Background: To investigate the merit of T1rho relaxation for the evaluation of liver fibrosis, inflammatory activity, and liver injury monitoring in a carbon tetrachloride (CCl 4)-induced rat model. Methods: Model rats from CCl 4-induced liver fibrosis (fibrosis group: n = 41; regression group: n = 20) and control (n = 11) groups underwent black blood T1rho magnetic resonance (MR) imaging (MRI). Injection of CCl 4 was done twice weekly for up to 12 weeks in the fibrosis group and for up to 6 weeks in the regression group. MR scanning time points were at baseline and at 2, 4, 6, 8, 10 and 12 weeks after CCl 4 injection in the fibrosis group and at baseline and at 2, 4, 6 (CCl 4 withdrawal), 7, 8, 10 and 12 weeks in the regression group. Results: In the fibrosis group, liver T1rho values increased gradually within week 8 and then decreased. In the regression group, T1rho values dropped gradually after the withdrawal of CCl 4 and fell below those at baseline. The T1rho values at S0 were lower than those at any other stage (all P < 0.05). The T1rho values at G0 were significantly lower than those at any other grade, and G1 was lower than G2 (all P < 0.01). The T1rho values mildly correlated with fibrosis stages (r = 0.362) and moderately correlated with grades of inflammation (r = 0.568). The T1rho values of rats with the same inflammation grades showed no significant difference among different fibrosis stages, and the T1rho values at S3 showed a significant difference among different grades of inflammation (P = 0.024). Inflammation grade was an independent variable associated with T1rho values (P < 0.001). Conclusion: T1rho MRI can be used to monitor CCl 4-induced liver injury, and inflammatory activity had a greater impact on liver T1rho values than fibrosis.
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