Wireless RF Coil Load Control for MRI B1 Field Shimming
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Solution Overview
Problem
Magnetic resonance imaging systems face challenges in tuning and decoupling local RF coils, particularly when patient loads vary and when using complex coil arrays, leading to unintended resonance modes and signal degradation.
Innovation Solution
A magnetic resonance system with a local RF coil that includes adjustable loads with capacitance, resistance, or impedance, monitored by a measuring device and controlled by a load controller to achieve a desired B1 field distribution, allowing for real-time adjustments of amplitude and phase, and communication with an off-coil sequence controller for optimal coupling with whole body coils.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If local RF coils are inductively coupled to the whole body coil, then the local coils can transmit RF pulses without power cables, but the coupling varies from patient to patient and position to position causing degradation in resonance signal quality
Solution Approach 1:
The patent applies dynamics by making the load impedance of each coil element adjustable during the MR procedure. The controller dynamically modifies the load impedance based on measured current amplitude and phase, allowing the coil to adapt to varying patient loads and positions, thereby maintaining reliable signal quality while preserving wireless operation.
Solution Approach 2:
The patent implements feedback by using measuring devices to monitor the current amplitude and phase on each coil element, then feeding this information back to the controller. The controller uses this feedback to adjust the load impedance, creating a closed-loop system that maintains optimal coupling and signal quality despite variations in patient load or position.
2Measurement precision
If complex coil arrays with multiple elements are used, then better signal reception and focusing capability is achieved, but unintended resonance modes are excited causing severe degradation in resonance signal quality
Solution Approach 1:
The patent applies local quality by independently controlling the load impedance of each individual coil element in the array. This allows each element to be optimized for its specific contribution to the desired resonance mode while suppressing unwanted modes, thereby maintaining high signal reception capability and quality simultaneously.
Solution Approach 2:
The patent changes the electrical parameters (load impedance, capacitance, resistance) of each coil element based on measured performance. By adjusting these parameters, the system optimizes the resonance characteristics of each element to enhance desired modes and suppress unintended modes, improving both signal capability and quality.
3Ease of manufacture
If manual tuning of tunable capacitors is performed during manufacture, then the whole body birdcage coil can be tuned, but the load of actual patients often differs from the average causing suboptimal performance
Solution Approach 1:
The patent implements self-service by enabling the coil system to automatically tune itself during the MR procedure. The measuring devices and controller automatically adjust the load impedance of each coil element based on real-time measurements, eliminating the need for manual tuning and allowing adaptation to each patient's specific load without requiring manufacturer intervention.
Solution Approach 2:
The patent makes the tuning process dynamic by allowing continuous adjustment of load impedance during the procedure rather than fixed manual tuning at manufacture. This dynamic adjustment enables the system to adapt to different patient loads and positions, improving versatility while maintaining ease of operation through automated control.
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
Enables precise tuning of local RF coils to actual patient loads, improves signal quality by controlling transmit RF frequency and phase, facilitates the use of complex coils, and supports time-multiplexed parallel imaging protocols.
Implementation Method 1
a local radio frequency coil configured to be inductively coupled to the whole body radio frequency coil and to inductively transmit with the whole body coil to generate a B1 field distribution
Implementation Method 2
each radio frequency coil element further includes an adjustable load, the load having at least one of an adjustable capacitance, resistance or impedance
Implementation Method 3
each radio frequency coil element further includes a measuring device connected to a control unit, the measuring device being configured to monitor amplitude and phase of the radio frequency pulses by measuring the current on the radio frequency coil element
Data Source
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AI summary
A local radio frequency (RF) transmitting coil (26) of a magnetic resonance imaging system (5) has a plurality of coil elements (100). Each coil element (100) has an adjustable load (62) which is adjusted by a control unit (60) to adjust a transmitted B1field distribution. The load can be adjusted to shim for a uniform B1 field distribution. Non-uniform B1 field distributions can be selected to perform magnetic resonance sequences that use such B1 field distributions, such as parallel imaging. The B1 field distribution can be changed during the magnetic resonance sequence to track a moving region of interest, time division multiplex parallel imaging, and the like.