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Gastrointestinal Imaging |
1 From the Department of Radiology, Kumamoto University School of Medicine, 1-1-1 Honjo, Kumamoto 860, Japan. Received April 6, 1999; revision requested May 21; revision received August 18; accepted August 25. Address reprint requests to Y.T. (e-mail: yitang23@hotmail.com).
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Abstract |
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MATERIALS AND METHODS: The study included 34 patients (20 men, 14 women; mean age, 65.5 years) who underwent surgery of the pancreaticobiliary ductal system. Half-Fourier RARE MRCP images were obtained after surgery. Qualitative evaluation included ratings by two observers for depiction of postoperative anatomy and for artifacts, as well as analysis of postoperative complications. Direct cholangiographic, computed tomographic, and ultrasonographic findings and 6-month follow-up results were the reference standard. Sensitivity, specificity, and accuracy were calculated for the evaluation of postsurgical complications seen at half-Fourier RARE MRCP.
RESULTS: The sensitivity, specificity, and accuracy of MRCP for the evaluation of postsurgical complications were each 100% for ductal dilatation; 100%, 87%, and 89%, respectively, for choledochoenteric anastomotic stricture; 100%, 86%, and 87%, respectively, for pancreaticoenteric anastomotic stricture; 100% each for intraductal stones and anastomotic leakage; and 80%, 100%, and 94%, respectively, for cholangitis.
CONCLUSION: Half-Fourier RARE MRCP is a reliable imaging technique for the evaluation of anatomy and of complications associated with a surgically altered pancreaticobiliary ductal system.
Index terms: Bile ducts, leakage, 76.458 • Bile ducts, MR, 76.121411, 76.121415 • Bile ducts, stenosis or obstruction, 76.458 • Bile ducts, surgery, 76.453, 76.458 • Cholangitis, 76.289 • Pancreas, surgery, 774.453, 774.458 • Pancreatic ducts, MR, 774.121411, 774.121415
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Introduction |
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TOPAbstractIntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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Magnetic resonance (MR) cholangiopancreatography (MRCP) is a recently developed noninvasive examination for the evaluation of abnormalities of the pancreaticobiliary ductal system. Several MRCP techniques have been applied in which either a breath-hold or non–breath-hold (signal averaging) technique is used (9). Non–breath-hold techniques necessitate a relatively long imaging time (approximately 4–6 minutes), and even the breath-hold techniques necessitate approximately 20–40 seconds per acquisition (10,11).
Recently, single-shot MRCP with the half-Fourier rapid acquisition with relaxation enhancement (RARE) sequence has enabled us to obtain excellent images in a few seconds (12–15). This technique does not require use of a contrast medium or any biliary intervention and can be performed in patients whose biliary tract has been surgically modified. It can be used to demonstrate the pancreatic and biliary ducts after hepaticojejunostomy, when a cannula cannot be endoscopically inserted into the anastomosis. On the basis of our previous experience, we postulated that half-Fourier RARE MRCP could provide a clear demonstration of the remnant ductal systems and the anastomotic sites. The aim of our work was to evaluate the accuracy of MRCP performed with the half-Fourier RARE sequence in demonstrating postsurgical anatomy and related complications.
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MATERIALS AND METHODS |
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Imaging was performed because of scheduled follow-up in 15 patients; persistent jaundice in five; recurrent fever in three; cholangitis and abnormal liver function in six; and a combination of transient jaundice, epigastric pain, and abnormal liver function in five. Seven patients subsequently underwent PTC for performance of a therapeutic procedure. Repeat surgery was performed in three patients for the purpose of anastomotic reconstruction. In 10 patients with dilatation of the ductal system (bile duct in seven patients and pancreatic duct in three) seen at MRCP or US, the follow-up study, which included physical examination, biochemical tests, and US, did not show any symptoms or signs of ductal obstruction; these patients underwent no further invasive procedures. The remaining patients, who underwent MRCP and US and displayed no dilatation of the remnant ducts, did not undergo any further invasive procedures. The absence of complications was confirmed during 6 months of follow-up.
Confirmation of the ductal dilatation was based on computed tomographic (CT) findings, US findings, or both. Confirmation of a stricture of the anastomotic site was based on ERC or PTC findings. Confirmation of the presence of intraductal stones was based on direct cholangiographic findings. Confirmation of anastomotic leakage was based on direct cholangiographic or T-tube cholangiographic ("fistulographic") findings. Confirmation of cholangitis was based on direct cholangiographic findings and laboratory evidence such as elevated white blood cell count with or without elevation of serum bilirubin level during follow-up.
Imaging Technique
All MR imaging studies were performed with a 1.5-T superconducting unit (Magnetom Vision; Siemens, Erlangen, Germany) equipped with a body phased-array coil. Prior to MRCP, T1-weighted fast low-angle shot (150/4.8 [repetition time msec/echo time msec], 75° flip angle, 128 x 256 matrix, 18-second acquisition time) and T2-weighted turbo spin-echo (2,000/120 [repetition time msec/effective echo time msec], echo train length of 15, 128 x 256 matrix, 14-second acquisition time) sequences were performed to localize the biliary and pancreatic trees.
MRCP was performed with a half-Fourier RARE sequence with the following parameters: 
/87 (effective), echo spacing of 10.9 msec, one signal acquired, flip angle of 150°–180° (depending on the timing of attempted acquisitions), and 240 x 256 matrix. Only half the k space was measured (echo train length of 128) at imaging; the k space was expanded with the half-Fourier method to 240 lines. Fat suppression was used to reduce signal from peritoneal fatty tissue. The half-Fourier RARE sequence enabled us to obtain MRCP images quickly.
Half-Fourier RARE MRCP was used for two data acquisition techniques: the single-section technique and the multisection technique. For the single-section acquisition, a section thickness of 20–50 mm was used to image the main pancreatic duct or intrahepatic ducts with an acquisition time of 1.4 seconds, which allowed comfortable breath holding even in severely ill patients. This technique provided an overall demonstration of the remnant ductal system. For the multisection technique, nine 3–5-mm-thick sequential sections were acquired. These sections were postprocessed with a maximum intensity projection reconstruction algorithm, which was completed in less than 1 second. The total imaging time for the multisection technique was 18 seconds, which permitted the use of breath holding. The source images obtained with this technique provided detailed information on lesions of interest.
For both techniques, the refocusing flip angles generally were 180° and varied to 150° to avoid the specific-absorption-rate limitation caused by multiple refocusing radio-frequency pulses when multiple attempts at acquisition were performed.
In all patients, coronal and paracoronal (usually -30° to +30° off the axis) images were acquired to display the remnant biliary duct and choledochoenteric anastomosis. Transverse images covering the whole range of the residual pancreas were acquired with a 3–5-mm section thickness. Several acquisitions were needed to demonstrate the anastomotic portion of the biliary tree and pancreatic duct with the small intestine and/or stomach. The field of view was 30 cm. Superimpositions of the fluid-containing spinal canal, bowel contents, and renal pelvis were eliminated by varying the imaging orientation, as well as by using a saturation slab.
Image Analysis
All MRCP images were recorded on film for analysis by the observers. Maximum intensity projection and source images were prospectively evaluated by two experienced diagnostic radiologists who were unaware of the results of prior imaging studies. Two sets of MRCP images were prepared so that the observers could mark diseased segments separately. In addition, the patients' symptoms and signs after surgery, as well as information about surgical procedures and biochemical data, were provided to the radiologists before the image evaluation. The two radiologists initially performed an independent review of the MR images; the independent review was followed by a consensus reading to resolve any differences in interpretation. Dilatation of the ductal systems (intrahepatic and extrahepatic bile ducts), pancreatic ducts, site of anastomosis, signs of cholangitis, stricture of an anastomosis, and presence of stones and anastomotic leakage were evaluated.
The diagnosis of dilatation of the remnant ductal system was based on measurement of dilated ducts. The criteria for biliary dilatation were diameter of an intrahepatic bile duct larger than 3 mm without gentle tapering, diameter of the common hepatic duct larger than 6 mm, and diameter of the common bile duct larger than 10 mm. The criterion for remnant main pancreatic ductal dilatation was diameter of the remnant duct larger than 5 mm. The diagnosis of cholangitis was determined on the basis of findings of irregularities and a beaded appearance of the major bile ducts. Ductal strictures were evaluated on source MR images. A diagnosis of anastomotic stricture was established on the basis of both the width of the anastomosis and dilatation of distal ducts. For choledochoenteric anastomoses, strictures were graded according to anastomotic width: mild, anastomosis 3–5-mm wide; moderate, anastomosis l–3-mm wide; and severe, loss of signal intensity at the level of the anastomosis. For pancreaticoenteric anastomoses, the diagnosis of stricture was based on distal ductal dilatation and loss of signal intensity at the anastomotic site. Maximum intensity projection images were not considered in the grading of strictures but were compared with source images.
The quality of MRCP images in all 34 patients was graded by the same two radiologists by means of consensus. Image quality was graded on the basis of the depiction of the intrahepatic bile ducts, the remnant common bile duct, the remnant pancreatic duct, and the level of the anastomosis. The capability of half-Fourier RARE MRCP images to depict anatomy after surgery was graded by using a five-point scale: score of 5, excellent depiction of the entire anatomic structure; score of 4, good depiction, (ie, most of the structure was visible); score of 3, fair depiction (ie, part of the structure was visible); score of 2, poor depiction (ie, the structure was difficult to detect); and score of 1, unacceptable (ie, the structure could not be detected). Depiction of the anastomotic site also was assessed with a five-point scale: score of 5, excellent depiction of the whole length of the anastomotic site; score of 4, good depiction (ie, most of the anastomotic site was visible); score of 3, fair depiction (ie, part of the anastomotic site was visible), score of 2, poor depiction (ie, the anastomotic site was difficult to detect); and score of 1, unacceptable (the anastomotic site was depicted as a signal void). Imaging artifacts were assessed with a three-point scale: score of 3, severe artifact that interfered with image interpretation; score of 2, mild artifact that caused slight interference with image interpretation; and score of 1, negligible artifact.
Findings from direct cholangiography, together with CT and US findings and results of 6-month clinical follow-up, served as the reference standard for calculation of the sensitivity, specificity, positive and negative predictive values, and accuracy of MRCP in facilitating assessment for the presence of stricture, signs of cholangitis, and stones. For the image evaluation, interobserver variation between the two radiologists was evaluated by means of the percentage of interobserver agreement.
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RESULTS |
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Among the eight patients with cholangitis, MRCP correctly demonstrated bile duct irregularities and the beaded appearance in six (Fig 4). There were two false-negative studies because of the poor spatial resolution of MRCP relative to that of conventional cholangiography.
The resultant sensitivity, specificity, positive predictive value, negative predictive value, and accuracy for the evaluation of postsurgical complications with half-Fourier RARE MRCP images are listed in Table 4.
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DISCUSSION |
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TOPAbstractIntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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Accurate diagnosis is a prerequisite for the management of postoperative complications. Surgery is indicated in cases of biliary stricture. Retained bile duct stones necessitate percutaneous, endoscopic, or surgical extraction, depending on location. Periductal leakage may necessitate surgical repair or stent placement. Large bilomas may be drained with US or CT guidance.
Abdominal US is the technique of choice for initial examination of the bile ducts, particularly in patients with jaundice (16). US is reportedly (17) less useful in patients with a surgically created choledochoenteric anastomosis, however, because gas in the bile ducts may mimic ductal stones and create artifacts. CT scans accurately show the dilated intrahepatic ducts, but the main disadvantage of CT is the lack of multiplanar imaging capability (18). Biliary scintigraphy is useful for help in confirming biliary leakage, but the biliary tree is demonstrated with limited spatial resolution (19). T-tube cholangiography (fistulography) is possible only in patients with an accessible opening for the introduction of contrast material. Conventional cholangiography is often of no diagnostic value, because of the lack of opacification of the biliary system in 30%–40% of cases and the high rate of complications (4).
ERC has been used in symptomatic patients treated with choledochoenteric anastomosis. However, its use is confined to patients with an anastomosis that is not located caudal to the duodenum and to patients who have not undergone gastrojejunostomy. In fact, ERC is difficult or impossible to perform in patients with an anastomosis of the bile duct to jejunal or Roux-en-Y loops. PTC is undoubtedly valuable, but it is expensive and invasive (8). Both ERC and PTC have advantages, especially in therapeutic procedures such as stone removal, stricture dilation, and stent placement to relieve biliary obstruction. Although ERC and PTC play important roles in the evaluation of choledochoenteric anastomoses, these procedures occasionally are associated with a high frequency of complications. In addition, ERC and PTC cannot demonstrate the postoperative anatomy of remnant pancreatic ducts.
MRCP is a noninvasive, non–operator-dependent technique that has recently gained an important role in the evaluation of bile duct disease. MRCP accurately demonstrates bile duct obstructions, choledocholithiasis, and malignant obstructions (12,20). Pavone et al (21) reported high accuracy for three-dimensional turbo spin-echo MRCP when used for evaluation of postoperative stenosis. Coakley et al (22) used breath-hold MRCP to help evaluate complex biliary disorders after cholecystectomy. In this study, we found half-Fourier RARE MRCP to be a valuable technique for use in patients with a surgically modified pancreaticobiliary ductal system.
Half-Fourier RARE MRCP produces high-quality images for postoperative delineation of the biliary and pancreatic ducts. With the application of multiple echo trains and half-Fourier imaging reconstruction algorithms, half-Fourier RARE MRCP generates "fluid-sensitive" images with negligible motion and susceptibility artifacts. The normal postoperative anatomy was satisfactorily demonstrated in all patients in our study.
For the evaluation of postoperative complications, MRCP had high sensitivity for the depiction of strictures of anastomotic sites. Source images were better for evaluation of the morphology and length of the strictures. In our study, an anastomotic stricture was depicted as an abrupt termination at the anastomotic site and dilatation of the distal bilie ducts. In fact, in many cases, MRCP images (both source and reconstructed images) did not depict the anastomotic site, which consequently resulted in overestimation of the stricture at the anastomosis. At least two factors may contribute to such overestimation. First, the anastomotic channel, although patent, usually is compressed by surrounding smooth muscles. This phenomenon is more prominent in patients with a pancreaticoenteric anastomosis. Second, the anastomotic site cannot be demonstrated when the small intestine is not filled with fluid. Analysis of source images, careful inspection of the distal bile ducts (dilated or not), and review of the patient's clinical information may lead to the correct diagnosis.
The evaluation of anastomotic leakage, like that of biloma and pancreatic leakage, can be difficult with US because the modified anatomy and overlapping gas can obscure the relationship between lesions and remnant ducts. Although spiral CT image data can be reconstructed in different planes, CT, unlike MR imaging, cannot be used for direct acquisition of multiplanar images. Half-Fourier RARE MRCP, with its multiplanar and fast image acquisition (18 seconds for a multisection acquisition, 1.4 seconds for a single-section acquisition) capabilities, allows several attempts at acquisition of a satisfactory image that shows the relationship between the remnant ductal system and leakage.
Stones are easily recognized on MRCP images as low-signal-intensity structures surrounded by high-signal-intensity bile (20). In our study, the smallest stone detected was 3 mm in diameter. The evaluation of source images is mandatory for correct assessment of the presence of stones. On maximum intensity projection images, stones can be obscured by the high signal intensity of the surrounding bile. Pneumobilia is displayed as a filling defect in the high-signal-intensity bile on MRCP images and may mimic biliary stones. The differentiation of pneumobilia from stones can be made by noting that for pneumobilia, air would be present in the nondependent portion of the duct, whereas the heavier stones would be present in the dependent portion. In addition, cholangitis, which manifested with a beaded appearance and as an irregularity of bile ducts, can be differentiated from bile duct stone by its concentric stricture (Fig 4). We did not encounter patients with a recurrent malignancy during our study.
In conclusion, half-Fourier RARE MRCP exhibited excellent test performance and resulted in excellent interobserver agreement for the evaluation of changes in patients' anatomy after pancreaticobiliary ductal system surgery. This imaging method is fast, safe, and noninvasive and can be used to follow up patients, screen symptomatic patients for treatment, and help guide further therapeutic procedures.
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Acknowledgments |
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Footnotes |
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Author contributions: Guarantors of integrity of entire study, Y.T. Y.Y.; study concepts, Y.T., Y.Y.; study design, Y.T., Y.Y., A.A.; definition of intellectual content, Y.T., Y.Y., A.A.; literature research, Y.T.; clinical studies, Y.T., Y.Y., A.A., T.N., K.M., Y.A., K.K.; data acquisition, Y.T., T.N.; data analysis, T.N., Y.A., K.M., K.K.; statistical analysis, Y.T.; manuscript preparation, Y.T.; manuscript editing, Y.T., Y.Y.; manuscript review, M.T.
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References |
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TOPAbstractIntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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