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Hello Robert,<br>
<br>
Thanks for the detailed answer. I see how the magnetic dipole
forward solution gets selected now, and even found the code for it.
I'll try it out soon.<br>
<br>
Cheers,<br>
<br>
Jim<br>
<pre class="moz-signature" cols="72">Jim McKay
Candoo Systems Inc. - Magnetic field sensors, systems, and site surveys
Tel. 778-840-0361
<a class="moz-txt-link-abbreviated" href="mailto:jim.mckay@candoosys.com">jim.mckay@candoosys.com</a>
<a class="moz-txt-link-abbreviated" href="http://www.candoosys.com">www.candoosys.com</a></pre>
<div class="moz-cite-prefix">On 2015-03-03 12:54 PM, Robert
Oostenveld wrote:<br>
</div>
<blockquote
cite="mid:063154D1-6549-463C-BCAA-AA42A78026EC@donders.ru.nl"
type="cite">
<meta http-equiv="Content-Type" content="text/html;
charset=windows-1252">
Hi Jim
<div><br>
</div>
<div>You can do an inverse solution with any method (including
dipole fitting) by specifying cfg.vol=[] in the corresponding
high-level function (e.g. ft_prepare_leadfield, ft_dipolefitting
or ft_sourceanalysis). This causes the forward model to be
computed with a magnetic dipole.</div>
<div><br>
</div>
<div>If you want to track this down to the lower lever code, have
a look at these lines in the code</div>
<div><br>
</div>
<div>
<div style="margin: 0px; font-family: Menlo;">“forward/ft_voltype.m"
line 115 of 138 --83%-- col 11</div>
</div>
<div>
<div style="margin: 0px; font-family: Menlo;">“forward/ft_compute_leadfield.m"
line 280 of 611 --45%-- col 12</div>
</div>
<div><br>
</div>
<div>My appologies for this not being documented better. I have
been using this myself to check on the localization of the
headcoils in the CTF “hz.ds” datasets, which worked fine.</div>
<div><br>
</div>
<div>I hope you can get it to work for the Sandia Labs system. For
the CTF system it is not needed to do these computations in
MATLAB, since the CTF electronics does this in (alomst)
real-time and the positions are streamed along with the MEG
channel data. That makes this this <a moz-do-not-send="true"
href="http://fieldtrip.fcdonders.nl/getting_started/realtime_headlocalizer">http://fieldtrip.fcdonders.nl/getting_started/realtime_headlocalizer</a>
easy for the system we have in Nijmegen. Arjen and I have also
been working on making it work for the Elekta system where the
fitting has to be done in MATLAB, but have not been able sofar
to get it to work robustly. You can find the experiences and
(still open) report at <a moz-do-not-send="true"
href="http://bugzilla.fcdonders.nl/show_bug.cgi?id=1792">http://bugzilla.fcdonders.nl/show_bug.cgi?id=1792</a>. </div>
<div><br>
</div>
<div>best regards</div>
<div>Robert</div>
<div><br>
</div>
<div><br>
</div>
<div><br>
</div>
<div>
<div><br>
</div>
<div>
<div>
<div>On 25 Feb 2015, at 22:40, Jim McKay <<a
moz-do-not-send="true"
href="mailto:jim.mckay@candoosys.com">jim.mckay@candoosys.com</a>>
wrote:</div>
<br class="Apple-interchange-newline">
<blockquote type="cite">Hello Fieldtrippers,<br>
<br>
I am consulting with the Sandia Labs on development of an
atomic magnetometer based MEG system prototype. One of the
areas I am working on is head localization, so I was
looking at the code for the realtime head localization in
Fieldtrip. I was surprised to see that although the
comments talk about using a magnetic dipole forward
solution, it actually used the FT dipolefit code which is
based on an equivalent current dipole, as far as I can
tell.<br>
<br>
There should be a significant difference in the forward
solutions between MD and ECD, so how does this work? Or am
I just missing something?<br>
<br>
Cheers,<br>
<br>
Jim<br>
<br>
-- <br>
Jim McKay<br>
Candoo Systems Inc. - Magnetic field sensors, systems, and
site surveys<br>
Tel. 778-840-0361<br>
<a moz-do-not-send="true"
href="mailto:jim.mckay@candoosys.com">jim.mckay@candoosys.com</a><br>
<a class="moz-txt-link-abbreviated" href="http://www.candoosys.com">www.candoosys.com</a><br>
<br>
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</blockquote>
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</blockquote>
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