MR susceptibility-weighted imaging in staging hepatic fibrosis of rabbits

Abstract

Objective To assess the value of susceptibility-weighted imaging (SWI) in staging hepatic fibrosis (HF) in rabbits. Methods Sixty healthy rabbits were randomly divided into HF group (n=44), control group (n=16). Rabbits in the HF group and supplementary group were injected subcutaneously with 50% CCl4 oily solution to establish hepatic fibrosis model. On the basis of preliminary test, 8 rabbits in the HF group and 4 rabbits in the control group were selected randomly at the 4th, 5th, 6th, 10th week after CCL4 injection ,respectively , to undergo liver MR scan, including conventional axial T1WI, T2WI and axial SWI, DWI scan. All rabbits were sacrificed after MR scan and the tissue of liver were sampled for pathological test and hepatic fibrosis staging. Rabbits were classified into group F0, F1-2 and F3-4 based on pathological results. Liver signal intensity (SI), and liver-to-muscle SI ratio were measured on SWI images and ADC values were measured on DWI images correspondently. One-way ANOVA analysis was performed to compare difference in liver SI, liver-to-muscle SI ratio and ADC values among group F0 (no fibrosis), F1-2 (mild-moderate fibrosis) and F3-4 (severe fibrosis) . Spearman correlation analysis was performed to correlate pathological staging and liver SI, liver-to-muscle SI ratio and ADC values. Receiver operating characteristic (ROC) curve analysis was performed to compare the diagnostic performance of SWI and DWI for staging HF. Results Two and 5 rabbits in the HF group died at the 5th and the 6th week after CCL4 injection , respectively due to acute hepatic necrosis, hepatorrhexis and systemic failure. Seven rabbits in supplementary group were used as supplement. Of the 16 rabbits in the control group, 1 was excluded from the study due to liver fibrosis. Fifteen rabbits in group F0, sixteen rabbits in group F1-2 and sixteen rabbits in group F3-4 underwent MRI and were included into this study. Liver-to-muscle SI ratio in group F0, F1-2 and F3-4 were 0.973±0.020, 0.880±0.090 and 0.649±0.140, respectively. Liver SI were 378±45, 374±19 and 317±34. ADC values were (1.473±0.320) ×10-3, (1.311±0.310) ×10-3 and (0.942±0.180) ×10-3mm2/s. There were statistically significant differences in liver SI, liver-to-muscle SI ratio and ADC values among group F0, F1-2 and F3-4 (F=46.571,15.803 and 15.317,P< 0.01). Liver-to-muscle SI ratio was highly negatively correlated with HF staging (r=-0.818,P<0.01), while liver SI and ADC values were moderately correlated with HF staging (r=-0.565, -0.630;P<0.01). Area under ROC curve (AUC) of liver-to-muscle SI ratio, liver SI and ADC value for differentiating hepatic fibrosis stage F0 and stage F1-4 were 0.916, 0.695 and 0.768, while the AUC for differentiating hepatic fibrosis stage F0-2 and stage F3-4 were 0.951, 0.904 and 0.900. Conclusion Liver-to-muscle SI ratio on SWI provide added diagnostic value and could be an useful parameter for staging hepatic fibrosis. Key words: Liver fibrosis; Liver cirrhosis; Magnetic resonance imaging