Unifilar Coiled Cable for MRI-Induced Heating Reduction

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Solution Overview

Problem

Implantable medical device leads experience elevated temperatures and undesired voltage induction in MRI environments due to electromagnetic energy pickup, leading to tissue heating issues.

Innovation Solution

A medical device lead featuring a small diameter unifilar coiled cable with a helically coiled filar design, optimized with a pitch of one to two times the filar diameter and an outer diameter less than 0.020 inch, which minimizes energy pickup and heating by reducing inductance and maximizing inductance, thereby reducing MRI-induced energy transmission to electrodes.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Temperature

If a conventional straight cable conductor is used, then the lead structure is simple and manufacturing is easy, but the inductance is high causing elevated temperatures and tissue heating in MRI environments

Engineering Contradiction:

Improveelectrode temperatureVSAvoidcable conductor structure

Core Design Contradiction:

TemperatureVSDevice complexity

Solution Approach 1:

The cable conductor is configured as a helical coil rather than a straight wire. The coiled geometry reduces inductance by changing the magnetic field distribution around the conductor, which directly addresses the temperature issue in MRI environments while maintaining structural integrity and flexibility.

Inventive Principle:

Principle #14Spheroidality (Curvature)

Solution Approach 2:

The patent specifies precise parameters for the helical coil including pitch (1-2 times the filar diameter), outer diameter (less than 0.020 inch), and number of turns. These parameter optimizations balance inductance reduction with mechanical flexibility and electrical performance requirements.

Inventive Principle:

Principle #35Parameter changes

2Temperature

If the cable conductor diameter is reduced to minimize inductance, then MRI-induced heating is reduced, but the mechanical strength and flexibility of the lead may be compromised

Engineering Contradiction:

Improvetissue heatingVSAvoidlead mechanical strength

Core Design Contradiction:

TemperatureVSStrength

Solution Approach 1:

The cable conductor is divided into multiple thin filars (unifilar construction with 1-3 filars) that are helically coiled. This segmentation allows each filar to be thin enough to minimize inductance and heating, while the coiled configuration provides mechanical flexibility and strength through the distributed structure.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The cable conductor uses composite construction with conductive filars (such as stainless steel or platinum-iridium) coated with dielectric material. This composite structure provides both electrical performance (low inductance) and mechanical properties (strength and flexibility) required for implantable leads.

Inventive Principle:

Principle #40Composite materials

3Object-affected harmful factors

If the cable conductor is coiled to reduce inductance, then energy pickup in MRI is minimized, but the manufacturing complexity increases

Engineering Contradiction:

ImproveMRI energy pickupVSAvoidcable conductor fabrication

Core Design Contradiction:

Object-affected harmful factorsVSEase of manufacture

Solution Approach 1:

The helical coil configuration is established during the manufacturing process using standardized coiling techniques and fixtures. The pitch, diameter, and number of turns are predetermined and controlled during fabrication, which simplifies the manufacturing process despite the complex geometry, and ensures consistency across production batches.

Inventive Principle:

Principle #10Preliminary action

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 unifilar coiled cable design significantly reduces MRI-induced heating at the electrodes, ensuring the safety and effectiveness of implantable medical devices during MRI procedures.

Implementation Method 1

the electromagnetic radiation produced by the MRI system may be picked up by implantable device leads used in implantable medical devices such as pacemakers or cardiac defibrillators. This energy may be transferred through the lead to the electrode in contact with the tissue, which may lead to elevated temperatures at the point of contact.

Methodology Applied

Scientific EffectElectromagnetic induction: Electromagnetic Induction

Implementation Method 2

This energy may be transferred through the lead to the electrode in contact with the tissue, which may lead to elevated temperatures at the point of contact.

Methodology Applied

Scientific EffectJoule heating: Joule Heating

Data Source

PatentUS8825179B2Implantable medical device lead including a unifilar coiled cable

Publication Date: 2014.09.02 CARDIAC PACEMAKERS INC

AI summary

A medical device lead includes a flexible body having a proximal region with a proximal end, and a distal region with a distal end. A connector is coupled to the proximal end of the flexible body of the lead to electrically and mechanically connect the lead to an implantable pulse generator. The medical device lead also includes an electrode in the distal region of the flexible body, and a cable conductor having a proximal end electrically coupled to the connector and a distal end electrically coupled to the electrode. The cable conductor consists of a single helically coiled filar including a plurality of co-radial turns and having an outer diameter of less than about 0.020 inch (0.508 mm).