Nissi M J, Rieppo J, Töyräs J, Laasanen M S, Kiviranta I, Jurvelin J S, Nieminen M T
Department of Physics, University of Kuopio, Kuopio, Finland.
Osteoarthritis Cartilage. 2006 Dec;14(12):1265-71. doi: 10.1016/j.joca.2006.06.002. Epub 2006 Jul 14.
The magnetic resonance imaging (MRI) parameter T(2) 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 T(2) relaxation time mapping and polarized light microscopy (PLM) for the determination of histological properties (i.e., zone and fibril organization) of articular cartilage.
T(2) 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.
Both T(2) 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 T(2) was accounted for by the changing anisotropy of collagen fibrils, confirming that T(2) contrast of articular cartilage is strongly affected by the collagen fibril anisotropy. A good correspondence was observed between the thickness of T(2)-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).
According to the present results, T(2) 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.
磁共振成像（MRI）参数T(2)弛豫时间已被证明对关节软骨的胶原网络结构敏感。本研究的目的是调查T(2)弛豫时间映射与偏振光显微镜（PLM）在确定关节软骨组织学特性（即区域和纤维组织）方面的一致性。
在9.4 T场强下测定健康成年人类、幼年牛和幼年猪髌软骨的T(2)弛豫时间，并将其与通过定量PLM测量的胶原各向异性和纤维角度相关联。
T(2)和PLM均显示出相互一致但数量不同的胶原相关层（人类、猪和牛软骨中分别为3层、3 - 5层或3 - 7层）。胶原纤维各向异性的变化解释了高达44%的T(2)深度方向变化，证实关节软骨的T(2)对比度受胶原纤维各向异性的强烈影响。从PLM各向异性测量确定的T(2)层厚度与胶原区域之间观察到良好的对应关系（人类、牛和猪标本的r分别为0.91、0.95和0.91）。
根据目前的结果，T(2)映射能够检测不同物种间软骨胶原结构的组织学差异，这可能与组织成熟度的差异密切相关。在实验研究中使用幼年动物组织作为成熟人类软骨的模型时，也应认识到健康关节软骨MRI表现的这种多样性。
