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Table of Contents
VTC (BrainVoyager QX's volume-based time-course) file format
Motivation
Most neuroimaging programs store functional data as a series of 3D volumes (separate files) or as a four-dimensional array, where still time is the slowest increasing index (in Matlab this refers to the last index). While this makes it convenient to display one of the volumes out of a time series, it usually makes regressing or plotting (averaged) timecourses a little more computational.
BrainVoyager QX's main developer, Rainer Goebel, thus decided for his software that storing data differently, such that time is the fastest increasing index, would be more suitable for data that is, in its most common application, used to either compute regression coefficients or being plotted against a time axis.
General setup
BrainVoyager's binary files are stored in little-endian byte ordering (for all platforms!) so as to allow cross-platform file exchange. Strings are stored as \0-terminated sequences of 8-bit integer values (ASCII charset, and not as either fixed-length or flag-specified-length strings).
The types in the list of fields are given as Matlab type (not in C notation).
Fields
| Loop / Condition | Field | Field type | Dimensions | Comment |
|---|---|---|---|---|
| FileVersion | uint16 | 1×1 | indicates which file version is used for a particular file (and thus which fields are stored in it) | |
| NameOfSourceFMR | string | \0-terminated | stores the filename of the FMR-file which was used to sample the data in VTC space | |
| FileVersion > 2 | NrOfLinkedPRTs | uint16 | 1×1 | indicates how many PRT files are referenced in the VTC header, for FileVersion up to 2 this defaults to 1 |
| NameOfLinkedPRT | string | NrOfLinkedPRTs \0-terminated strings | stores the filenames of the linked PRT files, for FileVersion up to 2 this can only store one filename, if no file is linked, set to empty string (a single 8-bit zero value) |
|
| FileVersion > 2 | NrOfCurrentPRT | uint16 | 1×1 | indicates which (out of multiple) linked PRT files is the currently active one |
| FileVersion > 2 | DataType | uint16 | 1×1 | indicates the data type used to store the functional data: 1 refers to uint16, 2 refers to single (32-bit float), for FileVersion up to 2, this defaults to 1 (VTC files can only store uint16 data!) |
| NrOfVolumes | uint16 | 1×1 | gives the number of volumes (timepoints) stored in the data field (with a maximum of 65535 volumes) | |
| Resolution | uint16 | 1×1 | indicates the spatial resolution in mm of the data (VTC files must store data in iso-metric resolution with an integer size argument; commonly supported values are 1, 2, and 3 representing 1mm-, 2mm-, and 3mm-resolution data; higher resolutions might not be fully supported by BrainVoyager) |
|
| XStart | uint16 | 1×1 | gives the X-coordinate (in BrainVoyager's internal coordinate system, this goes from front to back of the brain) where the data “starts” in space (a value between 0 and 255) |