A photoacoustic imaging method and system

Abstract

The application discloses a photoacoustic imaging method and system, relates to the technical field of medical imaging, and independently designs a fast photoacoustic imaging system of a ring-shaped fiber fusion ring-shaped array ultrasonic probe in the hardware aspect; the system can perform nondestructive imaging on a tissue; the imaging method is that laser pulses are emitted by a laser system; laser pulses are focused into a ring-shaped light spot by beam shaping; when the ring-shaped light spot irradiates a sample, local temperature rise caused by light absorption in the sample forms transient thermal expansion, and then ultrasonic waves are generated; the ultrasonic waves contain internal structure information of the sample; a plurality of ultrasonic sensors at the ring-shaped position simultaneously receive photoacoustic signals propagating back from different directions; the collected photoacoustic signals are processed, an image reconstruction algorithm is used, and the processed signals are converted into a three-dimensional photoacoustic image.

Description

Technical Field

[0001] This invention relates to the field of medical imaging technology, and in particular to a photoacoustic imaging method and system. Background Technology

[0002] Photoacoustic imaging is a non-invasive, multi-scale, and multifunctional imaging method widely used in the biomedical field. It combines the advantages of pure optical and pure ultrasound imaging, possessing characteristics such as high resolution, high contrast, and ideal penetration depth. The principle of photoacoustic imaging is based on the application of low-energy pulsed laser light to tissues. The tissue absorbs the light energy, undergoes periodic thermal expansion, and generates pressure waves, known as photoacoustic signals. These signals carry information about the tissue's light absorption and ultrasound transmission characteristics. Therefore, by analyzing the photoacoustic signals, structural and functional images related to the tissue's optical and acoustic properties can be reconstructed. Based on these principles, photoacoustic imaging is an important tool for studying the morphology, physiological characteristics, pathological features, and metabolic functions of biological tissues.

[0003] In recent years, photoacoustic technology has become increasingly important in the field of medical imaging. Photoacoustic imaging of biological tissues, including the concentrations of HbR, HbO2, and water (H2O), is crucial for the accuracy of lesion detection and diagnostic decisions, especially in image-guided cancer treatment. Currently, ultrasound examinations only provide two-dimensional tomographic results, offering limited accuracy in lesion detection based on the provided functional parameters. They cannot provide more accurate functional parameters of biological tissues, nor can they achieve three-dimensional photoacoustic imaging of the three-dimensional structure. Three-dimensional photoacoustic imaging can yield more effective functional parameters. Summary of the Invention

[0004] In order to overcome the shortcomings of the existing technology, which cannot provide more accurate functional parameters of biological tissues and cannot achieve three-dimensional photoacoustic imaging results of three-dimensional structures, the main objective of this invention is to provide a photoacoustic imaging method and system.

[0005] To achieve the above objectives, the present invention employs the following technical solution: a photoacoustic imaging method, comprising:

[0006] Emitting laser pulses through a laser system;

[0007] By using beam shaping, the laser pulse is focused into a ring-shaped spot;

[0008] When a ring-shaped light spot illuminates a sample, the light absorption in the sample causes a local temperature rise, resulting in instantaneous thermal expansion, which in turn generates ultrasonic waves; these ultrasonic waves contain structural information about the sample's interior.

[0009] Multiple ultrasonic sensors positioned in a ring shape are used to simultaneously receive photoacoustic signals propagating back from different directions.

[0010] The acquired photoacoustic signals are processed, and an image reconstruction algorithm is used to convert the processed signals into a three-dimensional photoacoustic image.

[0011] The photoacoustic image is used to solve for the tissue's elastic modulus and optical absorption coefficient using a delay summation algorithm;

[0012] A photoacoustic imaging system, comprising:

[0013] A laser system used to emit laser pulses;

[0014] The beam shaping module focuses the laser pulse into a ring-shaped spot;

[0015] A ring array probe, with multiple ultrasonic sensors in a ring position, is used to simultaneously receive photoacoustic signals propagating back from different directions;

[0016] The processing module is used to process the acquired photoacoustic signals and construct a three-dimensional photoacoustic image.

[0017] The processing module includes a 128-channel acquisition card, which amplifies and filters the acquired photoacoustic signals.

[0018] The detection plane of the ring array probe is coaxial with the ring spot formed by the beam shaping module at the same height.

[0019] The beam shaping module includes:

[0020] An optical fiber transmission tube, one end of which is connected to the laser system;

[0021] A ring-shaped fiber optic transmitter box has several holes evenly distributed on its inner ring sidewall;

[0022] A connecting tube, one end of which is connected to the other end of the optical fiber transmission tube, and the other end of the connecting tube is connected to the annular optical fiber transmitter box through an inlet formed on its side wall, the top of which is inclined.

[0023] The angle of inlet top is 40 degrees.

[0024] It also includes a lifting module, with the ring array probe located at the lifting end of the lifting module.

[0025] Compared with existing technologies, the beneficial effects of this invention are as follows: Through the design of the annular light spot and the annular array probe, a uniform annular light spot can be formed, ensuring maximum utilization of light energy. This is crucial for maximizing the sensitivity of signal generation and reception, especially for the reconstruction of three-dimensional photoacoustic image structures. It opens up new avenues for better differentiation between benign and malignant tumors. The elasticity contrast between malignant lesions and healthy tissue is very high, enabling effective reconstruction of physiological and elastic properties based on three-dimensional photoacoustic images, obtaining multiple functional parameters of the tissue, and thus improving the accuracy of lesion detection through analysis of these multiple functional parameters. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the beam shaping module of the present invention;

[0027] Figure 2 This invention relates to the photoacoustic imaging system for resolution detection and imaging of a mouse model of breast cancer.

[0028] Figure 3 This is a penetration depth experiment conducted using chicken breast in an embodiment of the present invention;

[0029] Figure 4 The three-dimensional image of a finger is constructed based on the collected acoustic and optical signals in this embodiment of the invention. Detailed Implementation

[0030] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0031] Example:

[0032] See Figure 1-4 A photoacoustic imaging method includes: emitting laser pulses through a laser system;

[0033] By using beam shaping, laser pulses are focused into a ring-shaped spot. When the ring-shaped spot illuminates the sample, the light absorption in the sample causes a local temperature rise, resulting in instantaneous thermal expansion, which in turn generates ultrasound. This ultrasound contains structural information about the sample's interior. Multiple ultrasound sensors located at the ring position simultaneously receive photoacoustic signals propagating back from different directions. The acquired photoacoustic signals are processed, and an image reconstruction algorithm is used to convert the processed signals into a three-dimensional photoacoustic image of the structure.

[0034] The photoacoustic image is used to solve for the elastic modulus and optical absorption coefficient of the tissue through a delay summation algorithm; the optical absorption coefficient of the diseased tissue is at least 5 times higher than that of normal tissue, and the elastic modulus of the diseased tissue is 2 to 6 times higher than that of normal soft tissue.

[0035] A photoacoustic imaging system, comprising:

[0036] A laser system used to emit laser pulses;

[0037] The beam shaping module focuses the laser pulse into a ring-shaped spot;

[0038] A ring array probe, with multiple ultrasonic sensors in a ring position, is used to simultaneously receive photoacoustic signals propagating back from different directions;

[0039] The processing module is used to process the acquired photoacoustic signals and construct a three-dimensional photoacoustic image.

[0040] The processing module includes a 128-channel acquisition card, which amplifies and filters the acquired photoacoustic signals.

[0041] The detection plane of the ring array probe is coaxial with the ring spot formed by the beam shaping module at the same height.

[0042] The beam shaping module includes:

[0043] An optical fiber transmission tube, one end of which is connected to the laser system;

[0044] A ring-shaped fiber optic transmitter box has several holes evenly distributed on its inner ring sidewall;

[0045] A connecting tube, one end of which is connected to the other end of the optical fiber transmission tube, and the other end of the connecting tube is connected to the annular optical fiber transmitter box through an inlet formed on its side wall, the top of which is inclined.

[0046] The angle of inlet top is 40 degrees.

[0047] It also includes a lifting module. The ring array probe is located at the lifting end of the lifting module. During the imaging process, the lifting module slowly rises or falls, which can realize multi-layer two-dimensional scanning. Through multi-layer two-dimensional scanning, three-dimensional imaging can be constructed. The lifting module can be a common hydraulic lifting platform or an existing lifting device with high stability. It will not be explained in detail here.

[0048] Example 2

[0049] See Figure 1-4 Based on Example 1, another implementation method is a photoacoustic imaging system, such as... Figure 1As shown, in this system, the light source consists of a laser system and an optical parametric oscillator (OPO) system. The OPO outputs a continuously tunable wavelength of 660–2300 nm. A 532 nm pump source is placed at the front end, and the OPO is internally located at the rear end. The crystal of the OPO converts the second harmonic of Nd:YAG (532 nm) into tunable light with near-infrared and visible red edges. The continuously tunable wavelength of 660–2300 nm can be used for photoacoustic imaging. Specific wavelengths can be selected; for example, 700 nm can be selected to calculate the optical absorption coefficient, and 900 nm can be selected to calculate the elastic modulus.

[0050] The imaging system can reconstruct three-dimensional photoacoustic images by accumulating and superimposing multiple two-dimensional scan results. The elastic modulus coefficient and optical absorption coefficient belong to functional image reconstruction. The system uses the finite element method to analyze the photoacoustic elastic modulus equation to realize three-dimensional optical absorption photoacoustic images and three-dimensional elastic modulus photoacoustic images. This function is helpful for the early diagnosis of diseases. For normal tissues, the absorption coefficient is approximately between 0.03 and 0.05 cm^-1.

[0051] For diseased tissue, due to the abundance and abnormal shape of surrounding blood vessels, the blood absorption coefficient, influenced by wavelength and hemoglobin oxygen saturation, is approximately between 1.0 and 10.0 cm^-1, at least five times higher than that of normal tissue. Furthermore, the elastic modulus of diseased tissue is 2 to 6 times higher than that of normal soft tissue. This laser system can output a dual-pump wavelength of 532 / 1064 nm, and the OPO crystal excited by the pump source can output a tunable spectrum of 680 nm to 2300 nm. In addition, the maximum output energy of this laser is 200 mJ, the maximum output pulse repetition frequency is 20 Hz, and the pulse width is 3-5 ns. The laser beam is transmitted through a single optical fiber, and after passing through the probe, it is finally output in a ring of 36 fiber bundles, forming a uniform ring spot. The optical fibers and the probe are fixed to the top of the lifting platform. In this embodiment, a common lifting platform with a conventionally usable height is selected. Then, multi-layer two-dimensional scanning is used to achieve three-dimensional imaging. Figure 1 As shown, the fixed mode of the annular light spot and the annular array probe is such that the annular light spot is obliquely illuminated and eventually coaxial with the detection plane of the annular array ultrasound probe. The annular array ultrasound probe can only receive signals from one cross section, and its receiving emission angle is very small. Therefore, if the annular light spot of the annular fiber illuminating the tissue is coaxial with the signal receiving surface of the probe, the utilization of light energy can be maximized, the generated ultrasound signal can be maximized, and the received signal can be maximized, thus ensuring the maximum sensitivity of signal generation and reception.

[0052] In the experiment, the probe and the optical fiber used for transmission were placed in a water tank. The generated photoacoustic signal was collected by the ring array probe and transmitted to a 128-channel acquisition system. After amplification and filtering, the signal was stored in a computer system and then further processed. The photoacoustic signal was used to obtain a structured photoacoustic image through a delay summation algorithm.

[0053] To solve for the elastic modulus of tissue, a finite element method combined with multi-wavelength analysis is used, and the equation is the photoacoustic elastic wave equation.

[0054]

[0055] In the above formula, p is the photoacoustic pressure, ω is the angular frequency, k0=ω / v0 is the wave number, and v0 and K0 are the speed of light in the medium and the elastic modulus of the medium, respectively.

[0056] To solve for the tissue optical absorption coefficient, a method combining Monte Carlo and photoacoustic wave equations is used, as follows:

[0057] Determine the distribution Ψ of absorbed light energy density i (i = 1, 2, ..., n, where n is the number of finite element nodes), a model-based reconstruction algorithm is adopted, which is based on the finite element solution of the photoacoustic wave equation in a homogeneous acoustic medium.

[0058]

[0059] In the formula, p represents the pressure wave; k0 = ω / c0 represents the wave number, ω represents the angular frequency, c0 represents the propagation speed of the sound wave in the medium, β represents the coefficient of thermal expansion, and c represents the specific heat C. p Absorbed light energy density Ψ, light absorption coefficient, and light energy product Φ, Ψ=μ a Φ.

[0060] The luminous flux distribution was calculated using Monte Carlo simulation. Then, the distribution of the light absorption coefficient was calculated using an optimization procedure based on a least-squares minimization scheme. The implementation of this least-squares minimization algorithm is as follows: considering a range of values ​​μ... a Uniform initial guess μ a0 =0.001, iteration step size Δμ a First, calculate the error as a function.

[0061]

[0062] In the formula, Ψ m The normalized absorbed light energy density recovered by the first step of PAT reconstruction, Ψ c The normalized absorbed light energy density obtained from Monte Carlo simulation, where Ψ c =μ a Φ cThen compare Ψ c and Ψ m The error between them; if the error is small enough, the iterative solution will stop; otherwise, update μ. a Through μ a =μ a0 +Δμ a (j-1) Repeat the iterative calculation according to the previous process (j is the iteration number).

[0063] It should be noted that, in this invention, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus.

[0064] The above embodiments are merely illustrative examples of the present invention and do not constitute a limitation on the scope of protection of the present invention. Any designs that are the same as or similar to the present invention are within the scope of protection of the present invention.

Claims

1. A photoacoustic imaging system, characterized by, include: A laser system used to emit laser pulses; The beam shaping module is used to focus laser pulses into a ring-shaped spot; A ring array probe, with multiple ultrasonic sensors in a ring position, is used to simultaneously receive photoacoustic signals propagating back from different directions; The processing module is used to process the acquired photoacoustic signals and construct a three-dimensional photoacoustic image. The ring array probe is located at the lifting end of the lifting module; The processing module includes a 128-channel acquisition card, which amplifies and filters the acquired photoacoustic signals. The detection plane of the ring array probe is coaxial with the ring spot formed by the beam shaping module at the same height; The beam shaping module includes: an optical fiber transmission tube, one end of which is connected to the laser system; an annular optical fiber transmitter box, on which a plurality of holes are evenly opened on the inner ring sidewall; and a connecting tube, one end of which is connected to the other end of the optical fiber transmission tube, and the other end of the connecting tube is connected to the annular optical fiber transmitter box through an inlet opened on its sidewall, the top of the inlet being inclined; the angle of inclination of the top of the inlet is 40 degrees.

2. A photoacoustic imaging method, characterized by, The method, when applied to the photoacoustic imaging system as described in claim 1, includes the following steps: Emitting laser pulses through a laser system; By using beam shaping, the laser pulse is focused into a ring-shaped spot; When a ring-shaped light spot illuminates a sample, the light absorption in the sample causes a local temperature rise, resulting in instantaneous thermal expansion, which in turn generates ultrasonic waves; these ultrasonic waves contain structural information about the sample's interior. Multiple ultrasonic sensors positioned in a ring shape are used to simultaneously receive photoacoustic signals propagating back from different directions. The acquired photoacoustic signals are processed, and an image reconstruction algorithm is used to convert the processed signals into a three-dimensional photoacoustic image.

3. The method of photoacoustic imaging of claim 2, wherein, The photoacoustic image is used to solve for the tissue's elastic modulus and optical absorption coefficient using a delay summation algorithm.

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