The collagen fibril structure in the superficial zone of articular cartilage by μMRI

SummaryObjectiveTo investigate the fibril architecture of the collagen matrix in the superficial zone (SZ) of articular cartilage non-destructively by microscopic magnetic resonance imaging (μMRI) T2 anisotropy.MethodSix 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° and at a step of 15°. At each rotation angle, a quantitative T2 image was constructed at 13 μm pixel resolution.ResultsA set of complex and depth-dependent patterns was found in the μMRI T2 anisotropy along the depth of the tissue. In the SZ, the T2 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 T2 anisotropy approximately doubles with respect to that in the SZ. In the initial part of the radial zone (RZ), the T2 anisotropy is also periodic but inverse to that in the SZ. In the deep part of the RZ, the T2 anisotropy becomes increasingly weaker and eventually disappears.ConclusionThere 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.