arterial catheterisation

Preferred over CT for specific indications where its superior soft-tissue characterisation or lack of radiation is particularly valuable - liver lesion characterisation, biliary tree assessment, and imaging in pregnancy or children where radiation avoidance matters
MRI liver protocols with hepatobiliary-specific contrast agents improve characterisation of indeterminate liver lesions found on other imaging (distinguishing benign from malignant, and characterising specific benign lesion types such as focal nodular hyperplasia vs adenoma)
MRCP is the investigation of choice when biliary/pancreatic ductal anatomy needs to be defined without an immediate therapeutic intervention planned - if a therapeutic intervention (stone extraction, stenting) is anticipated, proceeding directly to ERCP may be more efficient
Choledocholithiasis workup, indeterminate liver lesion characterisation, pancreatic ductal anomalies, imaging in pregnancy

Longer acquisition time than CT (motion artefact more of an issue, less suited to an unstable/acutely unwell patient), and standard contraindications apply (some older pacemakers/implants, severe claustrophobia)
MRCP found pathology (e.g. a bile duct stone) generally requires a subsequent ERCP for therapeutic extraction, since MRCP itself is diagnostic only

MRCP's non-invasive nature makes it the preferred first diagnostic step when biliary pathology is suspected but the probability of needing immediate therapeutic ERCP is uncertain - reserving ERCP itself for cases where therapeutic intervention is anticipated or MRCP has already confirmed a treatable finding

3 more sections, plus exam facts

Premium unlocks every note across every specialty, and the full exam fact library behind it.