OBJECTIVE To evaluate the longitudinal reproducibility and variations of cartilage T1ρ and T2 measurements using different coils, MR systems and sites. METHODS Single-Site study: Phantom data were collected monthly for up to 29 months on four GE 3T MR systems. Data from phantoms and human subjects were collected on two MR systems using the same model of coil; and were collected on one MR system using two models of coils. Multi-site study: Three participating sites used the same model of MR systems and coils, and identical imaging protocols. Phantom data were collected monthly. Human subjects were scanned and rescanned on the same day at each site. Two traveling human subjects were scanned at all three sites. RESULTS Single-Site Study: The phantom longitudinal RMS-CVs ranged from 1.8% to 2.7% for T1ρ and 1.8% to 2.8% for T2. Significant differences were found in T1ρ and T2 values using different MR systems and coils. Multi-Site Study: The phantom longitudinal RMS-CVs ranged from 1.3% to 2.6% for T1ρ and 1.2% to 2.7% for T2. Across three sites (n=16), the in-vivo scan-rescan RMS-CV was 3.1% and 4.0% for T1ρ and T2, respectively. Phantom T1ρ and T2 values were significantly different between three sites but highly correlated (R>0.99). No significant difference was found in T1ρ and T2 values of traveling controls, with cross-site RMS-CV as 4.9% and 4.4% for T1ρ and T2, respectively. CONCLUSION With careful quality control and cross-calibration, quantitative MRI can be readily applied in multi-site studies and clinical trials for evaluating cartilage degeneration.

To more sensitively detect OA changes in subchondral trabecular bone structure, a focus on osteoporotic changes in the lateral joint and the medial-lateral ratio would be useful. Detectability of early OA remains unknown, but based on a strong correlation with the degree of OA progression, trabecular structural analysis of subchondral bone may be a useful parameter to evaluate OA severity and evaluate treatment.

We analyzed the microstructure and degree of mineralization of the subchondral trabecular bone in hip osteoarthritis (OA) using synchrotron radiation computed tomography (SRCT) to identify the relationship between bone structure and bone turnover. Subchondral bone samples were extracted from femoral heads of 10 terminal-staged hip OA patients. The SRCT scan was performed at 30 keV energy and 5.9 mm voxel size. Trabecular bone structure, bone cyst volume, and the degree of trabecular bone mineralization were measured, and correlations between bone structure and the degree of mineralization were analyzed. In addition, the trabecular bone was divided into the area immediately surrounding the bone cyst and the remaining area, and they were compared. The average cyst volume fraction in the whole region was 31.8%, and the bone volume fraction in the bone region was 55.6%. Cyst volume was the only structural parameter that had a significant correlation with the degree of mineralization. The degree of mineralization was diminished when the bone cyst was larger (r ¼ À0.81, p ¼ 0.004). The trabecular bone immediately surrounding the bone cyst had a lower degree of mineralization when compared with the remaining trabecular bone (p ¼ 0.008). In the bone sclerosis of OA subchondral bone, there are many large and small bone cysts, which are expected to play a significant part in the high bone turnover of OA. ß

Primary culture of skeletal muscle stem cells (MuSCs) is indispensable to study the dynamics of muscle regeneration and homeostasis. Here we describe the modified pre-plating method for isolating MuSCs in culture with greatly improved purity, yield, and procedure time. The protocol is based on the distinct adhesion characteristics of MuSCs. We reduced the procedure time to 2.5 days to obtain highly purified MuSCs through a newly employed re-plating step, which repeats incubation and cell-suspension. The re-plating step efficiently traps remaining fibroblastic cells, but not MuSCs, on a collagen-coated dish. Additionally, we confirmed that MuSCs can be isolated from small amounts of human/mouse muscle tissues, enabling us to perform experiments with amount-limited specimens. Thus, our method can be performed with basic laboratory equipment suitable for most facilities and without sophisticated MuSC handling techniques.

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