Detunable Volume Coil for MRI via Magnetic Coupling
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Solution Overview
Problem
Existing radio frequency volume antennas face challenges in detuning without compromising efficiency, particularly due to issues with PIN diodes causing significant losses and risk of overvoltage during high-frequency operations in NMR and MRI applications.
Innovation Solution
A detuning circuit comprising resonant circuits with a PIN diode and capacitor, positioned to induce reactance without contact with longitudinal conductors, allowing for frequency modification and minimizing coupling when not in use, thereby maintaining antenna performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a PIN diode is used in parallel or series with a capacitor or self-induction coil to detune the volume antenna, then the resonant frequency can be modified, but significant performance losses occur due to residual resistance during transmission phase
Solution Approach 1:
The patent introduces a coupling loop as an intermediary element that magnetically couples the PIN diode circuit to the longitudinal conductors without direct electrical contact. This mediator allows frequency detuning functionality while isolating the high-resistance PIN diode from the high-current transmission path, thereby preventing performance losses.
Solution Approach 2:
The patent replaces direct electrical connection (mechanical/electrical contact) with magnetic coupling through the loop. This substitution allows the PIN diode to influence the resonant frequency without being part of the main current path, eliminating the performance loss caused by residual resistance during transmission.
2Adaptability or versatility
If a PIN diode is blocked during transmission phase, then detuning is achieved, but avalanche voltage is exceeded leading to non-linear behavior and exclusion from MRI use
Solution Approach 1:
The coupling loop acts as a buffer that distributes and limits the voltage stress on the PIN diode. By magnetically coupling rather than direct connection, the loop prevents avalanche breakdown while maintaining detuning functionality, ensuring reliable linear operation in MRI applications.
Solution Approach 2:
The patent designs the coupling loop with sufficient inductance to cushion against voltage spikes before they reach the PIN diode. This protective design prevents avalanche voltage exceedance during high-power transmission, maintaining reliability and preventing non-linear behavior.
3Measurement precision
If a second reception antenna is inserted into the transmission antenna, then sensitivity is improved, but the transmission antenna must be detuned during reception phase
Solution Approach 1:
The patent designs the transmission antenna with an integrated detuning mechanism that enables it to serve dual functions: high-power transmission when needed and non-interfering reception mode when the second antenna is active. This multi-functionality allows the same structure to support both transmission and reception operations effectively.
4Adaptability or versatility
If reactance is added or removed from each longitudinal rod to modify resonant frequency, then frequency detuning is achieved, but the efficiency of the natural mode is damaged
Solution Approach 1:
The coupling loop serves as a mediator that allows reactance modification for frequency detuning without directly altering the longitudinal conductors. By magnetically coupling the PIN diode circuit to the conductors through the loop, the system can shift resonant frequency while preserving the efficient current distribution and field generation of the original antenna mode.
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 efficient detuning of volume antennas while preserving initial efficiency, reducing losses and avoiding overvoltage risks, thus supporting reliable operation in high-frequency NMR and MRI applications.
Implementation Method 1
induce by inductive effect a reactance on each longitudinal conductor and to modify the resonant frequency of the natural mode of said antenna
Implementation Method 2
a PIN diode playing the role of an electrically controlled switch (open or closed) to modify the impedance and therefore to detune the TEM-type volume antenna
Data Source
Figure 1~2
Figure 3~4
Figure 5(a)~5(b)
AI summary
The present invention relates to a radio frequency volume antenna (100), comprising a plurality of longitudinal conductors (2) and a detuning circuit for modifying the resonant frequency of the natural mode of said antenna (100) capable of detuning said antenna without contact with said longitudinal conductors (2), said detuning circuit being composed of a plurality of resonant circuits (8) having a switching device (11) and resonating: at a first resonant frequency close to the resonant frequency of the natural mode of said antenna when the switching means (11) is in the closed position so as to induce by inductive effect a reactance on each longitudinal conductor (2) and to modify the resonant frequency of the natural mode of said antenna (100);at a second resonant frequency higher or lower than the resonant frequency of the natural mode of said antenna so as to minimize the coupling between the detuning circuit and the longitudinal conductors (2) when said switching means (11) is in the open position, said volume antenna being characterized in that the antenna is a quarter-wave antenna and in that the resonant circuits (8) are positioned longitudinally in the antenna (100) at a position where the magnetic field B1 is maximum.;