Source estimator

Source Estimator 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.  Source estimates may be output to MR Viewer for MRI overlay.

Functionality

Source Models

• 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 dipole time series may be estimated using minimum norm techniques. Confidence intervals may be estimated.
• 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.
• 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.

Head Models

• 3 shell sphere. Digitized electrode locations (e.g. from LOCATOR) may be used to determine a best-fit sphere origin. Measured electrode locations are then used to calculate field potentials.
• 1 shell sphere. External headshape data (e.g. from LOCATOR) may be used to determine a best-fit sphere origin for MEG source estimation. 1 shell sphere models may also be used for source analysis from ECoG data.
• Realistic headshape*. Using segmented image data obtained from the IMAGE PROCESSOR* module, boundary element modeling calculates field potentials, based on skull, scalp, and brain geometry (assuming homogeneous, isotropic compartments).

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 through VISUALIZER.

Inter-module 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.

Requirements	minimum required	recommended
CPU	Pentium
RAM	32 Mbyte	64+ Mbyte recommended for >32 channels
Hard drive	2 Mbyte for executable	64 Mbyte swap space + additional data storage requirements
Operating System	Win 95/98/ME/NT/2000/XP
Display	SVGA
Installation medium	CD-ROM
Input modules	DATA EDITOR

Copyright © Source Signal Imaging, Inc.