In a new study, researchers compared the orientations of nerve fibers in a human brainstem using two advanced imaging techniques: diffusion-weighted magnetic resonance imaging (dMRI)-based tractography and polarization-sensitive optical coherence tomography (PS-OCT). The findings could help combine these techniques, each offering unique advantages, to advance our understanding of brain microstructure and help inform new techniques for the early diagnosis of various brain disorders.
Isabella Aguilera-Cuenca from the University of Arizona will present this research at Frontiers in Optics + Laser Science (FiO LS), which will be held September 23-26, 2024 at the Colorado Convention Center in Denver.
Neurodegenerative diseases are becoming more prevalent as life spans increase and populations age – a better understanding of the relationship between brain microstructure and these diseases could lead to the development of improved methods of prevention, detection and management.”
Isabella Aguilera-Cuenca, University of Arizona
The orientation of nerve fibers is an important aspect of brain microstructure because of its influence on connectivity and communication pathways in the brain. One way to study this microstructure is to use dMRI, a non-invasive imaging method that uses the diffusion of water molecules to reveal structural connectivity. A specialized application of dMRI known as diffusion tensor imaging (DTI) can be used to reconstruct nerve fiber pathways through a process known as tractography. Although DTI is sensitive to differences between brain tissue environments, it cannot detect specific cellular changes and can only resolve neural pathways, not individual axon orientations.
PS-OCT is also useful for studying brain microstructure. It uses backscattered light properties and polarization variations to create cross-sectional images with depth resolution of tissue microstructures. This information can be used to identify fiber tracts with microscale resolution and distinguish between white and gray matter. However, in scattering media such as brain tissue, PS-OCT can only image to a depth of a few millimeters.
To perform a quantitative comparison of nerve fiber orientation distributions with dMRI- and PS-OCT-based tractography, the researchers used both techniques to image a human brainstem specimen fixed in paraformaldehyde and then stored in PBS with sodium azide .
The results showed that phase retardation and optical axis polarization properties can be used to map the presence and orientation of nerve fibers in brain tissue, similar to results obtained through dMRI. This indicates the strong potential of PS-OCT to validate dMRI data, providing valuable insights into the microstructural organization of nerve fibers, which is crucial for understanding the normal physiology and changes that may occur with neurodegenerative conditions.
“To advance this work further, we will study microstructural alterations in a range of brain regions from patients with different neurodegenerative conditions, with the aim of identifying changes that occur with the onset of the disease,” said Aguilera-Cuenca. “We hope that this work ultimately translates into new approaches for the early detection of these pathologies.”
