An umbrella-shaped antenna array and system for microwave three-dimensional brain imaging

Abstract

The present invention discloses an umbrella-shaped antenna array and system for microwave three-dimensional imaging of the brain, belonging to the field of microwave medical imaging technology. The umbrella-shaped antenna array is composed of antennas, characterized in that it includes: a planar array unit, an umbrella-top antenna unit and a coupling medium layer; the planar array unit is composed of antennas evenly arranged on a circular plane or a polygonal plane; the radius of the circular plane is, and the distance between adjacent antennas is; the umbrella-top antenna unit is vertically arranged directly above the geometric center of the plane, adopts a vertical polarization mode, and the radiation main lobe direction is orthogonal to the radiation direction of the planar array unit; the coupling medium layer is filled between the antennas and between the antennas and the surface of the brain. The present invention reduces the mutual coupling of three-dimensional antennas through an umbrella-shaped structure, improves the imaging accuracy in combination with a frequency domain iterative algorithm, and realizes high-precision three-dimensional imaging of the brain.

Description

Technical Field

[0001] The present invention belongs to the technical field of microwave medical imaging, and in particular relates to an umbrella-shaped antenna array and system for microwave three-dimensional brain imaging. Background Art

[0002] As a non-invasive method, microwave medical imaging technology has attracted considerable attention in the field of brain disease detection in recent years due to its radiation-free, low-cost, and real-time advantages. Microwave imaging is mainly divided into microwave tomography, microwave thermoacoustic imaging, and confocal microwave imaging (CMI). Microwave tomography analyzes the scattering and absorption characteristics of microwave signals in biological tissues to invert the dielectric constant distribution within the brain. This can be summarized as solving a type of inverse mathematical physics problem and is generally categorized into time-domain iterative imaging and frequency-domain iterative imaging. Time-domain iterative imaging methods have faster computational speeds because they do not require extensive calculations of electromagnetic field distributions, but are less sensitive to small anomalies. Frequency-domain iterative imaging is a typical inverse scattering imaging method that uses electromagnetic simulation calculations to approximate measured results during the iterative process. It is faster for small anomalies, but requires more iterations to approximate large anomalies.

[0003] Microwave detection imaging has attracted great attention in recent years for the detection of brain diseases. In 2021, researchers at the University of Queensland in Australia designed a flexible meandering line broadband antenna array and applied the antenna to experiments based on confocal imaging algorithms to reconstruct abnormal simulated target images. In 2022, an improved deformed Born iterative algorithm was designed in the imaging algorithm to achieve brain imaging. In 2023, Chalmers University of Technology in Sweden first proposed reducing surface waves by placing dielectric rods between the antenna's radiating element and the fuselage, providing a new approach to reducing external interference. Brain injury detection methods based on microwave imaging have bottlenecks such as unclear imaging and high computational complexity. Most research results on microwave detection classification are based solely on electromagnetic simulation, and there are still many problems in applying their results in practice.

[0004] Domestic research on microwave detection imaging of brain injuries started relatively late. Existing microwave brain imaging systems mostly use planar antenna arrays (such as circular or arc-shaped layouts). For example, the brain tumor detection system disclosed in patent CN105816172B uses antennas evenly distributed across the surface of the skull. While capable of two-dimensional tomographic imaging, this geometrical limitation of the planar arrangement makes it difficult to perform three-dimensional localization of lesions deep within the skull or in asymmetric regions. Furthermore, while three-dimensional distributed antenna arrays (such as the multi-channel portable microwave scanning device described in patent CN210990288U) theoretically offer improved spatial coverage, they suffer from severe electromagnetic mutual coupling issues in practice. When multiple antennas are densely distributed in three-dimensional space, near-field coupling between adjacent antennas can lead to signal phase distortion and energy attenuation, significantly reducing the imaging signal-to-noise ratio. Current microwave brain imaging systems still face significant technical bottlenecks in three-dimensional spatial resolution, antenna array design, and algorithm efficiency, hindering their widespread clinical application. To address the above issues, a new antenna array structure and efficient imaging algorithm are urgently needed to break through the spatial resolution limitation of three-dimensional imaging, suppress the antenna mutual coupling effect, and improve the computational efficiency and clinical adaptability of the algorithm. Summary of the Invention

[0005] The present invention aims to address the deficiencies of the existing technology and proposes an umbrella-shaped antenna array and system for microwave three-dimensional brain imaging. Through three-dimensional layout optimization, efficient iterative algorithms and adaptive signal processing, it breaks through the limitations of traditional technology and achieves high-precision and rapid reconstruction of the three-dimensional dielectric constant of the brain.

[0006] To achieve the above object, the present invention provides the following solution: an umbrella-shaped antenna array for microwave three-dimensional brain imaging, the umbrella-shaped antenna array is composed of The antenna structure includes: a planar array unit, an umbrella top antenna unit and a coupling medium layer;

[0007] The planar array unit is composed of The antennas are evenly arranged on a circular plane or a polygonal plane; the radius of the circular plane is , the distance between adjacent antennas is ;

[0008] The umbrella top antenna unit is vertically arranged just above the geometric center of the plane, with a height of satisfy ; Using vertical polarization and the radiation main lobe direction is orthogonal to the radiation direction of the planar array unit;

[0009] The coupling medium layer is filled between the antennas and between the antennas and the surface of the skull.

[0010] Further preferably, the coupling medium layer is composed of a biocompatible liquid or gel, including a glycerol-deionized water mixture, a polyvinyl pyrrolidone and deionized water mixture; the dielectric properties of the mixture are less than 10% different from the dielectric constant of brain white matter in the 0.5Ghz~6Ghz frequency band.

[0011] More preferably, The value of is 8, 12, 16, 24 or 32; the umbrella top antenna unit is fixed by an adjustable bracket with a vertical adjustment accuracy of ±1mm; the adjustable bracket is equipped with an electric lifting mechanism and an integrated pressure sensor, and the pressure sensor is used to monitor the contact pressure of the coupling medium layer in real time.

[0012] The present invention also provides a system for microwave cranial three-dimensional imaging, comprising: a front end and a back end;

[0013] The front end includes: an umbrella-shaped antenna array as described above, for transmitting and receiving microwave signals;

[0014] The backend includes: RF signal generator, RF transceiver module, data processing unit and display terminal;

[0015] The radio frequency signal generator is used to generate a broadband frequency modulated continuous wave signal or a pulse signal of 0.5 GHz to 6 GHz;

[0016] The RF transceiver module is used to switch and control the umbrella-shaped antenna array, complete the transmission, reception and collection of electromagnetic signals of the umbrella-shaped antenna array, and obtain the time domain waveform signal matrix ,in , indicating the antenna Post-launch antenna The received time domain waveform;

[0017] The data processing unit is used to process the collected electromagnetic signals to complete brain imaging;

[0018] The display terminal is used to display the results of cranial brain imaging.

[0019] Further preferably, the method for performing brain imaging by the data processing unit includes:

[0020] S1. Brain positioning and initialization: An adaptive confocal algorithm is used to perform three-dimensional positioning of the brain. The initial imaging area is a three-dimensional space 1.2 to 1.5 times the average diameter of the brain.

[0021] S2. Calculate the dielectric constant distribution;

[0022] S3. Perform threshold segmentation based on dielectric constant to complete brain imaging.

[0023] Further preferably, S1 includes the following steps:

[0024] S11. Based on the number and position of antennas, determine the distance and spatial coordinates between all antennas, and initialize the conical area formed by the umbrella antenna array as discrete points The initial space ;

[0025] S12, for all antennas in the initial space Effective radiation space within Mark and get the points , Antenna number Collection of ;

[0026] S13, point by point , select the antenna pair ,in , calculate the transmitting antenna arrive point, and then to the receiving antenna Signal transmission delay , based on the signal transmission delay The waveform signal collected during work Perform time-shift calculations The superposition value of the moment as a point The energy value of ;

[0027] S14, based on the energy distribution Calculate average energy intensity , and initialize the brain area as a cubic space containing the maximum energy distribution ,ensure Contains all satisfaction of At the same time, the cubic space The side length is 1.2 to 1.5 times the average diameter of the brain.

[0028] Further preferably, S2 includes the following steps:

[0029] S21, the cubic space The dielectric constant distribution is initialized to the uniform background value of the coupling medium;

[0030] S22, the waveform signal matrix obtained by the acquisition Convert to signal spectrum ;

[0031] S23. Based on the Born approximation and Green's function integral equation, the relationship between the scattered field and the dielectric constant perturbation is obtained, and the scattered field is analyzed. Calculation:

[0032] ,

[0033] Where, represents the wave number; represents the imaging space; represents the dielectric constant contrast; Indicates the transmitting antenna exist The incident field generated at Indicates the calculated Antenna transmitting The scattered electric field at represents the free space Green's function; Respectively represent antennas The spatial coordinates of represents the spatial coordinates of the source point in the integral;

[0034] S24. Calculate the measured signal and theoretical field The residual of ;

[0035] S25, the objective function Use the optimizer to perform optimization and iteratively update the dielectric constant distribution until the objective function converges or the number of iterations reaches the set threshold, and output the three-dimensional dielectric constant distribution result.

[0036] Further preferably, S3 includes the following steps:

[0037] S31, use a three-dimensional bilateral filter to remove noise, the filter's spatial domain standard deviation is 1mm~2mm, and the dielectric constant domain standard deviation is: 5%~10%;

[0038] S32 , setting a difference threshold of the dielectric constant, performing threshold segmentation based on the difference threshold, and completing brain imaging.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] The umbrella-shaped layout proposed in this invention, combined with orthogonal polarization design, achieves full-space coverage of the brain while reducing three-dimensional antenna mutual coupling, solving the defect that planar arrays cannot perform stereoscopic imaging. Compared with traditional microwave imaging algorithms, the combination of adaptive layered imaging and frequency-domain Born iteration reduces computational complexity and effectively improves reliability compared with traditional inversion algorithms. The adjustable bracket and wide-band design adapt to the brain sizes of different patients, and the coupling medium ensures that the signal penetration depth reaches more than 10 cm, meeting the needs of deep detection and having better clinical applicability; it has better imaging accuracy.

[0041] The present invention provides high-precision, low-cost three-dimensional imaging support through the coordinated optimization of an umbrella-shaped antenna array and an efficient algorithm, and has significant clinical application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the technical solution of the present invention, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0043] Figure 1 This is a schematic diagram of the three-dimensional structure of an umbrella-shaped antenna array according to an embodiment of the present invention;

[0044] Figure 2 This is a diagram showing the overall architecture of a microwave three-dimensional brain imaging system according to an embodiment of the present invention;

[0045] Figure 3 This is a connection block diagram of a microwave three-dimensional brain imaging system according to an embodiment of the present invention;

[0046] Figure 4 This is a flow chart of a method for performing brain imaging by a data processing unit according to an embodiment of the present invention;

[0047] Figure 5 This is a schematic diagram of the microwave three-dimensional brain imaging results of an embodiment of the present invention. DETAILED DESCRIPTION

[0048] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0049] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0050] Example 1:

[0051] like Figure 1 As shown, this embodiment provides an umbrella-shaped antenna array for microwave three-dimensional brain imaging. The umbrella-shaped antenna array is composed of The antenna structure includes: a planar array unit, an umbrella top antenna unit and a coupling medium layer;

[0052] Among them, the planar array unit is composed of The antennas are evenly arranged on a circular plane or a polygonal plane; The value of is 8, 12, 16, 24 or 32; the radius of the annular plane is , this embodiment is set to 8cm~16cm according to the actual application scenario, and can be adjusted according to the head circumference of different patients; the distance between adjacent antennas is ; For example, when When supporting antennas, the spacing , meeting the Nyquist sampling criterion. Planar array antenna options include Vivaldi antennas, linear antennas, microstrip antennas, helical antennas, and log-periodic antennas. All planar array antennas use horizontal polarization and are connected to the RF transceiver module via RF coaxial cables (characteristic impedance 50Ω).

[0053] The umbrella top antenna unit is set vertically above the geometric center of the plane, with a height of satisfy ;by For example, The antenna is adjustable from 3cm to 18cm. It uses vertical polarization, with the main lobe direction orthogonal to the planar array element's radiation direction. The umbrella-top antenna element is secured by an adjustable bracket with a vertical adjustment accuracy of ±1mm. The bracket is equipped with a motorized lift mechanism and an integrated pressure sensor, which monitors the contact pressure of the coupling dielectric layer in real time. When the contact pressure reaches the threshold, the lift stops, ensuring that the coupling dielectric effectively fills the gap between the test target and the antenna array.

[0054] The coupling medium layer is filled between the antennas and between the antennas and the brain surface to reduce mutual coupling. The coupling medium in the coupling medium layer is composed of a biocompatible liquid or gel, including: a glycerol-deionized water mixture, a polyvinyl pyrrolidone and deionized water mixture, etc.; the dielectric properties of the mixture are less than 10% different from the dielectric constant of the brain white matter in the 0.5Ghz~6Ghz frequency band. In this embodiment, the dielectric constant of the mixture at 1Ghz is The mixed liquid is injected into a 5mm thick silicone bag and adhered to the surface of the skull.

[0055] Example 2:

[0056] like Figure 2 As shown, this embodiment provides a system for microwave cranial three-dimensional imaging, including: a front end and a back end; the front end includes: an umbrella-shaped antenna array as provided in the first embodiment, which fits tightly against the patient's head and is used to transmit and receive microwave signals; the back end includes: a radio frequency signal generator, a radio frequency transceiver module, a data processing unit, and a display terminal. Figure 3As shown, the main function of the microwave cranial three-dimensional imaging system is to collect electromagnetic transceiver signals passing through the patient's head, perform data processing, and generate images. Specifically, the RF signal generator is used to generate a broadband frequency-modulated continuous wave signal between 0.5GHz and 6GHz; the RF transceiver module is used to switch and control the umbrella antenna array, completing the transmission, reception, and acquisition of electromagnetic signals from the umbrella antenna array; the RF transceiver module uses a multi-channel single-pole multi-throw switch with a switching time of ≤100ms and an insertion loss of ≤1dB. It is controlled by the data processing unit and sequentially selects the transmitting antenna according to a preset timing. The remaining antennas receive the RF signal synchronously, collecting the transmission loss and delay of the signal in the working frequency band. The data is then transmitted to the data processing unit via a USB interface. The data processing unit is used to process the collected electromagnetic signals and complete cranial imaging; the display terminal is used to display the results of cranial imaging.

[0057] In this embodiment, Figure 4 As shown, the method for performing brain imaging by the data processing unit includes:

[0058] S1. Brain positioning and initialization: broadband signal excitation, transmitting 0.5GHz~6GHz linear frequency modulation continuous wave, step frequency An adaptive confocal algorithm was used to locate the brain in three dimensions, and the initial imaging area was a three-dimensional space 1.2 to 1.5 times the average diameter of the brain.

[0059] Specifically, S1 includes the following steps:

[0060] S11. Based on the number and position of antennas, determine the distance and spatial coordinates between all antennas, and initialize the conical area formed by the umbrella antenna array as discrete points The initial space .

[0061] S12, for all antennas in the initial space Effective radiation space within Mark and get the points , Antenna number Collection of .

[0062] S13, point by point , select the antenna pair ,in , calculate the transmitting antenna arrive point, and then to the receiving antenna Signal transmission delay , based on signal transmission delay The waveform signal collected during work Perform time-shift calculations The superposition value of the moment as a point The energy value of .

[0063] S14, based on energy distribution Calculate average energy intensity , and initialize the brain area as a cubic space containing the maximum energy distribution ,ensure Contains all satisfaction of At the same time, the cube space The side length is 1.2 to 1.5 times the average diameter of the brain.

[0064] S2. Calculate the dielectric constant distribution.

[0065] In a further implementation, S2 includes the following steps:

[0066] S21. Cube Space The dielectric constant distribution is initialized to the uniform background value of the coupling medium;

[0067] S22, the waveform signal matrix obtained by the acquisition Convert to signal spectrum ;

[0068] S23. Based on the Born approximation and Green's function integral equation, the relationship between the scattered field and the dielectric constant perturbation is obtained, and the scattered field is analyzed. Calculation:

[0069] ,

[0070] Where, represents the wave number; represents the imaging space; represents the dielectric constant contrast; Indicates the transmitting antenna exist The incident field generated at Indicates the calculated Antenna transmitting The scattered electric field at represents the free space Green's function; Respectively represent antennas The spatial coordinates of represents the spatial coordinates of the source point in the integral;

[0071] S24. Calculate the measured signal and theoretical field The residual of ;

[0072] S25. Objective function Use the optimizer to perform optimization and iteratively update the dielectric constant distribution until the objective function converges or the number of iterations reaches the set threshold, and output the three-dimensional dielectric constant distribution result.

[0073] S3. Perform threshold segmentation based on dielectric constant to complete brain imaging.

[0074] Specifically, S3 includes the following steps:

[0075] S31. A three-dimensional bilateral filter is used to remove noise. The standard deviation of the filter in the spatial domain is 1mm~2mm, and the standard deviation in the dielectric constant domain is 5%~10%.

[0076] S32. Setting the Dielectric Constant Difference Threshold , threshold segmentation based on difference threshold , extract the region of interest and complete brain imaging.

[0077] like Figure 5 As shown, in this embodiment, a skull simulation model (18 cm in diameter, containing a simulated abnormal area with a diameter of 2 cm) was established and experiments were conducted. The imaging results can clearly distinguish between normal areas and abnormal areas.

[0078] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. An umbrella-shaped antenna array for microwave three-dimensional brain imaging, the umbrella-shaped antenna array consisting of N antennas, characterized in that: include: Planar array unit, umbrella top antenna unit and coupling dielectric layer; The planar array unit is composed of N-1 antennas evenly arranged on a circular plane or a polygonal plane; the radius of the circular plane is R, and the distance between adjacent antennas is 2πR / (N-1); The umbrella top antenna unit is vertically arranged just above the geometric center of the plane, and the height H satisfies ; A vertical polarization mode is adopted and the radiation main lobe direction is orthogonal to the radiation direction of the planar array unit; The value of N-1 is 8, 12, 16, 24, or 32; the umbrella top antenna unit is fixed by an adjustable bracket with a vertical adjustment accuracy of ±1 mm; the adjustable bracket is equipped with an electric lifting mechanism and an integrated pressure sensor, and the pressure sensor is used to monitor the contact pressure of the coupling medium layer in real time; The coupling medium layer is filled between the antenna and the surface of the skull.

2. The umbrella-shaped antenna array for microwave three-dimensional brain imaging according to claim 1, characterized in that: The coupling medium layer is composed of a biocompatible liquid or gel, including a glycerol-deionized water mixture, a polyvinyl pyrrolidone and deionized water mixture; the dielectric properties of the mixture are less than 10% different from the dielectric constant of brain white matter in the 0.5Ghz~6Ghz frequency band.

3. A method for cranial brain imaging applied to a microwave cranial brain three-dimensional imaging system, characterized in that: The cranial three-dimensional imaging system includes: a front end and a back end; The front end comprises: an umbrella-shaped antenna array as claimed in any one of claims 1 to 2, for transmitting and receiving microwave signals; The backend includes: RF signal generator, RF transceiver module, data processing unit and display terminal; The radio frequency signal generator is used to generate a broadband frequency modulated continuous wave signal or a pulse signal of 0.5 GHz to 6 GHz; The RF transceiver module is used to switch and control the umbrella-shaped antenna array, complete the transmission, reception, and acquisition of electromagnetic signals of the umbrella-shaped antenna array, and obtain a time domain waveform signal matrix T=[T(i,j)], where i, j=1,…N, representing the received time domain waveform of antenna j after antenna i transmits; The data processing unit is used to process the collected electromagnetic signals to complete brain imaging; The display terminal is used to display the results of cranial brain imaging; The step of the data processing unit performing brain imaging includes: S1. Brain positioning and initialization: An adaptive confocal algorithm is used to perform three-dimensional positioning of the brain. The initial imaging area is a three-dimensional space 1.2 to 1.5 times the average diameter of the brain. S2. Calculate the dielectric constant distribution; S3, threshold segmentation based on dielectric constant to complete brain imaging; S1 includes the following steps: S11. Based on the number and positions of antennas, determine the distances and spatial coordinates between all antennas, and initialize the conical area formed by the umbrella-shaped antenna array to an initial space V0 formed by discrete points r; S12, the effective radiation space V of all antennas in the initial space V0 n Marking is done to obtain the set M(r)={n|r∈V n }; S13. For each point r∈V0, select antenna pairs (i, j), where i, j∈M(r), and calculate the signal transmission delay t from the transmitting antenna i to point r and then to the receiving antenna j. i,r,j , based on the signal transmission delay t i,r,j The waveform signal T(i,j) collected during operation is time-shifted and the superposition value at time t=0 is calculated as the energy value of point r to obtain the energy distribution P(r); S14, calculating the average energy intensity P based on the energy distribution P(r) mean , and initialize the brain region to the cubic space V containing the maximum energy distribution, ensuring that V contains all the spaces that satisfy P(r)>P mean At the same time, the side length of the cubic space V is 1.2 to 1.5 times the average diameter of the brain; S2 includes the following steps: S21, initializing the dielectric constant distribution of the cubic space V to a uniform background value of the coupling medium; S22, converting the acquired waveform signal matrix T into a signal spectrum E = [E(i, j)]; S23. Based on the Born approximation and Green's function integral equation, the relationship between the scattered field and the dielectric constant perturbation is obtained, and the scattered field E is calculated. scat (r i ,r j ) calculation: ， Where k0 represents the wave number; V represents the imaging space; χ(r') represents the dielectric constant contrast; E inc (r i , r') represents the incident field generated by the transmitting antenna i at r'; E scat (r i , r j ) represents the calculated scattered electric field at antenna j when antenna i transmits; G (r j , r') represents the free space Green's function; r i , r j denote the spatial coordinates of antennas i and j respectively; r' denotes the spatial coordinates of the source point in the integral; S24, calculate the measured signal E(i,j) and the theoretical field E scat (i,j) residual, construct the objective function ; S25, optimizing the objective function L using an optimizer, and iteratively updating the dielectric constant distribution until the objective function converges or the number of iterations reaches a set threshold, and outputting a three-dimensional dielectric constant distribution result; S3 includes the following steps: S31, use a three-dimensional bilateral filter to remove noise, the filter's spatial domain standard deviation is 1mm~2mm, and the dielectric constant domain standard deviation is: 5%~10%; S32 , setting a difference threshold of the dielectric constant, performing threshold segmentation based on the difference threshold, and completing brain imaging.

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