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MAP (BrainVoyager QX's FMR-based map) file format


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).


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
xff_-_map_format.txt · Last modified: 2010/06/24 16:46 by jochen