DIFFUSION AND RELAXATION MAPPING OF CARTILAGE-BONE PLUGS AND EXCISED DISKS USING MICROSCOPIC MAGNETIC-RESONANCE-IMAGING

Spatially resolved maps of proton self-diffusion coefficients (D) and relaxation times (T-1 and T-2) were obtained on cartilage-bone plug sa mples and on excised disks of canine cartilage at a transverse resolut ion of 30 mu m, using microscopic magnetic resonance imaging (micro-MR I). Results are compared for excised disks of cartilage and intact car tilage-bone plugs. Correlations between the absolute water concentrati on, the self-diffusion coefficient and the T-1 relaxation are reported . The diffusion coefficient is not a linear function of water concentr ation. The thickness of the disks is 600 mu m, compared with the ca. 9 00 mu m observed for the cartilage-bone plugs, presumably due to the a bsence of the interfacial or tidemark layer of interdigitated cartilag e and bone in the former samples. Our results suggest that excised dis ks of cartilage are excellent models for the articular surface and the first 500 or so microns of tissue. The molecular parameters of spin-s pin and spin-lattice relaxation times, as well as the water self-diffu sion coefficient, are virtually identical in the two types of samples. However, the cartilage-bone plugs have the additional feature of perm itting the study of the tidemark region, a region that likely plays a major role in the transmission of mechanical force.