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template:sourcemodel [2018/10/21 15:06]
42.49.180.224 [Template models for source reconstruction]
template:sourcemodel [2017/08/17 11:21] (current)
127.0.0.1 external edit
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 Source models are a necessary ingredient for estimating the cortical activity from EEG or MEG data. Sources are typically modelled as equivalent current dipoles (ECDs), i.e. point sources with a location, orientation and strength. Source models are a necessary ingredient for estimating the cortical activity from EEG or MEG data. Sources are typically modelled as equivalent current dipoles (ECDs), i.e. point sources with a location, orientation and strength.
  
-===== Template models for source reconstruction =====+==== Grid search in dipole fitting ​==== 
 + 
 +When you do source reconstruction with dipole fit methods (as implemented in **[[:​reference:​ft_dipolefitting]]**),​ you usually assume a source model that consists of a single or a small number of equivalent current dipoles and you fit the source location, orientation and strength to the data. In this case you might start with an exhaustive grid search on a pre-defined grid, which in general is then followed by a non-linear optimization of the location of the dipoles. The initial grid on which the search is performed is not that important and is usually constructed on the fly as 3d grid  with a reasonable resolution. The resolution should not be too high, otherwise the grid search will take too long, but should also not be too low, otherwise the non-lienar search will have to start from a grid location that is still far of from the minimum. Both a too low and a too high grid resolution will cause the dipole fitting procedure to take more time. 
  
-Source models are a necessary ingredient for estimating the cortical activity from EEG or MEG data. Sources are typically modelled as equivalent current dipoles (ECDs), i.e. point sources with a location, orientation and strength. 
 ==== Scanning with a beamformer ==== ==== Scanning with a beamformer ====
  
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 ===== UPDATE: updated 3D source models uploaded on February 19, 2016 ===== ===== UPDATE: updated 3D source models uploaded on February 19, 2016 =====
-Essentially this update does not include a functional change, it only pertains to the structure in the data-structures. Before, the source model variable contained '​xgrid'/'​ygrid'/'​grid'​ fields. These fields since long have been obsolete. Also, the inside/​outside handling used to be in terms of index-vectors. More recently, the default functionality has been replaced by inside being a boolean vector, which is easier to handle in terms of bookkeeping. The sourcemodels now reflect these current standards.+Essentially this update does not include a functional change, it only pertains to the structure in the data-structures. Before, the source model variable contained '​xgrid'/'​ygrid'/'​grid'​ fields. These fields since long have been obsolete. Also, the inside/​outside handling used to be in terms of index-vectors. More recently, the default functionality has been replaced by inside being a boolean vector, which is easier to handle in terms of bookkeeping. The sourcemodels now reflect these current standards. ​