New Access to the Brain
Products
3D Mapping
The 3D Mapping option of Walter Graphtek’s PL-EEG creates 3D visualization of brain electrical activity on a realistic head.
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- 3D FFT mapping and spectral analysis over standard frequency bands and user-defined frequency bands
- Simultanous view of maps of all frequency bands or enlarged view of a single map of a selected frequency band
- Synchronized with EEG and optional video image – even while paging through the EEG
- Navigate around head and examine maps from all possible viewpoints or display rotating heads by simple mouse-clicks
- Advanced interpolation algorithm covering electrode sites next to adjacent electrode sites and maxima/minima between electrode sites
- Selectable montages: common reference, linked ears or source derivation with configurable weights
- Copy the maps to clipboard to paste them, for example, into a report
Specification
System requirements
Same as PL-Winsor, additionally:
- Graphics card not older than 2006, achievable frame rate depends on graphics card performance
Technical data
- Four user-definable or standard frequency bands
- Power scale: 30 µV²/Hz to 100,000 µV²/Hz
- Display modes: 3D or 2D maps with or without power spectra
- Scaling modes: linear scale of power, linear scale of amplitude or logarithmic scale
- Montages: Avg (common reference), A1 + A2 (linked ears) or Source (source derivation)
- Minimum segment length: 3 s
- Selectable “conservative” or advanced interpolation method (see column to the right)
- Selectable option to either attenuate interpolated values toward edge of map, or to assume values for smooth overall map display
- Selectable option for power maps to either interpolate the band power or the square root of the band power (RMS)
Interpolation algorithm
With the band power analysis, a Hanning window is applied to the selected EEG segments, the Fourier transformation is performed and the absolute values of the FFT transformed signals are averaged. The total frequency band power at the electrode positions is calculated by summation. The electrode sites are assumed to be on a spherical surface. Using the Mercator algorithm, the spherical surface is projected to the plane where the electrode sites build the edges of a square grid. The measured values at the electrode positions are not modified.
For each inner square point the interpolated value is calculated as weighted average of the four edges. Each square side length is fixed to 1. The weights are calculated as follows:
(2dx³ – 3dx² + 1) • (2dy³ – 3dy² + 1), where dx is the distance in x-direction, and dy the distance in y-direction.
Advanced algorithm:
Interpolation is done as spatial filtering (using a cascade of halfband filters) and the values between electrode sites can be taken as reconstructed values withing the technical limits (Nyquist's theorem). maxima and minima of the map not only can be at electrode sites, but also between them.