MRI-Compatible Pacemaker Switching Conductive Loops
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Solution Overview
Problem
Implanted cardiac rhythm management devices, such as pacemakers, are incompatible with MRI procedures due to induced currents caused by time-varying magnetic field gradients, which can interfere with the device's functioning and potentially harm the patient.
Innovation Solution
Incorporating a switch, such as a transistor-type or relay-type switch, in series with the integrated circuit protection diode to control low-frequency induced currents during MRI procedures, and optionally using a resistor in series with the diode to limit current flow, along with control circuitry to detect magnetic fields or induced currents to manage conductive loops.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional implanted medical device is used during MRI, then the device can provide continuous medical therapy, but induced currents from the MRI magnetic field interfere with device operation
Solution Approach 1:
The patent applies a switchable configuration where the conductive loop is dynamically opened during MRI procedures. The switch (S1) transitions from closed to open state when MRI is detected, preventing induced current flow while maintaining normal device operation during non-MRI periods. This dynamic reconfiguration resolves the contradiction by adapting the device state to external conditions.
Solution Approach 2:
The patent introduces an intermediary switch component between the conductive loop and the rest of the device circuitry. This switch acts as a mediator that selectively connects or disconnects the loop based on operational requirements, allowing the device to maintain therapy delivery while blocking harmful induced currents during MRI procedures.
2Object-affected harmful factors
If the conductive loop is opened during MRI to prevent induced currents, then device safety is improved, but device complexity increases due to additional control circuitry
Solution Approach 1:
The patent utilizes parameter changes in the switch state (open/closed) to control current flow paths. By changing the electrical connectivity parameter of the switch based on detected MRI conditions, the system achieves induced current prevention without requiring complex analog control circuits, thus limiting the increase in device complexity.
Solution Approach 2:
The device incorporates self-service capabilities through automatic MRI detection and autonomous switch actuation. The control circuitry automatically detects MRI presence and activates the switch without external intervention, reducing the need for additional complex control mechanisms and simplifying the overall system architecture.
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
Minimizes or eliminates low-frequency induced currents, preventing interference with the pacemaker's operation and ensuring safe and effective pacing during MRI examinations.
Implementation Method 1
A principle known as Faraday's law states that any change in a magnetic field around a conductive loop will cause a voltage to be induced in the conductive loop, and consequently, cause a current to flow in the conductive loop. In the case of a patient undergoing an MRI procedure, the time-varying magnetic field gradients of the MRI machine create the required changing magnetic field and elements of the implanted cardiac rhythm management device form a conductive loop, resulting in a current flow.
Data Source
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AI summary
An implantable medical device configured to be compatible with the environment inside an MRI machine. The implantable medical device (272) includes a housing (244) constructed of an electrically conductive material and pulse generation circuitry (238) within the housing for generating electrical voltage pulses. The implantable medical device further includes a first conductor that is configured to transmit the electrical voltage pulses from the pulse generation circuitry to a patient's cardiac tissue and a second conductor that is configured to provide an electrically conductive path from the patient's cardiac tissue back to the pulse generation circuitry. The implantable medical device further comprises a protection diode (Di) disposed in series with and between the housing (244) and the pulse generation circuitry (238), and a resistor (274) disposed in series with the protection diode (Di) and between the housing and the pulse generation circuitry (238).