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<p>Hi Steven,</p>
<p>when calculating the leadfields that form the input of the
optimization algorithm, electrodes are added to the mesh at all
positions defined by the EEG cap layout. For large electrodes,
neighboring electrodes will start to overlap and create a
continuous well-conductive layer covering major parts of the
scalp. When simulating TDCS current flow in a head model modified
like that, most of the currents will then just be shunted within
the well-conductive "electrode layer" and not enter the head nor
brain. In other words, leadfield-based optimization algorithms are
designed to work with small electrodes.<br>
</p>
<p>Best regards,</p>
<p>Axel</p>
<p><br>
</p>
<div class="moz-cite-prefix">On 21-03-2023 15:54, Beumer, Steven
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:AM0PR09MB3858A7AF94A5C83DA6B381C3E7819@AM0PR09MB3858.eurprd09.prod.outlook.com">
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<p class="MsoNormal"><span lang="EN-US">Dear SimNibs community,<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">I was trying to verify
the electric field obtained by an optimization with regular
simulations.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">For a cortical target
and 2 4*4cm patches, the resulting locations and currents
were fed into a regular simulation and interpolated to the
cortical surface.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">The obtained magnitude
of the electric field differs by approximately a factor of
two and I can’t seem to figure out the reason for that.
<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">In the figure below the
optimization and simulation are shown with the Electric
field plotted on the same scale.
<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">It might be a reasoning
error somewhere, but if someone could help me with that, I
would be grateful.
<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><span style="mso-fareast-language:NL"
lang="NL">Sincerely,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:NL"
lang="NL"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="color:black;mso-fareast-language:NL" lang="NL">Steven
Beumer MSc</span><span style="color:black" lang="NL"><o:p></o:p></span></p>
<p class="MsoNormal"><span
style="color:black;mso-fareast-language:NL"><img
style="width:1.95in;height:.5416in" id="Picture_x0020_15"
src="cid:part1.kfP9Kt5U.cT3oD3tu@drcmr.dk"
alt="TUe-logo-descriptor-line-scarlet-rgb" class=""
width="187" height="52"></span><span
style="color:black;mso-fareast-language:NL"><o:p></o:p></span></p>
<p class="MsoNormal"><span
style="color:black;mso-fareast-language:NL" lang="EN-US">PhD
candidate at the Electrical Engineering faculty<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">PS: For some reason,
this issue doesn’t show up with small circular electrodes<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><img
style="width:4.9666in;height:2.4916in"
id="Picture_x0020_1"
src="cid:part2.0L5Sc2Vu.Rz74GeC8@drcmr.dk" class=""
width="477" height="239"></span><span lang="EN-US"><o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
</div>
<br>
<fieldset class="moz-mime-attachment-header"></fieldset>
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</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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