Air-Core Transformer Lead Design for MRI RF Heating Reduction
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Solution Overview
Problem
Active Implantable Medical Devices (AIMDs) such as spinal cord stimulators face safety challenges during Magnetic Resonance Imaging (MRI) due to RF-induced heating in implanted leads, which can cause thermal injury.
Innovation Solution
The integration of an air-core transformer within the lead system increases the lead's inductance, reducing RF coupling and mitigating heating at the electrode-tissue interface, thereby enhancing MRI compatibility and safety.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the lead is made conductive to function as an electrical lead, then it can transmit electrical signals, but it acts as an antenna during MRI and causes RF-induced heating
Solution Approach 1:
An air-core transformer is introduced as an intermediary component within the lead system. The transformer couples magnetically to the lead without direct electrical connection, allowing the lead to function electrically while the transformer absorbs or redirects RF energy, preventing it from being converted to heat at the electrode-tissue interface.
Solution Approach 2:
The air-core transformer modifies the electrical parameters of the lead system, specifically increasing inductance and altering impedance characteristics. These parameter changes reduce the lead's effectiveness as an RF antenna during MRI, thereby reducing RF-induced heating while maintaining electrical signal transmission capability.
2Stability of the object's composition
If the lead is secured to muscular and fascial structures to prevent migration, then positional stability is improved, but RF energy coupling is increased leading to higher heating
Solution Approach 1:
The air-core transformer serves as a mediator between the lead and the surrounding tissue environment. It provides electromagnetic coupling that reduces RF energy transfer to the tissue, allowing the lead to remain secured to muscular and fascial structures for stability without transferring excessive RF energy that would cause heating.
3Object-affected harmful factors
If MRI scanning parameters are restricted to limit heating, then patient safety is improved, but imaging quality deteriorates
Solution Approach 1:
The air-core transformer converts the harmful RF energy that would otherwise be absorbed by the lead and converted to heat into useful magnetic coupling. The transformer utilizes the RF magnetic field from the MRI scanner to induce currents in its windings, which can be redirected or dissipated in a controlled manner, thereby reducing harmful heating while allowing standard MRI parameters to be used for optimal imaging quality.
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 air-core transformer configuration significantly reduces RF-induced heating, improving MRI safety for AIMD patients by minimizing power dissipation at the electrode-tissue interface and maintaining the lead's integrity and flexibility.
Implementation Method 1
The primary coil is created by winding one or more loops of the AIMD lead around a cylindrical form or bobbin. This primary coil acts as part of the air-core transformer, with the secondary coil situated coaxially within the primary. The higher inductance effectively reduces RF coupling into the lead array, mitigating heating at the electrode-tissue interface.
Data Source
AI summary
The present invention relates to a device for reducing MRI-induced RF heating in active implantable medical device (AIMD) leads, particularly spinal cord stimulator leads. The device incorporates an air-core transformer to increase inductance within the lead system, significantly reducing RF coupling and localized heating at the electrode-tissue interface during MRI procedures. The transformer features a primary coil formed by the lead and a secondary coil embedded in a biocompatible toroidal bobbin, which doubles as an anchoring mechanism. The bobbin securely holds the lead while maintaining flexibility for implantation. Anchoring is achieved through shape-memory retaining pins that adapt upon deployment, ensuring positional stability. This innovative design enhances MRI compatibility without compromising AIMD functionality, providing a safer and more effective solution for managing chronic pain and other neurological conditions. By addressing both lead stability and RF heating, the device supports safer imaging for AIMD patients.