Embedded Conductor RF Shielding for Implantable Leads

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Solution Overview

Problem

Implantable medical leads face issues with RF energy coupling to conductors during MRI scans, causing tissue heating due to body fluids infiltrating the polymer jacket and creating capacitive coupling between the shield and conductor.

Innovation Solution

Embedding a portion of the conductor's diameter within the lead body to fill the space between the shield and conductor, eliminating body fluid presence and reducing capacitive coupling.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If a conductive RF shield surrounds the conductor to block RF energy, then RF energy blocking is improved, but capacitive coupling increases due to body fluid infiltration between the shield and conductor

Engineering Contradiction:

ImproveRF energy blockingVSAvoidcapacitive coupling

Core Design Contradiction:

Object-affected harmful factorsVSReliability

Solution Approach 1:

The patent extracts and removes body fluid from the space between the RF shield and conductor by embedding the conductor within the lead body. The lead body material replaces the body fluid in this critical interface region, eliminating the dielectric medium that causes capacitive coupling while preserving the RF shielding function.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The lead body material acts as an intermediary substance between the RF shield and conductor. Instead of allowing body fluid to occupy this space and create capacitive coupling, the lead body material serves as a non-conductive barrier that eliminates the harmful electrical coupling while maintaining the structural integrity and RF blocking function.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Quantity of substance

If body fluid infiltrates the polymer jacket and fills the lumen, then fluid presence increases, but capacitive coupling between shield and conductor increases causing tissue heating

Engineering Contradiction:

Improvebody fluid presenceVSAvoidtissue heating

Core Design Contradiction:

Quantity of substanceVSTemperature

Solution Approach 1:

The patent applies preliminary anti-action by preemptively embedding the conductor within the lead body before body fluid infiltration can occur. This pre-configured structural arrangement prevents body fluid from establishing capacitive coupling pathways between the shield and conductor, thereby preventing the subsequent harmful effect of tissue heating during MRI procedures.

Inventive Principle:

Principle #9Preliminary anti-action

3Reliability

If the conductor is embedded within the lead body to fill the space between shield and conductor, then capacitive coupling is reduced, but lead body complexity increases

Engineering Contradiction:

Improvecapacitive coupling reductionVSAvoidlead body structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent merges the conductor embedding function with the existing lead body structure. Rather than adding a separate component or layer to prevent capacitive coupling, the design integrates the conductor directly into the lead body material, combining multiple functions (structural support, fluid barrier, and capacitive coupling prevention) into a unified structure.

Inventive Principle:

Principle #5Merging (Combining)

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

This approach effectively limits the increase in tissue heating by minimizing RF energy transfer to the conductor, ensuring safer MRI procedures for sensitive neurological tissues.

Implementation Method 1

Because the body fluid presents a high dielectric constant, capacitive coupling may occur to some degree between the shield and the conductor

Methodology Applied

Scientific EffectCapacitive coupling: Capacitance

Implementation Method 2

One technique is to include a conductive RF shield that surrounds the conductor. The RF energy is largely blocked from reaching the conductor

Methodology Applied

Scientific EffectElectromagnetic shielding: Faraday Cage

Implementation Method 3

Radio frequency (RF) energy that is present during the MM scan may couple to the conductor(s) within the lead which results in electrical current on the conductor that can cause potentially dangerous heating of tissue nearby the electrode

Methodology Applied

Scientific EffectRF energy coupling: Electromagnetic Induction

Data Source

PatentUS11612738B2Devices, systems and methods to reduce coupling of a conductor within an implantable medical lead

Publication Date: 2023.03.28 MEDTRONIC INC

AI summary

Conductors within an implantable medical lead that carry stimulation signal signals are at least partially embedded within a lead body of the medical lead over at least a portion of the length of the conductors while being surrounded by a radio frequency (RF) shield. A space between the shield and the conductors is filled by the presence of the lead body material such that body fluids that infiltrate the lead over time cannot pool in the space between the shield and the conductors. The dielectric properties of the lead body are retained and the capacitive coupling between the shield and the conductors continues to be inhibited such that current induced on the shield is inhibited from being channeled onto the conductors. Heating at the electrodes of the medical lead is prevented from becoming excessive.