Stimulation Current Source Feedback Control for MRI Perturbation Compensation
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Solution Overview
Problem
Electrical stimulation devices face interference from external conditions like MRI scans, causing unwanted currents due to induced voltages, which necessitate deactivation of unipolar stimulation therapy or high impedance settings, limiting treatment options.
Innovation Solution
The use of current sources with feedback voltage control to generate stimulation current and active recharge mechanisms, including switches for passive or active recharge based on external conditions, to maintain stable therapy delivery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If unipolar stimulation is provided during MRI scan, then stimulation therapy continues, but induced voltages cause problematic currents on the leads
Solution Approach 1:
The patent employs feedback control by monitoring the voltage on the coupling capacitor and adjusting the recharge current accordingly. The controller detects when the coupling capacitor voltage exceeds a threshold during MRI scanning and activates additional recharge current to compensate, thereby maintaining stable stimulation delivery despite the harmful induced voltages from the MRI scanner.
Solution Approach 2:
The system proactively counteracts the harmful effects of MRI-induced voltages by implementing a preliminary protective measure: during detected MRI scanning, the controller activates an active recharge mechanism that applies a compensating current through the coupling capacitor in advance and during the stimulation pulse, preventing the induced voltages from causing problematic currents in the leads.
2Loss of energy
If passive recharge is used to conserve battery life, then energy efficiency improves, but low impedance path creates vulnerability to induced voltages
Solution Approach 1:
The patent implements a dynamic recharge strategy where the system automatically switches between passive and active recharge modes based on real-time detection of MRI scanning conditions. During normal operation, passive recharge conserves battery life. When MRI scanning is detected, the system dynamically transitions to active recharge mode, providing compensating current to counteract induced voltages, and can switch back to passive mode after MRI scanning ends.
Solution Approach 2:
The system changes the operational parameters of the recharge mechanism based on external conditions. During MRI scanning, the controller modifies the recharge current parameter from passive (minimal current through switches) to active (controlled current through output transistors), thereby adapting the system's behavior to the changed electromagnetic environment while maintaining battery efficiency when possible.
3Object-affected harmful factors
If high impedance is presented to attenuate induced voltage, then current interference reduces, but stimulation therapy must be deactivated or limited to bipolar
Solution Approach 1:
The patent introduces an intermediary active recharge mechanism that acts as a mediator between the stimulation circuit and the MRI-induced electromagnetic interference. This intermediary system provides a controlled current path through the coupling capacitor during MRI scanning, allowing unipolar stimulation to continue while the intermediary recharge current compensates for the induced voltages, thereby maintaining both therapy effectiveness and safety.
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
Enables continuous and safe delivery of unipolar stimulation therapy during MRI scans by compensating for external perturbations, reducing induced currents and conserving battery life.
Implementation Method 1
a coupling capacitor in the stimulation path between the output transistor and the electrode
Implementation Method 2
utilize a feedback voltage of the stimulation path that is proportional to the stimulation current to control the generation of the stimulation current and thereby compensate for the perturbations
Data Source
AI summary
Devices and methods compensate for perturbations in a stimulation signal caused by external conditions such as a magnetic field of an MRI machine so that stimulation therapy may continue in the presence of the external condition. Compensation for the perturbations during a stimulation pulse of a stimulation phase may be provided by using feedback within a stimulation current source. Perturbations during a recharge phase may be addressed by utilizing an active recharge at least when the external condition is present. Furthermore, compensation for perturbations during a recharge pulse of the active recharge phase may be provided by using feedback within a recharge current source. Passive recharge may be used instead of active recharge when the external condition is not present to preserve battery life of the stimulation device. The stimulation device may include a sensor to detect the external condition so that an appropriate mode of recharge may be chosen.