Magnetic resonance radio frequency enhanced imaging method and system with metamaterial units bestrewed outside visual field
By arranging metamaterial units in the area outside the field of view of the radio frequency coil of the magnetic resonance imaging system, the radio frequency field distribution is changed, and the insufficient image quality caused by weak radio frequency signals in ultra-low field magnetic resonance imaging technology is solved, and higher imaging effects and imaging quality are achieved.
Patent Information
- Application Number
- CN202411738109.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-11-29
- Publication Date
- 2025-03-14
AI Technical Summary
Due to the low field strength of the existing ultra-low field magnetic resonance imaging technology, the radio frequency signal emitted by hydrogen protons in the human body is weak, and the image signal-to-noise ratio, contrast and resolution are insufficient.
The field of view is arranged in the field of view in the radio frequency coil of the magnetic resonance imaging system, and the distribution of the radio frequency field is changed through the unique structure of the metamaterial unit, weakening the radio frequency field in the field of view and enhancing the radio frequency field in the field of view.
By weakening the RF field in the outside area of the visual field and enhancing the RF field in the visual field, the imaging effect and imaging quality of magnetic resonance imaging are improved, and the image signal-to-noise ratio, contrast and resolution are improved.
Smart Images
Figure CN119619945A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of medical devices, and in particular to a method and system for magnetic resonance radio frequency enhanced imaging with metamaterial units distributed outside the field of view. Background Art
[0002] Magnetic Resonance Imaging (MRI) is a non-invasive medical imaging technology. Its basic principle is that a strong magnetic field aligns and arranges hydrogen protons in the human body. The transmitting coil emits radio frequency pulses of precise frequency to excite hydrogen protons in the body. The receiving coil receives the radio frequency signal emitted by the hydrogen protons during the process of returning to steady state. The computer processes the radio frequency signal into an image. Since the hydrogen proton density and relaxation time of different tissues in the human body are different, MRI can provide high-contrast images to distinguish different types of tissues. Compared with X-ray examinations and computer tomography, MRI has the advantages of high safety, three-dimensional imaging, and multi-sequence imaging, and has unique advantages in soft tissue imaging.
[0003] Ultra Low Field Magnetic Resonance Imaging (ULF MRI) refers to the technology of performing magnetic resonance imaging under significantly lower field strength conditions than traditional MRI, and the field strength is usually less than 0.1 Tesla. By using permanent magnets instead of superconducting electromagnets, ULF MRI has greatly improved safety while significantly reducing costs, and the equipment is more portable and easy to use. The openness of the ULF MRI magnet configuration and the lower sensitivity to metal implants are more patient-friendly, expanding the audience of ULF MRI. Despite the above advantages, the significantly lower field strength conditions of ULF MRI make the radio frequency signal emitted by hydrogen protons in the human body weaker and the radio frequency field strength lower. Since the radio frequency field strength and image signal-to-noise ratio are positively linearly correlated under the condition of consistent absorption power, although ULF MRI has fewer artifacts in image sensitivity, it still has shortcomings in image signal-to-noise ratio, contrast and resolution. Summary of the invention
[0004] The purpose of the present invention is to provide a method and system for MRI radio frequency enhanced imaging with metamaterial units distributed outside the field of view, so as to solve the problems existing in the above-mentioned prior art and enhance the imaging effect and imaging quality of MRI.
[0005] To achieve the above object, the present invention provides the following solutions:
[0006] The present invention provides a metamaterial unit, comprising: a plurality of strip-shaped conductors, wherein the plurality of the conductors are stacked in sequence, the two ends of any two adjacent conductors are connected, each of the conductors is bent or curved toward one side, and any two adjacent conductors are bent or curved toward opposite directions.
[0007] Preferably, the conductor is bent into a smooth arc structure or bent into a polygonal structure.
[0008] Preferably, the conductor is made of copper.
[0009] The present invention also provides a method for MRI radio frequency enhanced imaging with metamaterial units distributed outside the field of view, wherein the metamaterial units described above are distributed in the area outside the field of view of the radio frequency coil of the MRI system.
[0010] Preferably, as many metamaterial units as possible are arranged in the area outside the field of view of the radio frequency coil of the magnetic resonance device.
[0011] The present invention also provides a magnetic resonance imaging system, wherein the above-mentioned metamaterial unit is arranged in an out-of-field-of-view area of a radio frequency coil of the magnetic resonance imaging system.
[0012] Preferably, a plurality of the metamaterial units are sequentially arranged around the field of view on the same plane to form a metamaterial unit group, wherein the metamaterial unit group has a plurality of units stacked at intervals, and the metamaterial unit group has a plurality of units nested at intervals from the inside to the outside.
[0013] Preferably, the sizes of all the metamaterial units are not exactly the same.
[0014] Compared with the prior art, the present invention has achieved the following technical effects:
[0015] The structure presented by the metamaterial unit provided by the present invention is found in simulation to have the property of changing the distribution of radio frequency fields in different regions, so that the radio frequency field inside the metamaterial unit structure is weakened and the radio frequency field outside the metamaterial unit structure is enhanced. This can be applied to the magnetic resonance imaging system and used to be arranged in the area outside the field of view of the radio frequency coil to achieve the purpose of weakening the radio frequency field outside the field of view and enhancing the radio frequency field inside the field of view. BRIEF DESCRIPTION OF THE DRAWINGS
[0016] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.
[0017] Figure 1A schematic diagram of a structure in which multiple metamaterial units are arranged around a field of view;
[0018] Figure 2 for Figure 1 axonometric drawing;
[0019] Figure 3 for Figure 2 A front view of
[0020] Figure 4 for Figure 2 Right view of;
[0021] Figure 5 A schematic diagram of a structure in which a radio frequency coil and a plurality of metamaterial units are arranged around a field of view;
[0022] Figure 6 is a structural schematic diagram of a radio frequency coil;
[0023] Figure 7 is a graph showing the relationship between the radio frequency field intensity and the frequency of the magnetic resonance imaging system when there is no metamaterial unit;
[0024] Figure 8 is the RF field distribution diagram of the magnetic resonance imaging system without the metamaterial unit;
[0025] Fig. 9 is a graph showing the relationship between the radio frequency field intensity and the frequency of the magnetic resonance imaging system when there is a metamaterial unit;
[0026] Fig.10 is the RF field distribution diagram of the magnetic resonance imaging system with the metamaterial unit;
[0027] Fig.11 It is a schematic diagram of the plane of multi-circle dense paving of metamaterial units in the area outside the field of view of the RF coil;
[0028] Fig.12 It is a three-dimensional diagram of the metamaterial unit;
[0029] Fig.13 It is the front view of the metamaterial unit;
[0030] Fig.14 It is a top view of the metamaterial unit;
[0031] Fig.15 It is the left view of the metamaterial unit;
[0032] In the figure: 100-field of view; 1-metamaterial unit; 2-RF coil; 3-conductor. DETAILED DESCRIPTION
[0033] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.
[0034] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.
[0035] First, some technical terms involved in the embodiments of the present application are introduced.
[0036] Metamaterials are a class of composite materials that are artificially designed and manufactured. They have unique physical properties that natural materials do not have. The properties of metamaterials do not come from the original materials they are composed of, but from their carefully designed structures. These structures are usually designed on a subwavelength scale to control the interaction between the material and electromagnetic or sound waves, resulting in metamaterials having properties that can only be achieved by non-traditional materials, such as negative refractive index and extraordinary electromagnetic response. Metamaterials have a wide range of potential applications, including optics, acoustics, microwaves, terahertz and other fields.
[0037] Combine the following Figures 1 to 15 , describing an embodiment of the present invention.
[0038] The present invention provides a metamaterial unit 1, such as Figure 12 to Figure 15 As shown, it includes: a plurality of strip-shaped conductors 3, the plurality of conductors 3 are stacked in sequence, the two ends of any two adjacent conductors 3 are connected, each conductor 3 is bent or curved toward one side, and any two adjacent conductors 3 are bent or curved in opposite directions.
[0039] In the present invention, the metamaterial unit 1 is cylindrical as a whole, and the conductor 3 accounts for about 50% of its side area, forming a three-dimensional structure without causing electromagnetic shielding.
[0040] The structure presented by the metamaterial unit 1 provided by the embodiment of the present invention is found in simulation to have the property of changing the distribution of the radio frequency field in different regions, so that the radio frequency field inside the metamaterial unit 1 structure is weakened and the radio frequency field outside the metamaterial unit 1 structure is enhanced. This can be applied to the magnetic resonance imaging system, and used to be arranged in the area outside the field of view of the radio frequency coil 2, so as to achieve the purpose of weakening the radio frequency field outside the field of view and enhancing the radio frequency field inside the field of view.
[0041] The conductor 3 in the embodiment of the present invention is bent into a smooth arc structure or a bent polygonal structure. The arc structure may be a semicircular structure, and the polygonal structure may be a semi-square frame. The present invention is not limited to this.
[0042] In order to facilitate conduction between upper and lower adjacent conductors 3, both ends of the conductor 3 extend outward a certain distance along the tangent direction so that there is an overlapping portion between the upper and lower conductors 3, and then conduction is performed using the overlapping portion.
[0043] For fixing each metamaterial unit 1, a fixed shell can be provided, a positioning structure can be provided inside the fixed shell, and then the metamaterial units 1 are positioned one by one through the positioning structure. It should be noted that there should be no contact between the metamaterial units 1. For fixing each conductor 3, the ends of two adjacent conductors 3 can be welded to achieve the fixing between the conductors 3.
[0044] In some embodiments, the conductor 3 is made of copper, such as annealed copper or pure copper. It is understandable that in other embodiments, any material with a conductive function may be selected.
[0045] In some embodiments, the thickness and height of any two conductors 3 in the same metamaterial unit 1 may be the same or different.
[0046] In some embodiments, the longitudinal cross-section of the conductor 3 is a common closed plane shape, such as a rectangle or a circle.
[0047] The embodiment of the present invention further provides a method for MRI radio frequency enhanced imaging with metamaterial units distributed outside the field of view, wherein the metamaterial units 1 as described above are distributed in the area outside the field of view of the radio frequency coil 2 of the MRI system.
[0048] This embodiment has the effect of weakening the radio frequency field in the area outside the field of view and enhancing the radio frequency field in the field of view.
[0049] In some embodiments, as many metamaterial units 1 as possible are arranged in the out-of-field area of the radio frequency coil 2 of the magnetic resonance device.
[0050] This embodiment enhances the effect of the radio frequency field within the field of view as much as possible.
[0051] Specifically, each metamaterial unit 1 structure includes n semicircular ring conductors 3; the longitudinal section of the semicircular ring conductor 3 is a common closed plane figure, such as a rectangle or a circle; the inner diameter of the semicircular ring conductor 3 is di mm, the outer diameter is d_o mm, and the height is h mm; the length of the semicircular ring conductor 3 extending outward from both ends is e mm.
[0052] The number of layers of metamaterial units 1 is N, and m metamaterial units 1 are arranged in each layer; the spacing between the geometric centers of the combination of metamaterial units 1 in adjacent layers is H mm; the distance between the geometric center of each metamaterial unit 1 in each layer and the geometric center of the combination of metamaterial units 1 in this layer is D mm; the distance between the geometric centers of adjacent metamaterial units 1 in each layer is R mm.
[0053] The values of n, d_i, d_o, h, e, N, m, H, D, and R are selected so that the metamaterial units 1 are densely laid out in the plane and occupy as much space as possible outside the field of view of the RF coil 2, such as Figure 5 shown.
[0054] Of course, in some embodiments, multiple turns of metamaterial units 1 may be provided, such as Fig.11 shown.
[0055] The embodiment of the present invention further provides a magnetic resonance imaging system, in which the above-mentioned metamaterial unit 1 is arranged in the out-of-field area of the radio frequency coil 2 of the magnetic resonance imaging system.
[0056] This embodiment has the effect of weakening the radio frequency field in the area outside the field of view and enhancing the radio frequency field in the field of view.
[0057] In some embodiments, multiple metamaterial units 1 are sequentially arranged around the field of view 100 on the same plane to form a metamaterial unit group, wherein the metamaterial unit group has multiple units stacked at intervals, and the metamaterial unit group has multiple units nested at intervals from the inside to the outside.
[0058] The metamaterial units 1 in the embodiment of the present invention are arranged in multiple layers and multiple circles; the geometric centers of each layer composed of multiple metamaterial units are on the same line; the geometric center of each layer of metamaterial unit combination is within the polygon formed by the connecting lines of the geometric centers of adjacent metamaterial units 1 in each layer; the metamaterial units 1 are densely arranged in the out-of-field area within the plane where the above polygon is located, so as to maximize the proportion of the space occupied by the metamaterial units 1 in the out-of-field area within the coil.
[0059] In some embodiments, the sizes of all metamaterial units 1 are not exactly the same, and the size here refers to the structural characteristics of the metamaterial unit 1, such as height, thickness, diameter, length, width, etc.
[0060] The solution provided by the present invention is particularly suitable for ultra-low field magnetic resonance imaging.
[0061] The present invention has a unique radio frequency field enhancement method, which can be applied to various human structures and organs such as wrists, heads, and breasts by changing the size of the metamaterial unit 1, the position of each metamaterial unit 1, the overall number of metamaterial units 1, etc., and has a wide range of applications and good universality. Secondly, the metamaterial unit 1 provided by the present invention has a simple structure, easy to obtain materials, easy to process and produce, and high cost performance, and is more suitable for actual medical environments. At the same time, the radio frequency field enhancement method of the present invention is groundbreaking and has a broad space for research and exploration.
[0062] The present invention is modeled and simulated in professional electromagnetic simulation software.
[0063] The parameters of metamaterial unit 1 in the electromagnetic simulation are as follows:
[0064] Each metamaterial unit 1 includes 10 semicircular ring conductors 3; the longitudinal section of the semicircular ring conductor 3 is rectangular; the inner diameter of the semicircular ring conductor 3 is 31 mm, the outer diameter is 35 mm, and the height is 1 mm; the length of the two ends of the semicircular ring conductor 3 extending outward is 0.5 mm; the material of the semicircular ring conductor 3 is annealed copper.
[0065] The multiple metamaterial units 1 in each layer are called a metamaterial unit combination. The number of layers of the metamaterial unit combination arranged from the inside to the outside is 8, and 16 metamaterial units 1 are arranged in each layer; the spacing between the geometric centers of the metamaterial unit combinations of adjacent layers is 12 mm; the distance between the geometric center of each metamaterial unit 1 in each layer and the geometric center of the metamaterial unit combination of this layer is 89.5 mm; the distance between the geometric centers of adjacent metamaterial units 1 in each layer is 35 mm.
[0066] Constructing Ultra-Low-Field MRI of the Knee Without Metamaterials:
[0067] Simulate a Helmholtz coil for 70mT ultra-low field MRI, such as Figure 6 As shown, the operating frequency is 3MHz. The Helmholtz coil is a single-polarization coil that transmits and receives radio frequency signals. When working, there is a relatively uniform radio frequency field in the Helmholtz coil.
[0068] The left knee and adjacent leg of the male human model Gustav were imported, the position of the human model was adjusted to the center of the Helmholtz coil, and the port of the Helmholtz coil was used as the excitation source. Using the probe located at the geometric center of the Helmholtz coil, it was observed that the magnetic resonance system without metamaterials operated at 3MHz, such as Figure 7 Observe the RF field distribution of the longitudinal section at the center of the human body model without metamaterials. The RF field distribution is shown in Figure 8 shown.
[0069] Ultra-low-field MRI of the knee constructed with metamaterials:
[0070] The metamaterial structure of the present invention was introduced and adjusted to the position near the knee of the human model, and the port of the Helmholtz coil was used as the excitation source. Using a probe located at the geometric center of the Helmholtz coil, it was observed that the magnetic resonance system with the metamaterial worked at 3 MHz, such as Fig. 9 Observe the RF field distribution of the longitudinal section at the center of the human body model when there is a metamaterial. The RF field distribution is shown in Fig.10 shown.
[0071] Compare Figure 8 and Fig.10It can be seen that: when there is no metamaterial, the RF field distribution in the Helmholtz coil is relatively uniform, and the intensity is higher near the coil; when there is a metamaterial, the RF field intensity in the metamaterial unit 1 is significantly reduced, while the RF field intensity inside the metamaterial structure is increased to a certain extent. Figure 8 The area of the human body model in the white box is the field of view, that is, the target area for RF field enhancement. It is calculated that within the same field of view, the RF field intensity with metamaterials is 2.1 times that without metamaterials.
[0072] The present invention uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only used to help understand the method and core ideas of the present invention. At the same time, for those skilled in the art, according to the ideas of the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.
Claims
1. A metamaterial unit, characterized in that: A plurality of strip-shaped conductors are stacked in sequence, two ends of any two adjacent conductors are connected, each conductor is bent or curved toward one side, and any two adjacent conductors are bent or curved toward opposite directions.
2. The metamaterial unit according to claim 1, characterized in that: The conductor is bent into a smooth arc structure or a polygonal structure.
3. The metamaterial unit according to claim 1, characterized in that: The conductor is made of copper.
4. A method for magnetic resonance radio frequency enhanced imaging with metamaterial units distributed outside the field of view, characterized in that: The metamaterial unit according to any one of claims 1 to 3 is arranged in an area outside the field of view of a radio frequency coil of a magnetic resonance imaging system.
5. The method for MRI radio frequency enhanced imaging with metamaterial units distributed outside the field of view according to claim 4, characterized in that: The metamaterial units are arranged as much as possible in the out-of-field area of the radio frequency coil of the magnetic resonance device.
6. A magnetic resonance imaging system, characterized in that: The metamaterial unit according to any one of claims 1 to 3 is arranged in the out-of-field area of the radio frequency coil of the magnetic resonance imaging system.
7. The magnetic resonance imaging system according to claim 6, characterized in that: A plurality of the metamaterial units are sequentially arranged around the field of view on the same plane to form a metamaterial unit group. The metamaterial unit group has a plurality of units stacked at intervals, and a plurality of units nested at intervals from the inside to the outside.
8. The magnetic resonance imaging system according to claim 7, characterized in that: The sizes of all the metamaterial units are not exactly the same.