Implantable Sensor Detects MRI Gradient Fields via Vibration
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Solution Overview
Problem
Implantable medical devices (IMDs) face interference from magnetic fields generated by MRI systems, leading to incorrect cardiac signal detection and inappropriate therapy delivery due to the limitations of conventional sensors like GMR sensors, which become saturated and fail to differentiate between MRI and handheld magnetic fields.
Innovation Solution
The use of an implantable sensor configured to detect acceleration, sound, and/or vibration, such as an accelerometer or microphone, to determine exposure to time-varying gradient magnetic fields from MRI systems, allowing for mode switching between normal and MRI safe operations, and confirming with a static magnetic field detector sensor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional GMR sensors are used to detect magnetic fields, then the device can detect handheld magnets for mode switching, but the sensors become saturated in strong MRI magnetic fields and fail to differentiate between MRI and handheld fields
Solution Approach 1:
The patent divides the magnetic field detection task into two separate sensors: a GMR sensor for detecting handheld magnets (weak fields) and an accelerometer for detecting MRI scanner presence (strong fields). This segmentation allows each sensor to operate within its optimal range without saturation, resolving the contradiction between detection precision and reliability in different field strengths.
Solution Approach 2:
The accelerometer serves as an intermediary indicator for MRI scanner presence. Instead of directly measuring the strong magnetic field with a saturated GMR sensor, the system uses the accelerometer to detect vibrations characteristic of MRI scanner operation, which then triggers the appropriate MRI-safe mode. This intermediary approach allows reliable detection without direct exposure to saturating field strengths.
2Reliability
If the IMD switches to MRI safe mode upon detecting magnetic fields, then unnecessary therapy is prevented, but normal therapy delivery is inhibited when the magnetic field is from a handheld magnet
Solution Approach 1:
The patent segments the magnetic field source identification into two pathways: the GMR sensor identifies handheld magnets (triggering magnet mode), while the accelerometer identifies MRI scanners (triggering MRI-safe mode). This segmentation enables the system to respond appropriately to different magnetic field sources, maintaining normal therapy productivity for handheld magnets while ensuring safety for MRI scanners.
Solution Approach 2:
The system uses feedback from both the GMR sensor and accelerometer to determine the appropriate operational mode. The dual-sensor feedback mechanism allows the IMD to distinguish between handheld magnet exposure (where normal therapy should continue) and MRI scanner exposure (where MRI-safe mode should activate), thus maintaining productivity while ensuring reliability.
3Measurement precision
If the IMD requires a special external programmer for mode switching, then precise control is achieved, but the process becomes time-consuming and cumbersome
Solution Approach 1:
The patent enables the IMD to automatically detect magnetic field sources and switch modes autonomously using the GMR sensor and accelerometer. This self-service capability eliminates the need for a special external programmer and clinician intervention, significantly reducing mode switching time while maintaining precise control through automated sensor-based detection and decision-making.
Solution Approach 2:
The system performs preliminary detection of magnetic field sources using the GMR sensor and accelerometer before therapy delivery decisions are made. This preliminary action allows the IMD to pre-determine the appropriate operational mode, enabling rapid response without requiring time-consuming external programmer intervention when a magnetic field is detected.
4Loss of information
If the GMR sensor detects strong MRI magnetic fields, then MRI exposure is identified, but the sensor becomes saturated and cannot detect the field strength accurately
Solution Approach 1:
The patent segments the detection function: the GMR sensor handles weak field detection (handheld magnets) while the accelerometer handles strong field detection (MRI scanners). This segmentation prevents information loss by assigning each sensor to its optimal operating range, ensuring both presence detection and field strength measurement accuracy without saturation.
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
Accurate detection of MRI-generated magnetic fields enables IMDs to switch to a safe mode, preventing unnecessary therapy and ensuring optimal operation during MRI procedures, thereby reducing the risk of arrhythmias and improving therapy delivery.
Implementation Method 1
an implantable sensor configured to detect acceleration, sound and/or vibration, such as an accelerometer sensor
Implementation Method 2
an implantable sensor configured to detect acceleration, sound and/or vibration, such as a microphone sensor
Implementation Method 3
The GMR sensor operates by detecting a change in an electrical resistance characteristic of the sensor when the sensor transitions from not being exposed to a magnetic field to being exposed to a magnetic field
Implementation Method 4
such external magnetic fields may generate magnetic forces on an IMD and the leads and electrodes attached to the IMD. These forces may induce electric charges or potentials on the leads and electrodes
Data Source
AI summary
Embodiments of the present invention generally pertain to implantable medical devices, and methods for use therewith, that detect exposure to magnetic fields produced by magnetic resonance imaging (MRI) systems. In accordance with specific embodiments, a sensor output is produced using an implantable sensor that is configured to detect acceleration, sound and/or vibration, but is not configured to detect a magnetic field. Such a sensor can be an accelerometer sensor, a strain gauge sensor or a microphone sensor, but is not limited thereto. In dependence on the produced sensor output, there is a determination whether of whether the IMD is being exposed to a time-varying gradient magnetic field from an MRI system. In accordance with certain embodiments, when there is a determination that the IMD is being exposed to a time-varying gradient magnetic field from an MRI system, then a mode switch to an MRI safe mode is performed.