Hi Salil,
please send questions to the free surfer mailing list.
If you used the longitudinal stream for processing the etiv should be the same in all time points. It is computed in the 'base' = within subject template once for the entire series. It seems that you did not run your images through the longitudinal stream if your etiv is different across time points.
For longitudinal processing see here: http://freesurfer.net/fswiki/LongitudinalProcessing
Bes,t Martin
On Nov 10, 2013, at 3:37 PM, Salil Soman salsoman@stanford.edu wrote:
Dear Dr. Reuter,
I have performed freesurfer 5.3 with hippo subfields Analysis on patients that have 2 consecutive scans (pre and post surgery). I have generated Segstats statistics for each individual time point. I have noticed the etiv is different on all of the cases for each time point (scan 1 is different from 2). This has led me to worry that it may not be legitimate to perform analyses of changes in volumes of structures by computing differences in values between time points). I am writing to inquire if you were familiar with /had an opinion regarding this matter.
Best wishes,
Salil Soman, MD, MS Postdoctoral Research Fellow - Stanford Radiological Sciences Laboratory Fellow - Palo Alto War Related Illness and Injury Study Center WOC Neuroradiology Attending - Veterans Affairs Palo Alto Health Care System
--------------------------------- 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 Martin.
Just to clarify, then it is not valid to compare values of single point analyses (e.g. hippocampal volume from freesurfer analysis of time point 1 subtracted from hippocampal volume of from freesurfer analysis of time point 2).
Best wishes,
-Salil
On Mon, Nov 11, 2013 at 7:58 AM, Martin Reuter mreuter@nmr.mgh.harvard.eduwrote:
Hi Salil,
please send questions to the free surfer mailing list.
If you used the longitudinal stream for processing the etiv should be the same in all time points. It is computed in the 'base' = within subject template once for the entire series. It seems that you did not run your images through the longitudinal stream if your etiv is different across time points.
For longitudinal processing see here: http://freesurfer.net/fswiki/LongitudinalProcessing
Bes,t Martin
On Nov 10, 2013, at 3:37 PM, Salil Soman salsoman@stanford.edu wrote:
Dear Dr. Reuter,
I have performed freesurfer 5.3 with hippo subfields Analysis on patients that have 2 consecutive scans (pre and post surgery). I have generated Segstats statistics for each individual time point. I have noticed the etiv is different on all of the cases for each time point (scan 1 is different from 2). This has led me to worry that it may not be legitimate to perform analyses of changes in volumes of structures by computing differences in values between time points). I am writing to inquire if you were familiar with /had an opinion regarding this matter.
Best wishes,
Salil Soman, MD, MS Postdoctoral Research Fellow - Stanford Radiological Sciences Laboratory Fellow - Palo Alto War Related Illness and Injury Study Center WOC Neuroradiology Attending - Veterans Affairs Palo Alto Health Care System
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
The information in this e-mail is intended only for the person to whom it is addressed. If you believe this e-mail was sent to you in error and the e-mail contains patient information, please contact the Partners Compliance HelpLine at http://www.partners.org/complianceline . If the e-mail was sent to you in error but does not contain patient information, please contact the sender and properly dispose of the e-mail.
Hi Salil,
of course you can compare values like you say. Why shouldn't you?
The longitudinal stream is used to increase reliability of reported measures if you have 2 or more images from the same subjects.
Best Martin
On 11/11/2013 12:00 PM, Salil Soman wrote:
Thank you Martin.
Just to clarify, then it is not valid to compare values of single point analyses (e.g. hippocampal volume from freesurfer analysis of time point 1 subtracted from hippocampal volume of from freesurfer analysis of time point 2).
Best wishes,
-Salil
On Mon, Nov 11, 2013 at 7:58 AM, Martin Reuter <mreuter@nmr.mgh.harvard.edu mailto:mreuter@nmr.mgh.harvard.edu> wrote:
Hi Salil, please send questions to the free surfer mailing list. If you used the longitudinal stream for processing the etiv should be the same in all time points. It is computed in the 'base' = within subject template once for the entire series. It seems that you did not run your images through the longitudinal stream if your etiv is different across time points. For longitudinal processing see here: http://freesurfer.net/fswiki/LongitudinalProcessing Bes,t Martin On Nov 10, 2013, at 3:37 PM, Salil Soman <salsoman@stanford.edu <mailto:salsoman@stanford.edu>> wrote:Dear Dr. Reuter, I have performed freesurfer 5.3 with hippo subfields Analysis on patients that have 2 consecutive scans (pre and post surgery). I have generated Segstats statistics for each individual time point. I have noticed the etiv is different on all of the cases for each time point (scan 1 is different from 2). This has led me to worry that it may not be legitimate to perform analyses of changes in volumes of structures by computing differences in values between time points). I am writing to inquire if you were familiar with /had an opinion regarding this matter. Best wishes, Salil Soman, MD, MS Postdoctoral Research Fellow - Stanford Radiological Sciences Laboratory Fellow - Palo Alto War Related Illness and Injury Study Center WOC Neuroradiology Attending - Veterans Affairs Palo Alto Health Care System--------------------------------- 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 <tel:%2B1-617-724-5652> Email: mreuter@nmr.mgh.harvard.edu <mailto:mreuter@nmr.mgh.harvard.edu> reuter@mit.edu <mailto:reuter@mit.edu> Web : http://reuter.mit.edu <http://reuter.mit.edu/> The information in this e-mail is intended only for the person to whom it is addressed. If you believe this e-mail was sent to you in error and the e-mail contains patient information, please contact the Partners Compliance HelpLine at http://www.partners.org/complianceline . If the e-mail was sent to you in error but does not contain patient information, please contact the sender and properly dispose of the e-mail.-- Salil Soman, MD, MS Postdoctoral Research Fellow - Stanford Radiological Sciences Laboratory Fellow - Palo Alto War Related Illness and Injury Study Center WOC Neuroradiology Attending - Veterans Affairs Palo Alto Health Care System
freesurfer@nmr.mgh.harvard.edu
-
Martin Reuter -
Salil Soman