Composite four-channel receiving coil for movable magnetic resonance imaging and imaging equipment

Abstract

The invention discloses a composite four-channel receiving coil for movable magnetic resonance imaging and imaging equipment, the four-channel receiving coil comprises two breast sub-coils and two far-end sub-coils, and the breast sub-coils with multiple turns in a cap-shaped structure are used for imaging a breast area. A multi-turn far-end coil of a butterfly-shaped structure is adopted for imaging an upper root area of a mammary gland, and two sub-coils are orthogonally arranged on corresponding wiring structures respectively and used for mammary gland magnetic resonance imaging in a vertical magnetic field; according to the composite four-channel receiving coil, a pair of cap-shaped asymmetric wiring structures is adopted as a winding framework, a group of breast sub-coils and a group of far-end coils are wound respectively to cover a breast and a breast root area, and decoupling between the breast sub-coils is realized by designing lumped element types and parameter values in a decoupling circuit. According to the ultra-low field mammary gland imaging method, ultra-low field mammary gland imaging with high precision and large imaging range under the vertical magnetic field is realized, and certain reference can be provided for related research in the future.

Description

Technical Field

[0001] This invention relates to the structure of a magnetic resonance radio frequency receiving coil, and more specifically to a composite four-channel receiving coil and imaging device for portable magnetic resonance imaging. Background Technology

[0002] Ultra-low field magnetic resonance imaging (MRI) generally refers to MRI technology with a main magnetic field below 0.1T, resulting in lighter weight and lower energy consumption. Advances in this imaging technology have driven the lightweighting and portability of MRI equipment, making it a potential routine screening device for diseases such as breast cancer. However, because ultra-low field MRI typically uses a permanent magnet structure to provide a main magnetic field perpendicular to the human body, commonly available commercial breast surface coils are no longer suitable for ultra-low field MRI systems, and it is difficult to achieve accurate imaging of the entire breast area, necessitating a redesign of the coil structure.

[0003] Currently, there is a lack of research on breast coils for use in portable ultra-low field magnetic resonance imaging (MRI) devices. Existing research on MRI breast coils is usually based on devices with medium to low field strength horizontal main magnetic fields, which cannot provide a reference for receiving coils with vertical main magnetic fields. Furthermore, in research on ultra-low field MRI, there are no reports on the design and application of radio frequency coils for breast imaging. Therefore, conducting research on ultra-low field MRI breast imaging coils is valuable. Summary of the Invention

[0004] Purpose of the invention: The purpose of this invention is to provide a composite four-channel receiving coil for portable magnetic resonance imaging, so as to achieve high-precision imaging of the breast and the root region of the breast on a portable ultra-low field magnetic resonance device with a vertical main magnetic field.

[0005] Technical solution: The composite four-channel receiving coil of the present invention includes two breast sub-coils and two distal terminal coils. The multi-turn breast sub-coils with a cap-shaped structure are used for imaging the breast region, and the multi-turn distal terminal coils with a butterfly-shaped structure are used for imaging the upper root region of the breast. The two types of sub-coils are orthogonally arranged on their respective wiring structures for breast magnetic resonance imaging under a vertical magnetic field.

[0006] Optionally, the four-channel receiving coil is wired on two cap-shaped asymmetric wiring structures. Each cap-shaped asymmetric wiring structure is wound with a breast sub-coil and a far-terminal coil. The two cap-shaped asymmetric wiring structures are arranged symmetrically with a set angle and center distance based on imaging requirements.

[0007] Optionally, the bottom edge of the cap-shaped asymmetrical wiring structure is stretched to a radius greater than or equal to the target area radius of the breast sub-coil. The length of the cap-shaped edge is doubled to form the cap-shaped edge, and the opposite edge is stretched to a set length to form the cap brim structure. The loop wiring of the breast sub-coil is carried out on the extended cap-shaped edge to suppress the non-uniformity of the transmission field caused by the receiving coil. The far terminal coil wiring is carried out on the cap brim structure.

[0008] Optionally, the breast sub-coil adopts a multi-turn wiring structure after uniformity optimization: that is, on the hemispherical structure of the cap-shaped asymmetric wiring structure that fits the shape of the breast, it is divided into several wiring paths at equal intervals. Based on the optimization results of the received magnetic field uniformity and the total length limit of the breast sub-coil, the number of coil turns on each wiring path is determined to obtain the wiring scheme of the breast sub-coil.

[0009] Optionally, the calculation methods for the optimized results of the receiving magnetic field uniformity include:

[0010] Calculate the minimum horizontal non-uniformity δ of the synthesized RF field of the coil wound on each wiring path within the target optimization region:

[0011]

[0012] Where m represents the objective optimization region being divided into m smaller regions, B m Let [B] be the magnetic field strength in the m-th small region. m [B] represents the horizontal component dataset within the target optimization region based on coil combinations wound along n wiring paths, specifically the transverse radio frequency component perpendicular to the direction of the main magnetic field B0 of the magnetic resonance system. m The expression is:

[0013]

[0014] Where n is the number of wiring paths divided on each hemispherical skeleton, and matrix [B mn ] represents the magnetic field strength dataset within the target optimization region obtained from the simulation results of a single-turn coil on the nth wiring path, [k n [] represents the number of turns of the coil wound on the nth wiring path during the optimization process.

[0015] Optionally, the horizontal component B can be used in the optimization solution. y Or take the modulus value B xy Solve for B mn Thus, the number of coil turns [k] on the nth wiring path is obtained. n The optimal combination is the wiring scheme for the breast sub-coil.

[0016] Optionally, the total length of the breast sub-coil is limited to:

[0017] The total length of each breast sub-coil is less than the critical wavelength that produces the antenna effect, as expressed in the following formula:

[0018]

[0019] Where λ is the electromagnetic wavelength corresponding to the magnetic resonance frequency, [S n [k] represents the total length of the coils on the nth wiring path, where n is the number of wiring paths divided on each hemispherical skeleton. n [] represents the number of turns of the coil wound on the nth wiring path during the optimization process.

[0020] Optionally, the composite four-channel receiving coil further includes a cap-shaped asymmetric butterfly wiring structure and a decoupling circuit. The breast sub-coil and the far terminal coil are wound on the cap-shaped asymmetric wiring structure, and the two breast sub-coils are decoupled from each other through the decoupling circuit.

[0021] Optionally, the decoupling circuit includes a decoupling capacitor C. d Decoupling capacitor C d It is connected in series at one end of the two mammary gland sub-coils, and the other ends of the two mammary gland sub-coils are grounded together.

[0022] The portable magnetic resonance imaging device according to another embodiment of the present invention includes the aforementioned composite four-channel receiving coil.

[0023] Beneficial Effects: Compared with existing technologies, the significant technical advantages of this invention are as follows: The composite four-channel receiving coil is suitable for use in portable ultra-low field magnetic resonance imaging (MRI) devices with a vertical main magnetic field. Furthermore, compared to traditional breast coils, this coil can simultaneously image the breast and its root, offering a larger imaging range and higher accuracy, a better signal-to-noise ratio, and providing a reference for the future structural design of ultra-low field radio frequency coils. It also provides a routine examination method for diseases such as breast cancer. In ultra-low field MRI breast imaging, it has the advantages of a large detection area and high imaging accuracy. Attached Figure Description

[0024] Figure 1 This is a schematic diagram showing the structure and location of the ultra-low field magnetic resonance system with a composite four-channel receiving coil and a vertical magnetic field in this invention.

[0025] Figure 2 This is a schematic diagram of the planar structure and wiring scheme of the composite four-channel receiving coil in this invention;

[0026] Figure 3 This is a schematic diagram of the three-dimensional structure and wiring scheme of the composite four-channel receiving coil in this invention;

[0027] Figure 4 This is an equivalent circuit diagram of the decoupling circuit between the two breast sub-coils in this invention;

[0028] In the diagram: 01, composite four-channel receiving coil; 01a, cap-shaped asymmetric wiring structure; 01b, breast sub-coil; 01c, remote terminal coil; 02, decoupling circuit. Detailed Implementation

[0029] To make the above-mentioned objectives, features, advantages, and design methods of the present invention clearer, the present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0030] like Figure 1 As shown, the composite four-channel receiving coil 01 used in this invention for portable magnetic resonance imaging is placed at the center of the portable ultra-low field magnetic resonance imaging device. The design goal of this invention is to make its imaging area cover both breasts and their axillae, because most breast cancers occur in the upper outer quadrant of the breast and extend into the axilla. The composite four-channel receiving coil 01 includes two breast sub-coils and two distal terminal coils. The cap-shaped multi-turn breast sub-coils are used for imaging the breast region, and the butterfly-shaped multi-turn distal terminal coils are used for imaging the upper root region of the breast. The two types of sub-coils are orthogonally arranged on their respective wiring structures, thereby achieving high-precision, full-area breast magnetic resonance imaging under a vertical magnetic field.

[0031] The composite four-channel receiving coil is wired on two cap-shaped asymmetrical wiring structures. Each cap-shaped asymmetrical wiring structure is wound with a breast sub-coil and a far-terminal coil. The two cap-shaped asymmetrical wiring structures are arranged symmetrically with a certain angle and center distance based on specific imaging requirements to achieve accurate imaging of the entire area of ​​one breast.

[0032] Specifically, such as Figure 2 and Figure 3 As shown, the composite four-channel receiving coil 01 proposed in this invention includes a pair of cap-shaped asymmetric wiring structures 01a and a pair of breast sub-coils 01b and a pair of far-terminal coils 01c respectively wound on them. The optimized target area of ​​the breast sub-coil's radio frequency field is set to a hemisphere with radius r1, the volume of which is larger than the average breast volume of patients with breast diseases. The cap-shaped asymmetric wiring structure has slots to facilitate the winding of the two types of sub-coils. One edge of the bottom side of the cap-shaped asymmetric wiring structure is stretched to be greater than or equal to the radius of the target area of ​​the breast sub-coil. The length of the cap is doubled (i.e., stretched to r3) to form the hat-shaped edge, and the opposite edge is stretched to a set length (e.g., ...). Figure 2The stretching distance d) shown in the figure forms a brim structure; the breast sub-coil is wound along the slot on a hemispherical skeleton with an outer diameter r2, and the loop wiring of the breast sub-coil is carried out on the extended brim edge to suppress the non-uniformity of the transmission field caused by the receiving coil. The stretched brim structure provides wiring space for the far-terminal coil, that is, the far-terminal coil wiring is carried out on the brim structure. The center distance between the two asymmetric wiring structures of the brim is L, and the angle between the center line of the asymmetric wiring structure of the brim and the y direction is θ. Figure 3 The diagram on the right does not show the cap-shaped asymmetrical wiring structure 01a; it only shows the wiring diagram of the breast sub-coil 01b and the far-end coil 01c.

[0033] The breast sub-coil adopts a multi-turn wiring structure after uniformity optimization: that is, on the hemispherical structure that fits the shape of the breast in the asymmetric wiring structure of the hat, it is divided into several wiring paths with equal spacing. Based on the optimization results of the received magnetic field uniformity and the total length limit of the breast sub-coil, the number of coil turns on each wiring path is determined to reduce signal loss and achieve optimal magnetic field uniformity.

[0034] The wiring scheme for the breast sub-coil was determined based on optimization results for magnetic field uniformity. The specific parameter optimization process is as follows:

[0035] First, the hemispherical skeleton portion of the cap-shaped asymmetric wiring structure is divided into multiple wiring paths at a certain proportional spacing. The base circle radius of each wiring path is r2. A side current of 1A is applied to each turn of the coil wound on each wiring path, and the distribution of its three radio frequency (RF) components is obtained using the finite element method. Then, the minimum non-uniformity δ of the horizontal component of the composite RF field of the coil wound on each wiring path within the target optimization region is calculated. With the constraint that the total length of the sub-coil does not exceed 1 / 20 of the wavelength, the number of turns and spacing of the coil are optimized. The calculation method for the minimum non-uniformity δ of the horizontal component of the RF field is as follows:

[0036]

[0037] In the finite element simulation, the entire target area is divided into m smaller regions, B m Let [B] be the magnetic field strength in the m-th small region. m [B] represents the horizontal component dataset within the target optimization region based on coil combinations wound along n wiring paths, specifically the transverse radio frequency component perpendicular to the direction of the main magnetic field B0 of the magnetic resonance system. m The following formula is given:

[0038]

[0039] Where n is the number of wiring paths divided on each hemispherical skeleton, and matrix [B mn] represents the magnetic field strength dataset within the target optimization region obtained from the simulation results of a single-turn coil on the nth wiring path, [k n ] represents the number of turns of the coil wound on the nth wiring path during the optimization process. Based on the above formula and method, the magnetic field strength results calculated under different numbers of turns of the coil wound on different wiring paths are substituted into formula (1) for calculation. The number of turns of the coil wound on the wiring path is changed, and this process is iterated repeatedly until the minimum non-uniformity is obtained, thus obtaining the optimal wiring scheme. The above optimization constraint is given by the fact that the total length of a mammary sub-coil is less than the critical wavelength that produces the antenna effect, as shown in the following formula:

[0040]

[0041] Where λ is the electromagnetic wavelength corresponding to the magnetic resonance frequency, [S n Let be the total length of the coil along the nth wiring path. Since the main radio frequency field generated by this sub-coil is in the horizontal direction, the y-direction magnetic field strength B generated by the coil is selected according to the optimization requirements during the optimization solution. y Or the horizontal component magnitude B xy Fill [B] mn The dataset is used to optimize the magnetic field uniformity, thereby obtaining the number of coil turns [k] on the nth wiring path. n The optimal combination was determined by the wiring scheme of the breast sub-coil 01b. Based on this scheme, Litz wire was finally wound on the cap-shaped asymmetric wiring structure 01a. The above wiring scheme is optimized using the longest coil length, resulting in high inductance, high signal-to-noise ratio, and improved four-channel signal-to-noise ratio, thus leading to high imaging accuracy.

[0042] like Figure 4 As shown, in this invention, the two breast sub-coils 01b are decoupled using a lumped element decoupling circuit, which includes a decoupling capacitor C. d Decoupling capacitor C d A series capacitor is connected at one end of each of the two breast sub-coils, and the other ends of both breast sub-coils are grounded together. Simultaneously, a breakpoint capacitor, a tuning capacitor, and a matching capacitor are used to form an LC resonant circuit with the breast sub-coils to tune and match them. In the diagram, L1 and L2 are the inductance values ​​of the coils that generate the main coupling in the two breast sub-coils, respectively; M is the mutual inductance value; and C... p0 With C p1 For the breakpoint capacitor, c t0 With C t1 For the tuning capacitor, C m0 With C m1 To match the capacitance, the two breast sub-coils are analyzed as the primary and secondary coils, respectively. V0 and V1 are the voltages across the primary and secondary coils, respectively. s Ic I d and I t These represent the primary coil, secondary coil, decoupling capacitor, and current flowing to the signal line of the secondary coil, respectively. P0 and P1 are the ports of the primary and secondary coils, respectively, and GND is ground.

[0043] The two breast sub-coils are decoupled through a precisely calculated decoupling circuit. The calculation process for the decoupling circuit parameters is as follows:

[0044] When the mutual inductance M>0, considering the relatively low impedance of the Litz coil, to simplify the circuit model, the resistance in the breast sub-coil is ignored, and the current I is assumed to be... s The phase of V0 is zero, and the relationship between the amplitude and phase of V0 is given by the following formula:

[0045] V0 = I s ·jωL1=|I s ·ωL1|∠90° (4)

[0046] Where ω is the Larmor frequency of magnetic resonance, and j is the imaginary unit. Since M > 0, the voltage V1 induced in the secondary coil is:

[0047] V1 = I s ·jωM=|I s ·ωM|∠90° (5)

[0048] The current I induced in the secondary coil L2 c for:

[0049]

[0050] Assuming the two breast sub-coils are completely decoupled via a decoupling circuit, then V1 equals zero, and the decoupling capacitor C... d Current I d for:

[0051]

[0052] According to Kirchhoff's current law, the total current I flowing to the secondary coil signal line is... t by I c and I d Given, and by solving I t =0 yields the required decoupling capacitor C. d The capacitance value is:

[0053]

[0054] Through calculation and simulation using the above formula, C is determined. dThe value of can be used to decouple the two coupled breast sub-coils. Since the two distal terminal coils are far apart and orthogonal to the breast sub-coils, the coupling is small, and no other decoupling method is needed.

[0055] To make the features of this invention clearer, the following section uses the structure and circuit characteristics of a composite four-channel receiving coil used in breast imaging of a 2.13MHz portable ultra-low field magnetic resonance imaging instrument, selecting important parameter values, to provide a more detailed description of specific embodiments of this invention.

[0056] Based on the average breast volume data of Asian breast cancer patients, the optimized target region for the radio frequency field of the breast sub-coil of the composite four-channel receiving coil used in breast imaging of a 2.13MHz portable ultra-low field MRI scanner is a hemisphere with a radius of 60mm (r1), wound on a hemisphere skeleton with an outer diameter of 70mm (r2) and a wall thickness of 5mm. The bottom edge radius of one side of the cap-shaped asymmetric wiring structure is horizontally stretched to 85mm (r3), and the other side is stretched outward by 50mm (d) to form the cap-shaped edge. The two cap-shaped structures are arranged at a 60° angle (2θ) with a center distance of 200mm (L).

[0057] The distal terminal coil is a special planar butterfly coil, with one side of its coil shape being a quarter-circle fan-shaped loop. It is conformally positioned within the cap-shaped asymmetrical wiring structure to determine the B-shape of the bilateral breast sub-coils. 1- The received radio frequency field directions are arranged at a certain angle. The spacing between each preset wiring path of the breast sub-coil is 10mm, divided into 12 turns. Through optimization, the following winding scheme can be obtained, under which the coil uniformity is best, based on the horizontal component B. y And modulo value B xy The results of the magnetic field uniformity optimization are shown in the table below:

[0058]

[0059] The coils are fabricated according to the wiring method obtained from the horizontal component, resulting in an inductance of 23.9 μH for the breast sub-coil. To achieve impedance matching and decoupling between the two breast sub-coils, a 430 pF breakpoint capacitor C is installed on the coils. P0 With C P1 A 369pF tuning capacitor C is connected in parallel. t0 With C t1 A 138pF matching capacitor C is connected in series. m0 With C m1 And a 37.4pF decoupling capacitor C is used. d This allows for simultaneous impedance matching and decoupling of the two coils.

[0060] The example of a composite four-channel receiving coil used in breast imaging with a 2.13MHz portable ultra-low field magnetic resonance imaging instrument is provided as an illustrative illustration of the principles and functions of the present invention, and is not intended to limit the invention. All equivalent modifications made based on this invention should still be covered by the claims of this invention.

Claims

1. A composite four-channel receiving coil for portable magnetic resonance imaging, characterized in that, The four-channel receiving coil includes two breast sub-coils and two distal terminal coils. The cap-shaped multi-turn breast sub-coils are used for imaging the breast region, while the butterfly-shaped multi-turn distal terminal coils are used for imaging the upper root region of the breast. The two types of sub-coils are orthogonally arranged on their respective wiring structures for breast magnetic resonance imaging under a vertical magnetic field.

2. The composite four-channel receiving coil for portable magnetic resonance imaging according to claim 1, characterized in that, The four-channel receiving coil is wired on two cap-shaped asymmetric wiring structures. Each cap-shaped asymmetric wiring structure is wound with a breast sub-coil and a far-terminal coil. The two cap-shaped asymmetric wiring structures are arranged symmetrically with a set angle and center distance based on imaging requirements.

3. A composite four-channel receiving coil for portable magnetic resonance imaging according to claim 2, characterized in that, The bottom edge of the cap-shaped asymmetrical wiring structure is stretched to be greater than or equal to the radius of the target area of ​​the breast sub-coil. The length of the cap shape edge is doubled to form the cap edge, and the opposite edge is stretched to a set length to form the brim structure. The breast sub-coil loop wiring is carried out on the extended cap edge to suppress the non-uniformity of the transmission field caused by the receiving coil. The far terminal coil wiring is carried out on the brim structure.

4. A composite four-channel receiving coil for portable magnetic resonance imaging according to claim 2, characterized in that, The breast sub-coil adopts a multi-turn wiring structure after uniformity optimization: that is, on the hemispherical structure of the hat-shaped asymmetric wiring structure that fits the shape of the breast, it is divided into several wiring paths with equal spacing. Based on the optimization results of the received magnetic field uniformity and the total length limit of the breast sub-coil, the number of coil turns on each wiring path is determined, and the wiring scheme of the breast sub-coil is obtained.

5. A composite four-channel receiving coil for portable magnetic resonance imaging according to claim 4, characterized in that, The calculation methods for optimizing the uniformity of the receiving magnetic field include: Calculate the minimum horizontal non-uniformity δ of the synthesized RF field of the coil wound on each wiring path within the target optimization region: Where m represents the objective optimization region being divided into m smaller regions, B m Let [B] be the magnetic field strength in the m-th small region. m [B] represents the horizontal component dataset within the target optimization region based on coil combinations wound along n wiring paths, specifically the transverse radio frequency component perpendicular to the direction of the main magnetic field B0 of the magnetic resonance system. m The expression is: Where n is the number of wiring paths divided on each hemispherical skeleton, and matrix [B mn ] represents the magnetic field strength dataset within the target optimization region obtained from the simulation results of a single-turn coil on the nth wiring path, [k n [] represents the number of turns of the coil wound on the nth wiring path during the optimization process.

6. A composite four-channel receiving coil for portable magnetic resonance imaging according to claim 5, characterized in that, In the optimization solution, the horizontal component B is used. y Or take the modulus value B xy Solve for B mn Thus, the number of coil turns [k] on the nth wiring path is obtained. n The optimal combination is the wiring scheme for the breast sub-coil.

7. A composite four-channel receiving coil for portable magnetic resonance imaging according to claim 4, characterized in that, The total length of the breast sub-coil is limited to: The total length of each breast sub-coil is less than the critical wavelength that produces the antenna effect, as expressed in the following formula: Where λ is the electromagnetic wavelength corresponding to the magnetic resonance frequency, [S n [k] represents the total length of the coils on the nth wiring path, where n is the number of wiring paths divided on each hemispherical skeleton. n [] represents the number of turns of the coil wound on the nth wiring path during the optimization process.

8. A composite four-channel receiving coil for portable magnetic resonance imaging according to claim 1, characterized in that, The composite four-channel receiving coil also includes a cap-shaped asymmetric butterfly wiring structure and a decoupling circuit. The breast sub-coil and the far terminal coil are wound on the cap-shaped asymmetric wiring structure, and the two breast sub-coils are decoupled from each other through the decoupling circuit.

9. A composite four-channel receiving coil for portable magnetic resonance imaging according to claim 8, characterized in that, The decoupling circuit includes a decoupling capacitor C. d Decoupling capacitor C d It is connected in series at one end of the two mammary gland sub-coils, and the other ends of the two mammary gland sub-coils are grounded together.

10. A portable magnetic resonance imaging device, characterized in that, The device includes the composite four-channel receiving coil as described in any one of claims 1-9.

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