Implantable Lead Shield Termination for MRI Safety
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Solution Overview
Problem
Implantable medical leads are susceptible to tissue damage due to induced currents from electromagnetic radiation, particularly during MRI scans, as the existing insulation does not effectively shield conductive filars from radiofrequency (RF) energy, leading to potential heating and safety risks for patients with implanted medical devices.
Innovation Solution
Incorporating a shield within the jacket of the implantable medical lead, which is terminated in a way that prevents electrical contact loss and migration, using an inner and outer insulation layer with the shield positioned between them, and grounding the shield to either the IMD can or tissue to dissipate RF energy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a shield is added within the lead jacket to block RF energy, then protection against induced currents is improved, but device complexity increases
Solution Approach 1:
The shield is nested within the existing lead jacket structure, with the insulation layer containing the shield that is positioned between the inner and outer jacket layers. This nesting approach integrates the shielding function into the existing lead architecture without requiring a completely separate external shielding structure, thereby providing RF protection while minimizing additional complexity.
Solution Approach 2:
The lead construction utilizes composite material layers including an inner insulation layer, a shield layer, and an outer insulation layer. This multi-layer composite structure combines the insulating properties of the insulation materials with the RF-blocking properties of the shield, creating an integrated solution that addresses both electrical isolation and electromagnetic protection needs.
2Reliability
If the shield is terminated by folding back the ends, then electrical contact is maintained, but the shield may migrate or fray within the lead
Solution Approach 1:
The shield termination merges the shield layer with the inner insulation layer by folding the shield ends back and securing them within the inner insulation layer. This merging of the shield and insulation layer creates a unified structure that maintains electrical contact while preventing migration and fraying, as the shield termination is integrated into the insulating material rather than being a separate loose component.
Solution Approach 2:
The shield termination utilizes the flexible nature of the thin shield layer to fold it back and secure it within the inner insulation layer. The flexibility of the thin film shield allows it to be manipulated into a folded configuration that maintains electrical contact while being contained within the insulation layer, preventing fraying and migration.
3Ease of manufacture
If the outer insulation layer terminates before the inner insulation layer, then the shield can be properly terminated, but the lead structure becomes more complex
Solution Approach 1:
The insulation structure is segmented into distinct inner and outer insulation layers with different termination points. The outer insulation layer terminates before the inner insulation layer, creating separate functional zones that facilitate shield termination. This segmentation allows the shield to be properly contained and terminated within the inner insulation layer while the outer insulation layer provides additional protection and structural support.
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 shield effectively reduces induced currents on the filars, minimizing tissue damage and allowing patients with implanted medical devices to undergo MRI scans safely by blocking RF energy and providing a durable, flexible lead that maintains mechanical integrity.
Implementation Method 1
The implantable medical lead includes a shield within the jacket that may reduce the amount of current induced on the filars within the lead
Data Source
AI summary
A shield located within an implantable medical lead may be terminated in various ways at a metal connector. The shield may be terminated by various joints including butt, scarf, lap, or other joints between insulation layers surrounding the lead and an insulation extension. The shield may terminate with a physical and electrical connection to a single metal connector. The shield may terminate with a physical and electrical connection by passing between an overlapping pair of inner and outer metal connectors. The metal connectors may include features such as teeth or threads that penetrate the insulation layers of the lead. The shield may terminate with a physical and electrical connection by exiting a jacket of a lead adjacent to a metal connector and lapping onto the metal connector.