Re: [Freesurfer] longitudinal stream - template
Hi Martin, Thank you for your answer, but my idea was to compare the atrophy rates when using scans at 6 months (0 - 6 months) and scans at 12 months (0 - 12 months). If my templates are built with more time points, the results will be biased, right? Regards, Yolanda 2013/3/18 Martin Reuter mreu...@nmr.mgh.harvard.edu: Hi Yolanda, actually it is advantageous if the template is build from more time points. You don't need to process the images again, just do your statistical analysis with the time points you are interested in. But: why restrict the statistics to a subset of the data? If you are interested in yearly change, you can compute that from all time points. If you are interested in seeing if the atrophy rate increases over time, use a piecewise linear model (node at 6 months) and see if the slopes increase, etc. Removing time points from the statistics is usually a bad idea as you loose power. Best, Martin On 03/18/2013 01:15 PM, Yolanda Vives wrote: Dear FreeSurfer experts, I have run a longitudinal study considering multiple time points (7 scans/subject on average) with FS 5.1. However, I am interested in the percent changes between two time points only (between 0 and 6 months and between 0 and 1 year). Should I run the longitudinal stream from step 2 (template) two more times (1.- considering only 0 and 6 months scans and 2.- considering only 0 and 12 months scans) or is it correct even if my templates were built with all the time scans together? Thank you for your help, Yolanda ___ 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: mreu...@nmr.mgh.harvard.edu reu...@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. ___ Freesurfer mailing list Freesurfer@nmr.mgh.harvard.edu https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer
Re: [Freesurfer] longitudinal stream - template
Hi Yolanda, if you want to simulate a study where one obtains 2 time points (6 months apart) or 2 time points (12 months apart) and then compare the results, you would need to run these two independently through free surfers longitudinal stream (one time including 0 and 6 month, the other time including 0 and 12 months). If you are interested in measuring if for whatever reason there is a change in the slope at 6 months (e.g. a nonlinear trajectory) you can do the piecewise linear model that I described below on the full dataset. Best, Martin On Mar 19, 2013, at 4:26 AM, Yolanda Vives yvi...@pic.es wrote: Hi Martin, Thank you for your answer, but my idea was to compare the atrophy rates when using scans at 6 months (0 - 6 months) and scans at 12 months (0 - 12 months). If my templates are built with more time points, the results will be biased, right? Regards, Yolanda 2013/3/18 Martin Reuter mreu...@nmr.mgh.harvard.edu: Hi Yolanda, actually it is advantageous if the template is build from more time points. You don't need to process the images again, just do your statistical analysis with the time points you are interested in. But: why restrict the statistics to a subset of the data? If you are interested in yearly change, you can compute that from all time points. If you are interested in seeing if the atrophy rate increases over time, use a piecewise linear model (node at 6 months) and see if the slopes increase, etc. Removing time points from the statistics is usually a bad idea as you loose power. Best, Martin On 03/18/2013 01:15 PM, Yolanda Vives wrote: Dear FreeSurfer experts, I have run a longitudinal study considering multiple time points (7 scans/subject on average) with FS 5.1. However, I am interested in the percent changes between two time points only (between 0 and 6 months and between 0 and 1 year). Should I run the longitudinal stream from step 2 (template) two more times (1.- considering only 0 and 6 months scans and 2.- considering only 0 and 12 months scans) or is it correct even if my templates were built with all the time scans together? Thank you for your help, Yolanda ___ 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: mreu...@nmr.mgh.harvard.edu reu...@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. - 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: mreu...@nmr.mgh.harvard.edu reu...@mit.edu Web : http://reuter.mit.edu ___ Freesurfer mailing list Freesurfer@nmr.mgh.harvard.edu https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer 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.
[Freesurfer] longitudinal stream - template
Dear FreeSurfer experts, I have run a longitudinal study considering multiple time points (7 scans/subject on average) with FS 5.1. However, I am interested in the percent changes between two time points only (between 0 and 6 months and between 0 and 1 year). Should I run the longitudinal stream from step 2 (template) two more times (1.- considering only 0 and 6 months scans and 2.- considering only 0 and 12 months scans) or is it correct even if my templates were built with all the time scans together? Thank you for your help, Yolanda ___ Freesurfer mailing list Freesurfer@nmr.mgh.harvard.edu https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer 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.
Re: [Freesurfer] longitudinal stream - template
Hi Yolanda, actually it is advantageous if the template is build from more time points. You don't need to process the images again, just do your statistical analysis with the time points you are interested in. But: why restrict the statistics to a subset of the data? If you are interested in yearly change, you can compute that from all time points. If you are interested in seeing if the atrophy rate increases over time, use a piecewise linear model (node at 6 months) and see if the slopes increase, etc. Removing time points from the statistics is usually a bad idea as you loose power. Best, Martin On 03/18/2013 01:15 PM, Yolanda Vives wrote: Dear FreeSurfer experts, I have run a longitudinal study considering multiple time points (7 scans/subject on average) with FS 5.1. However, I am interested in the percent changes between two time points only (between 0 and 6 months and between 0 and 1 year). Should I run the longitudinal stream from step 2 (template) two more times (1.- considering only 0 and 6 months scans and 2.- considering only 0 and 12 months scans) or is it correct even if my templates were built with all the time scans together? Thank you for your help, Yolanda ___ 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: mreu...@nmr.mgh.harvard.edu reu...@mit.edu Web : http://reuter.mit.edu ___ Freesurfer mailing list Freesurfer@nmr.mgh.harvard.edu https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer 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.
