fetal MRI, brain development, manual segmentation, cerebral sulcation
Fetal brain development is a complex and dynamic process. During the third trimester of pregnancy the brain’s surface landscape changes from a smooth layer into a complex canopy with convolutions called gyri. The emergence of quantitative magnetic resonance imaging (MRI) has allowed for in vivo acquisition of high-resolution images of the fetal brain. Although a timeline for the emergence of important gyri exists; we currently lack an in vivo MRI model—or atlas—of the developing brain. Therefore, our objective was to develop a scheme to parcelate the third trimester in vivo fetal brain into lobes, and apply this scheme onto scans in healthy fetal MRI brains to create a spatiotemporal atlas.
Based on a previous parcellation scheme of the neonatal brain, and conventional anatomical landmarks for classic brain lobe divisions, we devised a scheme to parcellate the fetal brain between 29-37 weeks into five lobes: frontal, parietal, temporal, occipital, and insular. We used an atlas of T2 weighted MRI images from 80 fetuses without any known pathological conditions.
Fetal atlases at 31, 33, 35, and 37 gestational weeks were parcellated into five lobes. Gestational week 29, the youngest gestational age in our sample, could not be parcellated because the landmarks outlined in our parcelation scheme have not yet appeared in the brain at this gestational age.
Taken together, our results show that available conventional anatomical landmarks for the division of the third trimester brain into classic lobes are only reliably applicable down to gestational weeks 30-31. A parcellation scheme for the fetal brain younger than 30 weeks will require different anatomical parameters from higher resolution MR images. Nevertheless, the fetal brain lobe parcellations presented here can be used in their current form as a tool to identify regional, lobular brain growth disturbances in third trimester high-risk fetal populations.