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<p>Hi Joel,</p>
<p><br>
</p>
<p>a question for better understanding: When you set up the 2nd
pathway, do you then model ALL electrodes of the EEG10-20 system,
or only those which you actually need for the montage?</p>
<p><br>
</p>
<p>I am asking because adding many well-conducting electrodes to the
model will slightly increase the amount of current shunted through
the scalp(+electrodes). Think of it as covering many parts of the
scalp with well-conductive paste. We never quantified the size of
this effect, but it will cause the leadfield e-fields in the brain
to be consistently lower.<br>
</p>
<p><br>
</p>
<p>Best regards,</p>
<p>Axel</p>
<p><br>
</p>
<div class="moz-cite-prefix">On 19-10-2022 21:07, Joel Upston wrote:<br>
</div>
<blockquote type="cite"
cite="mid:CY1PR07MB271401D126AA612F026D1102BF2B9@CY1PR07MB2714.namprd07.prod.outlook.com">
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<div style="font-family: Calibri, Arial, Helvetica, sans-serif;
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Hi there,</div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif;
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<br>
</div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif;
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I have noticed a systematic difference between the two different
lines of simulating the same currents, electrodes and underlying
dataset. One is through processing through the leadfield and
using only the electrodes and currents as given and the other is
through only modeling those electrodes and currents without the
leadfield. Now the 2<span><sup>nd</sup> pathway (no leadfield)
is giving higher E_mag than the leadfield version (~7-12%),
the spatial maps look similar but just the intensity
differences. I think it has to do with the scaling that is
done after the solve by scaling the estimated current
calibration error, which if I understand correctly isn't done
in the leadfield processing. If this is the case I am trying
to establish which would be more accurate to use in your view
if I need a specific target value of (0.3 V/m for example). I
have attached an image of a case where this is shown with the
leadfield processed is on the left and the non-leadfield is on
the right. I have tried this on about 5 different datasets and
the pattern is consistent.</span></div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif;
font-size: 12pt; color: rgb(0, 0, 0);" class="elementToProof">
<span><br>
</span></div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif;
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<span>Thanks,</span></div>
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<span><br>
</span></div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif;
font-size: 12pt; color: rgb(0, 0, 0);" class="elementToProof">
Joel<span><br>
</span></div>
<br>
<fieldset class="moz-mime-attachment-header"></fieldset>
<pre class="moz-quote-pre" wrap="">_______________________________________________
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</pre>
</blockquote>
<pre class="moz-signature" cols="72">--
Dr. Axel Thielscher
Professor of Neurophysics and Neuroimaging
Danish Research Center for Magnetic Resonance
Copenhagen University Hospital Hvidovre
DK-2650 Hvidovre, Denmark
<a class="moz-txt-link-abbreviated" href="http://www.drcmr.dk">www.drcmr.dk</a>
&
Department of Health Technology
Technical University of Denmark
DK-2800 Kgs. Lyngby
<a class="moz-txt-link-freetext" href="http://www.healthtech.dtu.dk/">http://www.healthtech.dtu.dk/</a></pre>
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