Relationship between MRI T 1 rho value and histological findings of intact and radially incised menisci in microminipigs

Purpose To examine whether the T 1 rho value reflects histological changes in menisci we analyzed the relationship between T 1 rho value and histological findings in intact and radially incised menisci of pigs. Materials and Methods Seven microminipigs were used for this experiment. A radial incision was created and repaired in the medial meniscus, which was evaluated 4 weeks after surgery. Sagittal T 1 rho mapping images were taken by 3.0T magnetic resonance imaging (MRI). The region of interest was set by dividing the meniscus into six zones (from zone 1 to zone 6). For histological evaluation of intact menisci, characteristics of each zone were determined. In incised menisci, a histological score was used to evaluate pathological change. Results In intact lateral menisci, the zone where histological findings indicated fibrocartilage showed a lower T 1 rho value (34.2 ± 2.3 msec) than hyaline‐like cartilage (38.2 ± 2.5 msec) or fibrous tissue (37.2 ± 2.0 msec). In incised medial menisci, T 1 rho values increased (about 50–90 msec) in the zone where histological findings indicated that synovial ingrowth, scar tissue formation, and degenerative changes had occurred. There were correlations between T 1 rho values and histological scores in all zones ( r  = 0.62–0.92, P  = 0.001–0.026). Conclusion Zonal variations of the T 1 rho value were observed in intact menisci due to varying structure in each zone. T 1 rho values were correlated with histological changes such as collagen fiber organization and safranin‐o stainability in incised menisci. This study supports T 1 rho mapping as useful for evaluating ultrastructural composition in menisci. J. Magn. Reson. Imaging 2016;43:434–445.