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Gastrointestinal Imaging |
1 Department of Radiology, Brigham and Women's Hospital, Harvard Medical School, 75 Francis St, Boston, MA 02115.
| Abstract |
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MATERIALS AND METHODS: MR imaging was performed at 1.5 T in 39 patients with chronic (n = 30) or acute (n = 9) pancreatitis. The patients underwent a pancreas MR imaging protocol that included an MRCP sequence. Comparison was made with findings at endoscopic retrograde cholangiopancreatography (ERCP), performed within 30 days. Three blinded readers used a scoring system to evaluate nine segments of the pancreatic and biliary ducts as depicted on the ERCP and MRCP images. MRCP image quality was also evaluated.
RESULTS: Of 196 segments analyzed, 17 were not seen at MRCP (sensitivity, 91%). Of the segments visualized at MRCP, 14 were incorrectly characterized (accuracy, 92%). At MRCP, segments not detected or mischaracterized were either normal, slightly dilated, or narrowed. At ERCP, 42 segments in 19 patients were not visualized. MRCP findings were considered useful in all those cases. MRCP image quality was not interpretable in two cases due to artifacts.
CONCLUSION: Very good correlation between ERCP and MRCP findings was demonstrated. Both modalities failed to depict pathologic conditions depicted by the alternative method. MRCP may obviate ERCP, particularly in patients who cannot undergo ERCP or in whom ERCP has been unsuccessful.
Index terms: Bile ducts, MR, 76.12117, 76.12149 Endoscopic retrograde cholangiopancreatography (ERCP), 77.1222 Magnetic resonance (MR), comparative studies, 76.12117, 76.12149 Magnetic resonance (MR), rapid imaging, 77.121416 Pancreatic ducts, 774.297 Pancreatitis, 77.291
| Introduction |
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Endoscopic retrograde cholangiopancreatography (ERCP) is the standard of reference for imaging the bile duct and pancreatic duct (PD), providing images with the highest resolution and also offering the opportunity for therapeutic intervention. This procedure, while routinely performed by gastroenterologists, is not without adverse effects and has high cost. Adverse effects include a morbidity rate of 7% (procedure-induced pancreatitis, sepsis, bleeding, or gastroduodenal perforation), mortality rate of 1%, and unsuccessful cannulation of the ducts in 3%9% (8,11). MR cholangiopancreatography (MRCP) is a relatively simple, safe, and noninvasive imaging procedure. Its usefulness and accuracy have been documented in several studies (3,4,1215). The majority of studies, however, predominantly explore the usefulness of MRCP in patients with biliary tract disease.
The clinical question often posed is, "In patients with suspected or known pancreatitis, what is the state of the pancreaticobiliary tree?" The purposes of this study were to evaluate the usefulness of MRCPwith a breath-hold two-dimensional fast spin-echo technique, in a group of patients specifically referred for pancreatic imaging, with a clinical diagnosis of pancreatitisand to compare MRCP findings with those at ERCP.
| MATERIALS AND METHODS |
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The clinical diagnosis was established on the basis of a combination of the following signs and symptoms: upper abdominal pain (persistent over hours, pain aggravated by ingestion of food, epigastric pain radiating to the back), elevated amylase level (951,740 IU/L; normal, 3190 IU/L) and elevated lipase level (1206,000 IU/L; normal, 114286 IU/L) for acute pancreatitis, abnormal ERCP (main duct or secondary branch dilatation, duct beading, pancreatic calcifications), and abnormal CT (focal or diffuse pancreatic enlargement, peripancreatic stranding or inflammation or fluid collections, ductal dilatation, pancreatic atrophy, and calcifications). Owing to glandular fibrosis in patients with chronic pancreatitis, a normal range of amylase and lipase levels did not exclude that diagnosis. The final diagnosis was chronic pancreatitis in 30 patients and acute pancreatitis in nine.
The study patients included 17 women and 22 men, aged 3086 years (mean, 52 years; median, 49 years).
Imaging Studies
All MR imaging studies were performed with a 1.5-T system (Signa 5.3; GE Medical Systems, Milwaukee, Wis) with a circularly polarized body coil as a receiver and transmitter. Patients were imaged in the prone position. For the MRCP examination, a coronal two-dimensional spin-echo pulse sequence was used with the following imaging parameters: repetition time, 9,000 msec; echo time, 288 msec; echo train length, 32; section thickness, 3 mm; intersection gap, none; field of view, 3240 cm; one signal acquired; and matrix, 256 x 128. Fat suppression was used for all studies. Eighteen images were acquired in the coronal plane during a 36-second inspiratory breath hold. The MRCP sequence was prescribed from a breath-hold axial spoiled gradient-echo localizer image and was positioned to include at least the entire PD. No antispasmodic medications were administered, nor were patients given fasting instructions before the examination. With a standard maximum intensity projection algorithm, the technologist performing the study used the source images to reformat a coronal maximum intensity projection image and then rotate this in a 15° radial fashion over 180°. This resulted in 12 printed maximum intensity projection images along with the 18 printed source images. In addition, both the source and maximum intensity projection images were available for review on an independent workstation.
All ERCP examinations were performed by one of three experienced gastroenterologists with technologist-assisted fluoroscopy. Standard ERCP procedure was used. All printed images were included for review.
Image Analysis
MRCP and ERCP images were interpreted separately in a blinded, retrospective fashion. Hard-copy images of the ERCP and MRCP maximum intensity projection studies were randomly ordered for review. Although all MR images were available on an independent workstation for further review, their use was at the discretion of the individual readers. No attempt was made to quantify additional information gained through the interactive use of a workstation. The readers were three experienced radiologists, one a specialist in MR imaging (D.F.A.), one a specialist in gastrointestinal imaging (J.B.), and one a specialist in both MR and gastrointestinal imaging (G.T.S.). When discrepancies existed, consensus readings were obtained by reviewing the hard-copy images.
Seven segments of the pancreatic and biliary tree were evaluated: the central right intrahepatic duct (ID), the central left ID, the common hepatic duct, the common bile duct, and the PD head, PD body, and PD tail. The rating scale was 0, duct not seen; 1, duct seen and normal; 2, duct seen and abnormal. Ducts rated abnormal were classified as slightly, moderately, or markedly dilated or narrowed. The segment ratings were based on the clinical experience of the individual readers, and duct caliber measurements were not routinely obtained in the image analysis. In general, the common duct was considered dilated on the MRCP and ERCP (corrected with endoscope tip measurement) images if its caliber was greater than 7 mm or greater than 10 mm in patients after cholecystectomy. Similarly, the PD was considered dilated if its caliber was greater than 3 mm. Narrowing was diagnosed when focal caliber change was present in any segment or when the PD caliber was less than 2 mm. This reflects our standard practice in interpreting these studies.
Image quality was also evaluated as adequate, adequate with artifacts, or inadequate. Studies rated adequate or adequate with artifacts were deemed to be of sufficient diagnostic quality to render a clinical diagnosis, taking into account duct visualization, anatomic sharpness, contrast, and artifacts. Inadequate examinations were not included in the segment analysis. Artifacts, when present, were characterized and recorded.
Statistical Analysis
Findings on ERCP studies were used as the standard of reference. Sensitivity and specificity were calculated for individual duct segments depicted on the MRCP images. Interobserver variability was expressed as the percentage agreement between each reader and the consensus reading for both the ERCP and MRCP studies.
| RESULTS |
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ERCP demonstrated one or more segments of the biliary or PD system in each patient. As a result of either technical failure (ie, unsuccessful attempt related to either anatomy or pathologic conditions) or lack of attempt, at least one segment was not visualized with ERCP in 23 patients, for a total of 63 segments (right ID [n = 7], left ID [n = 6], common hepatic duct [n = 6], common bile duct [n = 6], PD tail [n = 18], PD body [n = 12], and PD head [n = 8]). These results are listed by patient in Table 1.
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In 10 patients, at least one duct segment was not identified at MRCP, for a total of 17 segments. Segments detected included the following: right ID, 30 with ERCP and 30 (100%) with MRCP; left ID, 31 with ERCP and 30 (97%) with MRCP; common hepatic duct, 31 with ERCP and 30 (97%) with MRCP; common bile duct, 31 with ERCP and 29 (94%) with MRCP; PD tail, 19 with ERCP and 17 (89%) with MRCP; PD body, 25 with ERCP and 21 (84%) with MRCP; and PD head, 29 with ERCP and 22 (76%) with MRCP (Fig 1). Duct segments not detected at MRCP were depicted at ERCP as normal (n = 11), slightly narrowed (n = 5), or slightly dilated (n = 1) (Table 3).
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| DISCUSSION |
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To our knowledge, after a search of the English literature, our study is the largest to demonstrate the usefulness of MRCP in the evaluation of the pancreaticobiliary system in patients with a clinical diagnosis of pancreatitis, including both acute and chronic pancreatitis. This is a particularly difficult imaging task, as the changes in the ductal system in these patients are often not overt but are more subtle narrowing or dilatation. Imaging technique plays an important role in differentiating these subtle changes from the normal state. Both breath-hold and nonbreath-hold techniques have been described and promoted. In designing this study, we believed use of a breath-hold technique was important to improve detection of fine structures. We used a torso surface coil to improve the signal-to-noise ratio. The resolution matrix, 256 x 128, was limited, however, by its effect on the length of the breath hold. Fat suppression, while improving maximum intensity projection image quality, also indirectly had an effect on increasing the breath-hold period.
Our results for detection are similar to those in previous studies (13,17), with sensitivity for detection of biliary segments of 94% or greater and for detection of pancreatic segments of 76% for the PD head, 84% for the PD body, and 90% for the PD tail. Segments not detected with MRCP were depicted at ERCP as normal (n = 11), slightly narrowed (n = 5), or slightly dilated (n = 1). Characterization accuracy for all segments was 86% or greater with MRCP. Segments incorrectly characterized at MRCP were all interpreted as normal; at ERCP, they were depicted as slightly dilated (n = 9) or slightly narrowed (n = 5).
Among the 39 study patients, only two had MRCP studies rated as inadequate, owing to excessive motion artifacts because they were not able to hold their breath for 36 seconds. This suggests that breath-hold imaging is a feasible technique in a large and diverse group of patients.
Although not specifically evaluated in this study, in those patients with technical failure in the imaging of at least one segment with ERCP, MRCP was believed to be clinically helpful in evaluation of the pancreaticobiliary tree, and the MRCP findings had a direct effect on patient treatment decisions.
Recently, the use of half-Fourier RARE or single-shot fast spin-echo techniques has been introduced for MRCP. While not yet widely available, these new techniques show great promise for improved imaging. At our institution, use of the single-shot fast spin-echo technique has allowed a shorter breath-hold period of approximately 20 seconds for a complete coronal acquisition, with a high-resolution matrix (256 x 256) with 3-mm section thickness. Use of an inversion pulse with this sequence nulls the signal from fat. Our preliminary experience with the results of this technique are impressive (unpublished data).
In summary, findings in this study demonstrate very good detection sensitivity and characterization accuracy of duct segments with MRCP to evaluate patients with pancreatitis, with ERCP as the standard of reference for comparison. Our results suggest that in patients with pancreatitis, MRCP provides diagnostic information similar to that with ERCP and thus could be used similarly to guide patient treatment. MRCP was also helpful in all patients with technically failed ERCP examinations. As techniques continue to improve, the clinical role of MRCP will almost certainly expand.
| Footnotes |
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Current address: Department of Radiology, Long Beach Memorial Hospital, Long Beach, Calif. ![]()
Current address: Department of Radiology, Northwestern University Medical Center, Chicago, Ill. ![]()
Address reprint requests to G.T.S.
From the 1995 RSNA scientific assembly.
Abbreviations: ERCP = endoscopic retrograde cholangiopancreatography ID = intrahepatic duct MRCP = MR cholangiopancreatography PD = pancreatic duct RARE = rapid acquisition with relaxation enhancement
Author contributions: Guarantors of integrity of entire study, G.T.S., D.F.A., J.B.; study concepts, G.T.S.; study design, G.T.S., J.B., D.F.A.; definition of intellectual content, G.T.S., D.F.A., J.B.; literature research, G.T.S., M.J.C., F.H.M., J.L.C.; clinical studies, G.T.S.; data acquisition, G.T.S., M.J.C., F.H.M., J.L.C.; data analysis, G.T.S., M.J.C.; statistical analysis, G.T.S.; manuscript preparation and editing, G.T.S.; manuscript review, all authors.
Received January 20, 1998;
revision requested April 2, 1998; revision received July 6, 1998;
accepted September 2, 1998.
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