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Source Estimator


EMSE Suite SOURCE ESTIMATOR module may be used for discrete or distributed dipole source analysis from EEG or MEG data which has been provided by the DATA EDITOR module. Three shell spherical models or realistic head models (using data from the IMAGE PROCESSOR module) may be used for field calculations. 3D source estimates may be displayed in VISUALIZER for rendering with surfaces or in MR VIEWER with MRI overlay.

Functionality

Data Domains

  • Electromagnetic Source Estimation (EMSE) may be applied to EEG or MEG data in the time domain (e.g., raw data or event-related average), in the frequency domain (e.g., power spectral density of ongoing or resting state data), or time-frequency domain (e.g., event-related evoked or induced oscillations).

Source Domains

  • Continuous domain: One or more equivalent current dipoles with artibrary positions and orientations within the brain compartment.
  • Tomographic lattice domain: 3-vectors of dipoles with x-, y-, and z-orientations distributed on a regular 3D grid that covers the brain compartment.
  • Cortical surface domain: Dipoles distributed on a cortical wireframe with unconstrained or surface-normal constrained orientations.   Cortical surface wireframes may be obtained via IMAGE PROCESSOR.

Head Models

  • Forward fields generated by current dipoles in the source domain are calculated at the sensors using a model of the head as a volume conductor.  Standard values for head tissue conductivities may be adjusted.
  • 3-shell sphere.  Digitized sensor locations (e.g. electrodes digitized from LOCATOR) or manufacturer-specified locations may be used to determine a best-fit center of a 3-compartment (intracranial, skull, scalp) spherical volume conductor model.
  • 1-shell sphere: May be used for MEG or ECoG source estimation.
  • Boundary Element Method (BEM):  3-compartment head models for realistic-geometry boundary surfaces (scalp, outer skull, and inner skull) obtained from an average head MRI (included) or from individual MRIs (via IMAGE PROCESSOR).  The BEM head model assumes nested, homogeneous, isotropic compartments.
  • Finite Element Method (FEM):  The most general realistic-geometry head model available in EMSE.*  Supports more than 3 tissue types which need not comprise nested compartments.  FEM meshes are obtained from an average head MRI (included) or from individual MRIs (via IMAGE PROCESSOR).  [*MEG not currently supported.  Anisotropic conductivity tensors available by special request.]

Inverse Methods

  • Spatiotemporal dipole modeling. Fit one or more dipoles to the data. By interacting with the data, the operator may use up to 32 dipoles to create source models. The dipoles are subject to a variety of user-controlled constraints (including free or fixed locations and/or orientations, mirror pairs, and maximal power constraints).  Multiple source waveforms may be estimated using pseudoinverse techniques.  Confidence intervals may be estimated.
  • Multi-start is an objective method for fitting multiple dipoles that minimizes user interaction with the data.  The spread of dipoles in point clouds indicates spatial extent and robustness of the source solutions.
  • Dipole modeling in Frequency and Time-Frequency domains. Dipoles may be fit directly in the complex domain to Fourier transformed data, permitting the estimation of generators of oscillatory activity directly. Source Estimation using wavelets is a powerful tool for both time and frequency domains.
  • Topographic mapping such as sphere-to-plane mapping, channel group selection (for dipole fitting), time-frequency display, Neuromag vector magnitude display, auto-update latency changes, context menus and a modeless dialog that lets you work while leaving the dialog open
  • Seeded Dipoles. Dipole locations may be obtained from fMRI or PET hotspots (using MR VIEWER) and transferred to SOURCE ESTIMATOR for constrained dipole time series analysis.
  • Beamformers and other local estimators. Local estimators reveal spatially constrained source activity.
  • Distributed source models. Source estimates are obtained from instantaneous data samples using maximum likelihood and Laplacian smoothing (LORETA) or covariance statistics (PRoMS) for a set of dipole current sources fixed to a lattice. Related options include minimum norm and MUSIC algorithm. The resulting analysis may be viewed as a tomographic display, either for a single time slice, or for a sequence of time slices (4D analysis)
  • Cortical surface restriction*. Distributed source estimates may be restricted to the cortical surface, obtained from the IMAGE PROCESSOR module.

Display

  • Dynamic linkage of graphical display windows permits selections in one window to update others automatically.
  • Discrete dipole location, orientation, and confidence intervals are represented in diagrammatic display (3 orthogonal planes).
  • Tomographic displays are available for distributed source estimates. 6D displays optionally include position and moment for each lattice point.
  • 3D rendering and animation of cortical surface source estimates is available through VISUALIZER.

Input/Output

  • User Interface. A conventional Microsoft Windows style graphical user interface is used throughout. Dynamic linking of graphical display windows permits selections in one window to update others automatically.
  • Number of channels. Up to a total of 256 channels (EEG and MEG) are supported s is available throughVISUALIZER.

Intermodule Communication

  • Input/Output. Requires DATA EDITOR.

File I/O

  • Input/Output. Requires DATA EDITOR.

Other I/O

  • Graphics may be transferred to clipboard for use by other graphics programs or for insertion into word processors.

Documentation

  • Printed. User manual, including file formats.
  • On-line. User manual and tutorial available as context sensitive hypertext.
Preview
Sample functionality in Source Estimator
Preview
Multi-start dipole modeling
Preview
Mapping on a realistic head shape (with dipoles)

Preview
Tomographic mapping

Preview
3D rendering and animation

Requirements minimum required  recommended
CPU X86 Pentium or better  
RAM 1 Gbyte 2+ Gbyte recommended for >64 channels
Hard drive 10 Mbyte for executable 512 Mbyte swap space + additional data storage requirements
Operating System Win 95/98/ME/NT/2000/XP/Vista/7  
Display SVGA or better  
Installation medium CD-ROM  
Input modules DATA EDITOR