Domino volume metamaterial resonator for enhancing signal-to-noise ratio of magnetic resonance imaging

Abstract

The invention relates to a domino volume metamaterial resonator for enhancing the signal-to-noise ratio of magnetic resonance imaging, which comprises a plurality of metamaterial units, each metamaterial unit comprises a dielectric substrate, a spiral wire and an external capacitor, the spiral wire is wound on the dielectric substrate, a gap exists between adjacent spiral coils, two ends of the spiral wire are connected through the external capacitor, and the spiral wire is wound on the dielectric substrate. The resonant frequency of the metamaterial unit is matched with the target frequency; a plurality of metamaterial units are stacked along the axial direction to form the hollow domino volume metamaterial resonator.

Description

Technical Field

[0001] The invention belongs to the technical field of MRI imaging, and in particular relates to a domino volume metamaterial resonator for enhancing the signal-to-noise ratio of magnetic resonance imaging. Background Art

[0002] Magnetic resonance imaging (MRI) uses the nuclear magnetic resonance phenomenon to obtain electromagnetic signals from the human body and reconstruct human information. It is a biological magnetic spin imaging technology that uses the characteristics of the spin motion of atomic nuclei. In an external magnetic field, after the radio frequency pulse stops, the atomic nuclei whose spin system has been excited cannot maintain this state and will return to the original arrangement state in the magnetic field, while releasing weak energy, which becomes radio signals. These many signals are detected by detectors and input into computers, and after computer processing and conversion, images are displayed on the screen. Nuclear magnetic resonance has been applied to imaging diagnosis of various systems in the body, and the best results are in the brain and spinal cord, heart and large blood vessels, joint bones, soft tissues and pelvic cavity. For cardiovascular diseases, not only can the anatomical changes of various chambers, large blood vessels and valves be observed, but also ventricular analysis can be performed for qualitative and semi-quantitative diagnosis. Multiple cross-sectional images can be made with high spatial resolution, showing the whole picture of the heart and lesions, and their relationship with surrounding structures, which is better than other X-ray imaging, two-dimensional ultrasound, radionuclide and CT examinations. When diagnosing brain and spinal cord lesions, coronal, sagittal and transverse images can be taken.

[0003] Metamaterials refer to artificial composite structures or composite materials with extraordinary physical properties that natural materials do not have. Through orderly structural design at the key physical scale of the material, it is possible to break through the limitations of certain apparent natural laws, thereby obtaining extraordinary material functions that exceed the ordinary properties inherent in nature. The properties and functions of metamaterials mainly come from their internal structure rather than the materials that constitute them. At present, the geometric shapes of existing metal artificial microstructures are open rings in the shape of "I" or "concave", but these structures cannot reduce the resonant frequency of metamaterials, nor can they achieve isotropy. Only by designing metal artificial microstructures with special geometric shapes can the artificial electromagnetic material reach a lower resonant frequency within a specific frequency band.

[0004] At present, the most commonly used MRI machines in clinical practice are divided into 1.5T, 3.0T and other high-field imagers according to the main magnetic field strength. Some patients are not suitable for high-field MRI due to the actual situation, such as the presence of implants such as steel plates and heart stents in the body, which will cause safety risks. However, the main magnetic field strength of ultra-low field MRI is low, which is expected to meet the requirements of these patients for MRI. Due to its low main magnetic field strength, the imaging signal is very weak, and it is necessary to provide a method that can enhance the imaging signal-to-noise ratio and obtain clear MRI images. Summary of the invention

[0005] The purpose of the present invention is to provide a domino volume metamaterial resonator for enhancing the signal-to-noise ratio of magnetic resonance imaging. By designing the number of spiral coils of the metamaterial unit, the width of the spiral coil, the gap between adjacent coils, the inner diameter of the spiral coil and the distance between the units, the resonant frequency is matched with the target frequency to achieve the enhancement of the signal-to-noise ratio of the magnetic resonance image. The technical solution of the present invention is as follows:

[0006] A domino volume metamaterial resonator for enhancing the signal-to-noise ratio of magnetic resonance imaging comprises a plurality of metamaterial units, each of which comprises a dielectric substrate, a spiral conductor and an external capacitor, the spiral conductor being arranged on the dielectric substrate, a gap existing between adjacent spiral coils, two ends of the spiral conductor being connected via an external capacitor, and the resonant frequency of the metamaterial unit matching a target frequency; a hollow domino volume metamaterial resonator is formed by stacking a plurality of metamaterial units axially.

[0007] Furthermore, the structural parameters of the metamaterial unit are determined through optimization design.

[0008] The structural parameters include the number of spiral coil turns, the gap between adjacent spiral coils, the width of the spiral coil, the inner diameter of the spiral coil, the thickness of the substrate and the value of the external capacitance.

[0009] Furthermore, the value of the external capacitor is determined according to the target frequency, so that the resonant frequency of the metamaterial unit matches the target frequency.

[0010] Furthermore, the spacing of the plurality of metamaterial units along the axis is determined according to the influence of the spacing between adjacent metamaterial units on the signal-to-noise ratio.

[0011] Furthermore, for the 70 mT magnetic resonance system, the determined structural parameters of the metamaterial unit are: the number of spiral coils n = 5, the gap between adjacent spiral wires g MR =1mm, spiral coil width w MR =1mm, inner diameter of spiral coil a MR-in =105mm, substrate thickness h MR =0.3mm, external capacitor C1 =0.4nF.

[0012] Furthermore, the distance between adjacent metamaterial units is D=12 mm. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 Diagram of the domino metamaterial resonator structure.

[0014] Figure 2 Diagram of the RF coil, metamaterial unit, and Model I system.

[0015] Figure 3 Spectral characteristics of the system.

[0016] Figure 4 Multi-voxel human wrist simulation model diagram and result diagram with and without domino metamaterial resonator, (a) Multi-voxel human wrist model diagram without domino metamaterial resonator; (b) Multi-voxel human wrist model diagram with domino metamaterial resonator; (c) Multi-voxel human wrist regional magnetic field diagram without domino metamaterial resonator; (d) Multi-voxel human wrist regional magnetic field diagram with domino metamaterial resonator; (e) Multi-voxel human wrist regional SAR without domino metamaterial resonator av.10g Figure; (f) Multi-voxel human wrist area SAR with domino metamaterial resonator av.10g picture.

[0017] Figure 5 SNR enhancement factor curve diagram, (a) SNR enhancement factor curve diagram along the white dotted line in the x direction; (b) SNR enhancement factor curve diagram along the white dotted line in the y direction. DETAILED DESCRIPTION

[0018] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0019] Figure 1 This is a structural diagram of the domino metamaterial resonator. Figure 2 Diagram of the RF coil, metamaterial unit, and Model I system. Figure 3 This is the spectrum characteristic diagram of the system. Figure 4 Figure 2 shows the simulation model and result diagrams of the multi-voxel human wrist with and without domino metamaterial resonators. (a) is the multi-voxel human wrist model diagram without domino metamaterial resonators; (b) is the multi-voxel human wrist model diagram with domino metamaterial resonators; (c) is the multi-voxel human wrist regional magnetic field diagram without domino metamaterial resonators; (d) is the multi-voxel human wrist regional magnetic field diagram with domino metamaterial resonators; (e) is the multi-voxel human wrist regional SAR diagram without domino metamaterial resonators. av.10g Figure 2: (f) shows the multi-voxel human wrist area SAR with domino metamaterial resonator. av.10g picture. Figure 5 (a) is the SNR enhancement factor curve along the white dotted line in the x direction; (b) is the SNR enhancement factor curve along the white dotted line in the y direction.

[0020] The specific process of this embodiment is as follows:

[0021] 1) Construct domino volume metamaterial units such as Figure 1As shown, it is composed of multiple metamaterial units, each of which is composed of a rectangular spiral copper wire, a dielectric substrate (FR-4) and an external capacitor C1. In actual use, the external capacitor C1 can be a variable capacitor, and its value should be determined according to the operating frequency (also called the target frequency) of different magnetic resonance systems. The method for making the rectangular spiral copper wire is: using relevant technology to draw a spiral copper wire pattern on the copper-clad surface of the dielectric substrate.

[0022] 2) Determine the structural parameters of the metamaterial unit, the number of spiral coils n = 5, the gap between adjacent wires g MR =1mm, spiral coil width w MR =1mm, inner diameter of spiral coil a MR-in =105mm, FR-4 substrate thickness h MR =0.3mm, external capacitor is C1=0.4nF;

[0023] 3) Analyze the effect of the spacing between adjacent metamaterial units on the signal-to-noise ratio. When the spacing D is in the range of 4mm-90mm, the signal-to-noise ratio enhancement factor at the center point increases first and then decreases with the increase of the spacing D. The maximum value of the SNR enhancement factor is 2.48 at D = 12mm, which is the optimal unit spacing of the resonator;

[0024] 4) According to the size of the RF coil, 18 metamaterial units are arranged along the y direction at the optimal spacing to construct a domino metamaterial resonator, such as Figure 1 As shown;

[0025] 5) Perform finite element simulations on a realistic multi-voxel human wrist model with and without domino metamaterial resonators, e.g. Figure 2 As shown;

[0026] 6) If Figure 3 As shown, the spectrum characteristic diagram of the system shows that the system resonates at 2.98MHz;

[0027] 7) Analysis of the magnetic field at the wrist in a 70mT MRI with and without the domino metamaterial resonator 10g-averaged specific absorption rate, SAR av.10g ) and signal-to-noise ratio (SNR) enhancement factor distribution, such as Figure 4 By comparison Figure 4 (c, d) It was found that the domino metamaterial resonator can significantly enhance the magnetic field. Figure 4 (e, f) show the SAR with and without the metamaterial resonator av.10g are far less than the safety limit. Figure 5As shown in (a), within the 70mm wrist area in the x-axis direction, the maximum signal-to-noise ratio is enhanced by 3.41 times, and the uniformity of the signal-to-noise ratio enhancement factor is as high as 93.7%. Figure 5 (b) shows that within the 80mm wrist area in the y-axis direction, the maximum SNR enhancement is 3.01 times, and the uniformity of the SNR enhancement factor reaches 90.7%. Therefore, the proposed domino metamaterial resonator can well enhance the SNR and has good SNR enhancement uniformity, which has great potential in improving the performance of 70mT MRI system.

[0028] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

[0029] The above are only embodiments of the present application and are not intended to limit the present application. For those skilled in the art, the present application may have various changes and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included within the scope of the claims of the present application.

Claims

1. A domino volume metamaterial resonator for enhancing the signal-to-noise ratio of magnetic resonance imaging, comprising a plurality of metamaterial units, each of which comprises a dielectric substrate, a spiral conductor and an external capacitor, the spiral conductor being arranged on the dielectric substrate, a gap existing between adjacent spiral coils, two ends of the spiral conductor being connected via an external capacitor, and the resonant frequency of the metamaterial unit matching the target frequency; a hollow domino volume metamaterial resonator is formed by stacking a plurality of metamaterial units axially.

2. The domino volume metamaterial resonator according to claim 1, characterized in that: Through optimized design, the structural parameters of the metamaterial unit are determined.

3. The domino volume metamaterial resonator according to claim 2, characterized in that: The structural parameters include the number of spiral coil turns, the gap between adjacent spiral coils, the width of the spiral coil, the inner diameter of the spiral coil, the thickness of the substrate and the value of the external capacitance.

4. The domino volume metamaterial resonator according to claim 1, characterized in that: The value of the external capacitor is determined according to the target frequency so that the resonant frequency of the metamaterial unit matches the target frequency.

5. The domino volume metamaterial resonator according to claim 1, characterized in that: The spacing of the plurality of metamaterial units along the axis is determined according to the influence of the spacing between adjacent metamaterial units on the signal-to-noise ratio.

6. The domino volume metamaterial resonator according to claim 1, characterized in that: For the 70 mT magnetic resonance system, the determined structural parameters of the metamaterial unit are: the number of spiral coils n = 5, the gap between adjacent spiral wires g MR =1mm, spiral coil width w MR =1mm, inner diameter of spiral coil a MR-in =105mm, substrate thickness h MR =0.3mm, external capacitor C1 =0.4nF.

7. The domino volume metamaterial resonator according to claim 6, characterized in that: The distance between adjacent metamaterial units is D=12 mm.

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