T2 mapping of rat patellar cartilage

PURPOSE: To investigate the usefulness of magnetic resonance (MR) T2 mappin g in characterizing the evolution of cartilage matrix content and thickness during the maturation and aging process. MATERIALS AND METHODS: Patellae from four groups of rats aged 4 weeks, 8 we eks, 4 months, and more than 6 months ("old rats") were studied ex vivo wit h an 8.5-T microimager. T2 values were calculated on transverse rat patella r sections and displayed with a color scale (the T2 map) on a pixel-by-pixe l basis. Biochemical and histologic studies were performed to evaluate the influence of proteoglycans and collagen contents on T2 values of the patell ar cartilage. RESULTS: On the T2 map, the maturation process until 10 weeks was character ized by a decrease in T2 values and in cartilage thickness. The biochemical data revealed a global decrease in proteoglycans and a progressive global increase in collagen content, whereas the histologic study revealed subtle zonal variation in matrix constituents with depth. As aging progressed, the T? values were low, without important variations, whereas the global carti lage thickness decreased. The cartilage matrix became globally more fibroti c, especially in the deepest zone. Biochemical analysis revealed that colla gen content was more determinant of MR signal intensity than was proteoglyc ans content during maturation and aging. CONCLUSION: T2 mapping allows characterization of variations in cartilage m atrix constituents and thickness.