Implantable Cardiac Device MRI Protection via Weak Field Sensor
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Solution Overview
Problem
Active implantable medical devices, such as cardiac pacemakers and defibrillators, malfunction or exhibit unpredictable behavior in strong magnetic fields generated by MRI equipment, leading to heating, torque, and misinterpretation of dynamic signals, posing risks during MRI examinations.
Innovation Solution
A software adaptation for existing microcontrollers in these devices uses a weak magnetic field sensor to detect the presence of a permanent magnet, transitioning the device into a standby mode before an MRI examination, and automatically switching back to normal mode post-examination, without requiring hardware modifications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a weak magnetic field sensor is used to detect permanent magnets for mode switching, then the device can transition to safe operating mode before MRI examination, but the sensor cannot detect strong MRI magnetic fields directly
Solution Approach 1:
The patent uses a permanent magnet as an intermediary object. The weak magnetic field sensor detects the permanent magnet's field, which serves as a proxy indicator for the upcoming strong MRI magnetic field. This indirect detection mechanism allows the device to anticipate and prepare for MRI exposure without requiring the sensor to directly measure the strong MRI fields.
Solution Approach 2:
The device enters a safe operating mode in advance before the actual MRI examination begins. By detecting the permanent magnet's presence ahead of time, the system performs preliminary mode switching to ensure safety during the subsequent strong magnetic field exposure, rather than reacting after the harmful effect has occurred.
2Productivity
If the device operates in normal mode during MRI examination, then continuous cardiac monitoring is maintained, but heating and torque forces are generated causing device malfunction
Solution Approach 1:
The device applies preliminary protective measures by switching to a special safe operating mode that pre-empts the harmful effects of MRI magnetic fields. This mode inhibits circuits susceptible to heating and torque forces before these harmful effects can occur during the actual MRI scan, thereby preventing malfunction while maintaining monitoring capability.
3Measurement precision
If hardware modifications are made to add strong magnetic field sensing capability, then direct detection of MRI fields is possible, but device complexity and manufacturing cost increase
Solution Approach 1:
The patent employs a simple, inexpensive permanent magnet as the detection trigger rather than investing in complex strong field sensors. This low-cost approach uses the permanent magnet's field, which is easily detectable by the existing weak field sensor, to accomplish the same functional goal of detecting upcoming MRI exposure without requiring expensive or complex hardware.
4Ease of operation
If the device uses a Reed magnetic switch to detect permanent magnets, then magnet mode can be activated, but unpredictable behavior occurs in strong MRI magnetic fields
Solution Approach 1:
The patent changes the operational parameters of the magnetic detection system by replacing the Reed switch with a weak magnetic field sensor that operates linearly and predictably across a wide range of field strengths. This parameter change ensures reliable and predictable device behavior both during normal operation and during MRI examination, eliminating the unpredictable responses associated with Reed switches in strong fields.
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 approach ensures the device remains functional and predictable during MRI scans, inhibiting sensitive circuits and maintaining seamless stimulation, thereby preventing malfunctions and ensuring patient safety without additional hardware costs.
Implementation Method 1
uses a weak magnetic field sensor to detect the presence of a permanent magnet
Data Source
AI summary
An implantable cardiac device that detects and protects against strong magnetic fields produced by MRI equipment is disclosed. The device has a magnetic field sensor for detecting the presence of a relatively weak static magnetic field (102, 110, 118, 122) of a level equivalent to that of a permanent magnet in the vicinity of the device. The device is switched from a standard operating mode (100) where the nominal functions of the device are active, to a specific protected MRI mode (114, 116) in the presence of a magnetic static field of a level corresponding to that emitted by MRI equipment. The device further temporarily switches the device from the standard operating mode (100) to an MRI stand-by state (108) when a magnetic field is detected by the magnetic field sensor such that a subsequent detection of a magnetic field switches the device from an MRI stand-by state to the specific protected MRI mode.