Probabilistic maps of the white matter tracts with known associated functions on the neonatal brain atlas: Application to evaluate longitudinal developmental trajectories in term-born and preterm-born infants

Abstract

Diffusion tensor imaging (DTI) has been widely used to investigate the development of the neonatal and infant brain, and deviations related to various diseases or medical conditions like preterm birth. In this study, we created a probabilistic map of fiber pathways with known associated functions, on a published neonatal multimodal atlas. The pathways-of-interest include the superficial white matter (SWM) fibers just beneath the specific cytoarchitectonically defined cortical areas, which were difficult to evaluate with existing DTI analysis methods. The Jülich cytoarchitectonic atlas was applied to define cortical areas related to specific brain functions, and the Dynamic Programming (DP) method was applied to delineate the white matter pathways traversing through the SWM. Probabilistic maps were created for pathways related to motor, somatosensory, auditory, visual, and limbic functions, as well as major white matter tracts, such as the corpus callosum, the inferior fronto-occipital fasciculus, and the middle cerebellar peduncle, by delineating these structures in eleven healthy term-born neonates. In order to characterize maturation-related changes in diffusivity measures of these pathways, the probabilistic maps were then applied to DTIs of 49 healthy infants who were longitudinally scanned at three time-points, approximately five weeks apart. First, we investigated the normal developmental pattern based on 19 term-born infants. Next, we analyzed 30 preterm-born infants to identify developmental patterns related to preterm birth. Last, we investigated the difference in diffusion measures between these groups to evaluate the effects of preterm birth on the development of these functional pathways. Term-born and preterm-born infants both demonstrated a time-dependent decrease in diffusivity, indicating postnatal maturation in these pathways, with laterality seen in the corticospinal tract and the optic radiation. The comparison between term- and preterm-born infants indicated higher diffusivity in the preterm-born infants than in the term-born infants in three of these pathways: the body of the corpus callosum; the left inferior longitudinal fasciculus; and the pathway connecting the left primary/secondary visual cortices and the motion-sensitive area in the occipitotemporal visual cortex (V5/MT+). Probabilistic maps provided an opportunity to investigate developmental changes of each white matter pathway. Whether alterations in white matter pathways can predict functional outcomes will be further investigated in a follow-up study.

Keywords: Diffusion tensor imaging; Functional pathway; Neonate; Preterm birth; Probabilistic map; Tractography.

Figure 1

Probabilistic maps of the white matter tracts with known associated functions, as well as other major white matter tracts, overlaid on the fractional anisotropy map of the JHU-neonate atlas. The three-dimensional (3D) surface of the fibers, determined by the 75% probability, was also visualized with the brain surface of the JHU-neonate-SS template (top row). AR = the acoustic radiation; BCC = the body of the corpus callosum, CG = the cingulum; CST = the corticospinal tract; GCC = the genu of the CC; IFO = the inferior fronto-occipital fasciculus; ILF = the inferior longitudinal fasciculus; MCP = the middle cerebellar peduncle; OR = the optic radiation; PMC = the primary motor cortex, PSC = the primary somatosensory cortex, SCC = the splenium of the CC, Thal = the thalamus, UNC = the uncinate fasciculus. V1-V4 = the pathway that connects the V1/V2 and the V4, V1-mt = the pathway that connects the V1/V2 and the V5/MT+.

Figure 2

Trace values of the white matter pathways. The three time points in each subject are connected with a solid line. Significant differences between term (cyan) and preterm (red) babies were identified in the body of the corpus callosum (BCC), the left inferior longitudinal fascicule (ILF), and the pathway that connects the V1/V2 and the V5/MT+ (V1-MT) and that are marked with an * and a black rectangle. AR = the acoustic radiation, CG = the cingulum, CST = the corticospinal tract, GCC = genu of the CC, IFO = the inferior fronto-occipital fasciculus, MCP = the middle cerebellar peduncle, OR = the optic radiation, PMC = the primary motor cortex, PSC = the primary somatosensory cortex, SCC = the splenium of the CC, Thal = the thalamus, UNC = the uncinate fasciculus. V1-V4 = the pathway that connects the V1/V2 and the V4.

Figure 3

Corrected trace value of each time point, plotted against gestational age at birth. BCC = the body of the corpus callosum, ILF = the inferior longitudinal fasciculus, T1 = time point 1, T2 = time point 2, T3 = time point 3. V1-MT = the pathway that connects the V1/V2 and the V5/MT+.