Hi Jason, it depends on what you are going to use it for. If you have a situation where distortion correction is going to be important at some point (eg, multi site study), then I would probably use the distortion corrected version. It is possible to apply it post hoc, but it is a pain. In the end, I don't think it will make much of a difference.

On 7/28/2026 12:44 PM, Jason Tourville wrote:

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Hi Freesurfer supporters, When collecting T1-weighted MEMPRAGE for input to FS recon, is it better to use the online distortion corrected RMS volume? Or the RMS volume without correction?

Best, Jason

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No idea. Depending upon the scanner, it is not always perfect, but it is better than nothing. There is some inevitable resampling and so some blurring, so some people will analyze the uncorrected data then apply the correction to the analysis. For 2D scans, I think they will only do the correction in 2D, which is pretty useless.

On 8/6/2026 1:01 PM, Jason Tourville wrote:

External Email - Use Caution

Hi Doug, Thanks for the reply. There's a good chance that the data will ultimately be used for a pooled analysis of data acquired across multiple sites at some point. In the relatively recent past, we've used the online-corrected scan without applying post hoc correction. When planning a new study, the staff here at BU warned against using that scan. Do you know why there is pushback on using the online corrected scan?

Best, Jason

On Mon, Aug 3, 2026 at 11:50 AM Douglas N. Greve dgreve@mgh.harvard.edu wrote:

Hi Jason, it depends on what you are going to use it for. If you
have a situation where distortion correction is going to be
important at some point (eg, multi site study), then I would
probably use the distortion corrected version. It is possible to
apply it post hoc, but it is a pain. In the end, I don't think it
will make much of a difference.


On 7/28/2026 12:44 PM, Jason Tourville wrote:

...

        External Email - Use Caution

Hi Freesurfer supporters,
When collecting T1-weighted MEMPRAGE for input to FS recon, is it
better to use the online distortion corrected RMS volume? Or the
RMS volume without correction?

Best,
Jason

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