A broadband large field of view thermoacoustic imaging system

Abstract

The application claims a broadband large field of view thermoacoustic imaging system, belonging 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 adjustable frequency microwave source, a coaxial line, a 1-6GHz broadband TEM horn antenna and a compensation reflection surface; the data acquisition module comprises a semi-ring concave array ultrasonic transducer, an array amplifier, an adding circuit and a data acquisition card; the image analysis processing module covers a reconstructed tissue thermoacoustic information spectrum graph and a multi-frequency information fusion graph. The application obtains thermoacoustic information of tissue under multiple frequency points through dynamic interval frequency microwave excitation, and through integrated analysis and processing of multi-frequency data and images, the problems of contrast deterioration and single dielectric property information under single frequency microwave excitation are relieved, the analysis and recognition ability of tissue and lesions is improved, the development of thermoacoustic imaging technology is promoted, and a new scheme is provided for the application of thermoacoustic imaging technology in biological tissue detection.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of microwave thermoacoustic imaging, and relates to an imaging system and method, in particular to a wideband and wide-field thermoacoustic imaging system and method. BACKGROUND

[0002] As a new biomedical imaging technology, microwave thermoacoustic imaging technology is non-ionizing and non-invasive, combining the advantages of deep penetration depth, high contrast of microwave imaging and high resolution of ultrasonic imaging. Its imaging principle is based on the thermoacoustic effect, that is, after the biological tissue absorbs pulsed microwave energy, it expands elastically and generates thermoacoustic signals that can be detected by an ultrasonic transducer. The thermoacoustic signals can be reconstructed into a thermoacoustic image of the spectral microwave energy absorption density distribution, which can reflect the differences in the dielectric properties of biological tissues under the assumption of uniform electric field distribution, and also reflect the structural information of biological tissues. Therefore, microwave thermoacoustic imaging technology can achieve dual representation in functional and anatomical information, providing more dimensional data support for disease diagnosis, and has shown wide application potential in research fields such as breast tumor screening, kidney imaging, brain imaging, and arthritis detection.

[0003] However, traditional microwave thermoacoustic imaging technology mainly uses single-frequency microwave excitation, mainly using the dielectric properties of biological tissues under single-frequency excitation for imaging, and does not fully utilize the characteristics of the dielectric properties of biological tissues changing with frequency in a wide frequency band. The imaging contrast between tissues with small differences in dielectric properties at some single frequency points is limited, and the thermoacoustic image cannot accurately reflect the conductivity information and structural information of these tissues. In addition, when using a single-frequency narrowband antenna to image large tissues, the microwave radiation range is limited, and only uniform radiation can be provided in a relatively small area, and usually only small tissues are imaged, which limits its application in clinical wide-field imaging. The patent of the same applicant as the present application, 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 variation of the theoretical microwave absorption coefficient of biological tissues with microwave frequency, two groups of thermoacoustic images under two different microwave frequencies are obtained by using two different microwave frequencies and short pulse width microwaves, and then the two groups of thermoacoustic images are fused to obtain a dual-frequency thermoacoustic image. The two groups of single-frequency thermoacoustic images are used to analyze biological tissues with strong microwave energy absorption and detect corresponding lesions, and the dual-frequency fused image is used to highlight tissues with weak microwave energy absorption and large changes in microwave energy absorption with frequency, i.e. using dual-frequency fusion to highlight low absorption areas, focusing on solving the detection problem of specific tissues and lesions.

[0004] The patent proposes a broadband large field of view thermoacoustic imaging system and method, aiming to overcome the limitations of single-frequency excitation in traditional microwave thermoacoustic imaging, and to obtain multiple frequency points of thermoacoustic information by using 1-6GHz dynamic microwave to stimulate biological tissues. Compared with dual-frequency microwave-induced thermoacoustic imaging, this patent can more comprehensively reflect and utilize the dielectric properties and dielectric property changes of tissues at different frequencies through the fusion of multi-frequency information in a wide frequency band; TEM horn antenna is used to generate short pulse width microwave at different frequencies within 1-6GHz, and to meet the high power coupling of hundreds of kilowatts and the large microwave radiation range (>20cm x 20cm x 10cm), and to improve the electric field intensity and uniformity by recycling and reflecting the microwave to the biological tissue through the compensation reflection surface, to alleviate the problem of weak electric field intensity and uneven field distribution caused by large field of view. This method can effectively improve the identification ability of tissue lesions, especially in complex biological tissues and large tissue detection, fully utilize the microwave dielectric function information of wide frequency band of tissues, improve the overall information richness of the image, and thus improve the application potential of microwave thermoacoustic imaging technology in complex tissue and large tissue detection. SUMMARY

[0005] The present application aims to solve the problems of the prior art. A broadband large field of view thermoacoustic imaging system is proposed. The technical scheme of the present application is as follows:

[0006] A broadband large field of view thermoacoustic imaging system, comprising a computer, a dynamic microwave excitation module, a data acquisition module and an image analysis module connected to the computer respectively, wherein:

[0007] The dynamic microwave excitation module comprises a 1-6GHz adjustable frequency microwave source, a coaxial line, a 1-6GHz broadband TEM horn antenna and a compensation reflection surface. The computer controls the 1-6GHz adjustable frequency microwave source to generate pulsed microwave with dynamic interval frequency, which is transmitted to the 1-6GHz broadband TEM horn antenna through the coaxial line, and the compensation reflection surface is combined to realize uniform electric field excitation inside the biological tissue to be measured. The biological tissue absorbs microwave energy to generate ultrasonic waves, i.e. thermoacoustic signals;

[0008] The data acquisition module comprises a semi-ring concave array ultrasonic transducer, an array amplifier, an addition circuit and a data acquisition card. The semi-ring concave array ultrasonic transducer is used to quickly detect the thermoacoustic signals of the tissue under the excitation of dynamic interval frequency microwave; the array amplifier is used to amplify the thermoacoustic signals; the addition circuit is used to accumulate, average and denoise the thermoacoustic signals; and the data acquisition card acquires and stores the denoised thermoacoustic signals to the computer to obtain multiple single-frequency thermoacoustic data of the tissue under the excitation of dynamic interval frequency microwave;

[0009] The image analysis module includes a reconstruction of tissue thermoacoustic information spectrum and a multi-frequency information fusion image; a plurality of single-frequency thermoacoustic data is reconstructed into a plurality of single-frequency thermoacoustic images by using a delay stacking algorithm in a computer, and single-frequency energy self-calibration is performed; a plurality of self-calibrated single-frequency point thermoacoustic data is integrated to construct a tissue thermoacoustic information spectrum; and a plurality of single-frequency thermoacoustic images are fused and reconstructed based on thermoacoustic information change differences and a fusion algorithm to form a multi-frequency information fusion image.

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

[0011] Further, the 1-6 GHz wideband 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, while satisfying a large microwave radiation range (>20 cm x 20 cm x 10 cm) to provide conditions for large field of view imaging.

[0012] Further, the compensation reflecting surface in the dynamic microwave excitation module uses the reflection characteristics of different wavelengths of microwaves to recycle and reflect microwaves into the measured tissue to enhance the microwave excitation electric field strength and uniformity.

[0013] Further, in the dynamic interval frequency short pulse width microwave excitation, the half-ring concave array ultrasonic transducer, array amplifier, addition circuit, data acquisition card, 1-6 GHz wideband TEM horn antenna, coaxial line, and measured biological tissue in the data acquisition module 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, a plurality of single-frequency thermoacoustic data is reconstructed into a plurality of single-frequency thermoacoustic images by using a delay stacking algorithm, which specifically includes: using the corresponding relationship between time delay and the distance from the ultrasonic transducer to the projection point, i.e. ultrasonic speed x time delay = distance from the ultrasonic transducer to the projection point, to project the thermoacoustic signals collected by the ultrasonic transducer to the projection angle range for projection and stacking, thereby realizing the reconstruction of single-frequency thermoacoustic images. Single-frequency thermoacoustic images can reflect the relative thermoacoustic signal relationship between biological tissues, depend on the equivalent conductivity distribution and electric field distribution of the tissues at the corresponding frequency, and can also directly reflect the equivalent conductivity relationship between the tissues in the case of uniform electric field distribution; in the uniformly distributed excitation electric field, a single-frequency energy self-calibration is performed by using a sample with known equivalent conductivity.

[0015] Further, in the uniformly distributed excitation electric field, a single-frequency energy self-calibration is performed by using a sample with known equivalent conductivity, which specifically includes:

[0016]

[0017] where σ eff is the equivalent conductivity of the imaged tissue at the corresponding microwave excitation frequency; |E| is the electric field; δ 盐 is the thermoacoustic signal of the imaged tissue; σ eff盐 is the equivalent conductivity of the known saline tube at the corresponding microwave excitation frequency; δ is the thermoacoustic signal of the saline tube; then the calculation formula of the tissue σ eff can be expressed as:

[0018]

[0019] Therefore, the single-frequency energy field self-calibration according to the known equivalent conductivity of the saline tube 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, including reconstructing the tissue thermoacoustic information spectrum diagram and the multi-frequency information fusion diagram.

[0020] Further, 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 pixel mean values of the target tissue at different frequencies are extracted as the thermoacoustic signal values, and the change trend of the thermoacoustic signal is analyzed; according to the obvious degree of change, i.e., the slope size, the interval of the corresponding microwave excitation frequency of different target tissues is determined, the interval between the excitation frequencies is reduced in the frequency range with a larger slope, and the interval between the excitation frequencies is increased in the frequency range with a smaller slope, thereby optimizing the new dynamic excitation frequency interval, and thus outputting the dynamic interval microwave excitation frequency sequence specific to different target tissues (if there are three target tissues in the measured biological tissue, the corresponding sequences can be denoted as f 11 , f 12 , f 13 , …, f 1n , f 21 , f 22 , f 23 , …, f 2n , and f 31 , f 32 , f 33 , …, f 3n , respectively).

[0021] Further, the reconstructed tissue thermoacoustic information spectrum diagram specifically comprises: using the microwave to perform single-frequency thermoacoustic imaging on the measured biological tissue by using a complete dynamic interval microwave excitation frequency sequence, and performing single-frequency energy self-calibration; under the respective dynamic microwave excitation frequency sequence of the target tissue, the average thermoacoustic signal value of the target tissue region ROI is calculated in the single-frequency thermoacoustic image after self-calibration, a thermoacoustic signal curve corresponding to the respective dynamic microwave excitation frequency sequence is formed, and the thermoacoustic signal curves of several target tissues are combined to construct the tissue thermoacoustic information spectrum diagram.

[0022] Further, the reconstructed multi-frequency information fusion diagram specifically comprises:

[0023] Based on the slope difference of the thermoacoustic signal change, the multi-frequency thermoacoustic data or image is subjected to fusion post-processing, and the fusion post-processing specifically comprises: linear fusion and nonlinear fusion are performed on the multiple groups of single-frequency thermoacoustic images after single-frequency energy self-calibration.

[0024] Linear fusion is to fuse high-frequency and low-frequency thermoacoustic images obtained under microwave excitation of different frequencies together according to a certain proportion, that is, multiple single-frequency thermoacoustic image pixel values under different frequency points are fused together according to a fusion proportion, and the fusion calculation formula can be expressed as:

[0025] M1*TA1+M2*TA2+…M n *TA n =y

[0026] M1+M2+…M n =1

[0027] Wherein, y represents thermoacoustic image information after linear fusion; TA represents thermoacoustic data, TA1 represents thermoacoustic data of biological tissue at frequency point f1; TA2 represents thermoacoustic data of biological tissue at frequency point f2; and TA n represents thermoacoustic data of biological tissue at frequency point f n ; M1, M2, …, M n represent linear fusion coefficients, and when M1=M2=…=M n , an average weighted thermoacoustic image can be obtained.

[0028] Nonlinear fusion is to use different fusion proportions for single-frequency thermoacoustic image pixel values, that is, a higher proportion of low-frequency point thermoacoustic data is used for a pixel with a lower TA value in the single-frequency image, and a higher proportion of high-frequency point thermoacoustic data is used for a pixel with a higher TA value; through the nonlinear fusion, the TA value of the high TA value pixel becomes higher, and the TA value of the low TA value pixel becomes lower, so that the contrast between the tissues is amplified, and the display effect of the image is improved.

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

[0030] The application adopts a 1-6GHz wideband TEM horn antenna, and combines a compensation reflecting surface technology to ensure microwave radiation in a large field of view (>20cm*20cm*10cm). The microwave is recycled and re-reflected by the reflecting surface to improve the microwave excitation field strength and uniformity in the biological tissue, alleviate the problem of reduced electric field strength and reduced signal-to-noise ratio caused by the large field of view, and improve the image contrast. This enables the application to realize imaging of a larger range and more complex structure of the tissue, and provides support for more extensive thermoacoustic clinical application research.

[0031] The application dynamically adjusts the microwave excitation frequency interval according to the change trend of the tissue thermoacoustic signal in a 1-6GHz wideband range, breaks through the limitation of traditional single-frequency excitation, and comprehensively covers the dielectric property difference of the target biological tissue with frequency change through multi-frequency signal acquisition. For the multi-frequency data, the single-frequency energy field is self-calibrated in combination with the equivalent conductivity of the known standard sample to eliminate system errors and ensure the energy consistency of the imaging data; further, the thermoacoustic information spectrum graph and the multi-frequency information fusion graph are reconstructed to perform multi-dimensional correlation analysis on the thermoacoustic signals and dielectric properties of the tissue at different frequency points. This method overcomes the problem of image contrast deterioration caused by single dielectric information under single-frequency excitation, identifies and detects the tissue through the frequency change response difference, provides more spectral feature information and tissue structure information for disease diagnosis, and significantly improves the lesion recognition and detection ability of tissue abnormalities.

[0032] The dynamic interval microwave excitation frequency is an innovation point, that is, a multi-frequency excitation sequence matched with the frequency-dependent dielectric property is constructed, and based on single-frequency energy self-calibration, the continuous feature extraction of the biological tissue thermoacoustic signal frequency response curve is realized in a wide spectral domain, which significantly improves the spectral integrity and effectively overcomes the inherent limitation of single dielectric property of the tissue 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 to construct a multi-frequency information fusion method based on the frequency-dependent law of the tissue dielectric property and the frequency change response difference, which effectively overcomes the limitation of the contrast of the traditional single-frequency image, and improves the imaging effect and the detection ability of tissue lesions.

[0034] The implementation method of wideband combined with large field of view range thermoacoustic imaging is an innovation point. Compared with the narrowband antennas such as dipole antennas, horn antennas and rectangular waveguide antennas commonly used in traditional single-frequency thermoacoustic imaging, the 1-6GHz wideband TEM horn antenna combined with the compensation reflecting surface is used for wideband large field of view thermoacoustic imaging, which can radiate hundreds of kilowatts of high-power short pulse width microwave with different center frequencies in a 1-6GHz wideband range, generate a large field of view (>20cm*20cm*10cm) radiation range and a relatively uniform microwave excitation field, and therefore realize imaging of a larger and more complex structure of the tissue. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of a broadband, large field-of-view thermal acoustic imaging system according to a preferred embodiment of the present invention;

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

[0037] 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.

[0038] The technical solution of the present invention to solve the above-mentioned technical problems is:

[0039] like Figure 1 As shown, this embodiment provides a wideband, large field-of-view thermal acoustic 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. The computer controls the 1-6 GHz tunable microwave source to generate short-pulse microwaves with different center frequencies. These microwaves are transmitted via the coaxial cable to the 1-6 GHz broadband TEM horn antenna, radiating a wide area of ​​the biological tissue under test. The compensating reflector then recovers the microwave energy that has passed through or been scattered and diffracted by the tissue and re-radiates it back to the biological tissue, thereby exciting the tissue to generate a thermoacoustic signal.

[0041] Based on the above embodiments, a computer-controlled 1-6 GHz tunable microwave source can rapidly switch the center frequency and initialize the frequency interval. With other variables kept constant, the tunable microwave source can generate short-pulse microwaves with different center frequencies within the 1-6 GHz frequency band. Alternatively, multiple single-frequency microwave sources can also generate short-pulse microwaves with different center frequencies.

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

[0043] On the basis of the above embodiment, the compensation reflection surface recovers and re-reflects the microwave into the measured tissue by using the reflection and radiation characteristics of different size metal compensation reflection surfaces for different wavelengths of microwave.

[0044] The data acquisition module includes a semi-ring concave array ultrasonic transducer, an array amplifier, a summing circuit and a data acquisition card. The thermoacoustic signals under different frequency excitations are detected by the semi-ring concave array ultrasonic transducer in turn, amplified by the array amplifier, denoised by the summing circuit, and the amplified and denoised thermoacoustic signals are collected and stored by the data acquisition card, so as to obtain the thermoacoustic data under multiple frequency excitations. The whole process is controlled by a computer self-programming labVIEW timing program.

[0045] On the basis of the above embodiment, when the microwave dynamic excitation is performed to obtain multiple frequency thermoacoustic data, the semi-ring concave array ultrasonic transducer, the array amplifier, the summing circuit, the data acquisition card, the 1-6GHz wideband TEM horn antenna, the coaxial line and the measured biological tissue remain unchanged, that is, while the microwave excitation frequency is changed, all other experimental conditions remain constant.

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

[0047] On the basis of the above embodiment, the single-frequency thermoacoustic image is reconstructed by using the traditional delay-and-sum algorithm, and the single-frequency energy field is self-calibrated by using a standard object or tissue with known equivalent conductivity (such as a salt water pipe), so as to perform joint analysis between the multi-frequency data.

[0048] Further, the dynamic interval microwave excitation sequence optimization and image analysis processing flow are as shown in Figure 2 The dynamic interval microwave excitation sequence optimization is specifically: a computer controls the 1-6GHz adjustable frequency microwave source to generate a microwave excitation frequency sequence with a fixed large interval (such as Δf=1GHz). Assuming that the starting frequency is f0 and the interval is Δf, the excitation frequency sequence is f0, f0+Δf, f0+2Δf, …, f0+nΔf. The single-frequency thermoacoustic image under each frequency excitation is self-calibrated, and the pixel mean value of the target tissue under different excitation frequencies is extracted. According to the frequency range in which the thermoacoustic signal changes greatly, the interval between the excitation frequencies is reduced, and according to the frequency range in which the thermoacoustic signal changes little, the interval between the excitation frequencies is increased, thereby optimizing the new dynamic excitation frequency interval, and thus outputting the dynamic interval microwave excitation frequency sequence specific to different tissues (if there are three target tissues in the measured biological tissue, the corresponding sequences can be denoted as f 11 ,f 12 ,f 13 ,…,f1n 21 22 23 2n 31 32 33 3n The new complete dynamic microwave excitation frequency sequence is obtained by taking the union of the sequences of dynamic microwave excitation frequencies specific to several target tissues.

[0049] Further, the reconstructed tissue thermoacoustic information spectrum map is specifically: imaging the biological tissue by using the dynamic interval microwave excitation frequency sequence (such as f 11 12 13 1n The thermoacoustic signal curves of the target tissues 1 to n corresponding to the respective specific dynamic microwave excitation frequency sequences are combined, and the tissue thermoacoustic information spectrum map is generated.

[0050] Further, the reconstructed multi-frequency information fusion map is specifically: the differences in the thermoacoustic signal change rates of different tissues under microwave excitation at different frequencies can be used to distinguish and identify different biological tissues or lesions. Linear fusion and nonlinear fusion are performed on the single-frequency thermoacoustic images after single-frequency energy self-calibration, that is, the high-frequency and low-frequency thermoacoustic data are fused into one image according to the same fusion ratio or different fusion ratios. In the nonlinear fusion, different fusion ratios are used according to the pixel values of the single-frequency thermoacoustic images, that is, the pixels with lower TA values in the single-frequency image use higher proportion of the thermoacoustic data at the low-frequency point, and the pixels with higher TA values use higher proportion of the thermoacoustic data at the high-frequency point. Through this nonlinear fusion, the TA values of the pixels with high TA values become higher, and the TA values of the pixels with low TA values become 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 improving the detection ability.

[0051] The system, device, module or unit illustrated in the above embodiments can be specifically implemented by a computer chip or entity, or by a product with certain functions.

[0052] ​​​​​​​​​​​It is also to be noted that the terms "comprising", "including", or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can also include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by "comprises a... " does not, without more constraints, exclude the existence of additional identical elements in the process, method, article, or apparatus that comprises the element.

[0053] The above examples are to be understood only as illustrative of the application and not a restriction on the scope of protection of the application. After reading the specification, the skilled person can make various changes or modifications to the application, and these equivalent changes and modifications also fall within the scope defined by the claims of the application.

Claims

1. A wideband, large field-of-view thermal acoustic imaging system, characterized in that, include: The system includes a computer, a dynamic microwave excitation module, a data acquisition module, and an image analysis module, all connected to the computer. The dynamic microwave excitation module includes a 1-6GHz tunable microwave source, a coaxial cable, a 1-6GHz broadband TEM horn antenna, and a compensation reflector. The computer controls the 1-6GHz tunable microwave source to generate pulsed microwaves with dynamic interval frequencies, which are transmitted to the 1-6GHz broadband TEM horn antenna via the coaxial cable. Combined with the compensation reflector, a uniform electric field excitation is achieved inside the biological tissue under test. The biological tissue absorbs microwave energy and generates ultrasonic waves, i.e., thermoacoustic signals. The data acquisition module includes a semi-ring concave array ultrasonic transducer, an array amplifier, an adder circuit, and a data acquisition card. The semi-ring concave array ultrasonic transducer is used to rapidly detect the thermoacoustic signal of tissue under dynamic interval frequency microwave excitation. The array amplifier is used to amplify the thermoacoustic signal. The adder circuit is used to accumulate, average, and denoise the thermoacoustic signal. The data acquisition card acquires and stores the amplified and denoised thermoacoustic signal in a computer to obtain multiple single-frequency thermoacoustic data of tissue under dynamic interval frequency microwave excitation. The image analysis module includes reconstructing a tissue thermoacoustic information spectrum map and a multi-frequency information fusion map; reconstructing multiple single-frequency thermoacoustic images from multiple single-frequency thermoacoustic data using a delay superposition algorithm in a computer, and performing single-frequency energy self-calibration; integrating multiple self-calibrated single-frequency point thermoacoustic data to construct a tissue thermoacoustic information spectrum map; and fusing and reconstructing multiple single-frequency thermoacoustic images based on differences in thermoacoustic information changes and a fusion algorithm to form a multi-frequency information fusion image.

2. The wideband, large field-of-view thermal acoustic imaging system according to claim 1, characterized in that, The short-pulse-width microwaves with different center frequencies within the 1-6GHz range generated by the 1-6GHz tunable microwave source in the dynamic microwave excitation module can be generated by multiple single-frequency microwave sources or by a single tunable microwave source.

3. The wideband, large field-of-view thermal acoustic imaging system according to claim 1, characterized in that, The 1-6GHz wideband TEM horn antenna in the dynamic microwave excitation module radiates hundreds of kilowatts of high-power short-pulse microwaves with different center frequencies within the 1-6GHz range, while simultaneously satisfying the requirement of a large microwave radiation range >20cm×20cm×10cm, providing conditions for achieving large field-of-view imaging.

4. The wideband, large field-of-view thermal acoustic imaging system according to claim 1, characterized in that, The compensation reflective surface in the dynamic microwave excitation module utilizes the reflective properties of its metallic material for microwaves of different wavelengths to recover microwaves and reflect them back into the tissue under test, thereby enhancing the intensity and uniformity of the microwave excitation electric field.

5. A wideband, large field-of-view thermal acoustic imaging system according to claim 1, characterized in that, During dynamic interval frequency short pulse width microwave excitation, the semi-ring concave array ultrasonic transducer, array amplifier, adder circuit, data acquisition card, 1-6GHz broadband TEM horn antenna, coaxial cable and biological tissue under test in the data acquisition module remain unchanged, that is, the microwave excitation frequency changes dynamically at equal or non-equal intervals while other experimental conditions remain unchanged.

6. A wideband, large field-of-view thermal acoustic imaging system according to claim 1, characterized in that, In the image analysis module, multiple single-frequency thermoacoustic images are reconstructed using a delay superposition algorithm based on multiple single-frequency thermoacoustic data. Specifically, this includes: utilizing the correspondence between time delay and the distance from the ultrasonic transducer to the projection point (i.e., ultrasonic velocity × time delay = distance from the ultrasonic transducer to the projection point), the thermoacoustic signals collected by the ultrasonic transducer are projected onto the detection angle range for projection superposition, thereby realizing the reconstruction of single-frequency thermoacoustic images. Single-frequency thermoacoustic images can reflect the relative thermoacoustic signal relationships between biological tissues, depending on the equivalent conductivity distribution and electric field distribution between tissues at the corresponding frequency. When the electric field distribution is uniform, it can also directly reflect the equivalent conductivity relationship between tissues. In a uniformly distributed excitation electric field, single-frequency energy self-calibration is performed using samples with known equivalent conductivity.

7. A wideband, large field-of-view thermal acoustic imaging system according to claim 6, characterized in that, In a uniformly distributed excitation electric field, single-frequency energy self-calibration is performed using a salt water sample with known equivalent conductivity. Specifically: in, This represents the equivalent conductivity of the imaged tissue at the corresponding microwave excitation frequency. For electric field; Thermoacoustic signal of the imaging tissue; Given the equivalent conductivity of the saline tube at the corresponding microwave excitation frequency; The thermoacoustic signal is from the saline tube; therefore, the tissue... The calculation formula can be expressed as: Therefore, by performing single-frequency energy field self-calibration based on a saline tube with known equivalent conductivity, it is possible to ensure that the thermoacoustic signals at each frequency are compared under a unified energy reference. This allows for the analysis of multiple single-frequency microwave thermoacoustic data or images, specifically including the reconstruction of tissue thermoacoustic information spectrum maps and multi-frequency information fusion maps.

8. The wideband, large field-of-view thermal acoustic imaging system according to claim 6, characterized in that, The dynamic interval frequency microwave excitation uses a microwave excitation frequency sequence (f0, f0+∆f, f0+2∆f, ⋯, f0+n∆f) with a fixed large interval ∆f=1GHz to perform multiple single-frequency thermoacoustic imaging and perform single-frequency energy self-calibration. Subsequently, the average pixel value of the thermoacoustic image of the target tissue at different frequencies was extracted as the thermoacoustic signal value, and the trend of thermoacoustic signal variation was analyzed. The spacing between microwave excitation frequencies for different target tissues is determined based on the degree of change, i.e., the slope. The spacing between excitation frequencies is reduced in the frequency range with a larger slope, and increased in the frequency range with a smaller slope. This optimizes the new dynamic excitation frequency spacing, thereby outputting a dynamic interval microwave excitation frequency sequence unique to different target tissues. The union of these dynamic microwave excitation frequency sequences unique to different target tissues is then used to obtain a new complete dynamic interval microwave excitation frequency sequence.

9. A wide-band, large-field-of-view thermal acoustic imaging system according to claim 6, characterized in that, The reconstructed tissue thermoacoustic information spectrum map specifically includes: performing multiple single-frequency thermoacoustic imaging of the tested biological tissue using microwaves with a complete dynamic interval microwave excitation frequency sequence, and performing single-frequency energy self-calibration. Under the unique dynamic microwave excitation frequency sequence of each target tissue, the average thermoacoustic signal value of the ROI of the target tissue region is calculated in the self-calibrated single-frequency thermoacoustic image to form a thermoacoustic signal curve corresponding to the unique dynamic microwave excitation frequency sequence of each tissue. The thermoacoustic signal curves of several target tissues are merged to construct the tissue thermoacoustic information spectrum map.

10. A wideband, large field-of-view thermal acoustic imaging system according to claim 6, characterized in that, The reconstructed multi-frequency information fusion map specifically includes: Based on the different slopes of the thermoacoustic signal changes, thermoacoustic data or images at multiple frequency points are fused and processed. The fusion and processing specifically includes linear fusion and nonlinear fusion of multiple sets of single-frequency thermoacoustic images after single-frequency energy self-calibration. Linear fusion is the process of combining high- and low-frequency thermoacoustic images obtained under microwave excitation at different frequencies according to a certain ratio. In other words, it involves fusing the pixel values ​​of multiple self-calibrated single-frequency thermoacoustic images at different frequency points according to a fusion ratio. The fusion calculation formula can be expressed as: Where y represents the linearly fused thermoacoustic image information; Represents thermal data. This represents the thermoacoustic data of biological tissue at frequency point f1; This represents the thermoacoustic data of biological tissue at frequency point f2; This indicates that biological tissue is at frequency point f. n Thermoacoustic data at locations M1, M2, ..., M n Represents the linear fusion coefficient, when M1=M2=⋯=M n At that time, the average weighted thermoacoustic image can be obtained; Nonlinear fusion uses different fusion ratios for pixel values ​​in a single-frequency thermoacoustic image. That is, pixels with lower TA values ​​in a 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 high-TA pixels can be made even higher, and the TA values ​​of low-TA pixels can be made even lower, thereby amplifying the contrast between tissues and improving the display effect of the image.

Images