Series spiral circular polarization magnetic resonance radio frequency coil

Abstract

The invention discloses a serial spiral circular polarization magnetic resonance radio frequency coil, which relates to the technical field of magnetic resonance imaging and comprises a first spiral coil, a second spiral coil, a third spiral coil and a fourth spiral coil which are used for surrounding a to-be-detected part, the first spiral coil and the second spiral coil are oppositely arranged; the third spiral coil and the fourth spiral coil are oppositely arranged and are respectively arranged below the first spiral coil and the second spiral coil; the first spiral coil and the fourth spiral coil are connected in series and are used for accessing a first feed to form a first loop, the second spiral coil and the third spiral coil are connected in series and are used for accessing a second feed to form a second loop, and the first loop and the second loop can form a superimposed magnetic field. The serial spiral circular polarization magnetic resonance radio frequency coil provided by the invention is suitable for an ultra-low field MRI system, can generate a rotary circular polarization magnetic field along the axial direction of the coil, has high receiving sensitivity, and remarkably improves the imaging signal-to-noise ratio.

Description

Technical Field

[0001] The present invention relates to the technical field of nuclear magnetic resonance imaging, and particularly to a series-wound helical circularly polarized magnetic resonance radiofrequency coil. Background Art

[0002] Magnetic Resonance Imaging (MRI) is a high-resolution non-ionizing imaging technique widely used in the field of clinical medical imaging. As one of the key components in the MRI system, the radiofrequency coil is responsible for generating the radiofrequency field and receiving the magnetic resonance signal, which is thus related to the final imaging quality. There are mainly two ways to increase the Signal to Noise Ratio (SNR). One is to obtain more spin hydrogen atoms by increasing the static magnetic field B0, and the other method is to enhance the radiofrequency B1 field generated by the radiofrequency coil. However, since the increase in field strength will lead to risks such as metal ejection and an increase in Specific Absorption Rate (SAR), and the weight and usage cost of the high-field MRI system will also increase exponentially. Therefore, in some specific application scenarios, the advantages of ultra-low-field MRI in terms of low cost, low risk, and low weight are more prominent, but it also faces some challenges accordingly.

[0003] Due to the low field strength, the signal intensity of ultra-low-field MRI is weak, resulting in poor imaging quality. And because the main magnet of ultra-low-field MRI generates a vertical static magnetic field, which is different from the axial main magnetic field of traditional superconducting magnets, there are more requirements for the magnetic field direction of the radiofrequency coil. The birdcage coil applied to high-field MRI can generate a circularly polarized radiofrequency field. By using two orthogonally excited channels and controlling the phase difference to be 90°, the SNR can be increased times, and the transmission efficiency can be saved during the transmission stage. However, due to the vertical field direction of the main magnetic field in ultra-low-field MRI, the rotating polarization vector generated by the birdcage coil is no longer perpendicular to the main magnetic field, making it difficult to meet the actual application requirements; most of the existing ultra-low-field MRI uses single-channel radiofrequency coils, such as solenoid coils, saddle coils, or butterfly coils. Such linearly polarized radiofrequency coils have low transmission efficiency and limited receiving sensitivity; currently, the design of ultra-low-field orthogonal circularly polarized radiofrequency coils is still based on the combination of two coils with orthogonal magnetic field directions. For example, the combination of Helmholtz coils and saddle coils. The magnetic field in the orthogonal direction will cause losses, and it is difficult to solve the coupling problem between the two coils. Summary of the Invention

[0004] The purpose of the present invention is to provide a series-wound helical circularly polarized magnetic resonance radiofrequency coil to solve the problems existing in the above-mentioned prior art. It is applicable to ultra-low-field MRI systems, and can orthogonally generate a rotating circularly polarized magnetic field along the axis of the coil, with high receiving sensitivity and significantly improving the imaging SNR.

[0005] To achieve the above object, the present invention provides the following solutions:

[0006] The present invention provides a series-connected spiral circularly polarized magnetic resonance radio frequency coil, comprising a body, the body including a first spiral coil, a second spiral coil, a third spiral coil, and a fourth spiral coil for surrounding a part to be detected; the first spiral coil and the second spiral coil are oppositely arranged; the third spiral coil and the fourth spiral coil are oppositely arranged and are respectively disposed below the first spiral coil and the second spiral coil; the first spiral coil is serially connected to the fourth spiral coil and is used for accessing a first feed to form a first loop, the second spiral coil is serially connected to the third spiral coil and is used for accessing a second feed to form a second loop, and the first loop and the second loop can form a superimposed magnetic field.

[0007] Preferably, variable tuning capacitors are serially connected on both the first loop and the second loop.

[0008] Preferably, the first spiral coil, the second spiral coil, the third spiral coil, and the fourth spiral coil have the same size, the winding directions of the first spiral coil and the third spiral coil are opposite, and the winding directions of the second spiral coil and the fourth spiral coil are opposite.

[0009] Preferably, the first spiral coil and the fourth spiral coil are connected end to end through a first connection line to form the first loop, and the second spiral coil and the third spiral coil are adjacent end to end through a second connection line to form the second loop; the first connection line is provided with the variable tuning capacitor and a first interface for accessing the first feed, and the second connection line is provided with the variable tuning capacitor and a second interface for accessing the second feed.

[0010] Preferably, the first interface and the second interface are respectively provided on the upper first connection line and the upper second connection line, and the lower first connection line and the lower second connection line are used for accessing the variable tuning capacitor.

[0011] Preferably, the phase difference between the first feed and the second feed is 90°.

[0012] Preferably, when the first spiral coil, the second spiral coil, the third spiral coil, and the fourth spiral coil are unfolded in a plane, they are all square.

[0013] Preferably, the number of turns of the first spiral coil, the second spiral coil, the third spiral coil, and the fourth spiral coil are the same.

[0014] Preferably, the first helical coil, the second helical coil, the third helical coil, and the fourth helical coil are all made of copper material.

[0015] Preferably, the body is arranged in a cylindrical shape, and the first helical coil, the second helical coil, the third helical coil, and the fourth helical coil have the same curvature.

[0016] The present invention has achieved the following technical effects compared with the prior art:

[0017] The series-connected helical circularly polarized magnetic resonance radio frequency coil provided by the present invention is composed of a first helical coil, a second helical coil, a third helical coil, and a fourth helical coil arranged around. The helical coils at the diagonal positions are respectively connected in series to form two series-connected helical coils. The series connection and connection to the corresponding feed make the helical coil form an effective current loop, forming a in-phase uniform and orthogonally superimposable magnetic field inside the coil, which conforms to the generation principle of the circularly polarized magnetic field, and can achieve a circularly polarized magnetic field in the plane along the axial direction of the coil. The series-connected helical coil structure design significantly improves the radio frequency field intensity, penetration depth, and uniformity of the imaging central region, and can make the coupling between the two channels lower than -10 dB. The design method of the orthogonal circularly polarized radio frequency coil for the ultra-low field magnetic resonance imaging system has a higher magnetic field utilization rate than the traditional linearly polarized or multi-channel radio frequency coil, and can significantly improve the imaging signal-to-noise ratio. Description of the Drawings

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required to be used in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0019] Figure 1 Schematic diagram of the series-connected helical circularly polarized magnetic resonance radio frequency coil provided for Embodiment 1;

[0020] Figure 2 Curve of the reflection coefficient of the series-connected helical circularly polarized magnetic resonance radio frequency coil provided for Embodiment 1 varying with frequency;

[0021] Figure 3 Curve of the coupling degree between the two-channel ports of the series-connected helical circularly polarized magnetic resonance radio frequency coil provided for Embodiment 1;

[0022] Figure 4 Curve of the magnetic field measured by the magnetic field probe at the center position of the coil of the series-connected helical circularly polarized magnetic resonance radio frequency coil provided for Embodiment 1 varying with frequency;

[0023] Figure 5For the series - helical circularly - polarized magnetic resonance radio - frequency coil provided in Embodiment 1 Magnetic field distribution diagram;

[0024] Figure 6 One - dimensional Magnetic field distribution curve along the central axis of the series - helical circularly - polarized magnetic resonance radio - frequency coil provided in Embodiment 1.

[0025] In the figure: 1 - body; 11 - first helical coil; 12 - second helical coil; 13 - third helical coil; 14 - fourth helical coil; 15 - variable tuning capacitor; 16 - first connecting wire; 17 - second connecting wire; 18 - first interface; 19 - second interface; Detailed implementation manners

[0026] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0027] The object of the present invention is to provide a series - helical circularly - polarized magnetic resonance radio - frequency coil to solve the problems existing in the above - mentioned prior art, which is applicable to an ultra - low - field MRI system, can generate a rotating circularly - polarized magnetic field along the coil axis, has high receiving sensitivity, and significantly improves the imaging signal - to - noise ratio.

[0028] In order to make the above - mentioned objects, features, and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific implementation manners.

[0029] Embodiment 1

[0030] This embodiment provides a series - helical circularly - polarized magnetic resonance radio - frequency coil. Please refer to Figure 1 , which includes a body 1. The body 1 includes a first helical coil 11, a second helical coil 12, a third helical coil 13, and a fourth helical coil 14 for surrounding the part to be detected; the first helical coil 11 and the second helical coil 12 are oppositely arranged; the third helical coil 13 and the fourth helical coil 14 are oppositely arranged and are respectively placed below the first helical coil 11 and the second helical coil 12; the first helical coil 11 and the fourth helical coil 14 are connected in series and are used to access the first feed to form a first loop, the second helical coil 12 and the third helical coil 13 are connected in series and are used to access the second feed to form a second loop, and the first loop and the second loop can form a superimposed magnetic field.

[0031] It is composed of the first spiral coil 11, the second spiral coil 12, the third spiral coil 13, and the fourth spiral coil 14 arranged around. The spiral coils at the diagonal positions are respectively connected in series and combined into two sets of series spiral coils. The series connection and connection to the corresponding feed make the spiral coils form an effective current loop, forming a homogeneous in-phase and orthogonally superimposable magnetic field on the axial plane inside the coil, which conforms to the generation principle of circularly polarized magnetic field and can realize the circularly polarized magnetic field in the axial plane of the coil. The series spiral coil structure design significantly improves the radio frequency field strength, penetration depth, and uniformity of the imaging central region, and can make the coupling between the two sets of channels lower than -10 dB. The design method of the orthogonal circularly polarized radio frequency coil for the ultra-low field magnetic resonance imaging system has a higher magnetic field utilization rate than the traditional linearly polarized or multi-channel radio frequency coil, and can significantly improve the imaging signal-to-noise ratio.

[0032] In an alternative embodiment of the present embodiment, preferably, variable tuning capacitors 15 are connected in series on both the first loop and the second loop to adjust the resonance frequency of the coil to meet the applications in different scenarios.

[0033] In an alternative embodiment of the present embodiment, preferably, the first spiral coil 11, the second spiral coil 12, the third spiral coil 13, and the fourth spiral coil 14 have the same size. The winding directions of the first spiral coil 11 and the third spiral coil 13 are opposite, and the winding directions of the second spiral coil 12 and the fourth spiral coil 14 are opposite; among them, the winding directions of the first spiral coil 11 and the fourth spiral coil 14 are the same and are symmetrically arranged so that the first loop and the second loop form a homogeneous in-phase and superimposable magnetic field.

[0034] In an alternative embodiment of the present embodiment, preferably, the first spiral coil 11 and the fourth spiral coil 14 are connected end to end through the first connecting line 16 to form the first loop, and the second spiral coil 12 and the third spiral coil 13 are adjacent end to end through the second connecting line 17 to form the second loop; the first connecting line 16 is provided with a variable tuning capacitor 15 and a first interface 18 for accessing the first feed, and the second connecting line 17 is provided with a variable tuning capacitor 15 and a second interface 19 for accessing the second feed. Specifically, the head end of the first spiral coil 11 and the tail end of the fourth spiral coil 14, as well as the tail end of the first spiral coil 11 and the head end of the fourth spiral coil 14, are both connected through the first connecting line 16, and the head end of the second spiral coil 12 and the tail end of the third spiral coil 13, as well as the tail end of the second spiral coil 12 and the head end of the third spiral coil 13, are both connected through the second connecting line 17.

[0035] In an alternative embodiment of the present example, preferably, a first interface 18 and a second interface 19 are respectively provided on the upper first connection line 16 and the upper second connection line 17, and a variable tuning capacitor 15 is to be connected to the lower first connection line 16 and the lower second connection line 17; symmetrically arranged so that the first loop and the second loop form a magnetic field that is in-phase, uniform, and superimposable. In addition, a first interface 18 and a second interface 19 may also be respectively provided on the lower first connection line 16 and the lower second connection line 17, and a variable tuning capacitor 15 is to be connected to the upper first connection line 16 and the upper second connection line 17.

[0036] In an alternative embodiment of the present example, preferably, the phase difference between the first feed and the second feed is 90°, so as to achieve a rotating circularly polarized radio frequency magnetic field in the axial plane of the body.

[0037] In an alternative embodiment of the present example, preferably, after the first spiral coil 11, the second spiral coil 12, the third spiral coil 13, and the fourth spiral coil 14 are unfolded in a plane, they are all square. In addition, other shapes such as circular can be selected according to needs during actual application.

[0038] In an alternative embodiment of the present example, preferably, the number of turns of the first spiral coil 11, the second spiral coil 12, the third spiral coil 13, and the fourth spiral coil 14 are the same, which is convenient for forming a magnetic field that is in-phase, uniform, and superimposable, and can significantly improve the signal-to-noise ratio.

[0039] In an alternative embodiment of the present example, preferably, the first spiral coil 11, the second spiral coil 12, the third spiral coil 13, and the fourth spiral coil 14 are all made of copper material, which can meet the requirements of conductivity and thermal stability.

[0040] In an alternative embodiment of the present example, preferably, the body 1 is arranged in a cylindrical shape, and the curvature of the first spiral coil 11, the second spiral coil 12, the third spiral coil 13, and the fourth spiral coil 14 is the same. Specifically, it is arranged in a cylindrical shape to fit the imaging detection of the part to be detected, such as the head, so as to meet the imaging requirements of a large aperture.

[0041] Specifically, to fully demonstrate the effect of the series - helical circularly - polarized magnetic resonance radio - frequency coil, i.e., the body, provided in this embodiment, the length of each helical coil is 360 mm, the width is 90 mm, the width of the helical wire is 4 mm, the number of turns of the helical coil is 5 turns, the pitch between turns of the helical wire is 4 mm, the distance between the upper and lower layers of helical coils is 20 mm, the four square helical coils are conformally arranged in a barrel - shaped bend with a radius of 130 mm. The capacitance value of the variable tuning capacitor 15 is set to 400 pF, enabling the body 1 to resonate at 2.98 MHz, corresponding to the Larmor resonance frequency of a 70 mT ultra - low - field MRI system. The phase difference between the two feeding and exciting ports is 90°, realizing a rotating circularly - polarized radio - frequency magnetic field in the plane along the axis of the coil.

[0042] As Figure 2 shown, it is the curve of the reflection coefficient of the body versus frequency. Due to the structural symmetry and the same tuning capacitor value, the two feeding ports achieve the same S - parameter (return loss) distribution. The radio - frequency coil realizes a good match between the port and the signal source at a frequency of 2.98 MHz, and the reflection coefficient S11 reaches below - 16 dB, meaning that the coil effectively resonates at the Larmor frequency required for a 70 mT magnetic - field - strength MRI system, and a higher quality factor will achieve higher acquisition signal sensitivity.

[0043] As Figure 3 shown, it is the forward transmission coefficient S21 between the two feeding ports of the body. The coupling of the two series - helical coils can be quantitatively analyzed through the S21 value at the resonance frequency. It can be seen from the figure that the S21 peak between the two feeding ports is below - 10 dB at a frequency of 2.98 MHz, proving that the port isolation degree of the two series - helical coils is relatively high, the coupling interference of the electromagnetic field can be ignored, and it can ensure a uniform magnetic - field distribution inside the series - helical circularly - polarized magnetic resonance radio - frequency coil.

[0044] As Figure 4 shown, it is the curve of the magnetic field measured by the magnetic - field probe placed at the center of the body versus frequency. The result shows that the coil resonates at a frequency of 2.98 MHz, and at the same time, magnetic - field components in the X - polarization direction and the Y - polarization direction are excited, verifying the circularly - polarized performance of the coil, effectively realizing the circularly - polarized magnetic - field working mode under an ultra - low - field system, getting rid of the limitation of the traditional circularly - polarized mode of ultra - low - field coils that requires a combination of two coils with orthogonal magnetic - field distributions, and providing new ideas and methods for the design of ultra - low - field circularly - polarized radio - frequency coils.

[0045] As Figure 5 shown, it is the magnetic - field distribution of the body in the sagittal plane and the cross - sectional plane. The result is normalized to an input power of 1 W, and a strong magnetic - field distribution can be generated inside the coil. The field rotates within the axial plane of the coil, demonstrating that the coil effectively achieves a circularly polarized magnetic field working mode. Due to the series-connected helical coil structure within the inner region of the coil center, the magnetic field becomes more uniform after superposition, and the high-intensity region can cover the detection part, enabling large-aperture and high-sensitivity detection applications. Based on the Biot-Savart law calculation, within the region of interest inside the coil the average field value can reach 5.4 μT, within the white dashed box in the central region the field uniformity reaches 89.2%. Compared with a 5-turn linearly polarized Helmholtz coil of the same size, the average field value inside the RF coil is 2.3 times higher than that of the Helmholtz coil, the signal reception sensitivity is higher, and the circularly polarized working mode also makes the emission efficiency of this coil higher.

[0046] As Figure 6 shown, it is a one-dimensional field distribution curve of the body along the central axis of the coil. It can be observed that within the central region inside the coil, there is a higher field intensity and uniformity compared to the edge. The series-connected helical coil structure design can excite a magnetic field with a strong penetration depth, and due to the circularly polarized design, it can further improve the image signal-to-noise ratio of the ultra-low field MRI system.

[0047] In this invention, specific examples are used to elaborate on the principle and implementation manner of the invention. The description of the above embodiments is only used to help understand the method of the invention and its core idea; at the same time, for those of ordinary skill in the art, according to the idea of the invention, there will be changes in the specific implementation manner and application scope. In summary, the content of this specification should not be construed as a limitation to the invention.

Claims

1. A series-connected spiral circularly polarized magnetic resonance radiofrequency coil, characterized in that: It includes a body (1), and the body (1) includes a first spiral coil (11), a second spiral coil (12), a third spiral coil (13) and a fourth spiral coil (14) for surrounding the part to be detected; the first spiral coil (11) and the second spiral coil (12) are oppositely arranged; the third spiral coil (13) and the fourth spiral coil (14) are oppositely arranged and are respectively placed below the first spiral coil (11) and the second spiral coil (12); the first spiral coil (11) and the fourth spiral coil (14) are connected in series and used for accessing a first feed to form a first loop, the second spiral coil (12) and the third spiral coil (13) are connected in series and used for accessing a second feed to form a second loop, and the first loop and the second loop can form a superimposed magnetic field.

2. The series-wound helical circularly polarized magnetic resonance radio frequency coil according to claim 1, wherein: A variable tuning capacitor (15) is connected in series on both the first loop and the second loop.

3. The series-connected spiral circularly polarized magnetic resonance radio frequency coil according to claim 1, wherein: The first spiral coil (11), the second spiral coil (12), the third spiral coil (13) and the fourth spiral coil (14) have the same size, the winding directions of the first spiral coil (11) and the third spiral coil (13) are opposite, and the winding directions of the second spiral coil (12) and the fourth spiral coil (14) are opposite.

4. The series-wound helical circularly polarized magnetic resonance radio frequency coil according to claim 2, characterized in that: The first spiral coil (11) and the fourth spiral coil (14) are connected end to end through a first connecting wire (16) to form the first loop, and the second spiral coil (12) and the third spiral coil (13) are connected end to end through a second connecting wire (17) to form the second loop; the first connecting wire (16) is provided with the variable tuning capacitor (15) and a first interface (18) for accessing the first feed, and the second connecting wire (17) is provided with the variable tuning capacitor (15) and a second interface (19) for accessing the second feed.

5. The series-connected spiral circularly polarized magnetic resonance radio frequency coil according to claim 4, wherein: The first interface (18) and the second interface (19) are respectively arranged on the upper first connecting wire (16) and the upper second connecting wire (17), and the lower first connecting wire (16) and the lower second connecting wire (17) are used for accessing the variable tuning capacitor (15).

6. The series-connected spiral circularly polarized magnetic resonance radio frequency coil according to claim 4, wherein: The phase difference between the first feed and the second feed is 90°.

7. The series spiral circularly polarized magnetic resonance radio frequency coil according to claim 4, wherein: After the first spiral coil (11), the second spiral coil (12), the third spiral coil (13) and the fourth spiral coil (14) are unfolded in a plane, they are all square.

8. The series-connected spiral circularly polarized magnetic resonance radio frequency coil according to claim 7, wherein: The number of turns of the first spiral coil (11), the second spiral coil (12), the third spiral coil (13) and the fourth spiral coil (14) are the same.

9. The series helical circularly polarized magnetic resonance radio frequency coil according to claim 1, wherein: The first spiral coil (11), the second spiral coil (12), the third spiral coil (13) and the fourth spiral coil (14) are all made of copper material.

10. The series-connected spiral circularly polarized magnetic resonance radio frequency coil according to claim 1, wherein: The body (1) is arranged in a cylindrical shape, and the first spiral coil (11), the second spiral coil (12), the third spiral coil (13) and the fourth spiral coil (14) have the same curvature.

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