CN114947739B - Dual-frequency microwave induced thermoacoustic imaging system and method - Google Patents

Abstract

The invention discloses a double-frequency microwave induced thermo-acoustic imaging system and a method, and belongs to the field of microwave thermo-acoustic imaging. The double-frequency microwaves are radiated to biological tissues by an antenna, the tissues absorb microwave energy to generate thermoacoustic signals, the thermoacoustic signals are received by an ultrasonic detector, and the signals are collected by a data collection card for image reconstruction after being amplified. The double-frequency microwaves are two different-frequency short pulse width microwaves, the tested tissue is excited successively during imaging, two groups of thermo-acoustic images under the excitation of the microwaves with different frequencies are correspondingly obtained, and then the two groups of thermo-acoustic images are fused to obtain the double-frequency thermo-acoustic image. The double-frequency microwave induced thermo-acoustic imaging system constructed according to the imaging method can obtain three groups of thermo-acoustic images by default, wherein two groups of single-frequency thermo-acoustic images are used for analyzing biological tissues with strong single-frequency microwave energy absorption and detecting corresponding lesions, and the double-frequency fusion image is used for highlighting tissues with weak single-frequency microwave energy absorption and large frequency-variable microwave energy absorption and detecting corresponding lesions.

Description

Dual-frequency microwave-induced thermoacoustic imaging system and method

Technical Field

The present invention belongs to the technical field of microwave thermoacoustic imaging, and relates to an imaging method and system, and in particular to a dual-frequency microwave induced thermoacoustic imaging method and system.

Background technique

Microwave thermoacoustic imaging is a new non-destructive biomedical imaging method that combines the advantages of microwave high-contrast excitation and deep penetration depth, and ultrasound high resolution. It can reflect the differences in microwave absorption characteristics between biological tissues, which depend on the dielectric properties of the tissue at the excitation frequency. As a new hybrid imaging mode that combines the advantages of microwave imaging and ultrasound imaging, microwave thermoacoustic imaging can reflect microwave dielectric functional information while displaying the structural characteristics of tissues. In recent years, it has attracted the attention of many scientific researchers. Over the past two decades, microwave thermoacoustic imaging technology has continued to develop, and research in application areas has continued to expand, highlighting its potential in related pre-clinical and clinical applications.

However, traditional microwave thermoacoustic imaging technology is mainly based on single-frequency excitation, which has better imaging effect for tissues with strong microwave absorption under single-frequency excitation, but not obvious for tissues with weak microwave absorption. Weak microwave absorption of biological tissues can be caused by weak microwave absorption coefficient of tissues; or it can be caused by the small size of tissues, which is smaller than the projection thickness of the detector layer, resulting in weak overall microwave absorption and thus being affected by the surrounding large-sized tissues, resulting in poor imaging effect.

The patent of the same applicant as the present invention, publication number CN114176554A, a multi-pulse width microwave-excited multi-scale thermoacoustic imaging method and system, belongs to the field of microwave thermoacoustic imaging. The biological tissue to be imaged is irradiated with microwaves of different pulse widths, which can excite the biological tissue to produce thermoacoustic signals with different spectral information. The signal can be detected by ultrasonic detectors with different center frequencies, thereby presenting thermoacoustic images of different depths and resolutions. The microwave source outputs microwaves of different pulse widths to irradiate the biological tissue, causing the biological tissue to produce thermoacoustic signals with different spectral information. The thermoacoustic signal is detected by the ultrasonic detector and transmitted to the amplifier, amplified and filtered by the amplifier, and then collected by the data acquisition card, and finally transmitted to the computer, where the thermoacoustic signal is reconstructed in the computer to restore the multi-scale thermoacoustic image. The multi-scale thermoacoustic imaging system is more flexible than the traditional thermoacoustic imaging system, and can reconstruct images of biological tissues of different scales to achieve the best imaging depth and resolution.

The principle of this patent is different from that of this patent. The principle of a multi-pulse-width microwave-excited multi-scale thermoacoustic imaging method is to use microwave radiation of different pulse widths to image tissues to generate different thermoacoustic signals. These signals are detected by ultrasonic detectors of different center frequencies, thereby presenting thermoacoustic images of different depths and resolutions. The principle of dual-frequency microwave-induced thermoacoustic imaging is based on the law of variation of the theoretical microwave absorption coefficient between biological tissues with microwave frequency. Two short-pulse-width microwaves of different microwave frequencies are used to obtain two groups of thermoacoustic images corresponding to microwave excitation of different frequencies, and then the two groups of thermoacoustic images are fused to obtain dual-frequency thermoacoustic images. The two groups of 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 images are used to highlight tissues with weak single-frequency microwave energy absorption and large microwave energy absorption changes with frequency changes and detect corresponding lesions. The purpose is different. The multi-pulse-width microwave-excited multi-scale thermoacoustic imaging method is to balance the different requirements of biological tissues of different sizes for penetration depth and resolution. The dual-frequency microwave-induced thermoacoustic imaging method solves the problem that traditional single-frequency microwave-excited thermoacoustic imaging does not clearly image tissues with weak microwave absorption and is difficult to detect corresponding lesions. The two have different purposes and focuses.

Summary of the invention

The present invention aims to solve the above problems of the prior art. A dual-frequency microwave induced thermoacoustic imaging system and method are proposed. The technical solution of the present invention is as follows:

A dual-frequency microwave-induced thermoacoustic imaging system, comprising: a dual-frequency microwave source, a coaxial line, an antenna, an array ultrasonic detector, an array amplification circuit, a multi-channel data acquisition card and a computer, wherein the dual-frequency microwave source is used to generate short-pulse microwaves of different frequencies, which are successively transmitted to the antenna through the coaxial line, and the microwaves are radiated to the measured tissue, and the measured tissue absorbs the microwave energy to generate ultrasonic waves, i.e., thermoacoustic signals, which are excited by microwaves of different frequencies are successively detected by the array ultrasonic detector, and the detected signals are amplified by the array amplification circuit, and the amplified signals are collected by the multi-channel data acquisition card, thereby obtaining two groups of Thermoacoustic data under different frequency excitations, the whole process is controlled by a computer, and two sets of single-frequency thermoacoustic images are reconstructed using a delayed superposition or filtered back projection algorithm according to the relationship between time domain information and spatial position, and then the two sets of single-frequency thermoacoustic data or images are fused using a dual-frequency thermoacoustic image, the frequency in the dual-frequency microwave induction refers to the microwave center frequency, the two sets of single-frequency thermoacoustic images are used to analyze biological tissues with strong single-frequency microwave energy absorption and detect corresponding lesions, and the dual-frequency fusion image is used to highlight the tissues with weak single-frequency microwave energy absorption and large changes in microwave energy absorption with frequency changes and detect corresponding lesions.

Furthermore, the short pulse width microwaves of different frequencies generated by the dual-frequency microwave source can be generated by the same variable frequency microwave source or by two single frequency microwave sources, and both need to keep the generated pulse microwave width and peak power consistent.

Furthermore, the antenna is a non-frequency-variable antenna covering a dual-frequency range or for two required radiation frequency points; or a wide-band antenna covering a dual-frequency range, and both must ensure that the field distribution of the two frequency points used for excitation imaging remains consistent.

Furthermore, the array ultrasonic detector, array amplification circuit, and multi-channel data acquisition card constitute a thermoacoustic signal acquisition module. When dual-frequency microwave excitation switching is performed, the array ultrasonic detector, array amplification circuit, multi-channel data acquisition card, antenna, and biological tissue under test remain stationary, that is, other experimental conditions except the excitation microwave frequency remain unchanged.

Further, the dual-frequency microwave source, the coaxial line and the antenna constitute a microwave excitation module, wherein the dual-frequency microwave source is composed of two independent microwave sources that can output the same short pulse width and the same power but different frequencies, or a microwave source with a variable frequency but ensuring that other short pulse width microwave parameters including pulse width, pulse power, and pulse repetition frequency remain unchanged;

The antenna uses a wide-band antenna covering a dual-frequency range, but the frequency point is not the boundary frequency point of the wide-band antenna, or a non-frequency-variable antenna is used for two required radiation frequency points or covering a dual-frequency range; short-pulse microwaves change in frequency but other parameters including pulse width, pulse power, and pulse repetition frequency remain unchanged, and the tissue being tested is stimulated by an antenna with the same length and consistent loss parameters and field distribution. The information reflected by the dual-frequency image relies more on changes in the tissue's own intrinsic microwave absorption coefficient and reduces the impact of changes in external field distribution.

Furthermore, the computer reconstructs two sets of single-frequency thermoacoustic images using a delayed superposition or filtered back-projection algorithm based on the relationship between the time domain information and the spatial position, wherein the time domain information is the time required for the signal to propagate from the spatial point of the biological tissue to each array element of the array ultrasound detector, also known as time delay, and the spatial position is the distance from the array ultrasound detector to the spatial point. In the delayed superposition algorithm, there is a corresponding relationship between the two: thermoacoustic signal speed × time delay = distance from the array ultrasound detector to the spatial point. Thus, the signal intensity of the spatial point at each array element of the array ultrasound detector is obtained, and the total signal intensity of the spatial point of the biological tissue is the superposition of these signal intensities. Similarly, the total signal of other spatial points of the biological tissue is obtained in this way, and then it is expressed in the form of an image, namely a thermoacoustic image. Compared with delayed superposition, the difference of filtered back projection is that it contains a first-order derivative, so it has a high-pass filtering characteristic.

Furthermore, the method of obtaining a dual-frequency thermoacoustic image by using a fusion algorithm for two sets of single-frequency thermoacoustic data or images specifically includes: fusing two sets of single-frequency thermoacoustic images or directly fusing two sets of single-frequency thermoacoustic data, mainly involving subtraction fusion, an initial fusion weight factor is determined by a theoretical microwave absorption coefficient, and after obtaining the dual-frequency thermoacoustic image, smoothness and focus intensity of the tissue area to be highlighted are judged; if the tissue is smooth and focused, a dual-frequency fused image is directly outputted along with two sets of single-frequency images; if the tissue is not smooth and not focused, the weight factor is adjusted until the tissue is smooth and focused, and then a dual-frequency fused image is outputted along with two sets of single-frequency images.

A dual-frequency microwave-induced thermoacoustic imaging method based on the system comprises the following steps:

Step 2-1, for biological tissues to be extracted and reconstructed for highlighting with weak microwave absorption under single-frequency microwave excitation, a frequency range in which the theoretical microwave absorption coefficient thereof varies greatly while the microwave absorption coefficient of surrounding tissues varies less is selected, thereby selecting two boundary frequency points of this frequency range as two excitation frequency points for dual-frequency microwave induced thermoacoustic imaging;

Step 2-2, turn on each device and set parameters for initialization;

Step 2-3, fixing the biological tissue to be tested;

Step 2-4, using a computer to trigger the dual-frequency microwave source to generate a short-pulse-width microwave with a center frequency, and triggering the data acquisition card to start working: a short-pulse-width microwave pulse with a center frequency is radiated to the biological tissue to be tested through the antenna, and the tissue generates an ultrasonic wave, i.e., a thermoacoustic signal, based on the thermoacoustic effect. The thermoacoustic signal is detected by the ultrasonic detector, converted into an electrical signal by the ultrasonic detector, and collected by the data acquisition card, and then stored in the computer and subjected to single-frequency thermoacoustic image reconstruction processing, that is, the thermoacoustic imaging of this single-frequency excitation is completed;

Steps 2-5: Keep all experimental conditions unchanged;

Step 2-6, using a computer to trigger the dual-frequency microwave source to generate another short-pulse-width microwave with a center frequency, and triggering the data acquisition card to start working: another short-pulse-width microwave pulse with a center frequency is radiated to the biological tissue to be tested through the antenna, and the tissue generates ultrasonic waves, i.e., thermoacoustic signals, based on the thermoacoustic effect. The thermoacoustic signals are detected by the ultrasonic detector, converted into electrical signals by the ultrasonic detector, and collected by the data acquisition card, and then stored in the computer and processed by single-frequency thermoacoustic image reconstruction, that is, the thermoacoustic imaging of this single-frequency excitation is completed;

Step 2-7, post-processing the two completed single-frequency thermoacoustic images using a dual-frequency image fusion algorithm, or directly processing the two sets of single-frequency thermoacoustic data stored in the computer;

Step 2-8, export three groups of images, of which two groups of single-frequency thermoacoustic images are used to analyze biological tissues with strong single-frequency microwave energy absorption and detect corresponding lesions, and dual-frequency fusion images are used to highlight tissues with weak single-frequency microwave energy absorption but large changes in microwave energy absorption with frequency changes and detect corresponding lesions.

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

The present invention is based on the law of variation of the theoretical microwave absorption coefficient between biological tissues with frequency. For tissues with weak microwave absorption under single-frequency microwave excitation, a frequency range in which the microwave absorption coefficient of the tissues changes greatly while the microwave absorption coefficient of the surrounding tissues changes less is selected, thereby selecting two boundary frequency points of this frequency range as two excitation frequency points for dual-frequency microwave induced thermoacoustic imaging. Thus, the dual-frequency microwaves are short-pulse-width microwaves of two different frequencies. During the experiment, the biological tissues to be tested are excited successively through the antenna, and the generated thermoacoustic signals are successively detected by the ultrasonic detector, and the detected thermoacoustic signals are successively amplified by the amplifier and collected by the data acquisition card. Image reconstruction of the thermoacoustic signals detected under the excitation of two groups of microwaves with different frequencies can obtain two groups of thermoacoustic images under the excitation of microwaves with different frequencies, and the two groups of thermoacoustic images are fused to obtain a group of dual-frequency thermoacoustic images. Three sets of thermoacoustic images can be obtained by default through this method, of which two sets of single-frequency thermoacoustic images are used to analyze biological tissues with strong single-frequency microwave energy absorption and detect corresponding lesions, while dual-frequency fusion images are used to highlight tissues with weak single-frequency microwave energy absorption but large changes in microwave energy absorption with frequency changes and detect corresponding lesions, thereby achieving overall high-quality imaging and improving lesion detection capabilities.

Compared with the traditional single-frequency thermoacoustic imaging technology, the present invention has better imaging effect and lesion detection ability for biological tissues with weak microwave energy absorption. The dual-frequency microwave thermoacoustic imaging method uses two short-pulse microwaves of different frequencies to perform thermoacoustic imaging, which can not only be used to analyze biological tissues with strong single-frequency microwave energy absorption and detect corresponding lesions, but also can be used to highlight tissues with weak single-frequency microwave energy absorption but large microwave energy absorption changes with frequency and detect corresponding lesions.

In the field of thermoacoustic imaging, the innovation of dual-frequency microwave-induced thermoacoustic imaging method is to use short-pulse microwaves of two different frequencies for thermoacoustic imaging, thereby obtaining two sets of single-frequency thermoacoustic images at corresponding frequencies. These two sets of thermoacoustic images can be used to analyze biological tissues and their lesions with strong microwave energy absorption coefficients at the corresponding single frequency. The image obtained by fusing the above two sets of thermoacoustic images using a dual-frequency fusion algorithm is used to highlight the tissues that are insufficiently displayed in single-frequency thermoacoustic images due to weak single-frequency microwave energy absorption and to detect their lesions.

The dual-frequency thermoacoustic fusion algorithm is an innovation, which uses two sets of single-frequency thermoacoustic imaging data for combined fusion, mainly involving subtraction fusion. The weight coefficient of the subtraction fusion is comprehensively determined based on the theoretical microwave absorption coefficient and the imaging smoothness or focusing effect of the tissue to be extracted and reconstructed to highlight.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic diagram of a dual-frequency microwave-induced thermoacoustic imaging system according to a preferred embodiment of the present invention.

FIG. 2 shows the steps for executing dual-frequency microwave-induced thermoacoustic imaging in this embodiment.

Among them, a dual-frequency microwave source (1-1; 1-2), a coaxial line (1-3; 1-4), an antenna (1-5), an array ultrasonic detector (1-7), an array amplifier circuit (1-8), a multi-channel data acquisition card (1-9) and a computer (1-10)

Detailed ways

The following will describe the technical solutions in the embodiments of the present invention in detail in conjunction with the accompanying drawings in the embodiments of the present invention. The described embodiments are only part of the embodiments of the present invention.

The technical solution of the present invention to solve the above technical problems is:

The purpose of the present invention is to overcome the shortcomings of current microwave thermoacoustic imaging and provide a dual-frequency microwave induced thermoacoustic imaging method and system. The dual-frequency fusion image obtained by this method and system can highlight tissues that have weak single-frequency microwave energy absorption but large changes in microwave energy absorption with frequency, thereby improving the detection capability of corresponding tissue lesions.

As shown in FIG1 , a dual-frequency microwave-induced thermoacoustic imaging system comprises: a dual-frequency microwave source 1-1; 1-2, coaxial lines 1-3; 1-4, an antenna 1-5, an array ultrasonic detector 1-7, an array amplifier circuit 1-8, a multi-channel data acquisition card 1-9 and a computer 1-10, wherein the dual-frequency microwave source 1-1; 1-2 is used to generate short-pulse microwaves of different frequencies, which are successively transmitted to the antenna 1-5 through the coaxial lines 1-3; 1-4, and the microwaves are radiated to the measured tissue 1-6. The measured tissue 1-6 absorbs microwave energy to generate ultrasonic waves, i.e., thermoacoustic signals. The thermoacoustic signals under the excitation of microwaves of different frequencies are successively detected by the array ultrasonic detector 1-7, and the detected signals are successively transmitted to the array amplifier circuit 1-8. The amplified signal is collected by a multi-channel data acquisition card 1-9, thereby obtaining two groups of thermoacoustic data under different frequency excitations. The entire process is controlled by a computer 1-10. According to the relationship between time domain information and spatial position, two groups of single-frequency thermoacoustic images are reconstructed using a delayed superposition or filtered back projection algorithm. Then, the two groups of single-frequency thermoacoustic data or images are fused using a fusion algorithm to obtain a dual-frequency thermoacoustic image. The frequency in the dual-frequency microwave induction refers to the microwave center frequency. The two groups of 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 changes and detect corresponding lesions.

Preferably, the present invention is based on the law of variation of the theoretical microwave absorption coefficient between biological tissues with frequency. For tissues with weak microwave absorption under single-frequency microwave excitation, a frequency range in which the microwave absorption coefficient of the tissue varies greatly while the microwave absorption coefficient of the surrounding tissue varies less is selected, thereby selecting two boundary frequency points of this frequency range as two excitation frequency points for dual-frequency microwave induced thermoacoustic imaging.

Therefore, dual-frequency microwaves are short-pulse microwaves of two different frequencies. During the experiment, the biological tissue under test is stimulated by the antenna successively, and the generated thermoacoustic signals are detected by the ultrasonic detector successively. The detected thermoacoustic signals are amplified by the amplifier and collected by the data acquisition card successively. Image reconstruction of the thermoacoustic signals detected under the two sets of microwave excitations with different frequencies can obtain two sets of thermoacoustic images under the microwave excitations with different frequencies. The two sets of thermoacoustic images are fused to obtain a set of dual-frequency thermoacoustic images.

Furthermore, three sets of thermoacoustic images can be obtained by default through this method, of which two sets of single-frequency thermoacoustic images are used to analyze biological tissues with strong single-frequency microwave energy absorption and detect corresponding lesions, while dual-frequency fusion images are used to highlight tissues with weak single-frequency microwave energy absorption but large changes in microwave energy absorption with frequency changes and detect corresponding lesions, thereby achieving overall high-quality imaging and improving lesion detection capabilities.

Furthermore, the dual-frequency microwaves can be generated by the same variable-frequency microwave source or by two single-frequency microwave sources, and the width and peak power of the generated pulse microwaves must be kept consistent. It should be clarified that the frequency in the dual-frequency microwave induction refers to the microwave center frequency.

Furthermore, the antenna can be a non-frequency-variable antenna covering a dual-frequency range or for two required radiation frequency points, or a wide-band antenna covering a dual-frequency range, and both must ensure that the field distribution of the two frequency points used for excitation imaging remains consistent.

Furthermore, the thermoacoustic signal acquisition module includes an ultrasonic detector, a signal amplifier and a data acquisition card. When the dual-frequency microwave excitation is switched, the antenna and the biological tissue under test remain stationary, that is, other experimental conditions except the excitation microwave frequency remain unchanged.

Furthermore, single-frequency thermoacoustic image reconstruction can use traditional microwave thermoacoustic imaging algorithms such as delayed superposition algorithm or filtered back projection algorithm, and it is only necessary to ensure that the same algorithm is used for the reconstruction of the corresponding two sets of single-frequency thermoacoustic data. The dual-frequency fusion algorithm is based on two sets of single-frequency thermoacoustic imaging, mainly involving subtraction fusion, and the weight coefficient of subtraction fusion is comprehensively determined based on the theoretical microwave absorption coefficient and the imaging smoothness or focusing effect of the tissue extracted and reconstructed to highlight.

Furthermore, the dual-frequency fusion algorithm can be performed on the basis of the two sets of reconstructed single-frequency thermoacoustic images, or the two sets of single-frequency thermoacoustic data can be directly processed.

Furthermore, the dual-frequency microwave source can be composed of two independent microwave sources that can output the same short pulse width and the same power but different frequencies, or it can be a microwave source with a variable frequency but ensuring that other short pulse width microwave parameters remain unchanged, among which a variable frequency microwave source is preferred.

Furthermore, the antenna can be a wideband antenna covering a dual frequency range, but the frequency point is not at the boundary frequency point of the wideband antenna as much as possible. It can also be a non-frequency-variable antenna for two required radiation frequency points or covering a dual frequency range, among which the non-frequency-variable antenna is preferred.

Furthermore, short-pulse microwaves change in frequency but not other parameters, and they excite the tissue under test through coaxial lines of the same length and with consistent loss parameters and antennas with consistent field distribution. The information reflected by the dual-frequency image relies more on changes in the tissue's intrinsic microwave absorption coefficient and reduces the impact of changes in external field distribution.

Furthermore, the array detector ultrasonic detector, array amplifier and multi-channel data acquisition card constitute a signal detection module to detect two groups of thermoacoustic signals under different frequency excitations. When the number of array channels cannot be completely matched, multiplexing technology is used to ensure real-time imaging, thereby avoiding jitter interference during in vivo imaging.

Furthermore, the system can perform in vivo, ex vivo and living body imaging. When performing dual-frequency imaging to collect thermoacoustic signals under different microwave frequency excitations, other experimental conditions except the frequency are kept as unchanged as possible.

Furthermore, the dual-frequency fusion algorithm can be performed on the basis of the two sets of reconstructed single-frequency thermoacoustic images, or the two sets of single-frequency thermoacoustic data can be directly processed, and finally three sets of thermoacoustic images are obtained, including two sets of single-frequency thermoacoustic images and one set of dual-frequency thermoacoustic images. Among them, the dual-frequency fusion is preferably performed on the basis of the two sets of reconstructed single-frequency thermoacoustic images.

The dual-frequency microwave sources 1-1 and 1-2 generate short-pulse microwaves of different frequencies, which are transmitted to the antenna 1-5 through the coaxial lines 1-3 and 1-4 respectively, and radiate the microwaves to the tissue 1-6 to be tested. The tissue absorbs the microwave energy to generate ultrasonic waves, that is, thermoacoustic signals. The thermoacoustic signals under the excitation of microwaves of different frequencies are detected by the array ultrasound detector 1-7 in turn. The detected signals are amplified by the array amplifier circuit 1-8, and the amplified signals are collected by the multi-channel data acquisition card 1-9, thereby obtaining two sets of thermoacoustic data under the excitation of different frequencies. The whole process is controlled by the computer 1-10. According to the relationship between the time domain information and the spatial position, the two sets of single-frequency thermoacoustic images are reconstructed using the delayed superposition or filtered back-projection algorithm, and then the two sets of single-frequency thermoacoustic data or images are fused by the algorithm to obtain the dual-frequency thermoacoustic image. It should be clarified that the frequency in the dual-frequency microwave induction refers to the microwave center frequency.

As shown in FIG2 , a dual-frequency microwave-induced thermoacoustic imaging method based on the system includes the following steps:

Step 2-1, for biological tissues to be extracted and reconstructed for highlighting with weak microwave absorption under single-frequency microwave excitation, a frequency range in which the theoretical microwave absorption coefficient thereof varies greatly while the microwave absorption coefficient of surrounding tissues varies less is selected, thereby selecting two boundary frequency points of this frequency range as two excitation frequency points for dual-frequency microwave induced thermoacoustic imaging;

Step 2-2, turn on each device and set parameters for initialization;

Step 2-3, fixing the biological tissue to be tested;

Step 2-4, using a computer to trigger the dual-frequency microwave source to generate a short-pulse-width microwave with a center frequency, and triggering the data acquisition card to start working: a short-pulse-width microwave pulse with a center frequency is radiated to the biological tissue to be tested through the antenna, and the tissue generates an ultrasonic wave, i.e., a thermoacoustic signal, based on the thermoacoustic effect. The thermoacoustic signal is detected by the ultrasonic detector, converted into an electrical signal by the ultrasonic detector, and collected by the data acquisition card, and then stored in the computer and subjected to single-frequency thermoacoustic image reconstruction processing, that is, the thermoacoustic imaging of this single-frequency excitation is completed;

Steps 2-5: Keep all experimental conditions unchanged;

Step 2-6, using a computer to trigger the dual-frequency microwave source to generate another short-pulse-width microwave with a center frequency, and triggering the data acquisition card to start working: another short-pulse-width microwave pulse with a center frequency is radiated to the biological tissue to be tested through the antenna, and the tissue generates ultrasonic waves, i.e., thermoacoustic signals, based on the thermoacoustic effect. The thermoacoustic signals are detected by the ultrasonic detector, converted into electrical signals by the ultrasonic detector, and collected by the data acquisition card, and then stored in the computer and processed by single-frequency thermoacoustic image reconstruction, that is, the thermoacoustic imaging of this single-frequency excitation is completed;

Step 2-7, post-processing the two completed single-frequency thermoacoustic images using a dual-frequency image fusion algorithm, or directly processing the two sets of single-frequency thermoacoustic data stored in the computer;

Step 2-8, export three groups of images, of which two groups of single-frequency thermoacoustic images are used to analyze biological tissues with strong single-frequency microwave energy absorption and detect corresponding lesions, and dual-frequency fusion images are used to highlight tissues with weak single-frequency microwave energy absorption but large changes in microwave energy absorption with frequency changes and detect corresponding lesions.

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

It should also be noted that the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, commodity or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, commodity or device. In the absence of more restrictions, the elements defined by the sentence "comprises a ..." do not exclude the existence of other identical elements in the process, method, commodity or device including the elements.

The above embodiments should be understood to be only used to illustrate the present invention and not to limit the protection scope of the present invention. After reading the contents of the present invention, technicians 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 (7)

1. A dual-frequency microwave-induced thermo-acoustic imaging system, comprising: a dual frequency microwave source (1-1; 1-2), coaxial lines (1-3; 1-4), an antenna (1-5), an array ultrasonic detector (1-7), an array amplifying circuit (1-8), a multi-channel data acquisition card (1-9) and a computer (1-10), wherein the dual-frequency microwave source (1-1; 1-2) is used for generating short pulse width microwaves with different frequencies, the short pulse width microwaves are respectively transmitted to the antenna (1-5) through the coaxial lines (1-3; 1-4) in sequence, microwave radiation is transmitted to a tested tissue (1-6), the tested tissue (1-6) absorbs microwave energy to generate ultrasonic waves, namely thermal acoustic signals, the thermal acoustic signals under the excitation of different frequencies are sequentially detected by the array ultrasonic detector (1-7), the detected signals are amplified by the array amplifying circuit (1-8), the amplified signals are acquired by the multi-channel data acquisition card (1-9) so as to obtain two groups of thermal acoustic data under the excitation of different frequencies, the whole flow is controlled by the computer (1-10), the thermal acoustic data under the time domain information and spatial position relationship, the thermal image is restored by using a single-frequency or inverse projection algorithm, the thermal image is obtained by using the dual-frequency image fusion algorithm, the thermal image is obtained by the thermal image of the dual-frequency acoustic image fusion algorithm, two groups of single-frequency thermo-acoustic images are used for analyzing biological tissues with strong single-frequency microwave energy absorption and detecting corresponding lesions, and the double-frequency fusion images are used for highlighting tissues with weak single-frequency microwave energy absorption and large change of microwave energy absorption along with frequency change and detecting corresponding lesions;

For biological tissues to be extracted and reconstructed to be highlighted, which are weak in microwave absorption under single-frequency microwave excitation, selecting a frequency range with a large theoretical microwave absorption coefficient change and a small surrounding tissue microwave absorption coefficient change, and selecting two boundary frequency points of the frequency range as two excitation frequency points for performing double-frequency microwave induced thermo-acoustic imaging;

Short pulse width microwaves with different frequencies generated by the double-frequency microwave source (1-1; 1-2) need to keep the generated pulse microwave width consistent with the peak power;

The antennas (1-5) need to ensure that the field distribution of the two frequency points used for excitation imaging remains uniform.

2. A dual-frequency microwave-induced thermo-acoustic imaging system as claimed in claim 1, wherein,

The short pulse width microwaves with different frequencies generated by the double-frequency microwave source (1-1; 1-2) can be generated by the same variable frequency microwave source or two single-frequency microwave sources.

3. A dual-frequency microwave induced thermo-acoustic imaging system according to claim 1, characterized in that the antenna (1-5) is a non-frequency-changing antenna covering a dual-frequency range or for two desired radiation frequency points; or a wideband antenna covering a dual frequency range.

4. A dual-frequency microwave-induced thermo-acoustic imaging system as claimed in claim 1, wherein,

The array ultrasonic detector (1-7), the array amplifying circuit (1-8) and the multichannel data acquisition card (1-9) form a thermoacoustic signal acquisition module, and when double-frequency microwave excitation switching is carried out, the array ultrasonic detector (1-7), the array amplifying circuit (1-8) and the multichannel data acquisition card (1-9) are kept motionless with the antenna (1-5) and the tissue of the tested organism (1-6), namely, other experimental conditions are kept unchanged except the excitation microwave frequency.

5. A dual-frequency microwave induced thermo-acoustic imaging system according to claim 1, characterized in that the dual-frequency microwave source (1-1; 1-2), the coaxial line (1-3; 1-4) and the antenna (1-5) constitute a microwave excitation module, wherein the dual-frequency microwave source consists of two independent microwave sources which can output the same short pulse width, the same repetition frequency, the same power but different frequencies, or one microwave source which is variable in frequency but ensures that other short pulse width microwave parameters including pulse width, pulse power and pulse repetition frequency are unchanged;

The antenna adopts a broadband antenna covering a double-frequency range, but the frequency points are not boundary frequency points of the broadband antenna, or adopts a non-frequency-variable antenna aiming at two required radiation frequency points or covering the double-frequency range; the short pulse width microwave divides the frequency change, other parameters include pulse width, pulse power and pulse repetition frequency, the same length coaxial line with consistent loss parameters is used for exciting the tested tissue through the antenna with consistent field distribution, and the information reflected by the double-frequency image is more dependent on the change of the internal microwave absorption coefficient of the tissue itself to reduce the influence of the change of external field distribution.

6. The dual-frequency microwave-induced thermo-acoustic imaging system according to claim 1, wherein the obtaining the dual-frequency thermo-acoustic image from the two sets of single-frequency thermo-acoustic data or images by using a fusion algorithm specifically comprises: the method mainly comprises the steps of fusing two groups of single-frequency thermo-acoustic images or directly fusing two groups of single-frequency thermo-acoustic data, wherein the method mainly relates to subtraction fusion, an initial fusion weight factor is determined by a theoretical microwave absorption coefficient, smoothness and focusing strength judgment are carried out on a tissue region to be highlighted after the double-frequency thermo-acoustic images are obtained, if the tissue is smooth and focused, the double-frequency fusion image is directly output and accompanied with the two groups of single-frequency images, and if the tissue is not smooth and not focused, the weight factor is adjusted until the tissue is smooth and focused, and then the double-frequency fusion image is output and accompanied with the two groups of single-frequency images.

7. A dual-frequency microwave induced thermo-acoustic imaging method based on the system of claim 6, comprising the steps of:

step 2-1, selecting a frequency range with a larger theoretical microwave absorption coefficient change and a smaller surrounding tissue microwave absorption coefficient change for a biological tissue to be extracted and reconstructed for highlighting under single-frequency microwave excitation, so as to select two boundary frequency points of the frequency range as two excitation frequency points for performing double-frequency microwave induced thermo-acoustic imaging;

step 2-2, starting each device, and setting parameters for initialization;

step 2-3, fixing the biological tissue to be detected;

Step 2-4, triggering a double-frequency microwave source to generate short pulse width microwaves with a central frequency by using a computer, and triggering a data acquisition card to start working: the method comprises the steps that short pulse width microwave pulses with central frequency are radiated to biological tissues to be detected through an antenna, the tissues generate ultrasonic waves, namely thermoacoustic signals, based on thermoacoustic effects, the thermoacoustic signals are detected by an ultrasonic detector, are converted into electric signals through the ultrasonic detector and are collected by a data collection card, and then the electric signals are stored in a computer and subjected to single-frequency thermoacoustic image reconstruction processing, namely thermoacoustic imaging of single-frequency excitation is completed;

Step 2-5, maintaining all experimental conditions unchanged;

step 2-6, triggering a double-frequency microwave source to generate short pulse width microwaves with another center frequency by using a computer, and triggering a data acquisition card to start working: the other kind of short pulse width microwave pulse with center frequency is radiated to the biological tissue to be measured through the antenna, the tissue generates ultrasonic wave based on the thermoacoustic effect, namely thermoacoustic signal, the thermoacoustic signal is detected by the ultrasonic detector, the electrical signal is converted into electrical signal by the ultrasonic detector and is collected by the data acquisition card, and then the electrical signal is stored in the computer and is subjected to single-frequency thermoacoustic image reconstruction processing, namely the thermoacoustic imaging of the single-frequency excitation is completed;

Step 2-7, performing post-processing on the two completed single-frequency thermo-acoustic images by utilizing a double-frequency image fusion algorithm, or directly processing two groups of single-frequency thermo-acoustic data stored in a computer;

And 2-8, deriving three groups of images, wherein two groups of single-frequency thermo-acoustic images are used for analyzing biological tissues with strong single-frequency microwave energy absorption and detecting corresponding lesions, and the double-frequency fusion image is used for highlighting tissues with weak single-frequency microwave energy absorption and large change of microwave energy absorption along with frequency change and detecting corresponding lesions.