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Spatiotemporal changes in diffusivity and anisotropy in fetal brain tractography.
Fedel Machado-Rivas1, Onur Afacan1, Shadab Khan1
1Computational Radiology Laboratory (CRL), Department of Radiology, Boston Children's Hospital, and Harvard Medical School, Boston, Massachusetts, USA.
Human Brain Mapping
|September 6, 2021
Summary
This study utilized a fetal diffusion tensor imaging (DTI) atlas to map brain development, revealing unique, nonlinear changes in white matter tracts related to gestational age and myelination. The findings highlight significant variations in developmental trajectories within specific brain pathways.
Area of Science:
- Neuroimaging
- Developmental Neuroscience
- Medical Imaging Analysis
Background:
- Population-averaged diffusion atlases offer less biased characterization of microstructural changes compared to individual subject data.
- Understanding fetal brain development requires advanced imaging techniques to track microstructural maturation in vivo.
- Diffusion tensor imaging (DTI) provides insights into white matter integrity and organization.
Purpose of the Study:
- To investigate tract-based changes in anisotropy and diffusivity in the developing fetal brain using a DTI atlas.
- To characterize age-related microstructural development of major white matter tracts from 23 to 38 weeks of gestational age (GA).
- To evaluate within-tract developmental heterogeneity in specific white matter pathways.
Main Methods:
- A fetal DTI atlas was generated from 3T MRI scans of healthy fetuses (23-38 weeks GA) using motion-tracked registration and tensor-to-tensor diffeomorphic registration.
- Deterministic tractography was employed to delineate key white matter tracts, including the forceps major, forceps minor, corticospinal tracts (CST), inferior fronto-occipital fasciculus (IFOF), inferior longitudinal fasciculus (ILF), and uncinate fasciculus (UF).
- Mean fractional anisotropy (FA) and mean diffusivity (MD) were calculated for each tract, with further segmentation for detailed within-tract analysis of forceps major, CST, and IFOF.
Main Results:
- Tract-specific, nonlinear, age-related changes in FA and MD were observed across the gestational age range.
- Early gestational changes were influenced by cytoarchitectonic development, while later changes correlated with myelination progression.
- Significant local heterogeneity in developmental trajectories was noted within the forceps major, CST, and IFOF.
Conclusions:
- Fetal DTI atlases are effective tools for characterizing in vivo white matter development, revealing complex, age-dependent microstructural changes.
- The study demonstrates distinct developmental patterns for different white matter tracts, influenced by both early cytoarchitecture and later myelination.
- Significant regional variations within major tracts underscore the complexity of fetal brain maturation.
