“All-in-one” imaging protocols for the evaluation of potential living liver donors: Comparison of magnetic resonance imaging and multidetector computed tomography



In order to compare the performance of “all-in-one” magnetic resonance imaging (MRI) and “all-in-one” multidetector computed tomography (MDCT) in the preharvest evaluation 25 potential living donors underwent both MRI and MDCT. MRI was performed on a high-performance 1.5-T scanner, computed tomography (CT) on a 4-row multidetector-scanner. Both scan protocols included angiography of the arterial and venous hepatic systems. CT additionally included infusion of a biliary contrast agent. Data analysis was performed by 4 reviewers, based on source images, multiplanar reformats, and three-dimensional (3D) postprocessing. Determination of image quality was based on a 4-point image quality rating (IQR) scale, ranging from 1 = nondiagnostic to 4 = excellent. Preoperative and intraoperative (n = 13) findings were correlated. Magnetic resonance (MR) examinations were generally well tolerated. Within the CT scan, 2 candidates presented moderate adverse reaction to the biliary contrast agent. MRI and CT showed the same benign parenchymal lesions (IQR MR: 3.7; IQR CT: 3.4). Determination of liver volumes was easier based on CT (IQR MR: 3.3; IQR CT: 3.6). Magnetic resonance angiography (MRA) revealed 10 variants of the arterial liver supply (IQR: 3.0) and computed tomographic angiography (CTA) revealed 13 variants (IQR: 3.5). Magnetic resonance cholangiopancreatography (MRCP) identified 4 biliary variants (IQR: 1.3) and CT cholangiography identified 17 (IQR: 3.5). MRI and CT each showed 4 hepatic and portal venous variants (IQR MR: 3.4, CT: 2.8). CT and MR findings correlated well with intraoperative findings. In conclusion, both techniques proved to be efficient to evaluate potential living liver donors' anatomy in a single diagnostic step. The main advantage of CT lies in the ability to accurately assess the biliary anatomy. (Liver Transpl 2005;11:776–787.)

Living donor liver transplantation has evolved into a widely accepted therapeutic option to alleviate the persistent shortage of cadaveric liver transplants.1–3 This innovative procedure allows healthy adults to donate a portion of their liver to compatible recipients suffering from end-stage liver disease.4–7

Besides of augmenting the transplant organ pool, living donor liver transplantation involves the advantage of performing an elective operation, access to a graft in best condition, and lowering the likelihood of recipient death while waiting for a suitable organ.8 In combination with improved surgical technique and highly developed immunosuppression,9 this results in recipient survival rates as good as those obtained after conventional liver transplantation with full-sized deceased donor organs.10

The critical issue of this procedure is the risk to the donors, who were healthy until the transplantation; this risk is now estimated to be 0.5% mortality and 21% postoperative morbidity.1, 11, 12 To reduce such risk to a minimum, and also to avoid donor-recipient mismatch, the potential donors have to undergo an extensive stepwise evaluation process before being admitted to donation. Special attention is hereby paid to the determination of the liver volumes13–17 and the recognition of vascular anomalies.18–20 In fact, a majority of the candidates is eliminated mostly due to unfavorable hepatic parenchymal, biliary, or vascular morphology.

In the recent past, this preharvest assessment employed a multimodal radiologic evaluation protocol, including computed tomography (CT) or magnetic resonance imaging (MRI) for liver planimetry and exclusion of parenchymal lesions, catheter digital subtraction angiography for the display of the hepatic vascular system, endoscopic retrograde cholangiopancreatography for assessing the biliary anatomy and liver biopsy for the assessment of hepatic-cellular infiltration.21, 22

In an attempt to simplify and shorten such a time consuming and costly23 procedure to a minimum, both comprehensive “all-in-one” MRI and multidetector computed tomography (MDCT)-protocols have been advocated.24–28 Both approaches combine the advantage of minimal invasiveness with the simultaneous assessment of the hepatic parenchymal morphology and a detailed analysis of the biliary and vascular anatomy in a single diagnostic step.

Based on the preharvest evaluation of 25 potential living donors undergoing both MR and MDCT28 imaging, the purpose of this study was to compare both methods and to determine their specific advantages and disadvantages.


MR, magnetic resonance; MRI, magnetic resonance imaging; CT, computed tomography; MDCT, multidetector computed tomography; 3D, 3-dimensional; IQR, image quality rating; MRA, magnetic resonance angiography; CTA, computed tomographic angiography; MRCP, magnetic resonance cholangiopancreatography; 2D, 2-dimensional; TR, time of repetition; TE, time of echo; T1, spin-lattice relaxation time; FLASH, fast low angle shot; True FISP, true fast imaging with steady-state precession; RARE, rapid acquisition with relaxation enhancement; T2, spin-spin relaxation time; Gd-BOPTA, gadolinium-BOPTA-gadobenate dimeglumine; HASTE, half-Fourier single shot turbo spin echo.

Patients and Methods

Patient Population

Between May and October of 2001, 25 consecutive potential living liver donors (age range: 20–55 years, mean: 33 years) were prospectively evaluated both with “all-in-one” MDCT and “all-in-one” MRI protocols for the liver. A total of 14 women (age range: 22–55 years, mean: 34 years) and 11 men (age range: 20–42 years, mean: 31 years) were enrolled in the study. This study was conducted in accordance with guidelines set forth by the local ethics committee. A total of 2 of the female candidates and 1 male candidate were evaluated for donation of a left lobe segment and underwent a digital subtraction angiography study in addition, which represented a mandatory step in the evaluation protocol for this sub-collective. For ethical reasons, in all other subjects the application of digital subtraction angiography and endoscopic retrograde cholangiopancreatography was limited to those, in whom multiphase MDCT and/or MR imaging was deemed insufficient to display the relevant vascular or biliary anatomy. Laboratory analysis had revealed normal liver function for all potential donors prior to the examinations.

The delay between both examination protocols ranged between 1 and 53 days (mean: 20.4) days. A total of 12 candidates obtained MDCT as the primary imaging study; in the remaining 13 subjects MRI was performed prior to MDCT.

CT Protocol

CT imaging was performed using a 4-row CT scanner (Volume-Zoom; Siemens, Erlangen, Germany). The protocol included successive acquisition of 3 image sets of the liver using the following parameters: 120 kVp, 150–180 mAs, collimated slice-thickness 1 mm, feed/rotation 6 mm, pitch 1.5. The in-plane matrix size was 512 × 512. Each image set was collected over 20 to 25 seconds. The “in-room” time was closely monitored.

The first CT image set was acquired 30 (±5) minutes following infusion of 100 mL of a biliary contrast agent (Biliscopin; Schering, Berlin, Germany) at a rate of 0.1 mL/s through a 20-gauge catheter placed in an antecubital vein. The agent was administered to opacify the biliary system, thus enabling a detailed appreciation of the contrast-enhanced intra- and extrahepatic biliary tree.

Subsequently, computed tomographic angiography (CTA) was performed for display of the arterial hepatic anatomy. For this purpose, 140 mL of an iodinated contrast agent (Imeron 350; Bracco SpA., Milan, Italy) was administered intravenously with an automated injector (CT9000; Liebel-Flarsheim, Cincinnati, OH) at a rate of 5 mL/s. Automated bolus tracking with bolus detection at the level of the ascending aorta assured accurate timing of an early arterial phase. For the display of the portal and hepatic venous anatomy, a third CT image set was acquired 25 seconds following the arterial data.

MR Protocol

MRI was performed on a 1.5-T scanner (Magnetom Sonata; Siemens, Erlangen, Germany), equipped with high-performance gradients (amplitude of 40 mT/m, slew rate of 200 mT/m/ms). A standard phased-array torso surface coil was used for signal reception. The scan protocol was based on a 32–36-cm field of view and included intravenous administration of Gd-BOPTA (Multihance; Bracco SpA.) at a dose of 0.2 mmol/kg body weight. The contrast agent was infused at a rate of 3 mL/s using an automated injector system (Spectris; Medrad, Pittsburgh, PA). The management of the contrast media included a test bolus technique in the aorta at the level of the celiac trunk to determine the arrival time of contrast for arterial enhancement29 and an intermittent 25-second delay before scanning the portal and hepatic venous systems.

The following sequences were acquired:

  • 1Axial T1-weighted two-dimensional (2D) FLASH (TR/TE: 110/2.0 ms, flip angle: 60°, 8-mm sections, matrix size: 256 × 256).
  • 2Axial T1-weighted TrueFISP (TR/TE: 3.5/1.7 ms, flip angle: 80°, 7-mm sections, matrix size: 256 × 256).
  • 3Axial T2-weighted 2D HASTE (TR/TE: 1,000/60 ms, flip angle: 160°, 8-mm sections, matrix size: 256 × 256).
  • 4Coronal HASTE for magnetic resonance cholangiopancreatography (MRCP) (TR/TE: 1,000/60 ms, section thickness: 8 mm, matrix size: 218 × 256).
  • 5Coronal RARE for MRCP (TR/TE: 2,800/1,100 ms, 1 80-mm section, matrix size: 240 × 512).
  • 6Coronal 3D FLASH for magnetic resonance angiography (MRA) (TR/TE: 2.4/1.0 ms, flip angle: 25°, 48 contiguous 2-mm sections, matrix size: 256 × 256, 1 arterial and 1 portal/hepatic venous data set collected within a single breathhold over 17 seconds and separated by the 25-second interval, during which the candidate was permitted to breathe).
  • 7Postcontrast axial T1-weighted 2D FLASH including fat saturation (TR/TE: 114/2.0 ms, flip angle: 60°, 10-mm sections, matrix size: 256 × 256).

Image Analysis

Analysis of the image data was based on source images, multiplanar reformats, and 3D volume renderings. All 3D data sets both from MRI and MDCT were postprocessed using commercially available software and hardware (Virtuoso; Siemens, Erlangen, Germany). To provide a more realistic 3D impression, the data was also reviewed in “Stereo” mode, including visual enhancement by artificial coloring. Data interpretation was based on the consensus of 2 radiologists with over 8 and 11 years of experience (T.S. and S.G.R.), and 2 transplant surgeons with over 11 and more than 20 years of experience, who were also familiar with the review technique (M.M. and S.N.).

Analysis of the image data was focused on the following aspects:

  • 1Exclusion of focal liver lesions: The hepatic parenchyma was assessed for the presence of masses based on all collected image sets. Similarly other organs were assessed for concomitant disease.
  • 2Size of hepatic lobes: Based on 10-mm contiguous, nonoverlapping intervals of the venous image sets (MRI: axial T1-weighted 2D FLASH) the hepatic volumes were determined by manually tracing the contours of the entire liver (Fig. 1) and the graft (liver segments 5–8 or 2/3), excluding the inferior vena cava and the gallbladder fossa.14, 30, 31 The virtual hepatectomy plane followed the middle hepatic vein, corresponding to the performed surgery. To avoid interobserver variability all volumetric data was determined by consensus reading of the same radiologist and transplant surgeon (T.S. and M.M.).
  • 3Morphology of the biliary system: The biliary anatomy was analyzed and assessed for anatomic variants. According to the classification of Couinaud,32 “standard” anatomy was considered a simple bifurcation at the upper biliary confluence.
  • 4Morphology of the hepatic arterial system: Hepatic arterial anatomy was analyzed according to the classification of Michels (Table 1)19 for the origins of the right and left hepatic artery and the presence of any accessory hepatic arteries.
  • 5Morphology of the portal veins: The portal venous system was evaluated by separately analyzing the extra- and intrahepatic branches. Simple bifurcation of the main stem was considered normal anatomy.18 Special attention was paid to the assessment of the stem lengths and of branches crossing the dissection line.
  • 6Morphology of the hepatic veins: A triplet of hepatic veins draining separately into the inferior vena cava was considered to represent normal anatomy. Special attention was paid to the assessment of big accessory branches necessitating separate anastomosis in the recipient.
Figure 1.

Semiautomated assessment of total and segmental liver volumes based on manually tracing the contours of the liver portions on nonoverlapping 10-mm slices and subsequent addition of calculated areas. (A) MRI (axial T1-weighted 2D FLASH). (B) CT.

Table 1. Michels Classification Scheme of Hepatic Arterial Anatomy
INormal anatomy: proper hepatic artery divides into right and left hepatic arteries
IILeft hepatic artery replaced, most often to left gastric artery
IIIRight hepatic artery replaced, most often to superior mesenteric artery
IVBoth right and left hepatic arteries replaced
VAccessory left hepatic artery replaced, most often to left gastric artery
VIAccessory right hepatic artery replaced, most often to superior mesenteric artery
VIIAccessory right and left hepatic arteries
VIIIReplaced right hepatic artery and accessory left hepatic artery or replaced left hepatic artery with accessory right hepatic artery
IXProper hepatic artery arising from the superior mesenteric artery
XProper hepatic artery arising from the left gastric artery

Image Quality Rating and Statistical Analysis

To objectify the diagnostic performance of CT and MRI in the visualization of the single anatomical systems, a 4-point “image quality rating” (IQR) was introduced, ranging from 1 to 4: 1 = nondiagnostic; 2 = sufficient; 3 = good; 4 = excellent.

In a stepwise fashion, image analysis was performed for each candidate separately after acquisition of all individual CT and MR data. The first step included analysis of the 2D source images and generation of 3D multiplanar reformats and volume renderings by 2 experienced radiologists (T.S. and S.G.R.). Subsequently, the 2D and 3D data was reviewed together with 2 transplant surgeons (M.M. and S.N.). This succession was chosen to assure both the highest possible information extraction of the radiological data and an appropriate understanding of the operation anatomy. Following this consensus reading, all 4 reviewers rated the achieved image quality blinded to each other.

To test for statistical differences, the Wilcoxon rank test was used; P values of less than 0.05 were regarded as statistically significant differences.

Intraoperative Comparisons

The preharvest MDCT and MRI determinations regarding the biliary and vascular morphology and the estimated volumes were correlated with intraoperative findings, which served as standard of reference. A total of 13 of the evaluated candidates were elected as donors and underwent right-lobe transplantation surgery. The predicted transplant volumes and the intraoperatively determined transplant weight were compared on the basis of a 1:1 conversion factor.33–35


All CT and MR examinations were diagnostic regarding the display of the parenchymal and vascular morphology, thereby obviating the need for subsequent digital subtraction angiography and/or endoscopic retrograde cholangiopancreatography, apart from the 3 left-lobe donation candidates.

All MR examinations (100%) and 23 (92%) of 25 CT examinations were well tolerated. During the CT examination, 2 candidates presented moderate adverse reactions on the biliary contrast agent, including feeling of heat, nausea, and erythema on face and arms. After standard antihistaminic treatment in both cases complete recovery was achieved within 20 minutes.

The “in room” time in the MR scanner ranged between 15 and 23 minutes (mean: 19 minutes), compared to CT “in-room” time of between 9 and 13 minutes (mean: 11 minutes). Subsequent data analysis including manual planimetry and assessment of the biliary and vascular morphology required between 25 and 60 (mean: 35) minutes for the MR data, compared to 25–55 (mean: 33) minutes required for the CT data (Table 2).

Table 2. Practical Aspects of Both “All-in-One” Protocols
“In-room” times15–23 minutes (mean: 19)9–13 minutes (mean: 11)
Time for data analysis25–60 minutes (mean: 35)25–55 minutes (mean: 33)

Liver Volumes

The determined total liver volumes ranged between 1,030 and 2,166 mL (mean: 1,384 mL) in MDCT and between 1,095 and 2,381 mL (mean: 1,467 mL) in MRI. The peak values were found in the same patients.

The transplant volumes estimated based on the MR, in all cases showed higher liver and graft volumes. The difference between CT and MRI ranged between 0 and +215 mL (mean: 83 mL) or 0 and +10% (mean: 6%), respectively.

The estimated proportions (graft volume/total liver volume) in the 2 modalities were similar, both for the right- and the left-lobe donors, showing maximum differences of 3% (mean: 1.2%).

The mean IQR in the determination of the liver volumes was 3.6 for CT, compared with 3.3 for MRI.

Liver Parenchyma and Parenchymal Lesions

The same number of hepatic lesions was depicted by both modalities (Table 3). Characterization was, however, easier based on MRI (mean IQR: 3.7) than on MDCT (mean IQR: 3.4).

Table 3. LDLT-Relevant Findings in Living Donor Transplant Candidates
Hepatic arterial variants15 in 10 candidates18 in 13 candidates
Portal venous variants4 in 4 candidates4 in 4 candidates
Hepatic venous variants4 in 4 candidates4 in 4 candidates
Intrahep. biliary variants4 in 4 candidates17 in 13 candidates
Hepatic lesions4 in 4 candidates (1 adenoma, 1 hemangioma, 2 × cysts)4 in 4 candidates (1 adenoma, 1 hemangioma, 2 × cysts)

A total of 19 patients did not show any parenchymal abnormalities. One patient presented a lesion 2.0 × 2.5 × 2.0 cm showing pathognomonic signs of a hemangioma in segment 8. In another patient, a 1.5 × 2.0 × 2.0 cm lesion of undetermined dignity was identified in segment 6. Diagnostic biopsy revealed an adenoma. Two patients showed multiple small cysts (<4 mm) in the right hepatic lobe. Data from 2 patients showed signs of liver steatosis.

Biliary System

CT cholangiography visualized the intrahepatic biliary tree up to the second-, third-, and fourth-level branches (Fig. 2A).

Figure 2.

3D cholangiography (oblique coronal views) in a 39-year-old male donor. Classical appearance showing bifurcation into right and left hepatic duct at the upper confluence (arrow). (A) MDCT cholangiography after infusion of a biliary contrast agent, displaying the biliary tree at least up to the third level of intrahepatic branches. (B) MRCP, visualizing the biliary system only up to the upper confluence/the first level of intrahepatic branches.

According to the classification of Couinaud32 “standard” anatomy, including a simple bifurcation at the upper biliary confluence (Type A), was seen in 12 (48%) of the 25 candidates.

A total of 13 candidates (52%) presented a biliary variant (Table 3): trifurcation of the upper biliary confluence (Type B; n = 3); drainage of a right sectorial duct into the common hepatic duct (Type C; n = 4); drainage of a right sectorial duct into the left hepatic duct (Type D; n = 5); and absence of a defined upper biliary confluence with all sectorial ducts joining separately (Type E; n = 1).

In comparison, MRCP reliably displayed the biliary system only up to the level of the first hepatic side branch (Fig. 2B). Biliary variants were found in 4 candidates, which represents less than one third of those depicted by CT (Table 3): 1 Type B, 1 Type C, and 2 Type Ds. All MR findings were seen also on CT.

The diagnostic quality achieved by CT cholangiography was rated with a mean IQR of 3.5, compared to an MRCP mean IQR of 1.3.

Hepatic Arteries

By CTA, “standard” arterial anatomy, defined as proper hepatic artery dividing into sole right and left hepatic arteries (Type 1),19 was determined in 12 (48%) of 25 subjects. A total of 13 candidates (52%) presented variants of the hepatic arterial supply (Table 3): left hepatic artery replaced to the left gastric artery (Type 2; n = 2), right hepatic artery replaced to the superior mesenteric artery (Type 3; n = 1), both right and left hepatic artery replaced (Type 4; n = 1), accessory left hepatic artery (Type 5; n = 4), accessory right and left hepatic arteries (Type 7; n = 2), proper hepatic artery originating from the superior mesenteric artery combined with an accessory left hepatic artery (Type 8; n = 1), and proper hepatic artery arising from the superior mesenteric artery (Type 9; n = 2).

In comparison, MRA (Fig. 3B) revealed variants in 10 subjects (40%) (Type 2: n = 1, Type 3: n = 1, Type 4: n = 1; Type 5: n = 2, Type 7: n = 2, Type 8: n = 1; Type 9: n = 2), whereas normal arterial anatomy was seen in 15 candidates (60%). All MR findings were visualized by CT as well. While visible on CT, MRI missed 1 replacement of the left hepatic artery and 2 accessory left hepatic arteries; however, this did not affect right lobe donation. The right hepatic variants were similarly determined as on CT.

Figure 3.

3D arteriograms (oblique coronal views) in the same 39-year-old male donation candidate. CTA (A) and MRA (B), both presenting standard anatomy of the hepatic arteries. The biliary system in the CT scan (A) is still contrast enhanced, showing the right hepatic artery (arrowhead) crossing the common hepatic bile duct ventrally.

Considering the achieved diagnostic quality, CTA was rated with an overall IQR of 3.5, whereas the mean IQR for MRA was 3.0.

Portal Veins

Both CT and MR imaging of the portal veins (Fig. 4A–B) revealed 4 variants (Table 3), including: origin of the portal venous branch to the dorsolateral liver segments directly from the portal bifurcation (n = 2); short (<1 cm) stem of the right portal vein (n = 1); and doubled right portal vein (n = 2). The IQRs determined were 2.8 for the CT data and 3.4 for the MR data.

Figure 4.

3D angiography of the portal/hepatic venous systems (oblique coronal views) in the same 39-year-old male donation candidate. CTA (A) and MRA (B), both presenting standard vascular anatomy. Delineation of the vasculature is much sharper in the MR scans (B). The biliary system in the CT scan (A) is still contrast enhanced, showing the topographic relationship of both systems.

Hepatic Veins

Both CT and MR imaging of the hepatic veins (Fig. 4A–B) revealed 4 variants relevant for operation (Table 3), including common drainage of the middle and the left hepatic vein into the inferior vena cava (n = 2) and accessory branches crossing the dissection line (n = 2), thus requiring an additional anastomosis. The determined mean IQRs were 2.8 for the CT data and 3.4 for the MR data.

The Wilcoxon rank test showed statistical significance (P < 0.05) for all mentioned differences between the image qualities of CT and MRI (Table 4).

Table 4. Image Quality Ratings (IQRs) Determined by 4 Observers
Average IQR of 4 ObserversHepatic LesionsLiver VolumesHepatic ArteriesPortal VeinsHepatic VeinsIntrahepatic Bile Ducts
Mean IQR3.
Wilcoxon rank testPDiff < 0.05PDiff < 0.05PDiff < 0.05PDiff < 0.05PDiff < 0.05PDiff < 0.05

Intraoperative Comparisons

A total of 16 candidates were elected as donors. Of these subjects, 13 underwent transplantation surgery, all donating a right lobe liver portion (segments 5–8). One of the potential recipients died before transplantation, 2 patients received deceased donor transplants. A total of 9 donation candidates were excluded for inadequate liver volumes (n = 7), unsafe donor anatomy (n = 1), and withdrawal of consent (n = 1).

Intraoperatively, the graft volume was determined by actual weighing and assuming a 1:1 conversion factor from grams to milliliters. Compared to the values predicted by CT, the resected transplant volumes (total: n = 13) showed a mean difference of 9% (±2%) from the values predicted by MDCT, more often overestimating (n = 10) than underestimating (n = 3) the graft volume. Compared to the values predicted by MRI a mean difference of 12% (±3%) was found, in all cases (n = 13) overestimating the graft volume.

Concerning the hepatic arterial anatomy all variants predicted by CT were confirmed intraoperatively (Fig. 5A and B). No further variants were detected and none of the depicted was missed in the preoperative imaging. Considering the extensive matching of the positive MR findings with the CT findings (Fig. 5B and C), all variants not determined by MRI could be classified as false negatives.

Figure 5.

Intraoperative comparison in the same 39-year-old male donation candidate; oblique coronal views onto the proper/right hepatic artery and the upper biliary confluent (arrow: common hepatic duct; arrowhead: right hepatic artery). (A) Intraoperative appearance. (B) 3D CT arteriogram with underlying biliary tree. (C) 3D MR arteriogram.

Preoperative CT cholangiography matched the intraoperative findings in all 13 donors. Intraoperatively, no further variants were detected and none of those depicted were missed in the CT. As the 4 preoperative MR findings were concurrent with the CT findings, those were intraoperatively confirmed as well.

The concurrent CT and MR findings concerning the venous systems were also intraoperatively verified. No further variants were detected and none of those depicted were missed in the preoperative imaging.


Both “all-in-one” MDCT and “all-in-one” MRI proved to be feasible and robust concepts to evaluate potential living liver donors in a single diagnostic step. Despite shorter scan times, the entire CT protocol is more time consuming, due to the necessity of administering the biliary contrast agent prior to the scan. Moreover, with regard to the several focuses of the preharvest liver analysis, both approaches show specific strengths and weaknesses.

Biliary System

Regarding the high incidence of biliary variants,32, 36–38 thorough analysis of the biliary anatomy is essential for the surgical outcome in living donor liver transplantation. Failure to recognize even minor intrahepatic branches crossing the dissection line can result in severe postoperative biliary leakage.39 Even though the preoperative acquired information will rarely lead to exclusion of the donation process or a dramatic change of the surgical approach, awareness of biliary variations may prompt thorough exploration to localize the critical structures. Furthermore, a better understanding of the anatomy allows for operating in a more goal-directed manner.

Contrast enhanced CT cholangiography displayed the biliary tree at least up to the second intrahepatic branches in all patients. In comparison, MRCP allowed reliable visualization of the biliary system only up to the bifurcation of the common hepatic duct (Fig. 2). For the entire patient collective MRCP revealed about one third of the biliary variants displayed on CT cholangiography. This not only demonstrates the superiority of MDCT cholangiography, but also supports the importance of preoperative cholangiography in general. This is also mirrored by an excellent correlation with intraoperative findings and is supported by recent reports demonstrating complete agreement between CT cholangiography and endoscopic retrograde cholangiopancreatography.40, 41

It has to be considered, however, that the technique used for MRCP was based on heavily T2-weighted images and did not involve any “positive” enhancement of the biliary tree. Since this technique has been shown to be accurate regarding the analysis of the central bile ducts,42 the detection of ductal dilatation, and presence of calculi or masses,43–45 it has been established as the diagnostic standard in many centers.

The results of this study, however, illustrate that the anatomical detail achievable by this technique is not sufficient to depict the crucial intrahepatic branches in healthy liver donors. To compensate for such weakness, new MRCP techniques—either based on optimized sequences or involving the administration of dedicated biliary contrast agents (e.g., mangafodipir trisodium)—are under investigation. Even though recent studies report a significantly improved delineation of the intrahepatic biliary tree,46, 47 the value of such techniques remains being controversially discussed. Recently, Yeh et al.47 performed comparison of contrast-enhanced CT and MR cholangiography in potential liver donors confirmed a significantly better visualization of the biliary tract by CT. However, further clinical experience needs to be gained.

Hepatic Arteries

The patency of all supplying and draining vessels is mandatory for the graft and the remnant liver survival; therefore, careful analysis of the hepatic vasculature prior to living donor liver transplantation is indicated. In several studies, both MRA26, 48 and CTA28 proved to have a diagnostic accuracy comparable to catheter angiography and an excellent intraoperative correlation.

However, in our study, the display of the hepatic arterial system was deemed more accurate and reliable on the CT images, which is mirrored both by a higher number of detected variants and by a higher rated image quality. This is considered an effect of a higher spatial resolution achievable by MDCT. Particularly in combination with high intravascular contrast enhancement, the delineation of the small intrahepatic branches is easier.

An interesting side-effect of the CT protocol refers to the simultaneous display of biliary and vascular structures, which enables depiction of their topographic relationships (Fig. 3A; Fig. 5A–B), thus enhancing an intuitive understanding of the hepatic anatomy and thus facilitating the operation planning process.

Portal and Hepatic Veins

Even though the anatomical information was similar, the display of the hepatic and the portal venous systems and the delineation of the intrahepatic veins from the surrounding tissue was more convenient in the MR data sets (Fig. 4A–B). This is supposedly related to the minimal albumin binding of the administered MR contrast agent, thus leading to an extended intravascular phase and a higher intravascular signal intensity.49 The importance of this aspect lies in the fact that the liver outflow represents a crucial predictor for the transplant function. Combined with 3D renderings, the enhanced contrast conspicuity represents an important contributing factor to greater diagnostic confidence, even when compared with digital subtraction angiography.50, 51

Liver Parenchyma and Parenchymal Lesions

To exclude diffuse liver disease and hepatic masses capable of compromising liver function in the remnant or the transplant hepatic graft, both imaging protocols included dynamic data sets of the arterial and the portal/hepatic venous phases. Even though CT and MRI showed the same kind and number of parenchymal abnormalities, characterization of such was considered easier based on MRI, which is an experience that is shared by other authors.52, 53 The advantages of MRI hereby relate to the better soft tissue contrast and multiple sequence protocols with different contrast weightings.

The diagnostic performance of the CT protocol presented, however, can be limited by the fact that it does not include a real precontrast scan, hence a fatty infiltration of the liver might be masked by the initially administered biliary contrast. However, this potential weakness is considered acceptable, because the value of cross-sectional imaging for this indication is a matter of controversy.27, 54 Owing to the greater sensitivity of histologic analysis, to our knowledge, in all preharvest protocols hepatic biopsy still represents a mandatory step in the evaluation process.

Transplant Volumes

An accurate liver volumetry is of paramount importance to avoid subjecting the donor to unnecessary risks and to reduce the risk of graft failure.16, 17, 22, 55 Therefore, an excellent cross-sectional image quality providing sufficient contrast of the liver organ relative to surrounding tissues is required. Both the venous CT scan and the venous T1-weighted MR sequence fulfilled these criteria. The CT images, especially, showed sharp demarcation of the liver organ and all surrounding structures. As a result of sporadic “blurring” of edges, the MR contrast of the liver relative to the surrounding tissues was rated a little lower, yet sufficient to permit accurate planimetry.

A remarkable aspect is the general tendency to overestimation, which became apparent both on the CT and—more distinctively—the MR scans. This is astonishing, since several studies in the recent past employing the same techniques showed good correlation between the preoperatively predicted graft volumes and the intraoperatively determined graft weights.31 This is most likely caused by the lack of perfusion of the graft when it is weighed,35 which induces a systemic bias for the comparison with the preoperative in situ hepatic volumes. Such interpretation is supported by the study of Lemke et al.,34 which proposes a conversion factor of 0.75 between the preoperative graft volume and the effective weight of the nonperfused graft.

Side Effects

Both “all-in-one” approaches harbor potential risks, which must be weighed against the inherent benefits. Even though potential donors are willing to take a personal risk, it is therefore an ethical obligation to perform the examination with highest possible care.

A considerable disadvantage of the CT protocol is the associated exposure to ionizing radiation. The effective dose is estimated to range between 15 and 20 mSv. This compares to 7–12 mSv for a standard CT scan of the abdomen, to 0˜.2 mSv for a chest X-ray in 2 projections, and to 2˜.4 mSv of natural radiation exposure per year. Another disadvantage of the CT protocol is the necessity of administering considerable volumes of potentially nephrotoxic iodinated contrast agents. Therefore, confirmation of normal renal function prior to the CT examination is mandatory. In particular, the biliary contrast agent has been known to be associated with a high incidence of adverse reactions, ranging from mild and self-resolving symptoms like sensation of warmth, nausea, and erythema (2˜%) to moderate and severe systemic adverse reactions up to shock-syndrome and death (0˜.01%).40, 56 In addition, the administration of the biliary agent requires normal hepatic (secretory) function and a bilirubin level below 2–4 mg/dL.41 Since only patients with normal hepatic laboratory parameters enter the donor program, this aspect does not represent a true limitation.

The MR strategy, on the other hand, obviates the need for exposing the potential donor to ionizing radiation and the administration of nephrotoxic contrast agents. The Gd-based agents used for MRA are characterized by a much superior safety profile as compared to iodinated contrast agents; there is no renal nephrotoxicity57 and anaphylactic reactions are exceedingly rare.58 On the downside, the long examination might produce discomfort to the most and serious limitations to claustrophobic donation candidates.


Both “all-in-one” MDCT and “all-in-one” MRI are well suited to extensively assess the liver anatomy of potential donors in a single diagnostic step. This might reduce the need for multimodality evaluation protocols, hence relieving the medical infrastructure, but also augmenting the candidate's acceptance of the pretransplantation survey.

The favorable choice at present is, however, MDCT, owing to its superiority in the display of the intrahepatic bile ducts and arteries, its easy accessibility, and its shorter examination time. In our institution, MDCT currently represents the standard procedure, almost completely eliminating the need of further examinations to determine the candidate's anatomy. Due to its lack of harm to the voluntary donation candidates and the positive results of other research groups, “all-in-one” MRI nevertheless represents both a promising and a desirable evaluation strategy for the future. Further experiences with dedicated MR contrast agents and improved scan techniques are expected to clarify whether the current preferences can be changed.