Dear Lee,
If you can define your ROI/VOI on the raw scans, it would be the easiest way
to read them into a 4D-matrix (e.g.: with variable name of ana) in MATLAB,
using scan/time as the 4th dim.
Then if you image one of the scan of interest with MATLAB command
"image(ana(:,:,z,t))", where z is slice number, t is scan/time, you can use
"bw = roipoly;", to define a ROI-mask. You will probably need to scale this
image with about 10 or 20 to see a "readable" image:
image(ana(:,:,z,t)/10);
Next you have to put this 2D mask into a 3D mask, like one of your analyze
matrix:
mask = false(max_x,max_y,max_z); where max_x, max_y are your in-plane
resolution, max_z is the number of slices.
mask(:,:,z) = bw; where z is the same as used in command image
After it, you can use this mask to get your signal alteration according to
scan/time:
for i = 1:t
a = ana(:,:,:,i);
sign(i) = mean(a(mask));
end
sign will be your signal alteration data, which you can transform into %
change:
for i = 1:t
sign_p(i) = (sign(i)/sign(1)-1)*100;
end
I hope it works,
Auer, Tibor M.D.
PhD-student
University of Pécs, Medical Faculty
Department of Neurosurgery
Rét u. 2, Pécs, H-7623, Hungary
Tel.: +36-20-986-9341
E-mail: [log in to unmask]
-----Original Message-----
From: SPM (Statistical Parametric Mapping) [mailto:[log in to unmask]] On
Behalf Of Lee Walsh
Sent: Friday, May 18, 2007 8:46 AM
To: [log in to unmask]
Subject: [SPM] Mean % Signal change over a box volume
Hello again SPM users,
I currently have a problem where I am trying to determine the mean
percent signal change of the voxels within a box shaped volume. These
voxels may or may not be above threshold in the statistical parametric
map. I can't find any way to do this in SPM5. Generally speaking I can
only get SPM5 to give information on one voxel at a time and never about
a non-significant voxel.
One suggestion I have had is that there might be "some way" to determine
if the voxels are in volume are significantly different from each
other. If they are not, then I could sum or avg them and look at the %
signal change of the result. However I am at a loss to find any
documentation or literature which can tell me what this "some way" is.
I would appreaciate any ideas, information or snippets of information
that might help me solve this problem.
Thanks again
Lee.
--
Lee Walsh
Prince of Wales Medical Research Institute
Sydney, Australia
Ph: +61 2 9399 1014
Fax: +61 2 9399 1027
Email: [log in to unmask]
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