ARRS 2022 Abstracts

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1522. Normal Microstructural Development of the Fetal Cortex and Deep Gray Matter
Authors * Denotes Presenting Author
  1. Fedel Machado Rivas; Boston Children's Hospital; Harvard Medical School
  2. Camilo Calixto *; Bogota Hospital
  3. Sebastian Gallo Bernal; Harvard Medical School; Massachusetts General Hospital
  4. Clemente Velasco-Annis; Boston Children's Hospital
  5. Simon Warfield; Boston Children's Hospital; Harvard Medical School
  6. Ali Gholipour; Boston Children's Hospital; Harvard Medical School
  7. Camilo Jaimes Cobos; Boston Children's Hospital; Harvard Medical School
Objective:
The microstructure of the cortex and deep gray matter changes rapidly in the late fetal stage. We aim to characterize microstructural changes in the cortex and deep grey matter of typically developing fetuses using DTI.

Materials and Methods:
A total of 124 motion-corrected fetal DTI acquisitions were used to create gestational-age specific DTI atlases (one atlas per week of gestation from 24-38 weeks [w]). We placed ROIs in the cerebral lobes (frontal, parietal, occipital, temporal), the thalami, and the lentiform nuclei; these were reviewed and edited by a neuroradiologist with expertise in fetal imaging. The relationship between FA and MD with GA was modeled using linear and quadratic terms. Based on previously described fetal diffusion trajectories, we divided our analysis into early developmental stage (EDS) (=30w, centered at 27w) and late developmental stage (LDS) (>30 w, centered at 34w).

Results:
In the cortex, FA decreased linearly for all GA, whereas MD increased in EDS and decreased in LDS. The FA in the frontal cortex decreased at -.0085 units/week (u/w), in the parietal cortex at -.0076 u/w, in the temporal cortex at -.0064 u/w, and in the occipital cortex at -.0112 u/w (all P<.001). In a four-way comparison, the only significant between-group difference was faster decrease of FA in the occipital cortex relative to the temporal cortex (Bonferroni adjusted [BA] P=.011). The MD in the fontal cortex was stable in EDS (-.0010 mm/s2 /w, P=.864) and decreased in LDS (-.0229 mm/s2 /w, P=.001); the parietal cortex increased in EDS (.0254 mm/s2 / w, P<.001) and decreased in LDS (-.0375 mm/s2 /w, P<.001); the temporal cortex increased in EDS (.0217 mm/s2 /w, P<.001) and decreased in LDS (-.0498 mm/s2 /w, P<.001); and the occipital cortex increased in EDS (.0221 mm/s2 /w, P<.001) and decreased in LDS (-.0431 mm/s2 /w, P<.001). During the EDS, a four-way comparison revealed faster MD increase in the parietal cortex relative to the frontal cortex (BA adjusted P=.007). In the LDS, the only significant difference was faster MD decrease in the temporal cortex relative to the frontal cortex ( BA adjusted P=.016). The thalamus increased in FA in EDS (.0038 u/w, P<.001); this trend plateaued in the LDS (.0004 u/w, P=.456 ). MD in the thalamus was stable in the EDS (-.0012 mm/s2 /w, P=.729) and decreased in LDS (-.0234 mm/s2 /w, P<.001). The FA in the lentiform nuclei decreased in EDS (-.0014 u/w, P<.001) and remained stable in LDS (.00018 u/w, P=.623); the MD remained stable in EDS (.0031 mm/s2 /w, P<.170) and decreased in LDS (-.0213 mm/s2 /w, P<.001).

Conclusion:
Microstructural development of the fetal gray matter is heterogeneous. FA decreased with age in the cortex and increased with age in the thalamus. MD in the cortex peaks around 30 weeks and then decreases; in the deep gray matter, age-related decrease accelerated late in development. Deviations from these trends could help identify pathology on fetal MRIs.