CN112285621A - Gradient coil, gradient system and magnetic resonance imaging system - Google Patents
Gradient coil, gradient system and magnetic resonance imaging system Download PDFInfo
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
- G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
- G01R33/38—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field
- G01R33/385—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field using gradient magnetic field coils
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
- G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
- G01R33/42—Screening
- G01R33/421—Screening of main or gradient magnetic field
- G01R33/4215—Screening of main or gradient magnetic field of the gradient magnetic field, e.g. using passive or active shielding of the gradient magnetic field
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
- G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
- G01R33/48—NMR imaging systems
Abstract
The application relates to a gradient coil, a gradient system and a magnetic resonance imaging system. The gradient coil includes coaxial first coil, second coil and the reverse coil that sets up, and the current direction in first coil and the second coil is opposite, and the current direction in the reverse coil is opposite with the current direction in the second coil, and the distance between first coil and the second coil is less than the twice of the radius of first coil, and the reverse coil sets up between first coil and second coil, and the distance between reverse coil and the first coil is greater than the distance between reverse coil and the first coil. Set up reverse coil through the position that is close to the second coil, shortened the distance between first coil and the second coil, under the prerequisite of guaranteeing gradient coil working property, shortened gradient coil's length, with gradient coil's volume control in finite space, but make gradient coil's range of application wider, it is more convenient to use.
Description
Technical Field
The present application relates to the field of magnetic resonance imaging technology, and in particular, to a gradient coil, a gradient system, and a magnetic resonance imaging system.
Background
MRI (Magnetic Resonance Imaging) uses the Magnetic Resonance phenomenon to obtain electromagnetic signals from a human body and reconstruct human body information, and is one of important medical diagnosis and scientific research instruments. The gradient coil is one of core components of an MRI system, the main function of the gradient coil is to convert electric energy into magnetic energy, a magnetic field is generated by passing current in the coil, the intensity of the magnetic field is in direct proportion to the intensity of the passing current in a certain range, and the linearity is an important index for measuring the performance of the gradient coil.
In a conventional gradient coil, a maxwell coil pair is usually used as a Z gradient coil, and if the coil pair is spaced by 2R and the radius R is greater than twice the radius of an imaging space, the linearity of the gradient coil is better. However, the distance between the two coils of the coil pair is relatively long, which is not favorable for the space planning of the magnetic resonance imaging system due to the structural limitation of the magnet, so that the gradient coil is not convenient to use.
Disclosure of Invention
In view of the above, it is necessary to provide a gradient coil, a gradient system and a magnetic resonance imaging system to solve the problem that the conventional gradient coil is not convenient to use.
A gradient coil comprises a first coil, a second coil and a reverse coil which are coaxially arranged, wherein the current directions in the first coil and the second coil are opposite, the current directions in the reverse coil and the second coil are opposite, the distance between the first coil and the second coil is smaller than twice of the radius of the first coil, the reverse coil is arranged between the first coil and the second coil, and the distance between the reverse coil and the first coil is larger than the distance between the reverse coil and the second coil.
The gradient coil comprises a first coil, a second coil and a reverse coil which are coaxially arranged, the current directions in the first coil and the second coil are opposite, the current direction in the reverse coil is opposite to the current direction in the second coil, the distance between the first coil and the second coil is smaller than twice of the radius of the first coil, the reverse coil is arranged between the first coil and the second coil, and the distance between the reverse coil and the first coil is larger than the distance between the reverse coil and the first coil. Set up the reverse coil through the position that is close to the second coil, the current direction in the reverse coil is opposite with the current direction in the second coil, can make the distance between first coil and the second coil be less than the radial twice of first coil, the distance between first coil and the second coil has been shortened, under the prerequisite of guaranteeing gradient coil working property, the length of gradient coil has been shortened, with the volume control of gradient coil in finite space, make gradient coil's range of application wider, it is more convenient to use.
In one embodiment, the radius of the counter coil matches the radius of the first coil.
In one embodiment, the radius of the second coil is greater than or equal to the radius of the first coil.
In one embodiment, the distance between the first coil and the second coil matches the radius of the first coil.
In one embodiment, the cross-sectional dimensions of the first coil, the second coil and the counter coil are matched.
In one embodiment, the current in the counter coil is less than or equal to the current in the second coil.
In one embodiment, the gradient coil further comprises a shield coil disposed on a side of the second coil remote from the first coil.
In one embodiment, the number of the reverse coils is more than two.
A gradient system comprises a gradient controller, a digital-to-analog converter, a gradient amplifier and the gradient coil.
The gradient system comprises a first coil, a second coil and a reverse coil which are coaxially arranged, the current directions in the first coil and the second coil are opposite, the current direction in the reverse coil is opposite to the current direction in the second coil, the distance between the first coil and the second coil is smaller than twice of the radius of the first coil, the reverse coil is arranged between the first coil and the second coil, and the distance between the reverse coil and the first coil is larger than the distance between the reverse coil and the first coil. Set up the reverse coil through the position that is close to the second coil, the current direction in the reverse coil is opposite with the current direction in the second coil, can make the distance between first coil and the second coil be less than the radial twice of first coil, the distance between first coil and the second coil has been shortened, under the prerequisite of guaranteeing gradient coil working property, the length of gradient coil has been shortened, with the volume control of gradient coil in finite space, make gradient coil's range of application wider, it is more convenient to use.
A magnetic resonance imaging system comprising a magnet system, a radio frequency system and a gradient system as described above.
The magnetic resonance imaging system comprises a first coil, a second coil and a reverse coil which are coaxially arranged, the current directions in the first coil and the second coil are opposite, the current direction in the reverse coil is opposite to the current direction in the second coil, the distance between the first coil and the second coil is smaller than twice of the radius of the first coil, the reverse coil is arranged between the first coil and the second coil, and the distance between the reverse coil and the first coil is larger than the distance between the reverse coil and the first coil. Set up the reverse coil through the position that is close to the second coil, the current direction in the reverse coil is opposite with the current direction in the second coil, can make the distance between first coil and the second coil be less than the radial twice of first coil, the distance between first coil and the second coil has been shortened, under the prerequisite of guaranteeing gradient coil working property, the length of gradient coil has been shortened, with the volume control of gradient coil in finite space, make gradient coil's range of application wider, it is more convenient to use.
Drawings
FIG. 1 is a schematic diagram of a gradient coil in one embodiment;
FIG. 2 is a plot of individual coil parameter selections in a gradient coil in one embodiment;
FIG. 3 is a block diagram of a gradient coil in one embodiment;
FIG. 4 is a block diagram of a gradient coil in another embodiment;
FIG. 5 is a schematic diagram of a gradient coil in another embodiment.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described more fully below by way of examples in conjunction with the accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
Gradient coils are key components of a magnetic resonance imaging system, and have the function of generating a gradient field with good linearity under a certain current. The gradient coil comprises an X-axis coil, a Y-axis coil and a Z-axis coil, wherein the X-axis coil, the Y-axis coil and the Z-axis coil are mutually orthogonal, and three groups of coils can respectively generate X, Y magnetic fields in three directions of Z, so that the spatial position of the examination part is jointly determined. The X-axis coil and the Y-axis coil can be linear systems or saddle coils, the Z-axis coil is arranged according to Maxwell pairs of coils, two circular coils with the same radius are oppositely arranged, and the current directions between the two coils are opposite, so that a gradient field in the Z-axis direction can be generated.
In one embodiment, please refer to fig. 1, a gradient coil is provided, which includes a first coil 110, a second coil 120, and a reverse coil 200 coaxially disposed, wherein the directions of currents in the first coil 110 and the second coil 120 are opposite, the direction of current in the reverse coil 200 is opposite to the direction of current in the second coil 120, the distance between the first coil 110 and the second coil 120 is less than twice the radius of the first coil 110, the reverse coil 200 is disposed between the first coil 110 and the second coil 120, and the distance between the reverse coil 200 and the first coil 110 is greater than the distance between the reverse coil 200 and the second coil 120. Through set up reverse coil 200 in the position that is close to second coil 120, the current direction in the reverse coil 200 is opposite with the current direction in the second coil 120, can make the distance between first coil 110 and the second coil 120 be less than the twice of first coil 110's radius, the distance between first coil 110 and the second coil 120 has been shortened, under the prerequisite of guaranteeing gradient coil working property, the length of gradient coil has been shortened, with gradient coil's volume control in finite space, make gradient coil's applicable scope wider, it is more convenient to use.
Specifically, the first coil 110, the second coil 120 and the counter coil 200 are coaxially arranged, which means that the center points of the first coil 110, the second coil 120 and the counter coil 200 are on the same straight line. The shapes of the first coil 110, the second coil 120 and the reverse coil 200 are not exclusive, and in the embodiment, the first coil 110, the second coil 120 and the reverse coil 200 are all circular coils by default, and the centers of the three coils are on the same straight line. The first coil 110 and the second coil 120 have similar functions as the maxwell coil pair, the directions of currents in the first coil 110 and the second coil 120 are opposite, and the first coil 110 and the second coil 120 form two coaxial reverse current loops, so that a gradient field can be generated in the Z-axis direction. When the distance between the first coil 110 and the second coil 120 is twice the radius of the first coil 110, and the radius of the first coil 110 is larger than twice the radius of the DSV1(diameter of sphere) imaging space, assuming that a DSV1 imaging space of 45 × 45cm is required, if the minimum radius of the coil is 0.5m, the linearity is calculated by the magnetic field of 12 gauss points on the surface of the DSV1, and a better magnetic field linearity (about-2.78/1.11%) can be obtained. If the distance between the first coil 110 and the second coil 120 is shortened to the original half, i.e., 0.5cm, assuming that the midpoint between the first coil 110 and the second coil 120 is taken as the Z-axis zero point, the maximum axial position is 0.25m instead of 0.5m, and the magnetic field linearity is poor (about-10.13/15.18%) when calculated from the magnetic fields of 12 gauss points on the surface of the DSV 1.
Generally, if the coil layout is close to the DSV1 region, the coil generates a much smaller magnetic field in the central axis than along the surface of DSV 1. The opposite is true when the coil is placed away from the DSV1 region. The two results were found to be substantially equal at positions near the maxwell coil by simulation optimization. Therefore, the reversing coil 200 is added between the first coil 110 and the second coil 120, the reversing coil 200 is arranged at a position close to the second coil 120, and after the current in the reversing coil 200 is set to be opposite to the current direction in the second coil 120, the linearity deterioration caused by the shortening of the distance between the first coil 110 and the second coil 120 can be compensated, the working performance of the gradient coil is not influenced, the length of the gradient coil can be shortened, the detectable types of the gradient coil are more abundant, and the practicability is stronger. Specifically, the length between the first coil 110 and the second coil 120 is not exclusive, and may be adjusted according to actual requirements as long as the length is smaller than the distance between the primary macseivi coil pair.
Through set up reverse coil 200 in the position that is close to second coil 120, the current direction in the reverse coil 200 is opposite with the current direction in the second coil 120, can make the distance between first coil 110 and the second coil 120 be less than the twice of first coil 110's radius, the distance between first coil 110 and the second coil 120 has been shortened, under the prerequisite of guaranteeing gradient coil working property, the length of gradient coil has been shortened, with gradient coil's volume control in finite space, make gradient coil's applicable scope wider, it is more convenient to use.
In one embodiment, the radius of the counter coil 200 matches the radius of the first coil 110. Specifically, the radius of the reverse coil 200 is not unique, and in this embodiment, when the radius of the reverse coil 200 matches the radius of the first coil 110, the compensation effect of the reverse coil 200 on the magnetic field linearity is better, which is beneficial to obtain a clearer detection result. The radius of the reverse coil 200 may be matched with the radius of the first coil 110, and the radius of the reverse coil 200 may be equal to or similar to the radius of the first coil 110, and the difference between the two may be within an allowable error range. The specific values of the radius of the reverse coil 200 and the radius of the first coil 110 are not unique, and in this embodiment, the radius of the reverse coil 200 and the radius of the first coil 110 are both 0.5m, which can meet the detection requirements of most people. It is understood that in other embodiments, the radius of the reverse coil 200 and the radius of the first coil 110 may have other values, as long as the skilled person realizes.
In one embodiment, the radius of the second coil 120 is greater than or equal to the radius of the first coil 110. Specifically, the radius of the second coil 120 is not unique, and in a standard Maxwell coil pair, the radius of the second coil 120 is generally equal to the radius of the first coil 110. In this embodiment, the radius of the second coil 120 may be greater than or equal to the radius of the first coil 110, and in cooperation with the addition of the reverse coil 200, the influence of the deterioration of the linearity of the magnetic field due to the shortening of the distance between the first coil 110 and the second coil 120 may be reduced. The specific value of the radius of the second coil 120 may be adjusted according to various factors, for example, the radius of the second coil 120 may be determined according to the distance between the first coil 110 and the second coil 120, the position of the reverse coil 200, and/or the current magnitude in the reverse coil 200, as long as the requirement can be met.
In one embodiment, the distance between the first coil 110 and the second coil 120 matches the radius of the first coil 110. Specifically, the distance between the first coil 110 and the second coil 120 refers to the length of a connection line between the center of the first coil 110 and the center of the second coil 120, the first coil 110 and the second coil 120 are arranged in parallel, and the direction of the connection line between the centers of the first coil 110 and the second coil 120 is the axial direction of the first coil 110 and the second coil 120. When the first coil 110 or the second coil 120 includes a multi-turn winding, a distance between the first coil 110 and the second coil 120 may be a distance between a midpoint of a circle center connection line of the multi-turn winding in the first coil 110 to a midpoint of a circle center connection line of the multi-turn winding in the second coil 120. In a standard maxwell coil pair, the distance between the first coil 110 and the second coil 120 is equal to twice the radius of the first coil 110, so that the obtained magnetic field can better meet the detection requirement. In the present application, the distance between the first coil 110 and the second coil 120 is less than twice the radius of the first coil 110, and the distance between the first coil 110 and the second coil 120 is shortened, so that the length of the gradient coil is effectively shortened, the space utilization rate of the gradient coil is improved, and the application range of the gradient coil is expanded. The specific value of the distance between the first coil 110 and the second coil 120 is not exclusive, and in the embodiment, the distance between the first coil 110 and the second coil 120 matches the radius of the first coil 110, and compared with a standard maxwell coil pair, the distance between the first coil 110 and the second coil 120 is shortened by half, so that the shape of the gradient coil is well controlled in a limited space. It is understood that in other embodiments, the distance between the first coil 110 and the second coil 120 may have other values, as long as the skilled person realizes.
In one embodiment, the cross-sectional dimensions of the first coil 110, the second coil 120 and the counter coil 200 are matched. When the cross-sectional dimensions of the first coil 110, the second coil 120 and the counter coil 200 are matched, the integrity of the gradient coil is better maintained, thereby improving the operating performance of the gradient coil.
Specifically, the cross-sectional dimension of the first coil 110 is generally referred to as a gauge of the first coil 110, the cross-sectional dimension of the second coil 120 is generally referred to as a gauge of the second coil 120, and the cross-sectional dimension of the reverse coil 200 is generally referred to as a gauge of the reverse coil 200, which is generally a diameter of a cross-section of a wire constituting the first coil 110, the second coil 120, or the reverse coil 200. The matching of the cross-sectional dimensions of the first coil 110, the second coil 120 and the reverse coil 200 may be that the cross-sectional dimensions of the first coil 110, the second coil 120 and the reverse coil 200 are equal, or that the cross-sectional dimensions of the first coil 110, the second coil 120 and the reverse coil 200 are similar, and the difference value between them is within an allowable error range. The first coil 110, the second coil 120 and the opposing coil 200 may be of the same construction to maintain the integrity of the gradient coil and also to facilitate adjustment of the operational performance of the gradient coil. The first coil 110, the second coil 120 and the counter coil 200 are not exclusive in structure, and generally include an inner wire and an outer insulating layer, the inner wire being surrounded by the outer insulating layer. The matching of the cross-sectional dimensions of the first coil 110, the second coil 120 and the counter coil 200 means that the cross-sectional dimensions of the inner leads and the cross-sectional dimensions of the outer insulation of the first coil 110, the second coil 120 and the counter coil 200 are all matched. It is understood that the first coil 110, the second coil 120 and the reverse coil 200 may have other structures in other embodiments, as long as the implementation is realized by those skilled in the art.
In one embodiment, the current in the reversing coil 200 is less than or equal to the current in the second coil 120. Specifically, the current in the counter coil 200 is not unique, and in a standard maxwell coil pair, the counter coil 200 is not present, and the currents in the first coil 110 and the second coil 120 are opposite in direction and equal in value. In the present embodiment, when the gradient coil includes the counter coil 200, the current in the counter coil 200 is smaller than or equal to the current in the second coil 120, and the effect of the deterioration of the magnetic field linearity due to the shortening of the distance between the first coil 110 and the second coil 120 can be reduced in conjunction with the effect exerted by the position where the counter coil 200 is located. The specific value of the current in the reverse coil 200 may be adjusted according to various factors, for example, the current in the reverse coil 200 may be determined according to the distance between the first coil 110 and the second coil 120, the position of the reverse coil 200, and/or the radius ratio between the second coil 120 and the first coil 110, as long as the requirement may be met.
For example, when the middle point of the center connecting line of the first coil 110 and the second coil 120 is taken as the Z-axis zero point, and the distance between the first coil 110 and the second coil 120 is equal to the radius of the first coil 110 and is 0.5m, when the inverse coil 200 is located at Z of 0.16m, and the ratio of the radius of the second coil 120 to the radius of the first coil 110 is 100%, the current in the inverse coil 200 may be 0.67A, so that the gradient efficiency of the obtained gradient coil is 1.07uT/m/a, and the nonlinearity of the gradient coil is 5.3%; when the inverse coil 200 is located at Z0.05 m and the radius ratio of the second coil 120 to the first coil 110 is 112%, the current in the inverse coil 200 may be 1A, so that the gradient efficiency of the resulting gradient coil is 0.97uT/m/a and the nonlinearity of the gradient coil is 4.93%; when the inverse coil 200 is located at Z of 0.15m and the radius ratio of the second coil 120 to the first coil 110 is 118%, the current in the inverse coil 200 may be 0.4A, so that the gradient efficiency of the resulting gradient coil is 1.09uT/m/a and the nonlinearity of the gradient coil is 3.97%; when the inverse coil 200 is located at Z of 0.17m and the radius ratio of the second coil 120 to the first coil 110 is 114%, the current in the inverse coil 200 may be 0.5A, so that the gradient efficiency of the resulting gradient coil is 0.89uT/m/a and the nonlinearity of the gradient coil is 3.25%; when the inverse coil 200 is located at Z0.2 m and the radius ratio of the second coil 120 to the first coil 110 is 134%, the current in the inverse coil 200 may be 0.33A, and the gradient efficiency of the resulting gradient coil is 0.65uT/m/a and the nonlinearity of the gradient coil is 1.1%.
In an embodiment, the gradient coil further comprises a shield coil 3, the shield coil 3 being arranged on a side of the second coil 120 remote from the first coil 110. In the process of realizing space positioning of the gradient coil, eddy current can be generated in metal near the gradient coil due to rapid cutting-off of gradient current, and the magnetic field generated by the eddy current is superposed in an original gradient magnetic field, so that the gradient coil is inaccurate in positioning, and eddy current artifacts and image distortion are generated. When the gradient coil comprises the shielding coil 3, the shielding coil 3 changes the magnetic field of the target area to zero, so that no induced eddy current is generated on the pole head, the shielding effect is achieved, and the improvement of the working performance of the gradient coil is facilitated. It should be noted that although the shield coil 3 is located on the side of the second coil 120 away from the first coil 110, when the distance between the first coil 110 and the second coil 120 is shortened, the length of the overall structure formed by the first coil 110, the second coil 120 and the shield coil 3 is also shortened, and the space utilization rate of the gradient coil can still be improved.
In one embodiment, the number of the reverse coils 200 is more than two. When the number of the counter coils 200 is two or more, the counter coils 200 can be disposed at different positions, so that the gradient coil can satisfy more demands.
Specifically, the number of the inversion coils 200 is not unique and may be determined according to the structure of the gradient coil or the detection requirements. Further, when the gradient coil includes the shield coil 3, the counter coil 200 may also be provided near the shield coil 3. The addition of the reverse coil 200 can not only improve the linearity of the coil, but also facilitate the balance of the coil force and the balance of the torsional force, and can effectively reduce the gradient noise. In practical application, the length of the coil can be shortened, the difficulty of coil design is reduced, and the performance of the coil is improved simultaneously by increasing the number of layers of the coil according to practical conditions, wherein each layer is composed of a plurality of current loops, and a reverse current loop is added into each layer.
For a better understanding of the above embodiments, the following detailed description is given in conjunction with a specific embodiment. In one embodiment, the radius of the first coil 110 is R, the distance between the first coil 110 and the second coil 120 is R, and the inverse coil 200 may be disposed at Z < R/2 with the midpoint of a connection line between the center of the first coil 110 and the center of the second coil 120 as the Z-axis origin. Generally, if the coil layout is close to the DSV1 region, the coil generates a much smaller magnetic field in the central axis than along the surface of DSV 1. The opposite is true when the coil is placed away from the DSV1 region. It was found by simulation optimization that at the maxwell coil position, the two results were substantially equal. Therefore, the above effects can be compensated by placing a counter coil 200 at the position Z < R/2.
To further improve the operating performance of the gradient coil, the radius of the second coil 120 may be enlarged to further reduce the influence due to the shortened distance between the first coil 110 and the second coil 120. The second coil 120 is a forward current loop, and the reverse coil 200 is a reverse current loop. The following are several examples: the forward current loop is first arranged at a different radius and unit current at a position Z +0.25m, the reverse current loop is arranged at a different position from the center and less current at a position r 0.5m, the optimum magnetic field linearity is obtained by adjusting the Z value of the reverse current loop, the result is compared to the theoretical gradient field by a calculated magnetic field offset along the 12 gauss point.
Example 1 is the most common case where there are two current loops in the same layer at r-0.5 m. It can be seen that the reverse current loop at Z-0.16 m improves the magnetic field linearity well from 15.18% to 5.30%. Example 2 shows that by increasing the reverse current intensity and moving the current loop position toward the center of the magnet, the gradient efficiency is better and the linearity of the magnetic field is improved sufficiently. Examples 3 and 4 reverse current was only half or less than half of the forward current, and there was a sufficient improvement in linearity. Example 5 the reverse current loop was closer to the outer boundary and the field was even more nonlinear than the maxwell coil pair, reaching-0.81/1.10%. By laying out the reverse current loop, it is possible to design the Z-coil of a short-bore gradient system, and depending on the actual spatial situation, a suitable configuration can be found with reference to the table of fig. 2.
In the actual design of the gradient coil Z coil, please refer to fig. 3 and 4, the shield coil 3 needs to be designed, so that the Z coil itself includes two layers of the shield coil 3 and the main coil 2, and the current values flowing through all the coils are kept equal, which is convenient for application. In addition, the addition of the reverse current loop can not only improve the linearity of the coil, but also be beneficial to the balance of the force and the torque of the coil, and effectively reduce the gradient noise.
In practical application, the difficulty of coil design can be reduced and the performance of the coil can be improved by increasing the number of layers of the coil according to practical conditions, and an actual Z-coil design is shown in fig. 5. Due to the special requirements of the system, the shape of the gradient coil is in a step shape as shown in fig. 5, a three-layer coil mode is adopted, a plurality of current loops are used in each layer, the forward current is used in the bottommost layer, the reverse current is used in the two layers, the gradient performance meets the design requirements, and meanwhile, the shape of the coil is well controlled in a limited space.
The gradient coil comprises a first coil 110, a second coil 120 and a reverse coil 200 which are coaxially arranged, the current directions in the first coil 110 and the second coil 120 are opposite, the current direction in the reverse coil 200 is opposite to the current direction in the second coil 120, the distance between the first coil 110 and the second coil 120 is smaller than twice of the radius of the first coil 110, the reverse coil 200 is arranged between the first coil 110 and the second coil 120, and the distance between the reverse coil 200 and the first coil 110 is larger than the distance between the reverse coil 200 and the first coil 110. Through set up reverse coil 200 in the position that is close to second coil 120, the current direction in the reverse coil 200 is opposite with the current direction in the second coil 120, can make the distance between first coil 110 and the second coil 120 be less than the twice of first coil 110's radius, the distance between first coil 110 and the second coil 120 has been shortened, under the prerequisite of guaranteeing gradient coil working property, the length of gradient coil has been shortened, with gradient coil's volume control in finite space, make gradient coil's applicable scope wider, it is more convenient to use.
In one embodiment, a gradient system is provided comprising a gradient controller, a digital-to-analog converter, a gradient amplifier and a gradient coil as described above. Specifically, the gradient controller is connected with a digital-to-analog converter, the digital-to-analog converter is connected with a gradient amplifier, and the gradient amplifier is connected with a gradient coil. The gradient controller can change an instruction input by an operator into a digital signal and then transmit the digital signal to the digital-to-analog converter, the digital-to-analog converter converts the digital signal into an analog voltage control signal and then transmits the analog voltage control signal to the gradient amplifier, and the gradient amplifier amplifies the analog signal to be enough to push the gradient coil to work to generate a magnetic field, so that the gradient coil can work normally.
The gradient system comprises a first coil 110, a second coil 120 and a reverse coil 200 which are coaxially arranged, the current directions in the first coil 110 and the second coil 120 are opposite, the current direction in the reverse coil 200 is opposite to the current direction in the second coil 120, the distance between the first coil 110 and the second coil 120 is smaller than twice of the radius of the first coil 110, the reverse coil 200 is arranged between the first coil 110 and the second coil 120, and the distance between the reverse coil 200 and the first coil 110 is larger than the distance between the reverse coil 200 and the first coil 110. Through set up reverse coil 200 in the position that is close to second coil 120, the current direction in the reverse coil 200 is opposite with the current direction in the second coil 120, can make the distance between first coil 110 and the second coil 120 be less than the twice of first coil 110's radius, the distance between first coil 110 and the second coil 120 has been shortened, under the prerequisite of guaranteeing gradient coil working property, the length of gradient coil has been shortened, with gradient coil's volume control in finite space, make gradient coil's applicable scope wider, it is more convenient to use.
In one embodiment, a magnetic resonance imaging system is provided comprising a magnet system, a radio frequency system and a gradient system as described above. The magnet system can generate static magnetic fields, the radio frequency system is mainly used for radio frequency excitation and receiving and processing magnetic field signals, and the gradient system is a core component of magnetic resonance and is related to the scanning speed and the resolution of imaging images.
The magnetic resonance imaging system comprises a first coil 110, a second coil 120 and a reverse coil 200 which are coaxially arranged, the current directions in the first coil 110 and the second coil 120 are opposite, the current direction in the reverse coil 200 is opposite to the current direction in the second coil 120, the distance between the first coil 110 and the second coil 120 is smaller than twice of the radius of the first coil 110, the reverse coil 200 is arranged between the first coil 110 and the second coil 120, and the distance between the reverse coil 200 and the first coil 110 is larger than the distance between the reverse coil 200 and the first coil 110. Through set up reverse coil 200 in the position that is close to second coil 120, the current direction in the reverse coil 200 is opposite with the current direction in the second coil 120, can make the distance between first coil 110 and the second coil 120 be less than the twice of first coil 110's radius, the distance between first coil 110 and the second coil 120 has been shortened, under the prerequisite of guaranteeing gradient coil working property, the length of gradient coil has been shortened, with gradient coil's volume control in finite space, make gradient coil's applicable scope wider, it is more convenient to use.
The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.
The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.
Claims (10)
1. A gradient coil is characterized by comprising a first coil, a second coil and a reverse coil which are coaxially arranged, wherein the current directions in the first coil and the second coil are opposite, the current directions in the reverse coil and the second coil are opposite, the distance between the first coil and the second coil is smaller than twice of the radius of the first coil, the reverse coil is arranged between the first coil and the second coil, and the distance between the reverse coil and the first coil is larger than the distance between the reverse coil and the second coil.
2. The gradient coil of claim 1, wherein a radius of the opposing coil matches a radius of the first coil.
3. The gradient coil of claim 1, wherein a radius of the second coil is greater than or equal to a radius of the first coil.
4. The gradient coil of claim 1, wherein a distance between the first coil and the second coil matches a radius of the first coil.
5. The gradient coil of claim 1, wherein the cross-sectional dimensions of the first coil, the second coil, and the opposing coil are matched.
6. The gradient coil of claim 1, wherein the current in the opposing coil is less than or equal to the current in the second coil.
7. The gradient coil of claim 1, further comprising a shield coil disposed on a side of the second coil distal from the first coil.
8. The gradient coil of claim 7, wherein the number of the counter coils is two or more.
9. A gradient system comprising a gradient controller, a digital-to-analog converter, a gradient amplifier and a gradient coil as claimed in any one of claims 1 to 8.
10. A magnetic resonance imaging system comprising a magnet system, a radio frequency system and a gradient system as claimed in claim 9.
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