- Pictorial Review
- Open Access
Magnetic resonance cholangiopancreatography: the ABC of MRCP
© European Society of Radiology 2011
- Received: 30 May 2011
- Accepted: 9 September 2011
- Published: 28 September 2011
Magnetic resonance cholangiopancreatography (MRCP) is a technique that has evolved over the past two decades. It continues to have a fundamental role in the non-invasive investigation of many pancreatico-biliary disorders. The purpose of this review is to summarise the key concepts behind MRCP, the different techniques that are currently employed (including functional and secretin-stimulated MRCP), the pitfalls the reader should be aware of, and the main clinical indications for its use.
- MR cholangiopancreatography
- Bile duct calculi
- Bile duct neoplasms
- Bile duct abnormalities
- Pancreatic ducts
It has been exactly two decades since magnetic resonance cholangiopancreatography (MRCP) was first described . Over this time, the technique has evolved considerably, aided by improvements in spatial resolution and speed of acquisition. It has now an established role in the investigation of many biliary disorders, serving as a non-invasive alternative to endoscopic retrograde cholangiopancreatography (ERCP). It makes use of heavily T2-weighted pulse sequences, thus exploiting the inherent differences in the T2-weighted contrast between stationary fluid-filled structures in the abdomen (which have a long T2 relaxation time) and adjacent soft tissue (which has a much shorter T2 relaxation time). Static or slow moving fluids within the biliary tree and pancreatic duct appear of high signal intensity on MRCP, whilst surrounding tissue is of reduced signal intensity.
Heavily T2-weighted images were originally achieved using a gradient-echo (GRE) balanced steady-state free precession technique [1, 2]. A fast spin-echo (FSE) pulse sequence with a long echo time (TE) was then introduced shortly after , with the advantages of a higher signal-to-noise ratio and contrast-to-noise ratio, and a lower sensitivity to motion and susceptibility artefacts. Modified FSE sequences have been described, including rapid acquisition with rapid enhancement (RARE) , half-Fourier acquisition single-shot turbo spin-echo (HASTE) , and fast-recovery fast spin-echo (FRFSE)  sequences. Both breath-hold (using a single shot approach)  and non-breath-hold techniques (with respiratory triggering)  have been used, with images obtained either as a two-dimensional (2D) or three-dimensional (3D) acquisition. A 3D technique provides a higher signal to noise ratio, which is traded off for thinner contiguous slices. Acquiring images with near isotropic voxels allows improved post-processing manipulation of the images with multi-planar reconstruction, maximum intensity projection (MIP) and volume rendering. The introduction of faster gradients and a parallel acquisition technique has resulted in even greater spatial resolution and faster acquisition times. More recently, functional assessment of biliary excretion and pancreatic exocrine function has become possible with the use of hepatobiliary contrast media  and secretin  respectively.
The purpose of this pictorial review is to describe (1) the MRCP protocol used by our centre and additional/alternative sequences which can be employed, (2) the normal biliary anatomy on MRCP, (3) the potential pitfalls associated with this technique and (4) the main clinical indications for its use.
Patients are fasted for 4 h prior to the study in order to reduce fluid secretions within the stomach and duodenum, reduce bowel peristalsis and promote gallbladder distension. We do not routinely use an anti-peristaltic agent. Some centres use a negative oral contrast agent (e.g. iron oxide or blueberry juice) to reduce the signal intensity of overlapping fluid within the stomach and duodenum, although this is not part of our routine protocol.
Summary of MRCP imaging parameters
T2-weighted breath-hold HASTE (liver down to ampulla)
3D T2-weighted FSE with respiratory triggering
T2 weighted breath-hold HASTE fat-saturated thick slab
Number of averages
Field of view (mm)
350 × 263
380 × 380
350 × 350
256 × 146
384 × 380
384 × 300
Slice thickness (mm)
Slice gap (mm)
Number of slices
Phase encoding: 7/8
Parallel imaging acceleration factor
Receiver bandwidth (Hz/pixel)
Following this, we perform two 3D respiratory-triggered heavily T2-weighted FSE sequences in the coronal oblique plane. The imaging plane is selected from the initial axial T2-weighted images, with one acquisition aligned to the common bile duct (CBD) in the head of the pancreas and the second acquisition aligned to the pancreatic duct at approximately 90 degrees to the first imaging plane. Respiratory triggering is achieved with the use of a navigator sequence that employs an MR pre-pulse to monitor respiratory motion. The navigator is placed over the edge of the diaphragm on the coronal and sagittal localisers and image acquisition is triggered when the position of this diaphragm interface with the lung falls within a pre-specified acceptance window. In this way a consistent position of the imaging slice is obtained. The patient is asked to breathe regularly throughout this acquisition, which takes between 3-5 min to acquire. A stack of 40 slices are obtained, which are contiguous and each of 1.5 mm in thickness. As the images are heavily T2-weighted, the pancreatico-biliary tree is displayed as high signal intensity, whilst adjacent structures are of reduced signal intensity. This sequence is useful in detecting small filling defects or strictures in the biliary or pancreatic ducts. From this volume of data, a MIP reformat can be generated. This displays only the pixel with the highest signal intensity along a ray perpendicular to the plane of projection. It thus highlights bile-filled and fluid-filled structures very well. MIP reformats can be generated in various coronal and sagittal oblique planes. We conventionally create 18 MIP reformats at 10-degree intervals to each other over a radial array of 180 degrees.
In addition to, or as an alternative to the MIP reformats, a thick collimation slab can be obtained in the coronal plane. This involves performing a fat saturated HASTE sequence where a single slab of data 4 cm in thickness is acquired in a 1- to 2-s breath-hold. It is useful in depicting the entire pancreatico-biliary tree and no post-processing is required.
In order to evaluate the duct walls, and any focal parenchymal pathology, 3D fat suppressed T1-weighted GRE sequences before and after intravenous contrast administration can also be performed.
Functional MR cholangiography
This involves the use of MR lipophilic paramagnetic contrast agents, which when given intravenously, show hepato-biliary excretion. Contrast agents include gadobenate dimeglumine (Gd-BOPTA, Multihance; Bracco Imaging, Milan, Italy), gadolinium ethoxybenzyldiethylenetriamine penta-acetic acid (Gd-EOB-DTPA, Primovist; Bayer-Schering Pharma, Berlin, Germany) and, historically, mangafodopir trisodium (Teslascan; GE Healthcare, Oslo, Norway). Delayed imaging in the axial and coronal plane, performed between 10-120 min following intravenous administration, normally results in hyper-intense bile on 3D T1-weighted fat-saturated GRE images. The signal-to-noise ratio is higher than conventional T2-weighted MRCP, allowing better delineation of the bile ducts. This technique can be used for similar indications as for T2-weighted MRCP and in most cases has a similar diagnostic accuracy. It is more expensive than conventional T2-weighted MRCP and only the biliary tree is depicted. For these reasons, most centres continue to use conventional T2-weighted MRCP. However, functional MRCP does have a number of advantages, as follows: (1) it better demonstrates communications between cystic lesions and draining bile ducts in the diagnosis of congenital biliary disorders (e.g. Caroli’s disease) , (2) it helps to distinguish true obstruction in a dilated biliary system (where delayed or no biliary excretion is demonstrated) from pseudo-obstruction , and (3) it can demonstrate active extravasation of contrast in suspected bile leaks [12, 13]. Another advantage is that these gadolinium-based hepatobiliary-specific contrast agents initially distribute in the extracellular fluid compartment, thus allowing for early dynamic pre-contrast and post-contrast images in the arterial, portal venous and equilibrium phase prior to the functional cholangiogram.
In cases where there is significant biliary obstruction or impaired hepatocyte function, delayed images up to 24 h can be performed until contrast is seen in the gallbladder and duodenum.
The pancreatic duct should be no greater than 3 mm, with the main pancreatic duct of Wirsung normally draining into the major duodenal papilla along with the CBD (91% of individuals). An accessory pancreatic duct of Santorini may be present in 45% , which drains into the minor duodenal papilla. The cystic duct usually joins the extra-hepatic duct from the right lateral aspect in 50% of cases, although it may insert into its anterior or posterior aspect in 30% and medial aspect in 20% of individuals.
A number of pitfalls may arise which fall into four main categories: (1) artefacts related to technique and reconstruction; (2) normal variants mimicking pathology; (3) intra-ductal factors; (4) extra-ductal factors.
Technique and reconstruction artefacts
A long cystic duct running parallel to the CBD may simulate a dilated common duct, whilst a contracted choledochal sphincter may mimic an impacted stone or stricture in the distal CBD. En face visualisation of the cystic duct insertion into the bile duct may also simulate a filling defect. Performing MRCP in multiple imaging planes or carrying out repeat MRCP imaging will help resolve these problems.
Identification of congenital anomalies of the cystic and hepatic ducts
Post-surgical biliary anatomy and complications
ERCP is often not possible in patients with a previous biliary-enteric anastomosis. MRCP is then useful in the demonstration of post-surgical biliary anatomy and in the detection of biliary complications, with a 100% sensitivity in the diagnosis of anastomotic strictures and a 90% sensitivity for choledocholithiasis .
Anomalous pancreaticobiliary junction
Choledochal cysts are associated with anomalous union of the pancreaticobiliary duct, where the pancreatic duct and CBD unite outside the duodenal wall and form a long common channel greater than 15 mm in length. There are five different types of choledochal cyst described (Todani classification) with three main types of anomalous pancreaticobiliary junction. MRCP can assist detection of such variants when suspected clinically.
This is usually performed in patients presenting with obstructive liver function tests and with suspected gallstones and/or a dilated CBD on ultrasound. It is also carried out in patients who have persistent symptoms and abnormal liver function following cholecystectomy. A systematic review of the literature has shown that when compared with ERCP, MRCP has an aggregated sensitivity, specificity, positive predictive value and negative predictive value of 85%, 93%, 87%, and 82% respectively . Stones (as small as 2 mm) appear as dependent low-signal-filling defects within the CBD (Fig. 8a, b), surrounded by high-signal-intensity bile.
Benign biliary strictures
These usually develop following surgical injury (95%) from procedures such as laparoscopic cholecystectomy, hepatic resection, liver transplantation and biliary enteric anastomosis. Other causes include trauma, inflammation from choledocholithiasis, ischaemia involving the hepatic artery and primary sclerosing cholangitis (PSC). Typically a benign stricture involves a short segment, with a regular margin and symmetric narrowing. MRCP can demonstrate the site and extent of the stricture with a reported sensitivity of 91-100% .
Malignant biliary strictures
Pseudocysts are encapsulated fluid collections seen in both acute and chronic pancreatitis (Figs. 5, 6). These often develop within the lesser sac. MRCP is more sensitive than ERCP in demonstrating these fluid collections and may show their connection with the pancreatic duct. With ERCP, less than 50% of pseudocysts opacify with contrast .
Cystic pancreatic tumours
Differences in epidemiology and morphology on MRCP of cystic pancreatic tumours
Mucinous cystic neoplasms
Intraductal mucinous neoplasm (IPMN)
Typically older women >60 years
Typically younger women 30-50 years
Peak age 6th decade, no gender bias
Site of tumour
Anywhere in the pancreas, especially the head
75% in body/tail
Side branch type: usually pancreatic head/uncinate process, less frequently in the tail; tumour communicates with the main pancreatic duct
Main duct type: segmental or diffuse involvement of the main pancreatic duct
>6 cysts (<2 cm each), thin septations, central scar (calcification), does not communicate with the pancreatic duct
Cysts >2 cm, unilocular or multilocular, does not communicate with the pancreatic duct
Side branch type: macrocystic or microcystic appearances
Features of malignancy on MR denoted by thick septations, soft tissue nodules, and/or pancreatic duct dilatation
Main duct type: diffuse duct dilatation due to gross mucin production, micropapillary studding, pancreatic atrophy
Larger size with malignant tumours
High signal intensity on T1 and T2 (mucin/blood)
High signal intensity on T1 (mucin), intermediate signal intensity on T2
Malignant in 50%
Side branch type: usually associated with benign adenomas
Main duct type: malignant in 40%
Following transection of the bile ducts (usually following surgery), bile accumulates within the sub-hepatic space. Fluid collections can be appreciated on MRCP with transection of the affected bile duct. If functional MRCP is used, extravasation of contrast from the biliary tree is seen. A stricture may develop following accidental ligation or transection, with upstream dilatation demonstrated on MRCP.
The technique of MRCP has evolved considerably over the last 2 decades, with technological advances in both acquisition and post processing. It remains the investigation of choice for the non-invasive diagnosis of many pancreatico-biliary disorders. It is hoped that this review has helped remind the reader as to the basic concepts behind MRCP, the different sequences that can now be employed, the pitfalls one should be aware of, and why, even in modern day, it remains a test fit for purpose in the radiological investigation of biliary pathology.
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