Gradient coil for a magnetic resonance imaging system

Abstract

The application discloses a gradient coil of a nuclear magnetic resonance imaging system, which comprises an RF shielding layer, a primary winding layer surrounding the outside of the RF shielding layer, three target-axis primary windings, i.e., an X target-axis primary winding, a Y target-axis primary winding and a Z target-axis primary winding, each target-axis primary winding having multiple layers of primary coils, and the multiple layers of primary coils in the same target-axis primary winding being arranged in a radial direction of the gradient coil, a shielding winding layer surrounding the outside of the primary winding layer, three target-axis shielding windings, i.e., an X target-axis shielding winding, a Y target-axis shielding winding and a Z target-axis shielding winding, and a passive shimming layer arranged between the primary winding layer and the shielding winding layer. The application can simultaneously meet the requirements of miniaturization, light weight and small impedance value of a high-performance gradient coil.

Description

Technical Field

[0001] This invention relates to the field of magnetic resonance imaging technology, and more particularly to a gradient coil for a magnetic resonance imaging system. Background Technology

[0002] This section is intended to provide background or context for the embodiments of the invention set forth in the claims. The description herein is not an admission that it is prior art simply because it is included in this section.

[0003] Gradient coils are a core component in magnetic resonance imaging (MRI) systems used to generate gradient magnetic fields. Traditional gradient coils are cylindrical and symmetrical. To meet the requirements of whole-body imaging scans, their inner diameter, outer diameter, and length are relatively large, resulting in higher weight and cost. Furthermore, traditional whole-body gradient coils have high impedance values, requiring significant electrical energy and generating substantial heat to output a high gradient magnetic field, necessitating powerful power supply and auxiliary cooling equipment. Therefore, traditional whole-body gradient coils have stringent installation requirements and high purchase and operating costs, making them unsuitable for clinical application in small and medium-sized medical institutions.

[0004] While ensuring good performance of the gradient coil, miniaturization and weight reduction of the coil, along with a decrease in impedance, can effectively solve the aforementioned problems. However, currently, there is a lack of high-performance gradient coils that simultaneously satisfy miniaturization, weight reduction, and low impedance. Summary of the Invention

[0005] This invention provides a gradient coil for a magnetic resonance imaging system to solve the technical problem that current high-performance gradient coils cannot simultaneously meet the requirements of miniaturization, lightweight design, and low coil impedance.

[0006] The above-mentioned objectives of the present invention can be achieved by the following technical solutions: This invention provides a gradient coil for a magnetic resonance imaging system, comprising: a radio frequency (RF) shielding layer; and a primary winding layer surrounding the RF shielding layer. The primary winding layer includes three target-axis primary windings, namely, an X-axis primary winding for generating a gradient magnetic field along the X direction, a Y-axis primary winding for generating a gradient magnetic field along the Y direction, and a Z-axis primary winding for generating a gradient magnetic field along the Z direction. The Z direction is arranged along the axial direction of the gradient coil, and the X, Y, and Z directions are arranged orthogonally to each other. Each target-axis primary winding has multiple layers of primary coils, and the primary windings of the same target axis... The primary coils are stacked radially along the gradient coils; a shielding winding layer surrounds the primary winding layer, the shielding winding layer includes three target axis shielding windings, namely an X target axis shielding winding, a Y target axis shielding winding, and a Z target axis shielding winding. The X target axis shielding winding is corresponding to the X target axis primary winding, the Y target axis shielding winding is corresponding to the Y target axis primary winding, and the Z target axis shielding winding is corresponding to the Z target axis primary winding. Each target axis shielding winding has at least one shielding coil; a passive shimming layer is disposed between the primary winding layer and the shielding winding layer.

[0007] In the embodiments of the present invention, each primary coil layer of each target shaft primary winding includes at least one primary coil unit, and the two primary coil units corresponding to two adjacent primary coil layers in each target shaft primary winding have the following relationship: the winding directions are opposite and connected in series in the same direction, or the winding directions are the same and connected in series in opposite directions.

[0008] In embodiments of the present invention, each layer of the shielding coil in each target shaft shielding winding includes at least one shielding coil unit, and the shielding coil unit of each layer of the shielding coil in each target shaft shielding winding corresponds one-to-one with the primary coil unit of the primary coil in the same layer of the primary winding of the corresponding target shaft; wherein, the shielding coil unit of each layer of the shielding coil in each target shaft shielding winding has a relationship with the corresponding primary coil unit of the outermost primary coil in the corresponding target shaft primary winding: the winding direction is the same and they are connected in series in the same direction, or the winding direction is opposite and they are connected in series in opposite directions.

[0009] In an embodiment of the present invention, the inner diameter of the gradient coil increases stepwise along its axial direction to form a first scanning space and a second scanning space arranged in a stepped manner. An effective imaging area is provided in the first scanning space, and the center of the effective imaging area is offset from the center of the gradient coil in the Z direction and is set close to the second scanning space. The scanning part of the subject extends through the second scanning space into the effective imaging area of ​​the first scanning space.

[0010] In an embodiment of the present invention, each layer of primary coils of the Z-target axis primary winding has a coil center in the Z direction, and the coil center coincides with the center of the effective imaging area. Each layer of primary coils of the X-target axis primary winding and each primary coil of the Y-target axis primary winding have a winding center in the Z direction. Each winding center is located on the side of the effective imaging area away from the second scanning space, and each primary coil of the X-target axis primary winding and the Y-target axis primary winding is asymmetrically arranged relative to its winding center.

[0011] In an embodiment of the present invention, the outer wall surface of the radio frequency shielding layer has a first step surface and a second step surface arranged in a stepped manner. The first scanning space and the second scanning space are connected by at least one transition space. The first step surface corresponds to the first scanning space, and the second step surface corresponds to at least one of the transition spaces. The multi-layer primary coil of the X target axis primary winding and the multi-layer primary coil of the Y target axis primary winding are laid layer by layer around the first step surface. The multi-layer primary coil of the Z target axis primary winding is laid layer by layer around the second step surface and partially extends to the periphery of the Y target axis primary winding.

[0012] In an embodiment of the present invention, the outer wall surface of the radio frequency shielding layer further has a third stepped surface, which is connected to the second stepped surface via a connecting surface, and the inner diameter of the third stepped surface is larger than the inner diameter of the second stepped surface; one end of the passive shimming layer is inserted into the connecting surface, and the passive shimming layer is laid on the periphery of the second stepped surface and the first stepped surface and covers the setting areas of the X target axis primary winding, the Y target axis primary winding and the Z target axis primary winding; the three target axis shielding windings of the shielding winding layer are laid layer by layer on the periphery of the third stepped surface and cover the setting area of ​​the passive shimming layer.

[0013] In an embodiment of the present invention, each layer of primary coil of the X target axis primary winding includes a plurality of first primary coil units, each layer of primary coil of the Y target axis primary winding includes a plurality of second primary coil units, and each layer of primary coil of the Z target axis primary winding includes a third primary coil unit. The plurality of first primary coil units are disposed opposite to each other on the outside of the radio frequency shielding layer in the X direction, the plurality of second primary coil units are disposed opposite to each other on the outside of the radio frequency shielding layer in the Y direction, and the third primary coil unit is sleeved on the outside of the radio frequency shielding layer along the Z direction.

[0014] In embodiments of the present invention, each layer of shielding coil of the X-target axis shielding winding includes a plurality of first shielding coil units, each layer of shielding coil of the Y-target axis shielding winding includes a plurality of second shielding coil units, and each layer of shielding coil of the Z-target axis shielding winding includes a plurality of third shielding coil units. The plurality of first shielding coil units correspond to a plurality of first primary coil units of the same layer of primary coil of the X-target axis primary winding, the plurality of second shielding coil units correspond to a plurality of second primary coil units of the same layer of primary coil of the Y-target axis primary winding, and the plurality of third shielding coil units correspond to a third primary coil unit of the same layer of primary coil of the Z-target axis primary winding.

[0015] In the embodiments of the present invention, the first primary coil unit, the second primary coil unit, the first shielding coil unit, and the second shielding coil unit are all saddle-shaped, and the third primary coil unit and the third shielding coil unit are both solenoid-shaped.

[0016] In an embodiment of the present invention, the passive shimming layer includes multiple shimming strips, which are uniformly distributed along the circumference of the gradient coil; each shimming strip contains multiple shimming pads along the axial direction of the gradient coil.

[0017] In an embodiment of the present invention, the gradient coil further includes an encapsulation layer, in which the radio frequency shielding layer, the primary winding layer, and the shielding winding layer are encapsulated, and the encapsulation layer is made of glass fiber and epoxy resin.

[0018] In embodiments of the present invention, both the primary winding layer and the shielding winding layer are made of copper or aluminum plates or wires; the radio frequency shielding layer is a mesh structure made of copper or steel.

[0019] The present invention has the following beneficial effects: 1. The primary winding of the target axis is constructed by using multi-layer primary coils with stacked arrangement. This is beneficial for placing conductors with larger cross-sectional areas and increasing the number of coil turns. It also helps to control the coil resistance and Joule power at an acceptable engineering level. This reduces the gradient coil impedance value and the requirements for driving power and auxiliary heat dissipation during coil operation. It can achieve a sufficiently large effective imaging range and minimize the coil size, weight and cost. 2. The primary windings of the X target axis, Y target axis, and Z target axis all adopt multi-layer primary coils with stacked configurations, which generates a high-intensity and highly linear magnetic field along the X, Y, and Z directions, improving the linearity and uniformity of the gradient field. 3. By forming a smaller first scanning space and a larger second scanning space arranged in a stepped pattern within the gradient coil, and setting the effective imaging area within the first scanning space close to the second scanning space, the shoulders of subjects with a large shoulder width will not interfere with the outer edge of the gradient coil, allowing them to smoothly enter the larger second scanning space. The scanning area of ​​the subject can then smoothly reach the effective imaging area within the first scanning space. Furthermore, the inner diameter of the first scanning space can be smaller than the width of the subject's shoulders, thereby reducing the overall size of the gradient coil. 4. By aligning the center of the primary coil of the Z-axis primary winding with the center of the effective imaging area, and placing the winding centers of the primary coils of the X-axis and Y-axis primary windings on the side of the effective imaging area away from the second scanning area, the primary windings of the X-axis, Y-axis, and Z-axis cooperate to form the effective imaging area. 5. By setting a stepped radio frequency shielding layer, the multi-layer primary coil of the X target axis primary winding and the multi-layer primary coil of the Y target axis primary winding are laid on its first stepped surface, and the Z target axis primary winding is laid on its second stepped surface. This reduces the coil size and utilizes the distribution of gradient magnetic field. In addition, the radio frequency shielding layer effectively isolates the radio frequency field and minimizes eddy current heating, ensuring a good distribution of the radio frequency field and thus guaranteeing good image quality. 6. The passive shim layer located between the primary winding layer and the shielding winding layer can improve the adaptability of the coil to different magnetic resonance imaging systems. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. In the drawings: Figure 1 This is a schematic cross-sectional view of the gradient coil along the Z direction in an embodiment of the present invention; Figure 2 This is a partially enlarged view of the cross-section of the gradient coil along the Z direction in an embodiment of the present invention; Figure 3 This is a schematic diagram of the gradient coil along the X and Y directions in an embodiment of the present invention; Figure 4 This is a partially enlarged view of the cross-section of the gradient coil along the X and Y directions in an embodiment of the present invention; Figure 5 This is a schematic diagram of the structure of the primary winding of the X target axis not being covered by the primary winding of the Y target axis in an embodiment of the present invention (X-direction view). Figure 6 This is a schematic diagram (Y-direction view) of the structure in an embodiment of the present invention where the primary winding of the X target axis is not covered by the primary winding of the Y target axis. Figure 7 This is a schematic diagram of the primary winding of the X-axis target axis in an embodiment of the present invention (view from the Z direction). Figure 8 This is a schematic diagram (Y-direction view) of the structure of the Y-axis primary winding covered with the Z-axis primary winding in an embodiment of the present invention. Figure 9 This is a schematic diagram (X-direction view) of the structure of the Y-axis primary winding covered with the Z-axis primary winding in an embodiment of the present invention. Figure 10 This is a schematic diagram of the Y-axis primary winding structure in an embodiment of the present invention (Z-direction view).

[0021] In the picture: 1. RF shielding layer; 11. First step surface; 12. Second step surface; 13. Third step surface; 14. Connecting surface; 2. Primary winding layer; 21. X-target axis primary winding; 211. Primary coil; 2111. First primary coil unit; Ox. Winding center; 22. Y-target axis primary winding; 221. Primary coil; 2211. Second primary coil unit; Oy. Winding center; 23. Z-target axis primary winding; 231. Primary coil; 2311. Third primary coil unit; Oz. Coil center; 3. Shielding winding layer; 31. X-target axis shielding winding; 32. Y-target axis shielding winding; 33. Z-target axis shielding winding; 4. Passive shimming layer; 41. Shimming bar; 5. First scanning space; 51. Effective imaging area; 6. Second scanning space; 7. Transition space; 8. Encapsulation layer. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings. Here, the illustrative embodiments of the present invention and their descriptions are used to explain the present invention, but are not intended to limit the present invention.

[0023] The inventors believe that the size of the gradient coil is subject to strict limitations due to the presence of an RF coil inserted into the inner diameter space of the gradient coil and a magnet surrounding the outer diameter space of the gradient coil. Furthermore, magnet designers aim to reduce the inner diameter of the magnet, while RF coil designers aim to increase the outer diameter of the RF coil. This severely limits the space available for designing high-performance gradient coils, making the design process very challenging. Additionally, the small diameter of the miniaturized gradient coil can interfere with the subject's shoulder or other non-scanning areas, hindering the head or extremities from reaching the effective imaging area. Achieving high performance and an easily achievable effective imaging area within a miniaturized gradient coil further increases the design difficulty.

[0024] The gradient coil proposed in this invention boasts strong performance indicators and is miniaturized and lightweight. This gradient coil is a compact cylindrical device designed around the human head or limbs, aiming to generate a high-intensity and highly linear magnetic field along the X / Y / Z target axes. To achieve strong gradient strength and slewing rate, as well as good magnetic field uniformity and linearity within a small space, while reducing coil impedance, the primary winding of each target axis has multiple (two or more) primary coils stacked radially. The underlying concept is as follows: First, for the primary windings of the X-axis, Y-axis, and Z-axis of the gradient coil, multiple primary coils are arranged radially in a compact space to enhance the gradient field strength in the X, Y, and Z directions, improve the linearity and uniformity of the gradient field, and place a shielding winding layer in the space further outward in the radial direction to eliminate stray fields outside the gradient coil.

[0025] Second, the gradient coil forms a larger second scanning space and a smaller first scanning space along the Z direction inside, and the effective imaging area is set in the first scanning space with the inner diameter of each step decreasing step by step, so as to ensure that the scanned part can easily reach the effective imaging area.

[0026] Third, a passive shimming layer is added between the primary winding layer and the shielding winding layer to perform passive shimming of the main magnetic field.

[0027] Fourth, the RF shielding layer is used to isolate the primary winding layer from the RF field to ensure a good distribution of the RF field. By designing the RF shielding layer in a stepped shape, the primary windings of the X target axis and Y target axis are laid on its first step surface, and the primary winding of the Z target axis is laid on its second step surface. This reduces the size of the coil and is also beneficial to the distribution of the magnetic field.

[0028] The gradient coil proposed in the embodiments of the present invention will be described in detail below.

[0029] like Figure 1 , Figure 2 , Figure 3 as well as Figure 4 As shown, the gradient coil includes: an RF shielding layer 1; and a primary winding layer 2 surrounding the RF shielding layer 1. The primary winding layer 2 includes three target axis primary windings: an X-axis primary winding 21 for generating a gradient magnetic field along the X direction, a Y-axis primary winding 22 for generating a gradient magnetic field in the Y direction, and a Z-axis primary winding 23 for generating a gradient magnetic field in the Z direction. The Z direction is arranged along the axial direction of the gradient coil, and the X, Y, and Z directions are arranged orthogonally to each other. Each target axis primary winding has multiple layers of primary coils, and the multiple layers of primary coils in the same target axis primary winding are radially aligned with the gradient coil. (e.g., X and Y directions) Stacked arrangement; Shielding winding layer 3, surrounding the primary winding layer 2, the shielding winding layer 3 includes three target axis shielding windings, namely X target axis shielding winding 31, Y target axis shielding winding 32 and Z target axis shielding winding 33, X target axis shielding winding 31 is arranged corresponding to X target axis primary winding 21, Y target axis shielding winding 32 is arranged corresponding to Y target axis primary winding 22, Z target axis shielding winding 33 is arranged corresponding to Z target axis primary winding 23, each target axis shielding winding has at least one layer of shielding coil; Passive shimming layer 4, disposed between primary winding layer 2 and shielding winding layer 3.

[0030] It should be noted that the X and Y directions described in this invention are not limited to a specific direction, and can be any two perpendicular radial directions of the gradient coil. In this embodiment, Figure 3 The left and right directions shown are defined as the X direction. Figure 3 The vertical direction shown is defined as the Y direction.

[0031] It is well known that magnetic field strength is proportional to factors such as current and the number of conductor turns. However, the challenge in gradient coil design lies in finding space to accommodate more turns while keeping coil resistance and Joule power within acceptable engineering levels. A key solution is to use a multi-layered primary coil configuration to form the primary winding of the target axis. The gradient coil of this invention, by using a multi-layered primary coil configuration to form the primary winding of the target axis in various directions, can achieve a sufficiently large effective imaging range while minimizing coil size, weight, and cost. Furthermore, it helps to fully utilize limited axial and radial space, allowing for the placement of conductors with larger cross-sectional areas and increasing the number of coil turns, thereby improving magnetic field strength, magnetic field uniformity, and linearity, while reducing coil impedance and the need for drive power and auxiliary heat dissipation during coil operation.

[0032] like Figure 4 As shown, in order to generate a gradient magnetic field with higher magnetic field strength along the X direction by coordinating the multiple primary coils 211 in the X target axis primary winding 21, to generate a gradient magnetic field with higher magnetic field strength along the Y direction by coordinating the multiple primary coils 221 in the Y target axis primary winding 22, and to generate a gradient magnetic field with higher magnetic field strength along the Z direction by coordinating the multiple primary coils 231 in the Z target axis primary winding 23, in the embodiments of the present invention, each layer of primary coil in each target axis primary winding includes at least one primary coil unit, and the two primary coil units corresponding to two adjacent layers of primary coil in each target axis primary winding have the following relationship: the winding directions are opposite and connected in series in the same direction, or the winding directions are the same and connected in series in opposite directions.

[0033] Specifically, in combination Figure 7 As shown, each layer of primary coil 211 of the X-axis primary winding 21 includes multiple first primary coil units. Multiple first primary coil units 2111 and multiple first primary coil units 2111' are disposed opposite each other in the X direction outside the RF shielding layer 1. Adjacent first primary coil units 2111 and 2111' on the same side have the following relationship: either their winding directions are opposite and they are connected in series in the same direction; or their winding directions are the same and they are connected in series in opposite directions.

[0034] Combination Figure 4 , Figure 8 , Figure 9 as well as Figure 10 As shown, each layer of primary coil 221 of the Y-axis primary winding 22 includes multiple second primary coil units 2211. Both the multiple second primary coil units 2211 and the second primary coil units 2211' are disposed opposite each other in the Y direction outside the RF shielding layer 1. Adjacent second primary coil units 2211 and second primary coil units 2211' on the same side have the following relationships: either their winding directions are opposite and they are connected in series in the same direction; or their winding directions are the same and they are connected in series in opposite directions.

[0035] Combination Figure 4 , Figure 8 as well as Figure 9 As shown, each layer of primary coil 231 of the Z-axis primary winding 23 includes a third primary coil unit 2311, which is sleeved on the outside of the radio frequency shielding layer 1 along the Z direction. Adjacent layers of third primary coil units 2311 have the following relationship: either the winding directions are opposite and they are connected in series in the same direction; or the winding directions are the same and they are connected in series in opposite directions.

[0036] In this embodiment, as Figure 7 As shown, the primary windings 21, 22, and 23 of the X-target axis, Y-target axis, and Z-target axis all have two layers of primary coils, but can also be configured with three, four, or more layers. Specifically, the outer primary coil 211 of the X-target axis primary winding 21 includes two first primary coil units 2111, and the inner primary coil 211' of the X-target axis primary winding 21 includes two first primary coil units 2111', meaning the X-target axis primary winding 21 comprises a total of four first primary coil units. Figure 10 As shown, the outer primary coil 221 of the Y-target axis primary winding 22 includes two second primary coil units 2211, and the inner primary coil 221' of the Y-target axis primary winding 22 includes two second primary coil units 2211', meaning the Y-target axis primary winding 22 includes a total of four second primary coil units. Figure 5 and Figure 8 As shown, both the first primary coil unit 2111 and the second primary coil unit 2211 are saddle-shaped. Figure 8 and Figure 9 As shown, each layer of primary coil 231 in the Z target axis primary winding 23 includes a third primary coil unit 2311, that is, the Z target axis primary winding 23 has a total of two third primary coil units 2311, and the third primary coil unit 2311 is solenoid in shape.

[0037] In order to utilize the X-axis shielding winding 31, Y-axis shielding winding 32, and Z-axis shielding winding 33 to respectively shield the gradient magnetic field generated by the X-axis primary winding 21, Y-axis primary winding 22, and Z-axis primary winding 23, as follows: Figure 2 and Figure 4As shown, in the embodiments of the present invention, each layer of shielding coil in each target shaft shielding winding includes at least one shielding coil unit, and the shielding coil unit of each layer of shielding coil in each target shaft shielding winding corresponds one-to-one with the primary coil unit of the same layer of primary coil in the corresponding target shaft primary winding; wherein, the shielding coil unit of each layer of shielding coil in each target shaft shielding winding has a relationship with the corresponding primary coil unit of the outermost primary coil in the corresponding target shaft primary winding: the winding direction is the same and they are connected in series in the same direction, or the winding direction is opposite and they are connected in series in opposite directions.

[0038] Specifically, each layer of shielding coil in the X-axis shielding winding 31 includes multiple first shielding coil units; each layer of shielding coil in the Y-axis shielding winding 32 includes multiple second shielding coil units; and each layer of shielding coil in the Z-axis shielding winding 33 includes multiple third shielding coil units. The multiple first shielding coil units correspond to multiple first primary coil units 2111 of the same layer of primary coil 211 in the X-axis primary winding 21; the multiple second shielding coil units correspond to multiple second primary coil units 2211 of the same layer of primary coil 221 in the Y-axis primary winding 22; and the third shielding coil units correspond to the third primary coil units 2311 of the same layer of primary coil 231 in the Z-axis primary winding 23. The first shielding coil units on the same side and their corresponding outermost first primary coil units 2111 are related in that they have the same winding direction and are connected in series in the same direction. Similarly, the second shielding coil units on the same side and their corresponding outermost second primary coil units 2211 are also related in that they have the same winding direction and are connected in series in the same direction. The third shielded coil unit and its corresponding outermost third primary coil unit 2311 are related in that the winding directions are the same and they are connected in series in the same direction.

[0039] In this embodiment, the shielding coils in the X-axis shielding winding 31, Y-axis shielding winding 32, and Z-axis shielding winding 33 are all single-layered, although they can also be configured as two, three, or more layers. The first and second shielding coil units are both two in number and saddle-shaped. The third shielding coil unit is one in number and is solenoid-shaped.

[0040] like Figure 1As shown, in order to reduce the size of the gradient coil while enabling the subject's scanning area to quickly and smoothly enter the effective imaging region 51, in this embodiment of the invention, the inner diameter of the gradient coil gradually increases along its axial direction to form a stepped arrangement of the first scanning space 5 and the second scanning space 6. The effective imaging region 51 is provided in the first scanning space 5, and the effective imaging region 51 is offset from the center O of the gradient coil in the Z direction and is located close to the second scanning space 6. The subject's scanning area extends through the second scanning space 6 into the effective imaging region 51 of the first scanning space 5. The radial dimension of the second scanning space 6 can be slightly larger than the width of the shoulder and torso of a subject with a larger shoulder width, while the first scanning space 5 can be slightly larger than the width of the subject's head or extremities. This structure allows subjects with a larger shoulder width to enter the second scanning space 6, enabling the scanning area to quickly and smoothly reach the effective imaging region 51.

[0041] The inner cavity of the gradient coil can be in a two-stage stepped shape, that is, it only includes the first scanning space 5 and the second scanning space 6. Alternatively, as shown in this embodiment, it can be in a three-stage stepped shape, where the second scanning space 6 is connected to the first scanning space 5 through a transition space 7, wherein the radial dimension of the transition space 7 is larger than the radial dimension of the first scanning space 5 but smaller than the radial dimension of the second scanning space 6. Optionally, the inner cavity of the gradient coil can also be in a four-stage or more stepped shape, that is, more transition spaces can be provided between the first and second scanning spaces.

[0042] Specifically, the effective imaging region 51 is spherical or ellipsoidal. The gradient coil is asymmetrical with respect to its center O in the Z direction, wherein the gradient coil has an entry end for the subject in the Z direction, and the opening end of the second scanning space 6 is the entry end for the subject. The effective imaging region 51 is close to the second scanning space 6, and the center Os of the effective imaging region 51 is offset from the center O in the Z direction of the gradient coil (i.e., the geometric center of the entire gradient coil). In addition, in one embodiment, the inner cavity of the gradient coil also needs to integrate radio frequency transmitting and receiving coils disposed in the scanning space, as well as a subject lying or transport device.

[0043] To ensure that the gradient magnetic field within the effective imaging region 51 exhibits good uniformity and linearity, in embodiments of the present invention, such as... Figure 5 and Figure 6 As shown, each layer of primary coils 211 in the X-target axis primary winding 21 has a winding center Ox, and each winding center Ox is located on the side of the effective imaging area 51 away from the second scanning space 6. Each primary coil 211 of the X-target axis primary winding 21 is asymmetrically arranged relative to its winding center Ox, thereby confining the gradient magnetic field distributed along the X direction within a compact space around the coil. Figure 8 as well as Figure 9 As shown, each primary coil 221 of the Y-axis primary winding 22 has a winding center Oy in the Z direction. Each winding center Oy is located on the side of the effective imaging area 51 away from the second scanning space 6. Furthermore, each primary coil 221 of the Y-axis primary winding 22 is asymmetrically arranged relative to its winding center Oy, thereby confining the gradient magnetic field distributed along the Y direction within a compact spatial range around the coil. Combined with... Figure 8 and Figure 9 As shown, each layer of primary coils 231 of the Z-target axis primary winding 23 has a coil center Oz in the Z direction, and the coil center Oz coincides with the center of the effective imaging area 51, thereby confining the gradient magnetic field distributed along the Z direction within a compact space around the coil.

[0044] To achieve better uniformity and linearity in the gradient magnetic field within the effective imaging region 51, such as... Figure 2 As shown, in an embodiment of the present invention, the outer wall surface of the RF shielding layer 1 has a first stepped surface 11 and a second stepped surface 12 with progressively increasing outer diameters. The first stepped surface 11 corresponds to the first scanning space 5, and the second stepped surface 12 corresponds to the transition space 7. The multilayer primary coil 211 of the X target axis primary winding 21 and the multilayer primary coil 221 of the Y target axis primary winding 22 are laid layer by layer around the first stepped surface 11. The multilayer primary coil 231 of the Z target axis primary winding 23 is laid layer by layer around the second stepped surface 12 and partially extends to the periphery of the Y target axis primary winding 22. In this embodiment of the present invention, by adding at least one transition space 7 between the first scanning space 5 and the second scanning space 6, the outer wall surface of the RF shielding layer 1 can form at least one corresponding second stepped surface 12 (i.e., an intermediate stepped surface), thereby using an intermediate stepped surface to set the Z target axis primary winding 23.

[0045] To ensure that the shielding winding layer 3 can better perform its magnetic field shielding performance, and that the passive shimming layer 4 can better perform its shimming performance. For example... Figure 2 As shown, in an embodiment of the present invention, the outer wall surface of the radio frequency shielding layer 1 further has a third stepped surface 13. The third stepped surface 13 is connected to the second stepped surface 12 through a connecting surface 14, and the inner diameter of the third stepped surface 13 is larger than the inner diameter of the second stepped surface 12. One end of the passive shimming layer 4 is inserted into the connecting surface 14. The passive shimming layer 4 is laid on the periphery of the second stepped surface 12 and the first stepped surface 11 and covers the setting area of ​​the X target axis primary winding 21, the Y target axis primary winding 22, and the Z target axis primary winding 23. The three target axis shielding windings of the shielding winding layer 3 are laid layer by layer on the periphery of the third stepped surface 13 and cover the setting area of ​​the passive shimming layer 4. Specifically, as shown... Figure 2As shown, the X-axis shielding winding 31, Y-axis shielding winding 32, and Z-axis shielding winding 33 of the shielding winding layer 3 are laid out from the inside out.

[0046] like Figure 3 and Figure 4 As shown, the passive shimming layer 4 includes multiple shimming strips 41, which are uniformly distributed along the circumference of the gradient coil. Each shimming strip 41 contains multiple shimming pads along the axial direction of the gradient coil. The number of shimming strips 41 can be determined according to actual conditions, for example, 24, 30, or 36 strips. Within each shimming strip 41, shimming pads calculated using a specified algorithm are added at different positions along the Z-axis, based on the actual distribution of the main magnetic field in the planned magnetic resonance imaging system. The passive shimming layer 4 can effectively cancel high-order harmonic components in the main magnetic field, significantly improve the uniformity index of the main magnetic field, and enhance the adaptability of the gradient coil to different magnetic resonance imaging systems.

[0047] like Figures 1 to 4 As shown, the gradient coil also includes an encapsulation layer 8. The radio frequency shielding layer 1, the primary winding layer 2, and the shielding winding layer 3 are encapsulated within the encapsulation layer 8, which is made of glass fiber and epoxy resin. The inner cavity of the encapsulation layer 8 constitutes the inner cavity of the gradient coil and is generally stepped. The primary winding layer 2 and the shielding winding layer 3 are both made of copper or aluminum plates or wires; the radio frequency shielding layer 1 is a mesh structure made of copper or steel.

[0048] The following is a reference dimension; see [reference] Figure 1 The example uses a three-tiered structure: the effective imaging area 51 of the sphere has a diameter of 26 cm; the innermost step of the encapsulation layer has an inner diameter of 36 cm, the second step (middle step) has an inner diameter of 48 cm, and the outermost step has an inner diameter of 52 cm; the outer diameter of the encapsulation layer 8 is 56 cm, and its length along the Z direction is 1000 cm; the distance from the center of the effective imaging area 51 to the leftmost end of the encapsulation layer 8 is 30 cm. This ensures that the head or extremities of adults and minors can easily reach the area shown in the effective imaging area 51. The miniaturized high-performance gradient coil designed according to the method and reference dimensions of this invention can simultaneously achieve the following performance: within a spherical effective imaging region 51 with a diameter of 26 cm, the nonlinearity of the gradient magnetic field is less than 8%, and the non-uniformity is less than 40%; the gain of the primary winding of each target axis is higher than 0.18 millitalas per ampere, and the DC resistance is less than 100 milliohms; it can support continuous imaging scanning with a maximum gradient intensity greater than 110 millitalas per meter and a continuous gradient intensity greater than 30 millitalas per meter, and the overall power dissipation of the coil is less than 9 kilowatts.

[0049] See Figure 1When the encapsulation layer 8 has 3 steps, the primary winding 21 of the X target axis and the primary winding 22 of the Y target axis are wound around the outer periphery of the innermost step of the encapsulation layer 8. The Z-target axis primary winding 23 is wound around the outer periphery of the intermediate step of the encapsulation layer 8. The X-axis shielding winding 31, the Y-axis shielding winding 32, and the Z-axis shielding winding 33 are wound around the outermost step of the encapsulation layer 8.

[0050] When the stepped inner cavity of the gradient coil has more than three layers, there are multiple steps in the middle layer. Therefore, the primary winding 33 of the Z target axis can be wound around any one of the layers.

[0051] In summary, the gradient coil proposed in this embodiment of the invention employs a target axis primary winding composed of multiple primary coils, which facilitates the placement of conductors with larger cross-sectional areas and increases the number of coil turns. It also helps control the coil resistance and Joule power at acceptable engineering levels, reducing coil impedance and the need for driving power and auxiliary heat dissipation during gradient coil operation. This allows for a sufficiently large effective imaging range while minimizing coil size, weight, and cost. The primary winding layer simultaneously includes X-target axis primary windings, Y-target axis primary windings, and Z-target axis primary windings, generating high-intensity and highly linear magnetic fields along each target axis (X / Y / Z), improving the linearity and uniformity of the gradient field. The effective imaging area 51 is located near the subject entry end, and the inner diameter of the stepped inner cavity of the gradient coil gradually increases along the subject entry direction. The gradient coil features an asymmetric electromagnetic and mechanical design along the Z-direction for both the X-axis and Y-axis primary windings. This design allows the subject's head or extremities to easily reach the effective imaging area within a smaller inner diameter constraint. Furthermore, subjects with larger shoulder widths will not experience interference with the outer edge of the gradient coil, allowing them to pass smoothly through the larger inner diameter area outside the coil. The passive shimming layer between the primary winding layer and the shielding winding layer enhances the gradient coil's adaptability to different magnetic resonance imaging systems. A stepped radio frequency shielding layer covering the inner cavity of the gradient coil effectively isolates the radio frequency field and minimizes eddy current heating, ensuring a good distribution of the radio frequency field and thus guaranteeing excellent image quality.

[0052] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A gradient coil for a magnetic resonance imaging system, characterized in that, include: Radio frequency shielding layer; A primary winding layer surrounds the outside of the radio frequency shielding layer. The primary winding layer includes three target axis primary windings, namely, an X target axis primary winding for generating a gradient magnetic field in the X direction, a Y target axis primary winding for generating a gradient magnetic field in the Y direction, and a Z target axis primary winding for generating a gradient magnetic field in the Z direction. The Z direction is arranged along the axial direction of the gradient coil. The X direction, the Y direction, and the Z direction are arranged orthogonally to each other. Each target axis primary winding has multiple primary coils, and the multiple primary coils in the same target axis primary winding are stacked radially along the gradient coil. A shielding winding layer surrounds the primary winding layer. The shielding winding layer includes three target axis shielding windings, namely an X target axis shielding winding, a Y target axis shielding winding, and a Z target axis shielding winding. The X target axis shielding winding is correspondingly arranged with the X target axis primary winding, the Y target axis shielding winding is correspondingly arranged with the Y target axis primary winding, and the Z target axis shielding winding is correspondingly arranged with the Z target axis primary winding. Each target axis shielding winding has at least one layer of shielding coil. A passive shim is disposed between the primary winding layer and the shielding winding layer; The inner diameter of the gradient coil increases gradually along its axial direction to form a first scanning space and a second scanning space arranged in a stepped manner. An effective imaging area is provided in the first scanning space. The outer wall of the radio frequency shielding layer has a first step surface and a second step surface arranged in a stepped manner. The first scanning space and the second scanning space are connected by at least one transition space. The first step surface corresponds to the first scanning space, and the second step surface corresponds to at least one of the transition spaces. The multi-layer primary coil of the primary winding of the X target axis and the multi-layer primary coil of the primary winding of the Y target axis are laid layer by layer on the periphery of the first step surface. The multi-layer primary coil of the Z-target axis primary winding is laid layer by layer on the periphery of the second step surface and extends partially to the periphery of the Y-target axis primary winding.

2. The gradient coil of the nuclear magnetic resonance imaging system as described in claim 1, characterized in that, Each primary coil layer of each target shaft primary winding includes at least one primary coil unit, and the two primary coil units corresponding to two adjacent primary coil layers in each target shaft primary winding have the following relationship: the winding directions are opposite and connected in series in the same direction, or the winding directions are the same and connected in series in opposite directions.

3. The gradient coil of the nuclear magnetic resonance imaging system as described in claim 2, characterized in that, Each layer of the shielding coil in each target shaft shielding winding includes at least one shielding coil unit, and the shielding coil unit of each layer of the shielding coil in each target shaft shielding winding corresponds one-to-one with the primary coil unit of the primary coil in the same layer of the primary winding in the corresponding target shaft primary winding. The shielding coil unit of each layer of the shielding coil in each target shaft shielding winding has a relationship with the corresponding primary coil unit of the outermost primary coil in the corresponding target shaft primary winding: the winding directions are the same and they are connected in series in the same direction, or the winding directions are opposite and they are connected in series in opposite directions.

4. The gradient coil of the nuclear magnetic resonance imaging system as described in claim 1, characterized in that, The center of the effective imaging region is offset from the center of the gradient coil in the Z direction and is set close to the second scanning space. The subject's scanning part extends through the second scanning space into the effective imaging region of the first scanning space.

5. The gradient coil of the magnetic resonance imaging system as described in claim 4, characterized in that, Each layer of primary coils in the Z-axis primary winding has a coil center in the Z direction, and the coil center coincides with the center of the effective imaging area. Each layer of primary coils in the X-axis primary winding and each primary coil in the Y-axis primary winding have a winding center in the Z direction. Each winding center is located on the side of the effective imaging area away from the second scanning space, and each primary coil in the X-axis primary winding and the Y-axis primary winding is asymmetrically arranged relative to its winding center.

6. The gradient coil of the nuclear magnetic resonance imaging system as described in claim 5, characterized in that, The outer wall surface of the radio frequency shielding layer also has a third stepped surface, which is connected to the second stepped surface through a connecting surface, and the inner diameter of the third stepped surface is larger than the inner diameter of the second stepped surface. One end of the passive shimming layer is inserted into the connecting surface. The passive shimming layer is laid on the periphery of the second step surface and the first step surface and covers the setting areas of the X target axis primary winding, the Y target axis primary winding and the Z target axis primary winding. The three target shaft shielding windings of the shielding winding layer are laid layer by layer around the third step surface and cover the area where the passive shimming layer is set.

7. The gradient coil of the magnetic resonance imaging system according to any one of claims 1-6, characterized in that, Each layer of the primary coil of the X-axis primary winding includes multiple first primary coil units, each layer of the primary coil of the Y-axis primary winding includes multiple second primary coil units, and each layer of the primary coil of the Z-axis primary winding includes a third primary coil unit. The multiple first primary coil units are disposed opposite each other in the X direction outside the RF shielding layer, the multiple second primary coil units are disposed opposite each other in the Y direction outside the RF shielding layer, and the third primary coil unit is sleeved on the outside of the RF shielding layer along the Z direction.

8. The gradient coil of the nuclear magnetic resonance imaging system as described in claim 7, characterized in that, Each layer of shielding coil in the X-axis shielding winding includes multiple first shielding coil units; each layer of shielding coil in the Y-axis shielding winding includes multiple second shielding coil units; and each layer of shielding coil in the Z-axis shielding winding includes a third shielding coil unit. The multiple first shielding coil units correspond to multiple first primary coil units of the same layer of primary coil in the X-axis primary winding; the multiple second shielding coil units correspond to multiple second primary coil units of the same layer of primary coil in the Y-axis primary winding; and the third shielding coil units correspond to the third primary coil units of the same layer of primary coil in the Z-axis primary winding.

9. The gradient coil of the nuclear magnetic resonance imaging system as described in claim 8, characterized in that, The first primary coil unit, the second primary coil unit, the first shielded coil unit, and the second shielded coil unit are all saddle-shaped, while the third primary coil unit and the third shielded coil unit are both solenoid-shaped.

10. The gradient coil of the magnetic resonance imaging system according to any one of claims 1-6, characterized in that, The passive shimming layer includes multiple shimming strips, which are uniformly distributed along the circumference of the gradient coil; each shimming strip contains multiple shimming pads along the axial direction of the gradient coil.

11. The gradient coil of the magnetic resonance imaging system according to any one of claims 1-6, characterized in that, The gradient coil also includes an encapsulation layer, in which the radio frequency shielding layer, the primary winding layer, and the shielding winding layer are encapsulated. The encapsulation layer is made of glass fiber and epoxy resin.

12. The gradient coil of the magnetic resonance imaging system according to any one of claims 1-6, characterized in that, Both the primary winding layer and the shielding winding layer are made of copper or aluminum plates or wires; the radio frequency shielding layer is a mesh structure made of copper or steel.

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