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1
Department of Radiology, Medical College of Virginia of Virginia Commonwealth
University, 401 N. 12th St., Rm. 3-407B, P. O. Box 980615, Richmond, VA
23298-0615.
2
Present address: Department of Radiology, St. Mary's Hospital, 5875 Bremo Rd.,
South Bldg., G-6, Richmond, VA 23229.
3
Present address: Department of Radiology, University of Virginia Health
Sciences Center, Lee St., Rm. 1075, Charlottesville, VA 22908.
4
Present address: Department of Surgery, University of Rochester Medical
Center, 601 Elmwood Ave., Rm. 2-6114A, Rochester, NY 14642.
Received August 17, 2000;
accepted after revision November 7, 2000.
Address correspondence to A. S. Fulcher.
Abstract
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MATERIALS AND METHODS. Twenty-eight right hepatic lobe donors underwent preoperative evaluation with MR imaging, MR cholangiography, and MR angiography. Two abdominal radiologists independently and randomly reviewed these studies. Points of assessment included focal and diffuse liver disease, calculation of right lobe volumes, depiction of the biliary tract and ductal anomalies, and depiction of the liver vasculature and vascular anomalies. Comparison was made with intraoperative cholangiograms (n = 20) and digital subtraction angiograms (n = 28).
RESULTS. MR imaging revealed and characterized focal liver lesions in eight of 28 patients. Calculated right lobe volumes agreed with surgically determined volumes within 7% for reviewer 1 and within 15% for reviewer 2. Intrahepatic bile ducts were depicted completely with MR cholangiography in 25 of 28 patients and with intraoperative cholangiography in nine of 20 patients. MR cholangiography revealed ductal anomalies in six patients. MR imaging and MR angiography depicted the portal veins more completely than digital subtraction angiography. MR imaging and MR angiography correctly excluded portal venous anomalies in all patients and revealed surgically confirmed accessory hepatic veins in six of 28 patients. Angiographically confirmed arterial anomalies were correctly detected in three of 28 patients by at least one reviewer on MR imaging and MR angiography.
CONCLUSION. MR imaging, MR cholangiography, and MR angiography provide a comprehensive, accurate means of evaluating donors for factors that may preclude or complicate right hepatic lobe donation.
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Adult-to-adult right lobe living donor liver transplantation, which entails resection of the right hepatic lobe from a living donor, is emerging as a viable alternative to cadaveric, left lobe, and split liver transplantation [6, 8,9,10,11,12]. Preoperative evaluation of the donor is required to exclude focal hepatic masses, diffuse disease of the hepatic parenchyma such as steatosis, vascular abnormalities such as portal vein thrombosis, vascular anomalies, and anomalies of the biliary tract that might complicate right hepatic lobe resection and transplantation. Accurate preoperative determination of liver volume is essential to ensure that an adequate volume of liver is resected for the recipient and that an adequate volume remains for the donor [13, 14]. Therefore, a noninvasive, comprehensive means of evaluating donors for factors that would preclude or complicate right hepatic lobe donation is sought.
The purpose of this study was to report our experience in the preoperative evaluation of 28 right hepatic lobe donors with MR imaging, MR cholangiography, and MR angiography and to compare these findings with findings at surgery, intraoperative cholangiography, and digital subtraction angiography.
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Imaging Techniques
Abdominal MR imaging.—MR imaging of the abdomen was
performed with a 1.0-T Magnetom Expert (Siemens, Erlangen, Germany) with a
maximum gradient strength of 20 mT/min and a rise time of 1 msec. A phased
array body coil was used in all cases. MR sequences included unenhanced
T1-weighted breath-hold spoiled gradient echo (TR/TE, 48/5; flip angle,
70°; slice thickness, 10 mm; gap, 30%; field of view, 300 mm; number of
acquisitions, 1; matrix, 112 x 256), unenhanced and enhanced T1-weighted
breath-hold fat suppression (200/4.4; flip angle, 70°; slice thickness, 8
mm; gap, 20%; field of view, 380 mm; number of acquisitions, 1; matrix, 128
x 256), and unenhanced T2-weighted breath-hold fast spin echo
(TR/TEeff, 3500/138; slice thickness, 8 mm; gap, 25%; field of
view, 350 mm; number of acquisitions, 1; matrix, 116 x 256; echo train
length, 29). Gadolinium (Magnevist; Berlex, Wayne, NJ) was IV administered in
a dose of 0.1 mmol/kg as a bolus followed by a normal saline flush. Dynamic
imaging of the liver was conducted with the previously described T1-weighted
breath-hold fat-suppressed sequence immediately after gadolinium
administration as well as at 1, 3, and 5 min after the administration of
gadolinium.
MR cholangiography.—MR cholangiography was performed with a half-Fourier rapid acquisition with relaxation enhancement (RARE) sequence. The biliary tract was localized with thick-slab (40-mm) rapid acquisition with relaxation enhancement images in coronal-oblique (25°) and axial planes.
The thick-slab images were then used as guides to evaluate the biliary tract with half-Fourier RARE thin-slab (5-mm) images in the coronal-oblique plane oriented parallel to the longitudinal axis of the extrahepatic bile duct. The thin-slab MR cholangiographic acquisitions were obtained at various angles that allowed optimal visualization of the bile duct. The thin-slab parameters included TR/TEeff, infinite, 88.0; refocusing flip angle, 140°; slice thickness, 5 mm with no gap; field of view, 270 x 270 mm; number of acquisitions, 1; matrix, 240 x 256; and acquisition time, 18 sec. Thirteen images were obtained during each 18-sec acquisition. Fat saturation and shim adjust were used in all cases. Postprocessing techniques were not used. Both the thick-slab and thin-slab images were obtained during breath-hold. The patients did not fast before MR cholangiography. Antiperistaltic agents were not used.
MR angiography.—MR angiography was conducted in the coronal plane with a two-dimensional time-of-flight sequence. The MR angiogram parameters included the following: TR/TEeff, 50/9.8; flip angle, 30°; slice thickness, 5 mm; overlap, 20%; field of view, 450 x 450 mm; number of acquisitions, 1; matrix, 220 x 256; and acquisition time, 13 sec for each section. Maximum-intensity-projection images were generated from the source images.
Intraoperative cholangiography.—Intraoperative cholangiography was performed by transplant surgeons who cannulated the cystic duct and injected diatrizoate meglumine (Hypaque-Cysto; Nycomed, Princeton, NJ) under fluoroscopic control before right hepatic lobe resection. An attempt was made in all patients to opacify the intrahepatic and extrahepatic bile ducts. Selected images of the biliary tract were recorded on film.
Digital subtraction angiography.—Digital subtraction angiograms of the abdominal aorta, celiac axis, and superior mesenteric artery were conducted by one of three angiographers using standard angiographic techniques on an angiography machine (DFP-2000A; Toshiba Medical Systems, Irvine, CA). The portal vein was evaluated with delayed images obtained after selective catheterization of the superior mesenteric artery and celiac axis and the administration of 50 mg of papaverine.
Image Analysis
The abdominal MR images, MR cholangiograms, and MR angiograms were
interpreted independently and randomly by two abdominal radiologists who were
unaware of patient identification and the findings at intraoperative
cholangiography and digital subtraction angiography. The images were reviewed
at an interactive workstation. The same two radiologists then conducted
independent, random reviews of the intraoperative cholangiograms and digital
subtraction angiograms. To avoid memory—recollection bias, a minimum of
8 weeks separated the reviews of the MR images, MR cholangiograms, and MR
angiograms and the reviews of the intraoperative cholangiograms and digital
subtraction angiograms. All findings were recorded in an electronic database.
At the time of this study, one of the study radiologists had practiced for 5
years and the other for 10 years as abdominal radiologists.
Abdominal MR images and volumetric analysis.—The abdominal MR images were evaluated for focal and diffuse abnormalities of the hepatic parenchyma as well as for depiction of the main, right, and left portal veins; the right, middle, and left hepatic veins; the origin of the common hepatic artery; the presence of inferior accessory right hepatic veins and anomalous unions of the right and middle hepatic veins; and hepatic artery variants such as replaced right hepatic arteries. Depiction of the vessels was graded using the following scale: excellent (complete depiction), good (depiction of 90% or more of the vessel), fair (depiction of less than 90% of the vessel), and nonvisualization (failure to depict any portion of the vessel). Discrepancies involving the degree of vessel depiction were resolved by consensus.
Volumetric analysis of the right hepatic lobe, medial and lateral segments of the left hepatic lobe, and caudate lobe was conducted independently by each of the two study radiologists. The radiologists identified the boundaries of the lobes and segments on enhanced T1-weighted, fat-suppressed images using vascular landmarks, and they electronically traced the margins of the hepatic lobes and segments on each of the axial images (Fig. 1A,1B,1C,1D). Areas (cm2) were automatically calculated using software available on the scanner for the regions of interest on each slice. The areas on each of the slices were added and multiplied by the slice thickness plus the gap (cm) yielding a volumetric measurement in cubic centimeters. The volumes calculated by the two radiologists for the right hepatic lobes were compared with the weight of the exsanguinated, resected right hepatic lobe measured to the nearest gram. One gram of liver was presumed to be equivalent to 1 mL of calculated liver volume [15].
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MR cholangiograms and intraoperative cholangiograms.—The MR cholangiograms and intraoperative cholangiograms were evaluated for depiction of the central right and left hepatic ducts using the following scale: excellent (complete depiction), good (depiction of 90% or more of the central ducts), fair (depiction of less than 90% of the central ducts), and nonvisualization (failure to depict any portion of the central ducts). Discrepancies between the two radiologists involving the degree of ductal depiction were resolved by consensus. An assessment was also made by the two radiologists for the presence and types of ductal anomalies.
MR angiograms and digital subtraction angiograms.—The MR angiograms and the digital subtraction angiograms were evaluated for depiction of the main, right, and left portal veins and the origin of the common hepatic artery. The MR angiograms were evaluated for depiction of the right, middle, and left hepatic veins. The same grading scale used for depiction of the vessels at abdominal MR imaging was used for this assessment. Discrepancies between the two radiologists involving the degree of vessel depiction were resolved by consensus.
The MR angiograms and digital subtraction angiograms were also evaluated for patency of the portal veins and common hepatic artery, and for the presence of anomalies. In addition, the MR angiograms were evaluated for patency of the hepatic veins, anomalous unions of the right and middle hepatic veins, and inferior accessory right hepatic veins.
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Volumetric Analysis of Right Hepatic Lobe
The volumes of the resected right hepatic lobes determined by weighing the
exsanguinated livers in the operating room differed from the calculated
volumes by a mean of 66 mL (range, 4-315 mL) or a mean percentage of 7%
(range, 0.5-30%) for reviewer 1 and by a mean of 147 mL (range, 9-361 mL) or a
mean percentage of 15% (range, 1-36%) for reviewer 2.
The calculated volumes exceeded the surgically determined volumes in 21 of 28 patients for reviewer 1 and in all 28 patients for reviewer 2. Both reviewers 1 and 2 overestimated the right lobe volumes by more than 20% in three patients. Review of the volumetric analysis in these three patients revealed that the course of the middle hepatic vein was not completely visualized near the dome of the liver. Therefore, the radiologists were forced to extrapolate the middle hepatic vein course on the basis of images obtained inferior to the hepatic dome in these three patients. In no patient was the overestimation or underestimation of calculated volume sufficient to preclude right lobe resection. Hepatic dysfunction did not occur in any of the 28 donors or recipients after right lobe resection or after transplantation.
In the seven patients in whom reviewer 1 underestimated right lobe volume, the calculated and the surgically determined volumes differed by a mean of 66 mL (range, 3-135 mL) and a mean percentage of 5% (range, 1-5%). The underestimation of volume is attributed to the need in some instances to estimate the medial margin of the right hepatic lobe near the dome of the liver where the course of the middle hepatic vein may not be well defined.
Evaluation of the Biliary Tract
The MR cholangiograms permitted excellent depiction of the central
intrahepatic ducts in 25 of 28 patients and good visualization in the
remaining three patients. Intraoperative cholangiograms were available for
comparison in 20 of the 28 patients. In contrast to the MR cholangiograms, the
intraoperative cholangiograms permitted depiction of the central intrahepatic
ducts as follows: excellent (n = 9), good (n = 5), fair
(n = 5), and no visualization (n = 1). Two discrepancies
occurred between the two reviewers in the analysis of depiction of the central
bile ducts on MR cholangiography. Reviewer 1 rated the depiction as excellent
in two donors, whereas reviewer 2 rated the depiction as good. The reviewers
agreed in all instances regarding the degree of ductal depiction at
intraoperative cholangiography.
Of the 20 intraoperative cholangiograms available for review, three revealed trifurcation anomalies. Both reviewers 1 and 2 detected the three trifurcation anomalies at MR cholangiography (Fig. 2). Reviewer 1 noted accessory hepatic ducts that drained a small portion of the right hepatic lobe and entered the extrahepatic bile duct distal to the confluence in three patients; all were confirmed at intraoperative cholangiography and measured 1-2 mm in diameter. In one of the three patients with an accessory right hepatic duct, there was also noted at MR cholangiography a duct draining segment IV that entered the right hepatic duct; this anomaly was confirmed at intraoperative cholangiography. Reviewer 2 noted none of the three small accessory ducts or the aberrant hepatic duct. Both reviewers 1 and 2 noted a dorsocaudal branch of the right hepatic duct that crossed the midline to enter the central left hepatic duct (Fig. 3). Although the intraoperative cholangiogram was not available for this patient, this finding was confirmed at surgery. In another patient, a 1-mm dorsocaudal branch of the right hepatic duct was shown to enter the central left hepatic duct at intraoperative cholangiography but was not identified by reviewer 1 or 2 prospectively at MR cholangiography or even when the MR cholangiogram was reviewed in retrospect.
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Evaluation of the Hepatic Vasculature
The abdominal MR images and MR angiograms provided more complete depiction
of the main portal vein and its intrahepatic branches than did digital
subtraction angiography (Table
1). No discrepancies occurred between the two reviewers regarding
the depiction of the portal veins. The MR images and MR angiograms allowed
determination of patency of the portal veins (Fig.
4A,4B)
and showed patent main, right, and left portal veins in all patients; these
findings were confirmed with digital subtraction angiography. No portal vein
anomalies such as trifurcations were detected with MR imaging, MR angiography,
or digital subtraction angiography.
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The hepatic veins were depicted well with MR angiography and MR imaging; the hepatic veins were, of course, not shown with digital subtraction angiography (Table 1). A single discrepancy occurred between the two reviewers regarding depiction of the hepatic veins. Specifically, reviewer 1 rated depiction of the middle hepatic vein as excellent with MR angiography in one donor, whereas reviewer 2 rated the depiction as good. Lack of depiction of the left hepatic vein occurred in one of 28 patients at MR angiography and was related to failure to scan through the anterior aspect of the liver and the left hepatic vein. No anomalous unions of the right and middle hepatic veins were detected. Accessory right hepatic veins were identified in six of 28 patients by both reviewers on MR imaging and at MR angiography and were confirmed surgically (Figs. 5 and 6).
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The common hepatic arteries were identified completely in 26 of 28 patients with MR imaging, in 28 of 28 patients with MR angiography, and in 27 of 28 patients with digital subtraction angiography (Table 1). Minimal discrepancies occurred between the two reviewers in this analysis. Specifically, reviewer 1 rated depiction of the common hepatic artery as good in two patients with MR angiography, whereas reviewer 2 rated the depiction as excellent in these patients. In all other cases, the reviewers agreed. A replaced common hepatic artery was identified in one patient by both reviewers at MR angiography and on MR imaging and was confirmed with digital subtraction angiography (Fig. 7A,7B). Reviewer 1 detected replaced right hepatic arteries in two patients with MR angiography and MR imaging and these findings were confirmed at digital subtraction angiography; reviewer 2 did not detect the replaced right hepatic arteries. Reviewer 1 had one false-positive diagnosis of a replaced right hepatic artery with MR angiography; reviewer 2 had no false-positive diagnoses. Segment IV arteries arising from the right hepatic artery were not identified in any patient at MR angiography or digital subtraction angiography by reviewer 1 or 2.
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Before transplantation, potential donors undergo extensive evaluation with the intent of minimizing complications in the healthy donor and optimizing graft function in the recipient. Although donor evaluation protocols vary among institutions, in general, preoperative assessment of the donor is conducted in a series of steps beginning with simple and noninvasive examinations and progressing to more complex and invasive procedures [10]. At our institution, donor evaluation begins with a screening history and physical examination, a battery of laboratory tests, psychologic assessment, and cardiac and pulmonary function tests. On successful completion of these initial steps in the process, donors undergo liver biopsy to determine the presence and amount of steatosis, and they undergo radiologic studies.
The radiologic component of donor evaluation is pivotal in donor selection and exclusion. Its first objective is to detect factors that would preclude or complicate right hepatic resection and transplantation. Another major objective is to determine the volume of the right hepatic lobe, as well as the left hepatic lobe and caudate lobe, to ensure adequate hepatic function in the recipient and donor. CT and CT angiography may be used to assess donors for focal and diffuse liver disease and vascular abnormalities and anomalies, and to calculate liver volumes. Kamel et al. [16] report that multidetector helical CT performs well in this capacity, allowing accurate calculation of liver volume and permitting visualization of third-order intrahepatic arteries. However, CT requires exposure of healthy donors to ionizing radiation and nephrotoxic contrast material. In addition, CT does not provide information about intrahepatic bile duct anomalies unless performed with orally administered biliary contrast agents.
In our series of 28 donors, the final step in their preoperative assessment was a radiologic evaluation that comprised a comprehensive MR examination and digital subtraction angiography. The comprehensive MR examination included abdominal MR imaging for detection of focal and diffuse liver disease and for volumetric assessment of the liver; MR cholangiography for detection of biliary anomalies; and MR angiography for determination of patency and anomalies of the portal veins, hepatic veins, and hepatic arteries. Digital subtraction angiography was performed specifically to evaluate the arterial supply to segment IV.
In assessment of the liver parenchyma for focal lesions, MR imaging has been shown to be accurate for detecting and characterizing liver lesions [17,18,19]. In our series, simple cysts and hemangiomas were detected in five of 28 patients. Because MR imaging revealed signal intensity and morphologic features characteristic of these lesions, biopsy was avoided, and each of the five patients underwent right lobe donation. However, hepatic lesions that cannot be fully characterized with MR imaging require additional imaging or biopsy before donation. Because potential liver donors may undergo liver biopsy for quantification of steatosis before undergoing MR imaging, biopsy defects may be observed. Confusion of these defects with neoplasia can be avoided by noting that the biopsy defects appear as linear configurations, occur in the periphery of the middle and inferior thirds of the right hepatic lobe, and show no evidence of enhancement.
Donors must be evaluated not only for focal liver lesions, but also for the presence and extent of hepatic steatosis. Marsman et al. [20] note that the acceptable upper limit of steatosis in a donor liver is 30%; liver grafts with greater than 30% steatosis are at risk for dysfunction and nonfunction in the recipient. In the current series, a quantitative MR assessment for hepatic steatosis was not conducted because percutaneous biopsy was performed as part of the preoperative donor evaluation. It is possible that in-phase and opposed-phase MR sequences [21] and MR spectroscopy [22,23,24] may be of value in the quantification of steatosis. If additional, larger studies confirm the accuracy of MR imaging in the quantification of steatosis, MR imaging may render the performance of liver biopsy unnecessary.
A critical component of donor evaluation is determination of liver volume. Specifically, the volume of the resected right hepatic lobe and the volume of the remainder of the liver must be adequate to provide function in the recipient and donor, respectively. Although neither the minimum hepatic volume nor the optimal hepatic volume has been determined, graft-to-recipient body weight ratios have been used to predict graft function in the recipient. Kiuchi et al. [14] note that small-for-size grafts that represent less than 1% of the recipient's body weight are predisposed to lower graft survival than larger grafts, likely related to diminished metabolic and synthetic capacity. In the case of donors, Fan et al. [12] report that the remnant liver must equal at least 30% of the total liver volume to ensure function in the donor.
Sonography and CT have been used to successfully calculate liver volumes [15, 16, 25,26,27]. In our series, the MR imaging—determined right hepatic lobe volumes differed from the surgically determined volumes by a mean of 7% for reviewer 1 and by 15% for reviewer 2. In most instances, the calculated volume exceeded the surgically determined volume. In part, this overestimation is related to the surgeon's weighing the liver after the blood has been drained from it. Another factor that may contribute to the overestimation of volume may be related to the radiologist's drawing the margin of the right hepatic lobe immediately adjacent to the lateral margin of the middle hepatic vein. In contrast, the surgeon places the resection plane 1 cm lateral to the middle hepatic vein.
When using MR imaging to calculate liver volumes, radiologists should be aware of at least two sources of potential error. One source of error occurs in patients with large or elongated livers that may not be imaged on a single acquisition. When more than one acquisition is required to image the entire liver, the radiologist must ensure that volume calculations are not made using redundant sections because this would result in overestimation of volume. Likewise, one must also ensure that all portions of the liver are included on the two acquisitions to avoid underestimation of volume. A second source of error that may result in underestimation or overestimation of volume is related to the need to approximate the courses of the hepatic veins at the dome of the liver where the veins may not be visualized entirely or at all.
In addition to the liver parenchyma and liver volume, another important facet of right lobe donor evaluation is the biliary tract. Variations in the branching pattern of the intrahepatic bile ducts are common. In only 63% of cases is the normal branching pattern of the intrahepatic bile ducts observed [28]. This so-called normal pattern involves joining of the ventrocranial and dorsocaudal branches to form the right hepatic duct; the right hepatic duct in turn joins with the left hepatic duct to form the common hepatic duct. Although most biliary variants are of no consequence in the general population, some variants assume greater significance in the setting of right hepatic lobe resection. Such variants include a trifurcation anomaly, an accessory right hepatic duct, and a dorsocaudal branch of the right hepatic duct draining into the left hepatic duct. Although such variants do not usually preclude right lobe resection, their identification before resection prevents inadvertent ligation of major branches draining the right hepatic lobe or the remnant liver that would lead to atrophy of the involved portions of the liver.
Intraoperative cholangiography is the traditional method used to map the anatomy of the biliary tract before right hepatic lobe resection. Alternatively, MR cholangiography may also be used to detect variations in the branching pattern of intrahepatic bile ducts [29]. When the technique is optimized, intraoperative cholangiography provides high-quality images of the biliary tract. However, because of limitations imposed by the operative setting, the quality of intraoperative cholangiograms may be less than optimal. In the current series, only nine (45%) of the 20 intraoperative cholangiograms available for review permitted complete depiction of the central right and left hepatic ducts. In contrast, 25 (89%) of the 28 MR cholangiograms allowed complete depiction of the central ducts. In the assessment of ductal variants, all trifurcation anomalies and all accessory right hepatic ducts were identified by at least one reviewer at MR cholangiography. MR cholangiography failed to depict a 1-mm dorsocaudal branch of a right hepatic duct entering the left hepatic duct in one patient. With continued improvements in MR software and hardware, MR cholangiography has the potential to eventually replace intraoperative cholangiography in the setting of right lobe resection and thereby to reduce operative time.
In the evaluation of the hepatic vasculature, MR imaging and MR angiography provided better depiction of the main, right, and left portal veins compared with digital subtraction angiography. Unlike digital subtraction angiography, MR imaging and MR angiography permit depiction of the hepatic veins including anomalous unions of the hepatic veins and the presence of accessory hepatic veins. The value of MR imaging has been noted in the evaluation of hepatic veins in donors before left lobectomy or left lateral sementectomy for living liver transplantation [30]. In the detection of accessory hepatic veins, MR imaging and MR angiography performed equally well. At our institution, the detection of accessory right hepatic veins measuring 5 mm or greater in diameter is important because they are anastomosed to the inferior vena cava. However, because the hepatic veins and accessory hepatic veins were equally well depicted with MR imaging and MR angiography, the performance of MR imaging alone may be sufficient.
The common hepatic arteries were essentially equally well visualized with MR imaging, MR angiography, and digital subtraction angiography. The one replaced common hepatic artery and the two replaced right hepatic arteries that occurred in our series were identified both with MR imaging and MR angiography by at least one reviewer. However, a false-positive diagnosis of a replaced right hepatic artery was made by one reviewer in one of 28 patients. Regardless of the accuracy of MR imaging and MR angiography in the depiction of the portal veins and the common hepatic arteries, the performance of digital subtraction angiography is often required to depict the arterial supply to segment IV, which arises from the right hepatic artery in approximately 11% of patients [31]. Preservation of the vascular supply to segment IV is mandatory to ensure function of this segment in the donor [11].
The spatial resolution of the two-dimensional time-of-flight sequence used in the present study is not sufficient to detect such small vessels. We chose to use this unenhanced MR angiographic technique instead of an enhanced gradient-echo technique to reserve the use of gadolinium for evaluation of the liver for focal lesions and to allow optimal opacification of the hepatic veins. Optimal enhancement of the hepatic veins is important in the calculation of liver volume because the veins serve as markers for the boundaries of the hepatic lobes and segments. In addition, optimal enhancement of the hepatic veins on the axial images of the liver permits detection of anomalous unions of the right and middle hepatic veins that might complicate right hepatic lobe resection. However, newer techniques such as dynamic contrast-enhanced isotropic three-dimensional volumetric interpolated breath-hold MR imaging that permit simultaneous acquisition of parenchymal and angiographic images may allow detection and characterization of focal liver lesions and depiction of hepatic veins and small intrahepatic arterial branches with a single contrast dose [32]. If so, the performance of digital subtraction angiography may not be required.
In summary, although the data supporting MR imaging for the preoperative evaluation of liver donors requires validation in larger patient populations and multicenter trials, MR imaging, MR cholangiography, and MR angiography provide a comprehensive, accurate means of preoperatively evaluating donors for factors that may preclude or complicate right hepatic lobe donation and transplantation. Continued improvements in the quality of MR images related to advances in MR hardware and software may make the performance of intraoperative cholangiography and digital subtraction angiography unnecessary.
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