Broadband large-view-field thermoacoustic imaging system

Abstract

The invention discloses a broadband large-view-field thermoacoustic imaging system, and belongs to the field of thermoacoustic imaging. The system comprises a dynamic microwave excitation module, a data acquisition module and an image analysis processing module. The dynamic microwave excitation module comprises a computer, a 1-6GHz frequency-adjustable microwave source, a coaxial line, a 1-6GHz broadband TEM horn antenna and a compensation reflecting surface; the data acquisition module comprises a semi-ring concave array ultrasonic transducer, an array amplifier, a summing circuit and a data acquisition card; and the image analysis processing module covers the reconstructed tissue thermoacoustic information spectrogram and the multi-frequency information fusion image. The thermoacoustic information of the tissue at multiple frequency points is obtained through microwave excitation of dynamic interval frequency, the problems of contrast deterioration and single dielectric property information under single-frequency microwave excitation are relieved by integrating, analyzing and processing multi-frequency data and images, the analysis and recognition capability of the tissue and the focus is improved, development of the thermoacoustic imaging technology is promoted, and the application prospect is wide. And a new scheme is provided for application of the biosensor in biological tissue detection.

Description

Technical Field

[0001] The present invention belongs to the field of microwave thermoacoustic imaging, and relates to an imaging system and method, in particular to a broadband large field of view thermoacoustic imaging system and method. Background Art

[0002] As a new non-ionizing and non-invasive biomedical imaging technology, microwave thermoacoustic imaging combines the advantages of deep penetration depth and high contrast of microwave imaging and high resolution of ultrasonic imaging. Its imaging principle is based on the thermoacoustic effect, that is, after biological tissue absorbs pulsed microwave energy, it undergoes thermoelastic expansion, generating thermoacoustic signals that can be detected by ultrasonic transducers. The thermoacoustic signals can be reconstructed into thermoacoustic images depicting the microwave energy absorption density distribution through algorithms. Under the assumption of uniform electric field distribution, it can reflect the dielectric property differences of biological tissues and at the same time reflect the structural information of biological tissues. Therefore, microwave thermoacoustic imaging technology can achieve dual characterization in terms of functional and anatomical information, providing more dimensional data support for disease diagnosis, and has currently shown extensive application potential in research fields such as breast tumor screening, kidney imaging, brain imaging, and arthritis detection.

[0003] However, traditional microwave thermoacoustic imaging technology mostly uses single-frequency microwave excitation, mainly imaging based on the dielectric properties of biological tissues under single-frequency excitation, without fully utilizing the characteristics of the dielectric properties of biological tissues changing with frequency in the broadband range. The imaging contrast between tissues with little difference in dielectric properties at some single-frequency points is limited, and the thermoacoustic images cannot accurately reflect the conductivity information and structural information of these tissues. In addition, when traditional microwave thermoacoustic imaging technology uses a single-frequency narrowband antenna to image large tissues, its microwave radiation range is limited, and it can only provide uniform radiation in a relatively small area and usually only images local small tissues, which limits its application in clinical large field of view imaging. A patent with the same applicant as the present invention, application publication number CN114947739A, a dual-frequency microwave-induced thermoacoustic imaging system and method, belongs to the field of microwave thermoacoustic imaging. Based on the law of the theoretical microwave absorption coefficient of biological tissues changing with microwave frequency, thermoacoustic images under two different microwave frequency short pulse widths are obtained using two different microwave frequencies, and then the two thermoacoustic images are fused to obtain a dual-frequency thermoacoustic image. Among them, the two single-frequency thermoacoustic images are used to analyze biological tissues with strong single-frequency microwave energy absorption and detect corresponding lesions, while the dual-frequency fusion image is used to highlight tissues with weak single-frequency microwave energy absorption and large changes in microwave energy absorption with frequency and detect corresponding lesions, that is, using dual-frequency fusion to highlight the low-absorption area and focusing on solving the detection problem of specific tissues and lesions.

[0004] This patent proposes a wideband large field of view photoacoustic imaging system and method, aiming to overcome the limitations of single-frequency excitation in traditional microwave photoacoustic imaging. It uses 1-6 GHz dynamic microwave excitation of biological tissues to obtain photoacoustic information at multiple frequency points. Compared with dual-frequency microwave-induced photoacoustic imaging, this patent can more comprehensively reflect and utilize the dielectric properties and changes in dielectric properties of tissues at different frequencies through the fusion of multi-frequency information in a wide frequency band. It uses TEM horn antennas to generate short-pulse-width microwaves of different frequencies within 1-6 GHz, and meets the requirements of high-power coupling of hundreds of kilowatts and a large microwave radiation range (>20 cm × 20 cm × 10 cm). By compensating the reflector, the re-reflected microwaves are recycled back into the biological tissue to increase the electric field strength and uniformity, alleviating the problems of weakening of the electric field strength and non-uniform field distribution caused by the large field of view. This method can effectively improve the ability to identify tissue lesions, especially in the detection of complex biological tissues and large tissues. By making full use of the tissue microwave dielectric function information in a wide frequency band, it improves the overall information richness of the image, thus enhancing the application potential of microwave photoacoustic imaging technology in the detection of complex tissues and large tissues. Summary of the Invention

[0005] The present invention aims to solve the above problems of the prior art. A wideband large field of view photoacoustic imaging system is proposed. The technical solution of the present invention is as follows:

[0006] A wideband large field of view photoacoustic imaging system, which includes: a computer, a dynamic microwave excitation module, a data acquisition module, and an image analysis module, which are respectively connected to the computer, wherein:

[0007] The dynamic microwave excitation module includes a 1-6 GHz tunable microwave source, a coaxial cable, a 1-6 GHz wideband TEM horn antenna, and a compensating reflector. The computer controls the 1-6 GHz tunable microwave source to generate pulsed microwaves with dynamic interval frequencies, which are transmitted through the coaxial cable to the 1-6 GHz wideband TEM horn antenna. Combined with the compensating reflector, uniform electric field excitation inside the biological tissue to be measured is realized. The biological tissue absorbs microwave energy and generates ultrasonic waves, that is, photoacoustic signals;

[0008] The data acquisition module includes a semi-circular concave array ultrasonic transducer, an array amplifier, an adder circuit, and a data acquisition card; the semi-circular concave array ultrasonic transducer is used to quickly detect the photoacoustic signals of tissues under dynamic interval frequency microwave excitation; the array amplifier is used to amplify the photoacoustic signals; the adder circuit is used to perform cumulative averaging denoising processing on the photoacoustic signals; the data acquisition card collects and stores the amplified and denoised photoacoustic signals into the computer to obtain multiple single-frequency photoacoustic data of tissues under dynamic interval frequency microwave excitation;

[0009] The image analysis module includes reconstructing a spectrogram of tissue photoacoustic information and a multi-frequency information fusion map; reconstructing multiple single-frequency photoacoustic images from multiple single-frequency photoacoustic data using the delay superposition algorithm in a computer, and performing single-frequency energy self-calibration; integrating multiple self-calibrated single-frequency point photoacoustic data to construct a spectrogram of tissue photoacoustic information; and performing fusion reconstruction on multiple single-frequency photoacoustic images based on the differences in photoacoustic information changes and a fusion algorithm to form a multi-frequency information fusion image.

[0010] Further, the short-pulse-width microwaves with different center frequencies in the range of 1 - 6 GHz generated by the 1 - 6 GHz tunable microwave source in the dynamic microwave excitation module are generated by multiple single-frequency microwave sources or by a single tunable microwave source.

[0011] Further, the 1 - 6 GHz broadband TEM horn antenna in the dynamic microwave excitation module radiates hundreds of kilowatts of high-power short-pulse-width microwaves with different center frequencies in the range of 1 - 6 GHz, and at the same time satisfies a large microwave radiation range (>20 cm × 20 cm × 10 cm) to provide conditions for large field-of-view imaging.

[0012] Further, the compensation reflector in the dynamic microwave excitation module utilizes the reflection characteristics of its metal material for microwaves with different wavelengths to recycle the microwaves and then reflect them back into the tissue to be measured to enhance the electric field strength and uniformity of microwave excitation.

[0013] Further, when performing dynamic interval frequency short-pulse-width microwave excitation, the half-ring concave array ultrasonic transducer, array amplifier, adder circuit, data acquisition card in the data acquisition module, as well as the 1 - 6 GHz broadband TEM horn antenna, coaxial cable, and the biological tissue to be measured remain unchanged, that is, the microwave excitation frequency changes dynamically at equal intervals or non-equal intervals while other experimental conditions remain unchanged.

[0014] Further, in the image analysis module, reconstructing multiple single-frequency photoacoustic images from multiple single-frequency photoacoustic data using the delay superposition algorithm specifically includes: using the corresponding relationship between the time delay and the distance from the ultrasonic transducer to the projection point, that is, ultrasonic sound speed × time delay = distance from the ultrasonic transducer to the projection point, projecting the photoacoustic signals collected by the ultrasonic transducer within the detection angle range for projection superposition, thereby realizing the reconstruction of single-frequency photoacoustic images. The single-frequency photoacoustic image can reflect the relative photoacoustic signal relationship between biological tissues, depending on the equivalent conductivity distribution and electric field distribution between tissues at the corresponding frequency, and can also directly reflect the equivalent conductivity relationship between tissues when the electric field distribution is uniform; in a uniformly distributed excitation electric field, single-frequency energy self-calibration is performed using a sample with a known equivalent conductivity.

[0015] Further, in a uniformly distributed excitation electric field, performing single-frequency energy self-calibration using a saline sample with a known equivalent conductivity specifically includes:

[0016]

[0017] wherein, σ eff is the equivalent conductivity of the imaging tissue at the corresponding microwave excitation frequency; |E| is the electric field; δ 盐 is the photoacoustic signal of the imaging tissue; σ eff盐 is the equivalent conductivity of the known salt water pipe at the corresponding microwave excitation frequency; δ is the photoacoustic signal of the salt water pipe; then, the calculation formula of tissue σ eff can be expressed as:

[0018]

[0019] Therefore, by performing single-frequency energy field self-calibration based on the salt water pipe with known equivalent conductivity, it can ensure that the photoacoustic signals at each frequency are compared under a unified energy reference, and multiple single-frequency microwave photoacoustic data or images can be analyzed, specifically including reconstructing the photoacoustic information spectrogram and multi-frequency information fusion diagram of the tissue.

[0020] Furthermore, for the dynamic interval frequency microwave excitation, a microwave excitation frequency sequence (f 0 , f 0 +Δf, f 0 +2Δf, …, f 0 +nΔf) with a fixed large interval Δf = 1 GHz is used to perform multiple single-frequency photoacoustic imaging and single-frequency energy self-calibration; then, the pixel mean values of the photoacoustic images of the target tissue at different frequencies are extracted as the photoacoustic signal values, and the changing trend of the photoacoustic signals is analyzed; according to the obvious degree of the change, that is, the magnitude of the slope, the corresponding microwave excitation frequency spacing of different target tissues is determined. The spacing between the excitation frequencies is reduced within the frequency range with a larger slope, and the spacing between the excitation frequencies is increased within the frequency range with a smaller slope, thereby optimizing the new dynamic excitation frequency spacing, and thus outputting the dynamic interval microwave excitation frequency sequences unique to different target tissues (if there are three target tissues in the measured biological tissue, the corresponding sequences can be respectively denoted as f 11 , f 12 , f 13 , …, f 1n and f 21 , f 22 , f 23 , …, f 2n and f 31 , f 32 , f 33 , …, f 3n ), and taking the union of the dynamic microwave excitation frequency sequences unique to these several target tissues, the new complete dynamic interval microwave excitation frequency sequence is obtained.

[0021] Further, the reconstructed thermoacoustic information spectrogram of the tissue specifically includes: using microwaves with a complete dynamic interval microwave excitation frequency sequence to perform multi - single - frequency thermoacoustic imaging on the measured biological tissue and performing single - frequency energy self - calibration. Under the respective unique dynamic microwave excitation frequency sequences of the target tissues, calculate the average thermoacoustic signal value of the region of interest (ROI) of the target tissue in the self - calibrated single - frequency thermoacoustic images, form thermoacoustic signal curves corresponding to their respective unique dynamic microwave excitation frequency sequences, and merge the thermoacoustic signal curves of several target tissues to construct the thermoacoustic information spectrogram of the tissue.

[0022] Further, the reconstructed multi - frequency information fusion map specifically includes:

[0023] Based on the different slopes of the changes in thermoacoustic signals, perform post - processing fusion on the thermoacoustic data or images at multiple frequency points. The post - processing fusion specifically includes: performing linear fusion and non - linear fusion on multiple groups of single - frequency thermoacoustic images after single - frequency energy self - calibration;

[0024] Linear fusion is to fuse the high - and low - frequency thermoacoustic images obtained under different frequency microwave excitations together according to a certain ratio, that is, fuse the pixel values of multiple self - calibrated single - frequency thermoacoustic images at different frequency points according to a fusion ratio. Its fusion calculation formula can be expressed as:

[0025] M 1 ×TA 1 +M 2 ×TA 2 +…M n ×TA n =y

[0026] M 1 +M 2 +…M n =1

[0027] Where y represents the thermoacoustic image information after linear fusion; TA represents thermoacoustic data, TA 1 represents the thermoacoustic data of the biological tissue at the frequency point f 1 ; TA 2 represents the thermoacoustic data of the biological tissue at the frequency point f 2 ; TA n represents the thermoacoustic data of the biological tissue at the frequency point f n ; M 1 ,M 2 ,…,M n represent the linear fusion coefficients. When M 1 =M 2 =…=M n , the average weighted thermoacoustic image can be obtained;

[0028] Nonlinear fusion uses different fusion ratios for the pixel values of single-frequency thermoacoustic images. That is, pixels with lower TA values in the single-frequency image use a higher proportion of thermoacoustic data at lower frequency points, while pixels with higher TA values use a higher proportion of thermoacoustic data at higher frequency points. Through this nonlinear fusion, the TA values of pixels with high TA values can be made even higher, and the TA values of pixels with low TA values can be made even lower, thereby amplifying the contrast between tissues and improving the display effect of the image.

[0029] The advantages and beneficial effects of the present invention are as follows:

[0030] The present invention uses a 1-6 GHz broadband TEM horn antenna and combines a compensating reflector technology to ensure microwave radiation within a large field of view (>20 cm × 20 cm × 10 cm). By recycling and re-reflecting microwaves through the reflector, the microwave excitation electric field intensity and uniformity within biological tissues are improved, alleviating the problems of weakened electric field intensity and reduced signal-to-noise ratio caused by the large field of view, and enhancing the image contrast. This enables the present invention to achieve imaging of tissues with a larger range and more complex structures, providing support for more extensive clinical thermoacoustic application research.

[0031] Within the 1-6 GHz broadband range, the present invention dynamically adjusts the microwave excitation frequency interval according to the changing trend of tissue thermoacoustic signals, breaking through the limitations of traditional single-frequency excitation. By collecting multi-frequency signals, the dielectric property differences of the target biological tissue varying with frequency are comprehensively covered. For multi-frequency data, single-frequency energy field self-calibration is performed in combination with the equivalent conductivity of known standard samples to eliminate systematic errors and ensure the energy consistency of imaging data. Further, by reconstructing the thermoacoustic information spectrogram and multi-frequency information fusion map, multi-dimensional correlation analysis is carried out on the thermoacoustic signals and dielectric properties of different frequency points of the tissue. This method overcomes the problem of deteriorated image contrast caused by single-frequency excitation due to single dielectric information, and identifies and detects tissues through the difference in frequency change responses, providing richer spectral feature information and tissue structure information for disease diagnosis, and significantly enhancing the lesion recognition rate and the detection ability of tissue abnormalities.

[0032] The dynamic interval of microwave excitation frequency in the present invention is an innovation point. That is, by constructing a multi-frequency excitation sequence matching the frequency-varying dielectric properties and based on single-frequency energy self-calibration, continuous feature extraction of the thermoacoustic signal frequency response curve of biological tissues is achieved within a wide spectral domain, significantly enhancing the spectral integrity and effectively overcoming the inherent limitation of single dielectric property of tissues under single-frequency excitation.

[0033] The multi-frequency information fusion algorithm is an innovation point. That is, linear fusion and nonlinear fusion are performed on multiple groups of single-frequency thermoacoustic images, and a multi-frequency information fusion method based on the frequency-varying law of tissue dielectric properties and the difference in frequency change responses is constructed, effectively overcoming the problem of limited contrast in traditional single-frequency images and improving the imaging effect and the tissue lesion detection ability.

[0034] The implementation method of broadband combined with large field of view thermoacoustic imaging is the innovation point. Compared with narrowband antennas such as dipole antennas, pyramidal horn antennas, and rectangular waveguide antennas commonly used in traditional single-frequency thermoacoustic imaging, using a 1-6 GHz broadband TEM horn antenna combined with a compensating reflector for broadband large field of view thermoacoustic imaging can radiate hundreds of kilowatts of high-power short-pulse-width microwaves with different center frequencies in the 1-6 GHz broadband range, generating a large field of view (>20 cm × 20 cm × 10 cm) radiation range and a relatively uniform microwave excitation field, thus realizing imaging of larger and more complex tissue structures. Brief Description of the Drawings

[0035] Figure 1 is a schematic diagram of a broadband large field of view thermoacoustic imaging system provided by a preferred embodiment of the present invention;

[0036] Figure 2 is a schematic diagram of the optimization of the dynamic interval microwave excitation frequency sequence and the image analysis and processing flow according to an embodiment of the present invention. Detailed Description of the Preferred Embodiments

[0037] Next, the technical solutions in the embodiments of the present invention will be clearly and detailedly described in conjunction with the accompanying drawings in the embodiments of the present invention. The described embodiments are only a part of the embodiments of the present invention.

[0038] The technical solution for the present invention to solve the above technical problems is:

[0039] As Figure 1 shown, this embodiment provides a broadband large field of view thermoacoustic imaging system and method, which includes: a dynamic microwave excitation module, a data acquisition module, and an image analysis and processing module.

[0040] The dynamic microwave excitation module includes a computer, a 1-6 GHz tunable microwave source, a coaxial cable, a 1-6 GHz broadband TEM horn antenna, and a compensating reflector. Among them, the computer controls the 1-6 GHz tunable microwave source to generate short-pulse-width microwaves with different center frequencies. The microwaves are transmitted through the coaxial cable to the 1-6 GHz broadband TEM horn antenna, and the microwaves are radiated over a large range to the biological tissue to be measured. The compensating reflector recovers the microwave energy that passes through or is scattered and diffracted by the tissue through reflection and other means and then re-radiates it to the biological tissue to be measured, thereby exciting the biological tissue to generate thermoacoustic signals.

[0041] On the basis of the above embodiment, the computer controls the 1-6 GHz tunable microwave source to achieve rapid switching of the center frequency and can initialize the frequency interval. Under the condition of controlling other variables unchanged, the tunable microwave source can generate short-pulse-width microwaves with different center frequencies in the 1-6 GHz frequency band. In addition, short-pulse-width microwaves with different center frequencies can also be generated by multiple single-frequency microwave sources.

[0042] Based on the above embodiments, the 1-6 GHz broadband TEM horn antenna can radiate short-pulse microwaves with different center frequencies and 200 kW high power generated by a 1-6 GHz adjustable frequency microwave source to biological tissues over a large range (>20 cm×20 cm×10 cm) to generate thermoacoustic signals.

[0043] On the basis of the above embodiments, the compensating reflective surface utilizes the reflection and radiation characteristics of different-sized metal compensating reflective surfaces to microwaves of different wavelengths, recovers and reflects microwaves into the tissue to be tested. At different microwave excitation frequencies, using co-directional or reverse compensating reflective surfaces of different sizes can enhance the intensity and uniformity of the microwave excitation electric field.

[0044] The data acquisition module includes a semi-circular concave array ultrasonic transducer, an array amplifier, an addition circuit and a data acquisition card. The thermoacoustic signals under different frequency excitations are detected by the semi-circular concave array ultrasonic transducer, amplified by the array amplifier, and de-noised by the addition circuit. The amplified and de-noised thermoacoustic signals are collected and stored by the data acquisition card, thereby obtaining thermoacoustic data under multiple frequency excitations. The entire process is controlled by a computer-compiled labVIEW timing program.

[0045] On the basis of the above embodiments, when microwave dynamic excitation is performed to obtain thermoacoustic data at multiple frequencies, the semi-circular concave array ultrasonic transducer, array amplifier, adding circuit, data acquisition card, 1-6GHz broadband TEM horn antenna, coaxial cable and biological tissue to be tested remain unchanged, that is, while the system changes the microwave excitation frequency, all other experimental conditions remain constant.

[0046] The image analysis module includes reconstructing the tissue thermoacoustic information spectrum and multi-frequency information fusion map.

[0047] On the basis of the above embodiment, a single-frequency thermoacoustic image is reconstructed using a traditional delay-and-addition algorithm, and a single-frequency energy field self-calibration is performed using a standard object or tissue (such as a saline tube, etc.) with known equivalent conductivity to perform a joint analysis of multi-frequency data.

[0048] Furthermore, the dynamic interval microwave excitation sequence optimization and image analysis processing flow is as follows Figure 2 The dynamic interval microwave excitation sequence optimization is specifically: a microwave excitation frequency sequence with a fixed large interval (such as Δf = 1 GHz) is generated by computer-controlled 1-6 GHz adjustable frequency microwave source. Assuming the starting frequency is f 0 , the interval is Δf, then the excitation frequency sequence is f 0 ,f 0 +Δf,f 0 +2Δf,…,f 0+nΔf. The single - frequency thermoacoustic images under each frequency excitation are subjected to single - frequency energy self - calibration, and the mean values of the thermoacoustic image pixels of the target tissue at different excitation frequency points are extracted. According to the frequency range where the thermoacoustic signal changes greatly, the spacing between the excitation frequencies is reduced, and in the frequency range where the thermoacoustic signal changes little, the spacing between the excitation frequencies is increased. Thus, the new dynamic excitation frequency spacing is optimized, and then a dynamic microwave excitation frequency sequence unique to different tissues is output (if there are three target tissues in the measured biological tissue, the corresponding sequences can be respectively denoted as f 11 , f 12 , f 13 , …, f 1n ; f 21 , f 22 , f 23 , …, f 2n ; f 31 , f 32 , f 33 , …, f 3n etc.). The union of the dynamic microwave excitation frequency sequences unique to several target tissues is taken to obtain a new complete dynamic microwave excitation frequency sequence.

[0049] Furthermore, the specific method for reconstructing the thermoacoustic information spectrogram of the tissue is as follows: Using the dynamic interval microwave excitation frequency sequences unique to each tissue (such as f 11 , f 12 , f 13 , …, f 1n etc.) to image the biological tissue, the thermoacoustic data is reconstructed into a single - frequency thermoacoustic image through a delay - and - sum algorithm and subjected to single - frequency energy self - calibration. In the self - calibrated single - frequency thermoacoustic image, the average thermoacoustic signal value of the target tissue region (ROI) is calculated, and its corresponding frequency spectrum curve is plotted. By combining the thermoacoustic signal curves of the target tissues 1 to n corresponding to their respective unique dynamic microwave excitation frequency sequences, the thermoacoustic information spectrogram of the tissue can be generated.

[0050] Furthermore, the reconstructed multi-frequency information fusion map is specifically as follows: By utilizing the differences in the thermal acoustic signal change rates of different tissues under microwave excitations at different frequencies, different biological tissues or lesions can be distinguished and identified. Linear fusion and non-linear fusion are performed on multiple sets of single-frequency thermoacoustic images after single-frequency energy self-calibration, that is, high-frequency and low-frequency thermoacoustic data are fused into one image according to the same fusion ratio or different fusion ratios. Among them, for non-linear fusion, different fusion ratios are used according to the pixel values of the single-frequency thermoacoustic images. Specifically, pixels with lower TA values in the single-frequency image use a higher proportion of thermoacoustic data at lower frequency points, while pixels with higher TA values use a higher proportion of thermoacoustic data at higher frequency points. Through this non-linear fusion, the TA values of pixels with high TA values can be made even higher, and the TA values of pixels with low TA values can be made even lower, thereby amplifying the contrast between tissues, improving the display effect of the image, more comprehensively reflecting the characteristics of different types of tissues and lesions, and enhancing the detection ability.

[0051] The systems, devices, modules or units illustrated in the above embodiments can be specifically implemented by computer chips or entities, or by products with certain functions.

[0052] It should also be noted that the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, such that a process, method, commodity or device comprising a series of elements not only includes those elements but also includes other elements not explicitly listed, or further includes elements inherent to such process, method, commodity or device. Without further limitations, an element defined by the statement "comprising one..." does not exclude the existence of additional identical elements in the process, method, commodity or device comprising the said element.

[0053] The above embodiments should be understood as being only used to illustrate the present invention and not to limit the protection scope of the present invention. After reading the content recorded in the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent changes and modifications also fall within the scope defined by the claims of the present invention.

Claims

1. A broadband and large field of view thermoacoustic imaging system, characterized in that: include: A computer, a dynamic microwave excitation module, a data acquisition module and an image analysis module respectively connected to the computer, wherein: The dynamic microwave excitation module includes a 1-6 GHz adjustable frequency microwave source, a coaxial line, a 1-6 GHz wideband TEM horn antenna and a compensating reflective surface. The computer controls the 1-6 GHz adjustable frequency microwave source to generate pulse microwaves with dynamic interval frequencies, which are transmitted to the 1-6 GHz wideband TEM horn antenna through the coaxial line. The uniform electric field excitation inside the biological tissue to be tested is realized in combination with the compensating reflective surface. The biological tissue absorbs microwave energy to generate ultrasonic waves, i.e., thermoacoustic signals. The data acquisition module includes a semi-circular concave array ultrasonic transducer, an array amplifier, an addition circuit and a data acquisition card; the semi-circular concave array ultrasonic transducer is used to quickly detect the thermoacoustic signal of the tissue under the dynamic interval frequency microwave excitation; the array amplifier is used to amplify the thermoacoustic signal; the addition circuit is used to perform cumulative averaging and denoising on the thermoacoustic signal; the data acquisition card collects the amplified and denoised thermoacoustic signal and stores it in a computer to obtain multiple single-frequency thermoacoustic data of the tissue under the dynamic interval frequency microwave excitation; The image analysis module includes reconstructing a tissue thermoacoustic information spectrum diagram and a multi-frequency information fusion diagram; reconstructing a plurality of single-frequency thermoacoustic images using a delayed superposition algorithm on a plurality of single-frequency thermoacoustic data in a computer, and performing single-frequency energy self-calibration; integrating a plurality of self-calibrated single-frequency thermoacoustic data to construct a tissue thermoacoustic information spectrum diagram; fusing and reconstructing a plurality of single-frequency thermoacoustic images based on the difference in thermoacoustic information changes and a fusion algorithm to form a multi-frequency information fusion image.

2. A broadband and large field of view microwave thermoacoustic imaging system according to claim 1, characterized in that: The short-pulse-width microwaves with different center frequencies within the range of 1-6 GHz generated by the 1-6 GHz adjustable-frequency microwave source in the dynamic microwave excitation module are generated by multiple single-frequency microwave sources or by one adjustable-frequency microwave source.

3. The broadband and large-field microwave thermoacoustic imaging system according to claim 1, characterized in that: The 1-6 GHz broadband TEM horn antenna in the dynamic microwave excitation module radiates hundreds of kilowatts of high-power short-pulse microwaves with different center frequencies in the range of 1-6 GHz, while satisfying a large microwave radiation range (>20 cm×20 cm×10 cm) to provide conditions for achieving large field of view imaging.

4. The broadband and large-field microwave thermoacoustic imaging system according to claim 1, characterized in that: The compensating reflection surface in the dynamic microwave excitation module utilizes the reflection characteristics of its metal material to microwaves of different wavelengths, recycles microwaves and then reflects them into the tissue to be tested to enhance the microwave excitation electric field intensity and uniformity.

5. The broadband and large-field microwave thermoacoustic imaging system according to claim 1, characterized in that: When performing dynamic interval frequency short pulse width microwave excitation, the semi-circular concave array ultrasonic transducer, array amplifier, adding circuit, data acquisition card, 1-6GHz broadband TEM horn antenna, coaxial line and biological tissue to be tested in the data acquisition module remain unchanged, that is, the microwave excitation frequency dynamically changes with equal or non-equal intervals while other experimental conditions remain unchanged.

6. The broadband and large-field microwave thermoacoustic imaging system according to claim 1, characterized in that: In the image analysis module, multiple single-frequency thermoacoustic data are reconstructed into multiple single-frequency thermoacoustic images using a delay superposition algorithm, specifically including: utilizing the corresponding relationship between time delay and the distance from the ultrasonic transducer to the projection point, i.e., ultrasonic speed × time delay = distance from the ultrasonic transducer to the projection point, projecting the thermoacoustic signal collected by the ultrasonic transducer into the detection angle range for projection superposition, thereby realizing the reconstruction of the single-frequency thermoacoustic image. The single-frequency thermoacoustic image can reflect the relative thermoacoustic signal relationship between biological tissues, and depends on the equivalent conductivity distribution and electric field distribution between tissues at the corresponding frequency. When the electric field is uniformly distributed, it can also directly reflect the equivalent conductivity relationship between tissues; in a uniformly distributed excitation electric field, a sample with known equivalent conductivity is used for single-frequency energy self-calibration.

7. A broadband and large-field microwave thermoacoustic imaging system according to claim 6, characterized in that: In a uniformly distributed excitation electric field, a single-frequency energy self-calibration is performed using a salt water sample with known equivalent conductivity, specifically: Among them, σ eff is the equivalent conductivity of the imaging tissue at the corresponding microwave excitation frequency; |E| is the electric field; δ 盐 is the thermoacoustic signal of the imaging tissue; σ eff盐 is the equivalent conductivity of the known brine tube at the corresponding microwave excitation frequency; δ is the thermoacoustic signal of the brine tube; then, tissue σ eff The calculation formula can be expressed as: Therefore, single-frequency energy field self-calibration based on saline tubes with known equivalent conductivity can ensure that the thermoacoustic signals at each frequency are compared under a unified energy reference, and multiple single-frequency microwave thermoacoustic data or images can be analyzed, specifically including reconstruction of tissue thermoacoustic information spectrum and multi-frequency information fusion images.

8. The broadband and large-field microwave thermoacoustic imaging method according to claim 6, characterized in that: The dynamic interval frequency microwave excitation uses a microwave excitation frequency sequence (f0, f0+Δf, f0+2Δf, ..., f0+nΔf) with a fixed large interval Δf=1 GHz to perform multiple single-frequency thermoacoustic imaging and single-frequency energy self-calibration; Then, the mean value of the thermoacoustic image pixels of the target tissue at different frequencies is extracted as the thermoacoustic signal value, and the change trend of the thermoacoustic signal is analyzed; The microwave excitation frequency spacing corresponding to different target tissues is determined according to the degree of change, that is, the slope size. The spacing between the excitation frequencies is reduced in the frequency range with a larger slope, and the spacing between the excitation frequencies is increased in the frequency range with a smaller slope. In this way, the new dynamic excitation frequency spacing is optimized, thereby outputting dynamic interval microwave excitation frequency sequences specific to different target tissues (if there are three target tissues in the biological tissue being tested, the corresponding sequences can be recorded as f 11 ,f 12 ,f 13 ,…,f 1n and f 21 ,f 22 ,f 23 ,…,f 2n and f 31 ,f 32 ,f 33 ,…,f 3n ), take the union of the dynamic microwave excitation frequency sequences specific to these target tissues, and obtain a new complete dynamic interval microwave excitation frequency sequence.

9. The broadband and large-field-of-view thermoacoustic imaging method according to claim 6, characterized in that: The reconstruction of the tissue thermoacoustic information spectrum diagram specifically includes: using microwaves of a complete dynamic interval microwave excitation frequency sequence to perform multiple single-frequency thermoacoustic images of the biological tissue under test, and performing single-frequency energy self-calibration, under the dynamic microwave excitation frequency sequence unique to each target tissue, calculating the average thermoacoustic signal value of the target tissue region ROI in the self-calibrated single-frequency thermoacoustic image, forming thermoacoustic signal curves corresponding to the unique dynamic microwave excitation frequency sequence, and merging the thermoacoustic signal curves of several target tissues to construct the tissue thermoacoustic information spectrum diagram.

10. The broadband and large-field-of-view thermoacoustic imaging method according to claim 6, characterized in that: The reconstructing of the multi-frequency information fusion map specifically includes: Based on the different slopes of the thermoacoustic signal changes, the thermoacoustic data or images at multiple frequency points are fused and processed. The fusion post-processing specifically includes: linear fusion and nonlinear fusion of multiple groups of single-frequency thermoacoustic images after single-frequency energy self-calibration; Linear fusion is to fuse the high- and low-frequency thermoacoustic images obtained under microwave excitation of different frequencies together in a certain ratio, that is, to fuse the pixel values ​​of multiple self-calibrated single-frequency thermoacoustic images at different frequencies together according to a fusion ratio. The fusion calculation formula can be expressed as: M1×TA1+M2×TA2+…M n ×TA n =y M1+M2+…M n =1 Where y represents the thermoacoustic image information after linear fusion; TA represents the thermoacoustic data, TA1 represents the thermoacoustic data of biological tissue at frequency point f1; TA2 represents the thermoacoustic data of biological tissue at frequency point f2; TA n Represents biological tissue at frequency point f n Thermoacoustic data at M1, M2, …, M n Represents the linear fusion coefficient, when M1=M2=…=M n When , the average weighted thermoacoustic image can be obtained; Nonlinear fusion uses different fusion ratios for the pixel values ​​of single-frequency thermoacoustic images, that is, pixels with lower TA values ​​in the single-frequency image use a higher proportion of thermoacoustic data at low frequencies, while pixels with higher TA values ​​use a higher proportion of thermoacoustic data at high frequencies. Through this nonlinear fusion, the TA values ​​of pixels with high TA values ​​can be made higher, and the TA values ​​of pixels with low TA values ​​can be made lower, thereby amplifying the contrast between tissues and improving the image display effect.

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