MRI Compatible Electrode Wire RF Filtering Circuit
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Solution Overview
Problem
Current medical devices with elongated conductive structures, such as electrode wires, face significant challenges in reducing RF-induced heating during MRI scans, as existing solutions like high impedance wires, resonant LC filters, and co-radial electrodes either limit functionality or fail to adequately attenuate RF energy, leading to unsafe temperature rises and potential device damage.
Innovation Solution
A novel circuit construction incorporating multiple filter components, including resonant and non-resonant filters, strategically placed along the electrode wire to effectively block RF-induced currents, with non-resonant filters distributed along the wire length to attenuate currents before reaching resonant filters, ensuring safe operation and flexibility in MRI environments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If high impedance electrode wires are used to limit current flow, then RF-induced heating is reduced, but device functionality is limited
Solution Approach 1:
The electrode wire is segmented into multiple sections with different impedance characteristics. Distal sections have high impedance to block RF current, while proximal sections maintain lower impedance for pacing and sensing functions. This segmentation allows different parts of the same device to serve different purposes.
Solution Approach 2:
Different sections of the electrode wire are given different electrical properties. The distal end has high impedance to prevent RF heating, while the proximal end maintains low impedance for effective pacing. This local differentiation resolves the contradiction between RF safety and device functionality.
2Object-affected harmful factors
If resonant LC filters are placed at the wire/electrode interface to reduce RF current, then RF-induced heating is attenuated, but the filters themselves generate excessive heat
Solution Approach 1:
The harmful heat-generating resonant LC filters are extracted from the electrode wire assembly and placed in a separate, dedicated filter section. This allows the filters to be optimized for RF attenuation without directly contacting tissue, thereby reducing the risk of tissue heating while maintaining effective RF current blocking.
3Object-affected harmful factors
If non-resonant filters are distributed along the wire to attenuate RF current, then RF heating is reduced, but device complexity increases
Solution Approach 1:
Multiple non-resonant filter sections are merged into a single integrated component that can be formed as one piece. This combining approach reduces the number of separate parts and assembly steps while maintaining the distributed RF attenuation effect along the electrode wire.
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 proposed solution significantly reduces RF-induced heating, maintains device functionality, and prevents excessive temperature rises, ensuring safe operation and durability of medical devices during and after MRI scans, even in prolonged use scenarios.
Implementation Method 1
resonant LC filter placed at the wire/electrode interface may reduce the current delivered into the body through the electrodes
Implementation Method 2
non-resonant components placed at the wire/electrode may also reduce the current transmitted into the body
Implementation Method 3
RF induced currents in the electrode wire may cause Ohmic heating in the electrode wire, itself, and the resultant heat may transfer to the patient
Implementation Method 4
RF induced currents in the electrode wire may result in increased local specific absorption of RF energy in nearby tissue, thus increasing the temperature of the tissue. The foregoing phenomenon is referred to as dielectric heating
Data Source
AI summary
An MRI compatible electrode circuit construct is provided. The construct includes at least three filter components constructed from a continuous or non-continuous electrode wire. One filter component may be a resonant LC filter proximate an electrode/wire interface. A second filter component may be a resonant LC filter adjacent a proximal termination of the wire construct. The filters resolve the issue of insufficient attenuation by effectively blocking the RF induced current on the wire from exiting the wire through the electrode and at the terminal or proximal end. The third filter component may include one or more non-resonant filter(s) positioned along the length of the electrode wire that resolve(s) the issue of excessive heating of the resonant LC filters by significantly attenuating the current induced on the wire before it reaches the resonant LC filters.