There isn’t really anything available for the latter approach. I would suggest the former and potentially including site as a nuisance variable. You very much want to balance across site in terms of whatever effect you are looking for (e.g. don’t scan all your patients on one and all your controls on the other)

 

Cheers

Bruce

 

From: freesurfer-bounces@nmr.mgh.harvard.edu <freesurfer-bounces@nmr.mgh.harvard.edu> On Behalf Of AJ
Sent: Wednesday, July 21, 2021 1:15 PM
To: Freesurfer support list <freesurfer@nmr.mgh.harvard.edu>
Subject: Re: [Freesurfer] Intensity equalization

 

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Thank you so much for your reply.

 

I have subjects who got MRIs on either GE or PH.  There are mild image intensity differences between the two scanners.  To combine volumetric data from both scanners, an easier way would be to express volumes as percentage of sbTIV (a less variable measure than eTIV) from respective scanners using SAMSEG.  Or more involved process would be intensity normalization of scans to each other and then subsequent SAMSEG analysis.  I think the former approach is easier and still valid?  The later approach would require an additional program, if you would suggest one?

 

Many thanks 

 

AJ

 

On Wed, Jul 21, 2021, 09:40 Fischl, Bruce <BFISCHL@mgh.harvard.edu> wrote:

Hi AJ

 

No, not easily. Maybe you can tell us your overall goal to see if we can help?

 

Cheers
Bruce

 

From: freesurfer-bounces@nmr.mgh.harvard.edu <freesurfer-bounces@nmr.mgh.harvard.edu> On Behalf Of AJ
Sent: Wednesday, July 21, 2021 1:27 AM
To: Freesurfer support list <freesurfer@nmr.mgh.harvard.edu>
Subject: [Freesurfer] Intensity equalization

 

        External Email - Use Caution        

Hi,

I have 2 MRIs on different scanners. The tissue contrasts are slightly off and there is slight differences in the volumes of ROIs. Is there a way to make both MRIs have the same intensity? I.e., Im2's intensity follows Im1's intensity?

Many thanks

AJ

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