Rationale and Objectives
To evaluate, in a group of candidates for liver donation, the role of unenhanced computed tomography (CT) and magnetic resonance (MR) as noninvasive means to measure hepatic steatosis (HS).
Materials and Methods
Sixty-one consecutive candidates underwent CT and MR evaluation for liver donation within 3 weeks of liver biopsy. On CT, three methods of HS quantification were evaluated: the measurement of hepatic attenuation (CT L), the ratio of hepatic attenuation to splenic attenuation (CT L/S), and the difference between the hepatic and splenic attenuation (CT L-S). On MR, HS was reported in terms of fat signal fraction (FSF) using in-phase/opposed-phase and fat/non-fat- saturated images, with and without normalization with the spleen (T1W IP/OP FSF, T1W IP/OP FSF spleen and T2W±FS FSF, TW2±FS FSF spleen). The accuracy of each imaging index in the diagnosis of HS, according to various thresholds, was assessed using receiver operating characteristic analysis.
Results
On biopsy, 35 donors showed no significant HS (<5%); the remaining 26 showed HS ranging from 5% to 40%. With all CT and MR indices, there was a trend toward increasing diagnostic accuracy as the threshold levels of HS increased. When comparing all the indices, TW2±FS FSF(spl) showed higher accuracy at threshold levels of 5% and 10% of steatosis but without reaching statistical significance.
Conclusions
In candidates for living donation, MR and CT indices are similar in estimating liver-fat content; however, MR with T2W±FS FSF(spl) sequences shows higher accuracy when low threshold levels of steatosis (≤5% and ≤10% HS) are selected.
Assessment of hepatic steatosis (HS) is a key point in living liver donor selection because excessive liver fat can affect postoperative outcome for both the donor and the recipient . Although liver biopsy (LB) remains the reference standard for grading HS, it is not routinely performed because it is an invasive procedure with several limitations, including sampling errors . Computed tomography (CT) and magnetic resonance (MR) have been separately evaluated for their ability to detect and quantify hepatic fat in potential living liver donors with MR emerging as the technique of choice for noninvasive accurate estimation of HS . However, imaging techniques, including measuring methods and reference tests, differed among studies and few articles evaluated both CT and MR within the same population while using histopathology as a reference . There has also been a paucity of studies investigating the role of (T2) fat-saturation techniques in potential liver donors . The aim of our study was to compare the accuracy of different imaging biomarkers derived from unenhanced CT and MR with both opposed-phase T1-weighted and fat-saturated T2-weighted sequences for the quantitative estimation of hepatic fat content in a selected population of potential living liver donors.
Materials and methods
Study Population
Our institutional review board approved this retrospective study and waived the need for informed consent, although written informed consent was obtained for every procedure from all subjects. Between July 2004 and July 2010, 61 consecutive candidates, who underwent CT and MR evaluation protocol for liver donation within 3 weeks of LB, were identified in the radiology information system and pathology database at a single transplant center. All potential living liver donors undergo an extensive stepwise evaluation protocol, including CT for liver volumetry and depiction of the hepatic vascular system, and MR cholangiography for assessment of the biliary anatomy. Donors who are not excluded because of an unfavorable hepatic parenchymal, vascular, or biliary morphology advance to the biopsy phase. LB is performed not only to quantify liver fat but also to detect other clinically and serologically unsuspected donor diseases that might potentially affect recovery of the donor and recipient after surgery .
Imaging Techniques
CT examination
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MR Examination
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Image Interpretation
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Table 1
Imaging Biomarkers for Liver Fat Estimation
Unenhanced CT methods CT L = hepatic attenuation values in Hounsfield unit CT L/S = hepatic-to-splenic attenuation ratio CT L−S = difference between hepatic and splenic attenuation MRI methods T1W IP/OP GRE sequences IP/OP FSF = (L SI (IP) − L SI (OP))/L SI (IP) × 100 IP/OP FSF(spl) = (L SI (IP)/S SI (IP)) − (L SI (OP)/S SI (OP))/(L SI (IP)/S SI (IP)) × 100 T2W±FS FSE sequences ±FS FSF = (L SI NFS − L SI FS)/L SI NFS × 100 ±FS FSF(spl) = (L SI NFS/S SI NFS) − (L SI FS/S SI FS)/(L SI NFS/S SI NFS) × 100
CT, computed tomography; FS, fat saturation; FSE, fast spin-echo; FSF, fat signal fraction; GRE, gradient-echo; IP, in-phase; L, liver; NFS, non–fat saturation; OP, opposed-phase; S = spleen, SI = signal intensity; T1W, T1-weighted; T2W, T2-weighted.
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Donor Biopsy and Histologic Assessment
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Statistical Analysis
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Results
Clinical and Histologic Findings
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Accuracy of CT and MRI in Diagnosing HS
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Table 2
The Area under the Receiver Operating Characteristic Curve and 95% Confidence Intervals for CT and MR Indices According to the Various Threshold Levels of Steatosis
Cutoff ∗ IP/OP FSF IP/OP FSF(Spl) ±FS FSF ±FS FSF(spl) CT L CT L/S CT L−S 5% (26) 0.765 (0.642–0.888) 0.760 (0.636–0.884) 0.739 (0.609–0.868) 0.861 (0.769–0.954) 0.812 (0.703–0.921) 0.757 (0.627–0.887) 0.758 (0.629–0.887) 10% (20) 0.856 (0.750–0.960) 0.854 (0.749–0.960) 0.828 (0.718–0.937) 0.939 (0.883–0.996) 0.866 (0.770–0.960) 0.810 (0.670–0.950) 0.806 (0.667–0.946) 15% (14) 0.952 (0.866–1.000) 0.919 (0.816–1.000) 0.898 (0.807–0.988) 0.930 (0.866–0.994) 0.938 (0.869–1.000) 0.842 (0.695–0.988) 0.837 (0.689–0.985) 20% (11) 0.983 (0.959–1.000) 0.969 (0.925–1.000) 0.917 (0.832–1.000) 0.935 (0.864–1.000) 0.967 (0.922–1.000) 0.868 (0.692–1.000) 0.865 (0.689–1.000) 25% (8) 0.998 (0.991–1.000) 1.000 (1.000–1.000) 0.899 (0.788–1.000) 0.940 (0.880–0.999) 0.988 (0.967–1.000) 0.952 (0.895–1.000) 0.950 (0.892–1.000) 30% (5) 0.993 (0.975–1.000) 0.978 (0.944–1.000) 0.960 (0.904–1.000) 0.920 (0.825–1.000) 1.000 (1.000–1.000) 0.949 (0.862–1.000) 0.944 (0.855–1.000)
CT, computed tomography; FS, fat saturation; FSE, fast spin-echo; FSF, fat signal fraction; IP, in-phase; L, liver; MR, magnetic resonance; OP, opposed-phase; S, spleen.
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Discussion
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