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Depends on the data analysis that you want to do, the magnetic field strength
between the two scanners may be a problem that affects the intensity
distribution of the image overall that lead to under- or over-estimation. See,
the following paper as an example of longitudinal studies.
https://secure-web.cisco.com/1kuKpr8oUx5I2iJ2rXAjhzY3dtnZ4sGJaDJBmg4nk6qbhDV_eCKt9RquU-RNLJphtIX6pxvzRnrdgDOORmU-Z6OQkvw0dYAcurFAj8i8FJvKIeDLT22bV0e-mVGztS0wy6TTReNp8oU5JHGS1Bya0l00nQxK3YQ8VhxrR4EG1NKNnIzDmmddrW3ibCmdQZrPXJrUiIcdfrIMgTuq9xLS2uiiKHHbuL1zbCLd8mM4r8y5WzfgtIUaA4M1OrOhl87Hhc6oZCbj9iTj9JPc5yYYNsQ/https%3A%2F%2Fdoi.org%2F10.1016%2Fj.jneumeth.2021.109270
Best,
Ahmed,
U of Kentucky
From: freesurfer-boun...@nmr.mgh.harvard.edu
on behalf of Reuter, Martin,Ph.D.
Sent: Thursday, September 2, 2021 10:54 AM
To: Freesurfer support list
Subject: Re: [Freesurfer] recon-all Longitudinal processing (baseline on 1.5T;
followup on 3T)
CAUTION: External Sender
Hi Jay,
that would be possible, but we have no experience with such a setting.
The problem is that you will never know if any detected longitudinal change is
due to the field strength/scanner/head coil chances or the changes in the way
it is processed or real anatomical changes.
This is why such a longitudinal study design is problematic. You could look at
group differences (given that e.g. both groups are acquired/processed the same
way and under the assumption that there is no interaction with group).
However, the second assumption is probably not true, e.g. motion artefacts
would be correlated with age and with disease and may affect downstream
measurements differently across the two scanners.
Best, Martin
> On 31. Aug 2021, at 11:15, Jayachandra Raghava
> wrote:
>
> Hello Experts,
>
> I am planning to run the longitudinal processing pipeline (Freesurfer version
> 7.1.1). But I have a few subjects who were scanned on different scanner field
> strengths at baseline and followup.
>
> For example :
>
> Baseline was scanned on a 1.5T Siemens Scanner
> Followup was scanned on a 3.0T Siemes Trio Scanner
>
> I am planning to
> 1) run the cross-sectional processing for baseline without the 3T flag
> 2) run the cross-sectional processing for followup with the 3T flag
> 3) then generate the unbiased template and longitudinally process all the
> time points without any special flags.
>
> Is this the best way to process such data? Please let me know if there are
> any additional flags in the longitudinal processing pipeline to accommodate
> Scanner/Field strength changes.
>
> Best wishes
> Jay
>
>
>
>
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