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MR Cholangiography for Evaluation of Hilar Branching Anatomy in Transplantation of the Right Hepatic Lobe from a Living Donor

¹ Department of Diagnostic Radiology, Yonsei University Health System, 134 Shinchon-dong, Seodaemoon-ku, Seoul 120-752, Republic of Korea.
² Institute of Gastroenterology, Yonsei University Health System, Seoul, Republic of Korea.
³ Department of Biostatistics, Yonsei University Health System, Seoul, Republic of Korea.
⁴ Department of Surgery, Yonsei University Health System, Seoul, Republic of Korea.

Received September 11, 2007; accepted after revision February 10, 2008.

 
Address correspondence to M. J. Kim (kimnex{at}yuhs.ac.kr).

Abstract

Top Abstract Introduction Materials and Methods Results Discussion References

 
OBJECTIVE. Our objective was to determine the utility of 3D T2 MR cholangiography (MRC) for biliary visualization and predicting the number of ductal orifices during right lobe harvesting for ductal anastomosis in liver donors for right lobe transplantation.

MATERIALS AND METHODS. This study was composed of 33 donors who underwent right lobectomy for transplantation. Preoperative MRC techniques included 2D T2 MRC, 3D T2 MRC, and 3D contrast-enhanced T1 MRC. Qualitative analyses were performed for ductal visualization in each technique. The accuracies for predicting the numbers of orifices during right lobe harvesting were evaluated for 2D T2 MRC alone and for various other combined sets. MRI definitions of the predicted number of ductal orifices were compared with surgical findings.

RESULTS. Mean visualization scores of all ducts for 3D T2 MRC were significantly higher than for 2D T2 MRC and 3D contrast-enhanced T1 MRC. In predicting the number of orifices, all combined sets showed significantly higher accuracy than 2D T2 MRC. No significant difference in mean accuracies was observed within the comparison of the combined sets.

CONCLUSION. Three-dimensional T2 MRC provided superior biliary visualization than 2D T2 MRC and 3D contrast-enhanced T1 MRC. For predicting the number of orifices, the combined set of 2D and 3D T2 MRC enabled better accuracy than 2D T2 MRC alone and produced comparable results to other combined sets.

Keywords: anatomy • bile ducts • liver transplantation • MR cholangiopancreatography

Introduction

Top Abstract Introduction Materials and Methods Results Discussion References

 
The evaluation of the biliary anatomy in donor candidates for adult-to-adult living right lobe liver transplantation is essential because the pattern of second-order biliary tract branching can affect the surgical approach and biliary anastomotic technique or even preclude liver donation [1, 2]. The standard MR examination for defining biliary anatomy has been 2D T2-weighted MR cholangiography (MRC). However, previous studies have reported difficulties in depicting the nondilated normal bile ducts in potential living donors using 2D T2 MRC [1, 3]. In an attempt to better visualize the small caliber of normal-sized ducts, 3D contrast-enhanced T1-weighted MRC (3D contrast-enhanced T1 MRC) has been implemented over the past several years. And indeed, 3D contrast-enhanced T1 MRC using mangafodipir trisodium or gadobenate dimeglumine has shown promising results in defining intrahepatic biliary anatomy for liver transplantation [4, 5]. However, mangafodipir trisodium is no longer available in North American markets, and gadobenate dimeglumine–enhanced MRC has a problematic disadvantage in that it requires more than a 1-hour delay for ductal visualization.

Recently, several studies have reported that 3D T2 MRC can provide a similar visualization rate for the bile duct as that of conventional 2D techniques [6, 7]. However, to our knowledge, the usefulness of 3D T2 MRC has not been assessed for the preoperative biliary evaluation of living donor transplantation candidates. The standard method for defining biliary visualization has been 2D T2 MRC, which has a relatively short acquisition time (usually less than 2 minutes) and is available in all MR equipment. So, to improve the diagnostic accuracy of biliary visualization, a practical approach would be to combine the two or three examinations and to compare the diagnostic accuracies in the variable combined sets with 2D T2 MRC.

Therefore, this study had a twofold purpose. The first was to determine the utility of 3D T2 MRC for ductal visualization through comparison with 2D T2 MRC and 3D gadobenate dimeglumine–enhanced T1 MRC. The second was to compare the diagnostic accuracies of ductal anastomosis for right lobe transplantation in variable combined sets.

Materials and Methods

Top Abstract Introduction Materials and Methods Results Discussion References

 
Patients
Between April 2003 and July 2006, 33 healthy candidates underwent right lobectomy for living adult-to-adult right-lobe liver transplantation. There were a total of 23 men and 10 women (mean age, 30.7 years; age range, 18–51 years). Institutional review board approval was obtained for this retrospective study. Informed consent was not required.

MRI Protocols
All candidates underwent MRI performed at 1.5 T using a torso phased-array coil in one of two MR systems (Gyroscan Intera or Intera Achieva, Philips Healthcare). Twenty-five MRC examinations were performed using the former, and eight MRC examinations were performed using the latter. The donor candidates were instructed to fast for 4 hours before the MRI examination. In addition to undergoing MR cholangiography (described later in this article), the subjects underwent routine MRI before and after IV administration of 0.1 mmol per kilogram of body weight of gadobenate dimeglumine (MultiHance, Bracco) injected by an automatic infusion system (Spectris MR injector, Medrad Europe) at a rate of 2 mL/s.

Three methods for evaluating biliary anatomy were used, and no oral contrast agent was administered. First, breath-hold 2D T2 MRC was performed with a single-shot rapid acquisition with relaxation enhancement sequence (RARE) (TR/TE, 2,025/800; field of view, 240 mm; section thickness, 40 mm; matrix, 256 x 256; echo-train length, 256) in coronal oblique orientations (–45° through 45° with 15° intervals) using the single-section thick-slab technique. Seven images during seven breath-holds were obtained during the acquisition time of 9 seconds per section, which included scanning time and interleaved breathing time (total, 63 seconds).

Second, 3D T2 MRC images were obtained using a respiratory triggered 3D T2-weighted rapid acquisition with relaxation enhancement sequence with parallel acquisition technique in the coronal plane using the following parameters: 1,600/650; refocusing flip angle, 90°; field of view, 240–280 mm with rectangular field of view; matrix, 256 x 250; echo-train length, 128; slab thickness, 70 mm with 35 partitions and section thickness of 2 mm; interpolation to 70 slices at 1-mm intervals; parallel acquisition technique factor, 2; no phase wrap option; and acquisition time, approximately 170 seconds. Rotating maximum-intensity-projection (MIP) reconstructions of the 3D MR data were performed with a workstation to produce 19 coronal oblique MIP images (0–180°; slab thickness, 40 mm) rotating about the z-axis in 10° increments.

Third, the donors were brought back for contrast-enhanced T1-weighted MRC 60 minutes after the MR angiography obtained after IV administration of gadobenate dimeglumine. Three-dimensional volumetric breath-hold T1-weighted fast-field-echo acquisitions of the central biliary system were obtained in the coronal plane. The scanning parameters for the high-resolution sequences that were performed with a limited coverage included 5.1/1.47; refocusing flip angle, 40°; field of view, 340–380 mm with rectangular field of view; matrix, 320 x 225; slab thickness, 40 mm with 20 partitions and a section thickness of 2 mm; and interpolation to 40 slices at 1-mm intervals. Acquisition time was kept under 25 seconds to facilitate breath-holding. In addition, 19 coronal oblique MIP images (0–180°; slab thickness, 40 mm) were reconstructed.

Imaging Analysis of Biliary Tract Visualization
Three board-certified radiologists with subspecialty training in abdominal imaging independently and retrospectively reviewed all source and reconstructed MR images at a PACS (Centricity, GE Healthcare). The reviewers had 8, 9, and 10 years of experience.

The 2D T2 MRC, 3D T2 MRC, and 3D contrast-enhanced T1 MRC images were sequentially evaluated at separate sessions with a 2-week time difference between reading sessions to reduce recall bias. Three-dimensional images included source images and MIP images. A total of five biliary segments, the common (one segment), right and left first-order branch (two segments), and right second-order branch (two segments) bile duct segments were scored on a 4-point scale for each examination on the basis of previous literature [7]. A score of 1 indicated that the segment was not seen; a score of 2, that the segment was seen faintly; a score of 3, that the segment was well seen, but the confluence or a portion of the duct was not seen; and a score of 4, that there was excellent visualization of the segment from its proximal commencement to its distal confluence. Left secondary segmental duct visualization was not included because it is not associated with right lobe harvesting. The degrees of overall image quality were also scored in each examination as follows: 1, poor quality with severe artifacts; 2, satisfactory quality with a few artifacts; 3, good quality with minimal artifacts; and 4, excellent quality without artifacts.

Prediction of the Number of Orifices During Right Lobe Harvesting
Two months after the qualitative visualization analyses, the same three radiologists independently reviewed the uncombined set (2D T2 MRC) and the three combined sets (2D T2 MRC and 3D T2 MRC, 2D T2 MRC and contrast-enhanced T1 MRC, and the combined set of all three examinations) with a 2-week time interval between the reading sessions for each set. They recorded the predicted number of ductal orifices during right lobe harvesting (one or two; at our institution, living donor transplantation is performed even if dual orifices have been acquired during right lobe harvesting). The number of ductal orifices was determined according to hilar branching anatomy. The biliary anatomy bifurcation patterns were characterized into the patterns previously described in the literature [8]. Most notably, an emphasis was placed on discerning whether there was a right hepatic duct. The junction of the anterior segmental duct and the posterior segmental duct forming the right hepatic duct and the right hepatic duct, in turn, joining the left hepatic duct in the hilar confluence, were considered to be normal anatomy. This type was regarded as the case in which the single duct-to-duct anastomosis would be possible. However, there were three anatomic variations in which the anterior and posterior segmental bile ducts did not form a right hepatic duct, the posterior segmental duct joined the left hepatic duct, the anterior segmental duct joined the left hepatic duct, and a three-branch-type hilar confluence (trifurcation). The first two types were regarded as requiring the acquirement of two orifices. In a trifurcation pattern, the distinction between single and dual orifices was challenging, but our reviewers determined it according to dominant similarity to normal anatomy or aberrant insertion of the right segmental branch.

Each reviewer also recorded the diagnostic confidence on the predicted number on a scale of 1–5: 1, not confident; 2, mildly confident; 3, moderately confident; 4, highly confident; and 5, completely confident. The MRI predictions of the number of ductal orifices during right lobe harvesting were compared with the surgical findings.

Surgical findings during right lobectomy were obtained by reviewing the operative records to determine the anastomosed number of ductal orifices as the standard of reference. Of the 33 donors, 22 underwent intraoperative MRC. During laparotomy, acquisitions of right hepatic ductal lumen for biliary anastomosis were performed with a single lumen in 24 donors. However, in nine donors, dual lumen acquisitions were performed because of aberrant biliary ducts (right anterior duct to left duct: n = 2; right posterior duct to left duct: n = 7). These results on the number of orifices during right lobe harvesting were used as a reference standard to evaluate the accuracy of our MRC imaging sets.

Statistical Analysis
Statistical analyses were performed by using SAS software, version 9.1 (Statistical Analysis System). Interobserver agreement for biliary tract visualization scores was determined using a weighted kappa statistic. Interobserver agreement was classified as follows: A kappa value of 0.00–0.20 was considered to indicate poor 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.

View larger version (114K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1A —46-year-old male liver donor with normal right hepatic duct. Anterior segmental, posterior segmental, right hepatic, and left hepatic ducts are well visualized in 2D T2 MR cholangiography (MRC) (thick-slap) (A), 3D T2 MRC (maximum-intensity-projection [MIP]) (B), and 3D contrast-enhanced T1 MRC (MIP) (C) images.

View larger version (122K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1B —46-year-old male liver donor with normal right hepatic duct. Anterior segmental, posterior segmental, right hepatic, and left hepatic ducts are well visualized in 2D T2 MR cholangiography (MRC) (thick-slap) (A), 3D T2 MRC (maximum-intensity-projection [MIP]) (B), and 3D contrast-enhanced T1 MRC (MIP) (C) images.

View larger version (130K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1C —46-year-old male liver donor with normal right hepatic duct. Anterior segmental, posterior segmental, right hepatic, and left hepatic ducts are well visualized in 2D T2 MR cholangiography (MRC) (thick-slap) (A), 3D T2 MRC (maximum-intensity-projection [MIP]) (B), and 3D contrast-enhanced T1 MRC (MIP) (C) images.

Prediction of the number of orifices—Interobserver agreement for diagnostic confidence for predicting the number of orifices on all four imaging sets was determined with the weighted kappa statistic. Interobserver agreement was classified according to the previously mentioned criteria. Tests for significant differences in mean accuracies and diagnostic confidences were performed using nonparametric tests (Kruskal-Wallis test and Friedman test, respectively). Mean accuracies and mean confidences of the three reviewers regarding the predicted number of orifices were compared among the four image sets using the LSD test. A p value of less than 0.05 was considered a statistically significant difference.

Results

Top Abstract Introduction Materials and Methods Results Discussion References

 
Biliary Tract Visualization
The kappa values for the interobserver agreement of biliary tract visualization ranged from fair to good for 2D T2 MRC, 3D T2 MRC, and contrast-enhanced T1 MRC (Table 1). The acquired kappa values for the degree of image quality also ranged from fair to good for all three techniques (Table 1).

View larger version (116K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2A —35-year-old male liver donor with aberrant biliary anatomy. Two-dimensional T2 MR cholangiography (MRC) (A) and 3D T2 MRC (B) images show aberrant biliary anatomy with right posterior duct draining into left hepatic duct. Anterior (arrowhead, A, B, and D) and posterior segmental branches (arrow, A, B, and D) are well delineated in both sequences, but right segmental branches are not delineated on 3D contrast-enhanced T1 MRC (C) image. Intraoperative cholangiogram (D) confirmed aberrant biliary anatomy.

View larger version (98K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2B —35-year-old male liver donor with aberrant biliary anatomy. Two-dimensional T2 MR cholangiography (MRC) (A) and 3D T2 MRC (B) images show aberrant biliary anatomy with right posterior duct draining into left hepatic duct. Anterior (arrowhead, A, B, and D) and posterior segmental branches (arrow, A, B, and D) are well delineated in both sequences, but right segmental branches are not delineated on 3D contrast-enhanced T1 MRC (C) image. Intraoperative cholangiogram (D) confirmed aberrant biliary anatomy.

View larger version (121K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2C —35-year-old male liver donor with aberrant biliary anatomy. Two-dimensional T2 MR cholangiography (MRC) (A) and 3D T2 MRC (B) images show aberrant biliary anatomy with right posterior duct draining into left hepatic duct. Anterior (arrowhead, A, B, and D) and posterior segmental branches (arrow, A, B, and D) are well delineated in both sequences, but right segmental branches are not delineated on 3D contrast-enhanced T1 MRC (C) image. Intraoperative cholangiogram (D) confirmed aberrant biliary anatomy.

View larger version (103K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2D —35-year-old male liver donor with aberrant biliary anatomy. Two-dimensional T2 MR cholangiography (MRC) (A) and 3D T2 MRC (B) images show aberrant biliary anatomy with right posterior duct draining into left hepatic duct. Anterior (arrowhead, A, B, and D) and posterior segmental branches (arrow, A, B, and D) are well delineated in both sequences, but right segmental branches are not delineated on 3D contrast-enhanced T1 MRC (C) image. Intraoperative cholangiogram (D) confirmed aberrant biliary anatomy.

View larger version (20K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3A —Graphs show multiple comparisons of mean visualization scores and image quality for three MR cholangiography (MRC) techniques. White bars = 2D T2 MRC, light gray bars = 3D T2 MRC, dark gray bars = 3D contrast-enhanced T1 MRC, error bars indicate SD, asterisk indicates p < 0.05 in comparison of techniques. Branching ducts included bilateral first-order branches and right second-order branches. Overall ducts included a total of five segments. Graph shows mean visualization scores of common duct, branching ducts, and all ducts in three MR cholangiography techniques.

View larger version (16K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3B —Graphs show multiple comparisons of mean visualization scores and image quality for three MR cholangiography (MRC) techniques. White bars = 2D T2 MRC, light gray bars = 3D T2 MRC, dark gray bars = 3D contrast-enhanced T1 MRC, error bars indicate SD, asterisk indicates p < 0.05 in comparison of techniques. Branching ducts included bilateral first-order branches and right second-order branches. Overall ducts included a total of five segments. Graph shows mean scores of image quality of each technique.

View larger version (34K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 4A —Multiple comparisons of mean accuracy and diagnostic confidence for four sets of MR cholangiography (MRC) imaging techniques. Technique 1 = 2D T2 MRC alone, technique 2 = combined set of 2D T2 MRC and 3D T2 MRC, technique 3 = combined set of 2D T2 MRC and 3D contrast-enhanced T1 MRC, and technique 4 = combined set of all three techniques. Error bars indicate SD; asterisk indicates p < 0.05 in comparison of techniques. No significant difference was observed within comparison of combined sets for both accuracy and diagnostic confidence. Graph shows mean accuracy of 2D MRC alone and three combined sets for prediction of ductal orifice number during right lobe harvesting.

View larger version (100K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 5A —30-year-old male liver donor who underwent single lumen acquisition during right lobe harvest. Two-dimensional T2 MR cholangiography (MRC) (A), maximum-intensity-projection (MIP) image of 3D T2 MRC (B), source image of 3D T2 MRC (C), MIP image of 3D contrast-enhanced T1 MRC (D), and source image of 3D contrast-enhanced T1 MRC (E) show normal anatomy in which junction of anterior segmental duct and posterior segmental duct forms right hepatic duct (arrow). All reviewers predicted that acquisition of single lumen would be possible during right lobe harvesting on sets of all four techniques. Intraoperative cholangiogram (F) confirmed normal anatomy (arrow), and acquisition of single lumen was performed.

View larger version (100K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 5B —30-year-old male liver donor who underwent single lumen acquisition during right lobe harvest. Two-dimensional T2 MR cholangiography (MRC) (A), maximum-intensity-projection (MIP) image of 3D T2 MRC (B), source image of 3D T2 MRC (C), MIP image of 3D contrast-enhanced T1 MRC (D), and source image of 3D contrast-enhanced T1 MRC (E) show normal anatomy in which junction of anterior segmental duct and posterior segmental duct forms right hepatic duct (arrow). All reviewers predicted that acquisition of single lumen would be possible during right lobe harvesting on sets of all four techniques. Intraoperative cholangiogram (F) confirmed normal anatomy (arrow), and acquisition of single lumen was performed.

View larger version (100K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 5C —30-year-old male liver donor who underwent single lumen acquisition during right lobe harvest. Two-dimensional T2 MR cholangiography (MRC) (A), maximum-intensity-projection (MIP) image of 3D T2 MRC (B), source image of 3D T2 MRC (C), MIP image of 3D contrast-enhanced T1 MRC (D), and source image of 3D contrast-enhanced T1 MRC (E) show normal anatomy in which junction of anterior segmental duct and posterior segmental duct forms right hepatic duct (arrow). All reviewers predicted that acquisition of single lumen would be possible during right lobe harvesting on sets of all four techniques. Intraoperative cholangiogram (F) confirmed normal anatomy (arrow), and acquisition of single lumen was performed.

View larger version (111K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 5D —30-year-old male liver donor who underwent single lumen acquisition during right lobe harvest. Two-dimensional T2 MR cholangiography (MRC) (A), maximum-intensity-projection (MIP) image of 3D T2 MRC (B), source image of 3D T2 MRC (C), MIP image of 3D contrast-enhanced T1 MRC (D), and source image of 3D contrast-enhanced T1 MRC (E) show normal anatomy in which junction of anterior segmental duct and posterior segmental duct forms right hepatic duct (arrow). All reviewers predicted that acquisition of single lumen would be possible during right lobe harvesting on sets of all four techniques. Intraoperative cholangiogram (F) confirmed normal anatomy (arrow), and acquisition of single lumen was performed.

View larger version (127K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 5E —30-year-old male liver donor who underwent single lumen acquisition during right lobe harvest. Two-dimensional T2 MR cholangiography (MRC) (A), maximum-intensity-projection (MIP) image of 3D T2 MRC (B), source image of 3D T2 MRC (C), MIP image of 3D contrast-enhanced T1 MRC (D), and source image of 3D contrast-enhanced T1 MRC (E) show normal anatomy in which junction of anterior segmental duct and posterior segmental duct forms right hepatic duct (arrow). All reviewers predicted that acquisition of single lumen would be possible during right lobe harvesting on sets of all four techniques. Intraoperative cholangiogram (F) confirmed normal anatomy (arrow), and acquisition of single lumen was performed.

View larger version (90K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 5F —30-year-old male liver donor who underwent single lumen acquisition during right lobe harvest. Two-dimensional T2 MR cholangiography (MRC) (A), maximum-intensity-projection (MIP) image of 3D T2 MRC (B), source image of 3D T2 MRC (C), MIP image of 3D contrast-enhanced T1 MRC (D), and source image of 3D contrast-enhanced T1 MRC (E) show normal anatomy in which junction of anterior segmental duct and posterior segmental duct forms right hepatic duct (arrow). All reviewers predicted that acquisition of single lumen would be possible during right lobe harvesting on sets of all four techniques. Intraoperative cholangiogram (F) confirmed normal anatomy (arrow), and acquisition of single lumen was performed.

View larger version (117K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 6A —38-year-old male liver donor who underwent dual-lumen acquisition during harvesting of right lobe. Right anterior and posterior segmental branches do not seem to be separated on 2D T2 MR cholangiography (MRC) (A) image. Two reviewers incorrectly interpreted that single lumen acquisition would be possible. However, maximum-intensity-projection (MIP) images of 3D T2 MRC (B) and 3D contrast-enhanced T1 MRC (C) depicted well absence of common right hepatic duct (arrowhead,B and C, right anterior segmental duct; arrow,B and C, right posterior segmental duct). Dual-lumen acquisition was performed during right lobe harvesting.

View larger version (106K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 6B —38-year-old male liver donor who underwent dual-lumen acquisition during harvesting of right lobe. Right anterior and posterior segmental branches do not seem to be separated on 2D T2 MR cholangiography (MRC) (A) image. Two reviewers incorrectly interpreted that single lumen acquisition would be possible. However, maximum-intensity-projection (MIP) images of 3D T2 MRC (B) and 3D contrast-enhanced T1 MRC (C) depicted well absence of common right hepatic duct (arrowhead,B and C, right anterior segmental duct; arrow,B and C, right posterior segmental duct). Dual-lumen acquisition was performed during right lobe harvesting.

View larger version (97K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 6C —38-year-old male liver donor who underwent dual-lumen acquisition during harvesting of right lobe. Right anterior and posterior segmental branches do not seem to be separated on 2D T2 MR cholangiography (MRC) (A) image. Two reviewers incorrectly interpreted that single lumen acquisition would be possible. However, maximum-intensity-projection (MIP) images of 3D T2 MRC (B) and 3D contrast-enhanced T1 MRC (C) depicted well absence of common right hepatic duct (arrowhead,B and C, right anterior segmental duct; arrow,B and C, right posterior segmental duct). Dual-lumen acquisition was performed during right lobe harvesting.

View larger version (34K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 4B —Multiple comparisons of mean accuracy and diagnostic confidence for four sets of MR cholangiography (MRC) imaging techniques. Technique 1 = 2D T2 MRC alone, technique 2 = combined set of 2D T2 MRC and 3D T2 MRC, technique 3 = combined set of 2D T2 MRC and 3D contrast-enhanced T1 MRC, and technique 4 = combined set of all three techniques. Error bars indicate SD; asterisk indicates p < 0.05 in comparison of techniques. No significant difference was observed within comparison of combined sets for both accuracy and diagnostic confidence. Graph shows mean diagnostic confidence of 2D MRC alone and three combined sets for prediction of ductal orifice number during right lobe harvesting.

View larger version (101K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 7A —21-year-old male liver donor with normal biliary anatomy. On 2D T2 MR cholangiography (MRC) image, right ductal anatomy is not well delineated. All three reviewers had relatively lower confidence.

View larger version (111K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 7B —21-year-old male liver donor with normal biliary anatomy. All three reviewers had relatively lower confidence, but all techniques combined showed relatively higher confidence grade in predicting single lumen acquisition: maximum-intensity-projection (MIP) image of 3D T2 MRC (B); source image of 3D T2 MRC (C); source image of 3D contrast-enhanced T1 MRC (D). Arrowhead indicates anterior segmental branch, short arrow indicates posterior segmental branch, and long arrow indicates right hepatic duct.

View larger version (110K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 7C —21-year-old male liver donor with normal biliary anatomy. All three reviewers had relatively lower confidence, but all techniques combined showed relatively higher confidence grade in predicting single lumen acquisition: maximum-intensity-projection (MIP) image of 3D T2 MRC (B); source image of 3D T2 MRC (C); source image of 3D contrast-enhanced T1 MRC (D). Arrowhead indicates anterior segmental branch, short arrow indicates posterior segmental branch, and long arrow indicates right hepatic duct.

View larger version (135K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 7D —21-year-old male liver donor with normal biliary anatomy. All three reviewers had relatively lower confidence, but all techniques combined showed relatively higher confidence grade in predicting single lumen acquisition: maximum-intensity-projection (MIP) image of 3D T2 MRC (B); source image of 3D T2 MRC (C); source image of 3D contrast-enhanced T1 MRC (D). Arrowhead indicates anterior segmental branch, short arrow indicates posterior segmental branch, and long arrow indicates right hepatic duct.

View larger version (95K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 7E —21-year-old male liver donor with normal biliary anatomy. Intraoperative cholangiogram confirmed normal anatomy, and acquisition of single lumen was performed. Arrowhead indicates anterior segmental branch, short arrow indicates posterior segmental branch, and long arrow indicates right hepatic duct.

Discussion

Top Abstract Introduction Materials and Methods Results Discussion References

 
The results of the present study showed that 3D T2 MRC enables significantly better visualization of all bile ducts than 2D T2 MRC or 3D contrast-enhanced T1 MRC. Three-dimensional MR techniques of these MRC examinations have potential advantages over 2D imaging including the capacity to provide thinner sections without interslice gaps and a higher signal-to-noise ratio (SNR). These advantages of the 3D T2 MRC may be the reason that it showed better visualization of all bile ducts than 2D T2 MRC. However, the 3D contrast-enhanced T1 MRC showed lesser visualization grade than 2D MRC despite the 3D acquisitions that were used. This result is curious and seemingly contradictory to the previous report [9] that there was no difference in biliary visualization between excretory T1-weighted MRC and 2D T2 MRC. Such a discrepancy may be caused by the differences in the biliary segments included. Papanikolaou et al. [9] included only the extrahepatic bile duct for comparison of biliary visualization. In the common duct visualization of our study, there was no significant difference in visualization between 2D T2 MRC and contrast-enhanced T1 MRC, similar to their results. In addition, this discrepancy might be attributed to the use of ultralong echo-trains in turbo spin-echo sequences on T2 MRC that provide selective ductal visualization with better background suppression in comparison with T1-weighted imaging [8].

In terms of image quality, our results also showed that 3D contrast-enhanced T1 MRC could produce better image quality than 2D T2 MRC or 3D T2 MRC. Recently, several studies on 3D contrast-enhanced T1 MRC have reported increased SNR relative to 2D T2 MRC [9, 10]. In addition, the better image quality in 3D contrast-enhanced T1 MRC may be due to lack of image blurring related to long echo-trains and artifacts by overlapping fluid-containing structures. A lesser degree of respiration artifacts than occurs in 3D T2-weighted imaging, which requires longer acquisition time, may be another causative factor. Between 2D T2 MRC and 3D T2 MRC, there was no significant difference of overall image quality. Although a breath-holding technique for the acquisition of 2D T2 MRC could have provided better image quality than 3D T2 MRC, higher SNR and better resolution in 3D T2 MRC might play a complementary role in improving overall image quality.

With regard to the prediction of the number of bile duct orifices exposed and requiring anastomosis during the right lobe harvest, our study results showed that the combination of two or three imaging techniques (2D T2 MRC and 3D T2 MRC or 2D T2 MRC and 3D contrast-enhanced T1 MRC or all three imaging techniques) may significantly improve the accuracy and confidence for predicting the number of bile duct orifices exposed compared with 2D T2 MRC alone. The advantages of 3D imaging such as 3D T2 MRC or 3D contrast-enhanced T1 MRC included higher spatial resolution when compared with 2D T2 MRC. The complex orthogonal relationships between the right anterior duct, right posterior duct, left hepatic duct, and common hepatic duct make it difficult to predict the orifice number with confidence on conventional 2D MR images. The higher spatial resolution of 3D imaging can be helpful when, for example, distinguishing among a normal short right hepatic duct (candidate for single lumen acquisition), trifurcation (possible candidate for single lumen acquisition), and right anterior or posterior duct draining into the left hepatic duct (which requires dual lumen acquisition during right lobe harvesting) and consequently selecting the appropriate patient and surgical plan.

Several studies have reported the usefulness of the combination of 2D T2-weighted imaging and mangafodipir trisodium MR cholangiography for making a better evaluation of the hilar bile duct anatomy [5, 11, 12]. However, this approach requires the combined use of two different contrast agents (manganese agent for MRC and gadolinium-based agent for MR angiography). The combination of imaging techniques in our study (3D T2 MRC and 3D contrast-enhanced T1 MRC) did not require the additional contrast agent for MR angiography because ductal anatomy can be depicted on the delayed phase images obtained after MR angiography acquisition using gadobenate dimeglumine as the contrast agent.

Nevertheless, the use of the added imaging techniques is not without potential disadvantages. The additional imaging sequences inevitably require additional acquisition time. Particularly, the 3D contrast-enhanced T1 MRC requires a 60- to 90-minute delay for biliary contrast agent excretion before imaging. In the comparison between the three combined sets (2D T2 MRC and 3D T2 MRC or 2D T2 MRC and 3D contrast-enhanced T1 MRC or all three imaging techniques), there was no significant difference. Therefore, it may be more logical to acquire the added sets of 3D T2 MRC than the added sets of 3D contrast-enhanced T1 MRC or both sequences. Contrast-enhanced T1 MRC may be limitedly helpful only when both 2D and 3D T2 MRC findings have poor imaging quality with severe artifacts.

Our study has some limitations. First, our study population was relatively small. Second, for biliary ductal visualization, we compared 3D images (3D T2 MRC and 3D contrast-enhanced T1 MRC) only with an established thick-slab heavily T2-weighted method [13, 14] and not with conventional 2D single-shot half-Fourier turbo spin-echo images. Usually, 2D T2 MRC may include either a thick-slab method or thin single-shot half-Fourier turbo spin-echo images. However, the addition of a thin-slice 2D T2 MRC sequence to thickslice 2D T2 MRC would further increase the examination time for the 2D T2 MRC and may not be appropriate for our aim of evaluating the biliary visualization of three comparable MR sequences.

In summary, we have shown that 3D T2 MRC significantly enables the best visualization of all bile ducts, and 3D contrast-enhanced T1 MRC provides the best image quality. For predicting the number of orifices as the ultimate goal of the ductal visualization, the combined set of 2D and 3D T2 MRC enabled better accuracy and diagnostic confidence than 2D T2 MRC alone and produced comparable results to other combined sets. Therefore, we suggest the combination sets of 2D T2 MRC and 3D T2 MRC for the preoperative biliary anatomy evaluation of living liver donor candidates for right lobe harvesting.

References

Top Abstract Introduction Materials and Methods Results Discussion References

 

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