CN111157930A

CN111157930A - Gradient coil for magnetic resonance imaging device and magnetic resonance imaging device

Info

Publication number: CN111157930A
Application number: CN201811318374.2A
Authority: CN
Inventors: 薛廷强; 彭卫平
Original assignee: Siemens Shenzhen Magnetic Resonance Ltd
Current assignee: Siemens Shenzhen Magnetic Resonance Ltd
Priority date: 2018-11-07
Filing date: 2018-11-07
Publication date: 2020-05-15

Abstract

Gradient coil for a magnetic resonance imaging apparatus, comprising a main coil (10), a shield coil (20), at least one insert (30) and a cast body (40). The main coil is used for forming a gradient imaging magnetic field. The shield coil is disposed around and spaced apart from the main coil. The shield coil is used for forming a gradient shield magnetic field. Each insert contains a phase change material and is arranged to be able to be in contact with the main coil and/or the shield coil. The cast body is formed by casting as one cast whole with the main coil, the shielding coil and the at least one insert to fix the mutual positions of the main coil, the shielding coil and the at least one insert. The gradient coil has small temperature fluctuation in the using process, high imaging quality, smaller size and energy conservation. Furthermore, a magnetic resonance imaging apparatus comprising the gradient coil is provided.

Description

Gradient coil for magnetic resonance imaging device and magnetic resonance imaging device

Technical Field

The invention relates to a gradient coil for a magnetic resonance imaging device, in particular to a gradient coil which has small temperature fluctuation during use, high imaging quality, smaller size and energy conservation, and a magnetic resonance imaging device comprising the gradient coil.

Background

Gradient coils are one of the core components of a Magnetic Resonance Imaging (MRI) system and serve primarily to generate a near linear, rapidly switchable gradient imaging magnetic field in the imaging region. Gradient coils rely on their main coils to form the gradient imaging magnetic field. For the gradient coil used in the superconducting magnetic resonance imaging apparatus, because the eddy current effect needs to be considered, a shielding coil is usually added outside the main coil to shield the magnetic field outside the gradient coil.

During use of the gradient coil, the wires therein generate a lot of heat, which results in a high temperature rise of the gradient coil, especially in areas with dense wires. Such temperature fluctuations directly affect the imaging quality of the magnetic resonance imaging apparatus. In the gradient coil molded by casting the resin polymer material, the resin polymer material has poor heat dissipation performance, so the heat dissipation problem is particularly obvious. The current method is mainly to arrange a cooling system on the gradient coil, that is, to insert a cooling pipe into the gradient coil, and a cooling medium flows in the cooling pipe under the driving of a cooling pump, so as to take away the heat in the gradient coil. However, such cooling systems take up a relatively large amount of space and consume relatively much energy during operation.

Disclosure of Invention

The object of the present invention is to provide a gradient coil for a magnetic resonance imaging apparatus which has a small temperature fluctuation during use, high imaging quality, and is more compact and energy-saving.

It is another object of the present invention to provide a magnetic resonance imaging apparatus in which the gradient coil has less temperature fluctuation during use, high imaging quality, and is more compact and energy-saving.

The invention provides a gradient coil for a magnetic resonance imaging device, comprising a main coil, a shielding coil, at least one insert and a cast body. The main coil is used for forming a gradient imaging magnetic field. The shield coil is disposed around and spaced apart from the main coil. The shield coil is used for forming a gradient shield magnetic field. Each insert contains a phase change material and is arranged to be able to be in contact with the main coil and/or the shield coil. The cast body is formed by casting as one cast whole with the main coil, the shielding coil and the at least one insert to fix the mutual positions of the main coil, the shielding coil and the at least one insert.

The gradient coil has the following advantages: 1) the temperature distribution of the gradient coil is more uniform, the temperature value is reduced under the same cooling condition, the temperature fluctuation of the gradient coil is reduced in the scanning imaging process of an MRI system, and the stability and the imaging quality of the system are facilitated; 2) the cooling power of a required cooling system (such as a water cooling system) is reduced, the cooling system can be miniaturized, the installation space is saved, the operation cost is reduced, and even the cooling system (heat is radiated to the surrounding air through the surface of the gradient coil) can be cancelled for a low-field strength system; 3) the distribution density and the length of a cooling pipeline in the gradient coil are reduced, the structure of the gradient coil is compact, and the cost is reduced.

In another exemplary embodiment of the gradient coil, the main coil comprises three main coil layers and the shield coil comprises three shield coil layers. At least one insert is arranged between the three main coil layers and/or at least one insert is arranged between the three shield coil layers and/or at least one insert is arranged between the main coil and the shield coil.

In a further exemplary embodiment of the gradient coil, at least one insert is arranged inside the main coil layer and contacts the conductor line and/or at least one insert is arranged inside the shield coil layer and contacts the conductor line. The insert contacts the wire and can directly absorb heat from the wire, which is beneficial to avoiding local high temperature in the use process of the gradient coil.

In a further exemplary embodiment of the gradient coil, the wires of the main coil and/or of the shielding coil are hollow wires, wherein the central volume accommodates at least one insert. Therefore, heat can be directly absorbed from the lead, and the integral temperature rise and temperature fluctuation of the gradient coil are rapidly reduced.

In a further exemplary embodiment of the gradient coil, at least one insert surrounds the wires of the main coil and/or the shielding coil. Therefore, heat can be directly absorbed from the lead, and the integral temperature rise and temperature fluctuation of the gradient coil are rapidly reduced.

In a further exemplary embodiment of the gradient coil, a cooling duct for accommodating a cooling medium is provided in the main coil and/or the shielding coil, the at least one insert contacting the cooling duct. The heat stored by the insert can be directly conducted to the cooling duct for output, thereby reducing temperature fluctuations throughout the gradient coil.

In yet another exemplary embodiment of the gradient coil, the phase change material is a solid-liquid phase change material. The insert is provided as a thermally conductive porous ceramic having a phase change material adsorbed thereon. The phase-change material is adsorbed on the heat-conducting porous ceramic, and cannot flow or leak randomly when the phase-change material is in a liquid state, so that the heat-conducting porous ceramic is convenient to use. In addition, the heat conduction porous ceramic can improve the heat conductivity, so that the embedded part can absorb or release heat quickly.

In yet another exemplary embodiment of the gradient coil, the phase change material is a solid-liquid phase change material. The insert is arranged to adsorb expanded graphite of a phase change material. The phase-change material is adsorbed on the expanded graphite, and when the phase-change material is in a liquid state, the phase-change material cannot flow or leak at will, so that the use is convenient. The expanded graphite also provides increased thermal conductivity, facilitating rapid heat absorption or release by the insert.

In yet another exemplary embodiment of the gradient coil, the phase change material is a solid-liquid phase change material. The insert is provided as a mixture of a phase change material and a thermally conductive material. The heat conducting material is one or the combination of more of quartz powder, graphite powder, alumina powder and aluminum nitride powder. Quartz powder, graphite powder, alumina powder and aluminum nitride powder can improve the heat conductivity of the embedding piece, and the embedding piece of being convenient for absorbs or releases the heat fast, further reduces the holistic temperature fluctuation of gradient coil in the use by this.

In a further exemplary embodiment of the gradient coil, the insert comprises a housing. The shell is provided with at least one sealed cavity, and the phase change material is arranged in the sealed cavity. Therefore, the leakage of the phase-change material when the phase-change material is changed into a liquid state or a gaseous state can be prevented.

In a further exemplary embodiment of the gradient coil, the phase change material is present in the form of phase change microcapsules, the properties of which are more stable.

In yet another illustrative embodiment of the gradient coil, the cast body is doped with phase change microcapsules. Therefore, the temperature fluctuation and the temperature rise of the whole gradient coil in the using process can be further reduced.

The invention also provides a magnetic resonance imaging device which comprises the gradient coil. The magnetic resonance imaging device has high system stability and imaging quality, and the whole installation space and operation cost of the device are low.

Drawings

The following drawings are only schematic illustrations and explanations of the present invention, and do not limit the scope of the present invention.

Fig. 1 is a schematic structural diagram of an exemplary embodiment of a gradient coil for a magnetic resonance imaging apparatus.

FIG. 2 is a partial cross-sectional view of the gradient coil shown in FIG. 1.

Figure 3 is a partial cross-sectional view of another illustrative embodiment of a gradient coil for a magnetic resonance imaging apparatus.

Fig. 4 is a diagram for explaining the structure of the lead wires of the gradient coil shown in fig. 3.

FIG. 5 is a schematic diagram illustrating the construction of an insert of yet another exemplary embodiment of a gradient coil.

Description of the reference symbols

10 main coil

11, 21 conducting wire

12, 22 cooling duct

13 main coil layer

20 shield coil

23 shield coil layer

30 insert

31 shell

32 sealed cavity

40 casting body

50 functional parts

L axis

Detailed Description

In order to more clearly understand the technical features, objects and effects of the present invention, embodiments of the present invention will now be described with reference to the accompanying drawings, in which the same reference numerals indicate the same or structurally similar but functionally identical elements.

"exemplary" means "serving as an example, instance, or illustration" herein, and any illustration, embodiment, or steps described as "exemplary" herein should not be construed as a preferred or advantageous alternative.

Fig. 1 is a schematic structural diagram of an exemplary embodiment of a gradient coil for a magnetic resonance imaging apparatus, wherein a partial cut-away process is performed to show the internal structure. As shown, the gradient coil comprises a main coil 10, a shield coil 20, a number of inserts 30 (only one of which is schematically shown) and a cast body 40.

Fig. 2 is a partial cross-sectional view of the gradient coil shown in fig. 1, showing the internal structure of the main coil 10 and the shield coil 20, viewed in the direction Z of fig. 1. The main coil 10 includes three main coil layers 13, which are, from bottom to top, an X main coil layer for forming a gradient magnetic field (magnetic field direction shown by X in the figure) varying in the X direction, a Y main coil layer for forming a gradient magnetic field (magnetic field direction shown by Y in the figure) varying in the Y direction, and a Z main coil layer for forming a gradient magnetic field (magnetic field direction shown by Z in the figure) varying in the Z direction. The gradient magnetic field changing along the X direction, the gradient magnetic field changing along the Y direction and the gradient magnetic field changing along the Z direction jointly form a gradient imaging magnetic field so as to realize magnetic resonance imaging. Generally, the X, Y, Z arrangement sequence of the three main coils can be adjusted according to actual conditions.

The shielding coil 20 is disposed around the main coil 10 and spaced apart from the main coil 10. The shield coil 20 includes three shield coil layers 23, which are, in order from top to bottom, a Y shield coil layer for forming a Y-direction shield magnetic field, an X shield coil layer for forming an X-direction shield magnetic field, and a Z shield coil layer for forming a Z-direction shield magnetic field. The X-direction shielding magnetic field, the Y-direction shielding magnetic field and the Z-direction shielding magnetic field jointly form a gradient shielding magnetic field of the gradient coil so as to reduce the eddy current effect and improve the magnetic resonance imaging quality. Generally, X, Y, Z the arrangement sequence of the three shielding coils can be adjusted according to actual conditions.

The insert 30 contains a phase change material and is arranged to be able to contact the main coil 10 and the shield coil 20. In the present exemplary embodiment, several inserts 30 are arranged between the main coil 10 and the shield coil 20, inside the main coil layer 13 and contacting the wire 11, and inside the shield coil layer 23 and contacting the wire 12. Without limitation, in other exemplary embodiments, the inserts 30 may also be disposed at any one or more of between the main coil 10 and the shield coil 20, inside the main coil layer 13 and contacting the wire 11, inside the shield coil layer 23 and contacting the wire 12, between the three main coil layers 13, and between the three shield coil layers 23, as desired. The inserts 30 may be particularly arranged according to the density of the wires, for example, more inserts 30 may be arranged at the positions where the wires are dense and the amount of heat generation is high. In other exemplary embodiments, the shape and number of the inserts 30 may be set as desired, for example, the number may be set to only one.

The cast body 40 is formed as one cast body with the main coil 10, the shield coil 20 and the insert 30 by casting to fix the mutual positions of the main coil 10, the shield coil 20 and the insert 30. The material of the casting body 40 is, for example, a resin-based polymer material such as epoxy resin, but is not limited thereto. Although only a portion of the cast body 40 existing between the main coil 10 and the shielding coil 20 is shown in fig. 1, it will be understood by those skilled in the art that the cast body 40 may actually penetrate into the interior of the main coil 10 and the shielding coil 20 during the casting process, and may also exist on the inside of the main coil 10 and the outside of the shielding coil 20.

In the MRI system using the gradient coil, the gradient coil may generate heat (joule heat) due to a large current passing through the gradient coil during the scanning imaging process, because the phase-change material in the insert 30 has a very high latent heat, while the MRI system is in an intermittent scanning mode, i.e., the current in the gradient coil is discontinuous, the joule heat generated by the current during the scanning may raise the temperature of the phase-change material to reach the phase-change temperature and generate phase change, the phase-change material may absorb a large amount of heat while maintaining the phase-change temperature during the phase-change process, and the heat stored in the phase-change material may be slowly released and carried away by a cooling medium in a cooling pipeline, for example, when the scanning gap or the system is not in. The gradient coil has the following advantages:

1) the temperature distribution of the gradient coil is more uniform, the temperature value is reduced under the same cooling condition, the temperature fluctuation of the gradient coil is reduced in the scanning imaging process of an MRI system, and the stability and the imaging quality of the system are facilitated;

2) the cooling power of a required cooling system (such as a water cooling system) is reduced, the cooling system can be miniaturized, the installation space is saved, the operation cost is reduced, and even the cooling system (heat is radiated to the surrounding air through the surface of the gradient coil) can be cancelled for a low-field strength system;

3) the distribution density and the length of a cooling pipeline in the gradient coil are reduced, the structure of the gradient coil is compact, and the cost is reduced.

In the present exemplary embodiment, the insert 30 is provided as a thermally conductive porous ceramic having adsorbed thereto a phase change material, which is paraffin wax, having a phase change temperature of 40 degrees. But not limited thereto, in other exemplary embodiments, the phase change material may be other solid-liquid phase change material, and the phase change temperature thereof may be 20 to 70 degrees. Because the phase-change material is adsorbed on the heat-conducting porous ceramic, the phase-change material cannot flow or leak randomly when being in a liquid state, and is convenient to use. The thermally conductive porous ceramic also increases thermal conductivity, facilitating rapid heat absorption or release by the insert 30.

In other exemplary embodiments, the insert 30 may be further configured as expanded graphite having a phase change material adsorbed thereon, and the phase change material will not flow or leak when it changes phase to a liquid state, which is convenient for use. The expanded graphite also increases thermal conductivity, facilitating rapid heat absorption or release by the insert 30.

In other exemplary embodiments, the insert 30 may be provided as a mixture of a phase change material and a thermally conductive material, the thermally conductive material being one or a combination of quartz powder, graphite powder, alumina powder, and aluminum nitride powder. The quartz powder, graphite powder, alumina powder, and aluminum nitride powder may increase the thermal conductivity of the insert 30 so that the insert 30 may rapidly absorb or release heat, thereby further reducing the overall temperature fluctuations of the gradient coil during use.

In other exemplary embodiments, the insert 30 may be the phase change material itself, i.e., composed solely of the phase change material.

In other exemplary embodiments, the phase change material may be a solid-solid phase change material, a solid-liquid phase change material, a solid-gas phase change material, a gas-liquid phase change material, an inorganic phase change material, an organic phase change material, or a composite phase change material. The organic phase-change material can be paraffin, carbohydrate and lipid, and the inorganic phase-change material is generally a hydrated salt material.

In the present exemplary embodiment, the space between the main coil 10 and the shield coil 20 (filled by the cast body 40) is substantially cylindrical. The cylinder extends in the direction of the Z-direction imaging field. The insert 30, which is disposed between the main coil 10 and the shield coil 20, extends in a direction parallel to the axis L of the cylinder. This makes it possible to dispose the insert 30 by making full use of the space between the main coil 10 and the shield coil 20, which is advantageous for miniaturization of the gradient coil.

In the present exemplary embodiment, the insert 30 positioned between the main coil 10 and the shield coil 20 directly contacts the wire 11 of the main coil 10 and the wire 21 of the shield coil 20, the insert 30 disposed inside the main coil layer 13 directly contacts the wire 11, and the insert 30 disposed inside the shield coil layer 23 directly contacts the wire 12. The direct contact wires can directly absorb heat from the wires, which is beneficial to avoiding local high temperature in the use process of the gradient coil.

In the present exemplary embodiment, cooling

ducts

12, 22 for receiving a cooling medium are provided in the main coil 10 and the shielding coil 20, and the heat stored in the insert 30 can be conducted to the

cooling ducts

12, 22 via the cast body 40 and output. In the exemplary embodiment, a plurality of inserts 30 are positioned in contact with

cooling ducts

12, 22, whereby heat stored by inserts 30 is conducted directly to cooling

ducts

12, 22 for output. Without limitation, in other exemplary embodiments, the insert 30 may not contact the

cooling ducts

12, 22. In the present exemplary embodiment, several inserts 30 are arranged to contact the

cooling ducts

12, 22 and the wires 21 simultaneously, whereby the heat generated by the wires can be conducted more quickly via the inserts to the

cooling ducts

12, 22 for output, thereby reducing temperature fluctuations throughout the gradient coil.

Fig. 3 is a partial cross-sectional view of another exemplary embodiment of a gradient coil for a magnetic resonance imaging apparatus, the view being in the direction Z of fig. 1. The gradient coil of the present exemplary embodiment is the same as or similar to the gradient coil shown in fig. 1, and the differences are as follows.

In the present exemplary embodiment, the insert 30, which is arranged between the main coil 10 and the shielding coil 20, comprises a housing 31. The housing 31 is made of a hard material such as a glass fiber reinforced material or a plastic material. The housing 31 has a plurality of sealed cavities 32, and the phase change material is disposed in the sealed cavities 32. Therefore, the leakage of the phase-change material when the phase-change material is changed into a liquid state or a gaseous state can be prevented. The insert 30 provided with the sealed cavity 32 is suitable for use with a variety of phase change materials, which may be, for example, solid-liquid phase change materials, liquid-gas phase change materials, or solid-gas phase change materials. Furthermore, the insert 30 with the housing 31 may be arranged in the immediate vicinity of the functional components 50 of the gradient coil (e.g. shim bars) for additional support. In other exemplary embodiments, the number of seal cavities 32 may be adjusted as desired, such as one. In other exemplary embodiments, the position of the insert 30 provided with the sealed cavity 32 may not be limited to only between the main coil 10 and the shield coil 20.

In the present exemplary embodiment, the phase change material exists in the form of a phase change microcapsule, which is relatively stable in properties. Without limitation, in other exemplary embodiments, the phase change material may not be encapsulated in microcapsules.

In the present exemplary embodiment, the cast body 40 is doped with phase change microcapsules, whereby temperature fluctuations and temperature rise of the gradient coil as a whole during use can be further reduced.

In the exemplary embodiment, the

wires

11, 21 of the main coil 10 and the shield coil 20 are hollow wires (see fig. 4), and the central cavity thereof accommodates the insert 30, so that heat can be directly absorbed from the

wires

11 and 21, and the temperature rise and temperature fluctuation of the gradient coil as a whole can be rapidly reduced. In the present exemplary embodiment, the central volume of the

wires

11, 21 is filled with the insert 30, but is not limited thereto, and in other exemplary embodiments, the central volume of the

wires

11, 21 may also be partially filled with the insert 30.

In other exemplary embodiments, the insert 30 may surround the

wires

11 and 21 of the main coil 10 and the shield coil 20 (see fig. 5), and may also absorb heat directly from the

wires

11 and 21, so as to rapidly reduce the temperature rise and temperature fluctuation of the gradient coil as a whole.

The invention also provides a magnetic resonance imaging apparatus which, in an exemplary embodiment, comprises a gradient coil as shown in figure 1. The gradient coil has the advantages that the system stability and the imaging quality of the magnetic resonance imaging device are high, and the installation space and the operation cost of the whole device are low.

It should be understood that although the present description has been described in terms of various embodiments, not every embodiment includes only a single embodiment, and such description is for clarity purposes only, and those skilled in the art will recognize that the embodiments described herein may be combined as suitable to form other embodiments, as will be appreciated by those skilled in the art.

The above-listed detailed description is only a specific description of a possible embodiment of the present invention, and they are not intended to limit the scope of the present invention, and equivalent embodiments or modifications such as combinations, divisions or repetitions of features, which do not depart from the technical spirit of the present invention, should be included in the scope of the present invention.

Claims

1. Gradient coil for a magnetic resonance imaging apparatus, comprising:

a main coil (10) for forming a gradient imaging magnetic field;

a shield coil (20) disposed around said main coil (10) and spaced apart from said main coil (10), said shield coil (20) being configured to form a gradient shield magnetic field;

at least one insert (30), each insert (30) containing a phase change material and being arranged to be able to be in contact with the main coil and/or the shielding coil; and

-a cast body (40) forming by casting a cast whole with said main coil (10), said shielding coil (20) and said at least one insert (30) to fix the mutual position of said main coil (10), said shielding coil (20) and said at least one insert (30).

2. The gradient coil of claim 1, wherein the main coil (10) comprises three main coil layers (13) and the shield coil (20) comprises three shield coil layers (23); at least one of the inserts (30) is arranged between the three main coil layers (13), and/or at least one of the inserts (30) is arranged between the three shield coil layers (23), and/or at least one of the inserts (30) is arranged between the main coil (10) and the shield coil (20).

3. Gradient coil according to claim 2, characterized in that at least one of the inserts (30) is arranged inside the main coil layer (13) and contacts a conductor (11) and/or at least one of the inserts (30) is arranged inside the shield coil layer (23) and contacts a conductor (12).

4. Gradient coil according to claim 3, characterized in that the wires (11, 21) of the main coil (10) and/or of the shield coil (20) are hollow wires, the central volume of which accommodates at least one of the inserts (30); and/or at least one insert (30) surrounds the conductor (11, 21) of the main coil (10) and/or of the shielding coil (20).

5. Gradient coil according to claim 1, characterized in that cooling ducts (12, 22) for accommodating a cooling medium are provided in the main coil (10) and/or the shield coil (20), at least one of the inserts (30) contacting the cooling ducts (12, 22).

6. The gradient coil of claim 1, wherein the phase change material is a solid-liquid phase change material; the insert (30) is arranged as a thermally conductive porous ceramic having the phase change material adsorbed thereon or as expanded graphite having the phase change material adsorbed thereon.

7. The gradient coil of claim 1, wherein the phase change material is a solid-liquid phase change material, the insert (30) is provided as a mixture of the phase change material and a thermally conductive material that is a combination of one or more of quartz powder, graphite powder, alumina powder, and aluminum nitride powder.

8. The gradient coil of claim 1, wherein the insert (30) comprises a housing (31), the housing (31) having at least one sealed cavity (32), the phase change material being disposed within the sealed cavity (32).

9. The gradient coil of claim 1, wherein the phase change material is in the form of a phase change microcapsule.

10. The gradient coil of claim 1, wherein the cast body (40) is doped with phase change microcapsules.

11. A magnetic resonance imaging apparatus comprising a gradient coil according to any one of claims 1 to 10.