Saturation-Based Inductance Sensing for MRI Field Discrimination
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Solution Overview
Problem
Existing implantable medical devices struggle to discriminate between weak and strong magnetic fields without requiring hardware modifications, leading to unpredictable behavior and performance issues during MRI examinations.
Innovation Solution
The device employs a magnetic-field-dependent signal generator with a saturation-dependent inductance to generate an oscillation signal, allowing discrimination between weak and strong magnetic fields by comparing the period of this signal with a reference frequency, enabling mode switching to safe operating modes without additional components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a low-magnetic-field sensor (e.g., Reed switch) is used to detect handheld magnets, then the device can be put in a safe operating mode, but the sensor cannot distinguish between weak permanent magnet fields and strong MRI static fields
Solution Approach 1:
The patent changes the operating parameters of the existing inductance element by utilizing its saturation characteristics at different magnetic field strengths. The inductance value changes non-linearly with magnetic field strength, allowing the system to distinguish between weak permanent magnet fields and strong MRI fields without adding new sensors. This parameter-based discrimination resolves the contradiction by enabling both detection reliability and measurement precision using the same component.
Solution Approach 2:
The patent makes the existing inductance element (which is already part of the device for other functions) serve an additional function of magnetic field strength discrimination. By utilizing the inherent saturation characteristics of the inductance element, the system enables self-diagnosis of magnetic field strength without requiring external assistance or additional dedicated components, thus resolving the contradiction between reliability and precision.
2Adaptability or versatility
If an additional sensor (e.g., Hall effect magnetic sensor) is provided to detect strong magnetic fields during MRI examination, then the device can automatically detect MRI fields, but hardware redesign is required which increases cost and constraints on miniaturization
Solution Approach 1:
The patent makes the existing inductance element perform multiple functions: its primary function in the circuit plus the additional function of magnetic field strength discrimination. By utilizing the saturation characteristics of this existing component, the system achieves automatic MRI field detection without adding dedicated sensors, thereby maintaining adaptability while minimizing device complexity and avoiding hardware redesign.
Solution Approach 2:
The patent combines the magnetic field detection function with the existing inductance element that already serves other purposes in the device. Instead of separating detection functions into dedicated components, the system merges multiple functions into a single existing component, reducing overall device complexity while maintaining the ability to detect both weak and strong magnetic fields automatically.
3Duration of action of stationary object
If the device remains functional throughout an MRI examination, then seamless stimulation can be provided, but the low-magnetic-field sensor exhibits unpredictable behavior in strong MRI fields
Solution Approach 1:
The patent implements a feedback mechanism that continuously monitors the inductance value changes and uses this information to determine the current magnetic field environment. Based on this feedback, the system automatically adjusts its operating mode to ensure predictable behavior and continuous functionality throughout the MRI examination, resolving the contradiction between duration of operation and reliability by making the system responsive to real-time conditions.
Solution Approach 2:
The patent makes the device operating mode dynamic rather than static. The system continuously adapts its behavior based on the detected magnetic field strength, switching between different operational states as conditions change. This dynamic adaptation ensures predictable behavior and continuous functionality throughout the MRI examination, resolving the contradiction between duration and reliability.
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 allows the device to function seamlessly during MRI examinations by automatically switching to MRI-safe modes, ensuring predictable stimulation and protecting the device from electromagnetic interference.
Implementation Method 1
a frequency determining element with a saturation-dependent inductance that depends on a magnetic field strength imposed on the implantable medical device
Data Source
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AI summary
This invention relates to an active implantable medical device that is configured to discriminate weak magnetic fields (e.g., for entering a magnet mode) from strong magnetic fields (e.g., for entering an MRI mode) without introducing additional components, by exploiting a saturation effect of an inductance that depends on the magnetic field strength and using the saturation-dependent inductance as frequency-determining element of a resonance-based signal generator such as an oscillator. The discrimination can then be achieved by comparing the resonance-based frequency with a predetermined reference frequency.