We are doing an fMRI ROI analysis using manually created (in MRIcro) ROI
image masks and the WFU pickatlas interface with SPM2 utilizing SVC. We
are finding that the volume our ROIs as drawn and the search volume
reported on the SPM results do not match.
Here are the steps we have followed:
1. Draw ROI on normalized structural image (2x2x2mm voxels) in MRIcro
2. Export ROI as Analyze image
3. In SPM Results, use ROI analysis (WFU Pickatlas interface), specify mask
image file.
In one case the ROI we drew had 119 voxels, but the SPM2 analysis search
volume was reported as 113 voxels with resels reported as 0.3 . In
another case the ROI was 86 voxels, but the SPM2 search volume was 23
voxels with 0.1 resels.
Why are we seeing the difference between the original ROI and the search
volume? How does SPM calculate the search volume when doing an ROI
analysis?
Thanks,
Chaitee Sengupta
Research Assistant
Cognitive Neuropsychology Lab
University of Washington, Seattle
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