T2 Mapping of Rat Patellar Cartilage

Abstract

To investigate the usefulness of magnetic resonance (MR) T2 mapping in characterizing the evolution of cartilage matrix content and thickness during the maturation and aging process. Patellae from four groups of rats aged 4 weeks, 8 weeks, 4 months, and more than 6 months ("old rats") were studied ex vivo with an 8.5-T microimager. T2 values were calculated on transverse rat patellar sections and displayed with a color scale (the T2 map) on a pixel-by-pixel basis. Biochemical and histologic studies were performed to evaluate the influence of proteoglycans and collagen contents on T2 values of the patellar cartilage. On the T2 map, the maturation process until 10 weeks was characterized 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 T2 values were low, without important variations, whereas the global cartilage thickness decreased. The cartilage matrix became globally more fibrotic, especially in the deepest zone. Biochemical analysis revealed that collagen content was more determinant of MR signal intensity than was proteoglycans content during maturation and aging. T2 mapping allows characterization of variations in cartilage matrix constituents and thickness.