Wiki Guides

Simulator

The Simulator module provides temporal interference (TI) simulation capabilities within the TI-Toolbox GUI, supporting multiple montage sources, electrode configurations, and simulation parameters.

User Interface

Simulator User Interface

The simulator GUI provides intuitive controls for all simulation parameters:

Main Controls

  • Subject Selection: Choose from available pre-processed subjects
  • Montage Source: Radio buttons for montage list, flex mode, and free-hand
  • Simulation Mode: Unipolar/multipolar selection with current inputs
  • EEG Net: Dropdown selection of available electrode configurations

Advanced Options

  • Conductivity Model: Isotropic/anisotropic tissue modeling
  • Current Configuration: Individual electrode current settings
  • Batch Processing: Multiple subject simulation queues

Output Management

  • Real-time Logging: Simulation progress and status updates
  • Result Visualization: Automatic generation of field maps and statistics
  • Data Export: NIfTI files, electrode positions, and analysis reports

Montage Sources

The simulator supports three primary montage source types:

1. Montage List

Pre-defined electrode configurations organized by EEG net and stimulation mode:

  • Unipolar Montages: The traditiona two pairs electrode montage
  • Multipolar Montages: Multiple (currently only supporting four) pairs for higher focality
  • EEG Net Compatibility: Automatically filtered based on selected electrode configuration
  • Management: Add, remove, and refresh montage collections

2. Flex Mode

Automatic integration with the flex-search optimizer.

  • Optimize: Start by running the optimizer based on your needs
  • Simulate: Move to the simulator and use the automatic montage available from the flex-search

3. Free-Hand

Mode that allows exploration of untraditional montages

  • Flexible Positioning: Manual electrode placement for specialized protocols
  • Extension: Open up the electrode placement extension to freely place electrodes on subjects

Simulation Modes

Unipolar TI Left column unipolar (two channels) right column multipolar (four channels). Panels A,D: target and electrode montage. Panels B,E: high frequency fields. Panels C,F: modulation fields.

Unipolar Mode

  • Configuration: Single active electrode with dedicated return path
  • Current Settings: Two current inputs (active and return electrodes)
  • Applications: Focal stimulation with clear current flow direction
  • Montage Compatibility: Works with unipolar montage collections

Multipolar Mode

  • Configuration: Multiple active electrodes (up to 4 channels)
  • Current Settings: Four current inputs for complex stimulation patterns
  • Applications: Distributed stimulation, field steering, and complex targeting
  • Montage Compatibility: Works with multipolar montage collections

Available EEG Nets

The simulator automatically detects and supports various electrode configurations:

Standard EEG Nets

  • 10-10 System: High-density electrode placement (64+ electrodes)
  • 10-20 System: Standard clinical electrode placement (32 electrodes)
  • GSN-HydroCel-256: High-density research net (256 electrodes)
  • GSN-HydroCel-185: Research-grade net (185 electrodes)

Specialized Nets

  • EGI Systems: Multiple EGI electrode configurations
  • EasyCap: TMS-compatible electrode layouts
  • Custom Nets: User-defined electrode positions via CSV files

Net Detection

  • Automatic Scanning: Searches eeg_positions/ directories for available nets
  • Dynamic Updates: Montage lists refresh based on selected EEG net
  • Compatibility Filtering: Only compatible montages shown for selected net

Anisotropy

The simulator supports different tissue conductivity models:

Isotropic Model

  • Description: Uniform conductivity in all directions
  • Applications: Simplified modeling, faster computation
  • Limitations: May not accurately represent white matter anisotropy

Anisotropic Model

  • Description: Direction-dependent conductivity based on DTI data
  • Requirements: Diffusion tensor imaging (DTI) scans
  • Applications: More realistic modeling of white matter tracts
  • Processing: Accounts for fiber orientation in field calculations

Coordinate Spaces

Subject Space

  • Definition: Coordinates relative to individual subject anatomy
  • Origin: Centered on subject’s brain anatomy
  • Applications: Subject-specific targeting and analysis
  • File Format: Native FreeSurfer subject space coordinates

MNI Space

  • Definition: Standardized coordinate system (MNI152 template)
  • Origin: Based on Montreal Neurological Institute template
  • Applications: Cross-subject comparisons and group analysis
  • Transformations: Automatic conversion between subject and MNI space

Space Transformations

  • Automatic Conversion: Built-in coordinate transformation utilities
  • ROI Mapping: Support for both subject and MNI coordinate inputs
  • Visualization: Compatible with both coordinate systems for analysis