Maturation of thalamic radiations between 34 and 41 weeks' gestation: a combined voxel-based study and probabilistic tractography with diffusion tensor imaging

Abstract

Background and purpose: This study aimed to investigate brain maturation along gestational age with diffusion tensor imaging in healthy preterm and term neonates. Therefore, a voxel-based study of fractional anisotropy (FA) and mean diffusivity (D(av)) was performed to reveal the brain regions experiencing microstructural changes with age. With tractography, the authors intended to identify which fiber tracts were included in these significant voxels.

Materials and methods: There were 22 healthy preterm and 6 healthy term infants who underwent MR imaging between 34 and 41 weeks of gestation. A statistical parametric approach was used to evidence the effect of age on regional distribution of FA and D(av) values. The fiber tracts suspected to be included in the significant clusters of voxels were identified with neuroanatomy and tractography atlases, reconstructed with probabilistic tractography, and superimposed on the parametric maps.

Results: Parametric analysis showed that FA increases with age in the subcortical projections from the frontal (motor and premotor areas) and parietal cortices, the centrum semiovale, the anterior and posterior arms of the internal capsules, the optic radiations, the corpus callosum, and the thalami (P < .05, corrected). Superimposition of the parametric maps on tractography showed that the corticospinal tract (CST); the callosal radiations (CR); and the superior, anterior, and posterior thalamic radiations were included in the significant voxels. No statistically significant results were found for D(av) maps.

Conclusions: These results highlight that, besides the already-evidenced FA increase in the CST and CR, the thalami and the thalamic radiations experience microstructural changes in the early development of the human brain.

Fig 1.

Areas with significant FA increase with age are located in the thalami (A, B), the anterior and posterior arms of the internal capsules, and the optic radiations (C), the centrum semiovale (D), and the subcortical projection pathways of the frontal and parietal cortices (E) in the axial (A–E) and coronal (F) planes. The anatomic underlay is the FA image of the template. The color maps represent the F-scores. Only regions of more than 50 voxels attaining a corrected P value of less than .05 for the voxel-level of statistical inference were considered significant.

Fig 2.

Regression plots derived from gestational age in relationship to FA values at the most statistically significant voxels located in the CST (F = 59.63), the thalamus (F = 31.23), the STR (F = 30.54), the ATR (F = 29.61), the CR (F = 29.44), and the PTR (F = 25.27) on the right side of the brain. The positive slopes of the regression lines indicate that FA increases with age.

Fig 3.

Superimposition of statistical parametric maps (red-orange), probabilistic tractography images (blue, green, pink, yellow), and FA images of the template in the axial (A–E) and coronal (F) planes. The CST (green), the STR (blue), the ATR, the PTR (pink), and the CR (yellow) are included in the significant voxels of the parametric analysis.