Applied Radiology

Dr. Hartman is a Resident in Radiology and Dr. Barish is an Assistant Professor of Radiology in the Department of Radiology, Boston University Medical School, Boston Medical Center, Boston, MA.

Magnetic resonance cholangiopancreatography (MRCP) is becoming the primary noninvasive method for imaging the biliary tree and pancreatic duct. With heavily T2-weighted sequences, fluid-filled structures appear bright against a dark background. The gallbladder, biliary tree, and pancreatic duct are displayed in a similar manner as in invasive methods such as endoscopic retrograde cholangiopancreatography (ERCP) and percutaneous transhepatic cholangiography (PTC). The main role of MRCP has been to replace and eliminate the diagnostic portion of an ERCP or PTC. Frequently, a diagnostic MRCP can obviate an invasive procedure or suggest the need for a different invasive procedure from that which was originally planned. Magnetic resonance cholangiopancreatography should be considered the test of choice in all patients after a failed or incomplete ERCP. Magnetic resonance cholangiopancreatography has been shown to be useful in the detection of calculi, tumors, strictures, obstructions, and congenital anomalies. It is also helpful for presurgical planning and postsurgical follow-up.

Since MRCP images resemble those obtained during direct cholangiography, they are well accepted by gastroenterologists and surgeons. Magnetic resonance cholangiopancreatography pulse sequences are available on nearly all modern MRI scanners, and MRCP is well tolerated by patients. Since exogenous contrast material is not needed, patients with contrast allergies, renal failure, or a history of atopy can be imaged safely. Initial limitations of MRCP, such as metallic-clip artifacts, respiratory motion, and long procedure times, have been overcome. However, cardiac pacemakers, certain aneurysm clips, and other implanted medical devices may preclude the use of MRCP.

MRCP pulse sequences

Bile and pancreatic fluid are rich in protons, resulting in a T2 relaxation time that is much longer than that of surrounding tissues. On heavily T2-weighted sequences, fluid within the biliary tree, gallbladder, and pancreatic duct is bright, while background tissues are suppressed. Signal from background fat, which is usually high on fast T2-weighted sequences, can be decreased with the use of fat-suppression techniques. Magnetic resonance cholangiopancreatography is usually performed using one of the hybrid rapid acquisition with relaxation enhancement (RARE) sequences or their derivatives. ¹

The introduction of single-shot RARE techniques and half-Fourier acquisition single-shot turbo-spin echo (HASTE) imaging has reduced imaging times to within a single breath-hold. The trade-off associated with these more rapid sequences is a loss of spatial resolution. These breath-hold techniques are best applied in two forms: a single, thick coronal (or axial) slab and a multislice, thin coronal sequence.

MRCP versus ERCP

Direct cholangiography methods (ERCP and PTC) offer certain advantages that cannot be reproduced with MR methods. Both ERCP and PTC yield images with higher spatial resolution, and both techniques have therapeutic as well as diagnostic applications. However, even with the higher spatial resolution of these invasive methods, visualization of bile duct morphology with MRCP equals or exceeds that of ERCP ^2,3 without the associated morbidity or mortality. The risks of ERCP include pancreatitis, sepsis, hemorrhage, duodenal and bile duct perforation, and death. ⁴ Endoscopic retrograde cholangiopancreatography also causes pancreatitis in 1.5% to 3.9% of cases, and the mortality rate is 0% to 0.9%. ^4,5

Endoscopic retrograde cholangiopancreatography is also associated with failure rates as high as 3% to 10%. ^6-8 These failed examinations may occur because the operator has limited experience or because of complex ductal anatomy. Biliary-enteric anastomoses and obstructions can also make ERCP difficult, if not impossible. After a failed or incomplete ERCP, MRCP should be considered the diagnostic test of choice. In this group of patients, MRCP has been shown to have a sensitivity of 97%, a specificity of 100%, and an accuracy of 98% for the diagnosis of pancreaticobiliary disease. ^9,10

Forty percent to 70% of patients who undergo ERCP have negative findings. ¹¹ If MRCP were performed before ERCP, mortality, morbidity, and healthcare costs could therefore be reduced by limiting ERCP only to those individuals who would benefit from this more invasive procedure.

Stone disease

Biliary calculi are seen as relative areas of decreased signal surrounded by bright bile (figures 1 and 2). Many studies have investigated the use of MRCP for the detection of choledocholithiasis, and excellent results have been reported, with sensitivities of 85% to 100%, specificities of 90% to 99%, and accuracies of 89% to 97%. ^12-19 Positive- and negative-predictive values have ranged from 77% to 93% and 94% to 100%, respectively. ^12,13 Successful detection of stones as small as 2 mm has also been reported with MRCP. ^20,21 In fact, the detection of choledocholithiasis with MRCP is superior to that of other noninvasive techniques, such as ultrasound and computed tomography (CT), which have sensitivities of 20% to 65% and 45% to 85%, respectively. ^22-26

The accuracy of MRCP in diagnosing hepatolithiasis is 96%. ²⁷ Intrahepatic bile duct calculi may be seen as well-defined filling defects or as cast-like areas of low signal that conform to the wall of the duct (figure 3). ^26,28

Other abnormalities in the biliary tract that can be hypointense on MR (resembling calculi) include blood clots, tumors, air, metal clips, and parasites. However, calculi tend to have more angled edges than soft-tissue tumors, a finding that helps to differentiate these lesions. ²⁹ Pneumobilia after a biliary-enteric anastomosis or sphincterotomy can be recognized by examining axial images, preventing an erroneous diagnosis of choledocholithiasis. ³⁰ Intraductal air should also rise to the nondependent portion of the duct, whereas stones should remain dependent. ³¹ Low-signal surgical clips appear as eccentric foci of low signal on raw data images, indicating an extraductal source of these hypointense regions. ³¹ Ascariasis is characterized by a "bull's-eye" appearance of the common bile duct. ³²

Maximum-intensity projection (MIP) reconstructions can mask a small stone in the bile ducts if the stone is surrounded by hyperintense bile. When the breath-hold is not optimal, MIP images may also be characterized by ductal disconnections or duplications. ³³ For these reasons, source images should be reviewed meticulously.

Although it is well accepted that MRCP is an accurate test for the diagnosis of choledocholithiasis and hepatolithiasis, there is no consensus regarding its routine use. Since MRCP has a high-negative predictive value for common bile duct stones, it can be used to exclude stones in patients with suspected choledocholithiasis. However, only 30% to 52% of patients thought to be at high risk for common bile duct stones are actually found to have stones. ^12,13 In the future, MRCP could therefore be used to screen high-risk patients for common duct stones in order to determine whether a therapeutic ERCP is indicated. In this way, the more invasive procedure could be avoided in patients without choledocholithiasis.

Strictures

With MRCP, ducts are seen in their passive state because contrast material does not need to be injected forcefully to opacify them. Thus, images reflect the diameter of strictures more closely than they do with invasive cholangiography (figure 4). Magnetic resonance cholangiopancreatography has been reported to have a sensitivity of 100% and a specificity of 98% for the diagnosis of strictures. ^14,17 However, reduced spatial resolution and the inability to evaluate lack of distensibility during MRCP limits visualization of subtle strictures. Cholecystokinin may also have a role for evaluating the distensibility of the biliary tree at MRCP.

Extraductal metallic surgical clips, intravascular metallic coils, or gas in the stomach or duodenum may cause signal loss in the adjacent extrahepatic bile ducts. This may lead to a false-positive diagnosis of ductal narrowing. Also, MIP-reconstructed images can overestimate the length of strictures. This pitfall can be avoided by evaluating source images and the amount of bile duct dilatation proximal to an apparent stricture. ³⁴

Obstruction

Cholestasis is most commonly caused by choledocholithiasis or neoplasia (pancreatic carcinoma, ampullary carcinoma, and cholangiocarcinoma). Studies have shown that MRCP has a sensitivity and specificity >90% for the detection of biliary obstruction. ^35,36 Magnetic resonance cholangiopancreatography imaging does not depend on antegrade or retrograde flow of contrast material, so areas proximal and distal to an obstruction can be visualized.

Obstruction at the ampulla of Vater

Both benign and malignant disease can cause an obstruction at the ampulla of Vater with dilatation of the common bile duct and pancreatic duct. Causes include ampullary carcinoma, inflammatory stenosis, sphincter of Oddi dysfunction, and impacted stones. Semelka et al ³⁷ studied ampullary carcinoma and found that MRCP was helpful in determining both the degree of obstruction and the luminal margins of the tumor. Magnetic resonance cholangiopancreatography also aided in determining the degree of decompression after biliary stent placement.

Cholangiocarcinoma

Early cholangiocarcinoma can be a subtle disease. Classic MRCP findings of cholangiocarcinoma include an abrupt site of biliary obstruction with marked dilatation proximally (figure 5). In some cases, it may be difficult to distinguish duct wall thickening caused by pyogenic cholangitis from that caused by cholangiocarcinoma. ³⁸ Cholangiocarcinoma usually arises from the extrahepatic bile ducts, but may also arise from the intrahepatic ducts. ³⁹ When intrahepatic, cholangiocarcinoma occurs as a focal or infiltrating lesion. ³⁹ Magnetic resonance cholangiopancreatography is superior to CT for defining the proximal extent of biliary tract tumors. ⁴⁰

Hepatocellular carcinoma rarely manifests by intrahepatic bile duct obstruction, but this tumor should be considered in the differential diagnosis of cholangiocarcinoma if there is an intrabiliary tumor with an associated hepatic mass. ⁴¹

Malignant obstructions should be evaluated with a complete, conventional upper abdomen study with T1- and T2-weighted images. MR provides an "all-in-one" approach for evaluating malignant obstructions. The sensitivity, specificity, and accuracy of MRCP for differentiating benign and malignant lesions can be increased by 17% to 20% when T1-and T2-weighted images are obtained. ²⁹ The origin, size, and site (hilar, intrahepatic, and subhilar) of the tumor, definition of tumor margins, and stage of disease can be depicted without need for other imaging modalities such as CT or ERCP. Lymphadenopathy, infiltration by hepatic metastases, mesenteric vascular involvement, distant metastases, and occlusion of segmental and subsegmental bile duct branches can also be seen.

In some cases, MRCP is sufficient for planning appropriate therapeutic interventions. It can be used to determine if surgical revision, endoscopic or percutaneous biliary drainage, or balloon dilation of a stenotic segment with stent placement is the optimal therapy. Grading of hilar cholangiocarcinoma by MRCP may also prevent patients from undergoing an unnecessary ERCP when endoscopic drainage is not the optimal treatment (segmentally occluded ducts). ⁴²

Presurgery planning

Aberrant ducts

Laparoscopic cholecystectomy has largely replaced open cholecystectomy in patients with gallstones. Identification of aberrant ducts is important, as these ducts can be severed or ligated if they are mistaken for the cystic duct. Aberrant ducts tend to enter directly into the cystic duct or just distal to the confluence of the right and left hepatic ducts. ²⁸ The most common biliary tract anomaly is an aberrant right hepatic duct, ⁴³ which may drain into the common hepatic duct, common bile duct, or cystic duct. ²⁸ Magnetic resonance cholangiopancreatography has a sensitivity of 71%, a specificity of 100%, and an accuracy of 98% for the detection of aberrant right hepatic ducts. ⁴⁴ Although MRCP is well suited for detecting both aberrant ducts and choledocholithiasis, the routine use of MRCP prior to laparoscopic cholecystectomy cannot be justified because of the high cost and low true-positive rate of this technique for the detection of aberrant ducts.

Biliary cystic disease (choledochal cysts and choledochoceles)

Choledochal cysts are cystic dilatations of the biliary tree. Magnetic resonance cholangiopancreatography can accurately determine the presence and type of choledochal cyst, the length of the involved extrahepatic duct, and anomalous unions of the pancreatic and bile ducts. ⁴⁵ Choledochal cysts are best treated by surgical excision and biliary-enteric anastomosis. Determination of the length of the involved extrahepatic bile duct by MRCP is crucial for surgical planning. ^45,46

Evaluation after surgery

Post­biliary-enteric anastomosis

Surgical alterations of the gastrointestinal tract after biliary-enteric anastomoses can make ERCP difficult or impossible. Magnetic resonance cholangiopancreatography should be considered a first-line diagnostic method in these patients because it is capable of providing information about the biliary tree, which cannot be obtained by invasive procedures. ⁴⁷

Anastomotic strictures are usually caused by postoperative scarring and, less often, by ischemia. ²⁸ Magnetic resonance cholangiopancreatography can evaluate anastomotic sites and create a complete "roadmap" of the bile ducts. ³⁴

Postlaparoscopic cholecystectomy

Magnetic resonance cholangiopancreatography can evaluate the biliary tract proximal and distal to a duct lacerated at cholecystectomy. Endoscopic retrograde cholangiopancreatography may result in incomplete visualization of the biliary tree, showing only a cut-off sign of the distal bile duct, so that PTC is required to visualize the proximal biliary system. Information about anatomy proximal to the transection is important for determining the strategy for reconstructive surgery. This information can be provided by MRCP, reducing the need for PTC.

Post-liver transplant

Magnetic resonance cholangiopancreatography has a lower spatial resolution than conventional cholangiography, limiting depiction of strictures. However, in the case of liver transplantation patients, this does not represent a significant limitation because the lesions have a benign origin. ³⁴ These strictures can be classified either as anastomotic or nonanastomotic. Nonanastomotic strictures usually involve the hepatic duct bifurcation, peripheral ducts, or both, and occur in approximately 8% of patients. Nonanastomotic strictures are important because they may indicate rejection. Magnetic resonance cholangiopancreatography enables early visualization of intrahepatic duct dilatation, which can occur as a result of stricture formation. ⁴⁸ Clinicians can therefore be alerted, and action can be taken to prevent sepsis and graft failure. ⁴⁸

Endoscopic biliary drainage tubes

Magnetic resonance cholangiopancreatography can be used to assess endoscopic biliary drainage (EBD) tubes when malfunction, dislocation, or migration is suspected. Traditional methods for the assessment of EBD tubes include ultrasound, biochemical data, and abdominal radiography. The results of these tests are usually confirmed with ERCP. Endoscopic biliary drainage tubes do not generate MR signals. However, bile contained within the lumen generates high signal. As a result, EBD tubes are usually seen as paired low-signal lines with a high-signal line between them. ⁴⁹ If the bile becomes viscous or if debris accumulates, the high-signal intensity of bile in the tube may disappear (figure 6). ⁴⁹ Magnetic resonance cholangiopancreatography is also useful for assessing the location and patency of EBD tubes.

Pediatric applications

Magnetic resonance applications in the pediatric population are expanding. Magnetic resonance cholangiopancreatography rarely requires anesthesia; ERCP and PTC cannot be performed on children without anesthesia. ⁴⁸ However, conscious sedation is required when MRCP is performed on young or uncooperative patients. Respiratory-triggered MRCP enables evaluation of major and minor bile ducts, even in uncooperative, young patients. ⁴⁸ Images can be produced in which the common bile duct and hepatic ducts are clearly seen in infants as young as 3 days old. ⁵⁰

Biliary atresia

Biliary atresia can cause jaundice in infants. When this anomaly occurs, MRCP demonstrates nonvisualization of the common bile duct or common hepatic duct. ⁵⁰ Magnetic resonance cholangiopancreatography may also reveal a triangular-shaped area of high-signal intensity within the porta hepatis caused by cystic dilation of the bile duct proximally. ⁵¹ Unnecessary exploratory laparotomy in infants with cholestatic jaundice can also be avoided with MRCP.

Cystic fibrosis

Biliary manifestations of cystic fibrosis include cholelithiasis, narrowing or dilatation of the intrahepatic and extrahepatic bile ducts, and microgallbladder. These findings can all be demonstrated with MRCP. Magnetic resonance cholangiopancreatography is also useful for assessing the presence and severity of biliary complications in patients with cystic fibrosis without need for more invasive procedures.

Evaluation of the pancreas

Magnetic resonance cholangiopancreatography has been slower to develop as a diagnostic tool for the pancreas because of the smaller caliber of the pancreatic duct. Advances in breath-hold imaging, surface coils, and the use of pharmacologic agents has allowed MR pancreatography to become a useful means for evaluating pancreatic ductal anatomy and function. The use of breath-hold imaging with surface coils reduces blurring artifacts and improves visibility. Visualization of the pancreatic duct is further improved following the administration of secretin. This hormone causes an increase in pancreatic exocrine function, resulting in a transient increase in pancreatic ductal diameter, pancreatic fluid secretion, and pancreatic enhancement. Because of this increase in pancreatic ductal diameter, the accuracy of MRCP for the detection of strictures of the pancreatic duct is improved. ⁵²

Pancreas divisum

Pancreas divisum is the most common anatomic variant of the pancreas, occurring when the dorsal duct (duct of Wirsung) and ventral duct (duct of Santorini) fail to fuse. These two ducts normally fuse during the second month of gestation. When this process does not occur, the dorsal duct drains most of the pancreas, including the superior-anterior head, body, and tail, whereas the ventral duct drains the posterior-inferior head and uncinate process. The dorsal duct enters the major papilla and the ventral duct the minor papilla.

Pancreas divisum has important implications for ERCP, as cannulation of the major papilla opacifies only the dorsal duct, resulting in incomplete visualization of pancreatic ductal structures. Lack of opacification of ductal structures in the body or tail of the pancreas at ERCP also may erroneously suggest occlusion of the main pancreatic duct, leading to an incorrect diagnosis of pancreatic carcinoma. In contrast, MRCP is excellent for diagnosing pancreas divisum because this technique can show the ventral and dorsal ducts simultaneously without need for cannulation of the major and minor papillae.

Chronic pancreatitis

Chronic pancreatitis occurs after repeated bouts of acute pancreatitis, resulting in parenchymal atrophy and fibrosis. Side-branch ectasia is the most specific and prominent feature of chronic pancreatitis. The main pancreatic duct is also dilated, usually with areas of focal narrowing, producing a beaded appearance. The biliary tract may also become dilated as a result of fibrosis in the head of the pancreas. In severe pancreatitis, the normal tapering of the pancreatic duct in the tail of the pancreas is also lost.

Magnetic resonance cholangiopancreatography may be performed not only to support a clinical diagnosis of chronic pancreatitis but also to guide therapeutic planning, detect concurrent biliary abnormalities, and visualize complications of the disease. In patients with chronic pancreatitis, moderate and advanced disease is identified readily. However, early disease may not be detected, as changes may be present only in small side branches, which are below the resolution of MR. Therapeutic planning is affected by the location of strictures, ductal diameter, the presence of stones, and the presence and location of pseudocysts.

Pancreatic pseudocysts occur as a complication of acute or chronic pancreatitis. These pseudocysts are encapsulated collections of pancreatic fluid caused by microperforation of the pancreatic duct. The surgical definition of a pseudocyst requires the lesion to be present for at least 6 weeks. Evaluation of cystic lesions of the pancreas, such as pseudocysts, with ERCP is limited to lesions that communicate with the main pancreatic duct. However, <50% of pseudocysts communicate with the pancreatic duct and fill with contrast material. As a result, <50% of pseudocysts are detected at ERCP. In contrast, MRCP can visualize pseudocysts in the absence of communication with ductal structures, so this technique can detect virtually 100% of pseudocysts and other cystic lesions of the pancreas, including cystic neoplasms.

Neoplasms of the pancreas

Magnetic resonance cholangiopancreatography can be used to detect neoplasms of the pancreas and to determine staging, surgical resectability, and tumor recurrence. Neoplasms of the pancreas include exocrine and endocrine tumors. Exocrine tumors include adenocarcinomas, cystic neoplasms (serous microcystic adenomas and mucinous cystic neoplasms), and rare entities, such as acinar cell carcinomas, pleomorphic carcinomas, and epithelial neoplasms.

Adenocarcinoma represents 95% of all pancreatic carcinomas. The prognosis is poor, with mean 1-year survival rates <10%. Clinical signs of pancreatic carcinoma include jaundice, weight loss, and Courvoisier's sign (an enlarged nontender gallbladder caused by tumor obstructing the outflow of bile from the gallbladder). Dilatation of both the pancreatic and bile ducts should strongly suggest a malignant tumor in the head of the pancreas. Once the diagnosis of pancreatic adenocarcinoma has been made, evaluation of the status of the ductal structures is not usually necessary. Magnetic resonance cholangiopancreatography alone contributes little to the management of these patients, but conventional MR imaging provides important information for therapeutic planning, including tumor staging and detection of vascular encasement or other metastatic disease.

Cystic neoplasms are uncommon, representing only 5% to 15% of all cystic pancreatic masses. Cystic neoplasms can easily be evaluated with MRCP because of their high fluid content. Serous microcystic adenomas are benign lesions, typically occurring in patients older than 60 years of age. The tumors occur in a relatively equal distribution throughout the pancreas. Serous microcystic adenomas may appear as solid or cystic lesions. If the tumor is cystic, more than 6 cysts are usually seen, and the cysts are usually >2 cm in diameter. Approximately 40% of these tumors have calcifications, which are usually amorphous and may resemble starbursts. The soft-tissue component of serous microcystic adenomas exhibits hypervascular enhancement with intravenous administration of contrast material. Aspirated contents of the cysts are glycogen-positive. Roughly 15% of serous microcystic adenomas contain a central scar.

Mucinous cystic neoplasms include macrocystic adenomas and adenocarcinomas. These lesions should be considered malignant because the adenomas often evolve into adenocarcinomas. In contrast to serous microcystic adenomas, mucinous cystic neoplasms typically occur in patients younger than 60 years of age. The ratio of women to men having these neoplasms is 6:1. Almost all of these lesions are located in the body or tail of the pancreas. Fewer than 6 cysts are usually seen, and the cysts are usually >2 cm in diameter (figure 7). Twenty percent have calcifications, which typically occur along the rim of the cysts. In contrast to serous microcystic adenomas, these tumors are hypovascular, although the wall of the cysts enhances after administration of intravenous contrast material. ⁵³ Aspiration of the cysts yields mucin. The mucin is secreted into the pancreatic duct. At ERCP, this mucin may obstruct the flow of contrast material through the duct, limiting evaluation. Because of this limitation, MRCP is potentially more accurate than is ERCP in depicting mucinous cystadenomas and cystadenocarcinomas. A tumor that may represent a subset of mucinous cystic tumors is a duct-ectatic mucinous tumor. In this disease, a papillary tumor is present in the main pancreatic duct or a side branch of the pancreatic duct. In the benign form, the papillary tumor consists of hyperplastic epithelium; whereas in the malignant form, the tumor is composed of atypical hyperplastic epithelium with areas of adenocarcinoma. Magnetic resonance cholangiopancreatography can be used to detect excrescent nodules and septa in these tumors. The septa consist of a layer of connective tissue with pancreatic duct epithelium. The correlation of MRCP findings with histopathology is excellent. ⁵⁴ Duct-ectatic mucinous tumors extrude copious amounts of mucin. As with mucinous cystic neoplasms, duct-ectatic mucinous tumors may be better evaluated with MRCP than with ERCP, as mucin obstructs the flow of contrast material through the pancreatic ducts.

Irie et al ⁵⁵ evaluated the ability of MRCP to differentiate benign and malignant intraductal mucin-producing tumors of the pancreas with MRCP. When a malignant mucinous lesion is located in the main pancreatic duct, the duct is diffusely dilated and has a diameter >1.5 cm. With benign lesions involving the main pancreatic duct, however, the duct is segmentally dilated. When a malignant mucinous lesion is located in a branch duct, the main pancreatic duct is usually mildly dilated. With benign lesions involving a branch duct, however, the main pancreatic duct is not dilated.

Other neoplasms of the pancreas include endocrine tumors (insulinomas, gastrinomas, and nonfunctioning islet cell tumors), lymphoma, metastases, and connective tissue tumors. The ability of MRCP to depict these neoplasms has not yet been evaluated. However, MRCP has an overall sensitivity of 84% and specificity of 97% for diagnosing pancreatic carcinoma, whereas the corresponding sensitivity and specificity for ERCP are 70% and 94%, respectively. ⁵⁶

Limitations of MRCP

Inferior spatial resolution and inability to perform therapeutic procedures are the major limitations of MRCP when compared with invasive methods (ERCP and PTC). Artifacts occasionally may cause confusion when interpreting MRCP images. Pulsatile compression by normal vascular structures, including the right hepatic and gastroduodenal artery, can cause pseudo-obstruction of the extrahepatic bile ducts. ^57,33 The right hepatic artery passes posterior to the proximal common hepatic duct, sometimes causing a smooth, short narrowing in the duct. Arterial pseudo-obstruction artifact can be differentiated from true biliary obstruction by lack of dilatation upstream to the stenosis and by visualization of the flow void of the vessel crossing the duct at the level of the obstruction. ⁵⁸ A flow-sensitive sequence, axial T2-weighted sequence, or MR angiography may also be helpful for identifying these vascular structures. ⁵⁷

Portions of the biliary tree can be obscured on MIP images by overlapping ducts, bowel, and other structures containing fluid. This is rarely a problem with the source data images, as these images show small amounts of bile that are cancelled out on MIP images.

Conclusion

Magnetic resonance cholangiopancreatography is becoming the primary method for evaluating patients with a variety of biliary and pancreatic diseases. The absence of ionizing radiation and safety of this technique make MRCP an excellent diagnostic tool. With the increased use of MRCP, invasive techniques such as ERCP and PTC can be reserved for patients who require therapeutic procedures. AR