Dear Freesurfer Developers,
I'm following the very well-documented steps proposed by Marie Schaer for measuring local gyrification index in the paper "How to Measure Cortical Folding from MR Images: a Step-by-Step Tutorial to Compute Local Gyrification Index" (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3369773/). I have 2 questions I was wondering whether you might be able to answer:
1) Based on the contrast and FSDG files described in the paper (patients vs. controls, controlling for age and gender), would significant regions in blue refer to regions with reduced gyrification in patients relative to controls (patient LGI < control LGI) or vice versa?
2) When I try running the analysis in QDEC as opposed to command line with mri_glmfit, I get very different results - I think because QDEC is generating different contrast files than the one specified in the paper (1 1 -1 -1 0). Basically, this seems to be due to the difference in modelling LGI with doss (command line) or dods (default QDEC). I was wondering whether there were any reason doss was chosen for LGI instead of dods (see Step 5 in Section 4 Statistical Group Comparisons)?
Thank you in advance for your help.
Kindest regards, Colleen
On 02/21/2018 11:47 AM, C.P.E. Rollins wrote:
Dear Freesurfer Developers,
I'm following the very well-documented steps proposed by Marie Schaer for measuring local gyrification index in the paper "How to Measure Cortical Folding from MR Images: a Step-by-Step Tutorial to Compute Local Gyrification Index" (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3369773/). I have 2 questions I was wondering whether you might be able to answer:
- Based on the contrast and FSDG files described in the paper (patients
vs. controls, controlling for age and gender), would significant regions in blue refer to regions with reduced gyrification in patients relative to controls (patient LGI < control LGI) or vice versa?
Blue regions will be patient > control
- When I try running the analysis in QDEC as opposed to command line
with mri_glmfit, I get very different results - I think because QDEC is generating different contrast files than the one specified in the paper (1 1 -1 -1 0). Basically, this seems to be due to the difference in modelling LGI with doss (command line) or dods (default QDEC). I was wondering whether there were any reason doss was chosen for LGI instead of dods (see Step 5 in Section 4 Statistical Group Comparisons)?
It is not something related to LGI. It relates to how you think your data behave. See http://surfer.nmr.mgh.harvard.edu/fswiki/DodsDoss
Thank you in advance for your help.
Kindest regards, Colleen
freesurfer@nmr.mgh.harvard.edu
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C.P.E. Rollins -
Douglas N Greve