DocumentCode :
978197
Title :
Modified beamformers for coherent source region suppression
Author :
Dalal, Sarang S. ; Sekihara, Kensuke ; Nagarajan, Srikantan S.
Author_Institution :
Dept. of Radialogy, California Univ., San Francisco, CA, USA
Volume :
53
Issue :
7
fYear :
2006
fDate :
7/1/2006 12:00:00 AM
Firstpage :
1357
Lastpage :
1363
Abstract :
Many tomographic source localization algorithms used in biomagnetic imaging assume, explicitly or sometimes implicitly, that the source activity at different brain locations are either independent or that the correlation structure between sources is known. Among these algorithms is a class of adaptive spatial filters known as beamformers, which have superior spatiotemporal resolution abilities. The performance of beamformers is robust to weakly coherent sources. However, these algorithms are extremely sensitive to the presence of strongly coherent sources. A frequent mode of failure in beamformers occurs with reconstruction of auditory evoked fields (AEFs), in which bilateral auditory cortices are highly coherent in their activation. Here, we present a novel beamformer that suppresses activation from regions with interfering coherent sources. First, a volume containing the interfering sources is defined. The lead field matrix for this volume is computed and reduced into a few significant columns using singular value decomposition (SVD). A vector beamformer is then constructed by rejecting the contribution of sources in the suppression region while allowing for source reconstruction at other specified regions. Performance of this algorithm was first validated with simulated data. Subsequent tests of this modified beamformer were performed on bilateral AEF data. An unmodified vector beamformer using whole head coverage misplaces the source medially. After defining a suppression region containing the temporal cortex on one side, the described method consistently results in clear focal activations at expected regions of the contralateral superior temporal plane.
Keywords :
adaptive filters; hearing; magnetoencephalography; medical signal processing; signal reconstruction; singular value decomposition; spatial filters; adaptive spatial filters; auditory evoked fields; bilateral auditory cortices; biomagnetic imaging; brain; coherent source region suppression; modified beamformers; singular value decomposition; source activity; source reconstruction; spatiotemporal resolution; tomographic source localization algorithm; Biomagnetics; Brain modeling; Image reconstruction; Matrix decomposition; Robustness; Singular value decomposition; Spatial filters; Spatial resolution; Spatiotemporal phenomena; Tomography; Beamformer; MEG inverse problems; biomagnetism; functional neuroimaging; magnetoencephalography; neuromagnetic signal processing; Adult; Algorithms; Auditory Cortex; Brain Mapping; Computer Simulation; Diagnosis, Computer-Assisted; Evoked Potentials, Auditory; Female; Humans; Magnetoencephalography; Models, Neurological;
fLanguage :
English
Journal_Title :
Biomedical Engineering, IEEE Transactions on
Publisher :
ieee
ISSN :
0018-9294
Type :
jour
DOI :
10.1109/TBME.2006.873752
Filename :
1643404
Link To Document :
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