White matter tract crossing and bottleneck regions in the fetal brain

TL;DR

This study maps crossing and bottleneck regions in fetal brain white matter using diffusion MRI, revealing high prevalence of complex tract configurations and emphasizing the need for improved imaging techniques.

Contribution

It provides the first quantification of crossing tracts and bottlenecks in the fetal brain across gestational ages using probabilistic tractography.

Findings

20-25% of voxels have 2-3 crossing tracts

75-80% of voxels are bottlenecks involving 4 or more tracts

Highlights challenges in fetal brain tractography

Abstract

There is a growing interest in using diffusion MRI to study the white matter tracts and structural connectivity of the fetal brain. Recent progress in data acquisition and processing suggests that this imaging modality has a unique role in elucidating the normal and abnormal patterns of neurodevelopment in utero. However, there have been no efforts to quantify the prevalence of crossing tracts and bottleneck regions, important issues that have been extensively researched for adult brains. In this work, we determined the brain regions with crossing tracts and bottlenecks between 23 and 36 gestational weeks. We performed probabilistic tractography on 59 fetal brain scans and extracted a set of 51 distinct white tracts, which we grouped into 10 major tract bundle groups. We analyzed the results to determine the patterns of tract crossings and bottlenecks. Our results showed that 20-25% of the white matter voxels included two or three crossing tracts. Bottlenecks were more prevalent. Between 75-80% of the voxels were characterized as bottlenecks, with more than 40% of the voxels involving four or more tracts. The results of this study highlight the challenge of fetal brain tractography and structural connectivity assessment and call for innovative image acquisition and analysis methods to mitigate these problems.