To investigate the fibril architecture of the collagen matrix in the superficial zone (SZ) of articular cartilage non-destructively by microscopic magnetic resonance imaging (microMRI) T(2) anisotropy.
Six specimens of canine humeral cartilage were rotated in such a way that the normal axis of the articular surface of the cartilage specimen remained stationary and perpendicular to the static magnetic field, over a range of 180 degrees and at a step of 15 degrees. At each rotation angle, a quantitative T(2) image was constructed at 13 microm pixel resolution.
A set of complex and depth-dependent patterns was found in the microMRI T(2) anisotropy along the depth of the tissue. In the SZ, the T(2) anisotropy is clearly periodic, which demonstrates that the distribution of the collagen fibrils in the SZ is not random. In the transitional zone, the periodicity of the T(2) anisotropy approximately doubles with respect to that in the SZ. In the initial part of the radial zone (RZ), the T(2) anisotropy is also periodic but inverse to that in the SZ. In the deep part of the RZ, the T(2) anisotropy becomes increasingly weaker and eventually disappears.
There exists a certain degree of collagen anisotropy in all zones of articular cartilage. The anisotropic imaging data can be interpreted with the aid of a collagen architecture model.