The effect of atlas selection on voxel based analyses of DTI data

Introduction: In recent years, voxel based analysis (VBA) studies have demonstrated the potential of diffusion tensor imaging (DTI) to detect white matter (WM) damage in patients with various neurological or psychiatric disorders. In VBA, all DTI data sets are transformed to an atlas or template, whereafter the diffusion measures of control subjects and patients are evaluated in each voxel. In most VBA studies of DTI data sets, a standard template, such as the Montreal Neurologic Institute (MNI) atlas, is used. The advantage of the MNI atlas is that it contains coordinate, anatomic, and cytoarchitectonic labels and that the VBA results can be easily compared across studies using the MNI coordinates. However, since this atlas is not study-specific, it might fail to provide a good representation of the population that is studied, thereby potentially resulting in residual image misalignment after coregistration of the DTI data sets to this reference space. Mori et al. (2008) introduced a stereotaxic WM template (the ICBM-81 atlas) that was constructed from 81 DTI data sets of healthy subjects that were normalized with an affine transformation to the ICBM-152 template [1]. This template contains the tensor elements, so that they can be used in amulti-channel coregistration approach. Recently a population based, study specific DTI atlas was introduced, whereby the magnitudes of the deformation fields that are needed to warp the different images to the atlas are minimized, potentially leading to a decreased image misalignment in VBA [2]. The goal of this work was to examine the effect of the atlas selection on the reported VBA results. To this end, DTI data sets of multiple sclerosis (MS) patients and control subjects are examined with VBA using different DTI templates. These templates are (i) a study-specific population-based template (PA), (ii) a studyspecific subject-based atlas in MNI space (SA), and (iii) the ICBM-81 template of Mori et al. (2008) (MA).