Hi Freesurfer users,
For the longitudinal stream in FS5.1, there are only 4 options of measures (do-avg, do-rate, do-pc1 and do-spc). However, if I need other measures, such as the difference between two time points (thick2-thick1), how should I do to get the values and still be able to do the voxel-wise analysis for regional difference in cortical thickness (with glmfit)?
Many thanks
Keith Postdoc research fellow Toronto Western Hospital
1.
The temporal average is simply the average thickness: *avg = 0.5 * (thick1 + thick2)* 2.
The rate of change is the difference per time unit, so *rate = ( thick2 - thick1 ) / (time2 - time1)*. 3.
The percent change (pc1) is the rate with respect to the thickness at the first time point: *pc1 = rate / thick1*. 4.
The symmetrized percent change (spc) is the rate with respect to the average thickness: *spc = rate / avg*.
Ups, sorry, missed your mail.
you can get the difference by two ways:
- you simply subtract the thickness maps in each subject by yourself and then use that for the analysis
- you put 0 and 1 into the longitudinal qdec table for the two time points. When the time distance is 1, the rate will be the difference.
Best, Martin
On Oct 24, 2013, at 4:30 PM, Qi Wu qwu1975@gmail.com wrote:
Hi Freesurfer users,
For the longitudinal stream in FS5.1, there are only 4 options of measures (do-avg, do-rate, do-pc1 and do-spc). However, if I need other measures, such as the difference between two time points (thick2-thick1), how should I do to get the values and still be able to do the voxel-wise analysis for regional difference in cortical thickness (with glmfit)?
Many thanks
Keith Postdoc research fellow Toronto Western Hospital
The temporal average is simply the average thickness: avg = 0.5 * (thick1 + thick2) The rate of change is the difference per time unit, so rate = ( thick2 - thick1 ) / (time2 - time1). The percent change (pc1) is the rate with respect to the thickness at the first time point: pc1 = rate / thick1. The symmetrized percent change (spc) is the rate with respect to the average thickness: spc = rate / avg. _______________________________________________ Freesurfer mailing list Freesurfer@nmr.mgh.harvard.edu https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer
--------------------------------- Dr. Martin Reuter Assistant in Neuroscience - Massachusetts General Hospital Instructor in Neurology - Harvard Medical School MGH / HMS / MIT
A.A.Martinos Center for Biomedical Imaging 149 Thirteenth Street, Suite 2301 Charlestown, MA 02129
Phone: +1-617-724-5652 Email: mreuter@nmr.mgh.harvard.edu reuter@mit.edu Web : http://reuter.mit.edu
Thank you so much Martin. It is a very simple yet fantastic solution! Keith
On Wed, Nov 6, 2013 at 2:19 PM, Martin Reuter mreuter@nmr.mgh.harvard.eduwrote:
Ups, sorry, missed your mail.
you can get the difference by two ways:
- you simply subtract the thickness maps in each subject by yourself and
then use that for the analysis
- you put 0 and 1 into the longitudinal qdec table for the two time
points. When the time distance is 1, the rate will be the difference.
Best, Martin
On Oct 24, 2013, at 4:30 PM, Qi Wu qwu1975@gmail.com wrote:
Hi Freesurfer users,
For the longitudinal stream in FS5.1, there are only 4 options of measures (do-avg, do-rate, do-pc1 and do-spc). However, if I need other measures, such as the difference between two time points (thick2-thick1), how should I do to get the values and still be able to do the voxel-wise analysis for regional difference in cortical thickness (with glmfit)?
Many thanks
Keith Postdoc research fellow Toronto Western Hospital
- The temporal average is simply the average thickness: *avg = 0.5 *
(thick1 + thick2)* 2. The rate of change is the difference per time unit, so *rate = ( thick2 - thick1 ) / (time2 - time1)*. 3. The percent change (pc1) is the rate with respect to the thickness at the first time point: *pc1 = rate / thick1*. 4. The symmetrized percent change (spc) is the rate with respect to the average thickness: *spc = rate / avg*.
Freesurfer mailing list Freesurfer@nmr.mgh.harvard.edu https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer
Dr. Martin Reuter Assistant in Neuroscience - Massachusetts General Hospital Instructor in Neurology - Harvard Medical School MGH / HMS / MIT
A.A.Martinos Center for Biomedical Imaging 149 Thirteenth Street, Suite 2301 Charlestown, MA 02129
Phone: +1-617-724-5652 Email: mreuter@nmr.mgh.harvard.edu reuter@mit.edu Web : http://reuter.mit.edu
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Qi Wu