A microwave thermoacoustic imaging method based on optimized electric field distribution of reflector surface

Abstract

This invention claims protection for a microwave thermoacoustic imaging method based on optimized electric field distribution using a reflective surface, belonging to the field of microwave thermoacoustic imaging technology. In traditional microwave thermoacoustic imaging technology, the microwave thermoacoustic image reconstructed from sound pressure reflects the combined information of the dielectric properties of the imaged object and the excitation electric field in the surrounding area. To obtain accurate conductivity information of the imaged object, the excitation electric field during the microwave thermoacoustic imaging process needs to be sufficiently strong and as uniformly distributed as possible. Currently, thermoacoustic microscopy (TAM) systems face the limitation of low signal-to-noise ratio due to insufficient excitation electric field strength. The point-focusing metal reflective surface constructed according to this invention can increase the excitation electric field strength of the TAM system while improving its uniformity through reflection and focusing at a lower cost, thereby improving image quality. The optimization method of this invention is also applicable to improving the problem of reduced image contrast caused by uneven excitation electric field distribution in thermoacoustic tomography (TAT) systems.

Description

Technical Field

[0001] This invention belongs to the field of microwave thermoacoustic imaging technology, and relates to a microwave thermoacoustic imaging method that improves the electric field distribution by reflecting and focusing microwave energy, thereby enhancing the imaging effect. It also relates to two sets of point-focusing metal reflective surfaces and region-compensating metal reflective surfaces respectively used in TAM system and TAT system. Background Technology

[0002] With social development and improved living standards, the public's health awareness has gradually increased, leading to a continuous growth in demand for the medical market. Compared to clinical manifestations and laboratory tests, medical imaging examinations play an increasingly important role in disease diagnosis and treatment monitoring because they provide more objective or intuitive visual evidence. Consequently, the strategic layout of the medical imaging industry has been rapidly strengthened, and the medical imaging market has expanded rapidly. In recent years, routine clinical imaging techniques and methods have been continuously innovated, corresponding equipment has been continuously improved and perfected, and new imaging technologies and methods are constantly emerging.

[0003] As an emerging multi-physics hybrid imaging modality, microwave thermoacoustic imaging combines the high contrast and deep penetration of microwave imaging with the high resolution of ultrasound imaging. It presents tissue dielectric function information while simultaneously providing structural imaging, and is hailed as one of the most promising new medical imaging methods. Over the past two decades, thanks to the continuous development of microwave radiation sources and ultrasound hardware, microwave thermoacoustic imaging technology has developed rapidly and has been applied in research in areas such as breast cancer detection, brain imaging, joint imaging, bone imaging, and kidney imaging, demonstrating its potential in preclinical and clinical applications.

[0004] However, current microwave thermoacoustic imaging technology faces significant technical challenges: under the assumption of a uniform electric field distribution, microwave imaging results reflect the sound pressure distribution of the imaged object under pulsed microwave radiation, and this sound pressure distribution depends on the dielectric properties of the imaged object. However, the actual field distribution is not uniform, and this non-uniform electric field distribution affects the contrast of thermoacoustic imaging. Improving the uniformity of the excitation electric field to enhance imaging results, so that the thermoacoustic image reflects more of the tissue's own conductivity distribution rather than the external electric field distribution, is one of the important research directions in the field of microwave thermoacoustics.

[0005] Furthermore, microwave thermoacoustic microscopy (TAM) systems based on ultrashort pulse width microwaves combined with high-frequency point-focusing ultrasound detectors have been used in studies such as plant water content analysis. However, because TAM systems utilize ultrashort pulse width microwave pulses as input to achieve high resolution, even with peak power of tens of kilowatts for microwave excitation, the overall feed energy remains low, affecting the signal-to-noise ratio of the imaging results. Therefore, the problem of excessively low excitation electric field in TAM systems still needs further resolution.

[0006] A search revealed application CN114176554A, entitled "A Multi-Pulse Width Microwave Excitation Multi-Scale Thermoacoustic Imaging Method and System," belonging to the field of microwave thermoacoustic imaging. This method utilizes microwave radiation of different pulse widths to image biological tissue, exciting the tissue to generate thermoacoustic signals with varying spectral information. These signals can be detected by ultrasound detectors with different center frequencies, thus presenting thermoacoustic images with different depths and resolutions. The microwave source outputs microwave radiation of different pulse widths to the biological tissue, causing it to generate thermoacoustic signals with different spectral information. These signals are detected by ultrasound detectors and transmitted to an amplifier. After amplification and filtering, the signals are acquired by a data acquisition card and finally transmitted to a computer. The computer then performs image reconstruction on the thermoacoustic signals to restore multi-scale thermoacoustic images. This multi-scale thermoacoustic imaging system is more flexible than traditional thermoacoustic imaging systems, capable of reconstructing images of biological tissues at different scales, achieving optimal imaging depth and resolution.

[0007] This patent still suffers from image contrast degradation due to the uneven distribution of traditional microwave radiation fields. Taking brain imaging research as an example, the imaging target is brain tissue. An electric field of a certain intensity attenuates after passing through the surrounding tissues of the head, exciting the brain tissue to generate thermoacoustic signals. However, the electric field at the brain tissue is weaker than that of the surrounding tissues, resulting in decreased image contrast. The region-compensating metal reflective surface designed in this patent improves the overall uniformity of the excitation electric field by compensating for the lower-energy brain tissue regions, thereby enhancing image quality.

[0008] A search revealed application CN114587326A, a microwave thermoacoustic microscopy imaging system and method, belonging to the field of microwave thermoacoustic imaging. This method utilizes short-pulse microwave focusing to irradiate the biological tissue to be imaged. The tissue absorbs microwave energy, generating ultrasonic waves, i.e., thermoacoustic signals. A point-focusing ultrasonic detector is used for reflective scanning to receive these signals. After amplification, the signals are acquired by a data acquisition card for image reconstruction. During the reception of the thermoacoustic signals, a short-pulse microwave is focused and moved synchronously with the ultrasonic detector for reflective scanning. This results in a strong thermoacoustic signal near the detection point and a weaker signal further away, thereby improving the signal-to-noise ratio. It also ensures a uniform microwave field distribution on the imaging plane, mitigating the image contrast degradation caused by uneven microwave field distribution in traditional thermoacoustic imaging, and does not limit the scanning area. The microwave thermoacoustic microscopy imaging system constructed according to this invention features a high signal-to-noise ratio, high contrast, high resolution, and does not limit the scanning area, thus achieving high imaging quality.

[0009] This patent employs a focusing antenna that radiates microwave energy while the ultrasonic detector moves, thus mitigating the signal-to-noise ratio reduction caused by insufficient excitation electric field to some extent. However, the method of mounting the focusing antenna alongside the ultrasonic probe limits its size. Combined with the requirement of TAM systems to radiate high-power pulsed microwaves, this significantly increases the manufacturing cost of a suitable focusing antenna. The cost of such a focusing antenna is far higher than the combination of a high-power dipole antenna and a point-focusing metal reflector that moves with the ultrasonic detector used in this patent. Furthermore, this patent represents an optimized solution, allowing for direct, low-cost modifications to the existing TAM system to achieve a direct improvement in imaging performance, and it is also applicable to TAT systems. Summary of the Invention

[0010] This invention aims to solve the problems of the prior art. It proposes a microwave thermoacoustic imaging method based on optimizing the electric field distribution of the reflective surface to improve imaging quality. The technical solution of this invention is as follows:

[0011] A microwave thermoacoustic imaging method based on optimized electric field distribution of a reflector surface is applied in a microwave thermoacoustic microscopic imaging system (TAM). The TAM system comprises: a dipole antenna (1-1), a tissue under test (1-2), a point-focusing metal reflector surface (1-3), a point-focusing ultrasonic detector (1-4), and a microwave absorbing material (1-5). The dipole antenna (1-1) radiates microwaves to the tissue under test (1-2), and the point-focusing metal reflector surface (1-3) is located relative to the tissue under test. On the opposite side of the dipole antenna (1-1) of 1-2), the point-focusing metal reflector (1-3) is fixed on the point-focusing ultrasonic detector (1-4) and moves synchronously with the detector, focusing microwave energy onto the tissue under test (1-2) in the focusing area directly below the point-focusing ultrasonic detector (1-4). The tissue under test (1-2) absorbs microwave energy and generates ultrasonic waves, i.e., thermoacoustic signals. The thermoacoustic signals are detected by the point-focusing ultrasonic detector (1-4) wrapped with microwave absorbing material (1-5), and the thermoacoustic image is reconstructed by the image reconstruction algorithm.

[0012] Furthermore, the point-focusing ultrasonic detector (1-4) and the point-focusing metal reflector move synchronously under the control of a three-dimensional stepper motor to perform multi-point detection. The detected signal is amplified by an amplification circuit, and the amplified signal is acquired by a data acquisition card. Image reconstruction is performed based on the relationship between time domain information and spatial position. The entire process is controlled by a computer.

[0013] Furthermore, after the amplified signal is acquired by the data acquisition card, image reconstruction is performed based on the relationship between time-domain information and spatial location. Specifically, this includes: the product of the time delay of the signal generated by the tissue and the tissue sound velocity corresponds to the tissue spatial location, and the magnitude of the microwave energy absorption density of the tissue at this spatial location can be reflected by the amplitude at the time delay corresponding to the time-domain signal; the point-focusing ultrasound detector (1-4) moves along a two-dimensional plane perpendicular to the acoustic axis under the drive of a two-dimensional stepper motor to perform multi-point detection. At each detection point, the product of the time delay of the detected signal and the tissue sound velocity corresponds to the tissue spatial location along the acoustic axis of the detector, and the amplitude of the signal at this time delay corresponds to the microwave energy absorption of the tissue at this spatial location; the acoustic axis direction of the point-focusing ultrasound detector and the two-dimensional plane it moves to detect can constitute the three-dimensional space corresponding to the signal, and the microwave energy absorption density of the tissue at different locations in the three-dimensional space constitutes a three-dimensional thermoacoustic image.

[0014] Furthermore, the ultra-short pulse microwave radiation is applied to the biological tissue to be imaged. The biological tissue at the confocal region of the point-focusing metal reflector (1-3) and the point-focusing ultrasound detector (1-4) absorbs strong microwave energy and generates a large thermoacoustic signal. The non-microwave focusing area includes the non-focusing biological tissue and the non-focusing environment. The center of the point-focusing ultrasound detector (1-4) needs to coincide with the focusing center of the point-focusing metal reflector (1-3), so that the thermoacoustic signal is strong near the detection point and weak far from the detection point. The point-focusing metal reflector moves synchronously with the point-focusing ultrasound detector, so that each set of acquired data is the result of focusing and amplification by the point-focusing metal reflector. The excitation electric field in the imaging area with the point-focusing metal reflector is stronger and more uniformly distributed than that without the point-focusing metal reflector, thereby improving the signal-to-noise ratio and contrast.

[0015] A microwave thermoacoustic imaging method based on optimized electric field distribution of a reflective surface is applied in a microwave thermoacoustic tomography system (TAT). The TAT system comprises a horn antenna (1-6), a tissue under test (1-7), a region-compensating metal reflective surface (1-8), and an ultrasonic detector (1-9). The horn antenna (1-6) directionally radiates microwaves to the tissue under test (1-7). The microwave energy attenuates during propagation, resulting in a weaker excitation electric field in the central region of the tissue under test (1-7) compared to the surrounding tissue. The region-compensating metal reflective surface (1-8) is fixed opposite the horn antenna (1-6) to compensate for the lower energy region of the tissue under test. The tissue under test (1-7) absorbs microwave energy and generates ultrasonic waves, i.e., thermoacoustic signals. The ultrasonic detector (1-9) detects the thermoacoustic signals using a lateral circular scan (1-10). A subsequent image reconstruction algorithm is then used to reconstruct the thermoacoustic image.

[0016] Furthermore, a microwave thermoacoustic imaging method based on optimized electric field distribution using a reflective surface is characterized in that the region-compensating metal reflective surface (1-8) is placed on the opposite side of the horn antenna (1-6) relative to the object under test (1-7), reflecting the electromagnetic waves passing through the imaging object back to the imaging object, thereby compensating for the low excitation electric field region in the central area of ​​the imaging object, such as the brain tissue of a live rat, making it the same as the excitation electric field in the tissues around the head, so as to improve the uniformity of the overall excitation electric field and thus improve the imaging contrast.

[0017] The advantages and beneficial effects of this invention are as follows:

[0018] This patent addresses the electric field distribution problem in current microwave thermoacoustic imaging technology. It proposes a method based on electromagnetic wave reflection characteristics, using a metal reflective surface to improve the excitation electric field in current microwave thermoacoustic microscopy and microwave thermoacoustic tomography techniques, thereby improving imaging results. Taking microwave thermoacoustic microscopy as an example, current systems use dipole antennas to radiate microwave energy. While a single dipole antenna can radiate ultra-short pulse width microwaves with peak power of tens of kilowatts, the excitation electric field generated is still insufficient. Using a focusing antenna to radiate microwave energy requires the focusing antenna and ultrasonic detector to move together. The structure of the microscopy system limits the size of the focusing antenna, making it costly and difficult to fabricate a focusing antenna capable of radiating ultra-short pulse width microwaves with peak power of tens of kilowatts under small size constraints. This patent proposes a low-cost and efficient method: radiating high-power microwave energy using a dipole antenna, then focusing the microwave energy onto the focal region of a point-focusing ultrasonic detector using a point-focusing metal reflective surface, moving synchronously with the ultrasonic detector to achieve co-focusing. Each set of thermoacoustic signals acquired by the ultrasonic detector is generated from the excitation electric field after focusing by the point-focusing metal reflective surface.

[0019] This patent retains the high-power microwave radiation characteristic of a dipole antenna while employing a point-focusing metal reflector to achieve the feature that the microwave energy focusing point follows the movement of the ultrasonic detector. This patent offers the following three advantages: 1. The overall excitation electric field is higher than that of a single dipole antenna or focusing antenna, improving the signal-to-noise ratio of the imaging results. 2. The microwave energy focusing point following the movement of the ultrasonic detector results in a more uniform distribution of the excitation electric field in the focused area of ​​the ultrasonic detector, improving the contrast of the imaging results. 3. The cost of using a dipole antenna with a point-focusing metal reflector is lower than that of a high-power focusing antenna, and it is easier to implement and integrate into existing systems.

[0020] This patent utilizes the reflective properties of microwave energy to enhance the excitation electric field in the imaging region. This technology can be applied not only to microwave thermoacoustic microscopy systems but also to microwave thermoacoustic tomography (TAT). Taking current microwave thermoacoustic brain imaging research as an example, the attenuation of microwave energy by tissues such as the skull results in a lower excitation electric field in the brain tissue compared to surrounding tissues, leading to reduced imaging contrast. Employing a region-compensating metal reflective surface can compensate for the lower microwave energy in these areas, thereby improving the overall uniformity of the excitation electric field in the imaging region and ultimately enhancing the imaging contrast of the TAT system in brain imaging studies. Attached Figure Description

[0021] Figure 1 This invention provides a preferred embodiment of a metal reflective surface model for TAM and TAT systems.

[0022] Figure 2 Schematic diagram of scanning methods for TAM and TAT systems.

[0023] Figure 3 Simulation comparison results of TAM system with and without point-focusing metal reflective surface.

[0024] Figure 4 Comparative experimental results of TAM system with and without point-focusing metal reflective surfaces. Detailed Implementation

[0025] The technical solutions of the embodiments of the present invention will be clearly and thoroughly described below with reference to the accompanying drawings. The described embodiments are merely some embodiments of the present invention.

[0026] The technical solution of the present invention to solve the above-mentioned technical problems is:

[0027] like Figure 1As shown, a method for improving the quality of microwave thermoacoustic imaging based on a reflective surface is applied to both the TAM (Thermoacoustic Microscopy) system and the TAT (Thermoacoustic Tomography) system. The TAM system includes: a dipole antenna 1-1, a tissue under test 1-2, a point-focusing metal reflective surface 1-3, a point-focusing ultrasonic detector 1-4, and a microwave-absorbing material 1-5. The dipole antenna 1-1 radiates microwaves to the tissue under test 1-2. The point-focusing metal reflective surface 1-3 is located opposite the dipole antenna 1-1 relative to the tissue under test and is fixed to the point-focusing ultrasonic detector 1-4, moving synchronously with the detector. It focuses microwave energy onto the tissue under test 1-2 in the focal area directly below the point-focusing ultrasonic detector 1-4. The tissue under test 1-2 absorbs the microwave energy, generating ultrasonic waves, i.e., thermoacoustic signals. These signals are detected by the point-focusing ultrasonic detector encased in the microwave-absorbing material 1-5, and the thermoacoustic image is reconstructed using a subsequent image reconstruction algorithm. The TAT system includes: a horn antenna 1-6, a tissue under test 1-7, a region-compensating metal reflector 1-8, and an ultrasonic detector 1-9. The horn antenna 1-6 directionally radiates microwaves to the tissue under test 1-7. The microwave energy attenuates during propagation, resulting in a weaker excitation electric field in the central region of the tissue under test 1-7 compared to the surrounding tissue. The region-compensating metal reflector 1-8 is fixed on the opposite side of the horn antenna 1-6 relative to the tissue under test, providing energy compensation for the lower-energy region of the tissue under test. The tissue under test 1-7 absorbs microwave energy and generates ultrasonic waves, i.e., thermoacoustic signals. The ultrasonic detector 1-9 detects the thermoacoustic signals using a lateral circular scan 1-10. Subsequent image reconstruction algorithms then reconstruct the thermoacoustic image. This patent alleviates the problems of low signal-to-noise ratio and poor contrast in current microwave thermoacoustic imaging technology due to weak and unevenly distributed excitation electric fields at a lower cost.

[0028] Specifically, in the microwave thermoacoustic microscopy system based on a point-focusing metal reflector, a microwave generator produces ultrashort pulse microwaves, which are transmitted via a coaxial cable to a dipole antenna 1-1 to radiate the microwaves to the tissue under test 1-2. The point-focusing metal reflector 1-3 is located on the opposite side of the dipole antenna 1-1 relative to the object under test and is fixed on a point-focusing ultrasonic detector 1-4, moving synchronously with the detector. It focuses the microwave energy onto the tissue under test 1-2 in the focal area directly below the point-focusing ultrasonic detector 1-4. The tissue under test 1-2 absorbs the microwave energy and generates ultrasonic waves, i.e., thermoacoustic signals. The thermoacoustic signals are detected by reflection from the point-focusing ultrasonic detector 1-4. The point-focusing ultrasonic detector is wrapped with a microwave-absorbing material 1-5. The point-focusing ultrasonic detector 1-4 and the point-focusing metal reflector move synchronously under the drive of a three-dimensional stepper motor controlled by a motor controller to perform multi-point detection 2-a. The detected signals are amplified by an amplification circuit. The amplified signals are acquired by a data acquisition card and then used for image reconstruction based on the relationship between time-domain information and spatial position. The entire process is controlled by a computer.

[0029] Specifically, in the imaging algorithm of the microwave thermoacoustic microscopy system, the product of the time delay of the signal generated by the tissue and the velocity of sound in the tissue corresponds to the spatial location of the tissue. The magnitude of the microwave energy absorption density of the tissue at this spatial location can be reflected by the amplitude of the time delay corresponding to the time domain signal. The point-focusing ultrasound detector (1-4) moves along a two-dimensional plane perpendicular to the acoustic axis under the drive of a two-dimensional stepper motor to perform multi-point detection. At each detection point, the product of the time delay of the detected signal and the velocity of sound in the tissue corresponds to the spatial location of the tissue along the acoustic axis of the detector, and the amplitude of the signal at this time delay corresponds to the microwave energy absorption of the tissue at that spatial location. The acoustic axis of the point-focusing ultrasound detector and the two-dimensional plane in which it moves and detects can constitute the three-dimensional space corresponding to the signal. The microwave energy absorption density of the tissue at different locations in the three-dimensional space constitutes a three-dimensional thermoacoustic image.

[0030] Specifically, the point-focusing metal reflector radiates ultra-short pulse microwaves onto the biological tissue to be imaged. The biological tissue in the confocal region of the point-focusing metal reflector 1-3 and the point-focusing ultrasound detector 1-4 absorbs strong microwave energy, generating a large thermoacoustic signal. The non-microwave focusing area, including non-focusing biological tissue and environmental objects, absorbs no microwave energy or absorbs weak microwave energy, generating little or no useless noise. It is particularly important that the center of the point-focusing ultrasound detector 1-4 coincides with the focusing center of the point-focusing metal reflector 1-3, ensuring a strong thermoacoustic signal near the detection point and a weaker signal further away. The point-focusing metal reflector moves synchronously with the point-focusing ultrasound detector, ensuring that each set of acquired data is the result of focusing and amplification by the point-focusing metal reflector. The excitation electric field in the imaging region with the point-focusing metal reflector is stronger and more uniformly distributed than without it, thus mitigating the image degradation caused by the excitation electric field distribution in traditional thermoacoustic imaging, thereby improving the imaging signal-to-noise ratio and imaging contrast. Figure 3 , Figure 4 The simulation and phantom experiments are shown in the results.

[0031] Specifically, the microwave thermoacoustic tomography system based on the optimized region-compensated metal reflector uses a microwave generator to produce short-pulse microwaves, which are transmitted via a coaxial cable to a horn antenna 1-6 and then radiated onto the tissue under test 1-7. The microwave energy attenuates during propagation, causing the excitation electric field in the central region of the tissue under test 1-7 to be weaker than that of the surrounding tissue. The region-compensated metal reflector 1-8 is fixed to the opposite side of the horn antenna 1-6 relative to the object under test, providing energy compensation for the lower-energy region of the object. The tissue under test 1-7 absorbs microwave energy and generates ultrasonic waves, i.e., thermoacoustic signals. These signals are detected by an ultrasonic detector 1-9, which, driven by a three-dimensional stepper motor controlled by a motor controller, detects the thermoacoustic signals in a lateral circular scan 2-b manner. The detected signals are amplified by an amplifier circuit, and the amplified signals are acquired by a data acquisition card. Based on the acoustic time history between the tissue under test 1-7 and the ultrasonic detector 1-9, the thermoacoustic signals undergo delay processing and superposition processing to reconstruct the image of the tissue under test 1-7. The entire process is computer-controlled.

[0032] Specifically, the area-compensating metal reflector 1-8 is placed on the opposite side of the horn antenna 1-6 relative to the object under test 1-7. It reflects the electromagnetic waves that pass through the imaging object back to the imaging object, thereby compensating for the low excitation electric field region in the central area of ​​the imaging object, such as the brain tissue of a live rat, so that it is the same as the excitation electric field in the tissue around the head, thereby improving the uniformity of the overall excitation electric field and thus improving the imaging contrast.

[0033] The systems, devices, modules, or units described in the above embodiments can be implemented by computer chips or entities, or by products with certain functions. A typical implementation device is a computer. Specifically, a computer can be, for example, a personal computer, laptop computer, cellular phone, camera phone, smartphone, personal digital assistant, media player, navigation device, email device, game console, tablet computer, wearable device, or any combination of these devices.

[0034] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0035] The above embodiments should be understood as illustrative only and not as limiting the scope of protection of the present invention. After reading the description of the present invention, those skilled in the art can make various alterations 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 microwave thermoacoustic imaging method based on optimizing the electric field distribution of a reflecting surface, applied to a microwave thermoacoustic microscopic imaging system TAM, characterized in that, The microwave thermoacoustic microscopic imaging system TAM comprises a dipole antenna (1-1), a measured tissue (1-2), a point focusing metal reflecting surface (1-3), a point focusing ultrasonic detector (1-4) and an absorbing material (1-5), wherein the dipole antenna (1-1) radiates microwaves to the measured tissue (1-2), the point focusing metal reflecting surface (1-3) is located on the opposite side of the dipole antenna (1-1) relative to the measured tissue (1-2), the point focusing metal reflecting surface (1-3) is fixed on the point focusing ultrasonic detector (1-4) and moves synchronously with the detector, focuses and radiates the microwave energy to the measured tissue (1-2) in the focusing area directly below the point focusing ultrasonic detector (1-4), the measured tissue (1-2) absorbs the microwave energy to generate ultrasonic waves, i.e. thermoacoustic signals, the thermoacoustic signals are detected by the point focusing ultrasonic detector (1-4) wrapped with the absorbing material (1-5), and a thermoacoustic image is obtained through an image reconstruction algorithm.

2. The method of claim 1, wherein the method is characterized by, The point focusing ultrasonic detector (1-4) and the point focusing metal reflecting surface move synchronously under the driving of a three-dimensional stepping motor controlled by a motor controller to perform multi-point detection, the detected signals are amplified through an amplification circuit, the amplified signals are collected by a data acquisition card, and an image is reconstructed according to the relationship between time domain information and spatial position, and the whole process is controlled by a computer.

3. The method of claim 2, wherein the method is characterized by, After the amplified signals are collected by the data acquisition card, the image is reconstructed according to the relationship between time domain information and spatial position, specifically including that the product of the time delay of the signal generated by the tissue and the speed of the tissue corresponds to the spatial position of the tissue, and the microwave energy absorption density of the tissue at the spatial position can be reflected by the amplitude at the time delay corresponding to the time domain signal; the point focusing ultrasonic detector (1-4) moves along a two-dimensional plane perpendicular to the acoustic axis direction under the driving of a two-dimensional stepping motor to perform multi-point detection, at each detection point, the product of the time delay of the detected signal and the speed of the tissue corresponds to the spatial position of the tissue along the acoustic axis direction of the detector, and the amplitude of the signal at the time delay corresponds to the microwave energy absorption of the tissue at the spatial position; the acoustic axis direction of the point focusing ultrasonic detector and the two-dimensional plane where the point focusing ultrasonic detector moves, i.e. the three-dimensional space corresponding to the signal, corresponds to the microwave energy absorption density of the tissue at different positions in the three-dimensional space, i.e. constitutes a three-dimensional thermoacoustic image.

4. The method of claim 2, wherein the method is characterized by, The present application discloses a microwave thermoacoustic tomography system, which comprises a point-focusing metal reflector (1-3) and a point-focusing ultrasonic detector (1-4). The point-focusing metal reflector (1-3) is used for focusing microwave radiation on a biological tissue to be imaged, and the point-focusing ultrasonic detector (1-4) is used for detecting a thermoacoustic signal generated by the biological tissue in a co-focusing region of the point-focusing metal reflector (1-3) and the point-focusing ultrasonic detector (1-4). The point-focusing metal reflector (1-3) is synchronously moved with the point-focusing ultrasonic detector (1-4), so that each group of collected data is a result of focusing and amplification of the point-focusing metal reflector (1-3). The excitation electric field of an imaging region of the point-focusing metal reflector (1-3) is stronger and more uniformly distributed than that of a region without the point-focusing metal reflector (1-3), so that the signal-to-noise ratio and contrast are improved.

5. The method of claim 1, wherein the method is characterized by: The present application discloses a microwave thermoacoustic tomography system, which comprises a horn antenna (1-6), a measured tissue (1-7), a region-compensating metal reflector (1-8) and an ultrasonic detector (1-9). The horn antenna (1-6) is used for directing microwave radiation to the measured tissue (1-7). The excitation electric field of a central region of the measured tissue (1-7) is weaker than that of a surrounding region due to microwave energy attenuation during propagation. The region-compensating metal reflector (1-8) is fixed on the opposite side of the horn antenna (1-6) relative to the measured tissue (1-7), and is used for compensating energy of a region with lower energy of the measured tissue (1-7). The measured tissue (1-7) absorbs microwave energy to generate ultrasonic waves, i.e. a thermoacoustic signal. The ultrasonic detector (1-9) is used for detecting the thermoacoustic signal in a lateral ring scanning (1-10) manner. A thermoacoustic image is obtained through a subsequent image reconstruction algorithm.

6. The method of claim 5, wherein the method is characterized by, The region-compensating metal reflector (1-8) is placed on the opposite side of the horn antenna (1-6) relative to the measured tissue (1-7), and is used for re-reflecting electromagnetic waves through an imaging object to the imaging object, so as to compensate energy of a central region of the imaging object, such as a low-excitation electric field region of a living rat brain tissue, to be the same as that of a surrounding region of the head, so as to improve uniformity of the overall excitation electric field, and to improve imaging contrast.

Images