title: Volumetric imaging of brain activity with spatial-frequency decoding of neuromagnetic signals.
abstract: BACKGROUND
  The brain generates signals in a wide frequency range (∼2840 Hz). Existing magnetoencephalography (MEG) methods typically detect brain activity in a median-frequency range (1-70 Hz). The objective of the present study was to develop a new method to utilize the frequency signatures for source imaging.
  
  
  METHODS
  Morlet wavelet transform and two-step beamforming were integrated into a systematic approach to estimate magnetic sources in time-frequency domains. A grid-frequency kernel (GFK) was developed to decode the correlation between each time-frequency representation and grid voxel. Brain activity was reconstructed by accumulating spatial- and frequency-locked signals in the full spectral data for all grid voxels. To test the new method, MEG data were recorded from 20 healthy subjects and 3 patients with verified epileptic foci.
  
  
  RESULTS
  The experimental results showed that the new method could accurately localize brain activation in auditory cortices. The epileptic foci localized with the new method were spatially concordant with invasive recordings.
  
  
  METHODS
  Compared with well-known existing methods, the new method is objective because it scans the entire brain without making any assumption about the number of sources. The novel feature of the new method is its ability to localize high-frequency sources.
  
  
  CONCLUSIONS
  The new method could accurately localize both low- and high-frequency brain activities. The detection of high-frequency MEG signals can open a new avenue in the study of the human brain function as well as a variety of brain disorders.
authors.affiliation: MEG Center, Department of Neurology, Cincinnati Children's Hospital Medical Center, 3333 Burnet Avenue, Cincinnati, OH, USA. Electronic address: Jing.xiang@cchmc.org.
authors.forename: Jing
authors.initials: J
authors.lastname: Xiang
authors.affiliation: MEG Center, Department of Neurology, Cincinnati Children's Hospital Medical Center, 3333 Burnet Avenue, Cincinnati, OH, USA.
authors.forename: Abraham
authors.initials: A
authors.lastname: Korman
authors.affiliation: Department of Electrical Engineering, University of Cincinnati, Cincinnati, OH, USA.
authors.forename: Kasun M
authors.initials: KM
authors.lastname: Samarasinghe
authors.affiliation: Department of Mathematical Sciences, University of Cincinnati, Cincinnati, OH, USA.
authors.forename: Xiaopei
authors.initials: X
authors.lastname: Wang
authors.affiliation: Department of Communication Sciences and Disorders, University of Cincinnati, OH, USA.
authors.forename: Fawen
authors.initials: F
authors.lastname: Zhang
authors.affiliation: MEG Laboratory, Beijing Tiantan Hospital, Beijing, People's Republic of China.
authors.forename: Hui
authors.initials: H
authors.lastname: Qiao
authors.affiliation: MEG Laboratory, Beijing Tiantan Hospital, Beijing, People's Republic of China.
authors.forename: Bo
authors.initials: B
authors.lastname: Sun
authors.affiliation: MEG Laboratory, Beijing Tiantan Hospital, Beijing, People's Republic of China.
authors.forename: Fengbin
authors.initials: F
authors.lastname: Wang
authors.affiliation: Department of Electrical Engineering, University of Cincinnati, Cincinnati, OH, USA.
authors.forename: Howard H
authors.initials: HH
authors.lastname: Fan
authors.affiliation: Department of Electrical Engineering, Purdue University, Fort Wayne, IN, USA.
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Thompson
mesh_terms: D000161:Acoustic Stimulation; D000328:Adult; D001921:Brain / Q000502:physiology* / Q000503:physiopathology; D001931:Brain Mapping; D058256:Brain Waves / Q000502:physiology*; D003198:Computer Simulation; D003952:Diagnostic Imaging; D004569:Electroencephalography; D004827:Epilepsy / Q000473:pathology; D005260:Female; D005583:Fourier Analysis; D006801:Humans; D015225:Magnetoencephalography; D008297:Male; D008875:Middle Aged; D008959:Models, Neurological; D009424:Nervous System Physiological Phenomena; D012189:Retrospective Studies
keywords: Brain; High-frequency oscillation; Magnetoencephalography; Neuroimaging; Spatial filter; Wavelet