Abstract
Background
Recently, diffusion-weighted imaging (DWI) and quantitative enhancement ratio measured at the hepatobiliary phase (HBP) of Gd-EOB-DTPA–enhanced magnetic resonance imaging (MRI) has been established as an effective method for evaluating liver fibrosis.
Purpose
To evaluate which is a more favorable surrogate marker in predicting high-stage liver fibrosis, apparently diffusion coefficient (ADC) value or quantitative enhancement ratio measured on HBP.
Material and Methods
Eighty-three patients with 99 surgically resected hepatic lesions were enrolled in this study. DWI was performed with b-values of 100 and 800 s/mm2. Regions of interest were set on ADC map, and the HBP of Gd-EOB-DTPA–enhanced MRI, to calculate ADC value, liver-to-muscle ratio (LMR), liver-to-spleen ratio (LSR), and contrast enhancement index (CEI) of liver. We compared these parameters between low-stage fibrosis (F0, F1, and F2) and high-stage fibrosis (F3 and F4). Receiver operating characteristic analysis was performed to compare the diagnostic performance when distinguishing low-stage fibrosis from high-stage fibrosis.
Results
LMR and CEI were significantly lower at high-stage fibrosis than at the low stage (P < 0.01 and P = 0.04, respectively), whereas LSR did not show a significant difference (P = 0.053). No significant difference was observed in diagnostic performance between LMR and CEI (P = 0.185). The best sensitivity and specificity, when an LMR of 2.80 or higher was considered to be low-stage fibrosis, were 82.4% and 75.6%, respectively. ADC value showed no significant differences among fibrosis grades (P = 0.320).
Conclusion
LMR and CEI were both adequate surrogate parameters to distinguish high-stage fibrosis from low-stage fibrosis.
Keywords
Introduction
Liver fibrosis is a reaction of stellate cells for chronic inflammation caused by hepatitis B or C virus and many other causes. The fibrosis leads to cirrhosis, portal hypertension after many years, and eventually can be fatal. Moreover, the severe fibrosis restricts surgical indications. Liver biopsy is a widely accepted procedure for diagnosing and grading liver fibrosis. However, it is associated with major complications in 0.3% of patients and with mortality in 0.018% (1). Furthermore, because of the heterogeneity of liver fibrosis, sampling errors can also arise (2,3). Therefore, alternative non-invasive diagnostic methods that can precisely evaluate liver fibrosis are desirable. Some methods, such as elastography, diffusion-weighted imaging (DWI) and contrast enhancement index (CEI), have been introduced to evaluate liver fibrosis (4,5). DWI and CEI do not require special tools and can be performed within routine clinical work. DWI can evaluate the restricted diffusion by collagen fibers accumulated interstitially (4,6,7) in cirrhotic liver. The CEI for fibrosis evaluation is currently using gadolinium ethoxy-benzyl diethylenetriamine penta-acetic acid (Gd-EOB-DTPA). This method is affected by the number of functional hepatocytes. In case of cirrhosis, the number of hepatocytes decreases, and consequently, the enhancement at the hepatobiliary phase decreases (8–10). Some indexes of the enhancement ratio have been proposed, such as the liver-to-muscle ratio (LMR), liver-to-spleen ratio (LSR), and CEI (8–10). In these articles, the biopsy specimen was not always consistent with the data acquisition area on imaging. The direct comparison of the surgical resected specimen with that of the corresponding area on imaging is desirable. This method can set the region of interest (ROI) precisely and a sufficient amount of specimen for pathological evaluation can be obtained. Furthermore, previous papers included other bias, for example, all the selected patients had B or C virus infection or a habit of alcohol intake (8). Therefore, we intended to assess which index, which could be obtained during routine clinical work, was the best surrogate marker for evaluating liver fibrosis.
Material and Methods
Patients
Our institutional review board approved this retrospective study and informed consent was waived. We reviewed the imaging and clinical records. The inclusion criteria were as follows: participants who were examined with both abdominal magnetic resonance imaging (MRI) and hepatic resection because of suspicion of tumor between 2009 and 2014. The interval between abdominal MRI and surgery was three months. Two hundred patients were selected consecutively. The exclusion criteria were as follows: insufficient amount of specimen to evaluate pathologically; no tumor in specimen; needle biopsy; more than ten tumors in the liver; did not receive Gd-EOB-DTPA (Primovist®, Bayer Healthcare, Berlin, Germany); implementation of preoperative portal embolization; arterial chemo-embolization before the operation. Afterwards, we also excluded tumors which were located on the lateral segment of the liver because of the effect on the apparent diffusion coefficient (ADC) from the heartbeat (11). Finally, 83 patients with 99 lesions were enrolled in the study. Sixty-eight patients had one tumor, 14 patients had two tumors, and one patient had three tumors. The participants consisted of 59 men and 24 women. The mean age was 67.0 years (range = 28–87 years). The pathological results of tumors were as follows: hepatocellular carcinoma (n = 34); metastatic liver tumor (n = 55); and miscellaneous (gallbladder cancer, intrahepatic cholangiocellular carcinoma, combined hepatocellular and cholangiocellular carcinoma, angiomyolipoma, and others) (n = 10). The underlying liver diseases were alcoholism (n = 8), hepatitis C (n = 10), and hepatitis B (n = 5). Thirty-three patients (39.4%) underwent preoperative chemotherapy; most patients were given the FOLFOX regimen (5-fluorouracil, folinic acid, and oxaliplatin) (12). The mean time interval between the operation and the MRI study was 28 days (range = 2–79 days).
MRI technique
All MRI examinations were performed using a 1.5 T superconductive MRI scanner (Avanto; Siemens, Erlangen, Germany) with a 32-channel body array coil. The maximum gradient of the system was 45 mT/m and the maximum slew rate was 200 T/m/s. T1-weighted (T1W) images were acquired under breath-holding, including in-phase and opposed-phase images, and the parameters were as follows: repetition/echo time (TR/TE) = 120/4.76, 2.38 ms; flip angle = 75°; 1 averaging; matrix = 320 × 224; parallel acquisition technique with reduction factor 2 using the generalized autocalibration partially parallel acquisition (GRAPPA) algorithm; slice thickness = 6 mm; slice gap = 1.2 mm; and acquisition time = 13 s. T2-weighted (T2W) images were acquired with Sampling Perfection with Application optimized Contrasts using different flip angle Evolution (SPACE) under breath synchronization using two-dimensional prospective acquisition correction (2D-PACE); the parameters were as follows: TR/TE = 1600/149 ms; flip angle = 120°; flip angle mode = constant; matrix = 320 × 227; 1.4 averaging; field of view (FOV) = 400 × 275; slice per slab = 64; slice oversampling = 12.5%; PAT factor 2 with the GRAPPA algorithm; bandwidth = 710 Hz/pixel; slice thickness = 3 mm. DWI was also acquired under breath synchronization using 2D-PACE; the parameters were as follows: TR/TE = 3000/71 ms; flip angle = 120°; matrix = 128 × 128; slice thickness = 6 mm; intersection gap = 1 mm; 6 signals acquired; FOV = 40 cm; 30 sections in 5–8 min; chemical shift selective method; PAT factor 2 with the GRAPPA algorithm; b-factor = 100 and 800 s/mm2. The DWI motion-probing gradient pulses were placed in three orthogonal axes, and DWI was reconstructed by combining these three images. Quantitative ADC maps were created on a voxel-by-voxel basis using the software on the scanner. Dynamic Gd-EOB-DTPA–enhanced MRI was performed with a T1W 3D gradient echo sequence with fat saturation and volumetric interpolated breath-hold examination (VIBE). The sequence parameters were as follows: TR/TE = 3.96/1.79 ms; slice thickness = 2 mm; FOV = 400 mm; effective matrix size = 320 × 224; signal average = 1; acquisition time = 19 s; k-space trajectory = linear filling. Gd-EOB-DTPA (0.025 mmol/kg) was injected at a rate of 1 or 2 mL/s via the antecubital vein, followed by 40 mL of physiological saline at the same injection rate as the contrast media. Dynamic study included the hepatic arterial-dominant phase, portal-dominant phase, and the period 4 min after injection of the contrast material and hepatobiliary phase. The hepatobiliary phase was obtained at 20 min after injection of Gd-EOB-DTPA.
Evaluation of MRI and liver fibrosis
Two radiologists (with 4 and 25 years of experience, respectively) and a pathologist (with 17 years of experience) discussed where to set the ROIs on liver parenchyma to evaluate fibrosis, comparing MR images with the picture of resected specimen and pathology slides. After reaching consensus, the first ROI was set on ADC map at a distance of 5–10 mm from the tumor where fibrosis grade was assessed pathologically. We set a circular ROI not larger than 1 cm2 on MRI (Fig. 1). The mean signal intensity (SI) was used as data. The second ROI was set almost on the same location of the first ROI, but at the hepatobiliary phase (SI liver). The third and fourth ROI were set at the erector spinae muscle and spleen at the hepatobiliary phase, respectively (SI muscle, SI spleen). The fifth ROI was set on the same location as the second ROI on the pre-enhanced MRI on T1W 3D-VIBE (SI pre-liver). The ROIs corresponding to each other were placed using the copy and paste function, and minor adjustment was performed carefully by hand to remove errors caused by breath movement, without changing the form and size of the ROIs. All ROIs were set at the same slice if possible, and were set avoiding the lateral segment of the liver and major vessels. The ratios of the third, fourth, and fifth ROI to the second ROI were calculated as the LMR (10,13), LSR (8), and CEI (14) as represented by the following formulas:
ROI setting. Five ROIs set on ADC map and hepatobiliary phase image. Three ROIs were set at near the tumor on ADC map (a), hepatobiliary phase (b), and pre-enhanced MRI (d). The two remaining ROIs were set at erector spine and spleen on hepatobiliary phase (c).
Distribution of specimens according to degree of fatty change and fibrosis stage.
Statistical analysis
Data are represented as the mean ± standard deviation. Statistical analyses were mainly performed with SPSS version 22.0.0.0 (IBM Corp., Armonk, NY, USA). One-way analysis of variance (ANOVA) with Tukey post hoc comparison was used to correlate the parameters with histologic grade of fibrosis, and the unpaired t-test to compare the parameters of low-stage fibrosis (F0, F1, and F2) with those of high-stage fibrosis (F3 and F4). Pearson’s correlation was used to evaluate the effect of fat deposition on all parameters. A value of P < 0.05 was considered significant. Receiver operating characteristic curve (ROC) analysis was also performed to determine the sensitivity and specificity for diagnosing high-stage fibrosis. Statistical analyses of ROC were performed with EZR software (Saitama Medical Center, Jichi Medical University, http://www.jichi.ac.jp/saitama-sct/Saita maHP.files/statmedEN.html), which is a graphical user interface for R (The R Foundation for Statistical Computing, version 2.13.0).
Results
ADC value and fibrosis stage
ADC values were 0.85 ± 0.20, 0.82 ± 0.19, 0.81 ± 0.18, 0.70 ± 0.29, and 0.91 ± 0.16 × 10−3 mm2/s in fibrosis stages F0, F1, F2, F3, and F4, respectively. No significant differences were observed in ADC values among fibrosis stages (P = 0.320) (Fig. 2a), nor between high and low fibrosis grade (P = 0.634) (Fig. 2b).
ADC value and fibrosis stage. No significant differences were observed in ADC values among fibrosis stages (P = 0.320) (a), nor between high-grade and low-grade fibrosis (P = 0.634) (b).
CEI and fibrosis stage
CEI values were 2.17 ± 0.20, 2.30 ± 0.35, 2.15 ± 0.38, 2.11 ± 0.53, and 1.90 ± 0.35 in fibrosis stages F0, F1, F2, F3, and F4, respectively. CEI values showed significant differences among fibrosis stages (P = 0.013). A significant difference was observed between F1 and F4 (P = 0.014) (Fig. 3a). CEI values of low-stage fibrosis and high-stage fibrosis were 2.25 ± 0.34 and 2.00 ± 0.42, respectively, and a significant difference was observed (P = 0.04) (Fig. 3b).
CEI and fibrosis stage. CEI values showed significant differences among fibrosis stages (P = 0.013). A significant difference was observed between F1 and F4 (P = 0.014) (a). CEI values of low-stage fibrosis and high-stage fibrosis showed a significant difference (P = 0.04) (b).
LMR and fibrosis stage
LMR values were 3.16 ± 0.60, 3.31 ± 0.60, 2.93 ± 0.56, 2.72 ± 0.60, and 2.48 ± 0.49 in fibrosis stages F0, F1, F2, F3, and F4, respectively. LMR values showed significant differences among fibrosis stages (P < 0.001). Significant differences were observed between F0 and F4 (P = 0.047), and between F1 and F4 (P < 0.001) (Fig. 4a). LMR values of low-stage fibrosis and high-stage fibrosis were 3.21 ± 0.60 and 2.57 ± 0.53, respectively, and a significant difference was observed (P < 0.01) (Fig. 4b).
LMR and fibrosis stage. LMR values showed significant differences among fibrosis stages (P < 0.001). Significant differences were observed between F0 and F4 (P = 0.047), and between F1 and F4 (P < 0.001) (a). LMR values of low-stage fibrosis and high-stage fibrosis showed significant difference (P < 0.01) (b).
LSR and fibrosis stage
LSR values were 2.76 ± 0.77, 3.00 ± 0.75, 2.49 ± 0.56, 2.94 ± 0.54, and 2.24 ± 0.49 in fibrosis stages F0, F1, F2, F3, and F4, respectively. LSR values showed significant differences among fibrosis stages (P = 0.008). A significant difference was observed between F1 and F4 (P = 0.014) (Fig. 5a). LSR values of low-stage fibrosis and high-stage fibrosis were 2.86 ± 0.74 and 2.49 ± 0.60, respectively, and no significant difference was observed (P = 0.053) (Fig. 5b).
LSR and fibrosis stage. LSR values showed significant differences among fibrosis stages (P = 0.008). A significant difference was observed between F1 and F4 (P = 0.014) (a). LSR values of low-stage fibrosis and high-stage fibrosis showed no significant difference (P = 0.053) (b).
Comparison of ROC between LMR and CEI
The sensitivity and specificity, when a CEI of 2.05 or higher was considered to be low-stage fibrosis, were 76.5% and 75.6%, respectively. On the other hand, sensitivity and specificity, when an LMR of 2.80 or higher was considered to be low-stage fibrosis, were 82.4% and 75.6%, respectively. No significant difference was observed between CEI and LMR in diagnostic performance for distinguishing low-stage fibrosis and high-stage fibrosis (P = 0.185) (Fig. 6).
ROC curve between LMR and CEI. The sensitivity and specificity, when a CEI of 2.05 or higher was considered to be low-stage fibrosis, were 76.5% and 75.6%, respectively. On the other hand, sensitivity and specificity, when an LMR of 2.80 or higher was considered to be low-stage fibrosis, were 82.4% and 75.6%, respectively. No significant difference was observed between CEI and LMR in diagnostic performance for distinguishing low-stage fibrosis and high-stage fibrosis (P = 0.185).
Effect of fatty change on every parameter at stage 1 fibrosis
Table 1 shows the distribution of specimens according to degree of fat steatosis and fibrosis grade. The r-values of ADC, CEI, LMR, and LSR with fat deposition were r = –0.218, 0.116, −0.044, and −0.077, respectively, and only ADC had a significant correlation with fat deposition (P = 0.03) (Fig. 7).
Effect of fatty change at stage 1 fibrosis. Only ADC had a significant correlation with fat deposition (P = 0.03).
Discussion
This study revealed no significant correlation between ADC value and fibrosis stage. Several papers reported that significant correlation was observed (4,5,7), although very few papers reported no correlation (18). We supposed that the reasons why no significant correlation was observed between liver fibrosis and ADC value were as follows. First, the direct comparison method we adopted in our study was different from previous reports. Second, steatosis might have an effect on the ADC value. Poyraz et al. suggested that steatosis decreases ADC value because increased fat content of hepatocytes and extracellular fat accumulation reduce the interstitial space and restrict water diffusion (16,19). The results of this study are consistent with those of previous reports. Third, iron deposition might affect ADC value. ADC value was extremely low in a few cases, although with low fibrosis grade and steatosis grade. We supposed it to be the T2* shortening effect (20), because the signal intensity of liver parenchyma on in-phase imaging was lower than that of opposed-phase imaging. Actually, chronic liver disease can lead to iron overload (21), and this is critical for quantitative evaluation using ADC value.
LMR and CEI could differentiate high-grade fibrosis from low-grade fibrosis better than ADC value. Signal intensity at the hepatobiliary phase is affected by the number of functional hepatocytes. Therefore, the signal intensity of liver decreases in liver fibrosis (22). LMR and CEI have some advantages compared with ADC values, that is, steatosis, iron deposition, perfusion effect from neighboring major vessels, and heartbeat do not affect those parameters. The only disadvantage is that contrast media is necessary. LSR showed no significant difference between high-grade fibrosis and low-grade fibrosis. Nojiri et al. also reported that LSR is the worst parameter among some enhancement ratios (13). Some studies of elastography showed that spleen stiffness is comparable to liver stiffness (23,24). It indicates that spleen also changes pathologically along with the change in liver parenchyma. We supposed that spleen showed variable enhancement that was dependent on liver fibrosis and portal hypertension, and consequently LSR showed inaccurate data. On the other hand, muscle showed minimum enhancement and pathological change, and it is almost independent of liver disease. Therefore, LMR appeared to show consistent data.
LMR and CEI could differentiate high-grade fibrosis from low-grade fibrosis better than ADC, although the condition of the participants varied. Chemotherapy-associated liver injury is a different entity from viral or alcohol-induced liver injury. Several pathological changes, such as steatosis and sinusoidal dilatation, in chemotherapy-associated liver injury have been reported in several papers (25,26). Furthermore, fibrosis is associated with neoadjuvant 5-fluorouracil-based chemotherapy in combination with oxaliplatin (27). These pathological changes may affect the ADC and liver parenchymal enhancement. Actually, the present study clarified that ADC was affected by steatosis. Miscellaneous conditions as in the present study might lead to significant complexity. However, the usefulness of LMR and CEI was demonstrated.
There were some limitations in this study. First, some patients (40% of all participants) received chemotherapy and some bias might be included. Almost all of these patients received FOLFOX; however, the sinusoidal dilatation was not observed pathologically in all patients. Therefore, we believe that the effect of the chemotherapy was limited. Second, this study was retrospective and all the participants received surgery. This led to the small number of high-grade fibrosis specimens. This might include some bias. Furthermore, the sub-groups became small in number. However, we supposed that having sufficient specimens of liver parenchyma to evaluate the fibrosis and direct comparison were advantages of this study.
In conclusion, LMR and CEI were both adequate surrogate parameters to distinguish high-stage fibrosis from low-stage fibrosis, and these values are available in routine clinical examinations. On the other hand, the ADC value was ineffective in predicting the fibrosis grade. Our results included the potential bias from hepatic steatosis, which affected the ADC value of some patients in the present study.
Footnotes
Declaration of Conflicting Interests
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
The author(s) received no financial support for the research, authorship, and/or publication of this article.
