T2 relaxation time mapping reveals age- and species-related diversity of collagen network architecture in articular cartilage

SummaryObjectiveThe magnetic resonance imaging (MRI) parameter T2 relaxation time has been shown to be sensitive to the collagen network architecture of articular cartilage. The aim of the study was to investigate the agreement of T2 relaxation time mapping and polarized light microscopy (PLM) for the determination of histological properties (i.e., zone and fibril organization) of articular cartilage.MethodsT2 relaxation time was determined at 9.4 T field strength in healthy adult human, juvenile bovine and juvenile porcine patellar cartilage, and related to collagen anisotropy and fibril angle as measured by quantitative PLM.ResultsBoth T2 and PLM revealed a mutually consistent but varying number of collagen-associated laminae (3, 3–5 or 3–7 laminae in human, porcine and bovine cartilage, respectively). Up to 44% of the depth-wise variation in T2 was accounted for by the changing anisotropy of collagen fibrils, confirming that T2 contrast of articular cartilage is strongly affected by the collagen fibril anisotropy. A good correspondence was observed between the thickness of T2-laminae and collagenous zones as determined from PLM anisotropy measurements (r = 0.91, r = 0.95 and r = 0.91 for human, bovine and porcine specimens, respectively).ConclusionsAccording to the present results, T2 mapping is capable of detecting histological differences in cartilage collagen architecture among species, likely to be strongly related to the differences in maturation of the tissue. This diversity in the MRI appearance of healthy articular cartilage should also be recognized when using juvenile animal tissue as a model for mature human cartilage in experimental studies.