Department of Technical Physics, University of Eastern Finland, Kuopio, Finland.
Research Unit of Medical Imaging, Physics and Technology, University of Oulu, Oulu, Finland.
Phys Med Biol. 2023 Apr 3;68(8). doi: 10.1088/1361-6560/acc169.
To provide orientation-independent MR parameters potentially sensitive to articular cartilage degeneration by measuring isotropic and anisotropic components ofrelaxation, as well as 3D fiber orientation angle and anisotropy via multi-orientation MR scans.. Seven bovine osteochondral plugs were scanned with a high angular resolution of thirty-seven orientations spanning 180° at 9.4 T. The obtained data was fitted to the magic angle model of anisotropicrelaxation to produce pixel-wise maps of the parameters of interest. Quantitative Polarized Light Microscopy (qPLM) was used as a reference method for the anisotropy and fiber orientation.. The number of scanned orientations was found to be sufficient for estimating both fiber orientation and anisotropy maps. The relaxation anisotropy maps demonstrated a high correspondence with qPLM reference measurements of the collagen anisotropy of the samples. The scans also enabled calculating orientation-independentmaps. Little spatial variation was observed in the isotropic component ofwhile the anisotropic component was much faster in the deep radial zone of cartilage. The estimated fiber orientation spanned the expected 0°-90° in samples that had a sufficiently thick superficial layer. The orientation-independent magnetic resonance imaging (MRI) measures can potentially reflect the true properties of articular cartilage more precisely and robustly.. The methods presented in this study will likely improve the specificity of cartilage qMRI by allowing the assessment of the physical properties such as orientation and anisotropy of collagen fibers in articular cartilage.
通过测量各向同性和各向异性弛豫的各向异性分量，以及通过多方向 MR 扫描测量 3D 纤维方向角和各向异性，提供对关节软骨退变具有各向同性敏感性的 MR 参数。在 9.4T 下，使用 37 个方向的高角度分辨率（覆盖 180°）对 7 个牛骨软骨插件进行扫描。对获得的数据进行拟合，以得出各向异性弛豫的魔术角模型，从而生成感兴趣参数的像素级图谱。定量偏振光显微镜（qPLM）用作各向异性和纤维方向的参考方法。发现扫描的方向数量足以估计纤维方向和各向异性图谱。弛豫各向异性图谱与样本胶原各向异性的 qPLM 参考测量值具有高度一致性。这些扫描还可以计算各向同性图谱。在软骨的深层放射状区域，各向异性分量的变化速度明显快于各向同性分量。在具有足够厚的表层的样本中，估计的纤维方向跨越了预期的 0°-90°。各向同性磁共振成像（MRI）测量值具有潜在的优势，能够更准确、更稳健地反映关节软骨的真实特性。本研究中提出的方法通过评估关节软骨中胶原纤维的物理特性（如方向和各向异性），可能会提高软骨 qMRI 的特异性。
