A photoacoustic-ultrasonic volumetric imaging method and system based on a ring-shaped ultrasonic array

Abstract

This invention relates to the field of biomedical imaging technology and discloses a photoacoustic-ultrasound volumetric imaging method and system based on a ring-shaped ultrasound array. The method includes: reconstructing a two-dimensional photoacoustic image and a two-dimensional ultrasound image; after completing photoacoustic imaging and ultrasound synthetic aperture imaging on one imaging plane, moving the ring-shaped ultrasound array along a direction perpendicular to the imaging plane, repeating the process for the next imaging plane, reconstructing and stacking the photoacoustic and ultrasound images of each imaging plane to form a three-dimensional photoacoustic volumetric image and a three-dimensional ultrasound volumetric image; performing spatial impulse response deconvolution processing on the three-dimensional photoacoustic volumetric image; and fusing the processed three-dimensional photoacoustic volumetric image and the three-dimensional ultrasound volumetric image to generate a three-dimensional bimodal volumetric image. This invention utilizes a ring-shaped ultrasound array and motion scanning to achieve high temporal resolution photoacoustic-ultrasound bimodal three-dimensional stereoscopic imaging, and further ensures high spatial resolution of the image through a series of techniques.

Description

Technical Field

[0001] This invention relates to the field of biomedical imaging technology, specifically to a photoacoustic-ultrasound volumetric imaging method and system based on a ring-shaped ultrasound array. Background Technology

[0002] Traditional biomedical imaging systems suffer from inherent contradictions between spatial resolution, temporal resolution, imaging depth, and contrast. For example, while X-ray computed tomography (CT) systems offer high imaging resolution, they lack sensitivity to functional information and are accompanied by ionizing radiation; magnetic resonance imaging (MRI) and positron emission tomography (PET) systems, while capable of imaging deep tissues and functions, have low spatiotemporal resolution and rely on exogenous reagents or ionizing radiation; ultrasound (US) imaging systems can achieve real-time imaging but lack optical contrast; optical imaging systems, while possessing subcellular resolution and molecular sensitivity, have limited penetration depth. In contrast, photoacoustic imaging (PA) systems combine the advantages of rich optical contrast and high ultrasound resolution, achieving centimeter-level penetration depth, but they rely on the optical properties of tissues and are difficult to image in bone.

[0003] Dual-modal imaging technology, which combines ultrasound imaging and photoacoustic imaging, integrates the advantages of both. For example, photoacoustic imaging highlights blood vessels and can perform functional imaging, while ultrasound imaging highlights soft tissues and bones. The combination of the two ultimately achieves high spatial resolution, dual-contrast anatomical imaging, as well as functional and molecular imaging.

[0004] Among them, photoacoustic-ultrasound imaging systems based on ring ultrasound arrays have advantages such as compact structure, low cost, and dense planar sampling angles. Typical systems include the Transmission-Reflection Photoacoustic Ultrasound Computed Tomography System (TROPUS) and the Video Rate Full-Ring Ultrasound and Photoacoustic Tomography System (VF-USPACT). TROPUS combines photoacoustic tomography and transmission-reflection ultrasound to simultaneously present optical absorption, acoustic reflectivity, sound velocity (SOS), and acoustic attenuation information, achieving sub-millimeter-level anatomical structure imaging. VF-USPACT achieves dual-contrast imaging effects of optical absorption and ultrasonic reflectivity and has real-time video transmission capabilities. However, current photoacoustic-ultrasound volumetric systems based on ring ultrasound arrays have limitations such as difficulty in volumetric imaging and low spatiotemporal resolution.

[0005] In summary, current photoacoustic-ultrasound volumetric imaging methods and systems based on ring ultrasound arrays have a series of shortcomings, which hinder the further application of this technology (such as anatomical structure recognition, disease monitoring, and physiological information assessment), and also highlight the urgent need for high spatiotemporal resolution photoacoustic-ultrasound three-dimensional volumetric imaging methods and systems. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a photoacoustic-ultrasound volumetric imaging method and system based on a ring-shaped ultrasound array. This invention utilizes a ring-shaped ultrasound array and motion scanning to achieve high temporal resolution photoacoustic-ultrasound dual-modal three-dimensional stereoscopic imaging, and employs a series of techniques to ensure high spatial resolution of the images, thereby enabling detailed anatomical depiction of biological tissue morphology.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a photoacoustic-ultrasonic volume imaging method based on a ring-shaped ultrasonic array, comprising:

[0009] The object to be imaged and the ring ultrasound array are placed in a coupling medium;

[0010] Photoacoustic imaging: The object being imaged is illuminated by a pulsed laser, and the photoacoustic signals generated are collected by a ring ultrasonic array. A two-dimensional photoacoustic image is reconstructed by a filtering back projection algorithm that divides the sound into multiple sound velocity regions.

[0011] Ultrasonic synthetic aperture imaging: The ring-shaped ultrasonic array is controlled to emit ultrasonic waves in a preset sequence, and a two-dimensional ultrasonic image is reconstructed based on the received ultrasonic echo signal using a beamforming algorithm.

[0012] After completing photoacoustic imaging and ultrasonic synthetic aperture imaging of one imaging plane, the annular ultrasonic array is moved along a direction perpendicular to the imaging plane, and photoacoustic imaging and ultrasonic synthetic aperture imaging are repeated for the next imaging plane. The photoacoustic images and ultrasonic images of each imaging plane are reconstructed and stacked to form a three-dimensional photoacoustic volume image and a three-dimensional ultrasonic volume image.

[0013] Spatial impulse response deconvolution processing is performed on the three-dimensional photoacoustic volumetric image;

[0014] The processed three-dimensional photoacoustic volume image is fused with the three-dimensional ultrasonic volume image to generate a three-dimensional bimodal volume image.

[0015] In one embodiment, before or during the photoacoustic imaging step, there is also an ultrasonic element position calibration step: the point sound source is placed at multiple different positions within the imaging field of view, the corresponding photoacoustic signals are collected, and the actual geometric position of each ultrasonic element is iteratively calculated based on the photoacoustic signal propagation time from the point sound source to each ultrasonic element in the ring ultrasonic array and the ideal position coordinates of each ultrasonic element.

[0016] In one embodiment, the reconstruction of the two-dimensional photoacoustic image using a multi-velocity region segmentation filtering back-projection algorithm specifically includes:

[0017] Based on the acquired photoacoustic signals, the interface information between the imaged object and the surrounding medium is extracted, and different sound speed regions are adaptively divided. Different sound speed values ​​are assigned to each sound speed region and the image is reconstructed.

[0018] In one embodiment, the photoacoustic imaging step further includes an electrical impulse response deconvolution step after acquiring the photoacoustic signal: the microsphere is placed at the center of the ring ultrasonic array to acquire the photoacoustic signal, and the average value of the photoacoustic signal is used as the electrical impulse response for photoacoustic imaging of all ultrasonic elements of the ring ultrasonic array; when performing photoacoustic imaging subsequently, the acquired original photoacoustic signal is deconvolved with the electrical impulse response, and the deconvolved photoacoustic signal is used to reconstruct the photoacoustic image.

[0019] In one embodiment, the deconvolution of the acquired raw photoacoustic signal with the electrical impulse response specifically includes:

[0020] ;

[0021] ;

[0022] in, and These represent the original photoacoustic signal matrix and the deconvolutioned photoacoustic signal matrix, respectively. Let L represent the photoacoustic signal matrix in the iteration, where L is the sampling length and I is the identity matrix. It is the regularization parameter; H represents the cyclic matrix of the electrical impulse response, where h represents the average time-domain photoacoustic signal of the microsphere. This represents the value of the Lth sampling point of h. This indicates transpose.

[0023] In one embodiment, the spatial impulse response deconvolution processing of the three-dimensional photoacoustic volume image specifically includes:

[0024] The photoacoustic imaging spatial impulse response was obtained by numerical simulation. The three-dimensional photoacoustic volume image and the photoacoustic imaging spatial impulse response were deconvolved to obtain the processed three-dimensional photoacoustic volume image.

[0025] In one embodiment, the deconvolution processing of the three-dimensional photoacoustic volumetric image and the photoacoustic imaging spatial impulse response specifically includes:

[0026] The convolution model for a 3D photoacoustic volumetric image is as follows:

[0027] ;

[0028] Where y is the observed blurred 3D photoacoustic volume image; x is the 3D photoacoustic volume image before blurring, i.e., the processed 3D photoacoustic volume image; h is the 3D convolution kernel. Assuming that each pixel value of the 3D photoacoustic volume image is regarded as an independent random variable satisfying a Poisson distribution, the corresponding Poisson probability model is constructed as follows:

[0029] ;

[0030] Where r represents the position of a pixel in the image; This represents the probability that the observed blurred image is y when the original image is x. The factorial of the value of y at position r;

[0031] In spatial impulse response deconvolution processing, given y, the goal is to provide an estimate of x; p reaches its maximum value when the estimated value of x equals the true value of x; a negative log-likelihood function is constructed as the cost function to obtain the optimal estimate of x. as follows:

[0032] ;

[0033] By applying the Richardson–Lucy iterative formula and introducing an L2 regularization term, we obtain the k-th iteration result of x. and the result of the (k+1)th iteration Iterative relationship:

[0034] ;

[0035] It is a regularization parameter; to accelerate the iterative convergence process, the random heavy ball algorithm is applied, using the momentum term. To replace the iterative The final iterative formula for the random heavy ball algorithm containing L2 regularization is obtained:

[0036] ;

[0037] in, For momentum term: .

[0038] In one embodiment, fusing the processed three-dimensional photoacoustic volume image with the three-dimensional ultrasonic volume image to generate a three-dimensional bimodal volume image specifically includes:

[0039] The processed 3D photoacoustic volumetric image and 3D ultrasound volumetric image are normalized and color-fused to generate a 3D bimodal volumetric image that simultaneously contains photoacoustic and ultrasound feature information.

[0040] In a second aspect, the present invention provides an imaging system for implementing the method of any embodiment of the first aspect, comprising:

[0041] A water tank is used to hold the coupling medium and the object being imaged.

[0042] A ring-shaped ultrasonic array is set inside the water tank to emit ultrasonic waves and receive photoacoustic signals and ultrasonic echo signals from the object being imaged.

[0043] Pulsed laser module, used to generate pulsed laser;

[0044] An optical fiber bundle is used to conduct the pulsed laser and irradiate the imaged object with the pulsed laser.

[0045] A motion scanning module is used to drive the annular ultrasound array and the fiber optic bundle to move in a direction perpendicular to the imaging plane;

[0046] A signal transmission and acquisition module is connected to the ring ultrasonic array and is used to excite the ring ultrasonic array to emit ultrasonic waves and to acquire the photoacoustic signals and ultrasonic echo signals received by the ring ultrasonic array.

[0047] A synchronization module is used to synchronize the timing of the pulsed laser module and the signal transmission and acquisition module;

[0048] The control and reconstruction module is connected to the pulsed laser module, signal transmission and acquisition module, motion scanning module and synchronization module. It is used to control the operation of the imaging system, process the acquired photoacoustic signals and ultrasonic echo signals, and reconstruct and display two-dimensional photoacoustic images, ultrasonic images and three-dimensional dual-modal volumetric images.

[0049] In one embodiment, several sub-fiber bundles of the fiber bundle are uniformly fixed around the annular ultrasonic array by a fixator. In the photoacoustic imaging step, optical illumination and ultrasonic detection are confocalized: the tilt angle of the sub-fiber bundles is adjusted so that the pulsed laser forms a thin sheet-like illumination in the vertical direction and uniform illumination in the horizontal direction.

[0050] Compared with the prior art, the beneficial technical effects of the present invention are:

[0051] This invention presents a high spatiotemporal resolution photoacoustic-ultrasound volumetric imaging system based on a ring-shaped ultrasound array. This system effectively overcomes the imaging shortcomings of systems based on CT, MRI, PET, US, and PA, integrating the advantages of photoacoustic and ultrasound imaging. Using a ring-shaped ultrasound array with hundreds of elements, it achieves panoramic coverage and dense angular sampling in a photoacoustic-ultrasound dual-modal imaging system, where photoacoustic and ultrasound imaging are performed alternately. Combined with a linear translation platform, it can rapidly complete three-dimensional scanning, achieving high temporal resolution. Through methods such as optical illumination and ultrasound detection confocalization, ultrasound element position calibration, electrical impulse response deconvolution, sound velocity segmentation and multi-velocity filtered back-projection image reconstruction, and spatial impulse response deconvolution, it enhances in-plane detection sensitivity and ensures high spatial resolution of the images. It can resolve high spatiotemporal resolution three-dimensional blood vessels, soft tissues, and bone structures in mouse trunks and human fingers with good detail. Attached Figure Description

[0052] Figure 1 This is a system architecture diagram of the present invention;

[0053] Figure 2 This is a schematic diagram of the system in an embodiment of the present invention;

[0054] Figure 3 This is a schematic diagram of the fiber optic bundle correlation device in an embodiment of the present invention;

[0055] Figure 4 This is a timing diagram of photoacoustic imaging and ultrasonic imaging in an embodiment of the present invention;

[0056] Figure 5 This is a schematic diagram showing the results before and after ultrasonic element position calibration in an embodiment of the present invention;

[0057] Figure 6 This is a schematic diagram illustrating the effect of electrical impulse response before and after deconvolution in an embodiment of the present invention;

[0058] Figure 7 This is a schematic diagram of the imaging resolution result of the system before spatial impulse response deconvolution processing in an embodiment of the present invention;

[0059] Figure 8 This is a comparison diagram of the system's performance before and after spatial impulse response deconvolution processing in an embodiment of the present invention;

[0060] Figure 9 Image showing the in vivo imaging results in this embodiment of the invention;

[0061] Figure 10 Image showing the in vivo imaging results in this embodiment of the invention;

[0062] In the picture:

[0063] 1: Pulsed laser module; 2: Object being imaged; 3: Circular ultrasonic array; 4: Signal transmission and acquisition module; 5: Control, reconstruction and processing module; 6: Motion scanning module; 7: Synchronization module; 8: Fiber optic bundle; 81: Fiber optic fixture; 9: Water tank. Detailed Implementation

[0064] A preferred embodiment of the present invention will now be described in detail with reference to the accompanying drawings.

[0065] This invention provides a high spatiotemporal resolution photoacoustic-ultrasound volumetric imaging method and system based on a ring-shaped ultrasound array. Through the ring-shaped ultrasound array, it achieves panoramic coverage and dense angular sampling for two-dimensional photoacoustic-ultrasound dual-modal planar imaging, where photoacoustic imaging and ultrasound imaging are performed alternately. Combined with rapid motion scanning, high temporal resolution three-dimensional photoacoustic-ultrasound dual-modal volumetric imaging can be acquired. Furthermore, through methods such as confocal focusing of optical illumination and ultrasound detection, ultrasound array element position calibration, deconvolution of photoacoustic signal electrical impulse response, sound velocity segmentation and multi-velocity filtering back-projection photoacoustic image reconstruction, and spatial impulse response deconvolution, high spatial resolution photoacoustic-ultrasound images are obtained, enabling detailed anatomical depiction of biological tissue morphology.

[0066] The imaging system includes a pulsed laser module 1, a ring ultrasound array 3, a signal transmission and acquisition module 4, a control, reconstruction and processing module 5, a motion scanning module 6, a synchronization module 7, an optical fiber bundle 8, and a water tank 9, among which:

[0067] The pulsed laser module is used to generate pulsed lasers.

[0068] The fiber bundle is used to transmit pulsed laser light to the object being imaged 2, which then excites the object to generate ultrasonic waves through the photoacoustic effect. These ultrasonic waves are also known as photoacoustic signals.

[0069] A ring-shaped ultrasonic array is used to emit and collect ultrasonic waves, and has many ultrasonic array elements distributed on a circumference.

[0070] The signal transmission and acquisition module is used to acquire and store the ultrasonic signals acquired by the ring ultrasonic array, and can also be used to excite the ring ultrasonic array to emit ultrasonic waves.

[0071] The motion scanning module is used to move the annular ultrasound array and fiber optic bundle in the vertical direction, enabling the annular ultrasound array to acquire data at different heights and achieve volumetric imaging.

[0072] The control and reconstruction module is used to control and set the parameters of the pulsed laser module, signal transmission and acquisition module, motion scanning module, and synchronization module. It is also used to read and process raw data from the signal transmission and acquisition module and reconstruct and display two-dimensional and three-dimensional photoacoustic-ultrasound images.

[0073] The synchronization module is used to synchronize the start-up time of the pulse laser module and the signal transmission and acquisition module.

[0074] The water tank is used to hold water to ensure acoustic coupling between the object being imaged and the ring ultrasound array.

[0075] The operation of a high spatiotemporal resolution photoacoustic-ultrasound volume imaging system based on a ring ultrasound array includes the following steps:

[0076] Step 1: Place the object to be imaged and the ring ultrasound array in a water tank filled with water. The water tank is heated and circulated by a pump to ensure a suitable and uniform temperature.

[0077] Step 2: Photoacoustic imaging.

[0078] (1) Confocalization of optical illumination and ultrasonic detection. Several sub-fiber bundles of the fiber bundle are uniformly fixed on the ring ultrasonic array. The tilt angle of the sub-fiber bundles is adjusted so that the pulsed laser forms a thin sheet illumination in the vertical direction and uniform illumination in the horizontal direction, thereby realizing the confocalization of optical illumination and ultrasonic detection in the vertical direction, and thus improving the detection sensitivity of photoacoustic signal.

[0079] (2) Photoacoustic signal acquisition. Set the trigger signal output by the synchronization module, set the trigger mode of the pulse laser to external trigger, laser wavelength and other parameters, and set the trigger mode of the signal transmission and acquisition module to external trigger, signal acquisition and other parameters.

[0080] (3) Ultrasonic Array Element Position Calibration. The geometric positions of the ultrasonic array elements in the ring ultrasonic array are calibrated to improve the accuracy of subsequent photoacoustic and ultrasonic image reconstruction. The specific method is to use a microsphere as a point source and position it sequentially at multiple different positions within the imaging field of view. Then, photoacoustic signals are acquired, and the propagation time of the photoacoustic signal from the microsphere to each ultrasonic array element is extracted. The coordinates of the actual array elements are iteratively derived from the coordinates of the initial array elements (ideal array element position coordinates).

[0081] (4) Sound velocity segmentation: In order to reduce the impact of acoustic heterogeneity on image reconstruction, the arrival time of photoacoustic signals from the interface between the imaged object and the water body is extracted. The interface between the imaged object and the water body is adaptively segmented in combination with the sound velocity of the water, thereby assigning different sound velocities to the imaged object and the surrounding water body. Furthermore, the boundaries of different tissues (such as bones, muscles, and organs) in the imaged object can be extracted, and different tissues can be assigned different sound velocities, making the sound velocity segmentation more refined and the image reconstruction more accurate.

[0082] (5) Electrical Impulse Response Deconvolution: To improve the detection bandwidth of the ultrasonic array elements and enhance the quality of image reconstruction, the electrical impulse response of the ultrasonic array elements was measured. A microsphere was placed at the center of the ring-shaped ultrasonic array to acquire photoacoustic signals, and the average value of the photoacoustic signals was used as the electrical impulse response for photoacoustic imaging of all ultrasonic array elements. During subsequent photoacoustic imaging, the acquired original photoacoustic signals were deconvolved with the known electrical impulse responses, thereby improving the detection bandwidth of the ultrasonic array elements for photoacoustic signals.

[0083] (6) Photoacoustic image reconstruction: The control reconstruction module uses a multi-sound speed region division filtering back projection algorithm to reconstruct the photoacoustic image, and finally obtains a two-dimensional photoacoustic image.

[0084] Step 3: Ultrasonic synthetic aperture imaging.

[0085] (1) Ultrasonic signal acquisition. Set the signal transmission and reception parameters and the transmission and reception event sequence of the signal transmission and acquisition module for ultrasonic synthetic aperture imaging.

[0086] (2) Ultrasonic image reconstruction. Based on the corrected positions of the ultrasonic array elements, the ultrasonic image is reconstructed using a delay-sum beamforming algorithm to obtain a two-dimensional B-mode ultrasonic image.

[0087] Step 4: 3D Volume Imaging. The control and reconstruction module synchronizes the motion scanning module with the acquisition of photoacoustic and ultrasonic data. That is, after acquiring photoacoustic and ultrasonic signals for one section, the ring-shaped ultrasonic array and the fiber optic bundle mounted on it are moved vertically together. Steps 1 to 3 are repeated to acquire photoacoustic and ultrasonic signals for the next section. The photoacoustic and ultrasonic images of each section are reconstructed and stacked to form a volumetric image.

[0088] Step 5: Spatial Impulse Response Deconvolution. Perform three-dimensional photoacoustic volumetric imaging on a microsphere as described in Step 4. The imaging result serves as the photoacoustic imaging spatial impulse response of the system. Alternatively, numerical simulation can be used to obtain the photoacoustic imaging spatial impulse response of the system. In subsequent imaging processes, the original three-dimensional photoacoustic volumetric image obtained in Step 4 is deconvolved with the known photoacoustic imaging spatial impulse response to obtain a processed three-dimensional photoacoustic volumetric image, thereby improving the image resolution within the imaging plane and along the scanning direction.

[0089] Step 6: Fusion of photoacoustic and ultrasound images. The photoacoustic and ultrasound images are normalized and converted to RGB format. The photoacoustic and ultrasound images are then fused using different colors. The fused image retains the feature information from both the photoacoustic and ultrasound images simultaneously within a single image.

[0090] This invention constructs a photoacoustic-ultrasound volumetric imaging system based on a ring-shaped ultrasonic array and achieves high spatiotemporal resolution photoacoustic-ultrasound volumetric imaging through a series of strategies. Subsequently, the horizontal (imaging plane) resolution and vertical (scanning direction) resolution of the system are characterized. The system resolves two-dimensional and three-dimensional anatomical structures inside small animals and human fingers with high precision, demonstrating the unique advantages of the system, including photoacoustic-ultrasound dual-modal dual-contrast, volumetric imaging capability, and high spatiotemporal resolution.

[0091] In one embodiment, the pulsed laser module can be a tunable OPO laser manufactured by PhotoSonus M in Lithuania, with a pulse repetition rate of 20 Hz, a pulse width of 3-5 nanoseconds, and a tuning range of 650-1064 nm.

[0092] In one embodiment, the fiber bundle may be a fiber bundle produced by Nanjing Sushi Technology Co., Ltd. in China. The fiber bundle is divided into 12 sub-fiber bundles, each sub-fiber bundle having 54 fiber cores with a fiber core diameter of 200 μm and a numerical aperture of 0.22, and having a transmission efficiency of approximately 70% in the 200-1200 nm spectral range.

[0093] In one embodiment, the ring ultrasonic array can be a ring ultrasonic array with a radius of approximately 40 mm, a center frequency of 4.9 MHz, an aperture angle of 360°, a vertical curvature of 37 mm, and 512 ultrasonic elements, manufactured by Imasonic of France.

[0094] In one embodiment, the signal transmission and acquisition module can be a Vantage 256 programmable ultrasound system manufactured by Verasonics, Inc., equipped with 256 signal acquisition and transmission channels, a 14-bit analog-to-digital converter, and supporting a maximum sampling rate of 62.5 MHz and a gain of 54 dB.

[0095] In one embodiment, the control reconstruction module can be a computer that is paired with the signal transmission and acquisition module, and the computer is equipped with control and reconstruction software, including MATLAB and LabVIEW.

[0096] In one embodiment, the motion scanning module can be a PSA100-11-X type electric translation stage manufactured by Beijing Zhuoli Hanguang Instrument Co., Ltd., which can scan along the vertical axis.

[0097] In one embodiment, the synchronization module may be a DG4000 multi-channel arbitrary signal generator manufactured by Suzhou Riggen Precision Technology Co., Ltd.

[0098] In one embodiment, using Figure 2The system shown performs high spatiotemporal resolution photoacoustic-ultrasonic volumetric imaging of the object being imaged. The specific process of this embodiment is as follows:

[0099] (1) The object to be imaged and the ring ultrasonic array are placed in a water tank filled with water. The water tank is heated and circulated by a heating device and a circulation pump to ensure a suitable and uniform temperature.

[0100] (2) Photoacoustic imaging:

[0101] ① Confocal optical illumination and ultrasonic testing. The 12 sub-fiber bundles of the fiber bundle are evenly fixed at 30° intervals on a fiber optic fixture 81 on the ring ultrasonic array. The sub-fiber bundles are tilted approximately 32° relative to the horizontal plane. For details on the fiber bundle-related devices, please refer to [link to relevant documentation]. Figure 3 .

[0102] ② Photoacoustic signal acquisition. The synchronization module is set to output a 20Hz square wave signal. The pulsed laser's trigger mode is set to external trigger, and the output laser wavelength is set accordingly. The signal transmission and acquisition module's trigger mode is also set to external trigger, and the photoacoustic signal acquisition parameters are configured. After receiving the trigger signal from the synchronization module, the pulsed laser generates a negative pulse, triggering another output channel of the synchronization module to generate a 250-nanosecond-wide positive pulse. The rising edge of the positive pulse triggers the pulsed laser's flash, and the falling edge triggers the pulsed laser's Q-switch to generate a pulsed laser. Simultaneously, the signal transmission and acquisition system is activated to acquire photoacoustic signals, achieving precise synchronization between photoacoustic signal acquisition and laser emission. The total signal acquisition time is 50 microseconds. Since the signal acquisition and transmission module can only acquire 256 channels simultaneously, the first signal acquisition covers channels 1-256 of the ring ultrasonic array, and the second signal acquisition covers channels 257-512 of the ring ultrasonic array.

[0103] ③ Ultrasonic Array Element Position Calibration. To mitigate the impact of manufacturing errors, the geometric positions of the ultrasonic array elements are calibrated to improve the accuracy of subsequent photoacoustic and ultrasonic image reconstruction. A microsphere with a diameter of 200 micrometers is sequentially positioned at eight different locations within the imaging field of view. Photoacoustic signals are then acquired, and the propagation time of the photoacoustic signal from each array element to the microsphere is extracted. The coordinates of the actual array elements are iteratively derived from the initial array element coordinates (ideal array element position coordinates). See the results before and after calibration. Figure 5 .

[0104] ④ Sound velocity segmentation: To mitigate the impact of acoustic heterogeneity, the arrival time of the photoacoustic signal from the interface between the imaged object and the water body is extracted using the Akaike information criterion. Combined with the sound velocity of water, the interface between the imaged object and the water body is adaptively segmented, thereby assigning different sound velocities to the imaged object and the surrounding water body. For example, at 35℃, the sound velocity of water is set to approximately 1520 m / s, 1580 m / s for the mouse heart plane, 1590 m / s for the mouse liver plane, 1570 m / s for the mouse kidney / spleen plane, 1560 m / s for the mouse intestine plane, and 1540 m / s for human finger tissue.

[0105] ⑤ Electrical Impulse Response Deconvolution: To improve the detection bandwidth of the ultrasonic array elements, the electrical impulse response of the ultrasonic array elements is measured. A microsphere with a diameter of 40 micrometers is placed at the center of the transducer to collect photoacoustic signals, and the average value of the photoacoustic signals is used as the electrical impulse response of all ultrasonic array elements. During subsequent photoacoustic imaging, the acquired raw photoacoustic signals are deconvolved with the known electrical impulse responses, thereby improving the detection bandwidth of the ultrasonic array elements. See [link to image / deconvolution diagram] for the effect before and after electrical impulse response deconvolution. Figure 6 The specific deconvolution process is as follows:

[0106] .

[0107] .

[0108] in, and These represent the original photoacoustic signal matrix and the deconvolutioned photoacoustic signal matrix, respectively. Let L represent the photoacoustic signal matrix in the iteration, where L is the sampling length and I is the identity matrix. H is the regularization parameter; H represents the cyclic matrix of the electrical impulse response, where h represents the average time-domain photoacoustic signal of the microsphere.

[0109] ⑥ Photoacoustic image reconstruction: The control reconstruction module uses a dual-velocity sound filter back projection algorithm to reconstruct the photoacoustic image, and finally obtains a two-dimensional photoacoustic image.

[0110] (3) Ultrasonic synthetic aperture imaging.

[0111] ① Ultrasonic Signal Acquisition. The signal transmission and acquisition module is configured with parameters for transmitting and receiving ultrasonic signals for ultrasonic synthetic aperture imaging, as well as the event sequence for transmission and reception. Starting from the first element of the ring ultrasonic array, 64 elements are selected at intervals of 8 elements each (e.g., elements 1, 9, 17, ..., 505). Each time, one element is selected to transmit an ultrasonic wave, and the echo is received from that element and its 96 adjacent elements on either side. For example, when element 97 transmits a signal, the reception is completed by elements 1-193. Due to the mismatch between the number of channels in the information transmission and acquisition unit and the number of ultrasonic elements, some reception processes require two consecutive acquisitions to complete. For example, when element 1 transmits, the receiving elements are elements 1-97 and 417-512, thus requiring two acquisitions. The entire sequence ultimately contains 112 cycles, with a total duration of 15.12 milliseconds. Each cycle includes 100 microseconds of ultrasonic signal transmission and reception time and 35 microseconds of idle time.

[0112] ② Ultrasonic Image Reconstruction. Based on the corrected positions of the ultrasonic array elements, ultrasonic image reconstruction is performed using a delayed summation beamforming algorithm. First, image reconstruction is performed independently on 112 ultrasonic signal transmission and reception events, generating 64 low-resolution IQ images. Then, a single high-resolution IQ image is generated through coherent synthesis. The amplitude of the single high-resolution IQ image is extracted to finally obtain a two-dimensional B-mode ultrasound image.

[0113] (4) Three-dimensional volumetric imaging. The control and reconstruction module synchronizes the motion scanning module with the photoacoustic and ultrasonic data acquisition. That is, after the photoacoustic and ultrasonic signal acquisition of one section is completed, the ring ultrasonic array and the fiber bundle installed on it are moved vertically. The moving speed is set to 2-2.5 mm / s, and the moving interval is 200-250 micrometers. The photoacoustic and ultrasonic signal acquisition and image reconstruction of the next section are then performed. For the timing of ultrasonic imaging and photoacoustic imaging, please refer to [link to documentation]. Figure 4 The total scan time for a complete volumetric imaging of a mouse trunk or human finger is typically between 10 and 20 seconds, stacking photoacoustic and ultrasound images of each section to form a volumetric image.

[0114] (5) Spatial impulse response deconvolution. The photoacoustic imaging spatial impulse response of the system is obtained by numerical simulation. The original three-dimensional photoacoustic volume image obtained in (4) is deconvolved with the simulated photoacoustic imaging spatial impulse response to obtain the processed three-dimensional photoacoustic volume image. The imaging resolution is improved both in the imaging plane and in the scanning direction. The specific deconvolution process is as follows:

[0115] The convolution model for the 3D photoacoustic volumetric image is as follows:

[0116] ;

[0117] Where y is the observed blurred 3D photoacoustic volumetric image, x is the 3D photoacoustic volumetric image before blurring, i.e., the processed 3D photoacoustic volumetric image; h is the 3D convolution kernel, and each pixel value of the image is regarded as an independent random variable satisfying a Poisson distribution. The corresponding Poisson probability model is constructed as follows:

[0118] .

[0119] Where r represents the position of a pixel in the image. Let p represent the probability that the observed blurred image is y when the original image is x. In spatial impulse response deconvolution, given y, the goal is to provide an estimate of x. The likelihood probability p reaches its maximum when the estimated value of x equals the true value of x. Therefore, a negative log-likelihood function is constructed as the cost function to obtain the optimal estimate of x. as follows:

[0120] .

[0121] Applying the Richardson–Lucy (RL) iterative formula, the results of the k-th and (k+1)-th iterations of x. and It will have the following iterative relationship:

[0122] .

[0123] To suppress noise energy, an L2 norm term with respect to x is added to the cost function, resulting in an iterative relationship that introduces an L2 regularization term:

[0124] .

[0125] To accelerate the iterative convergence process, the Stochastic Heavy Ball (SHB) algorithm is applied, using the momentum term. To replace the iterative The final SHB iterative formula containing L2 regularization terms is obtained:

[0126] ;

[0127] Among them, the momentum term The expression is as follows:

[0128] .

[0129] (6) Fusion of photoacoustic and ultrasound images. The photoacoustic and ultrasound images are normalized to the range [0, 255] and converted to RGB format, where the photoacoustic image is a color image and the ultrasound image is a grayscale image. A weighted summation method is used for fusion processing, and the specific formula is as follows:

[0130] .

[0131] in, The value of is between 0 and 1, and it is a weighting factor determined based on the intensity of the photoacoustic image. The intensity of the photoacoustic image increases, and this adaptive weighting strategy ensures the visibility of photoacoustic and ultrasonic features in the fused image. This represents a fused image of photoacoustic and ultrasound images. This indicates photoacoustic tomography. This refers to ultrasound imaging.

[0132] (7) Characterization of system performance. Using 40-micrometer microspheres as point imaging objects, photoacoustic-ultrasonic volumetric imaging was performed. The characterization results of the photoacoustic and ultrasonic imaging resolution before deconvolution of the photoacoustic spatial impulse response are shown in [link to relevant documentation]. Figure 7 For the 3D photoacoustic volumetric images and resolution characterization of the photoacoustic spatial impulse response before and after deconvolution, please see [link to image / image]. Figure 8 .

[0133] Using mice and human fingers as imaging objects, photoacoustic-ultrasound volumetric imaging was performed to obtain the in vivo imaging results of the system. Figure 9 and Figure 10 .

[0134] Please refer to the relevant results of the embodiments. Figures 3 to 10 .

[0135] Figure 3 A schematic diagram of the fiber optic bundle-related device is shown. Pulsed lasers form a thin sheet of illumination in the vertical direction and uniform illumination in the horizontal direction. By adjusting the tilt angle, optical illumination and ultrasonic detection are confocalized in the vertical direction, thereby improving the sensitivity of photoacoustic signal detection.

[0136] Figure 4 The timing sequence of photoacoustic imaging and ultrasound imaging of the system was demonstrated. Due to the limited repetition frequency (20Hz) of the pulsed laser module output pulse and the two photoacoustic signal acquisitions, the final frame rate of the photoacoustic image is 10Hz. Ultrasound imaging is interspersed in the photoacoustic imaging interval, and the final frame rate of the ultrasound image is 20Hz. Therefore, the system has a high time resolution.

[0137] Figure 5 The ultrasonic element position calibration was demonstrated. Figure 5 In the diagram, 'a' represents the deviation between the actual and designed positions of the ultrasonic array. Figure 5 In the figure, b represents the roundness error of the ultrasound array. Figure 5 Figure c shows a comparison of photoacoustic images of a 200-micrometer microsphere before and after ultrasonic element position calibration. Figure 5In the image, 'd' represents a photograph of the leaf vein network. Figure 5 The figure 'e' shows a comparison of the photoacoustic images of the leaf vein network within the dashed box before and after ultrasonic element position calibration, demonstrating that the spatial resolution and accuracy of the photoacoustic images are significantly improved after ultrasonic element position calibration.

[0138] Figure 6 It demonstrates deconvolution of electrical impulse response. Figure 6 Figure 'a' shows the time-domain photoacoustic signal of a 40-micrometer microsphere, with the average of the time-domain photoacoustic signals of all ultrasonic elements taken as the electrical impulse response of all ultrasonic elements. Figure 6 Figure b shows the frequency domain photoacoustic signal of a 40-micrometer microsphere. Using the full width at half maximum (FWHM) as the quantization index, it can be seen that the detection bandwidth of the ultrasonic array element is 5.01 MHz. Figure 6 Figure 'c' shows the change in the frequency domain photoacoustic signal of a microsphere with a diameter of 130 micrometers before and after deconvolution of the electrical impulse response. It can be seen that after deconvolution of the electrical impulse response, the detection bandwidth of the ultrasonic array element is increased from 4.86MHz to 7.74MHz. Figure 6 Figures d and e show the photoacoustic images of the leaf vein network and the blood vessel phantom before and after deconvolution of the electrical impulse response, respectively, demonstrating that the spatial resolution and accuracy of the photoacoustic images are greatly improved after deconvolution of the electrical impulse response.

[0139] Figure 7 The imaging resolution results of the system before spatial impulse response deconvolution processing are shown. Figure 7 a, b, and c in the figure show the three-dimensional photoacoustic volume image, the photoacoustic image intensity curve in the horizontal direction, and the photoacoustic image intensity curve in the vertical direction of the 40-micrometer microsphere, respectively. The full width at half maximum (FWHM) is used as the quantification index, and the planar resolution of the photoacoustic image is 122 micrometers and the vertical resolution is 1 millimeter. Figure 7 In the figure, d, e, and f respectively show the three-dimensional ultrasound image of the microsphere, the ultrasound image intensity curve in the horizontal direction, and the ultrasound image intensity curve in the vertical direction. The full width at half maximum (FWHM) is used as the quantitative index. The planar resolution of the ultrasound image is 102 micrometers and the vertical resolution is 1.1 millimeters.

[0140] Figure 8 The comparison of the system before and after spatial impulse response deconvolution processing is shown (the spatial impulse response of photoacoustic imaging is obtained by numerical simulation). Figure 8 The image 'a' in the figure compares the three-dimensional photoacoustic volumetric images of a 40-micrometer microsphere before and after deconvolution processing, and it is clear that its point spread function is significantly reduced. Figure 8 b in Figure 8 The photoacoustic intensity of 'a' in the imaging plane and scanning direction was quantitatively analyzed, with the full width at half maximum (FWHM) as the indicator. The results showed that the resolution in the plane was improved from 112 micrometers to 41 micrometers after deconvolution processing, and the resolution in the scanning direction was improved from 1.00 millimeters to 0.36 millimeters. Figure 8 The image c compares the two-dimensional photoacoustic images of the fishing line on the imaging plane before and after deconvolution processing, showing a significant reduction in the width of the fishing line. Figure 8 d in Figure 8 The photoacoustic intensity at two positions of the fishing line in the image was quantitatively analyzed. After deconvolution processing, the full width at half maximum (FWHM) of the fishing line in the imaging plane was reduced from 120 micrometers to 65 micrometers, making it easier to distinguish adjacent fishing lines. Figure 8 The image 'e' shows a comparison of the two-dimensional photoacoustic images of the fishing line in the scanning direction before and after deconvolution processing, which also shows that the width of the fishing line is significantly reduced and the clarity is greatly improved. Figure 8 f in Figure 8 The photoacoustic intensity at two positions in the image was quantified, and the full width at half maximum (FWHM) of the two-dimensional photoacoustic image of the fishing line in the scanning direction decreased from 1.45 mm to 0.74 mm, further improving the discriminability of adjacent fishing lines. These results consistently demonstrate that the spatial resolution of the three-dimensional photoacoustic volumetric image is significantly improved in all dimensions after spatial impulse response deconvolution processing.

[0141] Figure 9 and Figure 10 The results of in vivo imaging of the system are shown, with photoacoustic images, ultrasound images, and photoacoustic-ultrasound images displayed from left to right. Figure 9 In the image, 'a' represents the three-dimensional image of the mouse's torso. Figure 9 In the image, b represents a two-dimensional image of a cross-section of a mouse liver. Figure 9 In the image, 'c' represents the 3D image of a human finger. Figure 10 The results are two-dimensional images of a human finger cross-section. Photoacoustic imaging clearly reveals the details of the three-dimensional vascular network, while ultrasound imaging highlights soft tissue and bone. Relevant features in both photoacoustic and ultrasound images maintain good visibility, and relevant anatomical structures in both animals and humans are clearly visible.

[0142] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. The terms “comprising,” “including,” etc., as used herein indicate the presence of the stated features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0143] It should be understood that although the steps in the flowcharts of the accompanying drawings are shown sequentially as indicated by the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless explicitly stated herein, there is no strict order restriction on the execution of these steps, and they can be executed in other orders. Moreover, at least some of the steps in the flowcharts of the accompanying drawings may include multiple steps or stages, which are not necessarily completed at the same time, but may be executed at different times, and the execution order of these steps or stages is not necessarily sequential, but may be performed alternately or in turn with other steps or at least some of the steps or stages of other steps.

[0144] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0145] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention, and no reference numerals in the claims should be construed as limiting the scope of the claims.

[0146] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A photoacoustic-ultrasonic volumetric imaging method based on a ring-shaped ultrasonic array, characterized in that, include: The object to be imaged and the ring ultrasound array are placed in a coupling medium; Photoacoustic imaging: The object being imaged is illuminated by a pulsed laser, and the photoacoustic signals generated are collected by a ring ultrasonic array. A two-dimensional photoacoustic image is reconstructed using a filtering back projection algorithm that divides the sound velocity regions. Specifically, it includes: extracting the interface information between the object being imaged and the surrounding medium based on the collected photoacoustic signals, adaptively dividing different sound velocity regions, assigning different sound velocity values ​​to each sound velocity region, and reconstructing the image. Before or during the photoacoustic imaging step, there is also an ultrasonic element position calibration step: the point sound source is placed at multiple different positions within the imaging field of view, the corresponding photoacoustic signals are collected, and the actual geometric position of each ultrasonic element is iteratively calculated based on the photoacoustic signal propagation time from the point sound source to each ultrasonic element in the ring ultrasonic array and the ideal position coordinates of each ultrasonic element. In the photoacoustic imaging step, after acquiring the photoacoustic signal, an electrical impulse response deconvolution step is also included: the microsphere is placed at the center of the ring ultrasonic array to acquire the photoacoustic signal, and the average value of the photoacoustic signal is used as the electrical impulse response for photoacoustic imaging of all ultrasonic elements of the ring ultrasonic array; when performing photoacoustic imaging subsequently, the acquired original photoacoustic signal is deconvolved with the electrical impulse response, and the photoacoustic image is reconstructed using the deconvolved photoacoustic signal. Ultrasonic synthetic aperture imaging: The ring ultrasonic array is controlled to emit ultrasonic waves in a preset sequence, and a two-dimensional ultrasonic image is reconstructed based on the received ultrasonic echo signal using a beamforming algorithm. After completing photoacoustic imaging and ultrasonic synthetic aperture imaging of one imaging plane, the annular ultrasonic array is moved along a direction perpendicular to the imaging plane, and photoacoustic imaging and ultrasonic synthetic aperture imaging are repeated for the next imaging plane. The photoacoustic images and ultrasonic images of each imaging plane are reconstructed and stacked to form a three-dimensional photoacoustic volume image and a three-dimensional ultrasonic volume image. The spatial impulse response deconvolution processing of the three-dimensional photoacoustic volume image is specifically included as follows: the photoacoustic imaging spatial impulse response is obtained by numerical simulation method, and the three-dimensional photoacoustic volume image and the photoacoustic imaging spatial impulse response are deconvolved to obtain the processed three-dimensional photoacoustic volume image. The deconvolution process of the three-dimensional photoacoustic volumetric image and the photoacoustic imaging spatial impulse response specifically includes: The convolution model for a 3D photoacoustic volumetric image is as follows: ； Where y is the observed blurred 3D photoacoustic volume image; x is the 3D photoacoustic volume image before blurring, i.e., the processed 3D photoacoustic volume image; h is the 3D convolution kernel. Assuming that each pixel value of the 3D photoacoustic volume image is regarded as an independent random variable satisfying a Poisson distribution, the corresponding Poisson probability model is constructed as follows: ； Where r represents the position of a pixel in the image; This represents the probability that the observed blurred image is y when the original image is x. The factorial of the value of y at position r; In spatial impulse response deconvolution processing, given y, the goal is to provide an estimate of x; p reaches its maximum value when the estimated value of x equals the true value of x; a negative log-likelihood function is constructed as the cost function to obtain the optimal estimate of x. as follows: ； By applying the Richardson–Lucy iterative formula and introducing an L2 regularization term, we obtain the k-th iteration result of x. and the result of the (k+1)th iteration Iterative relationship: ； It is a regularization parameter; to accelerate the iterative convergence process, the random heavy ball algorithm is applied, using the momentum term. To replace the iterative The final iterative formula for the random heavy ball algorithm containing L2 regularization is obtained: ； in, For momentum term: ; The processed three-dimensional photoacoustic volume image is fused with the three-dimensional ultrasonic volume image to generate a three-dimensional bimodal volume image; The step of deconvolving the acquired raw photoacoustic signal with the electrical impulse response specifically includes: ； ； in, and These represent the original photoacoustic signal matrix and the deconvolutioned photoacoustic signal matrix, respectively. Let L represent the photoacoustic signal matrix in the iteration, where L is the sampling length and I is the identity matrix. It is the regularization parameter; H represents the cyclic matrix of the electrical impulse response, where h represents the average time-domain photoacoustic signal of the microsphere. This represents the value of the Lth sampling point of h. This indicates transpose.

2. The photoacoustic-ultrasonic volumetric imaging method based on a ring-shaped ultrasonic array according to claim 1, characterized in that, The process of fusing the processed three-dimensional photoacoustic volume image with the three-dimensional ultrasonic volume image to generate a three-dimensional bimodal volume image specifically includes: The processed 3D photoacoustic volumetric image and 3D ultrasound volumetric image are normalized and color-fused to generate a 3D bimodal volumetric image that simultaneously contains photoacoustic and ultrasound feature information.

3. An imaging system for implementing the method according to any one of claims 1 to 2, characterized in that, include: A water tank is used to hold the coupling medium and the object being imaged. A ring-shaped ultrasonic array is set inside the water tank to emit ultrasonic waves and receive photoacoustic signals and ultrasonic echo signals from the object being imaged. Pulsed laser module, used to generate pulsed laser; An optical fiber bundle is used to conduct the pulsed laser and irradiate the imaged object with the pulsed laser. A motion scanning module is used to drive the annular ultrasound array and the fiber optic bundle to move in a direction perpendicular to the imaging plane; A signal transmission and acquisition module is connected to the ring ultrasonic array and is used to excite the ring ultrasonic array to emit ultrasonic waves and to acquire the photoacoustic signals and ultrasonic echo signals received by the ring ultrasonic array. A synchronization module is used to synchronize the timing of the pulsed laser module and the signal transmission and acquisition module; The control and reconstruction module is connected to the pulsed laser module, signal transmission and acquisition module, motion scanning module and synchronization module. It is used to control the operation of the imaging system, process the acquired photoacoustic signals and ultrasonic echo signals, and reconstruct and display two-dimensional photoacoustic images, ultrasonic images and three-dimensional dual-modal volumetric images.

4. The imaging system according to claim 3, characterized in that, Several sub-fiber bundles of the fiber bundle are uniformly fixed around the annular ultrasonic array by a fixator. In the photoacoustic imaging step, optical illumination and ultrasonic detection are confocalized: the tilt angle of the sub-fiber bundles is adjusted so that the pulsed laser forms a thin sheet-like illumination in the vertical direction and uniform illumination in the horizontal direction.

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