View source for Different beamformer types in the source analysis module

{{BESAInfobox
|title = Module information
|module = BESA Research Standard or higher
|version = BESA Research 6.1 or higher
}}

== Beamformer in BESA Research ==

A beamformer operator is designed to pass signals from the brain region of interest without attenuation, while minimizing interference from activity in all other brain regions. Traditional '''single source beamformers''' are known to mislocalize sources if several brain regions have highly correlated activity. Therefore, the BESA beamformer extends the traditional single-source beamformer in order to implicitly suppress activity from possibly correlated brain regions. This is achieved by using a '''multiple sources beamformer''' calculation that contains not only the leadfields of the source at the location of interest but also those of possibly interfering sources.

== Bilateral sources beamformer == 

As a default BESA Research uses a '''bilateral sources beamformer''', where specifically contributions from the homologue source in the opposite hemisphere are taken into account. This allows for imaging of highly correlated bilateral activity in the two hemispheres that commonly occurs during processing of external stimuli.

== Multiple sources beamformer ==

The beamformer computation can be repeated taking into account possibly correlated sources that are specified in the current solution. Interfering activities generated by the sources in the current solution (in the Source box of the source analysis window) that are in the '''On''' state are specifically suppressed.

Below figure shows an example for the multiple sources beamformer in time-domain. The source image for "Beamformer - single additional source" is computed after inserting a source on the right side peak of the source image for "Beamformer - bilateral sources". The activity of the inserted source on the right side is suppressed during the beamformer computation. Therefore, high source activity is only shown on the left side of the source image for "Beamformer - single additional source" and the source waveforms in the Source box are flat (zero).

[[File:Beamformer_SingleAdditionalSource.png|1200px]]

== Single source beamformer == 

The single source beamformer can be also used in the Source Analysis module.

'''Time-domain beamformer''' (This feature requires BESA Research 7.0 or higher)
* Method 1
*# Right click on the 3D window of the Source Analysis module to show the context menu.
*# Select “Image / Volume Image / Beamformer (single source)” entry in the context menu.
* Method 2
*# Open the "Standard Volume" tab of the "Image Settings" dialog ("Image / Settings…" menu entry).
*# Select "Single-source beamformer" option in the "Beamformer Options" section.

'''Time-frequency domain beamformer'''
# Right click on the 3D window of the Source Analysis module to show the context menu.
# Select “Image / Volume Image / Beamformer (single source)” entry in the context menu.


The below figure shows the difference between the bilateral sources beamformer and single source beamformer for an auditory experiment data.

[[File:Beamformer_Types.png|600px]]




[[Category:Source Analysis]]