CN116942103B - Dark-field photoacoustic tomography system and method - Google Patents

Abstract

The invention provides a dark field photoacoustic tomography system and a method, wherein a body to be measured absorbs energy of beam expansion pulse light to generate local pressure change, and ultrasonic signals are transmitted to a plurality of directions outside the body to be measured in an ultrasonic mode; the ultrasonic detection module in the system comprises a plurality of ultrasonic transducer units to form one or a plurality of ultrasonic transducer arrays, wherein the ultrasonic transducer arrays detect ultrasonic signals along a plurality of propagation directions in an effective ultrasonic detection range and convert the ultrasonic signals into voltage signals to be output; and the irradiation range of the beam expansion pulse light on the surface of the to-be-detected body and the effective ultrasonic detection range of the ultrasonic detection module do not have an overlapping area on the surface of the to-be-detected body, or the area of the overlapping area of the irradiation range of the surface of the to-be-detected body and the effective ultrasonic detection range of the ultrasonic detection module on the surface of the to-be-detected body is not more than 50 percent of the irradiation range on the surface of the to-be-detected body, and the system is used for restraining the shape and the azimuth of the surface of the to-be-detected body, so that photoacoustic tomography dark field illumination is realized in the surface area of the effective imaging area of the to-be-detected body.

Description

A dark-field photoacoustic tomography system and method

Technical field

The invention relates to biomedical imaging technology, and in particular to a dark field photoacoustic tomography system and method.

Background technique

As an emerging biomedical imaging technology, photoacoustic tomography has the characteristics of fast speed, high resolution, rich imaging information, safety and no radiation. It complements the advantages of traditional medical imaging technology and has begun to be translated into clinical practice in recent years. . Photoacoustic tomography technology uses pulsed light to illuminate biological tissue. The components of biological tissue that absorb light will generate ultrasonic signals under the photoacoustic effect. By detecting the ultrasonic signals, the image of the light-absorbing components in the biological tissue is reconstructed.

The mechanism of the photoacoustic effect is that when pulsed light irradiates an organism, tissue components that absorb light of this wavelength will produce a brief temperature increase, causing rapid changes in local pressure. This pressure change will propagate outside the body in the form of ultrasonic waves (also called photoacoustic signals) and be detected by surrounding ultrasonic transducers. Based on the photoacoustic signals of different intensities detected by the ultrasonic transducer at different positions and times, the image reconstruction algorithm measures the composition (such as hemoglobin), concentration, and location of the light-absorbing chromophore in the organism, and provides an image of the light-absorbing chromophore distribution. Therefore, in the photoacoustic tomography system, the cooperation of pulsed illumination and ultrasonic detection fundamentally determines the imaging performance of the photoacoustic tomography system.

After nearly two decades of development, photoacoustic imaging technology has made great progress. However, the design of existing photoacoustic tomography systems, especially the synergy between pulsed illumination and ultrasonic detection, has not been optimized and standardized. A common problem is that in existing photoacoustic tomography systems, pulsed illumination There is a large overlap between the illumination distribution on the surface of biological tissue and the ultrasonic detection range, resulting in a large difference in the distribution of light flux (light energy per unit area) within the ultrasonic detection area. Since light decays exponentially with depth after entering biological tissue, the photoacoustic signal received by the photoacoustic imaging system from the tissue surface is usually much stronger than the photoacoustic signal from the deep tissue. However, the large difference in photoacoustic signal amplitude within the effective imaging area will lead to superficial signal artifacts that cannot be ignored in deep tissue images when using image reconstruction algorithms such as back-projection or delayed summation. In addition, strong photoacoustic signals generated by strong light flux on the tissue surface will experience irregular scattering when propagating in biological tissues with non-uniform acoustic properties. After being received by the ultrasonic transducer, this invalid scattering signal will also Artifacts are produced in the reconstructed image.

Contents of the invention

In view of the shortcomings of existing photoacoustic tomography technology, the present invention provides a dark field photoacoustic tomography system and method.

A dark-field photoacoustic tomography system, including a light guide module, an ultrasonic detection module and a load-bearing shaping module;

The light guide module expands and/or shapes the pulse beam to form an expanded beam pulse light that irradiates the object to be measured. The component in the object to be measured that absorbs the expanded beam pulse light absorbs the energy of the expanded beam pulse light and generates local pressure. Changes, local pressure changes propagate ultrasonic signals in the form of ultrasonic waves in multiple directions outside the body to be measured; the ultrasonic detection module detects ultrasonic signals propagating in multiple directions, and converts the ultrasonic signals into voltage signals; the load-bearing plastic By installing a shaping groove, the shape module carries the object to be measured and constrains the surface shape and orientation of the object to be measured, thereby making the irradiation range and incident angle of the expanded beam pulse light on the surface of the object to be measured stable and controllable;

The light guide module adjusts the irradiation range of the expanded-beam pulse light on the surface of the object to be measured, thereby adjusting the relative position and angle between the effective ultrasonic detection range of the object to be measured and the ultrasonic detection module, so that the expanded-beam pulse light can illuminate the surface of the object to be measured. There is no overlapping area between the irradiation range of the surface and the effective ultrasonic detection range of the ultrasonic detection module on the surface of the object to be measured, or the area of the overlapping area is not greater than 50% of the irradiation range of the expanded beam pulse light on the surface of the object to be measured, forming dark field illumination;

The subject to be tested is one or several combinations of living organisms, biological tissues or non-living bodies;

The ultrasonic detection module includes multiple ultrasonic transducer units, which are distributed around the object to be measured. The multiple ultrasonic transducer units form one or more ultrasonic transducer arrays, and the ultrasonic transducer arrays are within the effective ultrasonic detection range. Detects the ultrasonic signals propagating in multiple directions generated by the expanded beam pulse light in the object to be measured, and converts the ultrasonic signals into voltage signals for output; each transducer unit can choose a self-focusing or non-self-focusing shape. The effective detection range of the transducer unit obeys the ultrasonic diffraction formula; the effective ultrasonic detection range of each ultrasonic transducer array or detection matrix also obeys the spatial sampling theorem;

The ultrasonic detection module can be designed in different forms according to different needs, specifically:

(1) The ultrasonic detection module includes one or more arc-shaped ultrasonic transducer arrays. The arc range of the ultrasonic transducer array is from 10 degrees to 359 degrees. The arc-shaped ultrasonic transducer array forms an arc-shaped ultrasonic transducer module;

(2) The ultrasonic detection module includes two or more linear ultrasonic transducer arrays, arranged to form a polygon or a part of a polygon;

(3) The ultrasonic detection module includes multiple ultrasonic transducer units, which are arranged as part of a sphere in space to form a spherical ultrasonic transducer array;

(4) The ultrasonic detection module includes multiple ultrasonic transducer units. The ultrasonic transducer units are arranged in space as part of a polyhedron to form a polyhedral ultrasonic transducer array;

Light guide modules are placed on both sides of the arc-shaped ultrasonic transducer array to form double-sided dark field illumination; light guide modules are placed on one side of the linear ultrasonic transducer array to form single-sided dark field illumination; spherical ultrasonic transducers Light guide modules are placed at the edge of the array to form annular dark field illumination; light guide modules are placed in the gaps between the ultrasonic transducer units of the polyhedral ultrasonic transducer array to form polygonal dark field illumination;

The load-bearing shaping module carries and shapes the object to be measured by installing a shaping slot near the imaging window. The shaping slot is made of solid or non-deformable material; the load-bearing shaping module leaves room for beam expansion pulses near the effective imaging area. The imaging window through which light and ultrasonic signals pass through is covered with a material that light and ultrasound can easily pass through. It ensures that the surface shape of the object to be measured is constrained while ensuring that it does not block the irradiation of the expanded beam pulse light on the object to be measured, nor does it block ultrasound. The detection module detects ultrasonic signals;

The effective imaging area is the area covered by the effective ultrasonic detection range of the ultrasonic detection module in the body to be measured, which is a section of a certain thickness of the body to be measured or the three-dimensional space of the body to be measured; the effective imaging area includes a surface area and a deep area, and the surface area is close to Bearing the shaping module, the deep area is far away from the bearing shaping module; the surface area of the effective imaging area is 0 to 1 mm away from the surface of the body under test close to the bearing shaping module, and the deep area of the effective imaging area is close to the bearing shaping module The vertical distance on the surface of the object to be measured is greater than 1 mm and less than 100 mm;

The irradiation direction of the expanded-beam pulse light points or approximately points to the center of the effective imaging area. The straight-line distance from the irradiation area on the surface of the object to be measured to the center of the effective imaging area does not exceed 5 cm. The expanded-beam pulse light propagates in the object to be measured. After attenuation, the luminous flux distribution intensity in the deep area of the imaging area is at least 1/1000 higher than the strongest luminous flux on the surface of the object to be measured;

The irradiation range and angle of the expanded beam pulse light on the surface of the object to be measured match the size and shape of the effective imaging area, so that the luminous flux distribution in the object to be measured after the expanded beam pulse light propagates and scatters in the object to be measured covers the effective imaging area In the deep area and surface area, the relationship between the strongest luminous flux in the effective imaging area and the weakest luminous flux in the effective imaging area is: the ratio of the strongest luminous flux to the weakest luminous flux is less than or equal to 200;

The dark-field photoacoustic tomography system also includes: a pulse generation module, a spatial scanning module, a data acquisition module and an image reconstruction module:

The pulse light generation module includes one or more light sources for generating single-wavelength or multi-wavelength pulse light beams; the spatial scanning module adjusts the relative position of the object to be measured and the main body of the photoacoustic imaging system; the data acquisition module The voltage signal output by the ultrasonic detection module is processed to output signal data; the image reconstruction module calculates the distribution of the concentration of each light-absorbing chromophore in the object to be tested based on the signal data, and generates an image of the object to be tested;

The spatial scanning module adjusts the effective imaging area of the object to be measured to overlap with the area that the operator expects to observe, and at the same time increases the imaging range of the photoacoustic tomography system; specifically, it feeds back the object to be tested and the photoacoustic layer through positioning lenses or marking positioning points. Analyze the relative position or angle of the main body of the imaging system; according to the placement position of the object to be measured, move or rotate the relative position of the main body of the photoacoustic imaging system and the object to be measured by any one or more of manual, automatic, and adaptive methods; The main body of the photoacoustic imaging system includes: pulse generation module, light guide module, ultrasonic detection module and data acquisition module;

The data acquisition module collects, processes, transmits and stores the voltage signal output by the ultrasonic detection module, and outputs signal data. The amplitude of the output signal data is proportional to the amplitude of the ultrasonic signal related to the type of object to be measured, and is also proportional to the amplitude of the ultrasonic signal to be measured. The local pressure change amplitude in the measuring body;

The image reconstruction module reconstructs the image of the object to be measured based on the time information and amplitude information contained in the signal data of the data acquisition module, and calculates the local pressure change amplitude in the effective imaging area. distribution, and then calculate the distribution of the concentration of each light-absorbing chromophore in the object to be tested, and generate an image of the object to be tested;

The local pressure change amplitude is proportional to the optical absorption coefficient of the light-absorbing component The product of the local luminous flux F, the optical absorption coefficient of the light-absorbing component/> It can characterize the concentration of each light-absorbing chromophore in the object to be measured, in order to based on the local pressure change amplitude/> Finally, the optical absorption coefficient of the light-absorbing component in the object to be measured is obtained/> , it is necessary to provide a relatively uniform or controllable light flux F distribution in the effective imaging area according to the pulse light generation module, light guide module and type of object to be measured.

A dark-field photoacoustic tomography method, implemented based on the above-mentioned dark field photoacoustic tomography system, includes the following steps:

Step 1: Design and test the effective ultrasonic detection range of the ultrasonic detection module;

Step 2: Install the load-bearing shaping module according to the effective ultrasonic detection range of the ultrasonic detection module, and fix the position of the load-bearing shaping module, thereby further calibrating the positional relationship between the pulse illumination area and the load-bearing shaping module;

Step 3: Determine the preliminary installation position and angle of the light guide module, install the light guide module, and guide the beam emitted by the pulse light generation module to illuminate the intended illumination area after shaping and expanding it; adjust the illumination range by adjusting the optical devices of the light guide module and angle, overlapping with the pulse illumination area calibrated in step 2 to achieve photoacoustic tomography dark field illumination;

Step 4: Place a bionic prosthesis with acoustic characteristics similar to that of the human body in the body-to-be-tested body-bearing shaping module to test its imaging effect. Optimize the imaging quality by fine-tuning the range and angle of illumination; after the optimization is completed, determine the area within the intended imaging area. Whether the optical energy density and power density comply with the US national laser safety standards; if they comply, the relative positions and angles of the pulse beam, ultrasonic detection module, and load-bearing shaping module can be optimized and relatively stable; if they do not comply, continue to adjust;

Step 5: According to the placement position of the object under test fed back by the load-bearing shaping module, use the spatial scanning module to manually, automatically or adaptively adjust the relative position of the object under test and the main body of the photoacoustic tomography system so that the target imaging area of the object under test is Overlap with the effective imaging area;

Step 6: After the test is completed, place the sample to be tested. Based on the dark-field photoacoustic tomography system, the illumination excitation, ultrasonic detection, spatial scanning, data acquisition, and image reconstruction are completed to obtain an image of the body to be tested.

Beneficial technical effects of the present invention:

In photoacoustic tomography, since the luminous flux of pulsed light generally attenuates exponentially with the increase of penetration depth after entering the object to be measured, the ultrasonic signal received by the traditional photoacoustic tomography system from the superficial area of the object to be measured is usually far away. Stronger than ultrasound signals from deeper areas. However, if there is a large difference in ultrasound signal amplitude within the imaging area, when using image reconstruction algorithms such as back-projection or delayed summation, signals from the superficial area will not be ignored in the deep area image of the object to be measured. artifacts. In addition, the strong ultrasonic signal generated by the strong light flux in the tissue surface area will experience irregular scattering when propagating in the tissue with non-uniform acoustic properties. After the invalid scattering signal is received by the ultrasonic transducer, it will also be measured in the Artifacts are produced in images of deep areas of the body. Due to the lack of constraints or restrictions on the shape and position of the surface of the object to be measured, the illumination distribution area on the surface of the object to be measured is usually less controllable, reducing the imaging quality stability of the photoacoustic tomography system. To this end, the present invention proposes a dark-field photoacoustic tomography imaging system and method, which uses photoacoustic tomography dark-field illumination to solve the shortcomings of the existing technology.

In the present invention, the object to be measured is supported and the surface shape is constrained by the load-bearing shaping module; the irradiation range of the expanded-beam pulse light on the surface of the object to be measured is different from the effective ultrasonic detection range of the ultrasonic detection module on the surface of the object to be measured. There is an overlapping area, or the area of the overlapping area between the irradiation range of the expanded beam pulse light on the surface of the object to be measured and the effective ultrasonic detection range of the ultrasonic detection module on the surface of the object to be measured is not larger than the irradiation range of the expanded beam pulse light on the surface of the object to be measured. 50%; the effective imaging area of the object to be measured is the area covered by the effective ultrasonic detection range of the ultrasonic detection module within the body to be measured. The effective imaging area includes the surface area and the deep area. The surface area is close to the load-bearing shaping module, and the deep area is far away from the load-bearing shaping module. module. Adjust the relative position and angle between the illumination range of the expanded beam pulse light on the surface of the object to be measured and the effective imaging area of the object to be measured. The expanded beam pulse light does not directly illuminate the surface area in the effective imaging area. The area realizes photoacoustic tomography dark field illumination, so that after the expanded beam pulse light propagates and attenuates in the object to be measured, it provides a more uniform light flux distribution in the effective imaging area than the traditional photoacoustic tomography system.

The method of the present invention can reduce the artifacts of strong photoacoustic signals in the surface area in the image, and also helps to reduce the requirements of the imaging system for the data sampling depth, that is, the digital resolution, in the data acquisition module. By optimizing the illumination area and ultrasonic detection range, standardizing the position and shape of the object to be measured, the artifacts of ultrasonic signals generated in the superficial area of the object to be measured in the deep area are greatly reduced, and the image clarity and image clarity of the photoacoustic tomography system are improved. Image quality stability.

Description of the drawings

Figure 1 is a schematic structural diagram of the photoacoustic tomography system of the present invention.

Figure 2 is a schematic diagram of dark field illumination of the photoacoustic tomography system of the present invention.

Figure 3 is an example of imaging the internal blood vessels of the female breast according to the present invention.

Figure 4 is a schematic diagram of placing light guide modules on both sides of the arc-shaped ultrasonic transducer array of the present invention to form double-sided dark field illumination.

Figure 5 is a schematic diagram of placing a light guide module on one side of the polygonal ultrasonic transducer array of the present invention to form single-sided dark field illumination.

Figure 6 is a schematic diagram of the bearing shaping module of the present invention.

Figure 7 is a schematic structural diagram of a hemispherical ultrasonic transducer array combined with annular dark field illumination according to the present invention.

Figure 8 is a schematic structural diagram of a polyhedral ultrasonic transducer array combined with polygonal dark field illumination of the present invention.

Detailed ways

In order to improve the imaging performance and image quality of the photoacoustic tomography system, the present invention proposes a dark-field photoacoustic tomography system; the technical solution of the present invention will be further described below in conjunction with the accompanying drawings and specific embodiments of the description.

A dark-field photoacoustic tomography system provided by the present invention is shown in Figure 1. The system includes a pulse light generation module 1, a light guide module 2, an ultrasonic detection module 3, a load-bearing shaping module 4, and a spatial scanning module 5. Data acquisition module 6 and image reconstruction module 7.

The pulse light generation module 1 includes one or more light sources for generating a single-wavelength or multi-wavelength pulse light beam; the pulse light is a single-wavelength light beam or a multi-wavelength light beam, with a wavelength range of 0.3 μm-3 μm. The pulsed light generation module 1 is an existing technology, such as Nd:YAG nanosecond pulse laser.

The light guide module 2 includes a reflector, a prism, a scattering sheet, a lens, an optical fiber and/or a light guide arm, and is used to expand and/or shape the pulse beam emitted by the pulse light generation module 1 to form an expanded pulse light. , the expanded beam pulse light is irradiated to the object to be measured, and the light-absorbing component in the object to be measured absorbs the energy of the expanded beam pulse light and undergoes local pressure changes, and propagates ultrasonic signals in the form of ultrasonic waves in multiple directions outside the body to be measured; the object to be measured is optional It is one or several combinations of living organisms, biological tissues, and non-living entities.

The expanded beam pulse light attenuates in the body to be measured, and its attenuation characteristics obey the Beer-Lambert law, that is, the luminous flux in the body to be measured at a distance z from the body surface , of which/> is the luminous flux on the surface of the object to be measured, and the effective attenuation coefficient of the object to be measured at the pulse light wavelength/> , of which/> is the optical absorption coefficient of the object under test at the pulse light wavelength,/> is the optically reduced scattering coefficient of the object under test at the pulse light wavelength.

The ultrasonic detection module 3 includes multiple ultrasonic transducer units distributed around the object to be measured. The multiple ultrasonic transducer units form one or more ultrasonic transducer arrays. The ultrasonic transducer arrays are used in effective ultrasonic detection. It detects the ultrasonic signals propagating in multiple directions generated by the expanded beam pulse light in the object to be measured, and converts the ultrasonic signals into voltage signals for output; each transducer unit can choose the shape of self-focusing or non-self-focusing, The effective detection range of each transducer unit obeys the ultrasonic diffraction formula; the effective ultrasonic detection range of each ultrasonic transducer array or detection matrix also needs to obey the spatial sampling theorem.

The effective ultrasonic detection range of the ultrasonic detection module 3 is related to the distribution range, adjacent spacing, and detection ultrasonic signal wavelength of the ultrasonic transducer units of the ultrasonic transducer array. The spatial sampling spacing of the ultrasonic transducer array of the ultrasonic detection module 3 within the effective detection range is shorter than half the wavelength of the ultrasonic signal.

As shown in Figure 4, the ultrasonic detection module 3 includes one or more arc-shaped ultrasonic transducer arrays. The arc range of the ultrasonic transducer array is from 10 degrees to 359 degrees. The arc-shaped ultrasonic transducer arrays are combined to form the ultrasonic detection module 3. . Light guide modules 2 are placed on both sides of the arc-shaped ultrasonic transducer array to form bilateral dark field illumination.

As shown in Figure 5, the ultrasonic detection module 3 includes two or more linear ultrasonic transducer arrays, arranged to form a polygon or a part of a polygon. The light guide module 2 is placed on one side of the linear ultrasonic transducer array to form single-sided dark field illumination.

As shown in FIG. 7 , the ultrasonic detection module 3 includes multiple ultrasonic transducer units. The ultrasonic transducer units are arranged as part of a sphere in space to form a spherical ultrasonic transducer array. The light guide module 2 is placed on the edge of the spherical ultrasonic transducer array to form annular dark field illumination.

As shown in FIG. 8 , the ultrasonic detection module 3 includes multiple ultrasonic transducer units. The ultrasonic transducer units are arranged as part of a polyhedron in space, forming a polyhedral ultrasonic transducer array. A light guide module is placed in the gap between the ultrasonic transducer units of the polyhedral ultrasonic transducer array to form polygonal dark field illumination.

The carrying shaping module 4 carries the object to be measured by installing the shaping groove and constrains the shape and orientation of the surface 10 of the object to be tested to be the same or similar to expected, thereby making the irradiation range and incident angle of the expanded beam pulse light on the surface of the object to be measured 10 stable. Controllable, as shown in Figure 6. The load-bearing shaping module 4 carries and shapes the object to be measured by installing a shaping groove 401 near the imaging window. The shaping groove 401 is made of solid or non-deformable materials, including epoxy resin, plastic, silicone, rubber, etc. The load-bearing shaping module 4 leaves a window 402 near the effective imaging area 9 for the expanded pulse light and/or ultrasound signals to pass through. The window is covered with a material that light and/or ultrasound can easily pass through, including glass, acrylic, and transparent resin. , transparent plastic and other materials, while ensuring to constrain the shape of the surface 10 of the object to be measured, it also ensures that it does not block the illumination of the expanded beam pulse light on the object to be measured, nor does it block the detection of ultrasonic signals by the ultrasonic detection module 3 .

The effective imaging area 9 of the object to be measured is the area covered by the effective ultrasonic detection range of the ultrasonic detection module 3 within the object to be measured, and is a section with a certain thickness of the object to be measured or the three-dimensional space of the object to be measured. The effective imaging area 9 includes a surface area and a deep area. The surface area is close to the bearing shaping module 4 and the deep area is far away from the bearing shaping module 4 . The vertical distance between the surface area of the effective imaging area 9 and the surface 10 of the object to be measured is 0 to 1 mm, and the vertical distance between the deep area of the effective imaging area 9 and the surface 10 of the object to be measured is greater than 1 mm and less than 100 mm.

The relative position and angle between the illumination range of the expanded-beam pulse light on the surface of the object to be measured 10 and the effective imaging area 9 of the object to be measured are adjusted by the light guide module 2, so that the expanded-beam pulse light is illuminated on the surface of the object to be measured 10. There is no overlapping area between the range and the effective ultrasonic detection range of the ultrasonic detection module 3 on the surface of the object to be measured 10, or the area of the overlapping area is not greater than 50% of the irradiation range of the expanded beam pulse light on the surface of the object to be measured 10, so that effective imaging is achieved The surface area of area 9 realizes photoacoustic tomography dark field illumination. As shown in Figure 2;

The irradiation direction of the expanded-beam pulse light points or approximately points to the center of the effective imaging area 9. The straight-line distance from the irradiation area of the surface 10 of the object to be measured to the center of the effective imaging area 9 does not exceed 5 cm. After propagating and attenuating in the body, the intensity of the light flux distribution in the effective imaging area is at least higher than 1/1000 of the strongest light flux on the surface 10 of the body to be measured.

The irradiation range of the expanded beam pulse light on the surface 10 of the object to be measured matches the size and shape of the effective imaging area 9, so that the expanded beam pulse light propagates in the object to be measured and is scattered by the object to be measured. The light flux distribution in the object to be measured is Covering the deep area and surface area of the effective imaging area 9, the relationship between the strongest luminous flux in the effective imaging area 9 and the weakest luminous flux in the effective imaging area 9 is: the ratio of the strongest luminous flux to the weakest luminous flux is less than or equal to 200.

The spatial scanning module 5 includes a motion module and a guide rail, which are used to adjust the relative position of the object to be measured and the ultrasonic detection module 3, so that the effective imaging area 9 in the object to be measured overlaps the area that the operator wishes to observe, and at the same time, the light is increased. Acoustic tomography system imaging range. The relative position or angle of the object to be measured and the photoacoustic tomography system is fed back through the positioning lens or marked positioning points.

The data acquisition module 6 amplifies, collects, processes, transmits and stores the voltage signal output by the ultrasonic detection module 3, and outputs signal data. The amplitude of the signal data is proportional to the ultrasonic signal amplitude and also proportional to the local pressure change amplitude in the body to be measured. . The data acquisition module 6 is an existing technology, such as PST's LEGION ADC.

The image reconstruction module 7 performs image reconstruction of the object to be measured based on the time information and amplitude information contained in the signal data of the data acquisition module 6, and calculates the local pressure change amplitude in the effective imaging area 9 distribution, and then calculate the distribution of the concentration of each light-absorbing chromophore in the object to be tested, and generate an image of the object to be tested.

Figure 3 shows an example of imaging of internal blood vessels in the female breast. The image reflects that there are still certain blood vessel signals at a depth of nearly 4cm that are not interfered by signals from the body surface, forming a clearer blood vessel image; while conventional photoacoustic tomography The imaging equipment will be severely interfered by strong signals from the body surface at a depth of 4cm, making it impossible to determine the exact source of the ultrasound signal at this location.

The local pressure change amplitude is proportional to the optical absorption coefficient of the light-absorbing component The product of the local luminous flux F, the optical absorption coefficient of the light-absorbing component/> Able to characterize the concentration of each light-absorbing chromophore in the object to be measured, in order to based on the local pressure change amplitude Finally, the optical absorption coefficient of the light-absorbing component in the object to be measured is obtained/> , it is necessary to provide a relatively uniform or controllable light flux F distribution for the effective imaging area 9 .

In this embodiment, each data acquisition channel of the data acquisition module 6 corresponds to each ultrasonic transducer unit of the ultrasonic transducer array 8 one-to-one. Therefore, a two-dimensional image of the object to be measured can be completed after each illumination pulse. Cross-sectional imaging. The spatial scanning module 5 can manually, automatically, or adaptively move or rotate the object under test or the photoacoustic tomography device according to the position of the object under test fed back by the positioning lens or the marked positioning point, thereby providing a larger view in the three-dimensional space. imaging range.

Specifically, the hemispherical ultrasonic transducer array 8, under the action of the spatial scanning module 5, can provide dense spatial sampling of the object to be measured in the three-dimensional space, and achieve uniform spatial resolution in all directions within the three-dimensional effective imaging area 9. At the same time, the array can also receive ultrasonic signals propagating in multiple directions in three-dimensional space.

The dark-field photoacoustic tomography method described in this embodiment is implemented based on the above-mentioned dark-field photoacoustic tomography system and includes the following steps:

Step 1: Design and test the effective ultrasonic detection range of the ultrasonic detection module 3. If the design process is under simulation conditions, the acoustic characteristics of the ultrasonic transducer array 8 can be calculated and simulated with the help of theoretical calculations, sound field simulation software or finite element analysis, and its sound field distribution and other parameters can be analyzed to determine its effective ultrasonic Detection range; if under experimental conditions, single-channel ultrasonic transducers, ultrasonic microphones and other testing tools can be used to measure the sound field characteristics of the ultrasonic transducer array 8 to determine its effective ultrasonic detection range;

Step 2: Install the load-bearing shaping module 4 according to the effective ultrasonic detection range of the ultrasonic detection module 3, and further calibrate the positional relationship between the pulse illumination area to be implemented and the body-to-be-tested load-bearing shaping module 4;

Step 3: Determine the position and size of the light spot in the pulse illumination area to be implemented according to the type of object to be measured and the size of the effective imaging area 9;

Select diffusers with different characteristics according to needs, specifically: select the size of the diffuser according to the spot size of the pulse beam emitted by the pulse light generation module 1, select the shape of the diffuser according to the installation method of the light guide module 2, and select the size of the diffuser according to the amplitude of the reconstructed image. The size of the diffusion angle, preliminary calculation of the approximate spatial distance from the diffusion sheet to the imaging window 402 on the load-bearing shaping module 4;

Apply the law of refraction Calculate the incident angle when the expanded beam pulse light enters the imaging window 402, so that the illumination area of the expanded beam pulse light is within the effective imaging area 9 of the ultrasonic detection module 3, and the illumination direction points to or approximately points to the center of the effective imaging area 9;

Based on the spatial distance and incident angle calculated by the above theory, the light guide module 2 is installed to guide the light beam emitted by the pulse light generation module 1 to illuminate the intended illumination area after shaping and expanding. Further, by adjusting the optical device of the light guide module 2, the illumination range and angle are adjusted to overlap with the pulse illumination area calibrated in the theoretical calculation, so as to realize photoacoustic tomography dark field illumination. In this step, optical measurement devices such as laser developing paper, energy/power meter, or spot measuring instrument can be placed in the area to be illuminated to determine the actual illumination range, angle, energy uniformity and other parameters;

Step 4: Place a bionic prosthesis (such as agar) with acoustic characteristics similar to the human body in the body-to-be-tested body-bearing shaping module 4 and test its imaging effect. Optimize the imaging quality by fine-tuning the range and angle of illumination. After the optimization is completed, confirm that the optical energy density and power density in the intended imaging area comply with the American National Laser Safety Standard (ANSI, z136.131–2014). Since then, the relative positions and angles of the pulse beam, the ultrasonic detection module 3, and the load-bearing shaping module 4 have been optimized and relatively stable;

Step 5: Install and adjust the spatial scanning module 5. The relative position of the object to be measured and the photoacoustic tomography system can be adjusted manually, automatically, or adaptively according to the placement position of the object to be tested as fed back by the shaping module 4, so that The target imaging area in the object to be measured overlaps with the ultrasonic imaging detection area;

Step 6: Place the sample to be tested and complete illumination excitation, ultrasonic detection, spatial scanning, data collection, and image reconstruction.

Claims (1)

1. A dark-field photoacoustic tomography system, characterized in that it includes a light guide module, an ultrasonic detection module and a load-bearing shaping module; The light guide module expands and/or shapes the pulse beam to form an expanded beam pulse light that irradiates the object to be measured. The component in the object to be measured that absorbs the expanded beam pulse light absorbs the energy of the expanded beam pulse light and generates local pressure. Changes, local pressure changes propagate ultrasonic signals in the form of ultrasonic waves in multiple directions outside the body to be measured; the ultrasonic detection module detects ultrasonic signals propagating in multiple directions, and converts the ultrasonic signals into voltage signals; the load-bearing plastic By installing a shaping groove, the shape module carries the object to be measured and constrains the surface shape and orientation of the object to be measured, thereby making the irradiation range and incident angle of the expanded beam pulse light on the surface of the object to be measured stable and controllable; The light guide module adjusts the irradiation range of the expanded-beam pulse light on the surface of the object to be measured, thereby adjusting the relative position and angle between the effective ultrasonic detection range of the object to be measured and the ultrasonic detection module, so that the expanded-beam pulse light can illuminate the surface of the object to be measured. There is no overlapping area between the irradiation range of the surface and the effective ultrasonic detection range of the ultrasonic detection module on the surface of the object to be measured, or the area of the overlapping area is not greater than 50% of the irradiation range of the expanded beam pulse light on the surface of the object to be measured, forming dark field illumination; The subject to be tested is one or several combinations of living organisms, biological tissues or non-living bodies; The ultrasonic detection module includes multiple ultrasonic transducer units, which are distributed around the object to be measured. The multiple ultrasonic transducer units form one or more ultrasonic transducer arrays, and the ultrasonic transducer arrays are within the effective ultrasonic detection range. Detects the ultrasonic signals propagating in multiple directions generated by the expanded beam pulse light in the object to be measured, and converts the ultrasonic signals into voltage signals for output; each transducer unit can choose a self-focusing or non-self-focusing shape. The effective detection range of the transducer unit obeys the ultrasonic diffraction formula; the effective ultrasonic detection range of each ultrasonic transducer array or detection matrix also obeys the spatial sampling theorem; The ultrasonic detection module can be designed in different forms according to different needs, specifically: (1) The ultrasonic detection module includes one or more arc-shaped ultrasonic transducer arrays. The arc range of the ultrasonic transducer array is from 10 degrees to 359 degrees. The arc-shaped ultrasonic transducer array forms an arc-shaped ultrasonic transducer module; (2) The ultrasonic detection module includes two or more linear ultrasonic transducer arrays, arranged to form a polygon or a part of a polygon; (3) The ultrasonic detection module includes multiple ultrasonic transducer units, which are arranged as part of a sphere in space to form a spherical ultrasonic transducer array; (4) The ultrasonic detection module includes multiple ultrasonic transducer units. The ultrasonic transducer units are arranged in space as part of a polyhedron to form a polyhedral ultrasonic transducer array; Light guide modules are placed on both sides of the arc-shaped ultrasonic transducer array to form double-sided dark field illumination; light guide modules are placed on one side of the linear ultrasonic transducer array to form single-sided dark field illumination; spherical ultrasonic transducers Light guide modules are placed at the edge of the array to form annular dark field illumination; light guide modules are placed in the gaps between the ultrasonic transducer units of the polyhedral ultrasonic transducer array to form polygonal dark field illumination; The load-bearing shaping module carries and shapes the object to be measured by installing a shaping slot near the imaging window. The shaping slot is made of solid or non-deformable material; the load-bearing shaping module leaves room for beam expansion pulses near the effective imaging area. The imaging window through which light and ultrasonic signals pass through is covered with a material that light and ultrasound can easily pass through. It ensures that the surface shape of the object to be measured is constrained while ensuring that it does not block the irradiation of the expanded beam pulse light on the object to be measured, nor does it block ultrasound. The detection module detects ultrasonic signals; The effective imaging area is the area covered by the effective ultrasonic detection range of the ultrasonic detection module in the body to be measured, which is a section of a certain thickness of the body to be measured or the three-dimensional space of the body to be measured; the effective imaging area includes a surface area and a deep area, and the surface area is close to Bearing the shaping module, the deep area is far away from the bearing shaping module; the vertical distance between the surface area of the effective imaging area and the surface of the body under test that is close to the bearing shaping module is 0 to 1 mm, and the distance between the deep area of the effective imaging area is close to the surface of the bearing shaping module. The vertical distance on the surface of the object to be measured is greater than 1mm and less than 100mm; The irradiation direction of the expanded-beam pulse light points or approximately points to the center of the effective imaging area. The straight-line distance from the irradiation area on the surface of the object to be measured to the center of the effective imaging area does not exceed 5cm. The expanded-beam pulse light propagates in the object to be measured and After attenuation, the light flux distribution intensity in the deep area of the imaging area is at least 1/1000 higher than the strongest light flux on the surface of the object to be measured; The irradiation range and angle of the expanded beam pulse light on the surface of the object to be measured match the size and shape of the effective imaging area, so that the luminous flux distribution in the object to be measured after the expanded beam pulse light propagates and scatters in the object to be measured covers the effective imaging area In the deep area and surface area, the relationship between the strongest luminous flux in the effective imaging area and the weakest luminous flux in the effective imaging area is: the ratio of the strongest luminous flux to the weakest luminous flux is less than or equal to 200; The dark-field photoacoustic tomography system also includes: a pulse light generation module, a spatial scanning module, a data acquisition module and an image reconstruction module: The pulse light generation module includes one or more light sources for generating single-wavelength or multi-wavelength pulse light beams; the spatial scanning module adjusts the relative position of the object to be measured and the main body of the photoacoustic imaging system; the data acquisition module The voltage signal output by the ultrasonic detection module is processed to output signal data; the image reconstruction module calculates the distribution of the concentration of each light-absorbing chromophore in the object to be tested based on the signal data, and generates an image of the object to be tested; The spatial scanning module adjusts the effective imaging area of the object to be measured to overlap with the area that the operator expects to observe, and at the same time increases the imaging range of the photoacoustic tomography system; specifically, it feeds back the object to be tested and the photoacoustic layer through positioning lenses or marking positioning points. Analyze the relative position or angle of the main body of the imaging system; according to the placement position of the object to be measured, move or rotate the relative position of the main body of the photoacoustic imaging system and the object to be measured by any one or more of manual, automatic, and adaptive methods; The main body of the photoacoustic imaging system includes: pulse generation module, light guide module, ultrasonic detection module and data acquisition module; The data acquisition module collects, processes, transmits and stores the voltage signal output by the ultrasonic detection module, and outputs signal data. The amplitude of the output signal data is proportional to the amplitude of the ultrasonic signal related to the type of object to be measured, and is also proportional to the amplitude of the ultrasonic signal to be measured. The local pressure change amplitude in the measuring body; The image reconstruction module reconstructs the image of the object to be measured based on the time information and amplitude information contained in the signal data of the data acquisition module, calculates the distribution of local pressure change amplitude p ₀ in the effective imaging area, and then calculates each light absorption in the object to be measured The distribution of chromophore concentration generates an image of the object to be measured; The local pressure change amplitude is proportional to the product of the optical absorption coefficient μ _α of the light-absorbing component and the local light flux F. The optical absorption coefficient μ _α of the light-absorbing component can characterize the concentration of each light-absorbing chromophore in the object to be measured. In order to based on the local pressure change amplitude p ₀ To finally obtain the optical absorption coefficient μ _α of the light-absorbing component in the object to be measured, it is necessary to provide a relatively uniform or controllable light flux F distribution in the effective imaging area according to the pulse light generation module, light guide module and type of object to be measured; The imaging method based on the above-mentioned dark field photoacoustic tomography system includes the following steps: Step 1: Design and test the effective ultrasonic detection range of the ultrasonic detection module; Step 2: Install the load-bearing shaping module according to the effective ultrasonic detection range of the ultrasonic detection module, and fix the position of the load-bearing shaping module, thereby further calibrating the positional relationship between the pulse illumination area and the load-bearing shaping module; Step 3: Determine the preliminary installation position and angle of the light guide module, install the light guide module, and guide the beam emitted by the pulse light generation module to illuminate the intended illumination area after shaping and expanding it; adjust the illumination range by adjusting the optical devices of the light guide module and angle, overlapping with the pulse illumination area calibrated in step 2 to achieve photoacoustic tomography dark field illumination; Step 4: Place a bionic prosthesis with acoustic characteristics similar to that of the human body in the body-to-be-tested body-bearing shaping module to test its imaging effect. Optimize the imaging quality by fine-tuning the range and angle of illumination; after the optimization is completed, determine the area within the intended imaging area. Whether the optical energy density and power density comply with the US national laser safety standards; if they comply, the relative positions and angles of the pulse beam, ultrasonic detection module, and load-bearing shaping module can be optimized and relatively stable; if they do not comply, continue to adjust; Step 5: According to the placement position of the object under test fed back by the load-bearing shaping module, use the spatial scanning module to manually, automatically or adaptively adjust the relative position of the object under test and the main body of the photoacoustic tomography system so that the target imaging area of the object under test is Overlap with the effective imaging area; Step 6: After the test is completed, place the sample to be tested. Based on the dark-field photoacoustic tomography system, the illumination excitation, ultrasonic detection, spatial scanning, data acquisition, and image reconstruction are completed to obtain an image of the body to be tested.