Medical Electrical Lead Conductor Inductance
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Solution Overview
Problem
Implantable medical device leads face challenges in compatibility with MRI RF fields due to low inductance in existing conductor designs, leading to excitation heating and inadequate electrical contact, particularly for small electrodes.
Innovation Solution
A strength-enhanced conductor design featuring a multi-filar coil wrapped around a non-conducting central core, which increases inductance while maintaining torque transmission capabilities, by optimizing the number of filars, pitch, and using compression sheathing to restrict radial expansion and ensure mechanical strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a multi-filar cable with a straight central filar is used, then the conductor has good mechanical properties including flexibility and weldability, but the inductance is very low leading to excitation heating during MRI
Solution Approach 1:
The patent replaces the straight central filar with a coiled or spiral configuration. This curvature transformation increases the inductance of the conductor, which reduces excitation heating during MRI procedures while maintaining the mechanical integrity needed for electrode crimping and torque transmission.
Solution Approach 2:
The patent modifies the geometric parameters of the central filar by changing it from a straight configuration to a coiled or spiral configuration. This parameter change directly increases the inductance value, transforming the conductor from low-inductance (prone to heating) to high-inductance (resistant to heating) while preserving mechanical properties.
2Object-affected harmful factors
If the inductance is increased to minimize excitation effects from RF fields, then MRI compatibility is improved, but the mechanical strength and torque transmission may be compromised
Solution Approach 1:
The patent employs a composite structure where the central filar is made of non-conductive or low-conductive material (such as polymer or insulated wire) rather than solid conductor. This composite approach allows the outer multi-filar coil to provide both mechanical strength and the necessary inductance, while the central core provides structural support without contributing to RF excitation.
Solution Approach 2:
The patent introduces a non-conductive or low-conductive central core as an intermediary element that replaces the traditional conductive central filar. This intermediary provides the necessary mechanical strength and torque transmission capability while not contributing to RF current flow, thereby increasing overall inductance and reducing excitation heating.
3Object-affected harmful factors
If a coiled configuration is used to increase inductance, then MRI RF field compatibility is improved, but the cable diameter and complexity increase
Solution Approach 1:
The patent segments the conductor into multiple independent filars that are individually insulated and then twisted or coiled together. This segmentation allows each filar to be optimized independently and reduces the overall complexity by breaking down the single coiled structure into manageable, modular components that can be manufactured and assembled separately.
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 enhanced conductor design effectively minimizes excitation heating from MRI RF fields and maintains strong electrical and mechanical connections, ensuring reliable operation of medical electrical leads during MRI procedures.
Implementation Method 1
it is necessary to expose the patient and the IMD to a radio-frequency field, which is used to generate the MRI image. Generally, it is desirable for a lead conductor to have increased inductance in order to minimize excitation effects from RF fields generated during magnetic resonance imaging
Implementation Method 2
The present invention comprises a strength-enhanced conductor for a medical electrical lead... The multi-filar coil includes an inductance of approximately 0.5 μH or greater
Data Source
AI summary
A conductor for connecting an electrode near a distal end of a medical electrical lead with an implantable medical device connected with a proximal end of the medical electrical lead includes a multi-filar coil wrapped around a central core. The multi-filar coil has an inductance of approximately 0.5 μH or greater, and the central core is non-conducting and provides reinforcement for the multi-filar coil.