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Hi Kody -

In my view, its best not to do group comparisons using data from scanners of different field strengths. Even between scanners of same magnetic field strength (e,g., 3T Siemens and 3T GE), there are large variations that need to be covaried out. This is especially important when you are looking longitudinally (Change over time).

However, if you are curious, you could do the analysis using field strength as covariate to see where the data is taking you and for generating hypotheses.

best,

Alan

On Mon, Jun 18, 2018 at 12:10 PM, zalewk zalewk@uw.edu wrote:

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Hello Freesurfer Team,

Sorry to bother you guys again, any word on what you think is the best approach going forward here?

Best, Kody Zalewski

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*From:* zalewk *Sent:* Thursday, June 7, 2018 10:39 AM *To:* freesurfer@nmr.mgh.harvard.edu *Subject:* Longitudinal analysis of multiple scanner acquisitions

Good afternoon Freesurfer team,

I want to run the longitudinal pipeline on multiple groups of subjects, the problem is we are at the mercy of the scanners available to us at the various time-points. We have two different Siemens 1.5 scanners (same type of scanner, there was an effort made to match them) at time point 1 and 2 with a Phillips 3T at time point 3. Is it worth the time to attempt a longitudinal analysis on this cohort?

Best, Kody Zalewski

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