Introduction to VTC / VDW Creation
After creating a functional project from measured DICOM files (or other file formats), the original voxel data is stored in STC (slice time course) files. This data is usually preprocessed to improve data quality. At any stage (prior or after preprocessing), the FMR-STC data can be statistically analyzed using e.g. the General Linear Model. In order to perform whole-brain group analyses, the original FMR-STC data needs to be transformed into a common space (usually Talairach or MNI space). The FMR-STC data sets transformed into a normalized 3D space are called volume time course (VTC) files. The files from a single subject are usually linked to the subject's normalized anatomical VMR data set creating VMR-VTC projects. The conversion process from FMR-STC to VMR-VTC data is controlled by several spatial transformation (TRF) files that are obtained from the FMR-VMR coregistration step and the anatomical brain normalization step and that are provided as input parameters in the Create VTC dialog. The VTC files from multiple subjects can then be submitted to multi-subject group statistical analyses.
Note that it is possible to create VTC files in non-normalized spaces such as "native" space or ACPC space. Native space corresponds to the space of the measured 3D anatomical data set to which the functional data is coregistered. The resulting native or ACPC VTC data sets can not be used for group analyses but they may be interesting for individual analyses or for preparing data for specific applications such as TMS neuronavigation. Transformations to native and ACPC space are linear operations preserving the original brain shape, i.e. millimeters in the VMR-VTC data correspond to physical millimeters of the subject and not to normalized millimeters in MNI or Talairach space. The creation of VTC data in these non-normalized spaces is performed in the same Create VTC dialog simply by excluding brain normalization files.
While spatial transformation is usually described for VTC data, the same tools are also available for diffusion-weighted data. Insteas of creating VTC files from FMR-STC data, VDW (volume diffusion weighted) files are created from DMR-DWI data.
Creation of VTCs with Voxel Data Identical to FMR-STC Data
The usual goal to create VTC files is to bring the FMR-STC data from different subjects (and from different sessions of the same subject) into a common (normalized) space allowing group analyses. For some applications it might be useful to create VTC data sets without resampling of the original FMR-STC data, i.e. the VTC data would be identical to the one in source FMR-STC files.
Creation of High-Resolution Sub-Millimeter VTCs
In most cases the voxel resolution of functional data is not below 1 mm and can, thus, be handled by the normal processing pipeline in BrainVoyager with 1 mm VMR data sets in native, ACPC or Talairach space. It is also possible to create VTC files containing sub-millimeter functional resolution data. For a description on how to handle such high-resolution data that is usually obtained from ultra-high field scanners (7 Tesla and beyond), see the topic Creation of High-Resolution VTCs.
Copyright © 2020 Rainer Goebel. All rights reserved.