Dear Fieldtrip users,<br><br>I'm trying to create a forward model for a fixed number of dipoles with fixed positions and orientations (extracted from a MRI image using freesurfer and a downsampling algorithm) so I can use it with my inverse algorithm. <br>
<span style="font-family: arial,helvetica,sans-serif;">I read this </span><a style="font-family: arial,helvetica,sans-serif;" href="http://fieldtrip.fcdonders.nl/tutorial/headmodel">tutorial</a><span style="font-family: arial,helvetica,sans-serif;">, a few </span><a style="font-family: arial,helvetica,sans-serif;" href="http://fieldtrip.fcdonders.nl/example/compute_forward_simulated_data_and_apply_a_dipole_fit">examples</a><span style="font-family: arial,helvetica,sans-serif;"> and </span><a style="font-family: arial,helvetica,sans-serif;" href="http://fieldtrip.fcdonders.nl/reference/ft_dipolefitting">function headers</a><span style="font-family: arial,helvetica,sans-serif;">, but I still didn't find exactly what I'm trying to do.</span><br>
<br>Is it possible to have as a result of <b>ft_compute_leadfield</b>, (and<b> ft_prepare_leadfield</b>?,<b> ft_prepare_sourcemodel</b><span style="font-family: arial,helvetica,sans-serif;">?</span>) a leadfield that depends only on the *intensity* of the dipole? Because it has a fixed orientation, and the idea is exactly reduce the number of unknowns. I noticed that SPM creates what I'm trying to do (as copied below), but I'm trying to stay within fieldtrip definitions so I can use it's inverse solutions to compare with mine, although I only found examples for beamformers inverse solutions, and not sparse methods. So this is the second question: is there any example of source-space based sparse methods inverse solutions?<br>
<br>Thanks in advance for any help,<br><br>Best Regards<br>Leonardo Barbosa<br><br>Here is the SPM code (inside <b>spm_eeg_lgainmat</b>)<br><br><span id="hotword"><span style="cursor: default; background-color: transparent;" id="hotword" name="hotword"></span></span><span style="font-family: courier new,monospace;"> % Forward computation</span><br style="font-family: courier new,monospace;">
<span style="font-family: courier new,monospace;"> %--------------------------------------------------------------------------</span><br style="font-family: courier new,monospace;"><span style="font-family: courier new,monospace;"> [vol, sens] = forwinv_prepare_vol_sens(vol, sens, 'channel', forward(ind).channels);</span><br style="font-family: courier new,monospace;">
<span style="font-family: courier new,monospace;"> nvert = size(vert, 1); </span><br style="font-family: courier new,monospace;"><br style="font-family: courier new,monospace;"><span style="font-family: courier new,monospace;"> spm('Pointer', 'Watch');drawnow;</span><br style="font-family: courier new,monospace;">
<span style="font-family: courier new,monospace;"> spm_progress_bar('Init', nvert, ['Computing ' modality ' leadfields']); drawnow;</span><br style="font-family: courier new,monospace;"><span style="font-family: courier new,monospace;"> if nvert > 100, Ibar = floor(linspace(1, nvert,100));</span><br style="font-family: courier new,monospace;">
<span style="font-family: courier new,monospace;"> else Ibar = [1:nvert]; end </span><br style="font-family: courier new,monospace;"><br style="font-family: courier new,monospace;"><span style="font-family: courier new,monospace;"> Gxyz = zeros(length(forward(ind).channels), 3*nvert);</span><br style="font-family: courier new,monospace;">
<span style="font-family: courier new,monospace;"> for i = 1:nvert</span><br style="font-family: courier new,monospace;"><br style="font-family: courier new,monospace;"><span style="font-family: courier new,monospace;"> Gxyz(:, (3*i- 2):(3*i)) = forwinv_compute_leadfield(vert(i, :), sens, vol);</span><br style="font-family: courier new,monospace;">
<br style="font-family: courier new,monospace;"><span style="font-family: courier new,monospace;"> if ismember(i, Ibar)</span><br style="font-family: courier new,monospace;"><span style="font-family: courier new,monospace;"> spm_progress_bar('Set', i); drawnow;</span><br style="font-family: courier new,monospace;">
<span style="font-family: courier new,monospace;"> end </span><br style="font-family: courier new,monospace;"><br style="font-family: courier new,monospace;"><span style="font-family: courier new,monospace;"> end </span><br style="font-family: courier new,monospace;">
<br style="font-family: courier new,monospace;"><span style="font-family: courier new,monospace;"> spm_progress_bar('Clear');</span><br style="font-family: courier new,monospace;"><span style="font-family: courier new,monospace;"> spm_progress_bar('Init', nvert, ['Orienting ' modality ' leadfields']); drawnow;</span><br style="font-family: courier new,monospace;">
<br style="font-family: courier new,monospace;"><span style="font-family: courier new,monospace;"> G{ind} = zeros(size(Gxyz, 1), size(Gxyz, 2)/3);</span><br style="font-family: courier new,monospace;"><span style="font-family: courier new,monospace;"> for i = 1:nvert</span><br style="font-family: courier new,monospace;">
<br style="font-family: courier new,monospace;"><span style="font-family: courier new,monospace;"> G{ind}(:, i) = Gxyz(:, (3*i- 2):(3*i))*norm(i, :)';</span><br style="font-family: courier new,monospace;">
<br style="font-family: courier new,monospace;">
<span style="font-family: courier new,monospace;"> if ismember(i, Ibar)</span><br style="font-family: courier new,monospace;"><span style="font-family: courier new,monospace;"> spm_progress_bar('Set', i); drawnow;</span><br style="font-family: courier new,monospace;">
<span style="font-family: courier new,monospace;"> end </span><br style="font-family: courier new,monospace;"><br style="font-family: courier new,monospace;"><span style="font-family: courier new,monospace;"> end </span><br style="font-family: courier new,monospace;">
<br style="font-family: courier new,monospace;"><span style="font-family: courier new,monospace;"> spm_progress_bar('Clear');</span><br style="font-family: courier new,monospace;"><br><br><br>