Imaging white matter in human brainstem

Area of Science:

• Neuroimaging
• Neuroanatomy
• Biophysics

Background:

• The human brainstem controls vital functions and information transfer.
• Current in vivo imaging methods for brainstem white matter are limited by motion and anatomical complexity.
• Ex vivo studies provide detailed anatomy but cannot be applied to living subjects.

Purpose of the Study:

• To investigate the limits of diffusion MRI tractography for mapping brainstem white matter architecture.
• To assess the impact of spatial resolution on the accuracy of tractography in the brainstem.

Main Methods:

• High angular resolution diffusion imaging (HARDI) was performed on an excised human brainstem at 11.1 Tesla.
• Acquisitions were conducted at isotropic resolutions of 0.333 mm, 1 mm, and 2 mm.
• Tractography algorithms were applied to reconstruct white matter pathways at each resolution.

Main Results:

• At 0.333 mm resolution, dense fiber architecture and distinct pathways like corticopontine/corticospinal tracts (CPT/CST), cerebellar peduncles (SCP, MCP), and medial lemniscus (ML) were discernible.
• Lower resolutions (1 mm and 2 mm) resulted in artificial enlargement of CPT/CST, SCP, and MCP due to fiber crossing and insufficient spatial resolution.
• The ML pathway appeared smaller at lower resolutions, indicating failure to resolve finer structures.

Conclusions:

• High spatial resolution is critical for accurate in vivo diffusion MRI tractography of the human brainstem.
• Current clinical resolutions may not adequately resolve complex white matter pathways in the brainstem.
• Excised brainstem tractography data can inform and guide in vivo diffusion MRI studies of brainstem architecture.