Wang Nian, Mirando Anthony J, Cofer Gary, Qi Yi, Hilton Matthew J, Johnson G Allan
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. 2020 Aug;84(2):908-919. doi: 10.1002/mrm.28181. Epub 2020 Jan 21.
To evaluate the complex fiber orientations and 3D collagen fiber network of knee joint connective tissues, including ligaments, muscle, articular cartilage, and meniscus using high spatial and angular resolution diffusion imaging.
Two rat knee joints were scanned using a modified 3D diffusion-weighted spin echo pulse sequence with the isotropic spatial resolution of 45 μm at 9.4T. The b values varied from 250 to 1250 s/mm with 31 diffusion encoding directions for 1 rat knee. The b value was fixed to 1000 s/mm with 147 diffusion encoding directions for the second knee. Both the diffusion tensor imaging (DTI) model and generalized Q-sampling imaging (GQI) method were used to investigate the fiber orientation distributions and tractography with the validation of polarized light microscopy.
To better resolve the crossing fibers, the b value should be great than or equal to 1000 s/mm . The tractography results were comparable between the DTI model and GQI method in ligament and muscle. However, the tractography exhibited apparent difference between DTI and GQI in connective tissues with more complex collagen fibers network, such as cartilage and meniscus. In articular cartilage, there were numerous crossing fibers found in superficial zone and transitional zone. Tractography generated with GQI also resulted in more intact tracts in articular cartilage than DTI.
High-resolution diffusion imaging with GQI method can trace the complex collagen fiber orientations and architectures of the knee joint at microscopic resolution.
使用高空间和角分辨率扩散成像评估膝关节结缔组织（包括韧带、肌肉、关节软骨和半月板）的复杂纤维方向和三维胶原纤维网络。
使用改良的三维扩散加权自旋回波脉冲序列对两只大鼠膝关节进行扫描，在9.4T场强下各向同性空间分辨率为45μm。对于一只大鼠膝关节，b值在250至1250 s/mm之间变化，有31个扩散编码方向。对于另一只膝关节，b值固定为1000 s/mm，有147个扩散编码方向。同时使用扩散张量成像（DTI）模型和广义Q采样成像（GQI）方法研究纤维方向分布并进行纤维束成像，并通过偏振光显微镜进行验证。
为了更好地分辨交叉纤维，b值应大于或等于1000 s/mm。在韧带和肌肉中，DTI模型和GQI方法的纤维束成像结果具有可比性。然而，在胶原纤维网络更复杂的结缔组织（如软骨和半月板）中，DTI和GQI的纤维束成像表现出明显差异。在关节软骨的表层和过渡层发现了大量交叉纤维。与DTI相比，GQI生成的纤维束成像在关节软骨中也产生了更完整的纤维束。
采用GQI方法的高分辨率扩散成像能够在微观分辨率下追踪膝关节复杂的胶原纤维方向和结构。
