Implantable Lead TANK Filter Tuning for MRI EMI Suppression
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Solution Overview
Problem
Active implantable medical devices, such as cardiac pacemakers and implantable cardioverter defibrillators, face significant challenges during magnetic resonance imaging (MRI) procedures due to induced electromagnetic interference (EMI), which can lead to adverse effects like pacemaker reed switch closure, displacement, heating, and altered pacing rates, posing risks to patient safety.
Innovation Solution
The implementation of novel resonant TANK filters placed at strategic locations along medical device lead wires, designed to resonate at specific frequencies (e.g., 64 MHz for 1.5 Tesla MRI systems), creating high impedance and preventing current circulation, thereby reducing RF currents and EMI-induced heating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If MRI procedures are performed on patients with implantable medical devices, then diagnostic imaging capability is improved, but electromagnetic interference and induced currents cause harmful effects on the device and patient safety
Solution Approach 1:
The patent introduces TANK filters as intermediary components placed in the lead wire system between the implantable device and the external environment. These filters act as mediators that selectively block MRI-frequency electromagnetic interference while allowing normal device operation, thus enabling MRI compatibility without exposing the device to harmful EMI
Solution Approach 2:
The patent modifies the electrical parameters of the lead wire system by incorporating resonant TANK filters tuned to specific MRI frequencies. By changing the impedance characteristics at MRI frequencies through the filter's resonant circuit (L and C values), the system selectively attenuates harmful RF currents while maintaining normal functionality at other frequencies
2Length of stationary object
If lead wire length is increased to reach distant implantation sites, then device accessibility is improved, but induced currents and RF energy absorption increase
Solution Approach 1:
The patent applies TANK filters at specific locations along the lead wire system, particularly at the distal end and at points where lead length is substantial. This local placement creates targeted zones of electromagnetic filtering that protect vulnerable sections of the lead without requiring changes to the overall lead length or implantation geometry
3Reliability
If TANK filters are added to reduce EMI, then patient safety is improved, but device complexity increases
Solution Approach 1:
The patent integrates TANK filters into the existing lead wire structure by nesting the filter components within the lead insulation or housing. The inductor and capacitor elements are contained within compact assemblies that fit within the existing lead wire diameter, avoiding additional external components and minimizing surgical implantation complexity
Solution Approach 2:
The patent combines multiple functions into the TANK filter assembly: electromagnetic filtering, lead wire structural support, and electrical connection pathways are merged into a single integrated component. This consolidation reduces the number of separate parts and simplifies the overall device architecture despite adding EMI protection functionality
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 TANK filters effectively mitigate EMI and associated heating in medical devices, enhancing patient safety by reducing the risk of adverse effects during MRI procedures and ensuring compatibility with MRI systems.
Implementation Method 1
The TANK filter can be designed to resonate at or near 64 MHz and thus create a high impedance (ideally an open circuit) in the lead wire system at that selected frequency
Implementation Method 2
The effects of MRI on patients' pacemaker systems have only been analyzed retrospectively in some case reports. There are a number of papers that indicate that MRI on new generation pacemakers can be conducted up to 0.5 Tesla (T).
Data Source
AI summary
A TANK filter is provided for a lead wire of an active medical device (AMD). The TANK filter includes a capacitor in parallel with an inductor. The parallel capacitor and inductor are placed in series with the lead wire of the AMD, wherein values of capacitance and inductance are selected such that the TANK filter is resonant at a selected frequency. The Q of the inductor may be relatively maximized and the Q of the capacitor may be relatively minimized to reduce the overall Q of the TANK filter to attenuate current flow through the lead wire along a range of selected frequencies. In a preferred form, the TANK filter is integrated into a TIP and/or RING electrode for an active implantable medical device.