Non-uniform Winding Density for MRI Heating in Implantable Leads
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Solution Overview
Problem
Implantable electrical stimulation devices face challenges with MRI compatibility due to heating issues caused by changing magnetic fields, which are exacerbated by high impedance conductors that also shorten battery life.
Innovation Solution
The development of an implantable medical device with electrical conductors wound in a non-uniform density along the length axis, increasing impedance at MRI frequencies while maintaining low DC resistance for longer battery life, and using thin-film technologies to fabricate these conductors, with higher winding density at the distal end to mitigate heating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If electrodes with high impedance are used to reduce induced current densities and heating during MRI, then heating is reduced, but DC resistance increases which shortens battery lifetime
Solution Approach 1:
The patent changes the electrical parameters of the conductor by introducing windings that increase impedance at MRI frequencies (high frequencies) while maintaining low DC resistance (low frequencies). This frequency-dependent parameter change allows the same conductor to satisfy both requirements: reducing heating during MRI and preserving battery lifetime during normal operation.
Solution Approach 2:
The conductor's electrical characteristics become dynamic rather than static - the impedance varies with frequency. At MRI frequencies, the winding-induced impedance is high, but at stimulation frequencies, the DC resistance remains low. This dynamic behavior allows the system to adapt to different operational modes without compromise.
2Object-affected harmful factors
If the density of windings is uniformly distributed along the lead system, then impedance is increased at MRI frequencies, but the length of electrical conductors increases which increases DC resistance
Solution Approach 1:
The patent applies non-uniform winding density along the lead system, concentrating windings in specific regions where heating problems are most severe (such as near the distal end with electrodes) while using fewer or no windings in other regions. This local differentiation optimizes the balance between reducing MRI-induced heating and minimizing DC resistance.
Solution Approach 2:
The lead system is segmented into different regions with different winding densities. Rather than applying a uniform winding pattern throughout, the conductor is divided into sections with varying winding characteristics, allowing optimization for different functional requirements along the lead's length.
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 configuration reduces tissue heating during MRI scans, ensuring device safety and extending battery life, while being applicable across various electrical stimulation applications including deep brain stimulation.
Implementation Method 1
the impedance of the probes can be increased at high frequencies (MRI frequencies) due to self-inductance from the windings
Implementation Method 2
heating resulting from MRI scanning with an implanted medical device is non-uniformly distributed along the device
Data Source
AI summary
The present invention relates to a medical device (2) for electrical stimulation. The device comprising an implantable elongated lead system (20) having a distal end (21) and a proximal end (22), the lead system comprises one or more electrical conductors (23) for connection to one or more electrodes (24). The one or more electrical conductors are wound along a length axis (25) of the lead system with a plurality of windings, and wherein the density of windings is non-uniformly distributed along the length axis. In an embodiment, the medical device is in the form of a deep brain stimulation (DBS) device.