| Objective: To evaluate the value of MR physiological imaging in articular cartilage of osteoarthritis, we applied MR physiological imaging and measured articular cartilage of rabbit's knee of normal and osteoarthritis quantitatively. Materials and methods: 20 cases of New Zealand White rabbits were divided into 4 groups randomly. The left knee of the first groug were scaned with conventional MR imaging, then were executed afer MR imaging. The cartilage of femoral condyles were examined by hematoxylin and eosin staining (HE) and alcian blue staining (AB) and were assessed for proteoglycan . Every left knees of the second to the fourth group were scaned conventional MR imaging,T2 mapping and magnetization transfer contrast (MTC),then delayed gadolinium enhanced MRI of cartilage(dGEMRIC) imaging at last. Afer MR imaging , every left knees of three groups were injected with papain(10units/knee) 0.2ml. Afer injection, every left knees of three groups were scaned with same MR imaging and same sequence as previously at 24h,48h and 72h respectively. All rabbits were executed afer MR imaging, both cartilage of femoral condyles were examined by HE and AB staining and were assessed for proteoglycan . At coronal slice, T1,T2 relaxation time and magnetization transfer ratio of articular cartilage were calculated. Mean signal intensity was calculated from 12 dots of interest. Dot of interest came from medial,middle and lateral sites at cartilage of medial tibia,lateral tibia,medial femoral condyle and lateral femoral condyle. Differences in experiment and contrast were analyzed with statistical analysis. Meanwhile, the difference was compared with the assessment of proteoglycan concentration by biochemical analysis and histochemical staining. Results: The mean content of proteoglycan were 5.32 ug/mg before injection of papain, and decreased to 1.91 ug/mg and 2.52 ug/mg after injection of papain at 24h and 48h. The differences were statistically significant by compare with before injection of papain (p=0.048 and 0.045 respectively) . The mean content of proteoglycan were 3.70 ug/mg after injection of papain at 72h. The difference was not statistically significant by compare with before injection of papain (p=0.455) . The cartilage surface was intact and showed no obvious changes of chondrocyte by histochemical hematoxylin and eosin staining before and after injection of papain. Alcian blue staining showed dense before injection of papain. After injection of papain at 24h and 48h, alcian blue staining showed obviously light. At 72h after papain treatment, the intensity of alcian blue staining showed dense again. The cartilage's color of T1 map showed pink before injection of papain to blue after injection of papain. The T1 relaxation time was decreased 316.09ms,244.01ms and 143.98ms after injection of papain at 24h 48h and 72h respectively. The differences at 24h and 48h were statistically significant by t-test (p=0.047 and 0.045 respectively). The cartilage's color of T2 map showed yellowish red before injection of papain to red after injection of papain. The T2 relaxation time was rised 30.14ms 20.92ms and 16.17ms after injection of papain at 24h 48h and 72h respectively. The difference at 24h was statistically significant by t-test (p=0.04). The magnetization transfer ratios after injection of papain were decreased respectively in comparison with those before injection of papain, and the magnetization transfer ratio after injection of papain at 24h was obviously lowest. But the differences of magnetization transfer ratio of three groups were not statistically significant. Conclusion This animal model that we designed can analogy the biochemical change of osteoarthritis, and provide an ideal model for MRI that can detect biochemical change of articular cartilage of osteoarthritis. The T1,T2 relaxation time and magnetization transfer ratio came from dGEMRIC,T2 mapping and MTC imaging can detect quantitatively biochemical change of articular cartilage of osteoarthritis.
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