Implantable Lead Circuit for MRI RF Energy Dissipation
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Solution Overview
Problem
Implantable medical devices, particularly those with conductive leads, experience heating and potential damage during magnetic resonance imaging due to electromagnetic interference, leading to tissue burns and system malfunction.
Innovation Solution
An implantable electric circuit comprising capacitors and resistors is integrated into the lead or implantable pulse generator, dissipating radiofrequency energy through a network of resistors to reduce heating and electromagnetic interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If multi-layer coil conductor structure is used to reduce MRI heating, then heating reduction is achieved, but inductance increases significantly
Solution Approach 1:
The lead body is segmented into multiple lumens, with each lumen containing a separate conductor. This segmentation allows each conductor to be individually managed for RF energy dissipation while maintaining lower inductance compared to multi-layer coiled structures. The segmentation principle is applied by dividing the conductive path into separate parallel channels within the lead body.
Solution Approach 2:
A resistive material is introduced as an intermediary between the conductors and the surrounding tissue environment. This resistive material serves as a mediator that dissipates RF energy through controlled resistance, preventing excessive heating while not requiring the conductors to be coiled into multi-layer structures that would increase inductance.
2Temperature
If lead structure is modified to contain and conduct RF energy away, then heating is reduced, but device complexity increases
Solution Approach 1:
The lead body structure serves multiple functions: it provides mechanical support, contains multiple lumens for conductor placement, and incorporates resistive materials for RF energy dissipation. This multi-functionality reduces the need for separate dedicated components for each function, thereby managing device complexity while achieving heating reduction.
Solution Approach 2:
The conductors are nested within lumens of the lead body, which itself is nested within the implantable medical device housing. This nested arrangement allows efficient use of space and integrates RF energy management functionality within the existing lead structure without requiring additional external components.
3Temperature
If conductive filaments are coiled to provide parallel conductive paths, then heating is reduced, but manufacturing complexity increases
Solution Approach 1:
The resistive materials and conductor arrangements are pre-configured within the lead body during manufacturing. The lumens are pre-formed with appropriate dimensions and positions, and resistive materials are pre-placed or pre-coated onto conductor surfaces. This preliminary action during manufacturing simplifies the overall production process compared to post-manufacturing assembly of complex coiled structures.
Solution Approach 2:
The electrical resistance parameter of the conductors is modified by incorporating resistive materials with specific resistance values. This parameter change allows control of RF energy dissipation without requiring complex geometric modifications like tight coiling, thereby simplifying manufacturing while achieving heating reduction.
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 circuit effectively reduces heating and electromagnetic interference, minimizing tissue damage and system malfunctions during MRI, ensuring safe operation of implantable medical devices.
Implementation Method 1
Each of the plurality of capacitors (301) is configured to couple radio frequency energy from one of a plurality of electrically conductive filaments (5) of a lead to the network of resistors (302)
Implementation Method 2
The network of resistors (302) is configured to connect the plurality of capacitors (301) together to dissipate the radio frequency energy between the plurality of electrically conductive filaments
Data Source
AI summary
This disclosure relates to an implantable electric circuit (300) for medical stimulation The circuit comprises a plurality of capacitors (301) and a network of resistors (302). Each of the plurality of capacitors (301) is configured to couple radio frequency energy from one of a plurality of electrically conductive filaments (5) of a lead to the network of resistors (302). Further, the network of resistors (302) is configured to connect the plurality of capacitors (301) together to dissipate the radio frequency energy between the plurality of electrically conductive filaments. The network of resistors dissipates the energy between the filaments, which reduces negative impacts for the patient when subjected to MRI imaging. Further, no ground is required and as a result, the circuit can be placed into a header of an implantable pulse generator or into the lead itself.