MRI Receive Antenna Detuning Circuit for Transmit Field Protection
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Solution Overview
Problem
Existing MRI receive antennas face challenges in maintaining image quality due to the need for detuning circuits that are bulky and inflexible, which limits their placement near the patient's anatomy, and there is a risk of damage from high-power transmit fields during MRI scans.
Innovation Solution
A radio frequency (RF) circuit with an impedance matching and detuning circuit that includes multiple reactive impedance elements and switches, allowing for controllable impedance configuration to match the amplifier's input impedance during receive mode and increase impedance during transmit mode, reducing antenna sensitivity and preventing current flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a receive antenna is placed close to the patient's anatomy to increase signal quality, then the receive signal quality is improved, but the antenna is exposed to high-power transmit fields that can cause damage or safety risks
Solution Approach 1:
The patent implements dynamic switching of the detuning circuit between transmit and receive modes. During transmit mode, the circuit is configured to detune the antenna from the resonant frequency, preventing excessive current flow. During receive mode, the circuit is switched to allow the antenna to resonate at the Larmor frequency for optimal signal reception. This dynamic reconfiguration resolves the contradiction by adapting the antenna's electrical characteristics to the operational phase.
Solution Approach 2:
The patent changes the electrical parameters (impedance, resonant frequency) of the antenna system based on operational mode. By using switching elements to reconfigure the detuning circuit, the antenna's resonant frequency is shifted away from the transmit frequency during excitation and restored during reception. This parameter transformation allows the same antenna to safely operate in both high-power transmit and sensitive receive conditions.
2Reliability
If a detuning circuit is added to protect the antenna during transmit mode, then the safety and reliability are improved, but the device complexity and bulkiness increase
Solution Approach 1:
The patent combines the detuning function with the existing antenna structure and transmission line. The detuning circuit is integrated into the RF pathway between the antenna and the receiver, sharing space and functional pathways with existing components. This merging approach provides protection functionality without adding significant external bulk or complexity to the overall system.
Solution Approach 2:
The detuning circuit is designed to serve multiple functions: protecting during transmit mode, maintaining receive sensitivity, and potentially providing fail-safe operation. By making the circuit multi-functional, the patent reduces the need for separate dedicated components for each function, thereby minimizing overall device complexity while achieving reliable protection.
3Reliability
If a detuning circuit is added to prevent current flow during transmit mode, then the safety is improved, but the antenna placement flexibility is reduced
Solution Approach 1:
The patent extracts the detuning functionality from bulky external enclosures and integrates it directly into the antenna assembly or nearby RF circuitry. By taking out the protection function and embedding it close to the antenna, the system maintains safety capabilities while reducing the spatial constraints that would limit antenna placement options on or near the patient's body.
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 enables flexible placement of receive antennas while ensuring patient safety and maintaining image quality by effectively detuning the antenna from the high-power transmit field, reducing the risk of damage and improving MRI scan efficiency.
Implementation Method 1
an impedance matching and detuning circuit electrically connected between the transmission line and the impedance transformation circuit... The two or more switches are operable to controllably switch between configuring RF connections between the multiple reactive impedance elements, to RF connect a first set of the multiple reactive impedance elements to the second end portion of the transmission line to cause matching of overall impedance of the RF circuit to a prescribed input impedance seen at the amplifier circuit
Implementation Method 2
The localized changing magnetic moments, can be converted into an electrical signal, referred to as a receive signal, using Faraday's law of induction, by placing a loop of wire near the sample
Implementation Method 3
a high-power radio frequency (RF) excitation pulse of energy is applied to create Larmor precession of protons in the x-y plane
Data Source
AI summary
A radio frequency (RF) circuit is provided for use with a magnetic resonance imaging (MRI) scanner to transmit an RF receive signal to an amplifier circuit, the RF circuit comprising: a transmission line; an antenna electrically connected to a first end portion of the transmission line; an impedance transformation circuit; an impedance matching and detuning circuit electrically connected between the transmission line and the impedance transformation circuit, wherein the impedance matching and detuning circuit includes: multiple reactive impedance elements; and two or more switches operable to controllably switch between configuring the multiple reactive impedance elements to cause matching of overall impedance of the RF circuit to a prescribed input impedance seen at the amplifier circuit at a prescribed RF frequency during a receive mode of the MRI scanner, and to cause an increase of impedance at the antenna, to reduce sensitivity of the antenna to RF signals at the prescribed frequency during an excitation mode of the MRI scanner.