Multilayer Helical Wave Filter for MRI Lead Safety
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Solution Overview
Problem
Implanted medical leads can overheat during MRI procedures due to induced RF currents, leading to tissue damage and other complications, as existing solutions like Specific Absorption Rate (SAR) monitoring are not predictive of heating and do not adequately protect against overheating.
Innovation Solution
A multilayer helical wave filter is integrated into the implanted leads, resonating at MRI RF frequencies to create a high impedance, preventing RF current flow and overheating by acting as a bandstop filter, with a design comprising helically wound segments and dielectric materials to manage parasitic capacitance and inductance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If SAR monitoring is used to limit MRI RF power, then patient safety is improved, but it is not predictive of actual lead heating and does not adequately protect against overheating
Solution Approach 1:
The patent introduces an intermediary element (the tuned circuit filter) between the MRI RF field and the implanted lead. This filter acts as a mediator that specifically targets and blocks RF currents at the lead's resonant frequency, providing direct protection rather than relying on indirect SAR monitoring of the entire body.
Solution Approach 2:
The patent changes the electrical parameters of the lead system by adding a tuned circuit filter with specific inductance and capacitance values that create a resonant frequency matching the MRI RF frequency. This parameter modification causes the lead to present a high impedance at the problematic frequency, directly preventing the heating issue.
2Reliability
If a simple bandstop filter is used, then RF current flow is blocked, but the filter may not adequately account for parasitic capacitance and inductance in the lead system
Solution Approach 1:
The patent applies local quality by placing the tuned circuit filter specifically at the distal end of the lead where the electrode interfaces with tissue, rather than uniformly throughout the lead. This localized approach targets the specific problem area (electrode-tissue interface heating) while keeping the rest of the lead simple.
Solution Approach 2:
The patent employs self-service by utilizing the existing parasitic capacitance and inductance in the lead construction as integral components of the tuned circuit filter. Rather than adding separate discrete components, the filter is formed by the lead's own structural elements, making the lead self-regulating at its resonant frequency.
3Reliability
If the lead impedance is increased at MRI frequencies, then RF current flow is reduced, but this may affect the lead's ability to deliver therapeutic electrical pulses
Solution Approach 1:
The patent applies dynamics by creating a frequency-dependent impedance characteristic where the lead presents high impedance only at the specific MRI RF frequency while maintaining low impedance at other frequencies. The tuned circuit filter's resonant nature allows it to dynamically respond to different frequencies, blocking harmful RF currents while permitting therapeutic pulses to pass.
Solution Approach 2:
The patent changes the impedance parameter of the lead system by introducing a resonant circuit that modifies the electrical characteristics only at the problematic frequency. This selective parameter change allows the lead to maintain its normal therapeutic function across the broad frequency spectrum while specifically addressing the narrowband MRI RF interference.
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 multilayer helical wave filter effectively prevents overheating of implanted leads and their electrodes during MRI scans, reducing the risk of tissue damage by attenuating RF energy and maintaining high impedance at resonance frequencies, thus ensuring safer MRI procedures for patients with implanted medical devices.
Implementation Method 1
The multilayer helical wave filter is designed resonate at one or more MRI RF pulsed frequencies. At resonance, the multilayer helical wave filter presents a very high impedance in the lead system which impedes RF current flow
Implementation Method 2
a first parasitic capacitance between adjacent coils of the first helically wound segment, a second parasitic capacitance between adjacent coils of the second helically wound segment
Implementation Method 3
a first inductance of the first helically wound segment, a second inductance of the second helically wound segment
Data Source
AI summary
A multilayer helical wave filter having a primary resonance at a selected RF diagnostic or therapeutic frequency or frequency range, includes an elongated conductor forming at least a portion of an implantable medical lead. The elongated conductor includes a first helically wound segment having at least one planar surface, a first end and a second end, which forms a first inductive component, and a second helically wound segment having at least one planar surface, a first end and a second end, which forms a second inductive element. The first and second helically wound segments are wound in the same longitudinal direction and share a common longitudinal axis. Planar surfaces of the helically wound segments face one another, and a dielectric material is disposed between the facing planar surfaces of the helically wound segments and between adjacent coils of the helically wound segments, thereby forming a capacitance.