Hi Dr Greve, Thank you very much for the great answers.
Kindly, I have one last question.
The range of the signal intensity within the voxels in the original SUV maps is
min=0.00 and max=3.017629
For the mgx images it is min=-43.74384 and max=88.468712
The difference in the range of signal intensity in the mgx images is largely
wide. It seems that PVC increases the signal intensity. Is this correct?
Am I doing something wrong. I plan to include these images in voxel-wise
analysis so I am curious about this difference between the images.
Thanks for any clarification!
On 8/18/17 10:20 AM, John Anderson wrote:
Hi Dr Greve,
I followed the steps in WIKI to do SUV-surface based analyses + PVC. I have the
following questions and I highly appreciate your input:
1. Why the dimension of the images (mgx.gm, mgx.ctx.gm and mgx.ctx.subgm) is
not like the original SUV image that has been fed to the pipeline. i.e. I start
with image-dimensions 128X128X128 : 2X2X2 and end up with 79X113X102 : 2X2X2
Also FOV is different as well between the original SUV image /256/ and the
output mgx images /158/. How this happen? I am I doing something wrong?
I set up mri_gtmpvc to reduce the field of view to a bounding box around the
head to reduce memory and computational loads. You can turn this off with
--no-reduce-fov
2. Some voxels in the mgx images has negative signal intensity. is this normal?
Yes. MG works by estimating the contribution of non-GM to GM and subtracting it
out. If the estimate is too high, then it can cause negative values.
Thank you for any clarification.
John
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