Relationship between MRI T1 rho value and histological findings of intact and radially incised menisci in microminipigs.

Abstract

To examine whether the T1 rho value reflects histological changes in menisci we analyzed the relationship between T1 rho value and histological findings in intact and radially incised menisci of pigs. 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 T1 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. In intact lateral menisci, the zone where histological findings indicated fibrocartilage showed a lower T1 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, T1 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 T1 rho values and histological scores in all zones (r = 0.62-0.92, P = 0.001-0.026). Zonal variations of the T1 rho value were observed in intact menisci due to varying structure in each zone. T1 rho values were correlated with histological changes such as collagen fiber organization and safranin-o stainability in incised menisci. This study supports T1 rho mapping as useful for evaluating ultrastructural composition in menisci.