Hall Sensor MRI Mode Logic Circuit
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Solution Overview
Problem
Implantable neurostimulation systems, such as IPGs, face the challenge of being deactivated during MRI procedures due to strong magnetic fields, which can induce unwanted stimulation currents and potentially damage the device, while also needing to monitor the magnetic field without deactivation.
Innovation Solution
An implantable medical device with a magnetic field sensing system that continuously asserts a signal in normal mode but intermittently asserts it during MRI mode, using a logic circuit and delay circuit to prevent deactivation and allow magnetic field monitoring.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a magnetic field sensing device (Hall sensor) is used to detect external magnets for IPG shutdown, then the IPG can be manually inactivated by placing a magnet over it, but the IPG will be automatically deactivated during MRI procedures due to strong magnetic fields, inducing unwanted stimulation currents and potentially damaging the device
Solution Approach 1:
The patent applies preliminary action by implementing an MRI mode that is activated before the MRI procedure begins. This mode preemptively disables the magnetic field sensing device and prevents automatic shutdown, so the device is already protected against the harmful effects of MRI magnetic fields before they occur. The system proactively configures the appropriate operational state in advance rather than reactively responding to the magnetic field exposure.
2Reliability
If the magnetic field sensing device continuously monitors for magnetic fields, then the IPG can respond to external magnets for shutdown, but the device cannot distinguish between external magnets applied by the patient and the strong magnetic fields present during MRI procedures
Solution Approach 1:
The patent applies dynamics by making the operational mode of the IPG changeable and adaptable. The system can dynamically switch between normal mode (where magnetic field sensing is active for manual shutdown) and MRI mode (where sensing is disabled to prevent false shutdown). This dynamic reconfiguration allows the same device to reliably perform different functions depending on the operational context, distinguishing between patient-applied magnets and MRI magnetic fields through mode-based adaptation rather than through complex field strength analysis.
3Object-affected harmful factors
If the IPG is deactivated during MRI to prevent damage, then unwanted stimulation currents are prevented, but the device cannot continue to provide therapeutic stimulation during the MRI procedure
Solution Approach 1:
The patent applies segmentation by separating the magnetic field sensing function from the therapeutic stimulation function during MRI procedures. The magnetic field sensing device is selectively disabled in MRI mode to prevent false shutdown, while the therapeutic stimulation circuitry continues to operate independently. This functional segmentation allows the protection mechanism (magnetic field sensing) to be decoupled from the therapeutic function, enabling continuous therapy delivery even when the sensing device would normally prevent operation.
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
Prevents unintended shutdown of the neurostimulation device during MRI procedures while enabling continuous magnetic field monitoring, ensuring safe operation and effective therapy delivery.
Implementation Method 1
a magnetic field sensing device 4, such as a reed switch or a Hall sensor
Data Source
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AI summary
An implantable medical device capable of being placed between a first operational mode and a second operational mode. The medical device comprises a magnetic field sensing device configured for outputting a signal in response to sensing a magnetic field. The medical device further comprises a logic circuit configured for continuously asserting the signal during a time period when the neurostimulation device is in the first operational mode, and intermittently asserting the signal during at least one time period when the neurostimulation device is in the second operational mode. The medical device further comprises a delay circuit configured for introducing a time delay into the asserted signal, the time delay being less than the time period, but greater than each of the at least one time period. The medical device further comprises control circuitry configured for performing a function in response to receiving the delayed signal at a first input terminal.