Apparent diffusion coefficient measurements and Gd-DTPA enhanced-imaging in staging hepatic fibrosis in rats

To evaluate the utility of ADC values and Gd-DTPA equilibrium phase MR imaging in staging hepatic fibrosis in rats. 48 rats were allocated into experimental and control groups. Experimental rats were subcutaneously injected with a mixture of CCl4. From 4th-12th weeks, MR images were obtained, which include pre-enhanced phase imaging, DWI and equilibrium phase imaging. Then the rat groups were subdivided according to the stages of fibrosis (S0, S1, S2, S3 and S4) after histopathological analysis. The original MRI data were forwarded to the workstation to obtain apparent diffusion coefficient (ADC) maps at b value of 500 s/mm(2). Pre-enhanced phase and equilibrium phase signal intensities and relative contrast enhancement index (RCEI) were measured as well. Lastly, the ADC values and RCEI of the experimental group were compared with each other and with the control group. All statistical analyses were carried out with SPSS, where P < 0.05 is considered to represent a significant difference. Hepatic ADC values are significantly different between the experimental and control groups (P = 0). There is a statistically significant difference between the experimental and control groups on RCEI (P = 0). Comparing the S1, S2, S3 and S4 groups, there is a statistically significant difference between the mild group (S1 and S2) and the severe group (S4) in terms of ADC values and RCEI (all P < 0.05). A statistically significant difference is also found between the moderate group (S3) and the severe group in ADC values. As the degree of fibrosis increases, there are a reduction in ADC values and an increase in RCEI. Comparing the groups with ADC values and enhancement index, there are statistically significant differences in sensitivity and specificity on diagnosis of hepatic fibrosis. The ADC values have the best sensitivity (93.1%) and specificity (83.3%). Quantitative ADC values and RCEI may be helpful to the staging of rat fibrosis, but their application in human is controversial.