Template MRI and missing fiducials

[Robert Oostenveld]

Hi Frederic

On 14 Jul 2008, at 17:21, Frederic Roux wrote:
> I was wondering if there is some sort of template brain or
> headmodel that one can use to perform a beamforming analysis of MEG
> data?

In principle you could use one anatomical MRI for anmother subject.
But I would recomment to use individual MRIs if you have them.

> Otherwise does someone know if it is possible to perform a
> sourceanalysis without having recorded fiducials during the
> anatomical MRI scan?
> I have the dicom files of all my subjects but I did not record
> fiducials during the MRI scan.

The position of the coils during the MEG measurement needs to be
marked in the MRI, otherwise it is not possible to localize the
activity during the MEG measurements onto the anatomical MRI.
Furthermore, as Tom pointed out, you need it to align the head model
(volume conduction model of the head) with the sensor positions.

In FieldTrip you can use the VOLUMEREALIGN function to specify the
fiducials. And you can use the PREPARE_LOCALSPHERES or
PRERARE_SINGLESHELL functions to make the head model. The only tricky
part is to read the anatomical MRI into Matlab without mixing up left
and right in the MRI. The READ_FCDC_MRI function can read dicom
files, but that is not 100% foolproof, so please check the output of
that function carefully (and use Matlab flipdim and permute functions).

best regards,
Robert

----------------------------------
The aim of this list is to facilitate the discussion between users of the FieldTrip  toolbox, to share experiences and to discuss new ideas for MEG and EEG analysis. See also http://listserv.surfnet.nl/archives/fieldtrip.html and http://www.ru.nl/fcdonders/fieldtrip.