Microstructural analysis of human white matter architecture using polarized light imaging: views from neuroanatomy

Abstract

To date, there are several methods for mapping connectivity, ranging from the macroscopic to molecular scales. However, it is difficult to integrate this multiply-scaled data into one concept. Polarized light imaging (PLI) is a method to quantify fiber orientation in gross histological brain sections based on the birefringent properties of the myelin sheaths. The method is capable of imaging fiber orientation of larger-scale architectural patterns with higher detail than diffusion MRI of the human brain. PLI analyses light transmission through a gross histological section of a human brain under rotation of a polarization filter combination. Estimates of the angle of fiber direction and the angle of fiber inclination are automatically calculated at every point of the imaged section. Multiple sections can be assembled into a 3D volume. We describe the principles of PLI and present several studies of fiber anatomy as a synopsis of PLI: six brainstems were serially sectioned, imaged with PLI, and 3D reconstructed. Pyramidal tract and lemniscus medialis were segmented in the PLI datasets. PLI data from the internal capsule was related to results from confocal laser scanning microscopy, which is a method of smaller scale fiber anatomy. PLI fiber architecture of the extreme capsule was compared to macroscopical dissection, which represents a method of larger-scale anatomy. The microstructure of the anterior human cingulum bundle was analyzed in serial sections of six human brains. PLI can generate highly resolved 3D datasets of fiber orientation of the human brain and has high comparability to diffusion MR. To get additional information regarding axon structure and density, PLI can also be combined with classical histological stains. It brings the directional aspects of diffusion MRI into the range of histology and may represent a promising tool to close the gap between larger-scale diffusion orientation and microstructural histological analysis of connectivity.

Automatic Segmentation of Human Cortical Layer-Complexes and Architectural Areas Using Ex vivo Diffusion MRI and Its Validation

“…Recently, new classifications are emerging, for instance based on neurotransmitter receptor architecture (Amunts et al, 2010). Moreover, new ways to probe the cyto- and myeloarchitectural of the brain have recently been developed, such as polarized light imaging (Axer and Keyserlingk, 2000; Axer et al, 2001; Axer H. et al, 2011; Axer M. et al, 2011) and optical coherence tomography (Wang et al, 2011; Magnain et al, 2015). These techniques allow to probe cyto- and myeloarchitecture in three dimensions at the resolution of few microns.…”

Quantification of anisotropy and fiber orientation in human brain histological sections

“…In the white matter, the myeloarchitecture accurately reflects the microstructure as a whole. This feature is exploited in polarized light microscopy to quantify the microstructural organization of tissue in thick sections, including through-plane fibers (Axer et al, 2011a,b). However, in the cortex and subcortical structures, the relatively greater proportions of other cells and subcellular elements, including neuronal somas, dendrites, and glial cells, all contribute to the measured diffusion signal.…”

FIBRASCAN: A novel method for 3D white matter tract reconstruction in MR space from cadaveric dissection

“…For instance, PLI (Axer et al, 2011a(Axer et al, , 2011b and OCT (Ben Arous et al, 2011;Goergen et al, 2012;Magnain et al, 2014) are very promising methods, sometimes regarded as "the" validation solutions for tractography. PLI attains a spatial resolution of the order of the micrometer for a given slice or series of neighboring slices.…”