Derivation of Fiber Orientations From Oblique Views Through Human Brain Sections in 3D-Polarized Light Imaging.

Daniel Schmitz,Nicole Schubert,Martina Minnerop,Martin Schober,Markus Axer,Sascha E A Muenzing,Katrin Amunts,Thomas Lippert

doi:10.3389/fnana.2018.00075

Abstract

3D-Polarized Light Imaging (3D-PLI) enables high-resolution three-dimensional mapping of the nerve fiber architecture in unstained histological brain sections based on the intrinsic birefringence of myelinated nerve fibers. The interpretation of the measured birefringent signals comes with conjointly measured information about the local fiber birefringence strength and the fiber orientation. In this study, we present a novel approach to disentangle both parameters from each other based on a weighted least squares routine (ROFL) applied to oblique polarimetric 3D-PLI measurements. This approach was compared to a previously described analytical method on simulated and experimental data obtained from a post mortem human brain. Analysis of the simulations revealed in case of ROFL a distinctly increased level of confidence to determine steep and flat fiber orientations with respect to the brain sectioning plane. Based on analysis of histological sections of a human brain dataset, it was demonstrated that ROFL provides a coherent characterization of cortical, subcortical, and white matter regions in terms of fiber orientation and birefringence strength, within and across sections. Oblique measurements combined with ROFL analysis opens up new ways to determine physical brain tissue properties by means of 3D-PLI microscopy.

Highlights

Understanding the human brain’s function and dysfunction requires a thorough knowledge about the brain’s fiber tracts, forming a dense network of connections within, and between the different brain regions
2.1.1. 3D-Polarized Light Imaging (3D-PLI) 3D-PLI utilizes the birefringence of nerve fibers which is measured in customized polarimeters
We introduced the least-squares algorithm Robust Orientation Fitting via Least Squares (ROFL) for the reconstruction of fiber orientation and the extraction of the relative section thickness from measurements with a tiltable specimen stage in 3D-Polarized Light Imaging (3DPLI)

Summary

Introduction

Understanding the human brain’s function and dysfunction requires a thorough knowledge about the brain’s fiber tracts, forming a dense network of connections within, and between the different brain regions. At ultra-high resolution two-photon microscopy (Laperchia et al, 2013), light-sheet microscopy (Silvestri et al, 2012), and electron microscopy (Knott et al, 2008), amongst others, have been exploited to image single cells and neurons in 3D space as well as their local connections. These techniques come with the cost of excessive measurement time, large amounts of data and limited fields of view (lateral and axial), impeding the study of larger brain volumes so far.

Methods

Results

Conclusion