Detection and Growth Pattern of Arcuate Fasciculus from Newborn to Adult

Abstract

Fractional anisotropy (FA) threshold is commonly used to perform diffusion MRI tractography. However, FA threshold may be one aspect of tractography that needs additional scrutiny in accurately assessing pathways in immature, developing brains, as well as in adult brains. Using high-angular resolution diffusion MRI (HARDI) tractography without an FA threshold, we identified the arcuate fasciculus (AF) of 83 healthy subjects ranging in age from 40 gestational weeks (GW) (newborns) to 28-year-old adults. The AF was identified in both hemispheres in all subjects with high inter-rater reliability. The detected AF included regions with very low FA values. The entire AF was segmented into anterior, posterior, and long tracts. Growth and laterality patterns were investigated using tract count (number of detected streamlines), total volume of imaging voxels (touched by the detected streamlines), mean length, mean FA, and mean apparent diffusion coefficient (ADC). Comparison of subjects under 3 years old, to those that were older, revealed the three AF tracts that took different developmental courses. As expected, the anterior and long tracts showed lower ADC values in subjects over 3 years old, while the posterior tract showed higher ADC in that same age range. The posterior tract did not show age-related effect in terms of FA, tract count, length, and volume. These results suggest that the posterior AF tract shows a matured state, indexed by most of the used measurements in early postnatal developmental ages, and ADC is a measurement that can detect further maturation of the posterior tract. Interestingly, in all tracts, hemispheric asymmetries were found in raw (left<right), and in whole brain (WB)-normalized (left>right) tract count, as well as in raw volume (left<right). In raw, and in WB-normalized length, as well as in WB-normalized volume, rightward asymmetry (left<right) was found only in the anterior tract; other tracts were not significantly affected by hemisphere. Although many previous studies have observed a leftward asymmetry in the AF, rightward asymmetry has also been reported in other studies, and together with the present report, the results in the literature are likely to reflect differences in the methods used.

A Brain for Speech. Evolutionary Continuity in Primate and Human Auditory-Vocal Processing

“…A recent study combining tractography and functional connectivity in a semantic decision task, found that the left AF is more robustly connected with the lateral temporal cortex in the left hemisphere, but with the inferior parietal lobe in the right hemisphere (Takaya et al, 2015 ). Nonetheless, a recent review indicates that there are some inconsistencies across studies when determining the asymmetry of the AF (Wilkinson et al, 2017 ).…”

Asymmetric Insular Connectomics Revealed by Diffusion Magnetic Resonance Imaging Analysis of Healthy Brain Development

“…High-angular resolution diffusion MR imaging (HARDI) tractography enables identification of complex crossing-fiber tissue coherence in the brain (Tuch et al, 2003), even in immature brains (e.g., Takahashi et al, 2012;Vasung et al, 2017;Wilkinson et al, 2017), which are typically more challenging to segment due to a surplus of unmyelinated fibers [see discussions in Wilkinson et al (2017)]. HARDI tractography allows for the reconstruction of water diffusivity in many different directions in each imaging voxel.…”

Evolution of connections and cell types: integrating diffusion MR tractography with gene expression data highlights increased cortico-cortical projections in primates

“…Diffusion spectrum and high angular resolution diffusion imaging can theoretically resolve crossing fibers (e.g. Takahashi et al, 2010Takahashi et al, , 2011Takahashi et al, , 2012, as well as pathways in poorly myelinated regions (Wilkinson et al, 2017). Indeed, our diffusion MR tractography successfully traced a number of well-characterized pathways.…”