CN214252552U

CN214252552U - Ultrahigh field emission shimming coil structure

Info

Publication number: CN214252552U
Application number: CN202023281636.8U
Authority: CN
Inventors: 魏子栋; 钟继凡
Original assignee: Shenzhen United Imaging Research Institute of Innovative Medical Equipment
Current assignee: Shenzhen United Imaging Research Institute of Innovative Medical Equipment
Priority date: 2020-12-29
Filing date: 2020-12-29
Publication date: 2021-09-21
Anticipated expiration: 2030-12-29

Abstract

The utility model relates to an ultra-high field emission shimming coil structure, including a plurality of dipole antenna unit, a plurality of dipole antenna unit encircle and distribute in the outside of load, and dipole antenna unit includes dielectric layer and dipole antenna, and dipole antenna sets up in one side of dielectric layer, and one side that dipole antenna was kept away from to the dielectric layer is close to the load setting, and wherein, at least one layer medium has multilayer medium and at least one deck medium in the multilayer medium of at least one dipole antenna unit is high dielectric material, and high dielectric material is located one side that corresponding dipole antenna unit is close to the load; the dielectric layer is arranged between the dipole and the load, so that the shimming adjusting capability of the antenna transmitting field can be improved, the uniformity of the antenna transmitting field can be additionally adjusted by arranging the high dielectric material, and the coil structure has better shimming adjusting capability and transmitting effect of the radio frequency field under an ultrahigh field compared with the existing birdcage structure.

Description

Ultrahigh field emission shimming coil structure

Technical Field

The utility model relates to a magnetic resonance medical imaging technical field especially relates to a super high field emission shimming coil structure.

Background

Magnetic Resonance Imaging (MRI) is the most advanced imaging technique that allows cross-sectional viewing of objects such as the human body with unprecedented tissue contrast. MRI is based on the principle of nuclear magnetic resonance, a spectroscopic technique used by scientists to obtain microscopic chemical-physical information about molecules. The basis for both nuclear magnetic resonance and MRI is the fact that nuclei with non-zero spin have a magnetic moment. In medical imaging, for example, hydrogen atoms are studied because they are present in high concentrations in the body (e.g., water). If a strong direct current magnetic field is applied, the nuclear spins of the elementary particles can resonate at the resonance frequency. The Magnetic Resonance (MR) frequency is determined by the magnetic flux level. In an MRI scanner, the magnetic field matches a selected resonance frequency only at locations in space. The presence of these particles can only be detected at this location. By changing the position, the image can be measured.

The required strong direct current magnetic field (B-field) is typically generated by a superconducting magnet. In order to vary the magnetic field such that it matches a given radio frequency at only one location, gradient coils are used to generate the magnetic field gradients. The magnetic field gradients can be varied over time to effect the scan.

To excite nuclear resonance, an RF coil (radio frequency coil) generates a high frequency magnetic field at the nuclear resonance. The magnetic field must be directed in a radial direction relative to the axis of the MRI scanner. In order to achieve a radial magnetic field in all directions, a rotating magnetic field is used, which points in any radial direction at a point in time during a period. This is achieved by using, for example, a so-called 'birdcage' arrangement. The current in the plate opposite the birdcage flows in the opposite direction, generating a radial field. The currents in adjacent plates have a phase shift causing the magnetic field to rotate.

The radio frequency coils used in nuclear magnetic resonance are typically high resonance antennas designed to generate a well defined magnetic field inside the human body. The side effect is that the electric field causes losses that strongly change the input impedance of the coil. This mainly affects the real part of the impedance, the relative change being related to the resonance quality factor change (also called the load factor).

In the prior art, in the field of ultrahigh-field nuclear magnetic resonance medical imaging, a birdcage structure is generally a cylindrical structure, but due to the regularity of the shape, the radio-frequency shimming adjustment capability of the birdcage structure is weak, the radio-frequency wavelength is shortened along with the improvement of an ultrahigh-field magnetic field, and the artifact caused by the medium effect of the radio-frequency field on tissues is more serious, so that the traditional birdcage structure has obvious use limitation.

SUMMERY OF THE UTILITY MODEL

In view of this, it is necessary to provide an ultra-high field transmission shimming coil structure to solve the technical problem in the prior art that the radio frequency shimming capability of the conventional transmission regular transmission birdcage structure is weak and the use requirement of the ultra-high field magnetic field cannot be met.

The utility model provides a super high field emission shimming coil structure, it includes a plurality of dipole antenna unit, and a plurality of dipole antenna unit encircle the outside of distributing at the load, dipole antenna unit includes dielectric layer and dipole antenna, dipole antenna set up in one side of dielectric layer, the dielectric layer is kept away from one side of dipole antenna is close to the load sets up, wherein, at least one deck medium that the dielectric layer of dipole antenna unit has in multilayer medium and the multilayer medium is high dielectric material, high dielectric material is located corresponding one side that dipole antenna unit is close to the load.

Preferably, the dipole antenna elements are arranged along the shape of the outer side surface of the load.

Preferably, the dipole antenna unit with the multilayer medium is arranged at a position where the magnetic field is unevenly distributed at the ultrahigh-field point.

Preferably, the high dielectric material is located on a side of the corresponding dipole antenna element close to the load.

Preferably, each dipole antenna unit corresponds to a transmission channel, and the amplitude and phase of different transmission channels can be independently adjusted.

Preferably, the dipole antenna further comprises a shielding element, wherein the shielding element is installed outside a ring surrounded by the dipole antenna units and used for weakening a magnetic field between different transmitting channels so as to reduce coupling.

Preferably, the shielding member is a hollow ring structure, and a ring surrounded by the dipole antenna units is located inside the ring of the shielding member.

Preferably, the different dipole antenna elements are equally spaced from the inner side wall of the shield.

Preferably, the shielding member includes a plurality of shielding caps, wherein the number of the shielding caps is not more than the number of the dipole antenna units, the shielding caps are respectively and correspondingly covered on the outer sides of the dipole antenna units, and the distances between the different dipole antenna units and the corresponding inner side walls of the shielding caps are equal.

Preferably, the dipole antenna unit is a strip, the dipole is a regular strip structure or an irregular serpentine structure at least partially in a curved shape, and a feed port of the dipole antenna unit is disposed at a middle position of the dipole.

The utility model provides an ultra-high field multichannel transmission shimming head coil structure, it can improve the shimming regulatory ability in antenna transmission field owing to set up the dielectric layer between dipole and load, and high dielectric material's setting can additionally adjust the homogeneity in antenna transmission field, and this coil structure has more excellent radio frequency field shimming regulatory ability and transmission effect under ultra-high field than current birdcage structure.

The above description is only an overview of the technical solution of the present invention, and in order to make the technical means of the present invention clearer and can be implemented according to the content of the description, the following detailed description is made of preferred embodiments of the present invention.

Drawings

Fig. 1 is a schematic structural diagram of an ultra-high field emission shim coil structure according to some embodiments of the present invention;

fig. 2 is a schematic structural diagram of an ultra-high field emission shim coil structure provided in some embodiments of the present invention;

fig. 3 is a schematic structural diagram of a dipole antenna unit according to some embodiments of the present invention;

fig. 4 is a schematic structural diagram of a dipole antenna element according to some embodiments of the present invention;

fig. 5 is a schematic structural diagram of a dipole antenna unit according to some embodiments of the present invention.

Detailed Description

The following detailed description of the preferred embodiments of the invention, which is to be read in connection with the accompanying drawings, forms a part of this application, and together with the embodiments of the invention, serve to explain the principles of the invention and not to limit its scope.

As shown in fig. 1 or fig. 2, the present embodiment provides an ultra-high field transmitting shim coil structure, which includes a plurality of dipole antenna units 10, where the plurality of dipole antenna units 10 are distributed around the outer side of a load T, and the distances between different dipole antenna units 10 and the center of the load T are not all equal, and as shown in fig. 3 to fig. 5, the dipole antenna unit 10 includes a dielectric layer 11 and a dipole antenna 12, the dipole antenna 12 is disposed on one side of the dielectric layer 11, and one side of the dielectric layer 11 away from the dipole antenna 12 is distributed near the load T.

In some embodiments of the present application, the load is part of the head or torso of a human body, and in other embodiments of the present application, the load is a laboratory animal, such as a dog, cat, or monkey; the following description will take the human head as an example.

It is understood that the plurality of dipole antenna elements 10 described in the embodiments of the present application are distributed around the outside of the load T, the ring merely represents that the plurality of dipole antenna elements 10 are distributed around the load T, and if the dipole antenna elements 10 are connected one by a line, a closed curve with the load T inside is formed, the shape of the closed curve can be theoretically any plane figure, including but not limited to a circle, a square or other irregular polygon, in the preferred embodiments of the present application, the dipole antenna elements 10 are arranged according to the shape of the outside of the load T, i.e. the distribution shape of the dipole antenna elements 10 is adapted to the shape of the head of the human body, so that the dipole antenna elements 10 can be closer to the target load when in use, and the transmission efficiency is further improved.

It should be noted that, in the embodiments of the present application, the number of dipole antenna elements is based on the number of actual use, and the number in the drawings is merely used to indicate one of the real-time states available in the present application, for example, the number of dipole antenna elements may be 6, 8, 10 or even more, generally, the greater the number of dipole antenna elements is, the more accurate the mri image is in use, but in consideration of cost or installation technical limitations, the increase and decrease may be performed by those skilled in the art according to actual situations.

In the embodiment of the present application, the dielectric layer 11 of at least one dipole antenna unit 10 has a multi-layer dielectric, and the dipole antenna unit 10 with the multi-layer dielectric is disposed at a position where the magnetic field of the ultra-high field point is unevenly distributed.

In some embodiments of the present application, the number of the dipole antenna units 10 with the multi-layer medium is one, in other embodiments of the present application, the number of the dipole antenna units 10 with the multi-layer medium is more than one, in still other embodiments of the present application, all the dipole antenna units 10 have the multi-layer medium, and the arrangement of the multi-layer medium of the medium layers can improve shimming adjustment capability of the radio frequency magnetic field of the dipole antenna units 10, and the dipole antenna units 10 with the multi-layer medium are arranged at positions where the magnetic field of the ultra-high field point is unevenly distributed, so that even distribution of the ultra-high field can be further improved.

At least one layer of the dielectric of the dipole antenna unit 10 with multiple layers of dielectric is the high dielectric material 111, the high dielectric material 11 is located on the side of the corresponding dipole antenna unit 10 close to the load T, and the uniformity of the antenna transmission field can be additionally adjusted by the arrangement of the high dielectric material 111.

Each dipole antenna element 10 corresponds to a transmission channel, and the amplitude and phase of different transmission channels can be adjusted independently.

In the prior art, a conventional birdcage transmitting structure is directly fed at a coil port by using a matching circuit, and is usually an orthogonal 2-channel or 4-channel regular birdcage transmitting structure, limited ports of the structure need to be orthogonal, so that the number of transmitting channels is low, and the dynamic shimming adjusting capability of a transmitting field is poor.

Since the multi-channel structure is adopted, the magnetic field coupling between different transmission channels is increased, and therefore, in the preferred embodiment of the present application, as shown in fig. 1, the coil structure further includes a shielding member 20, and the shielding member 20 is installed outside the loop formed by the dipole antenna unit 10, and is used for weakening the magnetic field between different transmission channels to reduce the coupling.

To achieve shielding, in some embodiments, as shown in fig. 2, the shielding element 20 is a hollow ring structure, and the ring surrounded by the dipole antenna unit 10 is located inside the ring of the shielding element 20; it will be appreciated that with conventional birdcage structures of the prior art, the shielding structure is generally circular in shape, which can naturally also be used in the coil structure of the present application.

In other embodiments of the present application, as shown in fig. 2, in order to increase the shielding effect, the different dipole antenna elements 10 are spaced equally from the inner sidewall of the shielding element 20, that is, the inner sidewall of the shielding element 20 has a conformal arrangement structure conforming to the arrangement shape of the dipole antenna elements 10, which can reduce the radiation loss and the coupling between the channels more effectively.

In order to save shielding material, in still other embodiments of the present application, as shown in fig. 1, the shielding member 20 includes a plurality of shielding caps 21, wherein the number of the shielding caps 21 is not more than the number of the dipole antenna elements 10, and preferably, the number of the shielding caps 21 is equal to the number of the dipole antenna elements 10, the shielding caps 21 are respectively covered on the outer sides of the dipole antenna elements 10, and the distance between the different dipole antenna elements 10 and the inner side walls of the corresponding shielding caps 21 is equal.

In the embodiment of the present application, the dipole antenna element 10 is a strip; as shown in fig. 3, in some preferred embodiments of the present application, the dipoles 12 are regular strip-like structures; in other preferred embodiments of the present application, the dipole 12 has an irregular serpentine structure with at least a partially curved shape, specifically, as shown in fig. 4, in some embodiments, the dipole 12 includes a straight portion 121 and a bent portion 122, and the bent portion 122 is distributed at a partial position of the straight portion 121, and in other embodiments, as shown in fig. 5, the dipole 12 is formed by the bent portion 122 bent in a continuous wave shape.

The utility model provides an ultra-high field multichannel transmission shimming head coil structure, it sets up different dipole antenna unit 10 to arrange according to the shape of the lateral surface of load T along with the shape, makes dipole antenna unit 10 can more press close to the load in the coil structure use, improves emission efficiency; in addition, as the dielectric layer 11 is arranged between the dipole 12 and the load T and the high dielectric material 111 is arranged at one side close to the load T, the shimming adjustment capability of the antenna transmitting field can be further improved, and therefore, the whole coil structure has better radio frequency field shimming adjustment capability and transmitting effect under an ultrahigh field compared with the traditional birdcage structure.

The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention should be covered by the present invention.

Claims

1. The ultra-high field emission shimming coil structure is characterized by comprising a plurality of dipole antenna units, wherein the dipole antenna units are distributed on the outer side of a load in a surrounding mode, each dipole antenna unit comprises a dielectric layer and a dipole antenna, the dipole antenna is arranged on one side of the dielectric layer, one side, far away from the dipole antenna, of the dielectric layer is arranged close to the load, and the dielectric layer of at least one dipole antenna unit is provided with a plurality of layers of dielectrics.

2. The ultra-high field transmitting shim coil structure of claim 1, wherein the dipole antenna elements are arranged in a conformal manner according to an outer side shape of the load.

3. The ultra-high field transmitting shim coil structure of claim 1, wherein the dipole antenna elements with multi-layer media are disposed at locations of non-uniform distribution of the ultra-high field point magnetic field.

4. The ultra-high field transmit shim coil structure of claim 1, wherein each dipole antenna element corresponds to a transmit channel, and the amplitude and phase of different transmit channels are independently adjustable.

5. The ultra-high field transmit shim coil structure of claim 4, further comprising shields mounted outside of the loop defined by the dipole antenna elements for attenuating magnetic fields between different ones of the transmit channels to reduce coupling.

6. The ultra-high field transmitting shim coil structure of claim 5, wherein the shield is a hollow ring structure, and the ring shape defined by the dipole antenna units is located inside the ring shape of the shield.

7. The ultra-high field transmitting shim coil structure of claim 6, wherein different ones of the dipole antenna elements are equally spaced from inner sidewalls of the shield.

8. The ultra-high field transmitting shim coil structure of claim 5, wherein the shield comprises a plurality of shield caps, the number of shield caps is no more than the number of dipole antenna elements, the shield caps are arranged on the outer sides of the dipole antenna elements in a one-to-one correspondence, and the distance between different dipole antenna elements and the inner side walls of the corresponding shield caps is equal.

9. The ultra-high field transmitting shim coil structure according to claim 1, wherein the dipole antenna unit is strip-shaped, the dipole is a regular strip-shaped structure or an irregular serpentine structure at least partially having a curved shape, and a feeding port of the dipole antenna unit is disposed at a middle position of the dipole.