If I understand you, my inclination would be to map the unthresholded
volume with interpolated voxel.
Then map the thresholded volume with enclosing voxel. Then use Surface:
ROI to select metric >=mythresh and draw an areal border around the
resulting cluster. Then render that border over your unthresholded
metric, to delimit the significant from not.
On 10/24/2013 11:27 AM, Michael Cohen wrote:
Hi,
I was wondering if you might be able to help clarify some uncertainty
that I've had with thresholding images in Caret.
I am using thresholded volumetric images from FSL, and mapping them
into Caret. I did see in an old post from the mailing list that this
is a common approach, which was good to see. But there are still a
few things that I'm uncertain about:
-- Is it OK to use the interpolated voxel algorithm with
pre-thresholded images? It seems to me that this could be
problematic, since it's averaging zeros in with the data. But if I
use the unthresholded images, I'd have to apply cluster correction in
Caret, rather than having FSL do it...which introduces other
complications.
-- Given that the interpolation yields a number of areas in which the
actual z score in Caret is less than our original z threshold, is it
advisable to re-threshold the image using Caret display options (under
Metric Settings) to eliminate all activations under our original
threshold (in this case, z = 2.3)? That seems to show much less
activity on the brain, which could be good or bad, I guess, but the
more important question is whether it's a more or less faithful
rendering of the original volumetric image, which I'm not sure about.
-- Is there some "trick" to setting a volume threshold when you import
data to Caret using the "Map volume to surface" option? I tried
enabling the volume threshold, and entered a number to use as a
threshold that was higher than the original threshold used on the
image file. But when it imported the image, that option didn't seem
to do anything at all. Is there something else that I need to do?
Thanks,
Michael
--
Michael S. Cohen, M.S., C. Phil
Ph.D. Candidate
Department of Psychology
University of California, Los Angeles
Los Angeles, CA 90095
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