Magnetic resonance cholangiopancreatography (MRCP) has undergone considerable advances. It provides a noninvasive imaging alternative to endoscopic retrograde cholangiopancreatography for diagnosis, ultimately limiting the use of invasive techniques to therapeutic procedures. This review presents some of the relative advantages and disadvantages of MRCP, important aspects of technique, and major clinical applications.
is an Assistant Professor of Radiology, and
is an Associate Professor of Radiology and Chief of Abdominal
Imaging, Department of Radiology, University of California, San
Magnetic resonance cholangiopancreatography (MRCP) is the
partial or complete selective imaging of the biliary system and
pancreatic duct, which utilizes the inherent contrast of the
fluid-filled ducts to generate images. The partial or complete
selectivity for ductal imaging distinguishes MRCP from other
imaging modalities used for imaging the pancreatobiliary system,
such as computed tomography (CT) or ultrasound. MR
cholangiopancreatography has undergone considerable technical
advances over the last 10 years, rendering it an alternative to
endoscopic retrograde cholangiopancreatography (ERCP) in most
clinical settings. This review will discuss some of the relative
advantages and disadvantages of MRCP, important aspects of
technique, and major clinical applications.
Advantages and disadvantages of MRCP
The major advantage of MRCP over ERCP or percutaneous
transhepatic cholangiography is the noninvasive nature of the
technique. Conventional cholangiography has a major complication or
adverse event rate of approximately 3%. Such events include sepsis,
bleeding, bile leak, and death.
In addition, MRCP does not require sedation and is more economical.
A further advantage of MRCP is the ability to partially or
completely selectively depict the ductal structures. Partial
selection of duct depiction enables assessment of the pancreatic
paren-chyma and adjacent tissues. Conventional cholangiography
depicts only the duct lumen, and periductal pathology can only be
inferred indirectly from these images.
Because MRCP relies on signal from fluid within ducts and not on
intraductal contrast injection, all fluid-filled structures within
the field-of-view are displayed. This offers the advantage of
visualizing excluded duct segments or cystic tumors that do not
communicate with the pancreaticobiliary tree.
The major disadvantage of MRCP compared with conventional
cholangiography is a lower spatial resolution, which limits
evaluation of subtle small duct changes, eg, side branch changes of
chronic pancreatitis and sclerosing cholangitis. Ductal distension
from the contrast injection during ERCP does not occur with MRCP,
which is a contributing factor to the limited assessment of small
branches. A potential criticism of MRCP is that endobiliary
therapeutic procedures cannot be performed. Many patients who
undergo ERCP do not have therapeutic intervention. In patients who
undergo ERCP for choledocholithiasis prior to cholecystectomy, 40%
to 70% of examinations were negative for the presence of common
bile duct stones.
MR cholangiopancreatography should be performed with surface
phased-array multicoils, because of the higher signal-to-noise
ratio and consequent increase in spatial resolution.
The basis of MRCP is the use of high-resolution breath-hold
T2-weighted sequences to image the pancreatic and biliary ducts.
Fluid is bright on T2-weighted sequences, which can be used to
visualize the ductal lumen. No exogenous contrast is required, as
the contrast mechanism is entirely endogenous. Single-shot rapid
acquisition with relaxation enhancement (SS-RARE) has emerged as
the optimal sequence for MRCP, with the combined advantage of rapid
image acquisition and relatively high spatial resolution.
This protocol is an ultra-fast T2-weighted sequence that enables
sub-second slice acquisition, which largely overcomes the problem
of motion artifact. Imaging of the pancreatic and biliary ducts can
be performed in a single breath-hold. Physiologic motion,
particularly breathing, is a major contributing factor to image
degradation, and has been the greatest obstacle to diagnostic
quality MRCP. Breath-hold imaging is essential to reducing this
source of image degradation. Section misregistration or motion
artifacts severely limit assessment of small structures.
Single-shot rapid acquisition with relaxation enhancement is less
sensitive to magnetic susceptibility artifacts than are
gradient-echo sequences. Common commercial versions of SS-RARE
include single-shot fast-spin-echo (SSFSE; GE Medical Systems,
Waukesha, WI) and half-Fourier acquisition single-shot
turbo-spin-echo (HASTE; Siemens Medical Systems, Iselin, NJ)
The SS-RARE sequences are performed using a long echo time (TE)
value (eg, 150 to 600 msec) with fat suppression, or by using an
extremely long TE value (eg, 600 to 1200 msec) without fat
Signal acquisition from a single thick slice, or maximum intensity
projection (MIP) postprocessing of multiple thin slices, can be
used to generate images resembling a cholangiogram. However, source
images may yield more information than cholangiogram-like images.
In a study of 108 patients,
the reported sensitivity for detection of stones was 87% using
source thin slices, 24% using MIP reconstruction, and 48% using
single thick-slice MRCP. An alternative approach to MRCP is to use
an intermediate TE value (eg, 100 msec) without fat suppression.
This enables visualization of both the fluid-filled ducts and
periductal structures, but MIP postprocessing is not possible. MR
cholangiopancreatography techniques therefore usually include both
sequences. Contiguous 3- to 5-mm slices result in good image
quality. Thinner slices may be excessively degraded by poor
signal-to-noise ratio. Smaller filling defects may be missed on
thicker slices. A 256 * 192 to 256 acquisition matrix is usually
adequate. In patients with limited breath-holding capacity, images
can be acquired as >= two or more contiguous or overlapping
stacks, rather than interleaved stacks, in order to reduce slice
misregistration. In uncooperative patients, reasonable quality
images may be acquired during quiet respiration.
Biliary disease and strictures
Ductal dilatation is depicted accurately by MRCP with
sensitivity of 95%.
The additional benefit of MRCP is the ability to localize the site,
length, and cause of obstruction. Strictures are seen as focal
ductal narrowing with proximal dilatation (Figure 1). The absence
of proximal dilatation may be indicative of a diffuse ductal
pathology, such as sclerosing cholangitis, or of a lack of duct
distensibility, such as in cases of cirrhosis. Tight strictures may
appear as segments of signal loss, limiting characterization. The
use of partially duct-selective MRCP enables depiction of
extra-ductal anatomy, which is useful in determining the cause of
obstruction. In a study of 79 patients, MRCP enabled correct
diagnosis of malignant obstruction with a sensitivity and
specificity of 86% and 98%, respectively.
MR cholangiopancreatography has demonstrated high accuracy in the
assessment of higher grade and larger duct strictures. In a recent
study of 34 post-operative patients, 6 of whom had strictures
proven by direct cholangiography, MRCP showed a sensitivity of 100%
and specificity of 87%.
Distinguishing distal common duct obstruction secondary to
ampullary stenosis, edema, or sphincter of Oddi dysfunction may be
problematic with MRCP and may require direct visualization of the
Primary sclerosing cholangitis
The diagnosis of subtle small duct changes of sclerosing
cholangitis is difficult with MRCP. However, in a recent study of
136 patients (34 diagnosed with sclerosing cholangitis at ERCP),
MRCP demonstrated a sensitivity of 85% to 88% and specificity of
92% to 97% for two independent readers.
Technologic advances and experience have led to improved
sensitivity and specificity of MRCP in choledocholithiasis from 81%
and 98% to 90% and 100%, respectively.
Further, recently reported accuracy of MRCP in choledocholithiasis
indicates results similar to ERCP.
Biliary stones are depicted as round or faceted foci of reduced
signal or signal void surrounded by high signal intensity bile
(Figure 2). Intraluminal filling defects may also be due to
pneumobilia, blood clots, intraductal tumors, and parasites.
Recognized pitfalls giving rise to false-positive findings also
include signal voids from surgical clips, and the right hepatic
artery as it traverses the upper portion of the common duct.
Despite the accurate depiction of biliary stones, the clinical role
of MRCP in choledocholithiasis is not yet clear. Patients with
strong clinical, biochemical, and sonographic or CT evidence of
choledocholithiasis typically require therapeutic ERCP. MR
cholangiopancreatography is valuable in confirming common bile duct
stones in cases in which ERCP is higher risk. This group of
patients includes those with acute pancreatitis, prior
biliary-enteric anastomosis, proximal enteric strictures, and
cardiopulmonary disease, as well as pregnant women.
MR cholangiopancreatography is also indicated following failed
ERCP cannulation. Reported failure rates for ductal cannulation
vary from 3% to 10%.
Difficult cannulation often requires repeated ERCP attempts and
precut papillotomy, with increased risk of complications, including
hemorrhage, pancreatitis, perforation, and cholangitis.
Unsuccessful ductal cannulation may require antegrade
cholangiography or laparotomy for common duct access. MR
cholangiopancreatography increases diagnostic accuracy and enables
appropriate patient selection prior to such invasive
MR cholangiopancreatography is indicated in patients with low to
moderate clinical suspicion for common duct stones, because the
relative risks of ERCP as a primary diagnostic modality may be
difficult to justify. MR cholangio-pancreatography is useful in
patients undergoing laparoscopic cholecystectomy. Common duct
calculi are found in 10% to 15% of patients who undergo
The high sensitivity and specificity of MRCP for
choledocholithiasis may be used to limit preoperative ERCP to those
patients requiring therapeutic intervention.
In a study of 37 patients, the reported MRCP sensitivity was 87%
to 100% for dilatation, 75% for narrowing, and 100% for ductal
calculi compared with ERCP.
In 1994, Outwater et al
published one of the more comprehensive studies of MRCP in chronic
pancreatitis. Two independent reviewers evaluated the MRCP findings
in 39 patients with chronic pancreatitis, using ERCP as the
standard of reference (Table 1). MR cholangiopancreatography had a
greater accuracy for the diagnosis of main duct changes rather than
the more subtle side branch abnormalities. These findings are
expected because of the limitations of spatial resolution with MRCP
(Figures 3 and 4).
The role of ERCP in acute pancreatitis is to remove retained
stones in the common bile duct or papilla. The benefit of early
ERCP in acute pancreatitis remains controversial. A benefit
suggested by early studies
was not supported in a recent controlled trial in patients without
continued jaundice or cholangitis.
MR cholangiopancreatography could limit the use of ERCP to patients
requiring therapeutic intervention.
Obstruction secondary to neoplasia presents a diagnostic and
therapeutic challenge. Treatment planning requires identification
of the level and cause of obstruction. Earlier studies were
disappointing; for example, Wallner et al
reported the level and cause of obstruction depicted by a
gradient-echo MRCP technique in only 7 (78%) and 5 (56%) of 9
patients. Recent studies have demonstrated better results, which
most likely reflect improved techniques. Schwartz et al
reported correct identification of the level of obstruction in 27
(84%) and 28 (88%) of 32 patients by two independent observers,
respectively, using breathhold SS-RARE MRCP without fat suppression
and an intermediate T2 value of 100 msec. The site of underlying
tumor was correctly identified in 27 (84%) and 29 (91%) of the
patients, with pathologically confirmed neoplastic duct
obstruction. Only the MRCP images were viewed, indicating that the
results reflect the ability of the MRCP technique in isolation to
provide the same information that would traditionally have been
expected from conventional cholangiography (Figure 5).
Intraductal papillary mucinous tumor of the pancreas
Intraductal papillary mucinous tumors (IPMT)
(mucin-hypersecreting tumor, duct ectatic mucinous cystic tumor)
arise from the epithelium of the main pancreatic duct or its
branches. Intraductal papillary mucinous tumor of the pancreas has
a primarily intraductal, papillomatous growth pattern associated
with excessive mucin secretion, resulting in progressive ductal
Tumors may arise from the main duct or side branches with a
predilection for the pancreatic head. Segmental or diffuse main
duct tumors are seen as ductal dilatation, which may be associated
with parenchymal atrophy,
and may be difficult to distinguish from chronic pancreatitis.
Diagnosis is confirmed on ERCP in the presence of a bulging,
dilated papilla with large amounts of mucin leaking from the
ampulla of Vater.
MR cholangiopancreatography can depict a bulging or gaping papilla,
which is suggestive of IPMT when it measures >1 cm.
Pancreatic cystic dilated tubular structures, which may or may not
be seen to communicate with the main duct, is suggestive of IPMT
(Figures 6 and 7). Malignant transformation of IPMT is recognized,
and resection is recommended where possible.
Pancreas divisum is the most common developmental anomaly of the
pancreatic duct and is due to nonunion of the duct of Wirsung and
the duct of Santorini, with main drainage through the duct of
Santorini to the minor papilla rather than to the ampulla of Vater.
The frequency of pancreas divisum varies from 4% to 14% at autopsy.
The key diagnostic findings are the passage of the main pancreatic
duct to the minor papilla with the ventral duct being smaller than
the dorsal duct, or not visible (Figure 8). In a study of 108
patients, (6 with pancreas divisum by ERCP), the sensitivity and
specificity of MRCP was reported as 100%.
The clinical importance of pancreas divisum is related to the
following factors: incomplete pancreatic duct visualization from
the standard major papilla cannulation during ERCP;
misinterpretation of the short ventral duct for other causes of
main duct cut-off, such as adenocarcinoma; and possible functional
obstruction from the minor papilla to pancreatic duct drainage in
some people with consequent elevation in duct pressure and
Several clinically significant congenital anomalies of the
biliary system have been described. These anatomical variants are
important because of the associated risk of bile duct injury during
laparoscopic cholecystectomy, or because they may represent
relative contrary indications to right hepatectomy in living
related liver donors. Prior to consideration of laparoscopic
cholecystectomy, it is important to recognize a low cystic ductal
insertion, a medial cystic ductal insertion, a long, paralleled
course of the cystic duct with the common duct, or a short cystic
duct. Aberrant drainage of the right posterior segmental duct to
the common duct confluence or left hepatic duct may represent a
relative contraindication to right hepatectomy in living related
liver donors (Figure 9). The variation in biliary ductal anatomy
may be depicted by MRCP. In a series of 171 patients, using direct
cholangiography as a standard of reference, MRCP showed a
sensitivity and specificity of 86% and 100%, respectively, for the
diagnosis of variant cystic duct anatomy. For the depiction of an
aberrant right posterior segmental duct, the reported sensitivity
and specificity were 71% and 100%, respectively.
Postcholecystectomy disorders are rare but are increasingly
frequent as a result of the rapid acceptance of laparoscopic
cholecystectomy. Such complications include bile duct injury,
retained bile duct stones, biliary leak, and biliary fistula.
Postcholecystectomy biliary complications have traditionally been
imaged with ultrasound or CT, followed by ERCP or percutaneous
transhepatic cholangiography. MR cholangiopancreatography has also
been used to demonstrate post-surgical complications. In a recent
study of 17 patients referred for evaluation of suspected
postcholecystectomy biliary disorders, investigators used
breath-hold SS-RARE MRCP to establish a diagnosis, which was
confirmed at surgery or by follow-up imaging.
Complications included biliary occlusion, peribiliary lesions,
nonspecific biliary dilatation, bile duct stones, and biliocolic
fistula. Two independent readers correctly categorized the
complications in 15 (88%) and 13 (76%) cases, respectively, with
excellent interobserver agreement (kappa = 0.82). Biliary
strictures and transections were not distinguished at MRCP, but
grouped together as occlusion.
MR cholangiopancreatography continues to evolve as a noninvasive
imaging technique of the biliary and pancreatic ductal system, with
results comparable to ERCP, but without the intrinsic risks. Common
current indications for MRCP include unsuccessful or
Patient preference for noninvasive imaging may also be a
consideration. MR cholangiopancreatography should be considered if
there is a low index of suspicion for pancreatic or biliary disease
and therapeutic ERCP is considered unlikely, as well as in patients
with suspected neoplastic pancreatic or biliary obstruction prior
to surgical or interventional planning.
An unresolved issue is whether MRCP should be performed alone,
with a limited charge, or as part of a full abdominal study. This
was recently addressed in a study of 62 patients with biliary
dilatation of known cause.
The diagnostic accuracy in the differentiation of benign from
malignant causes of obstruction was greater using combined MRCP
images, standard T1, T2, and postgadolinium images for both
readers. The possibility of missing tumors or other significant
pathology with the use of only MRCP images argues for mandatory
imaging with a full study. However, if imaging is requested to
answer a specific question, such as the evaluation of the common
duct for stones, it may be reasonable to perform a limited study,
provided the clinician is aware of the ramifications.
Currently recognized limitations of MRCP include lack of dynamic
information and limited resolution. Ongoing technical refinements
are likely to result in diagnostic improvements. For example,
stimulation of pancreatic exocrine secretion using secretin
infusion has demonstrated reduced duodenal filling and persistent
ductal distention secondary to papillary stenosis in patients with
suspected pancreatic disease.
The recent use of manganese as an intravenous biliary MR contrast
agent allows depiction of a functional component to MRCP, rather
like cholescintigraphy. Manganese facilitates T1 relaxation within
hepatocytes and was developed initially as a hepatic parenchyma
contrast agent. Intravenous manganese undergoes hepatobiliary
excretion, and on delayed images the biliary tree is depicted as
high signal intensity on T1-weighted images
(Figure 10). Such advances, in conjunction with improved
technology, should overcome concerns about the utility of MRCP. The
role of MRCP is to provide a noninvasive imaging alternative to
ERCP for diagnosis, ultimately limiting the use of invasive
techniques to therapeutic procedures.