Magnetic resonance radio frequency coil for improving magnetic field uniformity

Abstract

The invention discloses a magnetic resonance radio frequency coil for improving magnetic field uniformity, and relates to the technical field of magnetic resonance imaging. According to the magnetic resonance radio frequency coil for improving the magnetic field uniformity, the semicircular copper ring structures loaded at the two ends of the base coil are optimally designed, surface current distribution can be effectively dispersed, and uneven magnetic field distribution caused by the fact that current is concentrated near an excitation source is avoided. Due to the addition of the special semicircular structure, the equivalent capacitance values at the two ends of the coil are increased. The charges are gathered on the semicircular structure to form a current loop, and a more uniform magnetic field and an electric field can be excited. The design method provided by the invention can effectively improve the defect of non-uniform magnetic field distribution of the surface coil, has high receiving sensitivity, and improves the imaging definition.

Description

Technical Field

[0001] The present invention relates to the field of nuclear magnetic resonance imaging technology, and particularly to a magnetic resonance radio frequency coil for improving magnetic field uniformity. Background Art

[0002] Magnetic Resonance Imaging (MRI) is a non-ionizing medical imaging technology with excellent resolution and soft tissue contrast, capable of creating detailed images of the internal structure and function of the human body. Compared with other non-invasive medical imaging technologies, it has the advantages of no radioactivity, three-dimensional imaging, and high spatial resolution. As one of the key performance indicators of a magnetic resonance system, the imaging quality can be improved by optimizing the radio frequency field to enhance the signal-to-noise ratio of the echo signals obtained during scanning, thereby obtaining better imaging quality.

[0003] As a key component of an MRI system, the radio frequency coil functions to excite the atomic nuclei in the body and then receive the weak signals emitted by these atomic nuclei. The signals received by the radio frequency coil can be converted into electrical signals for creating images. The radio frequency coils used for MRI are mainly divided into body coils and surface coils. The body coil can excite a more uniform magnetic field, but has a relatively low signal-to-noise ratio. The surface coil, due to its smaller size, has more excellent reception sensitivity and signal-to-noise ratio, but the magnetic field uniformity is relatively poor. Therefore, in order to obtain higher-quality magnetic resonance images, a radio frequency coil with both signal-to-noise ratio and magnetic field uniformity is needed. Summary of the Invention

[0004] The purpose of the present invention is to provide a magnetic resonance radio frequency coil for improving magnetic field uniformity, which can be applied to a 1.5T MRI system. Based on optimizing the surface current distribution, the coil structure is designed. The coil has a high Q value, can generate a uniform magnetic field, and has a low SAR value. It can effectively improve the imaging quality and reduce the risk of overheating or even burning.

[0005] To achieve the above purpose, the present invention provides the following solution: A magnetic resonance radio frequency coil for improving magnetic field uniformity, comprising: The radio frequency surface coil is composed of copper wire, with four 45° chamfers provided on the rectangular copper ring and semi-circular copper ring structures added at both short sides; Two slits are symmetrically provided on each of the two long sides of the rectangular copper ring, two slits are provided on the right short side of the rectangular copper ring, and one slit is provided on the left short side of the rectangular copper ring; Capacitors are added to the five slits, and the resonance frequency of the coil is accurately adjusted by adjusting the capacitance value to improve the tuning efficiency; A discrete feed port with a 50-ohm impedance match is connected to the slit on the left short side of the rectangular copper ring; Optionally, the length of the rectangular copper ring of the radio frequency coil is 280 mm, the width of the rectangular copper ring is 60 mm, the width of the copper wire excluding the 45° chamfer is 6 mm, and the width of the crack is 2 mm; Optionally, the radius of the semi-circular copper ring is 24 mm, and the width of the semi-circular copper ring is 6 mm; According to the specific embodiments provided by the present invention, the following technical effects are disclosed: By adding a semi-circular copper ring structure at both short sides of the rectangular copper ring, the present invention can effectively improve the uniformity of the radio frequency magnetic field. The semi-circular copper ring structure can significantly solve the problem of uneven surface current distribution at both ends of the coil caused by unilateral excitation, thereby reducing the longitudinal electric field component, lowering the SAR value, and improving the imaging quality. Description of the Drawings

[0006] 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 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.

[0007] Figure 1 Schematic diagram of the structure of the magnetic resonance radio frequency coil for improving magnetic field uniformity provided by the embodiment of the present invention; Figure 2 Schematic diagram of the loading capacitor of the magnetic resonance radio frequency coil for improving magnetic field uniformity provided by the embodiment of the present invention; Figure 3 Schematic diagram of the loading model of the magnetic resonance radio frequency coil for improving magnetic field uniformity provided by the embodiment of the present invention; Figure 4 Graph of the port reflection coefficient of the magnetic resonance radio frequency coil for improving magnetic field uniformity provided by the embodiment of the present invention varying with frequency; Figure 5 Comparison of the surface current distribution diagrams of the magnetic resonance radio frequency coil for improving magnetic field uniformity provided by the embodiment of the present invention and the traditional 1.5T square loop radio frequency coil operating at 64 MHz; Figure 6 Comparison of the B1 - field distribution diagrams along the YOZ section of the model of the magnetic resonance radio frequency coil for improving magnetic field uniformity provided by the embodiment of the present invention and the traditional 1.5T square loop radio frequency coil operating at 64 MHz; Figure 7The SAR value distribution diagram along the YOZ section of the model for the magnetic resonance radio frequency coil provided by the embodiment of the present invention for improving magnetic field uniformity when operating at 64 MHz in a 1.5T magnetic resonance system.

[0008] Symbol description: C1 - C7 are the capacitors added in the cracks. Specific implementation manner

[0009] 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 creative efforts shall fall within the protection scope of the present invention.

[0010] To make the above objects, features, and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below in conjunction with the drawings and specific implementation manners.

[0011] In recent years, methods for improving the magnetic field uniformity using radio frequency coils in high - field MRI have been widely studied. However, in 1.5T MRI, it mostly focuses on improving the receiving sensitivity and penetration depth of the coil, or improving the magnetic field by setting metamaterial structures. However, the manufacturing process of metamaterials is complex and tuning is difficult. It is necessary to propose a coil that can effectively improve the radio frequency magnetic field uniformity, and has a high structural integration and is convenient for processing and optimization. As Figure 1 shown, this paper proposes a magnetic resonance radio frequency coil for improving magnetic field uniformity.

[0012] Step 1: Construct a radio frequency coil structure with a rectangular copper ring loaded with semi - circular copper rings at both ends.

[0013] The radio frequency surface coil is composed of copper wires. Four 45° chamfers are set on the rectangular copper ring, and semi - circular copper ring structures are added at the positions of the short sides at both ends; Two cracks are symmetrically set on each of the two long sides of the rectangular copper ring, two cracks are set on the left short side of the rectangular copper ring, and one crack is set on the right short side of the rectangular copper ring; Capacitors are added and connected in the five cracks, and the resonance frequency of the coil is accurately adjusted by adjusting the capacitance value to improve the tuning efficiency; A discrete feeding port with a 50 - ohm impedance match is connected to the crack on the left short side of the rectangular copper ring; In this embodiment, the length of the rectangular copper ring of the radio frequency coil is 280 mm, the width of the rectangular copper ring is 60 mm, the width of the copper wire except at the 45° chamfers is 6 mm, and the width of the crack is 2 mm; In this embodiment, the radius of the semi-circular copper ring is 24 mm, and the width of the semi-circular copper ring is 6 mm; Step 2: Set up a cuboid model to simulate the human chest cavity.

[0014] As Figure 3 shown, in this embodiment, the length of the cuboid model is set to 330 mm, the width is 230 mm, and the thickness is 140 mm; the dielectric constant of the model is 58.2, and the conductivity is 0.77 Siemens / m; the rectangular model is placed 20 mm away from the coil; Step 3: Add a capacitor at the crack and adjust the resonance frequency of the RF coil to 63.8 MHz.

[0015] In this embodiment, as Figure 2 shown, add the capacitor to the crack, and according to the required operating frequency of 63.8 MHz, set the capacitance values to C1 = 47 pF, C2 = C3 = C5 = C6 = C7 = 300 pF, and C4 = 90 pF respectively.

[0016] As Figure 4 shown, for the echo loss curve of the RF coil, the coil resonates at 63.8 MHz, and the reflection coefficient S 11 is -33.41 dB. The coil has a high quality factor, which means higher reception sensitivity and can better receive magnetic resonance signals.

[0017] Step 4: Analyze the surface current distribution of the RF coil.

[0018] As Figure 5 shown, compared with the traditional 1.5T square loop RF coil, the surface current distribution of the magnetic resonance RF coil for improving magnetic field uniformity provided by the embodiment of the present invention is more uniform; by setting the semi-circular structures at both ends, the surface current distribution can be effectively dispersed, avoiding the uneven magnetic field distribution caused by the current concentration near the excitation source. Due to the addition of this special semi-circular structure, the equivalent capacitance values at both ends of the coil increase. Charges accumulate on the semi-circular structures to form a current loop, which can excite a more uniform electric field.

[0019] Step 4: Analyze the B1 - field distribution of the RF coil.

[0020] As Figure 6 shown, compared with the traditional 1.5T square loop RF coil, the B1 -The field distribution is more uniform in the shallow surface area of the model, especially in the areas at both ends of the coil. Due to the addition of the semi-circular copper rings at both ends, the distribution of the surface current at both ends of the coil is optimized, thereby reducing the attenuation degree of the magnetic field at both ends of the coil. The results show that the magnetic resonance radio frequency coil provided by the embodiment of the present invention for improving the magnetic field uniformity generates a uniform and large coverage area B1 - field.

[0021] Step 5: Analyze the SAR distribution of the radio frequency coil.

[0022] As Figure 7 shown, the SAR of the magnetic resonance radio frequency coil provided by the embodiment of the present invention for improving the magnetic field uniformity is mainly distributed at both ends of the model, and the maximum 10g average SAR value is 1.36 W / kg. The surface charge distribution of the coil is uniform, effectively dispersing the longitudinal electric field component, thereby having a lower SAR value and reducing the risk of burning or even scalding in practical applications.

[0023] 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 can 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 be accorded the widest scope consistent with the principles and novel features disclosed herein.

[0024] 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 can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included within the scope of the claims of the present application.

Claims

1. A magnetic resonance radio frequency coil for improving magnetic field uniformity, characterized in that, Comprising: The radio frequency surface coil is composed of copper wire. Four chamfers are provided on the rectangular copper ring, and semi-circular copper ring structures are added at the positions of the two short sides at both ends. Two slits are symmetrically provided on each of the two long sides of the rectangular copper ring, two slits are provided on the right short side of the rectangular copper ring, and one slit is provided on the left short side of the rectangular copper ring; Capacitors are added to the five slits, and the resonance frequency of the coil is accurately adjusted by adjusting the capacitance value to improve the tuning efficiency; A feed port is connected to the slit on the left short side of the rectangular copper ring; The overall size of the magnetic resonance radio frequency coil for enhancing magnetic field uniformity is determined by the size of the detection area; Through the above steps, a magnetic resonance radio frequency line for enhancing magnetic field uniformity is designed.

2. The magnetic resonance radio frequency coil for enhancing magnetic field uniformity according to claim 1, wherein Perform surface current distribution analysis, radio frequency field distribution analysis and safety evaluation on the proposed magnetic resonance radio frequency coil for enhancing magnetic field uniformity, including: Construct a cuboid model to simulate the human chest cavity, and set the conductivity, permittivity and density of the cuboid model; Design a traditional rectangular copper ring radio frequency coil with a size close to that of the radio frequency coil as a control; Place the radio frequency coil 20 mm away from the surface of the rectangular phantom; Compare the surface current distributions of the radio frequency coil and the traditional rectangular copper ring radio frequency coil with a similar size; B1 of the radio frequency coil - Field distribution analysis to verify the enhanced effect of magnetic field uniformity; Calculate the 10g average SAR distribution and the maximum 10g average SAR value of the magnetic resonance radio frequency coil for enhancing magnetic field uniformity, and conduct a safety evaluation.

3. The magnetic resonance radio frequency coil for magnetic field uniformity according to claim 2, wherein, Set the length of the model cuboid model to 330 mm, the width to 230 mm, and the thickness to 140 mm; the permittivity of the model is 58.2 and the conductivity is 0.77 Siemens / m; place the rectangular model 20 mm away from the coil.

4. The magnetic resonance radio frequency coil for magnetic field uniformity according to claim 1, wherein The length of the rectangular copper ring of the radio frequency coil is 280 mm, the width of the rectangular copper ring is 60 mm, the width of the copper wire except at the 45° chamfer is 6 mm, and the width of the slit is 2 mm; the radius of the semi-circular copper ring is 24 mm and the width of the semi-circular copper ring is 6 mm.

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