meg realign

[Robert Oostenveld]

Hi Marie,

On 25-nov-2005, at 11:50, Marie Smith wrote:
> I was wondering if someone could clarify for me in some more detail
> how the meg-realign function works. From the function help it seems
> to perform a course source reconstruction and then re-project back
> to a standard gradiometer array.  I am most curious about how this
> course source representation is implemented.

You are right, it involves projecting the measured activity on a
sheet of dipoles that approximates the cortex, followed by a forward
computation of the field of those dipoles at the template gradiometer
locations.

The algorithm is described in combination with a simulation study in
the paper
   T.R. Knosche, Transformation of whole-head MEG recordings between
different sensor positions. Biomed Tech (Berl). 2002 Mar;47(3):59-62.

A similar algorithm, with the main difference being a different
source model, is described in the appendix of the paper
   de Munck JC, Verbunt JP, Van't Ent D, Van Dijk BW. The use of an
MEG device as 3D digitizer and motion monitoring system. Phys Med
Biol. 2001 Aug;46(8):2041-52.

I will send you a pdf version of both papers in a separate mail
addressed directly at you.

best regards,
Robert