The following steps must be performed:
- Selection of regions of interest (ROI):
As a first step, locations for the regions of interest must be defined. ROIs are defined as spheres whose centers and radii must be supplied by the user. In general, the same ROIs should be used for all subjects and conditions. The centers of the ROIs may for instance be obtained by using local maxima of a zmap. - Creation of a ROI-mask
In 'vmaskedit', the ROIs are defined as spheres that are given
in an ASCII file containing a list of points (sphere centers).
The format of this file is the same as that for the program 'vshowpts'.
Each line specifies one point and has the following format:
x y z id radius
Example:
10 20 35 1 2
10 23 24 1 2
18 33 17 2 3
This line produces two spheres of a two voxel radius and id '1', and one of a three voxel radius with id '2'.
Spheres with identical id's are treated as one entity in subsequent analyses steps.
If the radius is set to '0' then a single voxel is set in the mask.
The radius is given in voxels (not millimeters).
The dimension of the output image (its matrix size) can be specified using
the parameters '-nslices', '-nrows', '-ncolumns'. If set to '0', a default value
is used.
Example:
vmaskedit -in pts.txt -system talairach -resolution 3 -out roi.v
The output 'roi.v' is a file containing all ROIs specified in 'pts.txt'.
The parameter '-resolution' defines the voxel-size in mm. In this example,
voxels in the output-file are of size 3x3x3mm.
Hint:
The resulting file 'roi.v' can be visualized as follows:
vconvert -in roi.v -repn float -map linear -out roi_1.v
vlview -in normbrain.v -zmap roi_1.v
For details of vconvert see via-help.