CN112068055B - Halbach magnet for noninvasive nuclear magnetic resonance detection of blood sugar of human finger - Google Patents
Halbach magnet for noninvasive nuclear magnetic resonance detection of blood sugar of human finger Download PDFInfo
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- A61B5/14532—Measuring characteristics of blood in vivo, e.g. gas concentration, pH value; Measuring characteristics of body fluids or tissues, e.g. interstitial fluid, cerebral tissue for measuring glucose, e.g. by tissue impedance measurement
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Abstract
The invention discloses a Halbach magnet for noninvasive nuclear magnetic resonance detection of blood sugar of human fingers, which comprises a main magnet, three layers of shimming rings, a magnetic homogenizing sheet, a double-layer heat insulation device and a temperature control assembly. The main magnet is placed for trapezoidal magnet steel and rectangle magnet steel interval, is the hexadecimal shape. Three layers of shimming rings are symmetrically distributed on the inner side close to the main magnet along the central horizontal plane, the upper layer and the lower layer are respectively provided with an axial shimming gap, and the optimal structural parameters are obtained by applying a mode search algorithm optimization and finite element simulation analysis. The uniform magnetic sheet is glued on the uniform magnetic sheet moving and positioning structure, the spatial position of the uniform magnetic sheet can be accurately adjusted, the optimized position of the uniform magnetic sheet is obtained by solving through the steps of polynomial fitting, simulation parameter optimization, algorithm optimization and the like, and the high uniformity and stability of the magnetic field are guaranteed. The magnet design of the invention is highly suitable for finger samples, generates higher magnetic field intensity (1T), has excellent uniformity, and meets the implementation conditions of analysis methods such as relaxation analysis and magnetic resonance imaging of finger detection.
Description
Technical Field
The invention relates to the fields of electromagnetism, medical diagnosis, screening and the like, in particular to a Halbach magnet for noninvasive nuclear magnetic resonance detection of human finger blood sugar.
Background
With the change of living habits, the incidence of diabetes is increasing year by year. Recent statistics from the international diabetes association show that there are 2.382 billion diabetics worldwide by 2013, and the number of worldwide diabetics is expected to increase to 5.92 billion by 2035. In China, the incidence of diabetes reaches 9.7%. Therefore, the compound has important social value for preventing and treating diabetes. Blood glucose concentration is the main basis for the judgment of diabetes. At present, the common method for detecting the blood sugar of a human body clinically is to carry out blood biochemical analysis after blood is drawn by a needle or blood is drawn by a finger puncture. The biochemical analyzer has high precision, but frequent blood sampling has great burden on human body and mind, and is not suitable for continuous real-time dynamic monitoring. At present, the scientific problem of real-time noninvasive blood glucose monitoring is that monitoring methods based on electricity, optics, electromagnetism and other means exist, but the accuracy of the monitoring methods is greatly influenced by environmental factors.
As a non-contact detection means, the nuclear magnetic resonance has good application prospects in the aspects of biological detection, organic chemistry and medicine and pharmacology, and the monitoring of blood sugar in blood can be realized by utilizing the nuclear magnetic resonance technology in principle. A typical nmr system consists essentially of a magnet that generates a steady external magnetic field, a probe that emits a pulsed signal and receives a sample signal, and an electronic control system for signal analysis. The quality of an external magnetic field generated by the magnet directly influences the effect of the nuclear magnetic resonance experiment, and the quality is the basis for the nuclear magnetic resonance experiment. Compared with a superconducting magnet and an electromagnet, the permanent magnet type magnet has low requirement on the working environment, does not need to provide extra energy consumption, has the advantages of simple structure, low cost, convenience for miniaturization and the like, and is widely applied to the field of low and medium field nuclear magnetic resonance. In the permanent magnet type, on the premise of achieving the same central magnetic field intensity and uniformity, compared with a bipolar plate type permanent magnet, the size and the cost of the Halbach type permanent magnet are much lower. Moreover, for human body parts with obvious interference structures such as fingers, the conventional common Halbach magnet structure with the height-inner diameter ratio cannot meet the application requirements. Therefore, the research on the novel Halbach magnet for the noninvasive nuclear magnetic resonance detection of the blood sugar of the human finger has extremely important scientific research significance and social significance.
Noninvasive nuclear magnetic resonance detection of blood sugar of human fingers is a research with good application prospect. However, the permanent magnet structure used in the prior art has not a high-performance nmr magnet structure suitable for finger samples. Therefore, in order to meet the application requirement of noninvasive nuclear magnetic resonance detection of blood sugar of human fingers, a novel Halbach magnet which is highly adaptive to finger samples, relatively high in central magnetic field intensity (1T) and good in uniformity is needed.
Disclosure of Invention
The invention aims to solve the technical problem of the prior art, and provides a Halbach magnet for noninvasive nuclear magnetic resonance detection of human finger blood sugar, which has an extremely low height-inner diameter ratio, can be highly adapted to finger samples, and has relatively high (1T) central magnetic field intensity and excellent uniformity.
In order to solve the technical problems, the technical scheme adopted by the invention is as follows:
a Halbach magnet for noninvasive nuclear magnetic resonance detection of blood sugar of human fingers comprises a magnet assembly, a double-layer heat insulation device and a temperature control assembly.
The double layer insulation includes an outer insulation layer and an inner insulation layer. The inner heat insulation layer is a hollow prism with a regular 2N-edge shape, wherein N is more than or equal to 2.
The inner side wall of the inner heat insulation layer is provided with a uniform magnetic sheet layer, and a cavity in the uniform magnetic sheet layer forms a finger extending cavity.
The outer heat insulation layer is arranged around the inner heat insulation layer, and a heat insulation cavity is formed between the outer heat insulation layer and the inner heat insulation layer.
The temperature control assembly is used for controlling the temperature of the heat preservation cavity.
The magnet assembly comprises a main magnet, a shimming ring and a shimming sheet.
The main magnet is arranged in the heat-insulating cavity, and the ratio of the height of the main magnet to the inner diameter of the main magnet is not more than 2.
The main magnet is formed by alternately arranging N large isosceles trapezoid magnetic steels and N rectangular magnetic steels at intervals along the circumferential direction. The outer wall profile of main magnet is 2N polygon, and the inner wall profile of main magnet is positive 2N polygon. The upper bottom of the big isosceles trapezoid magnetic steel is equal to the wide side of the rectangular magnetic steel, and the big isosceles trapezoid magnetic steel and the wide side of the rectangular magnetic steel respectively form the sides of the inner wall of the positive 2N-edge main magnet. The center of each limit of 2N limit shape main magnet outer wall all sets up a trapezoidal magnet steel wall coaxially. Each trapezoidal magnetic steel wall is fixed on the inner wall of the outer heat insulation layer and used for bearing the radial force of the main magnet.
The shimming ring is arranged on the inner wall of the main magnet and is fixedly glued with the adjacent main magnet, so that the inner insulating layer is not stressed.
The uniform magnetic sheet layer comprises a uniform magnetic sheet and a uniform magnetic sheet moving and positioning structure, the uniform magnetic sheet carries out passive shimming by the uniform magnetic sheet moving and positioning structure, and the temperature coefficient of the uniform magnetic sheet is smaller than that of the main magnetic steel.
The shimming rings are provided with two groups, the two groups of shimming rings are respectively and symmetrically fixed at the upper part and the lower part of the inner wall of the main magnet, and an axial shimming gap is arranged between the two groups of shimming rings. Each group of shimming rings is provided with M layers of magnetic rings which are axially stacked, and M is more than or equal to 3. Each layer of magnetic ring is formed by sequentially arranging 2N small isosceles trapezoid magnetic steels with the same size along the circumferential direction. The lower bottom of each small isosceles trapezoid magnetic steel is equal to the upper bottom of the large isosceles trapezoid magnetic steel, and the small isosceles trapezoid magnetic steel and the large isosceles trapezoid magnetic steel are correspondingly attached and fixed one by one.
And the axial height and the radial thickness of M layers of magnetic rings in each group of shimming rings are used for solving an optimal solution through a mode search algorithm.
And the magnetizing direction of each small isosceles trapezoid magnetic steel is the same as that of the corresponding large isosceles trapezoid magnetic steel or the corresponding rectangular magnetic steel.
Each group of shimming rings are three layers of shimming rings.
N =8, the positive 2N polygon is a positive hexadecagon, and the 2N polygon is a hexadecagon.
The magnetization directions of the uniform magnetic sheets are all vertical to the maximum surface of the area of the uniform magnetic sheets.
The uniform magnetic sheet moving and positioning structure adopts a screw rod structure to move the uniform magnetic sheets in a three-dimensional space, and the positioning precision can reach a micron level.
The shimming ring and the main magnet are made of the same material and are made of rubidium, iron and boron. The even magnetic sheet material is samarium cobalt.
The temperature control assembly includes a flexible heating sheet and at least two patch temperature sensors. The paster temperature sensor is attached to different radial positions of the main magnet and used for monitoring the temperatures of the different radial positions of the main magnet.
The outer heat insulation layer is an outer vacuum heat insulation layer and comprises a vacuum outer shell, a vacuum inner shell, an upper sealing ring and a lower sealing ring.
The vacuum shell body comprises a shell top plate, a shell bottom plate and a shell side wall which is connected with the shell top plate and the shell bottom plate in a sealing mode.
The vacuum inner shell comprises an inner shell top plate, an inner shell bottom plate and an inner shell side wall which is connected with the inner shell top plate and the inner shell bottom plate in a sealing mode.
The top plate of the outer shell, the bottom plate of the outer shell, the top plate of the inner shell and the bottom plate of the inner shell are all provided with center holes communicated with the finger extending cavities.
The upper sealing ring is used for sealing the central holes in the top plate of the outer shell and the top plate of the inner shell. The lower sealing ring is used for sealing the central holes in the bottom plate of the outer shell and the bottom plate of the inner shell.
The side wall of the inner shell is heat-conducting and annular, and each trapezoidal magnetic steel wall is nested on the inner wall surface of the side wall of the inner shell. The flexible heating sheet is attached to the outer wall surface of the side wall of the inner shell, and the outer wall surface of the flexible heating sheet is provided with a heat insulation cushion layer. The heat insulation cushion layer, the inner shell top plate, the upper sealing ring, the outer shell top plate, the outer shell side wall, the inner shell bottom plate and the outer shell bottom plate are enclosed to form a vacuum cavity.
The invention has the following beneficial effects:
1. the device has extremely low height-to-inner diameter ratio, thereby solving the problem of interference when a finger is placed in a magnetic field as a sample, and being beneficial to the development of noninvasive nuclear magnetic detection application of human blood sugar.
2. The structural design of the shimming ring is based on a mode search algorithm and finite element simulation analysis, and the reduction of the magnetic field uniformity caused by the reduction of the ratio of the inner diameter to the height is fully compensated.
3. The uniform magnetic sheet and the uniform magnetic sheet moving and positioning structure enable the uniform magnetic sheet to realize accurate positioning of spatial position, and accuracy errors caused by actual engineering processing are greatly optimized.
4. The design of the double-layer heat insulation device is beneficial to furthest improving the constant temperature effect of the main magnet, so that the performance of the main magnet is highly stable, and the rubidium, iron and boron performance is prevented from being greatly influenced by the temperature.
In conclusion, the invention can be highly suitable for finger samples, and meanwhile, the central magnetic field intensity is relatively high (1T) and the uniformity is excellent, thereby greatly promoting the implementation of noninvasive nuclear magnetic resonance detection of blood sugar of human fingers.
Drawings
Fig. 1 shows a detection schematic diagram of a Halbach magnet for noninvasive NMR detection of blood sugar of human fingers.
Figure 2 shows a sectional view of an assembly of a Halbach magnet for noninvasive NMR detection of blood glucose in human fingers.
Fig. 3 shows a schematic view of the structure of the magnet assembly of the present invention.
Figure 4 shows a schematic structural view of the main magnet of the present invention.
Fig. 5 shows a schematic diagram of a three-layer shim ring according to the present invention.
FIG. 6 is a schematic diagram showing the structure of the uniform magnetic sheet and the moving and positioning structure of the uniform magnetic sheet.
Figure 7 shows a schematic of the magnetisation direction of the main magnet and the tri-layer shim ring of the invention.
Fig. 8 is a perspective view of the double-layered heat insulating apparatus according to the present invention.
Fig. 9 shows an exploded view of the structure of the double-layered heat insulating apparatus of the present invention.
FIG. 10 shows a schematic diagram of a temperature control assembly of the present invention.
Figure 11 shows a schematic diagram of the optimization of the three-layer shim ring of the present invention to the performance of the magnetic field in the main magnet.
FIG. 12 shows a graph of the magnetic field uniformity optimization analysis of the pattern search algorithm of the present invention.
Among them are:
100. a magnet assembly;
110. a main magnet; 111. big isosceles trapezoid magnetic steel; 1110. a large trapezoidal magnetic steel wall; 112. rectangular magnetic steel; 1120. a small trapezoidal magnetic steel wall; 113. an inner regular hexagon; 114. an outer hexadecagon shape;
120. shimming rings; 121. an upper shim ring; 122. a lower shim ring; 123. small isosceles trapezoid magnetic steel; 124. shimming gaps;
130. homogenizing magnetic sheet layers; 131. homogenizing magnetic sheets; 132. the even magnetic sheet moves the locating structure;
200. a double-layer heat insulation device; 201. an inner shell sidewall; 202. an inner shell bottom plate; 203. a top plate of the inner shell; 204. a housing sidewall; 205. a housing floor; 206. a housing top plate; 207. an upper seal ring; 208. a lower seal ring; 209. an inner insulating layer; 210. a padding block; 211. a base support leg;
300. a temperature control assembly; 301. a flexible heating sheet; 302 a patch temperature sensor; 303. a power source; 304. a relay; 305. a PID controller;
400. the fingers extend into the cavity.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and specific preferred embodiments.
In the description of the present invention, it is to be understood that the terms "left side", "right side", "upper part", "lower part", etc., indicate orientations or positional relationships based on those shown in the drawings, and are only for convenience of describing the present invention and simplifying the description, but do not indicate or imply that the referred device or element must have a specific orientation, be constructed in a specific orientation, and be operated, and that "first", "second", etc., do not represent an important degree of the component parts, and thus are not to be construed as limiting the present invention. The specific dimensions used in the present example are only for illustrating the technical solution and do not limit the scope of protection of the present invention.
As shown in fig. 1 and fig. 2, a Halbach magnet for noninvasive nmr detection of blood glucose in human fingers comprises a magnet assembly 100, a double-layer heat insulation device 200 and a temperature control assembly 300.
As shown in fig. 8 and 9, the double insulation unit comprises an outer insulation layer and an inner insulation layer 209.
The inner heat insulation layer is a hollow prism with a regular 2N-edge shape, wherein N is more than or equal to 2. In the invention, the number of the edges of the heat insulation layer is consistent with that of the magnetic steel; if the number of N is too small, the magnetic field uniformity is greatly influenced; and the effect is definitely better theoretically if the number of N is too large, but the processing difficulty and the cost are increased suddenly. Therefore, in this embodiment, it is determined that N = 8) is comprehensively considered, that is, the inner insulating layer is preferably a regular-hexadecimal hollow prism.
The inner side wall of the inner heat insulation layer is provided with a magnet homogenizing sheet layer 130, and a cavity in the magnet homogenizing sheet layer forms a finger extending cavity 400.
The outer heat insulation layer is arranged around the inner heat insulation layer, and a heat insulation cavity is formed between the outer heat insulation layer and the inner heat insulation layer.
In this embodiment, the outer insulation layer is preferably an outer vacuum insulation layer, as shown in fig. 9, and includes an outer vacuum casing, an inner vacuum casing, an upper sealing ring 207 and a lower sealing ring 208.
The vacuum housing body preferably has a regular octagonal prism in its outer contour, preferably comprising a housing top plate 206, a housing bottom plate 205, and a housing side wall 204 sealingly connecting the two.
The vacuum inner shell preferably has a cylindrical outer contour, preferably comprising an inner shell top plate 203, an inner shell bottom plate 202 and an inner shell side wall 201 sealingly connecting the two.
The side wall of the inner shell is heat-conducting and annular, the material of the side wall of the inner shell is preferably 6061 aluminum alloy after oxidation treatment, the strength is completely enough to bear radial magnetic force, and the inner wall of the side wall of the inner shell is preferably processed with 2N (sixteen) inverted trapezoidal grooves.
The top plate of the outer shell, the bottom plate of the outer shell, the top plate of the inner shell and the bottom plate of the inner shell are all provided with center holes communicated with the finger extending cavities.
The upper sealing ring is used for sealing the central holes in the top plate of the outer shell and the top plate of the inner shell. The lower sealing ring is used for sealing the central holes in the bottom plate of the outer shell and the bottom plate of the inner shell. Preferably, a block 210 is padded between the outer shell bottom plate and the inner shell bottom plate outside the lower sealing ring. Further, the bottom of the housing floor is preferably provided with base feet 211.
The temperature control assembly is used for controlling the temperature of the heat preservation cavity.
As shown in fig. 2 and 10, the temperature control assembly preferably includes a flexible heat patch 301, a patch temperature sensor 302, a power supply 303, a relay 304, and a PID controller 305.
The patch temperature sensors are preferably at least two and are respectively attached to different radial positions of the main magnet to monitor the temperature of the main magnet at different radial positions so as to determine whether the main magnet is constant in temperature and uniformly heated.
Further, the inner shell top plate is provided with a corresponding groove for accommodating the patch temperature sensor and the wiring thereof. The power supply, the relay and the PID controller form a power supply and electronic control part of the temperature control system. And the PID controller is connected with the upper computer through an electronic control cabinet in sequence.
The flexible heating sheet is preferably annular, is preferably attached or bonded to the outer wall surface of the side wall of the inner shell, and the outer wall surface of the flexible heating sheet is preferably provided with a heat insulation cushion layer (preferably heat insulation cotton). The heat insulation cushion layer, the inner shell top plate, the upper sealing ring, the outer shell top plate, the outer shell side wall, the inner shell bottom plate and the outer shell bottom plate are enclosed to form a vacuum cavity. The vacuum cavity is preferably filled with an air medium with extremely low heat conductivity coefficient, so that high-efficiency heat preservation is realized.
The heat insulating cushion layer forms a first heat insulating layer of the outer heat insulating layer, and the air medium layer filled in the vacuum cavity and the side wall of the shell form a second heat insulating layer of the outer heat insulating layer.
As shown in fig. 2 and 3, the magnet assembly 100 includes a main magnet 110, a shim ring 120, and a shim 130.
The main magnet is arranged in the heat-insulating cavity, the main magnet is preferably made of rubidium, iron and boron N48, the remanence is 1.4T, and as shown in FIG. 4, N (preferably eight) large isosceles trapezoid magnetic steels 111 and N (preferably eight) rectangular magnetic steels 112 are preferably arranged alternately at intervals along the circumferential direction; the magnetization direction is shown in fig. 7.
The outer wall profile of main magnet is 2N polygon (hexadecagon), and the inner wall profile of main magnet is positive 2N polygon (positive hexadecagon).
The upper bottom of the big isosceles trapezoid magnetic steel is equal to the wide side of the rectangular magnetic steel, and the big isosceles trapezoid magnetic steel and the wide side of the rectangular magnetic steel respectively form the sides of the inner wall of the positive 2N-edge (positive hexadecimal) main magnet.
The center of each edge of the outer wall of the 2N-edge (hexadecagon) main magnet is coaxially provided with a trapezoidal magnetic steel wall. The trapezoidal magnetic steel wall positioned on the outer wall of the large isosceles trapezoidal magnetic steel 111 is called as a large trapezoidal magnetic steel wall 1110; the trapezoidal magnetic steel wall located on the outer wall of the rectangular magnetic steel 112 is called a small trapezoidal magnetic steel wall 1120.
Each trapezoidal magnetic steel wall is preferably nested in an inverted trapezoidal groove on the inner wall of the outer heat insulation layer and used for bearing the radial force of the main magnet.
Compared with the pure trapezoidal magnetic steel, the structure of the main magnet in the embodiment is distributed in a hexadecimal shape, and better magnetic field uniformity can be obtained. In addition, in the main magnet, the large isosceles trapezoid magnetic steel and the rectangular magnetic steel are influenced by extremely strong attractive force and repulsive force, and resultant force borne by each magnetic steel in the main magnet presents extremely strong acting force inwards or outwards along the radial direction. In the conventional regular structure, radially outward force will be borne by the outer wall, and radially inward force will be borne by the inner wall; however, the inner space of the heat insulation layer is limited, so that the heat insulation layer is thin and difficult to bear large force. In this embodiment, preferably, the trapezoidal magnetic steel wall is embedded in the inner shell side wall, and the inner shell side wall is made of oxidized 6061 aluminum alloy and has enough thickness to completely bear large magnetic force inside and outside the radial direction, and the inner shell side wall is integrally designed, so that the resultant force of 16 large magnetic steels on the inner shell side wall is nearly zero, the shearing force received by the fixing screw between the inner shell side wall and the inner shell bottom plate is greatly reduced, and the structural stability is improved; the inner insulating layer will not be subjected to large magnetic forces anymore and is only used for insulation.
In the nuclear magnetic resonance detection, a sample must be placed in the very center of a magnet, namely, a finger is inserted into a cavity, so that the sample can be in a magnetic field with enough strength and good uniformity.
In the original Halbach magnet structure, the ratio of the height to the inner diameter of the magnet is at least more than 3 in consideration of the uniformity of the central area of a magnetic field; however, in the finger nuclear magnetic detection, one finger is required to be used as a sample to extend into the magnet, and the finger cannot extend into an excessively large depth due to interference of other fingers, a palm and the like, so that the height of the magnet is limited. Meanwhile, in the research of noninvasive nuclear magnetic detection of finger blood sugar, a scientific analysis result is inevitably difficult to obtain by using a single detection method, and methods such as relaxation analysis, magnetic resonance imaging, spectrum analysis and the like need to be combined. Therefore, the inside of the magnet is provided with enough space for placing passive shimming sub-magnetic sheets, active shimming coils, gradient coils and the like besides the probe. According to the original Halbach magnet structure design, the magnetic field uniformity can not meet the requirement far away.
In the invention, the ratio of the height to the inner diameter of the main magnet is not more than 2. In this embodiment, the height of the magnet can be made to be 100mm, and the inner diameter can be made to be 80mm, that is, the ratio of the height to the inner diameter of the main magnet is reduced to 1.25, so that the requirements of experiments and human comfort can be met.
As shown in fig. 5, the shim rings have two sets, an upper shim ring 121 and a lower shim ring 122.
Two groups of shimming rings are respectively fixed at the upper part and the lower part of the inner wall of the main magnet and are symmetrically distributed along the central horizontal plane of the main magnet.
There is an axial shim gap 124 between the two sets of shim rings.
Each group of shimming rings is provided with M layers of magnetic rings which are axially stacked, M is more than or equal to 3, the more M is, the higher uniformity can be achieved, but the actual processing difficulty is required. Each layer of magnetic ring is formed by sequentially arranging 2N small isosceles trapezoid magnetic steels 123 with the same size along the circumferential direction. The lower bottom of each small isosceles trapezoid magnetic steel is equal to the upper bottom of the large isosceles trapezoid magnetic steel, and the small isosceles trapezoid magnetic steel and the large isosceles trapezoid magnetic steel are correspondingly attached and fixed one by one.
In this embodiment, each set of shim rings is preferably a three-layer shim ring, i.e. M = 3. Each layer of magnetic rings is distributed in a regular hexadecimal shape, and preferably 16 small isosceles trapezoid magnetic steels 123 with the same size are sequentially arranged along the circumferential direction, namely the shimming ring is provided with 96 small isosceles trapezoid magnetic steels 123.
The material of each small isosceles trapezoid-shaped magnetic steel 123 is preferably the same as that of the main magnet, and considering that the inner heat insulation layer is not stressed, the outer wall surface of each small isosceles trapezoid-shaped magnetic steel 123 is prevented from being tightly attached to the inner part of the main magnet and is glued with the adjacent main magnet together, and the side wall of the inner shell is stressed.
The magnetization direction of each small isosceles trapezoid magnetic steel 123 is the same as the magnetization direction of its adjacent main magnetic steel (including the large isosceles trapezoid magnetic steel 111 and the rectangular magnetic steel 112), as shown in fig. 7. Simulation analysis shows that the magnetic field of the structure in the central target area and the magnetic field of the main magnetic steel are in complementary distribution; when the two magnetic fields are superposed, the uniformity of the magnetic field in the target area is obviously improved. The shim ring structure is therefore designed to compensate for field decay, the effect being shown in figure 11. However, the shimming ring has a plurality of parameter variables, and only through parameter classification discussion, the workload is extremely huge; at the same time, the optimality of the results is difficult to ascertain.
Aiming at the axial height and the radial thickness of M layers of magnetic rings in each group of shimming rings, the invention provides an application mode search algorithm, and optimization analysis is carried out by taking parameters such as the axial height and the radial thickness of each layer of magnetic rings and the like and taking the magnetic field uniformity in a central target region as an optimization target, as shown in figure 12.
The magnetic ring at the topmost layer of the upper shimming ring and the magnetic ring at the bottommost layer of the lower shimming ring are assumed to be first layer of small isosceles trapezoid magnetic steel; the middle layer magnetic ring of the upper shimming ring and the middle layer magnetic ring of the lower shimming ring are second layers of small isosceles trapezoid-shaped magnetic steel; the bottom magnetic ring of the upper shimming ring and the top magnetic ring of the lower shimming ring are third layer of small isosceles trapezoid magnetic steel.
And (3) solving the optimal axial height and radial thickness by applying a mode search algorithm, wherein the method specifically comprises the following steps of:
in the target area
The optimal solution is: the radial thickness of the first layer of small isosceles trapezoid magnetic steel is 6.75mm, the axial height is 10.2mm, the radial thickness of the second layer of small isosceles trapezoid magnetic steel is 8.4mm, the axial height is 9mm, the radial thickness of the third layer of small isosceles trapezoid magnetic steel is 7.65mm, the axial height is 10.8mm, and the uniformity in the region is optimized to 106 ppm.
In the target area
The optimal solution is: the radial thickness of the first layer of small isosceles trapezoid magnetic steel is 6.75mm, the axial height is 11.9mm, the radial thickness of the second layer of small isosceles trapezoid magnetic steel is 8mm, the axial height is 10mm, the radial thickness of the third layer of small isosceles trapezoid magnetic steel is 7.6mm, the axial height is 8.1mm, and the uniformity in the region is optimized to 20 ppm.
The number of the shimming ring layers is 3, and the workload and the complexity of actual processing are mainly considered; theoretically, the number of shimming rings can be increased to more layers, and more optimized magnetic field uniformity can be obtained through optimal solution analysis of a mode search algorithm.
As shown in fig. 6, it is necessary to provide a shim plate 131 in consideration of a process error due to actual processing, and it is necessary to provide a shim plate moving positioning structure 132 capable of accurately adjusting the spatial position of the shim plate in consideration of the positional accuracy of the shim plate.
The shim moving and positioning structure 132 and the shim 131 together form a shim layer 130.
The uniform magnetic sheet is located outside the heat preservation cavity, so the temperature coefficient is far smaller than that of the main magnet. The material of the uniform magnetic ring is preferably the same as that of the main magnet, and the uniform magnetic ring is rubidium, iron and boron N48. The uniform magnetic sheet is preferably samarium cobalt SmCo30, and has a remanence of 1.1T, etc.
The magnetization directions of the uniform magnetic sheets are all vertical to the maximum surface of the area of the uniform magnetic sheets.
The uniform magnetic sheets have six groups of sizes, are adhered to the moving and positioning structure of the uniform magnetic sheets, and the specific size depends on the actual shimming requirement. As shown in fig. 6, the uniform magnetic sheet moving and positioning structure preferably adopts a screw rod structure to move the uniform magnetic sheet in a three-dimensional space, and the positioning precision can reach micron level.
Determination principle of size of uniform magnetic sheet: in order to fully compensate each coefficient of the magnetic field unevenness component in the target area of the main magnet, the uniform magnetic sheets with multiple sizes are needed, and the change of the magnetic field difference in the area within the range of 0.01mT to 10mT can be met in strength.
Before shimming, the heat preservation cavity is completely closed (an outer heat insulation layer, an inner heat insulation layer and the like). The temperature control assembly is turned on and thermostated to 28 ℃ (should be above room temperature, but not too high). The heat generated by the flexible heating sheets is transmitted to the main magnetic steel and the three layers of shimming rings through the side wall of the inner shell, so that the main magnetic steel can be fully and uniformly heated.
The shimming method comprises the following steps:
step 1, detecting a magnetic field of a target area: the magnetic field in the target area before the homogenizing magnetic sheet is placed is measured by a gaussmeter and a Hall probe.
Step 2, calculating the unevenness of the magnetic field: the magnetic field distribution on the surface of the target region is formulated by polynomial fitting, and is expanded into a Taylor series form (mainly a constant term and a second order), and then the Taylor series form is in one-to-one correspondence with the spherical harmonic expansion of the magnetic field, so that a second order component coefficient of the magnetic field unevenness can be solved (the influence of the high order term is small, and the actual shimming is difficult to control).
Step 3, calculating the optimal compensation position of the uniform magnetic sheet: the simulation software can be used for simulating the magnetic field distribution of the target magnetic field after the positions of the uniform magnetic sheets are determined, and then the optimal compensation position of the non-uniformity component of the magnetic field in the target region of the main magnet is obtained by parameter optimization and genetic algorithm optimization.
Step 4, placing uniform magnetic sheets: and the uniform magnetic sheet is placed at the solved position by utilizing the uniform magnetic sheet moving and positioning structure.
And 5, detecting the magnetic field again: and measuring the magnetic field distribution of the target area by using the gauss meter and the Hall probe again.
And 6, repeating the steps 2 to 5 until the second-order component of the magnetic field unevenness cannot be further reduced, namely the uniformity cannot be continuously optimized.
Although the preferred embodiments of the present invention have been described in detail, the present invention is not limited to the details of the embodiments, and various equivalent modifications can be made within the technical spirit of the present invention, and the scope of the present invention is also within the scope of the present invention.
Claims (10)
1. The utility model provides a Halbach magnet that is used for human finger blood sugar to not have magnetic resonance detection of creating which characterized in that: the double-layer heat insulation device comprises a magnet assembly, a double-layer heat insulation device and a temperature control assembly;
the double-layer heat insulation device comprises an outer heat insulation layer and an inner heat insulation layer; the inner heat insulation layer is a hollow prism with a regular 2N-edge shape, wherein N is more than or equal to 2;
the inner side wall of the inner heat insulation layer is provided with a uniform magnetic sheet layer, and a cavity in the uniform magnetic sheet layer forms a finger extending cavity; the uniform magnetic sheet layer comprises a uniform magnetic sheet and a uniform magnetic sheet moving and positioning structure, the uniform magnetic sheet carries out passive shimming by the uniform magnetic sheet moving and positioning structure, and the temperature coefficient of the uniform magnetic sheet is smaller than that of the main magnet;
the outer heat insulation layer is arranged around the inner heat insulation layer, and a heat insulation cavity is formed between the outer heat insulation layer and the inner heat insulation layer;
the temperature control component is used for controlling the temperature of the heat preservation cavity;
the magnet assembly comprises a main magnet, a shimming ring and the shimming sheet;
the main magnet is arranged in the heat-insulating cavity, and the ratio of the height of the main magnet to the inner diameter of the main magnet is not more than 2;
the main magnet is formed by alternately arranging N large isosceles trapezoid magnetic steels and N rectangular magnetic steels at intervals along the circumferential direction; the contour of the outer wall of the main magnet is 2N-shaped, and the contour of the inner wall of the main magnet is regular 2N-shaped; the upper bottom of the large isosceles trapezoid magnetic steel is equal to the wide side of the rectangular magnetic steel, and the large isosceles trapezoid magnetic steel and the wide side of the rectangular magnetic steel respectively form the sides of the inner wall of the main magnet in a positive 2N-edge shape; the center of each edge of the outer wall of the 2N-edge main magnet is coaxially provided with a trapezoidal magnetic steel wall; each trapezoidal magnetic steel wall is fixed on the inner wall of the outer heat insulation layer and used for bearing the radial force of the main magnet;
the shimming ring is arranged on the inner wall of the main magnet and is fixedly glued with the adjacent main magnet, so that the inner insulating layer is not stressed.
2. The Halbach magnet for the noninvasive nuclear magnetic resonance detection of blood glucose of human fingers according to claim 1, is characterized in that: the shimming rings are provided with two groups, the two groups of shimming rings are respectively and symmetrically fixed at the upper part and the lower part of the inner wall of the main magnet, and an axial shimming gap is arranged between the two groups of shimming rings; each group of shimming rings is provided with M layers of magnetic rings which are axially stacked, and M is more than or equal to 3; each layer of magnetic ring is formed by sequentially arranging 2N small isosceles trapezoid magnetic steels with equal sizes along the circumferential direction; the lower bottom of each small isosceles trapezoid magnetic steel is equal to the upper bottom of the large isosceles trapezoid magnetic steel, and the small isosceles trapezoid magnetic steel and the large isosceles trapezoid magnetic steel are correspondingly attached and fixed one by one.
3. The Halbach magnet for noninvasive nuclear magnetic resonance detection of blood sugar of human fingers according to claim 2 is characterized in that: and the axial height and the radial thickness of M layers of magnetic rings in each group of shimming rings are used for solving an optimal solution through a mode search algorithm.
4. The Halbach magnet for the noninvasive nuclear magnetic resonance detection of blood glucose of human fingers according to claim 2, is characterized in that: and the magnetizing direction of each small isosceles trapezoid magnetic steel is the same as that of the corresponding large isosceles trapezoid magnetic steel or the corresponding rectangular magnetic steel.
5. The Halbach magnet for the noninvasive nuclear magnetic resonance detection of blood glucose of human fingers according to claim 2, is characterized in that: each group of shimming rings are three layers of shimming rings.
6. The Halbach magnet for the noninvasive nuclear magnetic resonance detection of blood glucose of human fingers according to claim 1, is characterized in that: n =8, the positive 2N polygon is a positive hexadecagon, and the 2N polygon is a hexadecagon.
7. The Halbach magnet for noninvasive nuclear magnetic resonance detection of blood sugar of human fingers according to claim 1 is characterized in that: the magnetization directions of the uniform magnetic sheets are all vertical to the maximum surface of the area of the uniform magnetic sheets.
8. The Halbach magnet for the noninvasive nuclear magnetic resonance detection of blood glucose of human fingers according to claim 7, is characterized in that:
the uniform magnetic sheet moving and positioning structure adopts a screw rod structure to move the uniform magnetic sheets in a three-dimensional space, and the positioning precision can reach a micron level.
9. The Halbach magnet for the noninvasive nuclear magnetic resonance detection of blood glucose of human fingers according to claim 7, is characterized in that: the shimming ring and the main magnet are made of the same material and are made of rubidium, iron and boron; the even magnetic sheet material is samarium cobalt.
10. The Halbach magnet for the noninvasive nuclear magnetic resonance detection of blood glucose of human fingers according to claim 1, is characterized in that: the temperature control assembly comprises a flexible heating sheet and at least two patch temperature sensors; the patch temperature sensors are attached to different radial positions of the main magnet and used for monitoring the temperatures of the different radial positions of the main magnet;
the outer heat insulation layer is an outer vacuum heat insulation layer and comprises a vacuum outer shell, a vacuum inner shell, an upper sealing ring and a lower sealing ring;
the vacuum shell body comprises a shell top plate, a shell bottom plate and a shell side wall which is connected with the shell top plate and the shell bottom plate in a sealing mode;
the vacuum inner shell comprises an inner shell top plate, an inner shell bottom plate and an inner shell side wall which is connected with the inner shell top plate and the inner shell bottom plate in a sealing mode;
the top plate of the outer shell, the bottom plate of the outer shell, the top plate of the inner shell and the bottom plate of the inner shell are all provided with central holes communicated with the finger extending cavities;
the upper sealing ring is used for sealing the central holes in the top plate of the outer shell and the top plate of the inner shell; the lower sealing ring is used for sealing the central holes in the bottom plate of the outer shell and the bottom plate of the inner shell;
the side wall of the inner shell is heat-conducting and annular, and each trapezoidal magnetic steel wall is nested on the inner wall surface of the side wall of the inner shell; the flexible heating sheet is attached to the outer wall surface of the side wall of the inner shell, and a heat insulation cushion layer is arranged on the outer wall surface of the flexible heating sheet; the heat insulation cushion layer, the inner shell top plate, the upper sealing ring, the outer shell top plate, the outer shell side wall, the inner shell bottom plate and the outer shell bottom plate are enclosed to form a vacuum cavity.
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| DE60231473D1 (en) * | 2001-01-12 | 2009-04-23 | Oxford Instr Superconductivity | METHOD AND DEVICE FOR GENERATING A MAGNETIC FIELD |
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| CN103892834B (en) * | 2014-03-21 | 2016-05-25 | 沈阳中北真空磁电科技有限公司 | A kind of permanent magnet for NMR imaging instrument |
| CN203966707U (en) * | 2014-06-23 | 2014-11-26 | 重庆大学 | A kind of monolateral nulcear magnetic resonance (NMR) magnet structure of oval arcuation that adopts passive shimming |
| CN104252944A (en) * | 2014-09-22 | 2014-12-31 | 苏州露宇电子科技有限公司 | Unilateral annular magnet high in magnetic field evenness and temperature stability |
| CN204178846U (en) * | 2014-09-22 | 2015-02-25 | 苏州露宇电子科技有限公司 | The monolateral toroidal magnet of the highfield uniformity, high-temperature stability |
| WO2016128043A1 (en) * | 2015-02-11 | 2016-08-18 | Siemens Aktiengesellschaft | System and non-invasive method for examining at least parts of the blood fractions, and use of said system |
| CN105044634B (en) * | 2015-08-12 | 2018-01-19 | 上海健康医学院 | Magnetic resonance analysis permanent magnet device |
| CN106153661B (en) * | 2016-06-17 | 2017-11-03 | 东南大学 | A kind of method for the noninvasive magnetic resonance detection of blood pressure and blood lipoid |
| CN110706877A (en) * | 2019-09-23 | 2020-01-17 | 东南大学 | Low-cost miniature Halbach magnet with adjustable magnetic field uniformity |
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