Frequency Selective Surface Array for MRI Signal Phase Control
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Solution Overview
Problem
In magnetic resonance imaging (MRI) systems, the reception gain is insufficient due to phase-inversion of signals reflected from RF shields canceling out MR signals from subjects, leading to discomfort for patients and inefficiencies in technician workflow when mounting receiver coils.
Innovation Solution
An arrayed structure with a cylindrical-shaped conductor layer and stacked frequency selective surfaces, where elements are periodically arranged with edges closer to the center, is integrated between the transmitter/receiver coil and gradient magnetic field coil to control the phase of reflected signals, ensuring they align with directly received signals, thus enhancing reception gain without the need for a receiver coil on the subject.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a receiver coil is mounted on the subject to improve signal reception, then the reception gain is improved, but the device complexity and ease of operation deteriorate due to troublesome setup and patient discomfort
Solution Approach 1:
An arrayed structure with frequency selective surfaces is introduced as an intermediary component between the whole body coil and the subject. This structure selectively reflects MR signals while allowing RF excitation pulses to pass through, thereby improving signal reception without requiring direct contact with the subject. The arrayed structure acts as a mediator that resolves the contradiction by providing signal enhancement while maintaining ease of operation.
Solution Approach 2:
The patent replaces the mechanical approach of mounting a receiver coil directly on the subject with an electromagnetic field-based arrayed structure. This substitution eliminates the need for physical contact and complex mechanical setup, thereby improving ease of operation while maintaining signal reception quality through electromagnetic signal manipulation.
2Reliability
If a receiver coil is mounted on the subject to improve signal reception, then the reception gain is improved, but the device complexity and ease of operation deteriorate due to cable assembly requirements
Solution Approach 1:
The arrayed structure serves as an intermediary that eliminates the need for complex cable assemblies. By positioning the frequency selective surfaces between the whole body coil and subject, the system achieves signal enhancement through electromagnetic field manipulation rather than direct electrical connections, thereby reducing device complexity.
Solution Approach 2:
The patent extracts the signal reception function from the traditional receiver coil system and implements it through a passive arrayed structure. This extraction removes the need for active electronic components and cable assemblies, thereby reducing device complexity while maintaining signal reception capability.
3Object-affected harmful factors
If an RF shield is arranged in the outer periphery to block external interference, then the shielding effectiveness is improved, but the reception gain deteriorates due to phase-inversion of reflected signals
Solution Approach 1:
The patent applies local quality by making the RF shield frequency-selective rather than uniformly reflective. The frequency selective surfaces are designed with specific resonant properties that allow them to reflect signals at certain frequencies (blocking interference) while transmitting signals at other frequencies (allowing MR signal passage). This local differentiation in reflective properties resolves the contradiction between shielding effectiveness and signal reception gain.
Solution Approach 2:
The patent changes the parameters of the RF shield by introducing frequency selectivity through the arrayed structure. By adjusting the resonant frequency and impedance characteristics of the frequency selective surfaces, the system achieves both effective interference blocking and maintained signal reception gain, resolving the contradiction between these two opposing requirements.
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 improves MR signal reception gain, simplifies the examination process by eliminating the need for a receiver coil on the patient, reducing discomfort and enhancing workflow efficiency.
Implementation Method 1
when a magnetic resonance (MR) signal from a subject is received by a whole body coil, which is a transmitter/receiver coil, the reception gain becomes insufficient. One of the reasons why the gain becomes insufficient is that, since a signal reflected from an RF shield arranged in an outer periphery of the whole body coil is phase-inverted, such a signal and the MR signal from the subject directly received by the receiver coil cancel each other out
Data Source
AI summary
According to one embodiment, an arrayed structure includes a cylindrical-shaped conductor layer and a cylindrical-shaped layer stack. The cylindrical-shaped layer stack is arranged on an inner periphery of the conductor layer and a plurality of frequency selective surfaces are arranged in layers and stacked. Each of the frequency selective surfaces has a plurality of elements which are periodically arranged. Each element of the plurality of elements is formed in such a manner that at least a portion of an edge of a first element that faces an adjacent element in the same layer is closer to a center of the first element than another portion of edge.