Current developments of white matter connectivity research in Schizophrenia; A study into voxel based versus track based DTI methodology

Abstract

Research in schizophrenia has shown that structural brain abnormalities exist in patients with this disorder, but while imaging studies mostly pointed in the direction of gray matter changes, post‐mortem studies were also finding abnormalities in neuronal cytoarchitecture and glial cells. These cells are highly important for the protection and formation of neuronal axons, and defective glial cells can lead to white matter changes. Newly developed MRI‐methods such as diffusion tensor imaging (DTI) are able to investigate white matter changes in schizophrenia in vivo. DTI measures describe the magnitude and orientation of water diffusion and the shape of the diffusion profile and are often described with a scalar value named the fractional anisotropy (FA). When diffusion weighted images are analyzed there are two different techniques available to determine and compare group differences in region‐specific FA variations. Voxel Based Morphometry analysis is the most straightforward method to look at group differences between FA values. It enables you to do whole brain analysis to indicate what regions have variations in FA values that exceed pure statistical chance. This means that it is a broad but coarse method. Tract‐based analysis is a method that compares FA values of specific white matter fiber paths. An a priori region of interest is necessary to be able to use this method. This method increases the statistical power compared to VBM methods, which will allow for more sensitive detection of FA group differences. In this thesis both methods will be discussed, as well as the current developments in both fields in schizophrenia research. Furthermore research methods like scan protocol, voxel size, patient groups and VBM blurring will be compared to better understand contradicting or overlapping research results.