Variable imaging size photoacoustic imaging device based on sector-shaped ultrasonic transducer array

Abstract

The present invention relates to a variable-size photoacoustic imaging device based on a sector-shaped ultrasonic transducer array. The device is characterized by employing N sector-shaped ultrasonic transducer array structures to receive photoacoustic signals, where N ≥ 2, and each sector-shaped ultrasonic transducer array structure is used to receive a photoacoustic signal. Another technical solution of the present invention provides a variable-size photoacoustic imaging method based on a sector-shaped ultrasonic transducer array, characterized by employing the aforementioned variable-size photoacoustic imaging device. The full-ring ultrasonic detection array structure provided by the present invention can adaptively adjust the size of the full-ring receiving surface for imaging targets of varying sizes, thereby significantly increasing the flexibility of the PAT imaging system.

Description

Technical Field

[0001] The invention relates to a photoacoustic imaging device with variable imaging size based on a sector-shaped ultrasonic transducer array and an imaging method using the photoacoustic imaging device. Background Art

[0002] Photoacoustic imaging has unique advantages because it combines the advantages of high optical contrast and high spatial resolution of ultrasound in signal morphology. Photoacoustic imaging based on the photoacoustic effect is a non-invasive biomedical imaging technology that is used in medical imaging for imaging of everything from cells to organs. The working principle of the photoacoustic imaging system is to evenly project a beam of instantaneous pulsed parallel light onto the imaging object. The absorption of light energy by the target object causes thermal expansion, thereby generating a photoacoustic signal (hereinafter referred to as PA signal, an ultrasound signal generated by the photoacoustic effect). In terms of imaging characteristics, on the one hand, the scattering of ultrasound signals by physiological tissues is 2 to 3 orders of magnitude lower than that of light scattering. Therefore, ultrasound signals are used to reconstruct images in photoacoustic imaging, which can provide higher spatial resolution when imaging deep tissues. On the other hand, compared with ultrasound imaging, photoacoustic imaging combines the characteristics of high optical contrast and can also provide a variety of functional information.

[0003] In photoacoustic tomography (PAT) systems, photoacoustic signals detected by an ultrasound array probe are used to reconstruct the photoacoustic image. The size of the photoacoustic signal region received by the ultrasound array probe determines the PAT imaging system's field of view. However, in current, commonly used PAT imaging systems, the size and shape of the ultrasound transducer array are fixed, making it incapable of adapting to imaging targets of varying sizes. This severely limits the PAT imaging system's imaging applications.

[0004] PAT imaging systems often use a ring-shaped ultrasonic detection array (UT array) with a fixed diameter. However, this UT array cannot adjust the ring radius for imaging targets of varying sizes, limiting the flexibility of PAT imaging systems in clinical applications. For example, breast cancer screening requires a PAT imaging system to perfectly match the female breast, which varies greatly in size. Summary of the Invention

[0005] The technical problem to be solved by the present invention is that in the currently common PAT imaging system, the size and shape of the ultrasonic transducer array are fixed and cannot adapt to imaging targets of different sizes.

[0006] In order to solve the above technical problems, a technical solution of the present invention is to provide a variable imaging size photoacoustic imaging device based on a fan-shaped ultrasonic transducer array, characterized in that N fan-shaped ultrasonic transducer array structures are used to receive photoacoustic signals, N ≥ 2, and each fan-shaped ultrasonic transducer array structure is used to receive photoacoustic signal;

[0007] Each sector-shaped ultrasonic transducer array structure includes a body, a side of which is formed with an arc-shaped receiving surface, and M ultrasonic receiving units are evenly distributed on the receiving surface, where M is greater than or equal to 2;

[0008] The receiving surfaces of all fan-shaped ultrasonic transducer array structures constitute a full-ring receiving surface, and the distance between the receiving surface of the fan-shaped ultrasonic transducer array structure and the imaging center is adjustable. After adjustment, the distance between the imaging field center and the receiving surface is less than, equal to, or greater than the arc radius of the receiving surface.

[0009] Preferably, the ultrasonic receiving units on the N sector-shaped ultrasonic transducer array structures respectively have N different center frequencies.

[0010] Another technical solution of the present invention is to provide a variable imaging size photoacoustic imaging method based on a sector-shaped ultrasonic transducer array, characterized in that the variable imaging size photoacoustic imaging device described above is used, and the method includes the following steps:

[0011] The receiving surfaces of the N sector-shaped ultrasonic transducer array structures form a full-ring receiving surface to receive photoacoustic signals;

[0012] If the distance between the center of the imaging field and the receiving surface is equal to the arc radius of the receiving surface, the annular ultrasonic array composed of N fan-shaped ultrasonic transducer array structures is regarded as an ideal annular ultrasonic array, and the photoacoustic image is reconstructed directly using the signals received by the N fan-shaped ultrasonic transducer array structures through a back-projection algorithm;

[0013] If the distance between the center of the imaging field and the receiving surface is greater than or less than the arc radius of the receiving surface, after obtaining the signals received by the N sector-shaped ultrasonic transducer array structures, a data shift operation in the digital domain is performed to eliminate errors caused by the physical gap. By performing data shift processing on the signal, the processed signal is regarded as the signal received by the ideal annular ultrasonic array, and the signal is used to reconstruct the photoacoustic image through a back-projection algorithm.

[0014] Preferably, when performing the data shift operation, the number of data shift bits of each ultrasonic receiving unit is calculated, and the number of data shift bits of the mth ultrasonic receiving unit on the receiving surface of the nth sector-shaped ultrasonic transducer array structure is s nm , then:

[0015]

[0016] In formula (1), d nmis the gap error between the position of the mth ultrasonic receiving unit on the receiving surface of the nth sector-shaped ultrasonic transducer array structure and the corresponding position on the receiving surface of the ideal annular ultrasonic array; v is the propagation speed of ultrasound in the imaging device; f s is the data acquisition sampling rate.

[0017] Preferably, if the distance between the center of the imaging field and the receiving surface (1-1) is greater than the arc radius of the receiving surface (1-1), the gap error d nm The calculation method includes the following steps:

[0018] Step 1: Line segment 1 connecting the center O2 of the ideal annular ultrasonic array and the edge of the receiving surface where the mth ultrasonic receiving unit is located, line segment 2 connecting the center O1 corresponding to the receiving surface and the edge on the same side of the receiving surface where the mth ultrasonic receiving unit is located, and line segment 3 connecting the center O2 and the center O1 form triangle 1. The length of line segment 1 is the radius r2 of the ideal annular ultrasonic array, the length of line segment 2 is the arc radius r1 of the current receiving surface, and the length of line segment 3 is the distance between the center O2 and the center O1. Then, the angle β between line segment 3 and line segment 2 is calculated using the law of cosines.

[0019] Step 2: Calculate the angle α between line segment 2 and line segment 4, where line segment 4 is a line segment connecting the center O1 and the location of the m-th ultrasonic receiving unit. The angle α is obtained by using the distribution position of the m-th ultrasonic receiving unit on the current receiving surface.

[0020] Step 3: Line segments 3, 4, and 5 form triangle 2. Line segment 5 is the line segment connecting the center O2 and the location of the mth ultrasonic receiving unit. The length of line segment 4 is the arc radius r1 of the current receiving surface. The angle between line segment 3 and line segment 5 is (α+β). The length a of line segment 5 is obtained by using the law of cosines. Then d nm =a-r2.

[0021] Preferably, if the distance between the center of the imaging field and the receiving surface is smaller than the arc radius of the receiving surface, the gap error d nm The calculation method includes the following steps:

[0022] Step 1: Line segment 6 connecting the center O2 of the ideal annular ultrasonic array and the edge of the receiving surface where the mth ultrasonic receiving unit is located, line segment 7 connecting the center O1 corresponding to the receiving surface and the edge on the same side of the receiving surface where the mth ultrasonic receiving unit is located, and line segment 8 connecting the center O2 and the center O1 form triangle 3. The length of line segment 6 is the radius r2 of the ideal annular ultrasonic array, the length of line segment 7 is the arc radius r1 of the current receiving surface, and the length of line segment 8 is the distance between the center O2 and the center O1. Then, the angle β between line segment 8 and line segment 7 is calculated using the law of cosines.

[0023] Step 2: Calculate the angle α between line segment 7 and line segment 9, where line segment 9 is a line segment connecting the center O1 and the location of the m-th ultrasonic receiving unit. The angle α is obtained by using the distribution position of the m-th ultrasonic receiving unit on the current receiving surface.

[0024] Step 3: Line segments 8, 9, and 10 form triangle 4. Line segment 10 is the line segment connecting the center O2 and the location of the mth ultrasonic receiving unit. The length of line segment 9 is the arc radius r1 of the current receiving surface. The angle between line segment 8 and line segment 9 is (β-α). The length a of line segment 10 is obtained by using the law of cosines. Then d nm =a-r2.

[0025] The full-ring ultrasonic detection array structure provided by the present invention can adaptively adjust the size of the full-ring receiving surface for imaging targets of different sizes, thereby significantly increasing the flexibility of the PAT imaging system. For clinical applications of photoacoustic imaging, such as photoacoustic imaging of the breast, the present invention can adjust the structure of the full-ring ultrasonic detection array for different breast sizes, better collect photoacoustic signals, and improve imaging quality. Similarly, the full-ring ultrasonic detection array structure provided by the present invention can be applied to imaging of special areas such as the neck, and the size of the receiving surface can be flexibly adjusted to suit the application scenario of neck imaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is a schematic diagram of a fan-shaped ultrasonic transducer array structure in an embodiment;

[0027] Figures 2 to 4 The full-ring ultrasonic detection array structures are shown in three different cases;

[0028] Figure 5A The distribution simulation of the fan-shaped ultrasonic transducer array structure with a radius of 6mm;

[0029] Figure 5B for Figure 5A Corresponding imaging results;

[0030] Figure 6A The radius is Distribution simulation of fan-shaped ultrasonic transducer array structure;

[0031] Figure 6B for Figure 6A Corresponding imaging results;

[0032] Figure 7A The distribution and error calibration model of the sector-shaped ultrasonic transducer array structure with an imaging area radius greater than 60 mm;

[0033] Figure 7BThe distribution and error calibration model of the sector-shaped ultrasonic transducer array structure when the imaging area radius is less than 60 mm;

[0034] Figure 8 This is a resizable PAT system setup based on four sector-shaped ultrasonic transducer array structures. In the figure: SUTA is the sector-shaped ultrasonic transducer array, WT is the water tank, Amp is the amplifier, DAQ is the data acquisition, PC is the personal computer, FG is the function generator, CnL is the convex lens, GrdG is the ground glass, and Syn-Trig is the synchronization trigger signal;

[0035] Figure 9A Take photos of blood vessels for 3D printing;

[0036] Figure 9B This is the PAT imaging result of the phantom. DETAILED DESCRIPTION

[0037] Below in conjunction with specific embodiment, further set forth the present invention.Should be understood that these embodiments are only used to illustrate the present invention and are not used in limiting the scope of the present invention.In addition, should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall equally within the scope limited by the appended claims of the application.

[0038] The transducer used for PA signal detection is an important component of the PAT imaging system. For the PAT imaging system setting, it is ideal to use a full 360° PA signal detection, such as using a ring ultrasound array to receive the PA signal for image reconstruction. Based on this, the present invention designs the following Figure 1 The illustrated sector-shaped ultrasonic transducer array structure includes a main body 1, with an arc-shaped receiving surface 1-1 formed on the side of the main body 1. The surfaces of the main body 1 that connect to the left and right edges of the receiving surface 1-1 are bonding surfaces 1-2. Thirty-two ultrasonic receiving units 2 are evenly distributed on the receiving surface 1-1, forming a sector-shaped distribution. In this embodiment, the spacing between two adjacent ultrasonic receiving units 2 is 0.2 mm. Each ultrasonic receiving unit 2 has a width of 2.317 mm and a height of 10 mm. In this embodiment, the arc radius R of the receiving surface 1-1 is designed to be 60 mm. The main body 1 has a length L = 90 mm, a width W = 90 mm, and a height H = 20 mm. In this embodiment, the sector arc of the receiving surface 1-1 is 70.8 degrees, which is one-fourth of the photoacoustic signal receiving portion. The 32 ultrasonic receiving units 2 are evenly distributed on the receiving surface 1-1.

[0039] The present invention discloses a fan-shaped ultrasonic transducer array structure having 32 ultrasonic receiving units 2 arranged into a fan-shaped ultrasonic transducer array for ultrasonic detection. Each fan-shaped ultrasonic transducer array is arranged within a 70.8-degree sector. The PAT imaging system uses four fan-shaped ultrasonic transducer array structures proposed in the present invention, and the four fan-shaped ultrasonic transducer arrays corresponding to the four fan-shaped ultrasonic transducer array structures are distributed around the imaging target at 90-degree intervals. The center frequencies of the four fan-shaped ultrasonic transducer arrays are 1 MHz, 2.5 MHz, 5 MHz, and 7.5 MHz, respectively, which can constitute multi-frequency PA signal reception, covering most of the frequency bandwidth of the PA signal in the PAT imaging system. The distribution radius of the four fan-shaped ultrasonic transducer arrays can be flexibly changed, so that the imaging target range can range from 50 mm to 90 mm, covering most application scenarios such as breast screening.

[0040] For most PAT imaging system configurations, the PA signal can be considered a broadband signal ranging from 1 MHz to 10 MHz. The present invention designs four fan-shaped ultrasonic transducer array structures with center frequencies of 1 MHz, 2.5 MHz, 5 MHz, and 7.5 MHz (those skilled in the art can also design ultrasonic transducers with other center frequencies based on system requirements, thereby realizing fan-shaped ultrasonic transducer array structures with other center frequencies). This can achieve full coverage of the PA signal spectrum. Each fan-shaped ultrasonic transducer array structure has a bandwidth exceeding 60%. The fan-shaped ultrasonic transducer array structure is encapsulated in a stainless steel housing to facilitate PA signal coupling and waterproofing.

[0041] The size-adjustable PAT imaging system proposed in this invention is based on the adjustment of different distributions of the sector-shaped ultrasonic transducer array structure. Depending on the distance from the imaging center to the receiving surface 1-1 in the sector-shaped ultrasonic transducer array structure, there are basically three distributions of the four sector-shaped ultrasonic transducer array structures:

[0042] like Figure 2 As shown, the distance from the imaging center to the receiving surface 1-1 of the sector-shaped ultrasonic transducer array structure 3 is less than the arc radius of the receiving surface 1-1, forming a small imaging range with a radius of 50 mm. It is suitable for small imaging targets with an imaging field radius of 50 mm. Moreover, in this case, the bonding surfaces 1-2 of two adjacent sector-shaped ultrasonic transducer array structures 3 are in contact, so that there is no gap between the four sector-shaped ultrasonic transducer array structures 3 around the imaging target, and the formed full-ring ultrasonic detection array structure can receive PA signals at all angles. Figure 3As shown, the distance from the imaging center to the receiving surface 1-1 of the sector-shaped ultrasonic transducer array structure 3 is equal to the arc radius of the receiving surface 1-1, forming an imaging range with a radius of 60mm. At this time, the arc centers of the receiving surfaces 1-1 of the four sector-shaped ultrasonic transducer array structures 3 completely coincide with the imaging field center. The distance between the imaging field center and the receiving surface 1-1 is the arc radius of the receiving surface 1-1. In order to obtain a larger imaging field of view, as shown in FIG. Figure 4 As shown, the distance from the imaging center to the receiving surface 1-1 of the sector-shaped ultrasonic transducer array structure 3 is greater than the arc radius of the receiving surface 1-1, forming a large imaging range with a radius greater than 60mm. The present invention can achieve an imaging area as large as 90mm, greatly expanding the imaging field of view.

[0043] The flexible distribution of the sector-shaped ultrasonic transducer array structure 3 allows for the formation of different ultrasonic detection areas, enabling adjustable PAT imaging fields. Different distributions of sector-shaped ultrasonic transducer array structures 3 follow different physical models. Therefore, when processing the received PA signal, the signal should be calibrated according to physical models with different parameters to facilitate PAT image reconstruction.

[0044] like Figure 3 As shown in the distribution of the fan-shaped ultrasonic transducer array structure 3, the annular ultrasonic array composed of four fan-shaped ultrasonic transducer array structures 3 can be regarded as an ideal annular ultrasonic array, and the photoacoustic image can be reconstructed directly by using the signals received by the four fan-shaped ultrasonic transducer array structures through the back projection algorithm.

[0045] like Figure 2 and Figure 4 The distribution of the sector-shaped ultrasonic transducer array structure 3 shown in Figure 3 shows that the ultrasonic receiving surface formed by the four sector-shaped ultrasonic transducer array structures 3 exhibits a signal reception distance error compared to an ideal annular ultrasonic array. Since the ultrasonic transducers in the sector-shaped ultrasonic transducer array structure 3 are non-focused, the error caused by the receiving direction is negligible. Therefore, the error caused by physical gaps can be eliminated through data shifting in the digital domain. After acquiring the signals received by the four sector-shaped ultrasonic transducer array structures, data shifting in the digital domain is performed to eliminate the error caused by physical gaps. After data shifting, the processed signals are treated as the signals received by the ideal annular ultrasonic array and used to reconstruct the photoacoustic image using a back-projection algorithm. Furthermore, as the imaging field increases, the gaps between each sector-shaped ultrasonic transducer array structure also increase. Therefore, for PAT image reconstruction, the PA signal should be interpolated based on nearby received signals to compensate for the missing reception angle.

[0046] When performing the data shift operation, the number of data shift bits of each ultrasonic receiving unit 2 is calculated. Suppose the number of data shift bits of the mth ultrasonic receiving unit 2 on the receiving surface 1-1 of the nth sector-shaped ultrasonic transducer array structure is s. nm , then:

[0047]

[0048] In formula (1), d nm is the gap error between the position of the mth ultrasonic receiving unit 2 on the receiving surface (1-1) of the nth sector-shaped ultrasonic transducer array structure and the corresponding position on the receiving surface of the ideal annular ultrasonic array; v is the propagation speed of ultrasound in the imaging device; f s is the data acquisition sampling rate.

[0049] like Figure 7A As shown, the distance between the center of the imaging field and the receiving surface 1-1 is greater than the arc radius of the receiving surface 1-1, then the gap error d nm The calculation method includes the following steps:

[0050] Step 1: Line segment 1 connecting the center O2 of the ideal annular ultrasonic array and the edge of the receiving surface 1-1 where the m-th ultrasonic receiving unit 2 is located, line segment 2 connecting the center O1 corresponding to the receiving surface 1-1 and the edge on the same side of the receiving surface 1-1 where the m-th ultrasonic receiving unit 2 is located, and line segment 3 connecting the center O2 and the center O1 form triangle 1. The length of line segment 1 is the radius r2 of the ideal annular ultrasonic array, the length of line segment 2 is the arc radius r1 of the current receiving surface 1-1, and the length of line segment 3 is the distance between the center O2 and the center O1. Then, the angle β between line segment 3 and line segment 2 is calculated using the law of cosines.

[0051] Step 2: Calculate the angle α between line segment 2 and line segment 4, where line segment 4 is a line segment connecting the center O1 and the position of the m-th ultrasonic receiving unit 2. The angle α is obtained by using the distribution position of the m-th ultrasonic receiving unit 2 on the current receiving surface 1-1.

[0052] Step 3: Line segments 3, 4, and 5 form triangle 2. Line segment 5 is a line segment connecting the center O2 and the location of the mth ultrasonic receiving unit 2. The length of line segment 4 is the arc radius r1 of the current receiving surface 1-1. The angle between line segment 3 and line segment 5 is (α+β). The length a of line segment 5 is obtained by using the cosine theorem, and d nm =a-r2.

[0053] like Figure 7B As shown, the distance between the center of the imaging field and the receiving surface 1-1 is smaller than the arc radius of the receiving surface 1-1, then the gap error d nmThe calculation method includes the following steps:

[0054] Step 1: Line segment 6 connecting the center O2 of the ideal annular ultrasonic array and the edge of the receiving surface 1-1 where the m-th ultrasonic receiving unit 2 is located, line segment 7 connecting the center O1 corresponding to the receiving surface 1-1 and the edge on the same side of the receiving surface 1-1 where the m-th ultrasonic receiving unit 2 is located, and line segment 8 connecting the center O2 and the center O1 form triangle 3. The length of line segment 6 is the radius r2 of the ideal annular ultrasonic array, the length of line segment 7 is the arc radius r1 of the current receiving surface 1-1, and the length of line segment 8 is the distance between the center O2 and the center O1. Then, the angle β between line segment 8 and line segment 7 is calculated using the law of cosines.

[0055] Step 2: Calculate the angle α between line segment 7 and line segment 9, where line segment 9 is a line segment connecting the center O1 and the position of the m-th ultrasonic receiving unit 2. The angle α is obtained by using the distribution position of the m-th ultrasonic receiving unit 2 on the current receiving surface 1-1.

[0056] Step 3: Line segments 8, 9, and 10 form triangle 4. Line segment 10 is a line segment connecting the center O2 and the location of the mth ultrasonic receiving unit 2. The length of line segment 9 is the arc radius r1 of the current receiving surface 1-1. The angle between line segment 8 and line segment 9 is (β-α). The length a of line segment 10 is obtained by using the law of cosines. Then, d nm =a-r2.

[0057] To verify the proposed size-adjustable PAT imaging system, different imaging fields were simulated using the MATLAB k-wave toolbox. The center frequencies of the ultrasound array of 32 ultrasound transducer units were 1 MHz, 2.5 MHz, 5 MHz, and 7.5 MHz, with a bandwidth of 60%, and the PA signals were detected at different radii. The sensor radius was set to 6 mm, and the radii of the imaging area were 6 mm and 7.5 mm, respectively. Simulate different PAT imaging areas, such as Figure 5A and 6A As shown in the figure, the four sector-shaped ultrasonic transducer arrays are oriented toward the center of the imaging area. A binary image of a vascular model simulated with the K-Wave Toolbox was used to generate the photoacoustic signal. To better simulate a realistic photoacoustic signal, a 40dB signal-to-noise ratio and a 100MHz sampling rate were set.

[0058] Figure 5B yes Figure 5A The reconstructed image is obtained by interpolating the simulated 128-channel data to 164 channels to compensate for the detection viewing angle limitation of the fan-shaped ultrasonic transducer array structure. The simulation results show that the present invention can clearly identify the contour of the blood vessel model and the artifacts can be ignored. Figure 6AIn the setup shown, the four fan-shaped ultrasonic transducer array structures that receive photoacoustic signals cannot be directly used for image reconstruction before calibration. In addition, the PA signal needs to be interpolated to compensate for the limited viewing angle. The reconstructed image is shown in Figure 6B As shown in Figure 3, the outline of the blood vessel model can be distinguished, but there are some artifacts. In addition, the signal processing of data shift will also produce some errors, resulting in some background artifacts.

[0059] The size-adjustable PAT imaging system proposed by the present invention is configured as follows: Figure 8 As shown. The laser pulse repetition frequency is 10 Hz and the wavelength is 755 nm. The PA signal is sampled using a 128-channel data acquisition (DAQ) module with a sampling rate of 40 MHz. The function generator is controlled by a computer and outputs a trigger signal to synchronize the laser with data acquisition. Adjustments are made through optical elements so that the laser is evenly irradiated on the imaging phantom. The imaging target is surrounded by four fan-shaped ultrasonic transducer array structures to ensure that the PA signal can be well detected. The center frequencies of the fan-shaped ultrasonic transducer array structures are 1 MHz, 2.5 MHz, 5 MHz and 7.5 MHz respectively. The four fan-shaped ultrasonic transducer array structures can form a ring array with a radius of 50 to 90 mm for PA signal detection.

[0060] The phantom is a 3D printed blood vessel model with a diameter of 0.5 mm, embedded in an agar block, such as Figure 9A The phantom imaging results are shown in Figure 9B As shown in the figure, the vascular model has clear contours and obvious background artifacts. Advanced image processing algorithms can further improve the imaging quality. The imaging results well demonstrate the feasibility of the proposed size-adjustable PAT imaging system.

Claims

1. A variable imaging size photoacoustic imaging device based on a sector-shaped ultrasonic transducer array, characterized in that: N fan-shaped ultrasonic transducer array structures are used to receive photoacoustic signals, N ≥ 2, and each fan-shaped ultrasonic transducer array structure is used to receive photoacoustic signal; Each sector-shaped ultrasonic transducer array structure comprises a body (1), a side surface of the body (1) is formed with an arc-shaped receiving surface (1-1), and M ultrasonic receiving units (2) are evenly distributed on the receiving surface (1-1), where M is greater than or equal to 2. The receiving surfaces (1-1) of all the sector-shaped ultrasonic transducer array structures form a full-ring receiving surface, and the distance between the receiving surface (1-1) and the imaging center of the sector-shaped ultrasonic transducer array structure is adjustable, so that after adjustment, the distance between the imaging field center and the receiving surface (1-1) is less than, equal to, or greater than the arc radius of the receiving surface (1-1); If the distance between the center of the imaging field and the receiving surface (1-1) is equal to the arc radius of the receiving surface (1-1), the annular ultrasonic array composed of N fan-shaped ultrasonic transducer array structures is regarded as an ideal annular ultrasonic array, and the photoacoustic image is reconstructed directly using the signals received by the N fan-shaped ultrasonic transducer array structures through a back-projection algorithm; If the distance between the center of the imaging field and the receiving surface (1-1) is greater than or less than the arc radius of the receiving surface (1-1), after obtaining the signals received by the N sector-shaped ultrasonic transducer array structures, a data shift operation in the digital domain is performed to eliminate errors caused by the physical gap, and the processed signal is regarded as a signal received by an ideal annular ultrasonic array by performing data shift processing on the signal, and the photoacoustic image is reconstructed using the signal through a back-projection algorithm; When performing the data shift operation, the number of data shift bits of each ultrasonic receiving unit (2) is calculated, and the number of data shift bits of the mth ultrasonic receiving unit (2) on the receiving surface (1-1) of the nth sector-shaped ultrasonic transducer array structure is s nm , then: In formula (1), d nm is the gap error between the position of the mth ultrasonic receiving unit (2) on the receiving surface (1-1) of the nth sector-shaped ultrasonic transducer array structure and the corresponding position on the receiving surface of the ideal annular ultrasonic array; v is the propagation speed of ultrasound in the imaging device; f s is the data acquisition sampling rate; If the distance between the center of the imaging field and the receiving surface (1-1) is greater than the arc radius of the receiving surface (1-1), the gap error d nm The calculation method includes the following steps: Step 1, a line segment 1 connecting the center O2 of the ideal annular ultrasonic array and the edge of the receiving surface (1-1) where the mth ultrasonic receiving unit (2) is located, a line segment 2 connecting the center O1 corresponding to the receiving surface (1-1) and the edge on the same side of the receiving surface (1-1) where the mth ultrasonic receiving unit (2) is located, and a line segment 3 connecting the center O2 and the center O1 form a triangle 1, the length of the line segment 1 is the radius r2 of the ideal annular ultrasonic array, the length of the line segment 2 is the arc radius r1 of the current receiving surface (1-1), and the length of the line segment 3 is the distance between the center O2 and the center O1, and the angle β between the line segment 3 and the line segment 2 is calculated using the law of cosines; Step 2: Calculate and obtain the included angle α between the second line segment and the fourth line segment, where the fourth line segment is a line segment connecting the center O1 and the position point of the mth ultrasonic receiving unit (2), and the included angle α is obtained using the distribution position of the mth ultrasonic receiving unit (2) on the current receiving surface (1-1); Step 3: Line segments 3, 4 and 5 form triangle 2. Line segment 5 is a line segment connecting the center O2 and the position point of the mth ultrasonic receiving unit (2). The length of line segment 4 is the arc radius r1 of the current receiving surface (1-1). The angle between line segment 3 and line segment 5 is (α+β). Then, the length a of line segment 5 is obtained by using the cosine theorem. Then d nm =a-r2; If the distance between the center of the imaging field and the receiving surface (1-1) is smaller than the arc radius of the receiving surface (1-1), the gap error d nm The calculation method includes the following steps: Step 1, a line segment 6 connecting the center O2 of the ideal annular ultrasonic array and the edge of the receiving surface (1-1) where the mth ultrasonic receiving unit (2) is located, a line segment 7 connecting the center O1 corresponding to the receiving surface (1-1) and the edge on the same side of the receiving surface (1-1) where the mth ultrasonic receiving unit (2) is located, and a line segment 8 connecting the center O2 and the center O1 form a triangle 3, the length of the line segment 6 is the radius r2 of the ideal annular ultrasonic array, the length of the line segment 7 is the arc radius r1 of the current receiving surface (1-1), and the length of the line segment 8 is the distance between the center O2 and the center O1, then the angle β between the line segment 8 and the line segment 7 is calculated using the law of cosines; Step 2: Calculate and obtain the angle α between line segment 7 and line segment 9, where line segment 9 is a line segment connecting the center O1 and the position point of the m-th ultrasonic receiving unit (2), and obtain the angle α using the distribution position of the m-th ultrasonic receiving unit (2) on the current receiving surface (1-1); Step 3: Line segments 8, 9 and 10 form triangle 4. Line segment 10 is a line segment connecting the center O2 and the position point of the m-th ultrasonic receiving unit (2). The length of line segment 9 is the arc radius r1 of the current receiving surface (1-1). The angle between line segment 8 and line segment 9 is (β-α). Then, the length a of line segment 10 is obtained by using the cosine theorem, and d nm =a-r2.

2. The variable imaging size photoacoustic imaging device based on a sector-shaped ultrasonic transducer array according to claim 1, characterized in that: The ultrasonic receiving units (2) on the N fan-shaped ultrasonic transducer array structures respectively have N different center frequencies.

3. A variable imaging size photoacoustic imaging method based on a sector-shaped ultrasonic transducer array, characterized in that: The variable imaging size photoacoustic imaging device according to claim 1 comprises the following steps: The receiving surfaces (1-1) of the N fan-shaped ultrasonic transducer array structures form a full-ring receiving surface to receive photoacoustic signals; If the distance between the center of the imaging field and the receiving surface (1-1) is equal to the arc radius of the receiving surface (1-1), the annular ultrasonic array composed of N fan-shaped ultrasonic transducer array structures is regarded as an ideal annular ultrasonic array, and the photoacoustic image is reconstructed directly using the signals received by the N fan-shaped ultrasonic transducer array structures through a back-projection algorithm; If the distance between the center of the imaging field and the receiving surface (1-1) is greater than or less than the arc radius of the receiving surface (1-1), after obtaining the signals received by the N sector-shaped ultrasonic transducer array structures, a data shift operation in the digital domain is performed to eliminate errors caused by the physical gap, and the processed signal is regarded as a signal received by an ideal annular ultrasonic array by performing data shift processing on the signal, and the photoacoustic image is reconstructed using the signal through a back-projection algorithm; When performing the data shift operation, the number of data shift bits of each ultrasonic receiving unit (2) is calculated, and the number of data shift bits of the mth ultrasonic receiving unit (2) on the receiving surface (1-1) of the nth sector-shaped ultrasonic transducer array structure is s nm , then: In formula (1), d nm is the gap error between the position of the mth ultrasonic receiving unit (2) on the receiving surface (1-1) of the nth sector-shaped ultrasonic transducer array structure and the corresponding position on the receiving surface of the ideal annular ultrasonic array; v is the propagation speed of ultrasound in the imaging device; f s is the data acquisition sampling rate; If the distance between the center of the imaging field and the receiving surface (1-1) is greater than the arc radius of the receiving surface (1-1), the gap error d nm The calculation method includes the following steps: Step 1, a line segment 1 connecting the center O2 of the ideal annular ultrasonic array and the edge of the receiving surface (1-1) where the mth ultrasonic receiving unit (2) is located, a line segment 2 connecting the center O1 corresponding to the receiving surface (1-1) and the edge on the same side of the receiving surface (1-1) where the mth ultrasonic receiving unit (2) is located, and a line segment 3 connecting the center O2 and the center O1 form a triangle 1, the length of the line segment 1 is the radius r2 of the ideal annular ultrasonic array, the length of the line segment 2 is the arc radius r1 of the current receiving surface (1-1), and the length of the line segment 3 is the distance between the center O2 and the center O1, and the angle β between the line segment 3 and the line segment 2 is calculated using the law of cosines; Step 2: Calculate and obtain the included angle α between the second line segment and the fourth line segment, where the fourth line segment is a line segment connecting the center O1 and the position point of the mth ultrasonic receiving unit (2), and the included angle α is obtained using the distribution position of the mth ultrasonic receiving unit (2) on the current receiving surface (1-1); Step 3: Line segments 3, 4 and 5 form triangle 2. Line segment 5 is a line segment connecting the center O2 and the position point of the mth ultrasonic receiving unit (2). The length of line segment 4 is the arc radius r1 of the current receiving surface (1-1). The angle between line segment 3 and line segment 5 is (α+β). Then, the length a of line segment 5 is obtained by using the cosine theorem. Then d nm =a-r2; If the distance between the center of the imaging field and the receiving surface (1-1) is smaller than the arc radius of the receiving surface (1-1), the gap error d nm The calculation method includes the following steps: Step 1, a line segment 6 connecting the center O2 of the ideal annular ultrasonic array and the edge of the receiving surface (1-1) where the mth ultrasonic receiving unit (2) is located, a line segment 7 connecting the center O1 corresponding to the receiving surface (1-1) and the edge on the same side of the receiving surface (1-1) where the mth ultrasonic receiving unit (2) is located, and a line segment 8 connecting the center O2 and the center O1 form a triangle 3, the length of the line segment 6 is the radius r2 of the ideal annular ultrasonic array, the length of the line segment 7 is the arc radius r1 of the current receiving surface (1-1), and the length of the line segment 8 is the distance between the center O2 and the center O1, then the angle β between the line segment 8 and the line segment 7 is calculated using the law of cosines; Step 2: Calculate and obtain the angle α between line segment 7 and line segment 9, where line segment 9 is a line segment connecting the center O1 and the position point of the m-th ultrasonic receiving unit (2), and obtain the angle α using the distribution position of the m-th ultrasonic receiving unit (2) on the current receiving surface (1-1); Step 3: Line segments 8, 9 and 10 form triangle 4. Line segment 10 is a line segment connecting the center O2 and the position point of the m-th ultrasonic receiving unit (2). The length of line segment 9 is the arc radius r1 of the current receiving surface (1-1). The angle between line segment 8 and line segment 9 is (β-α). Then, the length a of line segment 10 is obtained by using the cosine theorem, and d nm =a-r2.

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