High-Resolution DTI of Human Articular Cartilage with Long Diffusion Time: Preliminary Findings

NTRODUCTION The articular cartilage has a matrix structure of three layers superficial zone, middle zone and deep zone, which are divided by the different orientations of collagens. Recent publications have shown fractional anisotropy (FA) can reflect the orientation of the collagen fibers using diffusion tensor imaging (DTI) in MRI [1-3]. However, the FA contrasts were low especially between the superficial zone and middle zone in those literatures. This was possibly because they selected the short diffusion time (Δ < 10 ms) [1-3]. In our study, we chose both Δ = 10 ms and Δ = 30 ms and kept the same b = 500 s/mm in six directions of diffusion gradients. The FA contrast between superficial zone and middle zone in Δ = 30 ms increased by about 4 times of the FA contrast in Δ = 10 ms. After increasing Δ, the mean diffusivity (MD) in each zone decreased because MD depended not only on the self diffusion of fluid in cartilage but also on the pore size [4], while the maximum diffusivity (MaxD) kept almost unchanged since MaxD was along the principal diffusion direction and experienced less restricted diffusion. Our preliminary data shows the MaxD has the potential to be used as a marker of the proteoglycans (PGs) concentration. Future development of this approach may be important for detecting the early degeneration of cartilage.