[Mne_analysis] Trans-File Reuse

Eric Larson larson.eric.d at gmail.com
Mon Feb 4 08:16:52 EST 2019
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Once at the beginning should typically be fine.


On Mon, Feb 4, 2019, 02:11 Mar Tin <beetlejuice920 at gmail.com wrote:

>         External Email - Use Caution
> Hello Eric,
> allright, thank you for your response.
> For my experiments, I do the digitization only once at the beginning of
> the session with several measurements with a subject.
> Is it advisable to digitize more often in between the measurements?
> Thank you
> Martin
> Am Fr., 1. Feb. 2019, 18:12 hat Eric Larson <larson.eric.d at gmail.com>
> geschrieben:
>>         External Email - Use Caution
>> The first is determined by the coil-measurement at the beginn of the
>>> measurement(or in between with other equipment). The second by the
>>> coregistration in mne. Right?
>> Correct.
>>> Would it be incorrect to reuse the trans-file created in mne coreg from
>>> one measurement for all other measurements done with the same
>>> head-digitization on the same subject?
>> In principle it should not change, in practice it will depend on your
>> digitzation accuracy. While the MRI coordinate frame is determined by your
>> one Freesurfer recon so it (of course) will not change between
>> measurements, the head coordinate frame on the other hand is determined by
>> the locations of LPA/Nasion/RPA that you digitized for any given
>> measurement. So if you are confident that your digitization procedure
>> recorded the locations of these physical landmarks identically in each
>> measurement, then the trans should not change. Regardless, I would check by
>> loading the subsequent recordings in mne coreg, and load the trans from the
>> first recording to see how good it is. At the very least it should give you
>> a very good starting point for making a new, slightly adjusted one if
>> necessary.
>> Eric
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