Wirelessly powered magnetic resonance imaging signal amplification system for ingestible devices having L-C mesh circuit
Inventors
Qian, Chunqi • Murphy-Boesch, Joe • Koretsky, Alan • Dodd, Stephen John
Assignees
US Department of Health and Human Services
Publication Number
US-10203382-B2
Publication Date
2019-02-12
Expiration Date
2032-03-29
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Abstract
An implantable parametric circuit enables local signal amplification and wireless transmission of RF signals in connection with magnetic resonance imaging systems. The parametric circuit detects RF signal detected during magnetic resonance imaging procedure, amplifies the detected RF signal, and transmits the amplified RF signal in a wireless manner to an external pick-up coil. The parametric amplifier is also configured to use another RF signal generated by an external source as the primary power source. As a result, implanted or catheter coils could be used as a wireless signal transducer without the need for a battery or a power connection.
Core Innovation
The invention provides an implantable parametric circuit that enables local signal amplification and wireless transmission of radio frequency (RF) signals during magnetic resonance imaging (MRI) procedures. This parametric circuit detects RF signals emitted by tissue or blood in the vicinity of an interventional or ingestible device, amplifies these detected signals, and wirelessly transmits the amplified signals to an external pick-up coil. The system uses a second RF signal generated by an external source as its primary power source, thereby eliminating the need for a battery or physical power connection at the implanted or catheter coil site.
The problem addressed by the invention is the heating caused by long conductive transmission lines, such as coaxial cables that connect RF coils in interventional devices to MRI scanners. Such cables produce RF heating due to coupling with the MRI system’s RF field, posing a risk of tissue damage. Existing wireless transmission solutions relying on passive inductive coupling suffer from sensitivity loss, and conventional low-noise amplifiers require local DC power, which is challenging for implanted or catheter devices. Therefore, there is a need for an amplification system that can wirelessly amplify MRI RF signals without requiring local power connections to avoid safety hazards and improve signal sensitivity.
The system disclosed includes a pre-amplification circuit embedded in an ingestible or interventional device comprising at least one resonator configured to resonate at multiple frequencies: predominantly the MRI signal (Larmor frequency), a pumping frequency signal generated externally, and a third frequency resulting from mixing these signals. A varactor within the circuit performs frequency mixing to produce an amplified current at a difference frequency. The amplified RF signal is then wirelessly transmitted to an external coil for MRI image processing. This approach enables wireless amplification and transmission of MRI signals without local power sources, enhancing device visualization during MRI while minimizing RF heating risks associated with wired devices.
Claims Coverage
The patent includes one independent claim covering a wireless amplification system for MRI signal processing, detailing the structural and functional aspects of the system components.
Wireless RF signal amplification using dual L-C mesh pre-amplification circuit
The system includes a pre-amplification circuit in an ingestible device consisting of two loop current (L-C) meshes. The first L-C mesh is composed of a first inductor and a capacitor configured to resonate at the MRI signal frequency (first frequency) and generate an input current in response to the MRI RF signal.
Generation and use of pumping current from external frequency generator
The second L-C mesh comprises the shared capacitor, a second inductor, a varactor, and optionally a third inductor. This mesh resonates at a second frequency in response to an externally generated RF pumping signal and generates a pumping current. It also resonates at a third frequency corresponding to the amplified output signal produced by mixing the input and pumping currents via the varactor.
Wireless transmission of amplified RF signal via external coil
An external coil is configured to receive the amplified third RF signal wirelessly and transmit it to the MRI device for image processing, enabling signal acquisition without direct wired connections.
These inventive features collectively provide a wireless MRI RF signal amplification system that operates without local DC power sources by using dual L-C mesh resonators and varactor-based frequency mixing, enabling safe and sensitive signal acquisition from ingestible devices for MRI applications.
Stated Advantages
Enables operation of an amplification circuit without requiring a physical connection to a power source, eliminating the need for batteries or wiring in implanted or catheter devices.
Reduces RF heating associated with long conductive transmission lines by removing the requirement for physical coaxial cables.
Provides improved detection sensitivity through local signal amplification using parametric amplification principles.
Supports wireless transmission of amplified MRI signals, allowing enhanced visualization of interventional devices within the body during MRI analysis.
Documented Applications
Use with ingestible devices, such as capsules, for examining the gastrointestinal tract during MRI.
Integration with interventional medical devices like catheters, guidewires, and endoscopes to enable wireless signal amplification and transmission during MRI-guided procedures.
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