RF Switch-Isolated Q-Spoiling and Preamp Decoupling
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Solution Overview
Problem
Current MRI systems face challenges in compactly integrating Q-spoiling and preamp decoupling circuits without degrading performance, due to coupling issues and increased complexity when these circuits are co-located, which affects safety and image quality.
Innovation Solution
A radio frequency (RF) receive circuit design that includes an antenna with multiple reactive impedance elements in a loop configuration, coupled with an amplifier input impedance, and an RF switch circuit that isolates or couples combined impedances to achieve resonance and reduce current flow during transmit and receive modes, respectively, thereby preventing image distortion and parasitic induction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If Q-spoiling and preamp decoupling circuits are co-located to reduce system size and cost, then device complexity and manufacturing cost are reduced, but coupling issues arise that degrade circuit performance and reliability
Solution Approach 1:
The patent divides the receive circuit into separate functional segments: the Q-spoiling circuit with its parallel resonant circuit is separated from the preamp decoupling circuit with its series resonant circuit. This segmentation allows each circuit to operate independently without performance degradation from coupling, while still achieving the goal of compact integration by placing both circuits in close proximity within the same receive channel.
2Measurement precision
If receive antennas are placed close to the sample surface to increase signal sensitivity, then receive signal quality is improved, but the antennas are exposed to high-power transmit fields that can drive significant currents and distort the transmit field
Solution Approach 1:
The Q-spoiling circuit is activated during the transmit mode before the receive mode begins. By preliminarily detuning the antenna during transmit mode through the parallel resonant circuit, the antenna becomes invisible to the high-power transmit field, preventing dangerous current buildup and transmit field distortion. This preliminary action enables the antenna to safely be positioned close to the sample surface for optimal receive signal quality.
3Reliability
If the RF switch remains closed during receive mode to maintain Q-spoiling protection, then transmit field safety is maintained, but the amplifier input impedance cannot be transformed to resonance with the antenna, reducing receive sensitivity
Solution Approach 1:
The RF switch is designed to dynamically change state between transmit and receive modes. During transmit mode, the switch is closed to activate Q-spoiling protection. During receive mode, the switch opens to allow the series resonant circuit to transform the amplifier input impedance to resonance with the antenna, maximizing receive sensitivity. This dynamic switching enables both safety during transmit and sensitivity during receive.
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 safe and efficient operation by reducing current flow during transmit mode and minimizing parasitic induction between antennas, improving image quality and reducing the complexity and cost of MRI systems.
Implementation Method 1
the first combined impedance transforms impedance of the RF switch circuit to be in resonance with the at least one antenna impedance element
Implementation Method 2
the first combined impedance and the second combined impedance together transform the amplifier input impedance to be in resonance with the at least one antenna impedance element
Implementation Method 3
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
Data Source
AI summary
A radio frequency (RF) receive circuit for use in a magnetic resonance imaging (MRI) scanner, comprising: an antenna including multiple reactive impedance elements coupled in a loop configuration; an amplifier input impedance; a first transmission line coupled in parallel with at least one reactive impedance element; a second transmission line coupled in parallel with the amplifier input impedance; a first reactive impedance circuit between the first transmission line and the second transmission line; an RF switch configured to isolate a second combined impedance, that includes the second transmission line and the amplifier input impedance, from a first combined impedance, that includes the first transmission line and the first reactive impedance circuit, when the RF switch is closed and to couple the second combined impedance to the first combined impedance when the RF switch is open; wherein, when the RF switch is closed, the first combined impedance transforms impedance of the RF switch to be in resonance with the at least one antenna impedance element; and wherein, when the RF switch is open, the first combined impedance and the second combined impedance together transform of the amplifier input impedance to be in resonance with the at least one antenna impedance element.