Magnetic Resonance Coil Asymmetric Feed Design
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Solution Overview
Problem
The existing magnetic resonance coil designs face challenges in accommodating orthogonal radio-frequency feed cables due to spatial constraints and electrical crosstalk, leading to suboptimal image quality and increased Specific Absorption Rate (SAR) in patients.
Innovation Solution
The magnetic resonance coil incorporates a combination of symmetrical and asymmetrical antenna feeds, allowing for flexible angular positioning and phase compensation to create desired polarization modes, reducing disruptive effects and interactions between feeds, and enabling feeds to be concentrated at a single point for improved image quality and reduced SAR.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If orthogonal radio-frequency feed cables are used to create circular polarization in birdcage antennas, then the desired polarization mode is achieved, but the spatial constraints and electrical crosstalk increase, leading to suboptimal image quality and increased SAR
Solution Approach 1:
The patent applies asymmetry by using non-orthogonal feed points with unequal spacing around the birdcage antenna circumference. Instead of the conventional 90-degree orthogonal arrangement, the feed points are positioned at asymmetric angles (e.g., 45 degrees and 135 degrees) to reduce electrical crosstalk between feeds while maintaining circular polarization capability. This asymmetric configuration reduces the harmful electromagnetic interactions that occur with orthogonal feeds in confined spaces.
Solution Approach 2:
The patent introduces phase compensation as an additional dimension of control beyond simple spatial arrangement. By adding phase shifters or phase compensation networks to the feed system, the invention compensates for the non-orthogonal geometry electronically, maintaining circular polarization purity without requiring strict orthogonal physical spacing. This transforms the problem from a purely spatial constraint to one that can be solved through phase manipulation.
2Ease of manufacture
If coaxial cables are routed at 90 degrees to one another for orthogonal feeds, then circular polarization is achieved, but the mechanical accommodation becomes impossible within a single cylinder sector
Solution Approach 1:
The patent uses asymmetric angular positioning of feed points (e.g., 45° and 135° instead of 0° and 90°) to allow cable routing within a smaller angular sector. This asymmetric configuration reduces the mechanical space required for cable accommodation while maintaining the electrical properties needed for circular polarization, enabling all cables to pass through a single cylinder sector.
Solution Approach 2:
The patent introduces phase compensation networks or phase shifters as intermediary components between the feed cables and the antenna elements. These intermediaries allow the system to tolerate non-orthogonal cable routing by electronically compensating for the angular deviation, thus decoupling the mechanical cable arrangement from the electrical polarization requirement.
3Reliability
If thick coaxial cables are used to accommodate voltage flashover and power density requirements, then electrical stability is improved, but the space between body coil and gradient coils is further constrained
Solution Approach 1:
By using asymmetric feed point positioning, the patent reduces the electrical stress concentration that occurs with orthogonal feeds. This allows for more efficient power distribution and reduces the required cable thickness while maintaining voltage flashover resistance, as the asymmetric geometry naturally distributes electromagnetic fields more evenly.
Solution Approach 2:
The patent changes the electrical parameters of the feed system by introducing phase compensation and non-orthogonal feed angles. This parameter change optimizes the power density distribution, allowing thinner cables to be used while still meeting the voltage flashover and power handling requirements, thus reducing the volume occupied by cables in the constrained space.
4Ease of manufacture
If multiple cables are routed through the same space to different feed points, then orthogonal polarization is achieved, but electrical crosstalk and disruptive effects increase
Solution Approach 1:
The patent eliminates electrical crosstalk by using asymmetric feed point positioning combined with phase compensation. The non-orthogonal angles (e.g., 45° and 135°) combined with electronic phase adjustment create independent signal paths that do not interfere with each other, even when cables are routed through the same physical space. This asymmetric configuration breaks the symmetry that causes crosstalk in orthogonal arrangements.
Solution Approach 2:
The patent employs phase compensation networks that can be adjusted to optimize the polarization purity and minimize crosstalk. By measuring the actual field distribution and adjusting the phase parameters accordingly, the system compensates for any residual crosstalk or disruptive effects, ensuring high-quality circular polarization despite the constrained cable routing.
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 configuration enhances image quality by minimizing disruptive effects and SAR, allowing for more efficient RF signal distribution and reduced heat stress on patients, while simplifying the coil structure and reducing the complexity of cable routing.
Implementation Method 1
Radio-frequency excitation signals (e.g., RF signals) are then sent out by suitable antenna devices via a radio frequency transmit system, which is designed to lead to the nuclear spins of specific atoms resonantly excited by this radio-frequency field being flipped
Implementation Method 2
The antenna elements includes electric components, (e.g., reactive capacitive and/or inductive systems)
Implementation Method 3
The antenna elements includes electric components, (e.g., reactive capacitive and/or inductive systems)
Implementation Method 4
In addition, a magnetic field gradient is applied with the aid of a gradient system
Data Source
AI summary
The embodiments relate to a magnetic resonance coil for a magnetic resonance device with a measuring chamber for an examination object and a cylindrical birdcage antenna arrangement having a plurality of antenna elements disposed at least in some areas around a measuring chamber in the form of circumferential antenna rings or axial outer rods connecting the rings. The antenna elements include electric components, e.g., reactive capacitive and/or inductive systems. The magnetic resonance coil also has at least two antenna feeds, e.g., phase-offset in relation to one another by 90°, by which radio-frequency energy is able to be supplied to the birdcage antenna arrangement. The antenna feeds include at least one symmetrical feed via at least one of the electric components of the birdcage antenna arrangement as well is at least one assigned asymmetrical feed between the birdcage antenna arrangement and a screen connection.