On 5/11/17 3:25 PM, John Anderson wrote:
Hi Doug,
Why Qdec offer "volume, area, thickness ,...etc " in the drop down menu "measures"? In this menu there are many measures and I understand that I can run surface based analysis depending on the choice of this drop down menu. Is this Correct? Please see attached. Thank you for any clarification
volume in this context is "surface volume". The volume at a vertex is the volume of the triangles (truncated pyramids) adjacent to the vertex. So you are still doing map-based analysis
I'm not sure I follow. If I understand, you are finding sig diff in PCG volume when you extract it the volume value for each subject (scaled by
etiv) and process in SPSS. The part I don't understand is what you are doing with QDEC. I don't think QDEC can be used to test ROI volume.
On 05/09/2017 05:58 PM, John Anderson wrote:
Dear Dr Doug,
I have two groups of subjects (80 patients and 40 controls). I
analyzed the data using Freesurfer v6.0.
I want to study the difference between the groups in "precentral gyrus
volume". After "recon-all" I built Qdec table and I used Qdec to
compute the comparison by including eTIV a covariate. After correcting
the results using Monte Carlo simulation or adjusting for FDR I found
no difference between the groups in volume neither in surface area.
I adjusted the precentral gyrus volume values for eTIV using the
commands:
mri_label_volume -eTIV $SUBJECTS_DIR/${i}/mri/transforms/talairach.xfm
1948 $SUBJECTS_DIR/${i}/mri/wmparc.mgz 2017 mri_label_volume -eTIV
$SUBJECTS_DIR/${i}/mri/transforms/talairach.xfm
1948 $SUBJECTS_DIR/${i}/mri/wmparc.mgz 2024
I extracted the adjusted volume values to SPSS then I ran box plots
comparison between the groups and I found difference at (P<0.0001) Why
Qdec doesn't show the difference between the groups although the p
value is very small. What I am doing wrong in Qdec? Is it wrong to
include eTIV a covariate?
Thank you for any advice
John
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