CN115494437A - Hand-held low-gradient single-side nuclear magnetic resonance device for detecting full-thickness skin - Google Patents
Hand-held low-gradient single-side nuclear magnetic resonance device for detecting full-thickness skin Download PDFInfo
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Abstract
The invention relates to a handheld low-gradient unilateral nuclear magnetic resonance device for detecting full-thickness skin, and belongs to the technical field of nuclear magnetic resonance. The device comprises a single-side permanent magnet structure and a radio frequency transceiving integrated coil; the unilateral permanent magnet structure is used for generating a static magnetic field, and the finite element method and the sparrow search algorithm are adopted for optimizing to obtain the permanent magnet structure, wherein the direction of the magnetic field is parallel to the upper surface of the permanent magnet structure; the radio frequency transceiving coil is used for generating an excitation radio frequency magnetic field orthogonal to the main magnetic field and detecting a magnetic resonance echo signal generated by a tested sample arranged on the unilateral permanent magnet structure. The invention has the advantages of simple structure, small volume, light weight, low cost, reliable performance and main magnetic field B 0 The magnetic induction intensity is less than or equal to 100mT, the magnetic field gradient G along the direction vertical to the magnetic field direction at the center of the detection target area is about 2.96T/m, the nuclear magnetic resonance signal measurement of the skin full-thickness tissue can be realized, the non-invasive detection at the bedside is convenient, and the likeAnd (4) point.
Description
Technical Field
The invention belongs to the technical field of nuclear magnetic resonance, and relates to a handheld low-gradient unilateral nuclear magnetic resonance device for detecting full-thickness skin.
Background
In recent years, the portable unilateral nuclear magnetic resonance technology is widely applied to the fields of food analysis and quality control, material science, geophysical and the like. The structure is open, the volume is small, the movement is convenient, the nondestructive detection can be performed on an object from any angle at any position, meanwhile, the permanent magnet is adopted to provide a main magnetic field, the price is low, the energy consumption is low, and in addition, a plurality of information including relaxation time T1, T2 imaging, diffusion coefficient D, even chemical shift and the like given by the traditional nuclear magnetic resonance can be provided. Skin burn is a common disease, and at present, no accurate and noninvasive method exists for judging the degree of skin burn and diagnosing the skin rehabilitation condition after burn, the method is clinically mainly based on the subjective judgment of doctors and the feeling of patients, and the method is rough and subjective and is easy to further deepen the burn depth. The existing medical diagnosis methods such as Computed Tomography (CT), magnetic Resonance Imaging (MRI) and the like can image human skin, but have larger volume and are difficult to carry out clinical real-time monitoring and measurement; the existing high-frequency ultrasonic imaging system can obtain an image of the skin, but cannot distinguish vascular inflammation and edema deep in the dermis. Therefore, a quantitative and accurate method for judging the burn depth and the recovery degree of the skin of the burn patient is urgently needed clinically so as to accurately establish a treatment and rehabilitation scheme. The invention provides a handheld low-gradient unilateral nuclear magnetic resonance device for detecting full-thickness skin, which only relies on a permanent magnet to construct a main magnetic field and is provided with a radio frequency receiving and transmitting integrated coil to realize the measurement of magnetic resonance signals and the rapid detection of the full-thickness skin.
Disclosure of Invention
In view of the above, the present invention provides a handheld low gradient single-sided nmr apparatus for detecting the whole skin.
In order to achieve the purpose, the invention provides the following technical scheme:
hand-held low gradient single-sided nuclear magnetic resonance device for detecting full-thickness skin, the device comprising:
a single-side permanent magnet structure and a radio frequency transmit-receive integrated coil 4;
the unilateral permanent magnet structure comprises three groups of magnet structures;
the three groups of magnet structures are a left magnet group 1, a middle magnet 2 and a right magnet group 3 respectively;
the left magnet group 1 and the right magnet group 3 are on the same horizontal plane;
the middle magnet 2 is positioned between the left magnet group 1 and the right magnet group 3 and below the horizontal planes of the left magnet group 1 and the right magnet group;
the left magnet group 1 and the right magnet group 3 have the same specification;
in an XYZ coordinate system, the magnetic pole of the left magnet group 1 points in the Z direction, the magnetic pole of the middle magnet 2 points in the-Y direction, and the magnetic pole of the right magnet group 3 points in the-Z direction;
generating a main magnetic field B pointing from the left magnet group 1 to the right magnet group 3 above the unilateral permanent magnet structure 0 The magnetic pole points in the Y direction, and a uniform magnetic field is generated in the geometric center area of the middle magnet, and the geometric center area of the middle magnet is a detection target area 5;
the main magnetic field B 0 The magnetic induction intensity of (2) is less than or equal to 100mT, and the magnetic field gradient G of the center of the detection target area 5 along the direction vertical to the magnetic field is 2.96T/m;
the magnetic field distribution generated by the unilateral permanent magnet structure is calculated by adopting a finite element method, and the structural parameters of the unilateral permanent magnet are optimized by a sparrow search algorithm;
the radio frequency receiving and transmitting integrated coil 4 is a receiving and transmitting integrated double-layer planar coil, is designed by adopting a time-harmonic field inversion method and a flow function method, and is used for generating an excitation radio frequency magnetic field orthogonal to a main magnetic field and receiving an echo signal generated after a detected sample arranged in a detection target area is excited.
Optionally, the sizes of the left magnet group 1 and the right magnet group 3 are as follows: the length is 25.4mm, the height is 12.7mm, and the width is 12.7mm; the size of the middle magnet 2 is as follows: the length is 50.8mm, the height is 12.7mm and the width is 25.4mm.
Optionally, the optimization of the structural parameters of the unilateral permanent magnet through the sparrow search algorithm specifically includes:
the spatial position of the single-sided permanent magnet structure is represented as an n × d matrix X:
wherein n is the number of the permanent magnet structures, and d is the dimension of the permanent magnet structure to-be-optimized structure parameter; the position of the ith permanent magnet structure in space is X i ＝(x i,1 ,x i,2 ,…,x i,d ) (ii) a The adaptation value of the single-sided permanent magnet structure is expressed as a vector F X :
The optimizing capability of the sparrow searching algorithm is based on three parts: the finder, the joiner and the warner search for the optimal permanent magnet structure together; the location update formula for each generation of discoverers is as follows:
wherein T represents the current iteration number, T represents the total iteration number,
represents the information quantity of the jth dimension parameter in the ith permanent magnet structure at t iterations, and alpha is [0,1 ]]R is a random number representing the current warning value, and R belongs to [0,1 ]]ST denotes a safety value, ST ∈ [0.5,1]Q is a random number following a normal distribution, and L is 1 × d j Matrix of d j Is the dimension of the jth dimension parameter of the magnet group, and each element in the matrix is 1;
the location update formula for each generation of enrollees is as follows:
wherein the content of the first and second substances,
is the optimum position occupied by the finder at present, X worst Then the current global worst position is indicated; a is a 1 x d matrix in which each element is randomly assigned a value of 1 or-1, and A + ＝A T (AA T ) -1 ，
Is represented by A + The value of the j-th dimension of (d); when in use
When the joiner is in use, the joiner can positively follow the finder to move to a better position; when in use
In the process, the ith subscriber with a lower adaptive value needs to move to other positions, and the current poorer position is got rid of by combining the exp function characteristic to obtain a better adaptive value;
the position updating formula of each generation of alert person is as follows:
wherein, therein
Is the current global optimum position; beta is taken as a step length control parameter and is a random number which follows normal distribution with the mean value of 0 and the variance of 1; k ∈ [ -1,1]Is a random number, f i The adaptive value of the current magnet group is obtained; f. of g And f w Current global best and worst adaptation values, respectively; ε is the smallest constant to avoid zero denominator; when f is i >f g When the alarm is in the edge position, the adaptive value is low, and the alarm needs to be close to the center position; when f is i ＝f g In time, it means that the adaptation value of the permanent magnet structure in the middle position is low, and the permanent magnet structure needs to go to other positions to improve the adaptation value；
During magnetic field simulation, the FOV is cut along the Z-axis direction according to a certain step length to obtain N 1 Cutting into slices; sampling two middle shafts on each section according to the synchronous length of the phase, and obtaining N on each middle shaft 2 Magnetic induction intensity B i Evenness P on any axis i The calculation formula is as follows:
wherein B is c The magnetic induction intensity of the midpoint of the tangent plane is shown; the uniformity P of two middle axes in a tangent plane is obtained by the formula (6) xi And P yi Degree of uniformity H 1 The expression is as follows:
calculating the uniformity B of each section h ：
Wherein, B max Maximum value of magnetic induction in section, B min Is the minimum value of the magnetic induction intensity in the tangent plane; b for each slice by equation (8) h After solving, the uniformity H is obtained 2 ：
In conjunction with equations (7) and (9), the evaluation function H of the permanent magnet structure adaptation values is as follows:
H＝(H 1 +H 2 )·(|G-2|+|G-3|) (20)
wherein G is the magnetic field gradient of the detection target region along the Z axis, and in order to maintain the low gradient of G in the size of 2-3T/m during the design of the permanent magnet structure, the adaptive value is evaluated by using (| G-2| + | G-3 |) in the formula (10).
Optionally, the magnet marks of the left magnet group 1 and the right magnet group 3 are NdFe1, and the magnet mark of the middle magnet 2 is NdFe2;
the distance between the left magnet group 1 and the right magnet group 3 is d1; the distance between the lower bottom surfaces of the left magnet group 1 and the right magnet group 3 and the upper bottom surface of the middle magnet 2 in the Z-axis direction is d2, the inter-group distance between the left magnet group 1 and the right magnet group 3 is d3, the inter-group distance between the middle magnet 2 is d4, and the width of the middle magnet 2 is W;
optionally, the single-side permanent magnet structure is five neodymium iron boron magnets, the radio frequency transmit-receive integrated coil is designed by a time-harmonic field inversion method and a flow function method, and a matching radio frequency field orthogonal and related to the main magnetic field is designed according to the distribution of the main magnetic field; setting the length of a wiring area of the radio frequency transceiving integrated coil as Lx and the width as Ly; the current density of the inner surface of the plane where the radio frequency transmitting-receiving integrated coil is located is divided into two components: a current density component parallel to the main magnetic field B0 and a current density component perpendicular to the main magnetic field B0; the current density component is represented as,
P mn the coefficient is the coefficient required to be obtained;
from the principle of current continuity, the current function of the current density in the y =0 plane is expressed as:
the magnetic field component of each point in the ROI space of the target region is detected by the Bio Safaer theorem
R represents the distance from the field point to the source point, S 0 Represents the plane in which the current density lies;
wherein (x, y, z) represents the coordinates of any field point in the ROI, (x) 0 ,y 0 ,z 0 ) Representing the coordinate of any source point on the current density plane;
one aspect of the matching of the radio frequency field to the main magnetic field is the radio frequency field B generated by the radio frequency coil 1 The vector should be matched with the main magnetic field B generated by the unilateral magnet at each height 0 The vectors are orthogonal everywhere, i.e.:
B 1 ⊥B 0
is unfolded into
B 0x B 1x +B 0y B 1y +B 0z B 1z ＝0 (15)
Another aspect of the matching of the radio frequency field to the main magnetic field is the radio frequency field B 1 The magnitude of the magnetic field mode value of the magnetic field should be equal to the main magnetic field B generated by the unilateral magnet 0 The magnitude of the magnetic field modulus is proportional; therefore, each spinning hydrogen proton on the same plane of a detection target area can be simultaneously turned to the same plane, and a high-resolution correlation spectrum and a high signal-to-noise ratio are obtained under the condition that a radio frequency field is matched with a main magnetic field; this is to satisfy
||B 1 ||∝||B 0 || (16)
Is developed into equation
k-value radio frequency field B 1 With main magnetic field B generated by unilateral magnets 0 The ratio of (b) is usually a few thousandths;
substituting the series expression of the current density trigonometric function into the magnetic field expression to obtain the relation between the ith target field point and the ith current density source point, wherein i =1, ·, Q, l = m × N + N; l =1, ·, M × N, expressed as:
is provided with
P mn ＝P l ,K mn,i ＝K l,i ,D mn,i ＝D l,i ,H mn,i ＝H l,i ；
Wherein, the values of M, N and Q are determined by the memory resource of the computer according to the reality; generating a specific target RF field with a length and a width of-L x /2≤x≤L x /2,-L y /2≤y≤L y Per 2 finite Current Density in-plane calculation of P l In accordance with P l Two orthogonal components J of the current density in the plane are calculated x (x, z) and J z (x, z), i.e., the harmonic field object field method, followed by the use of the leave-function method, i.e., the flow function contour, to calculate the actual wiring trace.
Optionally, the single-side nuclear magnetic resonance device further comprises an aluminum shell, and the single-side permanent magnet structure and the radio frequency transceiving integrated coil are both arranged in the aluminum shell.
The invention has the beneficial effects that: the small nuclear magnetic resonance device for detecting the superficial skin provided by the invention has the advantages of simple structure, small volume, light weight and reliable performance, can realize signal measurement of nuclear magnetic resonance, and is convenient for on-site noninvasive detection.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the means of the instrumentalities and combinations particularly pointed out hereinafter.
Drawings
For the purposes of promoting a better understanding of the objects, aspects and advantages of the invention, reference will now be made to the following detailed description taken in conjunction with the accompanying drawings in which:
FIG. 1 is a schematic overall view of a hand-held low gradient single-sided NMR apparatus for detecting full-thickness skin according to the present invention;
FIG. 2 is a schematic diagram of an initial structure of a permanent magnet and variables to be optimized;
FIG. 3 is a flow chart of a sparrow search algorithm optimizing permanent magnet structure;
FIG. 4 is a schematic view of magnetic induction intensity along the Z-axis direction at the center of a detection target area;
FIG. 5 is a schematic diagram of the equipotential surfaces of the magnetic induction intensity in the target region;
fig. 6 is a schematic diagram of the matching of the quadrature and correlation of the rf field with the main magnetic field in the examination target region.
Figure 7 is a schematic diagram of a radio frequency coil configuration.
Reference numerals are as follows: 1-a left magnet set; 2-a middle magnet; 3-right magnet group; 4-radio frequency transmit-receive integrated coil; 5-detecting the target area.
Detailed Description
The following embodiments of the present invention are provided by way of specific examples, and other advantages and effects of the present invention will be readily apparent to those skilled in the art from the disclosure herein. The invention is capable of other and different embodiments and of being practiced or of being carried out in various ways, and its several details are capable of modification in various respects, all without departing from the spirit and scope of the present invention. It should be noted that the drawings provided in the following embodiments are only for illustrating the basic idea of the present invention in a schematic way, and the features in the following embodiments and examples may be combined with each other without conflict.
Wherein the showings are for the purpose of illustrating the invention only and not for the purpose of limiting the same, and in which there is shown by way of illustration only and not in the drawings in which there is no intention to limit the invention thereto; to better illustrate the embodiments of the present invention, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of an actual product; it will be understood by those skilled in the art that certain well-known structures in the drawings and descriptions thereof may be omitted.
The same or similar reference numerals in the drawings of the embodiments of the present invention correspond to the same or similar components; in the description of the present invention, it should be understood that if there is an orientation or positional relationship indicated by terms such as "upper", "lower", "left", "right", "front", "rear", etc., based on the orientation or positional relationship shown in the drawings, it is only for convenience of description and simplification of description, but it is not an indication or suggestion that the referred device or element must have a specific orientation, be constructed in a specific orientation, and be operated, and therefore, the terms describing the positional relationship in the drawings are only used for illustrative purposes, and are not to be construed as limiting the present invention, and the specific meaning of the terms may be understood by those skilled in the art according to specific situations.
Referring to fig. 1 to 7, fig. 1 is an overall schematic diagram of a handheld low-gradient single-sided nmr apparatus for detecting full-thickness skin, as shown in fig. 1, the apparatus includes:
a single-side permanent magnet structure and a radio frequency transmit-receive integrated coil 4;
the unilateral permanent magnet structure comprises three groups of magnet structures;
the three groups of magnet structures are a left magnet group 1, a middle magnet 2 and a right magnet group 3 respectively;
the left magnet group 1 and the right magnet group 3 are on the same horizontal plane;
the middle magnet 2 is positioned between the left magnet group 1 and the right magnet group 3 and below the horizontal planes of the left magnet group 1 and the right magnet group;
the left magnet group 1 and the right magnet group 3 have the same specification;
in an XYZ coordinate system, the magnetic pole of the left magnet group 1 points to the Z direction, the magnetic pole of the middle magnet 2 points to the-Y direction, and the magnetic pole of the right magnet group 3 points to the-Z direction;
a main magnetic field B pointing from the left magnet group 1 to the right magnet group 3 is generated above the unilateral permanent magnet structure 0 The magnetic pole points to the Y direction, and a uniform magnetic field is generated in the geometric central area of the middle magnet, and the geometric central area of the middle magnet is a detection target area 5;
the above-mentionedMain magnetic field B 0 The magnetic induction intensity of (2) is less than or equal to 100mT, and the magnetic field gradient G of the center of the detection target area 5 along the direction vertical to the magnetic field is 2.96T/m;
the magnetic field distribution generated by the permanent magnet structure is calculated by adopting a finite element method, and the structural parameters of the permanent magnet are optimized by a sparrow search algorithm; the radio frequency receiving and transmitting integrated coil 4 is a receiving and transmitting integrated double-layer planar coil, is designed by adopting a time-harmonic field inversion method and a flow function method, and is used for generating an excitation radio frequency magnetic field orthogonal to a main magnetic field and receiving an echo signal generated after a detected sample arranged in a detection target area is excited.
The permanent magnet initial structure is composed of six magnets in three groups, each group comprises two magnets, the three groups of magnets are arranged in a similar delta shape, the specifications and the signs of the left group of magnets and the right group of magnets are the same, the magnetic poles point to the opposite directions, the magnetic poles of the left group point to the vertical upward direction (Z direction), and the magnetic poles of the right group point to the vertical downward direction (Z direction); the magnetic poles of the middle group point to the horizontal direction and are in the same direction (Y direction) with the magnetic fields generated by the left and right groups of magnets at the positions, and the specifications of the magnetic poles of the middle group can be different from those of the left and right groups of magnets. When the permanent magnet is initialized, the sizes of four magnets of the left and right magnet groups are specified as follows: the length is 12.7mm, the height is 12 mm; the size of the middle group of magnets is as follows: the length is, the height is, the width is 25.4mm. A main magnetic field B0 directed from the left magnet group to the right magnet group (Y direction) is thus generated above the center of the magnet structure. The 7 parameters to be optimized for the permanent magnet initial structure comprise: the magnetic pole comprises a left magnet brand and a right magnet brand NdFe1, a middle magnet brand NdFe2, a distance d1 between the left magnet group and the right magnet group, a distance d2 between the lower bottom surfaces of the left magnet group and the right magnet group and the upper bottom surface of the middle magnet group in the Z-axis direction, an inter-group distance d3 between the left magnet group and the right magnet group, an inter-group distance d4 between the middle magnet group and a width W of the middle magnet. The initial structure of the permanent magnet and the variables to be optimized are shown in fig. 2.
After the permanent magnet of the permanent magnet structure is initially completed, the structure optimization of all the permanent magnet structures is carried out by using a sparrow search algorithm, and the flow of optimizing the permanent magnet structure by using the sparrow search algorithm is shown in fig. 3.
The magnetic induction in the Z-axis direction at the center of the detection target region is shown in fig. 4.
The magnetic field of the detection target area with the optimal structure of the permanent magnet has the characteristic of high uniformity, and the distribution of the equipotential surfaces of the magnetic induction intensity is shown in figure 5.
In the invention, the main magnetic field for detecting the target region is parallel to the skin surface and attenuates along the direction vertical to the skin depth, so as to ensure the radio frequency field B1 and the main magnetic field B 0 Orthogonal, then the direction of the radio frequency field must be the same as the perpendicular direction of the skin. Therefore, the radio frequency coil is designed by adopting a harmonic field inversion method and a flow function method, and a matching radio frequency field orthogonal and related to the main magnetic field is designed according to the distribution of the main magnetic field. FIG. 6 is a schematic illustration of the matching of the quadrature and correlation of the radio frequency field with the main magnetic field in the region of interest under examination. Fig. 7 is a schematic diagram of a radio frequency coil structure, showing only one layer of coil structure due to the same double layer coil structure.
Finally, the above embodiments are only intended to illustrate the technical solutions of the present invention and not to limit the present invention, and although the present invention has been described in detail with reference to the preferred embodiments, it will be understood by those skilled in the art that modifications or equivalent substitutions may be made on the technical solutions of the present invention without departing from the spirit and scope of the technical solutions, and all of them should be covered by the claims of the present invention.
Claims (6)
1. Detect unilateral nuclear magnetic resonance device of hand-held type low gradient of full skin, its characterized in that: the device includes:
a unilateral permanent magnet structure and a radio frequency transmit-receive integrated coil (4);
the unilateral permanent magnet structure comprises three groups of magnet structures;
the three groups of magnet structures are respectively a left magnet group (1), a middle magnet (2) and a right magnet group (3);
the left magnet group (1) and the right magnet group (3) are on the same horizontal plane;
the middle magnet (2) is positioned between the left magnet group (1) and the right magnet group (3) and is positioned below the horizontal planes of the left magnet group (1) and the right magnet group;
the left magnet group (1) and the right magnet group (3) have the same specification;
in an XYZ coordinate system, the magnetic poles of the left magnet group (1) point to the Z direction, the magnetic poles of the middle magnet (2) point to the-Y direction, and the magnetic poles of the right magnet group (3) point to the-Z direction;
a main magnetic field B pointing from the left magnet group (1) to the right magnet group (3) is generated above the unilateral permanent magnet structure 0 The magnetic pole points to the Y direction, and a uniform magnetic field is generated in the geometric center area of the middle magnet, and the geometric center area of the middle magnet is a detection target area (5);
the main magnetic field B 0 The magnetic induction intensity of (2) is less than or equal to 100mT, and the magnetic field gradient G of the center of the detection target area (5) along the direction vertical to the magnetic field is 2.96T/m;
the magnetic field distribution generated by the unilateral permanent magnet structure is calculated by adopting a finite element method, and the structural parameters of the unilateral permanent magnet are optimized by a sparrow search algorithm;
the radio frequency receiving and transmitting integrated coil (4) adopts a receiving and transmitting integrated double-layer planar coil, is designed by adopting a time-harmonic field inversion method and a flow function method, is used for generating an excitation radio frequency magnetic field orthogonal to a main magnetic field, and receives an echo signal generated after a detected sample arranged in a detection target area is excited.
2. The hand-held low-gradient single-sided nuclear magnetic resonance device for detecting full-thickness skin according to claim 1, wherein: the size of left side magnet group (1) and right side magnet group (3) is: the length is 25.4mm, the height is 12.7mm, and the width is 12.7mm; the size of the middle magnet (2) is as follows: the length is 50.8mm, the height is 12.7mm and the width is 25.4mm.
3. The hand-held low-gradient single-sided nuclear magnetic resonance device for detecting full-thickness skin according to claim 1, wherein: the optimization of the structural parameters of the unilateral permanent magnet through the sparrow search algorithm specifically comprises the following steps:
the spatial position of the single-sided permanent magnet structure is represented as an n × d matrix X:
wherein n is the number of the permanent magnet structures, and d is the dimension of the permanent magnet structure to-be-optimized structure parameter; the position of the ith permanent magnet structure in space is X i ＝(x i,1 ,x i,2 ,…,x i,d ) (ii) a The adaptation value of the single-sided permanent magnet structure is expressed as a vector F X :
The optimizing capability of the sparrow search algorithm is based on three parts: the finder, the joiner and the warner search the optimal permanent magnet structure together; the location update formula for each generation of discoverers is as follows:
wherein T represents the current iteration number, T represents the total iteration number,
represents the information quantity of the jth dimension parameter in the ith permanent magnet structure at t iterations, and alpha is [0,1 ]]R is a random number representing the current warning value, and R belongs to [0,1 ]]ST denotes a security value, ST ∈ [0.5,1]Q is a random number following a normal distribution, and L is 1 × d j Matrix of d j Is the dimension of the jth dimension parameter of the magnet group, and each element in the matrix is 1;
the location update formula for each generation of enrollees is as follows:
wherein, the first and the second end of the pipe are connected with each other,
is the order of eyesOptimal position occupied by pre-discoverer, X worst Then the current global worst position is indicated; a is a 1 × d matrix in which each element is randomly assigned a value of 1 or-1, and A + ＝A T (AA T ) -1 ，
Is represented by A + The value of the j-th dimension of (d); when in use
When the joiner is in use, the joiner can positively follow the finder to move to a better position; when the temperature is higher than the set temperature
In the process, the ith subscriber with a lower adaptive value needs to move to other positions, and the current poorer position is got rid of by combining the exp function characteristic to obtain a better adaptive value;
the position update formula for each generation of alert is as follows:
wherein, therein
Is the current global optimum position; beta is taken as a step length control parameter and is a random number which follows normal distribution with the mean value of 0 and the variance of 1; k ∈ [ -1,1]Is a random number, f i The adaptive value of the current magnet group is obtained; f. of g And f w Current global best and worst adaptation values, respectively; ε is the smallest constant to avoid zero denominator; when f is i >f g When the alarm is in the edge position, the adaptive value is low, and the alarm needs to be close to the center position; when f is i ＝f g When the adaptive value of the permanent magnet structure at the middle position is low, the permanent magnet structure needs to go to other positions to improve the adaptive value;
during magnetic field simulation, cutting the FOV along the Z-axis direction according to a certain step length to obtain N 1 Cutting into slices; sampling two middle shafts on each section according to the synchronous length of the phase, and obtaining N on each middle shaft 2 Magnetic induction intensity B i Uniformity P on any axis i The calculation formula is as follows:
wherein B is c The magnetic induction intensity of the midpoint of the tangent plane; the uniformity P of two middle axes in a tangent plane is obtained by the formula (6) xi And P yi Degree of uniformity H 1 The expression is as follows:
calculating the uniformity of each section B h ：
Wherein, B max Is the maximum value of magnetic induction intensity in a tangent plane, B min Is the minimum value of the magnetic induction intensity in the tangent plane; b for each slice by equation (8) h After solving, the uniformity H is obtained 2 ：
In conjunction with equations (7) and (9), the evaluation function H of the permanent magnet structure adaptation values is as follows:
H＝(H 1 +H 2 )·(|G-2|+|G-3|) (10)
wherein G is the magnetic field gradient of the detection target region along the Z axis, and in order to maintain the low gradient of G in the size of 2-3T/m during the design of the permanent magnet structure, the adaptive value is evaluated by using (| G-2| + | G-3 |) in the formula (10).
4. The hand-held low-gradient single-sided nuclear magnetic resonance device for detecting full-thickness skin according to claim 3, wherein: the magnet marks of the left magnet group (1) and the right magnet group (3) are NdFe1, and the magnet mark of the middle magnet (2) is NdFe2;
the distance between the left magnet group (1) and the right magnet group (3) is d1; the distance between the lower bottom surfaces of the left magnet group (1) and the right magnet group (3) and the upper bottom surface of the middle magnet (2) in the Z-axis direction is d2, the intra-group distance between the left magnet group (1) and the right magnet group (3) is d3, the intra-group distance between the middle magnet (2) is d4, and the width of the middle magnet (2) is W;
in the formula (1), d is the dimension of the parameters of the structure to be optimized of the permanent magnet structure, one parameter is 1 dimension, two parameters are 2 dimensions, and three parameters are 3 dimensions.
5. The hand-held low-gradient single-sided nuclear magnetic resonance device for detecting full-thickness skin according to claim 4, wherein: the single-side permanent magnet structure is five neodymium iron boron magnets, the radio frequency transmitting and receiving integrated coil is designed by adopting a time harmonic field inversion method and a flow function method, and a matching radio frequency field orthogonal and related to a main magnetic field is designed according to the distribution of the main magnetic field; setting the length of a wiring area of the radio frequency transceiving integrated coil to be Lx and the width of the wiring area to be Ly; the current density of the inner surface of the plane where the radio frequency transmitting-receiving integrated coil is located is divided into two components: a current density component parallel to the main magnetic field B0 and a current density component perpendicular to the main magnetic field B0; the current density component is represented as,
P mn the coefficients to be obtained;
from the principle of current continuity, the current function of the current density in the y =0 plane is expressed as:
the magnetic field component of each point in the ROI space of the target region is detected by the Bio Safaer theorem
R represents the distance from the field point to the source point, S 0 Represents the plane in which the current density lies;
wherein (x, y, z) represents the coordinates of any field point in the ROI, (x) 0 ,y 0 ,z 0 ) Representing the coordinate of any source point on the current density plane;
one aspect of the matching of the radio frequency field to the main magnetic field is the radio frequency field B generated by the radio frequency coil 1 The vector should be matched with the main magnetic field B generated by a single-sided magnet at each height 0 The vectors are orthogonal everywhere, i.e.:
B 1 ⊥B 0
is unfolded into
B 0x B 1x +B 0y B 1y +B 0z B 1z ＝0 (15)
Another aspect of the RF field matching the main magnetic field is the RF field B 1 The magnitude of the magnetic field mode value of the magnetic field should be equal to the main magnetic field B generated by the unilateral magnet 0 Proportional in magnitude of the magnetic field modulus; therefore, each spinning hydrogen proton on the same plane of a detection target area can be simultaneously turned to the same plane, and a high-resolution correlation spectrum and a high signal-to-noise ratio are obtained under the condition that a radio frequency field is matched with a main magnetic field; this is to satisfy
||B 1 ||∝||B 0 || (16)
Is developed into equation
k-value radio frequency field B 1 Main magnetic field B generated by single-side magnet 0 The ratio of (A) to (B), usually in parts per thousand;
substituting the series expression of the current density trigonometric function into the magnetic field expression to obtain the relation between the ith target field point and the ith current density source point, wherein i =1, ·, Q, l = m × N + N; l =1, ·, M × N, expressed as:
is provided with
P mn ＝P l ,K mn,i ＝K l,i ,D mn,i ＝D l,i ,H mn,i ＝H l,i ；
Wherein, the values of M, N and Q are determined by the memory resource of the computer according to the reality; generating a target-specific RF field having a length and a width of-L x /2≤x≤L x /2,-L y /2≤y≤L y Per 2 finite Current Density in-plane calculation of P l In accordance with P l Two orthogonal components J of the current density in the plane are calculated x (x, z) and J z (x, z), i.e., the harmonic field object field method, and then the actual wiring trace is calculated using the leave-function method, i.e., the flow function contour.
6. The hand-held low-gradient single-sided nuclear magnetic resonance device for detecting full-thickness skin according to claim 5, wherein: the unilateral nuclear magnetic resonance device further comprises an aluminum shell, and the unilateral permanent magnet structure and the radio frequency transceiving integrated coil are arranged in the aluminum shell.
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| CN116520206A (en) * | 2023-06-15 | 2023-08-01 | 潍坊新力超导磁电科技有限公司 | Automatic measuring device for gradient magnetic field |
| CN116520206B (en) * | 2023-06-15 | 2023-09-22 | 潍坊新力超导磁电科技有限公司 | Automatic measuring device for gradient magnetic field |
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