Improving epilepsy localization accuracy using a 1st-order multipole beamformer
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1
Henry Ford Hospital, Department of Psychology, Faculty of Arts and Sciences, United States
Significant improvements have been made to the SAM(g2) analysis for MEG epilepsy data. Changes include substitution of a 1st-order multipole beamformer in place of a dipole beamformer, addition of an integration window stage prior to computing excess kurtosis, and compensation for frequency dependencies in computing the virtual sensor waveforms. The multipole beamformer uses a dipole plus quadrupole forward model that accounts, in part, for extended sources along the curved cortical surface. This feature is shown to improve localization accuracy such that sources are associated with the cortical mantle, increase source signal-to-noise ratio – especially for hippocampal spikes, and provide better rejection of muscle artifacts. Muscle artifacts arise from superficial extended source that had been incorrectly localized within the brain by the dipole beamformer. The multipole beamformer localizes the muscle artifact external to the skull. For each coordinate, the multipole beamformer is used to compute the estimated source waveform in a 20 to 70 Hz bandpass. A 20 ms integration window is applied to the source waveform in order to reduce sensitivity to very short transients signals. Excess kurtosis (g2) is then computed for the smoothed source waveform. An image of spikiness is generated by mapping the g2 value at 5 mm intervals, throughout the head. Next, local maxima are located within the image. These are the centroids of spikiness. Last, the source waveforms are estimated at the locations of the maxima for the entire recording bandwidth. The image and source waveforms can then be interpreted by an epileptologist. A comparison showing between the previous SAM(g2) method and the improved method demonstrates that the new method improves localization, signal-to-noise, and artifact rejection. This research was supported by NIH/NINDS Grant R01 NS30914.
References
1. Grounded cognition. Barsalou LW, Annual Review of Psychology 59 (2008) 617–645.
2. The representation of object concepts in the brain. Martin A, Annual Review of Psychology 58 (2007) 25-45.
Conference:
Biomag 2010 - 17th International Conference on Biomagnetism , Dubrovnik, Croatia, 28 Mar - 1 Apr, 2010.
Presentation Type:
Poster Presentation
Topic:
Signal proccessing
Citation:
Robinson
S
(2010). Improving epilepsy localization accuracy using a 1st-order multipole beamformer.
Front. Neurosci.
Conference Abstract:
Biomag 2010 - 17th International Conference on Biomagnetism .
doi: 10.3389/conf.fnins.2010.06.00101
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Received:
23 Mar 2010;
Published Online:
23 Mar 2010.
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Correspondence:
Stephen Robinson, Henry Ford Hospital, Department of Psychology, Faculty of Arts and Sciences, Detroit, United States, robinson@neurnis.neuro.hfh.edu