Self-Resonant Inductor for MRI RF Attenuation in Implantable Leads
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Solution Overview
Problem
Active implantable medical devices, such as cardiac pacemakers and implantable cardioverter defibrillators, face risks during magnetic resonance imaging (MRI) procedures due to electromagnetic interference (EMI), leading to potential hazardous effects like overheating, asynchronous pacing, and inappropriate therapy delivery, as existing technologies fail to adequately protect these devices from MRI-induced electromagnetic fields.
Innovation Solution
A novel resonant tank band stop filter assembly is integrated into the lead wire system of active implantable medical devices, which becomes self-resonant at specific frequencies, such as 64 MHz for a 1.5 Tesla MRI system, to attenuate MRI RF pulsed frequencies, thereby reducing induced currents and protecting the device from overheating and arrhythmias.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a resonant tank band stop filter assembly is integrated into the lead wire system to attenuate MRI RF pulsed frequencies, then protection from overheating and arrhythmias is improved, but device complexity increases
Solution Approach 1:
The inductive coil is integrated within the lead wire structure itself, with the coil formed by winding the lead conductor around a core. This nesting approach allows the filter assembly to be embedded within the existing lead wire system without requiring separate external components, thereby providing MRI frequency attenuation while minimizing additional device complexity
Solution Approach 2:
The resonant tank filter assembly acts as an intermediary element between the MRI RF field and the active implantable medical device. By tuning the filter to resonate at specific MRI frequencies (e.g., 64 MHz for 1.5T MRI), it creates a high-impedance barrier that blocks harmful RF energy from reaching the device electronics, thus protecting against overheating and arrhythmias while allowing normal device operation
2Reliability
If the inductive coil is designed to be self-resonant at specific frequencies to attenuate MRI RF pulsed frequencies, then attenuation effectiveness is improved, but manufacturing precision requirements increase
Solution Approach 1:
The resonant frequency of the inductive coil is determined by its physical parameters (inductance L and capacitance C), which can be adjusted during design and manufacturing. By carefully selecting wire diameter, coil winding density, number of turns, and core material properties, the filter can be tuned to resonate at specific MRI frequencies (64 MHz for 1.5T, 128 MHz for 3T systems), achieving effective attenuation while accommodating standard manufacturing tolerances
Solution Approach 2:
The inductive coil utilizes the parasitic capacitance inherent in the lead wire insulation and surrounding structures to form the resonant tank circuit. This self-service approach eliminates the need for separate discrete capacitor components, reducing the number of precision-critical parts and simplifying manufacturing while maintaining the self-resonant property at target MRI frequencies
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 solution effectively attenuates MRI RF pulsed frequencies, reducing the risk of overheating and arrhythmias in active implantable medical devices, ensuring safer MRI procedures for patients with these devices.
Implementation Method 1
The inductive coil comprises a parasitic capacitance between its adjacent turns such that the inductive coil becomes self-resonant at a selected center frequency or across a range of frequencies about the selected center frequency
Implementation Method 2
The inductive coil comprises a parasitic capacitance between its adjacent turns
Implementation Method 3
The insulated and self-resonant inductive coil may include a tank filter performance. The tank filter performance may attenuate the MRI RF pulsed frequency
Data Source
AI summary
An implantable lead includes a lead conductor having a length extending from a proximal end to a distal end. A self-resonant inductor is connected in series along a portion of the length of the lead conductor. The self-resonant inductor includes a single length of conductive material including a dielectric coating substantially surrounding the single length of conductive material. The self-resonant inductor includes a first coiled or spiral conductor disposed along an inductor section spanning in a first direction from a first location to a second location. A second coiled or spiral conductor is disposed along the inductor section spanning in a second direction from the second location to the first location, where the second direction is opposite the first direction. A third coiled or spiral conductor is disposed along the inductor section spanning in the first direction from the first location to the second location.