FOCUS ON: Gastrointestinal Imaging
Original Research
JOURNAL CLUB: MRI Assessment of Biliary Ductal Obstruction: Is There Added Value of T1-Weighted Gadolinium-Ethoxybenzyl-Diethylenetriamine Pentaacetic Acid–Enhanced MR Cholangiography?
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OBJECTIVE. The goal of the present study was to determine the added value of gadolium-ethoxybenzyl-diethylenetriamine pentaacetic acid (gadoxetate disodium)–enhanced magnetic resonance cholangiography (MRC) to standard liver MRI including T2-weighted MRCP in assessment of biliary ductal obstruction.
MATERIALS AND METHODS. Thirty-eight patients (mean age, 48.1 ± 16.7 years) (40 total examinations) who underwent liver MRI (including T2-weighted MRCP and gadoxetate disodium–enhanced MRC) for suspicion of biliary disease were included in this institutional review board–approved, HIPAA-compliant retrospective study. Three blinded radiologists first evaluated MR images without gadoxetate disodium–enhanced MRC for presence and significance of biliary obstruction, underlying cause for obstruction, and confidence in final diagnosis. After inclusion of gadoxetate disodium–enhanced MRC, readers again determined presence and significance of biliary obstruction and confidence in final diagnosis. Reference standard was established using MRI along with ERCP, percutaneous transhepatic cholangiography, intraoperative cholangiography, or a combination thereof.
RESULTS. Overall sensitivity across all readers in diagnosing significance of obstruction was 60% without gadoxetate disodium–enhanced MRC and 91% with gadoxetate disodium– enhanced MRC (p < 0.001). Across all readers, assessment of significance of obstruction was changed when adding gadoxetate disodium–enhanced MRC in 40 of 120 cases (33%); significance of obstruction was correctly changed in 35 of 40 cases (87.5%). Biliary obstruction was graded of unknown significance in 27 of 120 cases (22.5%) across all readers when gadoxetate disodium–enhanced MRC was not reviewed. Significance of biliary obstruction was classified correctly after adding gadoxetate disodium–enhanced MRC in 25 of these 27 cases (93%). Confidence in final diagnosis was significantly higher with addition of gadoxetate di-sodium–enhanced MRC for two of three readers (p < 0.003).
CONCLUSION. Addition of gadoxetate disodium–enhanced MRC to liver MRI significantly improves sensitivity in assessing significance of biliary obstruction and can improve reader confidence in establishing a final diagnosis. This added information could have a substantial impact in the determination of the most appropriate therapeutic options.
Keywords: biliary obstruction, hepatobiliary contrast agent, MRCP
Current imaging techniques for evaluation of the biliary system include ultrasound, MRI, cholescintigraphy, and ERCP. MRI has been established as a highly sensitive method for assessment of the entire hepatobiliary system using a heavily T2-weighted sequence for bile duct evaluation (MRCP). The capability of hepatobiliary MRI has further increased with the availability of hepatobiliary-specific gadolinium-based MRI contrast agents, which can be taken up by hepatocytes and in part excreted through the biliary system in a delayed phase [1].
Gadobenate dimeglumine (Multihance, Bracco Diagnostics) and gadolinium-ethoxybenzyl-diethylenetriamine pentaacetic acid (gadoxetate disodium [Eovist, Bayer HealthCare Pharmaceuticals; or Primovist, Bayer Schering Pharma]) are the main gadolinium-based hepatobiliary contrast agents that combine the imaging properties of extracellular agents during arterial and portal venous phases with the properties of hepatobiliary contrast agents in the delayed phases. Another hepatobiliary contrast agent is the manganese-based compound mangafodipir trisodium (Teslascan, Nycomed Amersham). MRI with hepatobiliary contrast agents potentially has the capacity to provide functional information by depicting bile flow on hepatobiliary phase images, whereas conventional MRI with MRCP can depict bile flow or obstruction of bile flow only indirectly, on the basis of associated anatomic findings.
The concept of obtaining functional information on the biliary system by using hepatobiliary contrast agents and acquiring contrast-enhanced magnetic resonance cholangiographic (MRC) images in the delayed phase has been investigated in several previous studies using gadobenate dimeglumine [2, 3] and mangafodipir trisodium [4–9]. However, there are potential limitations with these agents. Specifically, mangafodipir trisodium does not allow dynamic imaging, a standard part of liver MRI, because it is administered as a slow infusion. Gadobenate dimeglumine provides high intravascular contrast enhancement, but only 3–5% of the dose is excreted through the biliary system, leading to achievement of the hepatocyte phase in about 40–120 minutes [10]. In contrast, gadoxetate disodium has a higher biliary excretion rate of approximately 50% and an earlier onset of biliary excretion, resulting in higher contrast enhancement of the biliary system, faster achievement of the hepatocyte phase (10–20 minutes), and potentially shorter examination time [10, 11]. Therefore, it could have advantages over gadobenate dimeglumine for the off-label assessment of the biliary system [12].
Gadoxetate disodium–enhanced MRI has been evaluated for diagnosing hepatic lesions [13, 14] and for defining biliary anatomy [10, 15–17]. Only one study evaluated the capability of gadoxetate disodium for functional assessment of the biliary system, namely for evaluation of cystic duct patency in acute cholecystitis [18]. To our knowledge, no study has directly investigated the value of contrast-enhanced MRC with gadoxetate disodium for functional assessment of bile duct obstruction. This could potentially have an impact on further treatment planning by not only diagnosing the presence and location of biliary obstruction but also revealing the degree of biliary obstruction [19]. Therefore, the purpose of our study was to determine the added value of gadoxetate disodium–enhanced MRC to standard liver MRI including T2-weighted MRCP in the assessment of bile duct obstruction.
| Materials and Methods |   |
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This retrospective, HIPAA-compliant study was approved by the local institutional review board, and waiver of informed consent was granted. A total of 354 contrast-enhanced liver MRI examinations with gadoxetate disodium including thin-section MRCP between October 2008 and May 2010 were identified for possible inclusion in this study. Inclusion criteria for MRI examinations were adequate correlative studies available as a reference standard (ERCP, percutaneous transhepatic cholangiography [PTC], and intraoperative cholangiography were defined as the reference standard examinations) and total bilirubin levels below 5 mg/dL. Because of lack of reference standard examinations, 296 MRI examinations were excluded from further analysis, and five MRI examinations were excluded because of total bilirubin levels above 5 mg/dL. Of the remaining 53 MRI examinations, six were excluded owing to incomplete ERCP (incomplete evaluation of the bile ducts), six were excluded owing to a time interval of more than 1 year between the MRI and the reference standard examination, and one was excluded owing to severe image artifacts rendering the examination nondiagnostic.
In total, 40 MRI examinations performed in 38 patients (23 women, 15 men; mean age, 48.1 ± 16.7 years; age range, 18–85 years) were included in this study. The indications for liver MRI and underlying diseases are listed in Table 1.
Liver MRI was performed on a 1.5-T system (Magnetom Avanto A Tim, Siemens Healthcare) using two anterior six-element body phased-array coils and three posterior three-element spine phased-array coils covering the upper abdomen. The liver MRI protocol included the following sequences: breath-hold coronal 2D HASTE T2-weighted sequence, breath-hold axial 3D gradient dual echo T1-weighted sequence with 2-point Dixon reconstructions, respiratory-triggered axial 2D fat-suppressed fast spin-echo (FSE) T2-weighted sequence, and contrast-enhanced breath-hold axial 3D fat-suppressed gradient-recalled echo (GRE) T1-weighted sequence during arterial, portal venous, and late dynamic phases. The T2-weighted MRCP imaging was performed before contrast administration using a breath-hold single-slab 2D fat-suppressed FSE sequence in the coronal and coronal oblique ± 20° planes, a breath-hold thin-section 2D fat-suppressed HASTE in the coronal plane, and a respiratory-triggered 3D fat-suppressed FSE sequence acquired in the coronal plane.
Contrast-enhanced MRC was performed in the hepatobiliary phase 10–20 minutes after gadoxetate disodium administration using a breath-hold 3D fat-suppressed GRE T1-weighted sequence in the axial and coronal planes. In patients with impaired liver function and delayed biliary excretion of contrast agent, additional delayed images were obtained up to 1 hour after contrast agent administration. Gadoxetate disodium (Eovist, Bayer HealthCare Pharmaceuticals) was injected at a fixed dose of 10 mL, which is a dosing strategy now routinely used at different institutions, with an injection rate of 2 mL/s followed by a 20-mL saline flush using an automatic power injector [20–22].
A fixed scan delay depending on patient age (if < 60 years old, 15 seconds; if ≥ 60 years old, 20 seconds) was used for the start of the dynamic contrast-enhanced MRI dataset [22]. The sequence parameters for liver MRI with T2-weighted MRCP and gadoxetate disodium–enhanced MRC are detailed in Table 2.
Three blinded board-certified radiologists (two radiologists near completion of their abdominal imaging fellowship, one abdominal imaging fellowship trained radiologist with 2 years of experience as a staff radiologist) performed image evaluation independently on a PACS workstation. The cases were randomized, and all patient identifiers were removed for image analysis. Readers knew that MRI examinations had been performed because of potential biliary disease but were blinded to any additional clinical information or results of other imaging studies. First, MR images including unenhanced and contrast-enhanced T1- and T2-weighted sequences and T2-weighted MRCP were evaluated without gadoxetate disodium–enhanced MRC. Readers were asked to record the presence and the location of biliary dilatation (intrahepatic bile ducts including 1st- to 3rd-order branches, extrahepatic bile ducts, or both). The degree of biliary dilatation was graded on a 5-point scale (1, mild; 2, mild to moderate; 3, moderate; 4, moderate to severe; 5, severe). The presence of other bile duct abnormalities, including narrowing and filling defects, was recorded with a pull-down menu. The presence and significance of biliary obstruction was graded (see explanation in the next paragraph). The final diagnosis was reported with free text. Finally, the readers rated their confidence in final diagnosis on a 5-point scale (1, < 25% confidence; 2, 25–50% confidence; 3, 50–75% confidence; 4, 75–90% confidence; 5, nearly 100% confidence).
Then, readers included gadoxetate disodium–enhanced MRC images in their evaluation and again determined the presence and significance of biliary obstruction in the same reading session. In addition, readers recorded any potential changes to the report regarding presence, location, and degree of biliary dilatation, as well as narrowing or filling defects of bile ducts. Finally, readers again determined the confidence in final diagnosis when including gadoxetate disodium–enhanced MRC images.
On MR images including unenhanced and contrast-enhanced T1-weighted and T2-weighted sequences and T2-weighted MRCP (without gadoxetate disodium–enhanced MRC), the significance of obstruction was graded, from low to high grade, in the following order: no obstruction, partial obstruction, complete obstruction, or obstruction of unknown significance. These grades were assigned according to secondary morphologic findings including upstream dilatation, abrupt change in caliber, and loss of bile duct continuity.
When gadoxetate disodium–enhanced MRC images were included, it was deemed that no obstruction was present if there was excretion of contrast material through the intrahepatic and extrahepatic biliary tree within 20 minutes and without an apparent obstructing lesion, regardless of whether biliary dilatation was present. Partial obstruction was deemed present when contrast enhancement was seen distal to an apparent obstruction. Complete obstruction was deemed present if no contrast enhancement was seen distal or, possibly, even proximal to the obstruction. In cases with an obstructing biliary lesion on one side and no obstructing lesion on the contralateral side, the obstructing lesion was defined either as partial obstruction if continuity of the contrast column in the affected bile duct branch to the common bile duct (CBD) was seen or as complete obstruction if no continuity of the contrast column was seen. In cases with different grades of obstruction in different biliary locations, the most severe type of obstruction was reported.
ERCP (n = 34), PTC (n = 5), or intraoperative cholangiography (n = 2), or a combination thereof (ERCP and PTC, n = 4) performed within 1 year of the MRI, and MRI served as reference standard examinations. Two different subspecialty trained board-certified radiologists, with 3 and 12 years of experience in abdominal MR imaging, who were not involved in the blinded image analysis and had access to clinical information, in consensus, evaluated the reference examinations for biliary abnormalities, presence and significance of biliary obstruction, and final diagnosis.
Continuous variables are expressed as means ± SD. Categoric variables are expressed as frequencies or percentages. The interobserver agreement between the independent readers' interpretations (reader 1 and 2) was determined by calculating kappa values and 95% CIs. The kappa values were tested for a significant difference from zero. A kappa value of 0.00 indicated no agreement; 0.01–0.20, slight agreement; 0.21–0.40, fair agreement; 0.41–0.60, moderate agreement; 0.61–0.80, good agreement; and 0.81–1.00, excellent agreement [23].
Sensitivity and specificity were calculated separately for presence and location of biliary dilatation as well as accuracy for degree of biliary dilatation. The accuracy for diagnosing whether there was no, partial, or complete obstruction was calculated as well as the overall accuracy for diagnosing the significance of obstruction.
Differences in the accuracy for diagnosing the significance of obstruction before and after addition of gadoxetate disodium–enhanced MRC were evaluated with the McNemar test. Differences in confidence in final diagnosis before and after addition of gadoxetate disodium–enhanced MRC were assessed with the Wilcoxon signed rank test.
Statistical analysis was performed using commercially available software (IBM SPSS Statistics, release 19.0, SPSS Inc.). Statistical significance was inferred at p < 0.05.
| Results | |
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According to the reference standard, 22 of 40 (55%) cases showed biliary dilatation— with involvement of the intrahepatic bile ducts in 10 cases, of the extrahepatic bile ducts in three cases, and of the intra- and extrahepatic bile ducts in nine cases. Biliary dilatation was mild in four cases, mild to moderate in five cases, moderate in seven cases, moderate to severe in four cases, and severe in two cases. Additional biliary findings were narrowing of the bile ducts in 18 of 40 (45%) cases and filling defects in 7 of 40 (18%) cases. No obstruction was seen in 31 of 40 (77.5%) cases, partial obstruction in 3 of 40 (7.5%), and complete obstruction in 6 of 40 (15%) cases. In 13 of 22 (59%) cases with biliary dilatation, no biliary obstruction was seen.
Sensitivity and specificity for the presence of biliary dilatation were 100% and 83% for reader 1, 82% and 89% for reader 2, and 91% and 94% for reader 3. The location of biliary dilatation was evaluated correctly by readers 1 and 3 in 71% and by reader 2 in 73% of all cases. The accuracy for grading the degree of biliary dilatation was 60%, 65%, and 70% for readers 1, 2, and 3, respectively. The sensitivity for narrowing of bile ducts was 89% for reader 1 and 83% for readers 2 and 3. The sensitivity for filling defects of the bile ducts was 86% for all readers. For the evaluation of the significance of biliary obstruction, the accuracy across all readers for the diagnosis of no obstruction was 69%; for partial obstruction, 22%; and for complete obstruction, 33% (Table 3). The overall accuracy for the evaluation of the significance of biliary obstruction was 60%. The details for each reader are given in Table 3.
The interreader agreement was moderate to good for the presence of biliary dilatation (κ = 0.55−0.70), fair to moderate for the location of biliary dilatation (κ = 0.38−0.55), fair for the degree of dilatation (κ = 0.28−0.37), and good for diagnosing narrowing and filling defects of bile ducts (κ = 0.66−0.67). For the assessment of significance of obstruction, interreader agreement was only slight to fair (κ = 0.18−0.36).
The mean confidence level in the overall evaluation of the bile ducts was 3.78 ± 0.53 for reader 1, 4.40 ± 1.08 for reader 2, and 4.58 ± 0.68 for reader 3.
The mean delay of contrast agent's appearing in the extrahepatic bile ducts on gadoxetate disodium–enhanced MRC images was 18 minutes (range, 9–28 minutes), with 34 of 40 (85%) examinations showing excretion within 20 minutes of contrast agent administration. In 6 of 40 examinations, additional gadoxetate di-sodium–enhanced MRC images were acquired 30 minutes after contrast agent administration; of these examinations, three showed no excretion, and no further delayed images were acquired for reasons of time efficiency.
In regard to the assessment of presence, location, and degree of biliary dilatation, narrowing, and filling defects of bile ducts, the report was changed in only one case when adding gadoxetate disodium–enhanced MRC images, where reader 3 found additional narrowing of the bile ducts. When gadoxetate di-sodium–enhanced MRC images were added, the accuracy across all readers for the diagnosis of no obstruction increased from 69% to 97% (p < 0.001); for partial obstruction, from 22% to 56% (p = 0.25); and for complete obstruction, from 33% to 78% (p = 0.039). The overall accuracy for the evaluation of the significance of biliary obstruction increased from 60% to 91% (p < 0.001). The details for each reader are given in Table 3.
The assessment of significance of biliary obstruction was changed in 45 of 120 (38%) cases across all readers when gadoxetate di-sodium–enhanced MRC images were added (Figs. 1 and 2 and Table 4). In 40 of 45 (89%) cases, the significance of obstruction was changed correctly. In 3 of 45 (6.7%) cases, the significance of obstruction was underestimated, and in 2 of 45 (4.4%) cases, biliary obstruction was overestimated.
 View larger version (188K) | Fig. 1A —36-year-old woman 10 months after laparoscopic cholecystectomy because of incidentally detected intrahepatic biliary dilatation during workup prior to appendectomy. A,Coronal-oblique multiplanar reformation (MPR) image derived from T2-weighted 3D fat-suppressed spin-echo sequence shows moderate dilatation of intrahepatic bile ducts and apparent discontinuity of common hepatic duct (arrow) related to susceptibility artifact from surgical clip. Significance of obstruction remains unclear. |
 View larger version (149K) | Fig. 1B —36-year-old woman 10 months after laparoscopic cholecystectomy because of incidentally detected intrahepatic biliary dilatation during workup prior to appendectomy. B, Coronal-oblique MPR image derived from 3D gradient-recalled echo T1-weighted images with fat saturation obtained 20 minutes after gadoxetate disodium administration shows normal timing of excretion of contrast material through common bile duct (arrow) and transit into small bowel (arrowhead). In combination with moderate dilatation of intrahepatic bile ducts, partial biliary obstruction was correctly diagnosed. |
In 29 of 45 (64%) cases, the significance of biliary obstruction was unknown when the images were interpreted without gadoxetate di-sodium–enhanced MRC (Fig. 1). After gadoxetate disodium–enhanced MRC images were added, 27 of these 29 (93%) cases were correctly interpreted as showing no obstruction (n = 21), partial obstruction (n = 2), or complete obstruction (n = 4). In 2 of these 29 (7%) cases, significance of obstruction was incorrectly interpreted, with one case overestimated as partial obstruction and one case underestimated as no obstruction instead of partial obstruction. The details for cases of unknown significance of obstruction are given in Table 4. Interreader agreement for the assessment of significance of biliary obstruction increased to good with kappa values of 0.60–0.65.
The confidence in the overall evaluation of the bile ducts significantly increased in readers 1 and 2, with a mean confidence level of 4.75 ± 0.59 (p < 0.001) for reader 1 and of 4.95 ± 0.22 (p = 0.003) for reader 2. The mean confidence level for reader 3 was 4.63 ± 0.54 (p = 0.212).
| Discussion | |
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Our study results show that the addition of gadoxetate disodium–enhanced MRC to liver MRI including T2-weighted MRCP significantly increased the accuracy of assessment of significance of biliary obstruction. In addition, the confidence in the overall evaluation of the bile ducts significantly increased for two of the three readers. Furthermore, a high proportion (59%) of cases with biliary dilatation showed no biliary obstruction.
These results are in line with those of a previous study that assessed the diagnostic performance of mangafodipir trisodium–enhanced functional MRC for the evaluation of biliary disorders [4]. In that study, the diagnostic confidence for the diagnosis of biliary duct obstruction significantly increased when adding functional, contrast-enhanced MRC images to conventional T2-weighted MRCP images. Similarly, the diagnosis of stricture of biliaryenteric anastomoses was made with greater confidence on the basis of mangafodipir tri-sodium–enhanced MRC images as compared with T2-weighted MRCP images in a study by Bridges et al. [6]. In another recent study, investigators found gadoxetate disodium–enhanced MRC to be helpful in addition to T2-weighted MRCP for visualization of bile ducts and diagnostic confidence in patients with primary sclerosing cholangitis [24].
The presence of biliary dilatation, narrowing, and filling defects can be reliably determined on T2-weighted MRCP images with sensitivities of 94–96% for biliary dilatation, 83–90% for narrowing of the bile ducts, and 84–100% for filling defects in previous studies [4, 25, 26]. The results seen in our study were comparable, with averaged sensitivities of 91% for the presence of biliary dilatation, 85% for narrowing of the bile ducts, and 86% for filling defects in the bile ducts.
Although the presence of a biliary obstruction can be diagnosed by identifying underlying diseases or abnormalitites as narrowing and filling defects of the bile ducts and consequent biliary dilatation on conventional T2-weighted MRCP, the functional significance of obstruction may remain unclear owing to lack of functional information. When MR images (including T2-weighted MRCP) without gadoxetate disodium–enhanced MRC images were evaluated, in 24.2% (29/120) of the cases, the significance of biliary obstruction was rated as “unknown” in our study. In 93% of these cases, the addition of gadoxetate disodium–enhanced MRC allowed a correct classification as no biliary obstruction, partial obstruction, or complete obstruction. In a study by Hottat et al. [7], the functionality of biliaryenteric anastomoses could be assessed with mangafodipir trisodium–enhanced MRC with a sensitivity of 100%, whereas T2-weighted MRCP showed a sensitivity of 50%. In another study, the presence of a significant biliary-enteric anastomotic stenosis was indeterminate in 6 of 25 (24%) cases on T2-weighted MRCP images, whereas a definite diagnosis was possible in all cases when evaluating gadoxetate disodium–enhanced MRC images [6].
In addition to the evaluation of biliary anastomoses, gadoxetate disodium–enhanced MRC images can be of potential value in patients with suspected biliary obstruction after cholecystectomy, in whom susceptibility artifacts of metallic clips may obscure bile ducts. A bile duct segment partially obscured by susceptibility artifacts can be easily misinterpreted as discontinuous owing to clipping of the bile duct, which would represent a potential complication after cholecystectomy (Fig. 1A). Evidence of biliary contrast enhancement distal to the obscured bile duct segment on gadoxetate disodium–enhanced MRC can confirm continuity of the bile duct as seen in a case in this study (Fig. 1B). The addition of the functional information of gadoxetate disodium–enhanced MRC images could help prevent unnecessary intervention in a case such as this one.
In cases with unilateral biliary obstruction or different degrees of biliary obstruction, gadoxetate disodium–enhanced MRC and standard liver MRI including T2-weighted MRCP can be complementary. For example, in a case where intrahepatic biliary dilatation is seen and discontinuity of the right and left bile duct branches with the CBD on T2-weighted MRCP suggests complete biliary obstruction, gadoxetate disodium–enhanced MRC images could help to differentiate complete obstruction from partial obstruction. The continuity of the contrast column from the intrahepatic bile ducts to the CBD would indicate partial obstruction whereas discontinuity of the contrast column on the opposite side with the CBD would indicate complete obstruction.
It has been suggested that further optimization of the hepatobiliary phase MR images and thus of gadoxetate disodium–enhanced MRC can be achieved by increasing the flip angle, which leads to a significant increase in the tissue contrast enhancement between bile ducts, vessels, and liver parenchyma [27]. The high contrast difference between bile ducts and liver parenchyma, analogous to T2-weighted MRCP, may improve the performance of gadoxetate disodium–enhanced MRC. Another possibility for optimization of hepatobiliary phase MR images is the use of a respiratory-triggered spoiled GRE sequence, which allows hepatobiliary phase imaging with high spatial resolution [28, 29].
The biliary excretion of gadoxetate disodium may be affected by various factors such as hepatic function and degree of obstruction. In patients with long-standing and high-grade biliary obstruction, liver function can be severely impaired with elevated total bilirubin levels. In these cases, the utility of gadoxetate disodium is limited because it acts as a competitive antagonist to bilirubin at the level of the receptor [30]; thus, limited or no hepatocyte uptake would occur. In our clinical experience, we have seen biliary excretion of gadoxetate disodium in patients with serum total bilirubin levels up to 5 mg/dL, therefore, we included patients with total bilirubin levels up to 5 mg/dL in our study [12].
 View larger version (161K) | Fig. 2A —55-year-old woman after cholecystectomy who presented with right upper quadrant pain and fever. A, Maximum intensity projection (MIP) image derived from T2-weighted 3D fat-suppressed spin-echo sequence shows filling defect in distal common bile duct (arrow), representing single common duct stone. Mild to moderate dilatation of intra- and extrahepatic bile ducts is present, suggesting complete obstruction. |
 View larger version (146K) | Fig. 2B —55-year-old woman after cholecystectomy who presented with right upper quadrant pain and fever. B, Multiplanar reformatted image derived from 3D gradient-echo T1-weighted images with fat saturation obtained 30 minutes after gadoxetate disodium administration shows contrast excretion through common bile duct. Stone in common bile duct (arrow) was determined to be partially obstructive because contrast material can be seen distal to stone with transit into small bowel (arrowhead). |
A potential pitfall of gadoxetate disodium–enhanced MRC can occur in patients with pigmented biliary stones with high signal intensity on T1-weighted images, where the hepatobiliary contrast agent on T1-weighted gadoxetate disodium–enhanced MRC can obscure the biliary stones. Therefore, it is important to carefully match gadoxetate disodium–enhanced MRC images with T2-weighted images.
The following study limitations have to be acknowledged. One limitation is potential selection bias owing to the choice of our reference standard. ERCP, PTC, and intraoperative cholangiography are considered the criterion standard in the evaluation of the biliary tree. However, because of the invasive nature of these examinations, they are not routinely performed at our institution in patients undergoing initial evaluation for biliary diseases. Thus, only a limited number of patients were eligible for our study.
Second, the assessment of bile duct visibility was not part of our study. Previous studies showed that the visualization of bile ducts is similar or better in nondilated bile ducts when using hepatobiliary contrast agents for gadoxetate disodium–enhanced MRC as compared with T2-weighted MRCP [4, 16, 31]. Therefore, our study focused on the value of gadoxetate disodium–enhanced MRC in adding functional information to liver MRI with conventional T2-weighted MRCP.
In conclusion, the addition of gadoxetate di-sodium–enhanced MRC to liver MRI significantly improved diagnostic accuracy in assessing the significance of biliary obstruction and can improve reader confidence in establishing a final diagnosis. To our knowledge, this is the first study to directly quantify the added value of gadoxetate disodium–enhanced MRC to liver MRI in this regard. The ability to differentiate degree of biliary obstruction on gadoxetate disodium–enhanced MRC could have a substantial impact in the determination of the most appropriate therapeutic options.
E. M. Merkle and R. T. Gupta are on the speakers’ bureau of and serve as consultants for Bayer Schering Pharma. M. R. Bashir serves as a consultant for Bayer Schering Pharma.
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| References | |
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This article has been selected for AJR Journal Club activity. The accompanying Journal Club study guide can be found on the following page.
| APPENDIX 1: AJR JOURNAL CLUB |
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Margaret Mulligan, Alan Mautz, Joseph J. Budovec*
*Please note that the authors of the Study Guide are distinct from those of the companion article.
Medical College of Wisconsin, Milwaukee, WI
[email protected], [email protected], [email protected]
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1. What is the clinical question being asked? How would you formally state the authors' hypothesis? How would you state the alternative hypothesis?
2. Is this study timely and relevant? What is the standard for the evaluation of biliary ductal obstruction? How sensitive and accurate is this assessment?
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3. What were the inclusion criteria for the study? What were the exclusion criteria?
4. Is it significant that two of the three radiologists who read cases for the study were completing fellowships in abdominal imaging?
5. What are the limitations of this study? Are these limitations adequately discussed?
6. What statistical tests were used in the analysis and in determining the sensitivity and specificity of the readers?
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7. Was the research question(s) answered? Were the hypotheses resolved?
8. Was the sample size large enough to draw conclusions on the benefit of adding gadoxetate disodium contrast-enhanced MR cholangiography to standard liver MRI studies?
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9. Briefly explain how gadoxetate disodium works. How is it eliminated? What is the standard dosing of gadoxetate disodium relative to conventional gadolinium chelates? What is the T1 relaxivity of gadoxetate disodium compared with conventional gadolinium chelates?
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10. At your institution, what is the standard imaging protocol for biliary ductal obstruction and classifying its significance? Given the cost of gadoxetate disodium relative to conventional gadolinium chelates, is there an advantage to using gadoxetate disodium? Would you change your current imaging protocol based on the results of this study?
11. What outcomes data might augment the power of this study? Is the study designed well enough and powerfully enough to evoke change in imaging for biliary obstruction?
