<html xmlns:v="urn:schemas-microsoft-com:vml" xmlns:o="urn:schemas-microsoft-com:office:office" xmlns:w="urn:schemas-microsoft-com:office:word" xmlns:m="http://schemas.microsoft.com/office/2004/12/omml" xmlns="http://www.w3.org/TR/REC-html40">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=us-ascii">
<meta name="Generator" content="Microsoft Word 15 (filtered medium)">
<style><!--
/* Font Definitions */
@font-face
{font-family:"Cambria Math";
panose-1:2 4 5 3 5 4 6 3 2 4;}
@font-face
{font-family:Calibri;
panose-1:2 15 5 2 2 2 4 3 2 4;}
@font-face
{font-family:"Segoe UI";
panose-1:2 11 5 2 4 2 4 2 2 3;}
/* Style Definitions */
p.MsoNormal, li.MsoNormal, div.MsoNormal
{margin:0cm;
font-size:11.0pt;
font-family:"Calibri",sans-serif;
mso-fareast-language:EN-US;}
.MsoChpDefault
{mso-style-type:export-only;
font-family:"Calibri",sans-serif;
mso-fareast-language:EN-US;}
@page WordSection1
{size:612.0pt 792.0pt;
margin:70.85pt 70.85pt 70.85pt 70.85pt;}
div.WordSection1
{page:WordSection1;}
--></style><!--[if gte mso 9]><xml>
<o:shapedefaults v:ext="edit" spidmax="1026" />
</xml><![endif]--><!--[if gte mso 9]><xml>
<o:shapelayout v:ext="edit">
<o:idmap v:ext="edit" data="1" />
</o:shapelayout></xml><![endif]-->
</head>
<body lang="NL" link="#0563C1" vlink="#954F72" style="word-wrap:break-word">
<div class="WordSection1">
<p class="MsoNormal"><span lang="EN-US">Hello,<br>
<br>
I am trying to compute leadfields for MEG data with magnetometers and planar gradiometers (neuromag306).<br>
After loading the header I convert the units to meters (<i>hdr.grad = ft_convert_units(hdr.grad,'m')</i>) to keep units everywhere the same (my headmodel and sourcemodel are also in m).<br>
While this converts variables such as chanpos and coilpos correctly, it also converts the values corresponding to the gradiometers in the hdr.grad.tra matrix.<br>
These values are e.g. -0.5952 and 0.5952 for the gradiometers and are 1 for magnetometers and are converted to -59.52 and 59.92 and 1 respectively.<br>
The next step is using ft_prepare_leadfield and therefore ft_compute_leadfield, which computes the lf for every coil and then transforms this to lf for every sensor with the line
<i>lf=sens.tra*lf</i>.<br>
The results is that the lf matrix gets scaled because the units of sens.tra were converted to m. This seems incorrect, as this step should only transform lf per coil to lf per sensor. <br>
Is this indeed incorrect? The question is if the values in hdr.grad.tra for gradiometers have a unit (T/cm or T/m) or that this should be a unitless scaling factor? Additionally, what is the unit of the leadfields?<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><br>
For clarity, this is the code I’m using:<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">hdr = ft_read_header(fif-file);<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">hdr.grad = ft_convert_units(hdr.grad,'m');<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">cfg = [];<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">cfg.grad = hdr.grad;<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">cfg.headmodel = headmodel; %The headmodel is based on OpenMEEG<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">cfg.sourcemodel = sourcemodel;<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">lf = ft_prepare_leadfield(cfg);<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" style="font-family:"Segoe UI",sans-serif;color:black;mso-fareast-language:NL">Kind regards,<br>
<br>
Bram Knipscheer</span><span lang="EN-US"><o:p></o:p></span></p>
</div>
<!-- --><hr>
<p><font size="-2" face="arial" color="black"><i>
De informatie opgenomen in dit bericht kan vertrouwelijk zijn en is
uitsluitend bestemd voor de geadresseerde. Indien u dit bericht onterecht
ontvangt, wordt u verzocht de inhoud niet te gebruiken en de afzender direct
te informeren door het bericht te retourneren. Het Universitair Medisch
Centrum Utrecht is een publiekrechtelijke rechtspersoon in de zin van de W.H.W.
(Wet Hoger Onderwijs en Wetenschappelijk Onderzoek) en staat geregistreerd bij
de Kamer van Koophandel voor Midden-Nederland onder nr. 30244197.
</i></font></p>
<p><font size="-2" face="arial" color="green"><i>
Denk s.v.p aan het milieu voor u deze e-mail afdrukt.
</i></font></p>
<hr>
<p><font size="-2" face="arial" color="black"><i>
This message may contain confidential information and is intended
exclusively for the addressee. If you receive this message
unintentionally, please do not use the contents but notify the sender
immediately by return e-mail. University Medical Center Utrecht is a legal
person by public law and is registered at the Chamber of Commerce for
Midden-Nederland under no. 30244197.
</i></font></p>
<p><font size="-2" face="arial" color="green"><i>
Please consider the environment before printing this e-mail.
</i></font></p>
</body>
</html>