Spatially filters each 3D volume of a VTC file in the frequency domain.
objDocument.SpatialSmoothingFD3D(intHighPass, intLowPass)
Valid only if objDocument
is of type VMR and if a VTC file has been linked. If the VTC file is referenced
but not in memory, BrainVoyager will load the VTC file prior to running
the spatial filter. The high- and low pass values are interpreted in cycles
per spatial dimension measured in voxels. Since there are three spatial
dimensions, the largest dimension is chosen as reference. Since VTC files
normally are in Talairach space, the largest dimension is the YTAL-dimension
corresponding to 174 mm or 174 voxels in a 1mm3
VMR data set (for details about the dimensions of VTC files, see chapter
"BrainVoyager File Formats"). Since the functional data in VTC
files consists typically of 3mm3
voxels, this results in a value of 174/3 = 58 when measured in voxels.
A low pass value equal to or greater than half of this value (> 26)
lets everyghing pass, it will have no effect (Nyquist theorem). In the
GUI version (3D Data Preprocessing dialog),
BrainVoyager sets the default value of the low pass filter to roughly
half of this value (14) which produces a modest spatial smoothing roughly
equal to spatial smoothing with a FWHM of 4mm in the spatial domain. In
the GUI version the high-pass filter is turned off since it is not useful
in the context of fMRI data analysis. To turn the high-pass filter off,
specify "1" as the intHighPass
value.
As in the GUI version, the spatial filter produces a new VTC file which
is saved to disk automatically under a new file name. The new file name
is based on the name of the linked VTC file prior to starting the filter
and adds a substring describing the preprocessing performed. If, for example,
the name of the linked VTC file was "cg_objects_SC_3DMC.vtc",
the new name will be "cg_objects_SC_3DMC_FSS-1-14.vtc". The
added substring "_FSS-1-14" describes that spatial smoothing
(SS) has been performed in the frequency domain (FSS) using a high-pass
filter of "1" and a low-pass filter of "14". All 3D
preprocessing steps add such descriptive substrings which makes it easy
to get the information about the sequence of steps which has been performed
to produce a particular VTC file. If you do not want to use the implicit
naming scheme, you might want to use the method SpatialSmoothingFD3DEx which allows
to specify the source VTC file and the target VTC file.
Note also that the resulting VTC file is linked automatically to objDocument which allows to run a cascade
of preprocessing commands without having to link intermediate files.
' VBScript
Set doc = BrainVoyager.OpenDocument("subject.vmr")
doc.LinkVTC "cg_objects_SC.vtc"
doc.TemporalSmoothingFD3D 3, 200 ' produces "cg_objects_SC_FTS-3-200.vtc"
doc.SpatialSmoothingFD3D 1, 14 ' produces "cg_objects_SC_FTS-3-200_FSS-1-14.vtc"
// JScript
doc = BrainVoyager.OpenDocument("subject.vmr");
doc.LinkVTC("cg_objects_SC.vtc");
doc.TemporalSmoothingFD3D(3, 200);
doc.SpatialSmoothingFD3D (1, 14);
#
PerlScript
$doc = $BrainVoyager->OpenDocument("subject.vmr");
$doc->LinkVTC("cg_objects_SC.vtc");
$doc->TemporalSmoothingFD3D(3, 200);
$doc->SpatialSmoothingFD3D (1, 14);