Implantable Stimulation Lead Tissue Coupler for MRI RF Compatibility
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Solution Overview
Problem
Conventional implantable electrical stimulation systems are incompatible with magnetic resonance imaging (MRI) due to their susceptibility to RF irradiation, which can cause tissue damage and premature failure of electronic components.
Innovation Solution
Incorporating RF-irradiation-susceptibility-reducing elements, such as tissue couplers and inductive elements, into the leads to couple patient tissue with conductors and alter electromagnetic properties, thereby reducing the propagation of undesired energy during RF exposure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional implantable electrical stimulation systems are used, then the systems can provide therapeutic stimulation, but the systems are incompatible with MRI due to RF irradiation susceptibility causing tissue damage and device failure
Solution Approach 1:
A tissue coupler is introduced as an intermediary component between the lead conductor and the surrounding tissue. The tissue coupler includes a capacitive element with conductive inner and outer members separated by a non-conductive spacer, creating a controlled coupling interface that redirects RF energy into the tissue rather than allowing it to propagate along the conductor, thereby protecting the device during MRI
Solution Approach 2:
The capacitive impedance of the tissue coupler is specifically designed to be low at MRI RF frequencies (e.g., 64 MHz for 1.5T MRI) while maintaining high impedance at therapeutic stimulation frequencies. This frequency-dependent parameter change allows the system to be MRI-compatible without compromising its therapeutic function
2Object-affected harmful factors
If tissue couplers are added to reduce RF susceptibility, then MRI compatibility is improved, but the device complexity increases
Solution Approach 1:
The tissue coupler is designed with a nested structure where the inner conductive member is surrounded by a non-conductive spacer, which is in turn surrounded by an outer conductive member. This nested configuration allows multiple functional elements to be integrated in a compact form factor that can be incorporated into existing lead designs without significantly increasing overall device complexity
Solution Approach 2:
The tissue coupler serves multiple functions simultaneously: it acts as a RF frequency bypass to ground, provides impedance matching, and maintains electrical coupling with the tissue. This multi-functionality reduces the need for additional separate components, thereby limiting the increase in device complexity
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 solution effectively reduces the susceptibility of electrical stimulation systems to RF irradiation, preventing tissue damage and device malfunction during MRI procedures, ensuring safer and more reliable operation.
Implementation Method 1
The tissue coupler includes a capacitive element having an inner member, a non-conductive spacer, and an outer member
Implementation Method 2
In another embodiment, the lead or lead extension includes an inductive element coupled to at least one conductor
Data Source
AI summary
An implantable electrical stimulation lead includes a plurality of conductors that extend along a lead body and that electrically couple electrodes to terminals. A first tissue coupler is electrically coupled to a first conductor of the plurality of conductors. The first tissue coupler includes a conductive first inner member, a non-conductive member disposed adjacent to at least a portion of the first inner member, and a conductive outer member disposed adjacent to at least a portion of the non-conductive member such that at least a portion of the non-conductive member is sandwiched between the first inner member and the outer member. The first inner member is electrically coupled to the first conductor. The outer member is disposed along a portion of an outer surface of the lead body such that the conductive outer member is exposed to patient tissue when the lead is implanted in a patient.