Inductive Coupling Tuning for Multi-Nuclear MRI Antennas
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Solution Overview
Problem
Dual or multi-resonant RF antennas for MRI require complex tuning and matching procedures, especially for non-proton nuclei like 19F, due to lower sensitivity and concentration, which complicates their applicability, especially for surface coils with varying coil positioning.
Innovation Solution
A dual or multi-resonant RF/MR transmit and/or receive antenna with inductive coupling, allowing adjustable magnetic flux and impedance matching, simplifying the tuning and matching process by using inductive coupling loops that can be mechanically displaced or adjusted, maintaining frequency broad-band characteristics and symmetry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If dual or multi-resonant RF antennas are used for MRI imaging of non-proton nuclei, then the ability to image different nuclei (e.g., 19F, 31P) is improved, but the complexity of tuning and matching procedures increases
Solution Approach 1:
The patent employs movable magnetic flux shielding structures that can be dynamically adjusted to independently control the magnetic coupling between coil legs. This dynamic adjustment mechanism allows the antenna to be tuned to different resonant frequencies (e.g., 1H at 63 MHz and 19F at 40 MHz) by simply moving the shielding, eliminating the need for complex electronic tuning circuits and matching networks for each frequency transition.
Solution Approach 2:
The antenna is divided into multiple independent coil legs (first and second sets) that can be independently coupled to the magnetic flux shielding. Each coil leg can be selectively activated for different nuclear species, allowing the system to switch between imaging modes (proton vs. non-proton nuclei) by adjusting which coil legs are coupled and how the magnetic flux is distributed, thereby simplifying the overall tuning process.
2Reliability
If surface coils are positioned close to the examination object, then the sensitivity and signal quality are improved, but the variability in coil positioning leads to large changes in coil loading that complicate tuning and matching
Solution Approach 1:
The magnetic flux shielding acts as an intermediary element between the coil legs and the examination object. By adjusting the position of the shielding, the system can compensate for variations in coil loading caused by different positioning conditions. The shielding mediates the interaction between the coil and the body, allowing the antenna to maintain stable tuning across varying loading conditions without requiring complex real-time adjustment procedures.
3Adaptability or versatility
If inductive coupling is used to connect the antenna to transmit/receive units, then the frequency broad-band characteristics and symmetry are maintained, but the magnetic flux must be precisely controlled for optimal coupling
Solution Approach 1:
The patent uses movable magnetic flux shielding that can be dynamically positioned to control the magnetic coupling between coil legs. This mechanical adjustment provides precise control over the magnetic flux without requiring complex electronic control systems. The shielding can be moved to specific positions to optimize coupling at different resonant frequencies, maintaining both frequency broad-band characteristics and symmetry while achieving the necessary coupling precision through mechanical rather than electronic means.
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
This solution simplifies the tuning and matching of dual or multi-resonant antennas to transmit and receive units, enabling easier operation across different resonant frequencies without compromising signal quality or symmetry, particularly beneficial for surface coils with varying loading conditions.
Implementation Method 1
The antenna is inductively coupled by means of an inductive coupling device... by which the magnetic flux between the antenna and the transmit/receive units can be varied
Implementation Method 2
a first resonant circuitry... which is tuned to a first Larmor frequency... a second resonant circuitry... which is tuned to a second Larmor frequency
Implementation Method 3
By transmitting an RF excitation pulse (B1 field) which is orthogonal to the B0 field, generated by means of an RF transmit antenna or coil, and matching the Larmor frequency of the nuclei of interest
Implementation Method 4
MR relaxation signals which are emitted by the relaxation processes, are detected by means of an RF/MR receive antenna or coil
Data Source
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AI summary
A dual- or multi-resonant RF/MR transmit and/or receive antenna (1, 2) especially in the form of a planar antenna or a volume array antenna (also called antenna array) is disclosed for MR image generation of at least two different nuclei like e.g. 1H, 19F, 3He, 13C, 23Na or other nuclei having different Larmor frequencies. Basically, the antenna is coupled by means of an inductive coupling device (LI) with related transmit/receive channels (T/R). By such an inductive coupling, the tuning and matching of the antenna at the different resonant frequencies is easier to be obtained than in case of a galvanic connection. Further, the invention relates to an MR imaging apparatus comprising such a dual- or multi-resonant RF/MR transmit and/or receive antenna.