Table of Contents
MAP (BrainVoyager QX's FMR-based map) file format
Motivation
The more common case of running statistics is in either 3D voxel (VTC/VMP) space, but there are still quite a few applications for running statistics with data that has been altered as little as possible (minimal preprocessing). The MAP format provides the ability to store a slice-based maps that match the FMR layout. At this point, there is no support for storing multiple statistics per FMR voxel.
General setup
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 |
|---|---|---|---|---|
| CombinedTypeSlices | uint16 | 1×1 | stores both the type of statistical map and number of slices; combination formula is (RESERVED_TOKEN + 1) * STATTYPE_VALUE + NR_OR_SLICES where RESERVED_TOKEN is set to 9999 (see below); supported types are: t-statistic (value 0), r-statistic (value 1), lag+r-statistic (value 2), F-statistic (value 3); see ReservedToken below |
|
| NrOfSlices | uint16 | 1×1 | stores the number of slices separately; if set to 0, number of slices is determined from the CombinedTypeNrOfSlices field |
|
| DimY | uint16 | 1×1 | stores the number of columns (2nd dim in Matlab) in each slice's map | |
| DimX | uint16 | 1×1 | stores the number of rows (1st dim in Matlab) in each slice's map | |
| ClusterSize | uint16 | 1×1 | if cluster thresholding enabled, value is set > 1 |
|
| LowerThreshold | single | 1×1 | lower statistics threshold, map values below are not shown | |
| UpperThreshold | single | 1×1 | upper statistics threshold, map values above are shown in same color as if being UpperThreshold |
|
STATTYPE_VALUE == 2 | NrOfLags | uint16 | 1×1 | for maps that contain combined r-statistic and lag value (description see below), this additional header parameter is read |
| ReservedToken | uint16 | 1×1 | used in computation to split statistics and number of slices; as this is given AFTER the NrOfLags field must be read, this value MUST remain set at 9999; otherwise BrainVoyager will not read those maps correctly! |
|
| FileVersion | uint16 | 1×1 | this is an exceptional case, normally the FileVersion is the first or at least one of the very first flags in any file format of BrainVoyager QX! | |
FileVersion > 2 | DF1 | uint32 | 1×1 | degrees of freedom for t/r-statistic, first d.f. parameter of F-statistic |
FileVersion > 2 | DF2 | uint32 | 1×1 | second d.f. parameter of F-statistic; important: while only required for F-statistic maps, this parameter is ALWAYS present (for FileVersion of 3 and above!) |
| NameOfSDMFile | string | \0-terminated | name of design matrix file that was used (empty of non-applicable | |
Loop over NR_OF_SLICES | ||||
| Map(LOOP_SLICE).Number | uint16 | 1×1 | number of map, 0-based (first slice has a value of 0) |
|
| Map(LOOP_SLICE).Data | single | DimX-by-DimY | statistics value; important: for r-statistics, the actual r-statistical value is computed as sign(MAP_VALUE) .* (1 - abs(MAP_VALUE)) (!) where an r-statistical value of 0 remains at 0 (prohibiting a value of 1), for r+lag-statistical maps, the value is comprised of MAP_VALUE = MAP_VALUE_R + MAP_VALUE_LAG so that, in reverse, the lag can be extracted as MAP_VALUE_LAG = floor(MAP_VALUE) and the internal r-value (1-r!) can be retrieved as MAP_VALUE_R = MAP_VALUE - MAP_VALUE_LAG |
|
End of Loop over NR_OF_SLICES |