Computes the spherical harmonic expansion of log(A(q)) in each voxel and uses an F-test
to determine the simplest model that gives a good fit to the data.
If F-test thresholds are specified, the program performs the F-Test and outputs the
highest spherical harmonic order required to fit the data: 0 for isotropic data, 2 for
anisotropic Gaussian, and 4 or more (up to the maximum) for anisotropic non-Gaussian
data. Voxels classified as background (see OPTIONS) have order -1.
If no f-test thresholds are specified on the command line, the program outputs all the
f-statistics in each voxel for independent processing. These results are suitable for
reading into the vcthreshselect program for interactive model selection. The format of
the output for each voxel is:
exit code
log b=0 intensity estimate
f statistic comparing order 0 and order 2 models
f for order 0 and 4
:
f for order 0 and n where n is the maximum order specified
f for order 2 and 4
:
f for order 2 and n
:
f for order n-2 and n
OPTIONS
-ftest <thresholds>
Specifies the F-test thresholds for adopting higher order models. A threshold must be
provided for every order between 0 and the maximum order. The program will not consider a
higher order model unless the result of the F-test is smaller than the relevant
threshold.
-bgthresh <minA0>
Classifies all voxels with A(0) < minA0 as background, without performing the F-test on
the voxel. Ignored if -ftest is not specified.
-csfthresh <maxA0>
Classifies all voxels with A(0) > maxA0 as isotropic, without performing the F-Test on
the voxel. Ignored if -ftest is not specified.
-bgmask <image>
Set an explicit brain / background mask. Overrides -bgthresh.
-order <maxOrder>
Set the maximum even spherical harmonic order that will be considered by the program.
Must be a positive even number. Default is 4.
EXAMPLES
Classify the data in image SubjectA.Bfloat, using no csf threshold. Classify all voxels
with A(0) < 50.0 as background. The threshold for selecting an order 2 model is 1E-20,
the thresholds for the order 4 and 6 model are 1E-6.
The next example does the same thing, but because no -ftest is specified, the program
outputs the raw F-Test data for later analysis (eg with vcthreshselect(1)).