KR-102964022-B1 - APPARATUS AND METHOD FOR DESIGNING METASURFACE

KR102964022B1KR 102964022 B1KR102964022 B1KR 102964022B1KR-102964022-B1

Abstract

A metasurface design apparatus and method are disclosed. A metasurface design apparatus according to an embodiment of the present invention is a metasurface design apparatus for designing a metasurface applicable to 7T brain magnetic resonance imaging, comprising a memory in which at least one instruction is stored, and a processor configured to execute at least one instruction stored in the memory. The processor acquires design information regarding an artificial magnetic field scatterer, acquires a plurality of high-frequency magnetic field ( B1 + ) modes that are distinct from one another using the acquired design information, detects an optimal combination of high-frequency magnetic field modes for homogenizing the high-frequency magnetic field, and designs an optimal metasurface based on the detected optimal combination.

Inventors

박남규
유선규
윤경섭

Assignees

서울대학교산학협력단

Dates

Publication Date: 20260512
Application Date: 20250113
Priority Date: 20240228

Claims (20)

As a metasurface design device for designing a metasurface applied to 7T brain magnetic resonance imaging, Memory in which at least one instruction is stored; and It includes a processor configured to execute at least one instruction stored in the memory, and The processor acquires design information regarding an artificial magnetic field scatterer, acquires a plurality of distinct high-frequency magnetic field ( B1 + ) modes using the design information, detects an optimal combination of high-frequency magnetic field modes for homogenizing the high-frequency magnetic field, and designs a metasurface applied to the 7T brain magnetic resonance imaging method based on the detected optimal combination. The processor generates an artificial magnetic field scatterer model by modeling the artificial magnetic field scatterer based on the design information, places the artificial magnetic field scatterer model in a virtual three-dimensional space, and then obtains information regarding the distribution of a high-frequency magnetic field induced inside a subject by repeatedly performing the process of moving the artificial magnetic field scatterer model in a preset direction by a preset distance, thereby obtaining the plurality of high-frequency magnetic field modes. The homogenization of the above high-frequency magnetic field is defined as a linear combination of complex weights for each of the plurality of high-frequency magnetic field modes, and The above complex weights are determined through a cost function that minimizes the coefficient of variation for the distribution of the absolute value of the high-frequency magnetic field in the region of interest of the above equalization, and The above optimal combination is defined as a combination of high-frequency magnetic field modes with the smallest coefficient of variation, a metasurface design device.
In Article 1, The above magnetic field scatterer is a metasurface design device having an elliptical cylinder structure composed of regularly arranged copper wires and parallel plate capacitors.
In Paragraph 2, A metasurface design device in which the effective material properties of the magnetic field scatterer and the magnetic field scattering by the magnetic field scatterer are determined by the capacitance value of the parallel plate capacitor.
In Article 1, The above high-frequency magnetic field mode is a metasurface design device representing the distribution of a high-frequency magnetic field induced inside a subject by an RF coil and a magnetic field scatterer.
In Article 1, A metasurface design device in which the region of interest for the above homogenization is the entire brain region.
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In Article 1, The above processor is a metasurface design device that adjusts the complex weights in a direction that minimizes the coefficient of variation using gradient descent.
In Article 1, A metasurface design device comprising: a processor deriving complex weights that minimize the coefficient of variation; calculating the importance of each of the plurality of high-frequency magnetic field modes; identifying the high-frequency magnetic field mode with the lowest importance; repeating the process of removing the identified high-frequency magnetic field mode until no high-frequency magnetic field mode exists; identifying a combination of high-frequency magnetic field modes with the smallest coefficient of variation; and detecting the identified combination as the optimal combination.
In Article 9, A metasurface design device in which the above importance is determined according to the absolute value of the above complex weights.
In Article 9, The above processor is a metasurface design device that detects the combination with the smallest number of included high-frequency magnetic field modes as the optimal combination when there are multiple combinations of high-frequency magnetic field modes having the smallest coefficient of variation.
In Article 1, The above processor is a metasurface design device that determines a metasurface having a combination of magnetic field scatterers that induce the optimal combination of high-frequency magnetic field modes as a metasurface to be applied to the 7T brain magnetic resonance imaging method.
As a metasurface design method for designing a metasurface applied to 7T brain magnetic resonance imaging, A step in which a processor acquires design information regarding an artificial magnetic field scatterer; The above processor acquires a plurality of distinct high-frequency magnetic field ( B1 + ) modes using the magnetic field scatterer; The above processor detects an optimal combination of high-frequency magnetic field modes for homogenizing the high-frequency magnetic field; and The processor includes the step of designing a metasurface applied to the 7T brain magnetic resonance imaging method based on the detected optimal combination, and In the step of acquiring the above plurality of high-frequency magnetic field modes, The processor generates an artificial magnetic field scatterer model by modeling the artificial magnetic field scatterer based on the design information, places the artificial magnetic field scatterer model in a virtual three-dimensional space, and then obtains information regarding the distribution of a high-frequency magnetic field induced inside a subject by repeatedly performing the process of moving the artificial magnetic field scatterer model in a preset direction by a preset distance, thereby obtaining the plurality of high-frequency magnetic field modes. The homogenization of the above high-frequency magnetic field is defined as a linear combination of complex weights for each of the plurality of high-frequency magnetic field modes, and The above complex weights are determined through a cost function that minimizes the coefficient of variation for the distribution of the absolute value of the high-frequency magnetic field in the region of interest of the above equalization, and A metasurface design method in which the optimal combination of high-frequency magnetic field modes for homogenizing the high-frequency magnetic field is defined as the combination of high-frequency magnetic field modes having the smallest coefficient of variation.
In Paragraph 13, A metasurface design method in which the above high-frequency magnetic field mode represents the distribution of a high-frequency magnetic field induced inside a subject by an RF coil and a magnetic field scatterer.
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In Paragraph 13, A metasurface design method in which gradient descent is used to adjust the complex weights in a direction that minimizes the coefficient of variation.
In Paragraph 13, In the step of detecting the optimal combination above, A metasurface design method wherein the processor derives complex weights that minimize the coefficient of variation, calculates the importance of each of the plurality of high-frequency magnetic field modes, identifies the high-frequency magnetic field mode with the lowest importance, and repeats the process of removing the identified high-frequency magnetic field mode until no high-frequency magnetic field mode exists, then identifies a combination of high-frequency magnetic field modes with the smallest coefficient of variation, and detects the identified combination as the optimal combination.
In Paragraph 18, A metasurface design method in which the above importance is determined according to the absolute value of the above complex weights.
In Paragraph 13, In the step of designing the above metasurface, A metasurface design method in which the processor determines a metasurface having a structure of a combination of magnetic field scatterers that induce the optimal combination of high-frequency magnetic field modes as a metasurface to be applied to the 7T brain magnetic resonance imaging method.

Description

Apparatus and Method for Designing Metasurface The present invention relates to a metasurface design apparatus and method, and more specifically, to a metasurface design apparatus and method for designing a metasurface applied to 7T brain magnetic resonance imaging. Magnetic resonance imaging is a medical imaging technology that non-invasively visualizes the internal structure of the human body. It involves inducing resonance by additionally applying a B1 + pulse with a frequency matching the Larmor frequency of a specific nuclide (mainly hydrogen) from an RF coil to the collective magnetic moment formed when nuclear spins within the human body align along B0 when a uniform main static magnetic field ( B0 ) is applied, and converting the resulting magnetic resonance signal into digital information to create an image. In particular, Ultrahigh Field MRI (UHF MRI) is a technique that utilizes a strong dominant static magnetic field (| B0 |≥7T), and the signal-to-noise ratio (SNR) and resolution of the image are significantly improved due to the magnetic resonance signal that increases with the intensity of B0 . However, as the Larmor frequency increases proportionally to the intensity of B0 , higher frequency B1 + pulses must be applied in Ultrahigh Field MRI. Consequently, the approximate wavelength of the electromagnetic waves transmitted into human tissue becomes similar to or smaller than the size of the skull, causing B1 + inhomogeneity, which is accompanied by inhomogeneity in the received magnetic resonance signal and degrades image quality. Similarly, the inhomogeneity of the high-frequency electric field causes an increase in local electric field strength, leading to an increase in the Specific Absorption Rate (SAR) within human tissue. The background technology of the present invention is disclosed in Korean Registered Patent Publication No. 10-1953350 (February 22, 2019). FIG. 1 is a block diagram showing a metasurface design device according to an embodiment of the present invention. FIG. 2 is an illustrative diagram for explaining the structure and operating principle of an artificial magnetic field scatterer according to an embodiment of the present invention. FIG. 3 is an illustrative diagram for explaining a method of modifying an artificial magnetic field scatterer according to an embodiment of the present invention. Figure 4 is an example diagram illustrating the process of designing an artificial magnetic field scatterer applicable to 7T magnetic resonance imaging. Figure 5 is an example diagram illustrating the process of deriving an optimal metasurface through pruning. Figure 6 is an example diagram illustrating the process of actually implementing an optimal metasurface. Figure 7 is an example diagram illustrating the structure of a metasurface that reflects a combination of optimized effective material properties. Figure 8 is an example diagram illustrating the distribution of high-frequency magnetic fields induced inside a subject when an optimized metasurface is applied. Figure 9 is an example diagram illustrating that a meta surface optimized for a specific head has excellent compatibility with various subjects. FIG. 10 is a first flowchart showing a metasurface design method according to an embodiment of the present invention. FIG. 11 is a second flowchart showing a metasurface design method according to an embodiment of the present invention. Preferred embodiments of the present invention will be described in detail below with reference to the attached drawings. Prior to this, terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings. Instead, based on the principle that the inventor may appropriately define the concepts of terms to best describe his invention, they should be interpreted in a meaning and concept consistent with the technical spirit of the present invention. Therefore, it should be understood that the embodiments described in this specification and the configurations illustrated in the drawings are merely some of the most preferred embodiments of the present invention and do not represent all of the technical spirit of the present invention; thus, various equivalents and modifications that can replace them may exist at the time of filing this application. Furthermore, as used in this specification, "comprise" or "include" and/or "comprising" or "including" specify the presence of the mentioned features, numbers, steps, actions, parts, elements, and/or groups thereof, and do not exclude the presence or addition of one or more other features, numbers, actions, parts, elements, and/or groups. In addition, when describing embodiments of the present invention, "may" and "may be" may include "one or more embodiments of the present invention." Additionally, to aid in understanding the invention, the attached drawings are not drawn to actual scale, and the dimensions of some components may be exa