Bone Conduction Implant Magnet Arrangement for MRI Safety
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Solution Overview
Problem
Existing implantable hearing prosthesis systems face issues with MRI compatibility due to interactions between implant magnets and external magnetic fields, leading to potential displacement, tissue damage, and imaging artifacts, necessitating limitations on MRI usage or surgical magnet removal.
Innovation Solution
A pair of implant magnets with reversed magnetic polarities, fixed beneath the skin and connected by a flexible member, are used to minimize magnetic interactions with external fields, featuring a planar disk shape and titanium housing to reduce volume and facilitate attachment to the skull bone, while maintaining effective mechanical stimulation signal delivery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single implant magnet is used for bone conduction hearing implant, then effective mechanical stimulation signal delivery is achieved, but MRI compatibility is compromised due to torque forces and displacement
Solution Approach 1:
The single implant magnet is divided into two separate magnets with opposite polarities. Each magnet is smaller in size and positioned to face opposite directions, reducing individual magnetic moment while maintaining functional effectiveness for bone conduction stimulation.
Solution Approach 2:
The two magnets are configured with opposite polarities facing each other, creating opposing magnetic fields that counterbalance each other. This configuration reduces the net magnetic moment of the implant, minimizing torque forces and displacement during MRI procedures while maintaining adequate stimulation capability.
2Device complexity
If a single implant magnet is used, then simpler implant structure is achieved, but surgical removal becomes necessary for MRI safety
Solution Approach 1:
The implant magnet system is segmented into two smaller magnets rather than one large magnet. This segmentation allows the magnets to be positioned in a common plane beneath the skin, facilitating easier access and removal during surgical procedures while maintaining structural functionality.
Solution Approach 2:
The magnets are arranged in a planar configuration (two-dimensional arrangement) rather than a single-point configuration. This dimensional change allows both magnets to be accessed and removed through the same surgical approach, eliminating the need for complex multi-site surgical removal procedures.
3Force
If larger implant magnets are used, then stronger magnetic field interaction is achieved, but implant volume increases requiring bone recess preparation
Solution Approach 1:
The magnetic field interaction function is distributed across two smaller magnets rather than concentrated in one large magnet. Each magnet generates a magnetic field that contributes to the overall stimulation effect, achieving adequate force while reducing individual magnet size and total implant volume.
Solution Approach 2:
The magnetic field strength is optimized locally at each magnet position rather than requiring uniform high strength throughout a large volume. The opposing polarity configuration creates focused magnetic field interactions at specific locations, maintaining effective stimulation with reduced overall implant volume.
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 allows for safe MRI compatibility without the need for surgical magnet removal, reducing the risk of torque forces and imaging artifacts, and enables efficient audio signal transmission to the cochlea while minimizing the implant's volume and complexity during implantation.
Implementation Method 1
a coil winding is held stationary by attachment to a non-vibrating structure within the middle ear 103 and microphone signal current is delivered to the coil winding to generate an electromagnetic field. A magnet is attached to an ossicle within the middle ear 103 so that the magnetic field of the magnet interacts with the magnetic field of the coil. The magnet vibrates in response to the interaction of the magnetic fields
Implementation Method 2
an implanted floating mass transducer (FMT) is affixed to the temporal bone. In response to an externally generated electrical audio signal, the FMT couples a mechanical stimulation signal to the temporal bone for delivery by bone conduction to the cochlea for perception as a sound signal
Data Source
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AI summary
An implantable magnet arrangement is described for a hearing implant in a recipient patient. A pair of implant magnets are fixable in a common plane beneath the skin of the patient to underlying skull bone. At least one of the magnets is adapted to transform a magnetic drive signal from an external signal drive coil into a corresponding mechanical stimulation signal for delivery by bone conduction of the skull bone as an audio signal to the cochlea. Each implant magnet includes a pair of internal magnets lying in parallel planes which meet along a common junction with repelling like magnetic polarities facing towards each other, and the magnetic polarities of each implant magnet are reversed from each other.