Center for In Vivo Microscopy, Duke University School of Medicine, Durham, North Carolina.
Department of Radiology, Duke University School of Medicine, Durham, North Carolina.
Magn Reson Med. 2019 Jun;81(6):3775-3786. doi: 10.1002/mrm.27652. Epub 2019 Jan 22.
To evaluate whole knee joint tractography, including articular cartilage, ligaments, meniscus, and growth plate using diffusion tensor imaging (DTI) at microscopic resolution.
Three rat knee joints were scanned using a modified 3D diffusion-weighted spin echo pulse sequence with 90- and 45-μm isotropic spatial resolution at 9.4T. The b values varied from 250 to 1250 s/mm with 4 times undersampling in phase directions. Fractional anisotropy (FA) and mean diffusivity (MD) were compared at different spatial resolution and b values. Tractography was evaluated at multiple b values and angular resolutions in different connective tissues, and compared with conventional histology. The mean tract length and tract volume in various types of tissues were also quantified.
DTI metrics (FA and MD) showed consistent quantitative results at 90- and 45-μm isotropic spatial resolutions. Tractography of various connective tissues was found to be sensitive to the spatial resolution, angular resolution, and diffusion weightings. Higher spatial resolution (45 μm) supported tracking the cartilage collagen fiber tracts from the superficial zone to the deep zone, in a continuous and smooth progression in the transitional zone. Fiber length and fiber volume in the growth plate were strongly dependent on angular resolution and b values, whereas tractography in ligaments was found to be less dependent on spatial resolution.
High spatial and angular resolution DTI and diffusion tractography can be valuable for knee joint research because of its visualization capacity for collagen fiber orientations and quantitative evaluation of tissue's microscopic properties.
使用扩散张量成像（DTI）以微观分辨率评估整个膝关节轨迹，包括关节软骨、韧带、半月板和生长板。
在 9.4T 下使用经过改良的 3D 扩散加权自旋回波脉冲序列对 3 个大鼠膝关节进行扫描，具有 90-μm 和 45-μm 的各向同性空间分辨率。b 值范围从 250 到 1250 s/mm，在相位方向上进行 4 倍欠采样。在不同空间分辨率和 b 值下比较各向异性分数（FA）和平均扩散系数（MD）。在不同的结缔组织中，在多个 b 值和角分辨率下评估轨迹，并与常规组织学进行比较。还定量了各种组织类型中的平均轨迹长度和轨迹体积。
DTI 指标（FA 和 MD）在 90-μm 和 45-μm 各向同性空间分辨率下显示出一致的定量结果。各种结缔组织的轨迹追踪对空间分辨率、角分辨率和扩散权重均敏感。较高的空间分辨率（45 μm）支持从浅层到深层连续且平滑地追踪软骨胶原纤维束在过渡区中的轨迹。生长板中的纤维长度和纤维体积强烈依赖于角分辨率和 b 值，而韧带中的轨迹追踪则发现对空间分辨率的依赖性较小。
高空间和角分辨率 DTI 和扩散轨迹追踪对于膝关节研究具有重要价值，因为它能够可视化胶原纤维方向，并对组织的微观特性进行定量评估。
