Neural Tissue Feedback Electrodes for CAP Artefact Cancellation
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Solution Overview
Problem
Existing neuromodulation systems face challenges in accurately measuring compound action potentials (CAPs) due to significant electrode artefact, which is exacerbated by the close proximity of stimulation and measurement electrodes, leading to impractical amplifier dynamic range requirements and difficulties in isolating the CAP signal from stimulus artefact.
Innovation Solution
A method and device utilizing a feedback amplifier system with a feedback sense electrode and compensation electrode to create a virtual ground, reducing stimulus artefact by driving the tissue to a desired electrical value, thereby improving the measurement of neural responses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If stimulation and measurement electrodes are placed in close proximity to measure compound action potentials, then measurement accuracy is improved, but electrode artefact increases significantly
Solution Approach 1:
A feedback sense electrode is introduced as an intermediary element between the stimulus electrode and the measurement system. This sense electrode detects the stimulus artefact and feeds it back through an amplifier to a compensation electrode, which then generates a counteracting signal that cancels the artefact in the measurement channel, enabling accurate CAP measurement despite close electrode proximity
Solution Approach 2:
The system employs a feedback mechanism where the stimulus artefact detected at the feedback sense electrode is amplified and fed back through the compensation electrode to actively cancel the artefact. This feedback loop continuously adjusts the compensation signal to maintain artefact cancellation while preserving the neural response measurement
2Measurement precision
If high amplifier gain is used to resolve microvolt-level CAP signals from multi-volt stimuli, then measurement precision improves, but device complexity and dynamic range requirements become impractical
Solution Approach 1:
The system converts the harmful stimulus artefact into a useful component by feeding it back through the compensation electrode. The artefact signal, which would normally obscure the measurement, is now used to generate a compensating signal that actively cancels itself in the measurement channel, allowing the amplifier to operate at lower gain settings while still resolving microvolt-level CAP signals
Solution Approach 2:
The feedback system performs preliminary anti-action by pre-cancelling the stimulus artefact before it reaches the measurement amplifier. The compensation electrode applies a counter-signal that neutralizes the artefact in advance, allowing the amplifier to focus on amplifying only the neural response without needing to handle the full dynamic range from multi-volt stimuli to microvolt signals
3Reliability
If monophasic pulses with capacitors are used to prevent DC flow, then tissue safety is improved, but capacitor charge recovery causes maximum artefact when the evoked response occurs
Solution Approach 1:
The feedback mechanism detects the capacitor charge recovery artefact and generates a compensating signal to cancel it. By continuously monitoring the artefact at the feedback sense electrode and applying the opposite signal through the compensation electrode, the system eliminates the harmful capacitor artefact while maintaining the safety benefits of monophasic pulsing
Solution Approach 2:
The feedback sense electrode acts as an intermediary that specifically detects the capacitor charge recovery artefact, allowing the system to distinguish between the artefact and the neural response. This enables selective cancellation of the capacitor artefact while preserving the evoked response measurement
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
The solution significantly reduces electrode artefact, allowing for accurate CAP measurements within the same spinal segment as the stimulus, simplifying amplifier design and reducing dynamic range requirements, enabling miniaturized and automated implanted systems for evoked response feedback.
Implementation Method 1
connecting a feedback signal from the feedback sense electrode to an input of a feedback amplifier, and referencing the amplifier to a desired electrical value; and connecting an output of the feedback amplifier to the compensation electrode such that the feedback amplifier drives the tissue via the compensation electrode in a feedback arrangement
Data Source
AI summary
An implantable device for controlling electrical conditions of body tissue. A feedback sense electrode and a compensation electrode are positioned proximal to the tissue to make electrical contact with the tissue. A feedback amplifier is referenced to ground, and takes as an input a feedback signal from the feedback sense electrode. The output of the feedback amplifier is connected to the compensation electrode. The feedback amplifier thus drives the neural tissue via the compensation electrode in a feedback arrangement which seeks to drive the feedback signal to ground, or other desired electrical value.