<i>T</i>₂ relaxation reveals spatial collagen architecture in articular cartilage: A comparative quantitative MRI and polarized light microscopic study

Abstract 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. Magn Reson Med 46:487–493, 2001. © 2001 Wiley‐Liss, Inc.