T2 relaxation reveals spatial collagen architecture in articular cartilage:: A comparative quantitative MRI and polarized light microscopic study

It has been suggested that orientational changes in the collagen network of articular cartilage account for the depthwise T-2 anisotropy of MRI through the magic angle effect. To investigate the relationship between laminar T-2 appearance and collagen organization (anisotropy), bovine osteochondral plugs (N = 9) were T-2 mapped at 9.4T with cartilage surface normal to the static magnetic field. Collagen fibril arrangement of the same samples was studied with polarized light microscopy, a quantitative technique for probing collagen organization by analyzing its ability to rotate plane polarized light, i.e., birefringence (BF). Depthwise variation of safranin O-stained proteoglycans was monitored with digital densitometry, The spatially varying cartilage T-2 followed the architectural arrangement of the collagen fibril network: a linear positive correlation between T-2 and the reciprocal of BF was established in each sample, with r = 0.91 +/- 0.02 (mean SEM, N = 9). The current results reveal the close connection between the laminar T-2 structure and the collagen architecture in histologic zones. (C) 2001 Wiley-Liss, Inc.