In vivo 3D Reconstruction of the Human Pallidothalamic and Nigrothalamic Pathways With Super-Resolution 7T MR Track Density Imaging and Fiber Tractography.

Dae-Hyuk Kwon,Zang-Hee Cho,Sun Ha Paek,Young-Bo Kim,Haigun Lee

doi:10.3389/fnana.2021.739576

Abstract

The output network of the basal ganglia plays an important role in motor, associative, and limbic processing and is generally characterized by the pallidothalamic and nigrothalamic pathways. However, these connections in the human brain remain difficult to elucidate because of the resolution limit of current neuroimaging techniques. The present study aimed to investigate the mesoscopic nature of these connections between the thalamus, substantia nigra pars reticulata, and globus pallidus internal segment using 7 Tesla (7T) magnetic resonance imaging (MRI). In this study, track-density imaging (TDI) of the whole human brain was employed to overcome the limitations of observing the pallidothalamic and nigrothalamic tracts. Owing to the super-resolution of the TD images, the substructures of the SN, as well as the associated tracts, were identified. This study demonstrates that 7T MRI and MR tractography can be used to visualize anatomical details, as well as 3D reconstruction, of the output projections of the basal ganglia.

Highlights

The basal ganglia (BG), which are broadly involved in various roles related to motor, associative, and limbic functions, are responsible for motor, cognitive, and mood changes typically caused by movement disorders such as Parkinson’s disease (PD; Obeso et al, 2014)
We identified the entire path of the pallidothalamic and nigrothalamic tracts and substructures of the thalamus, globus pallidus internal segment (GPi), and SN in super-resolution T2* and track-density imaging (TDI) images with an in-plane resolution of 0.2 mm (Figure 2 and Supplementary Figure 2)
Based on the sectional image and the streamline obtained from tractography, it was arranged with a reconstructed 3D model to provide a comprehensive understanding of the structures in vivo

Summary

Introduction

The basal ganglia (BG), which are broadly involved in various roles related to motor, associative, and limbic functions, are responsible for motor, cognitive, and mood changes typically caused by movement disorders such as Parkinson’s disease (PD; Obeso et al, 2014). It is difficult to apply observations of the pallidothalamic and nigrothalamic tracts in non-human primates to the human brain (Carpenter et al, 1976; Hazrati and Parent, 1991). Even with the recently developed 9.4 Tesla (T) magnetic resonance imaging (MRI; Massey et al, 2012) and ultra-high-field 11.7T diffusion tensor imaging (DTI; Oishi et al, 2020), it is difficult to visualize in detail the entire course of the tracts ex vivo. The pallidothalamic pathway and related structures have been visualized with the surface models in a recent study using a sectioned cadaveric brain (Chung and Park, 2020), detailed reconstruction studies in 3D space are needed to determine the exact anatomy of the tracts in vivo

Methods

Results

Conclusion