Computational Radiology Laboratory (CRL), Department of Radiology, Boston Children's Hospital, and Harvard Medical School, Boston, Massachusetts, USA.
Department of Pathology, Boston Children's Hospital, and Harvard Medical School, Boston, Massachusetts, USA.
Hum Brain Mapp. 2021 Dec 1;42(17):5771-5784. doi: 10.1002/hbm.25653. Epub 2021 Sep 6.
Population averaged diffusion atlases can be utilized to characterize complex microstructural changes with less bias than data from individual subjects. In this study, a fetal diffusion tensor imaging (DTI) atlas was used to investigate tract-based changes in anisotropy and diffusivity in vivo from 23 to 38 weeks of gestational age (GA). Healthy pregnant volunteers with typically developing fetuses were imaged at 3 T. Acquisition included structural images processed with a super-resolution algorithm and DTI images processed with a motion-tracked slice-to-volume registration algorithm. The DTI from individual subjects were used to generate 16 templates, each specific to a week of GA; this was accomplished by means of a tensor-to-tensor diffeomorphic deformable registration method integrated with kernel regression in age. Deterministic tractography was performed to outline the forceps major, forceps minor, bilateral corticospinal tracts (CST), bilateral inferior fronto-occipital fasciculus (IFOF), bilateral inferior longitudinal fasciculus (ILF), and bilateral uncinate fasciculus (UF). The mean fractional anisotropy (FA) and mean diffusivity (MD) was recorded for all tracts. For a subset of tracts (forceps major, CST, and IFOF) we manually divided the tractograms into anatomy conforming segments to evaluate within-tract changes. We found tract-specific, nonlinear, age related changes in FA and MD. Early in gestation, these trends appear to be dominated by cytoarchitectonic changes in the transient white matter fetal zones while later in gestation, trends conforming to the progression of myelination were observed. We also observed significant (local) heterogeneity in within-tract developmental trajectories for the CST, IFOF, and forceps major.
群体平均弥散张量成像图谱可用于描述复杂的微观结构变化，与个体数据相比，其偏差更小。在这项研究中，我们使用胎儿弥散张量成像（DTI）图谱来研究从 23 周到 38 孕周（GA）的体内基于束的各向异性和弥散率的变化。正常妊娠的志愿者在 3T 下进行成像。采集包括使用超分辨率算法处理的结构图像和使用运动跟踪的切片到体积配准算法处理的 DTI 图像。使用个体受试者的 DTI 生成 16 个模板，每个模板都特定于一周的 GA；这是通过张量到张量的仿射可变形配准方法与年龄相关的核回归相结合来实现的。确定性束追踪用于勾勒出钳状核、钳状小核、双侧皮质脊髓束（CST）、双侧下额枕束（IFOF）、双侧下纵束（ILF）和双侧钩束（UF）。记录了所有束的平均各向异性分数（FA）和平均弥散度（MD）。对于一小部分束（钳状核、CST 和 IFOF），我们手动将束追踪图分为解剖学上一致的片段，以评估束内变化。我们发现 FA 和 MD 存在与束相关的、非线性的、与年龄相关的变化。在妊娠早期，这些趋势似乎主要由短暂性白质胎儿区的细胞构筑变化主导，而在妊娠晚期，观察到与髓鞘化进展相符的趋势。我们还观察到 CST、IFOF 和钳状核内束内发育轨迹的显著（局部）异质性。
