Segmented Recording Electrode for TMS Artifact Reduction
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Solution Overview
Problem
Current recording electrodes for transcranial magnetic stimulation (TMS) fail to effectively suppress both short-term and long-term artifacts, particularly the relaxation artifact, which interferes with electrophysiological signal measurement, and often exacerbate the issue by concentrating electrical stress, leading to distorted signals.
Innovation Solution
The recording electrode is designed with a divided contact surface into multiple electrically separated areas, each connected through high resistance values, minimizing induced currents and impedance, thereby reducing both eddy current and relaxation artifacts, ensuring accurate signal measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the recording electrode uses a large undivided electrically conductive surface, then the electrical contact area with biological tissue is improved, but eddy currents are generated causing heating artifacts and potential tissue burns
Solution Approach 1:
The electrode surface is divided into multiple separate contact areas instead of using a single large continuous surface. This segmentation prevents the formation of large eddy current loops while maintaining adequate total contact area with the biological tissue, thereby reducing heating artifacts without compromising electrical contact.
2Object-affected harmful factors
If the recording electrode uses a divided contact surface with electrically separated areas, then eddy current artifacts are reduced, but the relaxation artifact is exacerbated due to concentrated electrical stress
Solution Approach 1:
A non-conductive substrate is introduced as an intermediary between the separate contact areas. This substrate provides mechanical support and maintains the geometric arrangement of contact areas while electrically isolating them, preventing direct current paths between areas and reducing concentrated electrical stress that causes relaxation artifacts.
3Object-affected harmful factors
If the recording electrode uses a divided contact surface, then eddy current heating is prevented, but the electrical impedance increases affecting signal quality
Solution Approach 1:
The geometric parameters of the contact areas (size, shape, spacing, and arrangement) are optimized to achieve the right balance between reducing eddy currents and maintaining low electrical impedance. By carefully controlling these parameters, the electrode minimizes heating artifacts while preserving adequate signal quality for electrophysiological measurements.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design significantly reduces both immediate and long-term artifacts, allowing for undistorted electrophysiological signal recording post-stimulation, enhancing the quality of TMS measurements by minimizing electrical stress and impedance.
Implementation Method 1
The induced electrical voltage in biological tissue during TMS is primarily used to stimulate the brain or spinal cord because their direct non-invasive electrical stimulation is complicated and very painful. Transcranial magnetic stimulation is performed by a short magnetic field pulse of the intensity of the order of tesla and of the duration of the order of several hundred microseconds
Implementation Method 2
Artifact caused by the heating of the recording electrodes, which is induced by the heat loss generated by eddy currents in large undivided electrically conductive electrode surfaces
Implementation Method 3
each separate contact area is connected to an output of the recording electrode via a resistor (4) having an electrical resistance of at least 100 Ω
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
The recording electrode (1) for measuring the electrophysiological signal from biological tissue is particularly suitable for use in magnetic stimulation. This recording electrode is provided with a contact area (2) designed to come into contact with biological tissue by direct contact or through electro-conductive gel to facilitate sensing of the electrophysiological signal from the biological tissue to the contact area (2), where the contact area (2) is electrically connected to the output of the recording electrode (1) for conducting the electrophysiological signal for further processing. The contact area (2) of the recording electrode (1) is divided into at least two separate contact areas (3) electrically separated from each other, each separate contact area (3) being connected to the output of the recording electrode (1) via its own resistor (4), whose electrical resistance is at least 100 Ω, while the resulting resistance of all resistors connecting the individual separate contact areas (3) with the output of the recording electrode (1), as measured between the biological tissue and the output of the recording electrode (1), is at least 50 Ω, which corresponds to at least half the size of the impedance of the biological tissue in magnetic stimulation.