Capacitive Voltage Divider for MRI EMI Protection in Implantable Devices
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Solution Overview
Problem
Implantable medical devices are susceptible to unintended cardiac stimulation due to electromagnetic interference from MRI scanning, leading to suboptimal treatment for patients with implanted devices, as they often require avoiding MRI scans to prevent adverse effects.
Innovation Solution
A protection circuit comprising a capacitive voltage divider and input protection diodes is deployed across cardiac electrodes, reducing MRI-induced voltage and currents within the device, thereby preventing rectification of EMI-induced signals and minimizing cardiac stimulation risks without affecting cardiac signals or stimulation operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a patient undergoes MRI scanning, then diagnostic imaging is obtained, but electromagnetic interference induces currents in implanted leads causing unintended cardiac stimulation
Solution Approach 1:
A capacitive voltage divider circuit is introduced as an intermediary component between the implanted lead and the device internal circuitry. This circuit acts as a mediator that reduces the amplitude of electromagnetic interference-induced voltages before they can cause harmful effects, while allowing normal cardiac signals to pass through to the sensing circuitry.
Solution Approach 2:
The protection circuit changes the electrical parameters (voltage amplitude, impedance) of the signal path during MRI scanning. By dynamically adjusting the voltage division ratio and impedance matching, the circuit reduces RF current flow through the lead while maintaining signal integrity for cardiac monitoring.
2Reliability
If MRI scanning is avoided for patients with implanted devices, then cardiac stimulation safety is maintained, but diagnostic treatment opportunities are lost
Solution Approach 1:
The capacitive voltage divider serves as a protective intermediary that enables patients to undergo MRI scanning by blocking harmful electromagnetic interference while preserving diagnostic image quality. This intermediary component removes the contraindiction between having an implanted device and receiving MRI treatment.
3Object-affected harmful factors
If protection circuitry is added to the implantable device, then electromagnetic interference protection is improved, but device complexity increases
Solution Approach 1:
The protection function is segmented into a separate capacitive voltage divider circuit that can be independently designed and tested. This modular approach allows the protection circuitry to be optimized for EMI reduction without unnecessarily complicating the entire device architecture, as the voltage divider is a discrete functional block.
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 effectively mitigates the effects of MRI-induced electromagnetic interference, allowing patients with implanted medical devices to undergo MRI scans without restrictions, ensuring safe and optimal treatment by reducing rectified RF current and preventing unwanted cardiac stimulation.
Implementation Method 1
a capacitive voltage divider that is deployed across cardiac electrodes (e.g., at least one cardiac lead electrode and, optionally, a case electrode) that are coupled to the internal circuitry
Implementation Method 2
pulsed magnetic gradients used during MRI scanning may induce voltage in an implanted cardiac lead connected to an implanted device
Data Source
AI summary
An RF protection circuit mitigates potentially adverse effects that may otherwise result from electromagnetic interference (e.g., due to MRI scanning of a patient having an implanted medical device). The RF protection circuit may comprise a voltage divider that is deployed across a pair of cardiac electrodes that are coupled to internal circuitry of the implantable medical device. Each leg of the voltage divider may be referenced to a ground of the internal circuit, whereby the different legs are deployed in parallel across different circuits of the internal circuitry. In this way, when an EMI-induced (e.g., MRI-induced) signal appears across the cardiac electrodes, the voltages appearing across these circuits and the currents flowing through these circuits may be reduced. The RF protection circuit may be used in an implantable medical device that employs a relatively low capacitance feedthrough to reduce EMI-induced (e.g., MRI-induced) current flow in a cardiac lead.