<p><span style="padding: 3px 10px; border-radius: 5px; color: #ffffff; font-weight: bold; display: inline-block; background-color: #ff0000;"> External Email - Use Caution </span></p><p></p><div dir="ltr"><div class="gmail_default" style="font-family:verdana,sans-serif">Eric, </div><div class="gmail_default" style="font-family:verdana,sans-serif"><br></div><div class="gmail_default" style="font-family:verdana,sans-serif">Please find the forward model and script for the 1632 magnetometer array in the following folder. Script is also attached.</div><div class="gmail_default" style="font-family:verdana,sans-serif"><a href="https://drive.google.com/drive/folders/1dX7YZSCa4RAcn_b4JH3I0CADe2ZOQIM-?usp=sharing">https://drive.google.com/drive/folders/1dX7YZSCa4RAcn_b4JH3I0CADe2ZOQIM-?usp=sharing</a><br></div><div class="gmail_default" style="font-family:verdana,sans-serif"><br></div><div class="gmail_default" style="font-family:verdana,sans-serif">A bit more context on the forward model: It places point magnetometers on 102 simulated rectangular 24mm x 24mm chips that are projected towards the scalp from the standard Neuromag sensor locations. The center point of each sensor cluster is 1.5mm above the nearest outer skin surface from the BEM. All sensors are sensitive in the z-direction and preserve the orientation vector from the derived Neuromag magnetometer.</div><div class="gmail_default" style="font-family:verdana,sans-serif"> </div><div class="gmail_default" style="font-family:verdana,sans-serif">This script generates the full set of lead fields in the Evoked object Y0. There are plenty of other instances where this occurs, not just dipole #364. Let me know if you have any questions about the construction of the forward model that I can answer for context. I'm curious to see what you think. </div><div class="gmail_default" style="font-family:verdana,sans-serif"><br></div><div class="gmail_default" style="font-family:verdana,sans-serif">Thanks,</div><div class="gmail_default" style="font-family:verdana,sans-serif">Taylor</div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Thu, Feb 6, 2020 at 4:12 PM Eric Larson <<a href="mailto:larson.eric.d@gmail.com">larson.eric.d@gmail.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><p><span style="padding:3px 10px;border-radius:5px;color:rgb(255,255,255);font-weight:bold;display:inline-block;background-color:rgb(255,0,0)"> External Email - Use Caution </span></p><p></p><div dir="ltr"><div>I'm not sure offhand what would cause this. Can you share a script to produce the bottom plot in the source 364, 1632-point-magnetometer case? That would help us look into what specifically what (at least: where in the code) is causing the value to become so large.</div><div><br></div><div>Eric</div><div><br></div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Thu, Feb 6, 2020 at 3:51 PM Taylor Williams <<a href="mailto:williams.taylor@gmail.com" target="_blank">williams.taylor@gmail.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><p><span style="padding:3px 10px;border-radius:5px;color:rgb(255,255,255);font-weight:bold;display:inline-block;background-color:rgb(255,0,0)"> External Email - Use Caution </span></p><p></p><div dir="ltr"><div class="gmail_default" style="font-family:verdana,sans-serif"><div id="gmail-m_295047079383459437gmail-m_-3037450622471036510gmail-:2bj" style="font-size:0.875rem;direction:ltr;margin:8px 0px 0px;padding:0px;font-family:Roboto,RobotoDraft,Helvetica,Arial,sans-serif"><div id="gmail-m_295047079383459437gmail-m_-3037450622471036510gmail-:2dq" style="overflow:hidden;font-variant-numeric:normal;font-variant-east-asian:normal;font-stretch:normal;font-size:small;line-height:1.5;font-family:Arial,Helvetica,sans-serif"><div dir="ltr"><div class="gmail_default" style="font-family:verdana,sans-serif"><div class="gmail_default">I've found something unusual in the lead fields computed using MNE-Python that I can't explain. When arrays containing a large number of magnetometer sensors are used with the 'sample' subject BEM (sample-5120-5120-5120-bem.fif) and the ico4 source space to create a forward model, there are some unusual strong spikes in the lead field. These spikes are not present when I use a spherical BEM model instead. </div><div class="gmail_default"><br></div><div class="gmail_default">To demonstrate, I created three different theoretical arrays of point magnetometers (coil_id: 2000) measuring roughly the normal component of the magnetic field with respect to the scalp surface. Each model contains an increasing number of total sensors (102 sensors, 1632 sensors, and 3672 sensors). </div><div class="gmail_default"><br></div><div class="gmail_default">Figure 1 shows the lead field for a particular dipole (#364 using ico4 source space) for each array using a spherical BEM model. A smooth dipolar response is shown for each that is roughly equivalent over the arrays. The peak response for each array doesn't change appreciably, but there is an improvement in detail of the lead field. All evoked topomap plots are fixed to the same color bar limits (400 fT).</div><div class="gmail_default"><br></div><div class="gmail_default">Figure 2 shows the same set of lead fields but with the 'sample' subject BEM instead. It shows curiously strong spikes present in the two high density arrays. These spikes vary in their location and magnitude. The main dipolar response is still present, and appears to be fairly consistent. However, due to the spikes, the peak response for each array is vastly different. Again, evoked topomap plots use a fixed color bar limit at 400 fT.</div><div class="gmail_default"><br></div><div class="gmail_default">Are these lead field patterns in Figure 2 explainable? They certainly seem like erroneous values, but perhaps something about the BEM model creates a focusing effect for the magnetic field response when we sample at different spatial frequencies? I'm happy to provide some sample forward models for inspection. </div><div class="gmail_default"><br></div><div class="gmail_default">Thanks,</div><div class="gmail_default">Taylor Williams</div></div></div></div></div></div></div>
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