34 - Imaging the Developing Brain Pathways in the Early Second Trimester of the Human Fetal Brain Using Ultra-High-Field (14T) Diffusion-weighted MRI

Poster Board Number: 34
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Odd poster #s – first hour
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Co-authors:

David Christopher Hike, PhD - Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Harvard Medical School; Yuanyuan Jiang, PhD - Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Harvard Medical School; Jose Luis Alatorre Warren, PhD - Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Harvard Medical School; Xin Yu, PhD - Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Harvard Medical School; Emi Takahashi, PhD - Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Harvard Medical School

Abstract Body : The second trimester of human fetal brain development is a vulnerable period when neurogenesis and neuronal migration in the telencephalon are markedly active. For this reason, advanced imaging techniques can provide insights into the structural and functional aspects of the developing fetal brain. Focusing on this critical period, we aimed to identify detailed emerging brain pathways in the fetal brain using diffusion MRI.

Fetal whole brains at 14-15 weeks gestation (N=3) were obtained from the Brain and Tissue Bank, University of Maryland School of Medicine. These samples were collected after miscarriage and found to have no nervous system abnormalities. Diffusion-weighted 3-D echo-planar MR images of the specimens with 200 µm isotropic resolution were acquired using the 14T Bruker scanner in the A. A. Martinos Center for Biomedical Imaging. Brain pathways were reconstructed using Diffusion Toolkit tractography analysis and manual placement of regions-of-interests, with Trackvis. The reconstructions were used for qualitative analysis.

The formation of the emerging axonal pathways, such as the anterior commissure, optic tract and chiasm, fornix, thalamocortical, and brainstem-related fibers of the transverse pontine and corticospinal tract, were identified. In addition, inter-thalamic connections and multiple pathways between the thalamus and insula were reconstructed. Pathways that appeared anatomically to be neuronal migration streams were identified within the thalamus and the ganglionic eminence (GE), a structure mainly for inhibitory neuronal migration. The three subregions of GE—medial, lateral, and dorsal—were identified. The endpoints of the medial and lateral GE pathways through the basal ganglia were also demonstrated.

In conclusion, we successfully identified the early development of white matter and neuronal migration pathways in fetal brains. Additionally, we identified subdivisions of the GE pathways with diffusion tractography for the first time. This is the first study to establish an ex vivo scan and analysis method of the human fetal brain pathways at the earliest ages using 14T MRI. Our next step involves analyzing the development of the cerebral wall gross anatomically to trace layers of the developing cerebral cortex as well as a histological assessment. We believe this will provide a basis for further studies such as early detection of neurodevelopmental disorders and identification of neuronal migration and white matter structural abnormalities.