Abstract： Objective To investigate the value of DWI in the early diagnosis and staging of hepatic fibrosis of rats.Methods Rat model with hepatic fibrosis was established by using carbon tetrachloride.By using completely randomized design random digits table,5 or 6 rats were assigned to model group and 1 or 2 rats to the control group.After drug administration from the second week to the end of 16th weeks,a total of 72 rats of model group and 30 rats of control group were included in this study to undergo DWI scanning.The signal intensity of DWI,the value of ADC and exponential apparent diffusion coefficient (EADC) for different b values (b =0,300,600,800 and 1000 s/mm2 respectively) were calculated.The rats were sacrificed to death to have pathologic examination in 4h after DWI scanning.Seventy-two model rats with hepatic fibrosis were grouped according to their pathological staging.The difference of the value of hepatic signal-to-noise ratio (SNR) of different b values,and the value of ADC and EADC among control group and model groups were compared by analysis of variance with completely randomized design data rank transformation and SNK multiple comparison.The correlation of SNR and b values,and staging of hepatic fibrosis and the value of ADC and EADC were tested by rank correlation analysis.Results (1) The signal intensity of DWI of the rats of model group showed the tendency of increase with the increase of stage of hepatic fibrosis.(2) SNR showed the tendency of decrease with the increase of b values.When b value was 600 s/mm2 or 800 s/mm2,SNR was 31.2 ± 11.6 and 24.8 ±6.8 respectively and the quality of images was good.(3)There were 17 rats in grade 1,21 rats in grade 2,19 rats in grade 3 and 15 rats in grade 4 of hepatic fibrosis.The value of ADC of control group and of grade 1 to 4 of hepatic fibrosis were (1.65 ±0.38) × 10-3,(1.34±0.32) × 10-3,(1.04 ±0.20) × 10-3,(0.99 ±0.19) × 10-3,(0.62 ±0.21) ×10-3 mm2/s respectively,and the value of EADC were (0.31 ± 0.08) × 10-3,(0.34 ± 0.09) × 10-3,(0.41 ±0.08) × 10-3,(0.46 ± 0.08) × 10-3,(0.59 ±0.11) × 10-3 mm2/s respectively.There were significant differences among control group and other groups(F =40.97 and 25.04,P ＜0.01).There were significant differences of the value of ADC between every two groups (P ＜ 0.05),except grade 2 and 3 (P ＞0.05).For the comparison of EADC values,there was no significant difference between control group and grade 1,or grade 2 and 3 (P =0.275 and 0.082 respectively).Differences among the rest of the groups were statistically significant (P ＜ 0.05).(4) There was a negative correlation between stage of liver fibrosis and ADC value (r =-0.77,P ＜ 0.01),and a positive correlation between stage of liver fibrosis and EADC (r =0.72,P ＜ 0.01).Conclusions (1) The signal intensity of DWI increases with the increase of staging of hepatic fibrosis.(2) The optimal b values of DWI of liver are 600 s/mm2 and 800 s/mm2.(3) A good correlation is found between the hepatic fibrosis and ADC and EADC,so it is possible to staging the hepatic fibrosis with ADC and EADC.