Hi Ryan,
FreeSurfers Longitudinal pipeline assumes head size is relatively fixed. The
problem with growing heads is that the surfaces from the subject-template will
not fit well to later (or earlier) time points and that the algorithm can
potentially not recover. If surfaces look OK it means it worked. I have no idea
how large the time delta is for it to fail but I guess if you scan a 4 year old
and then again when they are 12 that could be problematic.
You should use eTIV from the cross stream. In the long stream eTiv is fixed
across time.
Best, Martin
> On 9. Jul 2018, at 20:51, Nillo, Ryan Michael R
> wrote:
>
>External Email - Use Caution
>
> Hello FreeSurfer experts,
>
> I have a few questions on the longitudinal processing stream. I am interested
> in studying longitudinal morphometry changes in a pediatric population. The
> age range of this population is between 4-20 years with age deltas between a
> few months to < 2 years. I want to know what are appropriate/acceptable age
> deltas used for longitudinal processing. I looked through the archives and
> one researcher asked about age deltas. One of the answers was that “if the
> time delta is relatively small, this has good chances to work”. What does
> “relatively small” mean? If the time points exit the longitudinal pipeline
> without errors and the surfaces look correct, does this mean the data is
> relevant?? When I correct for head size, should I use the eTIV values from
> the cross-sectional directories or the longitudinal directories?
>
> Thanks in advance,
>
> Ryan Michael Nillo
> Staff Research Associate I
> University of California San Francisco
> Department of Radiology and Biomedical Imaging
>
>
> ___
> Freesurfer mailing list
> Freesurfer@nmr.mgh.harvard.edu
> https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer
>
>
___
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.
