Magnetically Actuated Switches for MRI-Induced Tissue Heating
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Solution Overview
Problem
Implantable medical leads face heating issues due to RF electromagnetic energy coupling during MRI scans, particularly in neurostimulation systems where electrodes are in vulnerable locations, as existing technologies fail to effectively manage high RF currents in varying magnetic field orientations.
Innovation Solution
Incorporating multiple magnetically actuated switches within the lead that respond to magnetic fields to create a high impedance path by disconnecting the electrode from the conduction path, reducing the conductive path length and minimizing tissue heating, regardless of magnetic field orientation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the lead maintains a continuous conduction path to the electrode, then electrical stimulation signals can be delivered effectively, but RF electromagnetic energy couples to the conductor and creates high levels of RF electrical current that heats tissue
Solution Approach 1:
The switch is pre-configured in a closed state during normal operation to maintain conduction path integrity for stimulation signals. Upon detection of MRI conditions (high magnetic field strength), the switch automatically opens to disconnect the electrode, preventing RF current flow and tissue heating before the harmful effect can occur
Solution Approach 2:
The conduction path is made dynamically controllable through a magnetically actuated switch that transitions between closed and open states. The switch responds to the strength of the magnetic field, remaining closed during normal stimulation delivery and opening when MRI conditions are detected, thereby adaptively managing the trade-off between signal delivery and RF current prevention
2Reliability
If a magnetic field sensor is added to detect MRI conditions, then the switch can be activated appropriately, but the device complexity increases
Solution Approach 1:
The switch utilizes the magnetic field itself as the actuating force through magnetic actuators (such as ferromagnetic materials or magnetically responsive components) that directly respond to the MRI magnetic field strength. This eliminates the need for separate magnetic field sensors and electronic control circuits, as the magnetic field automatically actuates the switch mechanism through physical force, thereby maintaining device simplicity while ensuring reliable activation
Solution Approach 2:
The patent replaces electronic sensing and control systems with a direct magnetic-mechanical actuation system. Magnetic actuators convert the magnetic field strength directly into mechanical motion that opens or closes the switch, eliminating the need for sensors, signal processing electronics, and control logic, thereby reducing device complexity while maintaining activation accuracy
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 tissue heating at the electrode to a safer level by creating a high impedance path when exposed to strong magnetic fields, ensuring patient safety during MRI scans.
Implementation Method 1
a first actuator that when in the presence of a magnetic field attempts to move from a first start position to a first stop position and reaches the first stop position when a force acting on the first actuator due to the presence of the magnetic field is adequate to produce such movement
Data Source
AI summary
Magnetic orientation-independent magnetically actuated switches may be made by producing an outer cylinder and an actuator cylinder from ferromagnetic sheets and non-ferromagnetic sheets in alternating order. A first ferromagnetic body is attached to an end of the outer cylinder. The actuator cylinder is positioned within a first bore of the outer cylinder, the actuator pin is positioned within a second bore of the actuator cylinder and a third bore of the first ferromagnetic body with a portion of the actuator pin extending beyond the third bore of the first ferromagnetic body. A second ferromagnetic body is attached to the portion of the actuator pin, thus forming the magnetic orientation-independent magnetically operated switch.