RESUMO
Objective To explore the optimal time and sequence for getting the best magnetic resonance (MR) imaging when MR image of synovium macrophages was used for the diagnosis of collageninduced arthritis (CIA) in a rat model,and whether it can be used to monitor the efficacy of drug treatment.Methods CIA was induced by subcutaneous injection of chicken type Ⅱ collagen and complete Freund's adjuvant (CFA).Arthritis rats were randomly divided into the model group,the leflunomide group and the control group.Knees of the model group rats were imaged before and 24 h,48 h,72 h after USPIO intravenous administration (300 μmol Fe/kg) on day 28,29,30,31,respectively.From day 28,the leflunomide group was given a gauge of drug at a dose of 8 mg/kg.Then they were imaged before and 24 hours after USPIO administration on day 42,43 respectively.MR sequences included SE T1WI,SE T2WI,GRE T2 * WI.After the completion of MR imaging,rats were sacrificed to obtain histopathologic samples of synovial membrane.LSD-t test and one-way analysis of variance (ANOVA) were used for statistical analysis.Results No distinct signal enhancements were observed on the 24 h,48 h,72 h post-contrast enhancement on T1WI.On T2WI,signal intensity ratio of synovium (SNR) pre-contrast and 24 h,48 h post-contrast were 24.13±1.96,17.09± 1.23,19.14±0.91,respectively.On T2 * WI,SNR pre-contrast and 24 h,48 h post-contrast were 22.28±0.92,11.40±0.53,17.18±0.63,respectively.Distinct signal changes were observed on 24 h,48 h post-contrast on T2WI and T2 * WI (P＜0.05).The changes between SNR at 24 h,48 h,72 h post-contrast and pre-contrast were-29.09±2.42,-20.83±2.90,-6.2±2.9 respectively on T2WI,which were-48.4±1.3,-22.9±0.8,-8.2±1.6 respectively on T2 * WI.Changes were more obvious at 24 h post-contrast than 48 h post-contrast on both T2WI and T2 * WI (P＜0.05).The quantitative analyses were coinci-dent with the visual differences in signal changes between pre-contrast and post-contrast images.Difference between △SNR of leflunomide group and the control group on T1WI was not significant,while that on T2WI and T2 * WI were significantly different (P＜ 0.01).Histological examination confirmed the uptake of iron in the macrophages of arthritic knees.Signal intensity changed more on GRE T2 * WI than SE T2WI in all arthritis rats.Conclusion GRE T2 * WI is more sensitive for the diagnose of rat CIA,and 24 h post-contrast is better than 48 h and 72h post-contrast to get better images.We successfully observed the effects of leflunomide through signal changes of synovium,and the technique maybe contribute to diagnosis and therapeutic monito-ring of rheumatoid arthritis.