Photoacoustic imaging system

Abstract

The application provides a photoacoustic imaging system, which is composed of a light source, a micro-ring resonator detector array and a signal processing unit, wherein the micro-ring resonator detector array comprises at least two detector arrays, and each detector array comprises at least two micro-ring resonator cavities. In the imaging process, the light source emits a laser signal, each micro-ring resonator cavity generates a corresponding resonance signal according to the laser signal, and the signal processing unit outputs an image signal according to each resonance signal. The micro-ring resonator detector array has small size, high on-chip integration, high sensitivity, large bandwidth and large receiving angle (about 75°), which cannot be compared with traditional detectors PZT, PMUTs and CMUTs, and can realize miniaturization of the imaging system. Meanwhile, the photoacoustic detector array based on the micro-ring resonator can realize high-resolution fast imaging, accurate positioning of the sound source and deep large-view-field imaging, and can further approach clinical application.

Description

Technical Field

[0001] The present invention relates to the field of imaging technology, and in particular to a photoacoustic imaging system. Background Art

[0002] Photoacoustic imaging (PAI) is a novel imaging method that combines the advantages of traditional optical imaging and ultrasonic imaging. Most PAI systems integrate detectors, such as piezoelectric ceramic-based ultrasonic transducers (PZTs), micromachined piezoelectric ultrasound transducers (PMUTs), and capacitive micromachined ultrasonic transducers (CMUTs). However, these detectors all suffer from limited bandwidth, large size, and a narrow acceptance angle. This results in low image resolution, large imaging systems, slow imaging speed, and low sound source localization accuracy.

[0003] Therefore, the existing technology needs to be improved. Summary of the Invention

[0004] The main purpose of the present invention is to provide a photoacoustic imaging system to at least solve the technical problems of the existing photoacoustic imaging system in the related art, such as large imaging system volume and slow imaging speed.

[0005] The present invention provides a photoacoustic imaging system, which includes a light source, a microring resonator detector array, and a signal processing unit; the microring resonator detector array includes at least two detector arrays, each detector array includes at least two microring resonators;

[0006] The light source is used to emit a laser signal, each of the microring resonant cavities is used to generate a corresponding resonance signal according to the laser signal, and the signal processing unit is used to output an image signal according to each of the resonance signals.

[0007] Optionally, the light source is a wavelength-tunable continuous wave laser, and the continuous wave laser is used to continuously emit laser signals with a wavelength range of 1530-1565 nm.

[0008] Optionally, the photoacoustic imaging system further includes an optical fiber and a coupler;

[0009] The optical fiber and the coupler are arranged between the light source and the microring resonant cavity.

[0010] Optionally, the signal processing unit includes a photoelectric balance detector, an amplifier, a data acquisition card and a control display; the photoelectric balance detector is electrically connected to the control display via the amplifier and the data acquisition card; the photoelectric balance detector is used to receive a resonant signal, the amplifier is used to amplify the resonant signal to obtain an amplified signal, the data acquisition card is used to acquire the amplified signal, and the control display is used to output an image signal based on the amplified signal.

[0011] Optionally, the data acquisition card is configured with acquisition channels whose number is the same as the number of the microring resonant cavities, and each acquisition channel is used to acquire the amplified signal corresponding to a corresponding microring resonant cavity.

[0012] The photoacoustic imaging system of the present invention is composed of a light source, a microring resonant cavity detector array and a signal processing unit, wherein the microring resonant cavity detector array includes at least two detector arrays, and each detector array includes at least two microring resonant cavities. During the imaging process, the light source emits a laser signal, each microring resonant cavity generates a corresponding resonance signal according to the laser signal, and the signal processing unit outputs an image signal according to each resonance signal. Based on the small size, high on-chip integration, high sensitivity, large bandwidth, and large receiving angle (~75°) of the microring resonant cavity detector array, it is incomparable to traditional detectors PZT, PMUTs and CMUTs, and can realize the miniaturization of the imaging system. At the same time, the photoacoustic detector array based on the microring resonant cavity can achieve high-resolution and rapid imaging, precise positioning of the sound source, and deep and large field of view imaging, which can further move closer to clinical applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments recorded in this application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0014] Figure 1 Schematic diagram of the structure of the photoacoustic imaging system provided in the embodiment of the present application;

[0015] Figure 2 This is a schematic diagram of the structure of the signal processing unit in an embodiment of the present application;

[0016] Figure 3 This is a schematic diagram of the connection between the optical fiber, coupler, light source, and microring resonator in an embodiment of the present application.

[0017] The features, functions and advantages of the present invention will be further described with reference to the accompanying drawings and in conjunction with the embodiments. DETAILED DESCRIPTION

[0018] It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0019] It should be noted that related terms such as "first", "second", etc. can be used to describe various components, but these terms do not limit the components. These terms are only used to distinguish one component from another. For example, without departing from the scope of the present invention, the first component can be referred to as the second component, and the second component can similarly be referred to as the first component. The term "and / or" refers to any one or more combinations of related items and description items. In addition, in order to better illustrate the present invention, numerous specific details are given in the specific embodiments below. Those skilled in the art will understand that the present invention can also be implemented without these specific details. In other examples, well-known structures and components are not described in detail in order to highlight the main purpose of the present invention.

[0020] Photoacoustic imaging (PAI) is a novel imaging method that combines the advantages of traditional optical imaging and ultrasonic imaging. It uses short laser pulses to illuminate an object, generating ultrasonic waves. These waves are then received by a detector and processed, creating an image that reveals the specific optical absorption characteristics of the object. Because the entire imaging process is contactless with the object, and the source of image contrast is the specific absorption of the excitation light by absorbers within the object, PAI is label-free and can be used to perform multi-wavelength imaging by varying the excitation light wavelength to calibrate the composition of the object.

[0021] Specifically, depending on the application scenario, photoacoustic imaging can be divided into photoacoustic tomography, photoacoustic microscopy (PAM), and photoacoustic endoscopy (PAE). The latter two imaging methods are based on the time of flight (TOF) method, using a single detector to scan point by point or rotationally to locate the photoacoustic source and then form an image. However, for PACT, because an expanded wide light source is used to illuminate the object, absorbers at different positions inside it release photoacoustic signals simultaneously. Therefore, even under ideal conditions, three-dimensional imaging of the object requires a single detector to move to three different positions or use three fixed-position detectors to receive photoacoustic signals to locate the photoacoustic source.

[0022] In the actual imaging process, the number of detectors and their various parameters determine the performance of the photoacoustic tomography system. For example, imaging speed depends on the number of detectors used; the imaging system's accuracy in localizing the sound source is determined by the size of the individual detector's detection surface, the receiving angle, and the number of detectors used; and imaging resolution and detection depth are determined by the size, bandwidth, sensitivity, and number of detectors. Therefore, arraying high-performance single detectors can improve the performance of the photoacoustic imaging system.

[0023] Specifically: The relevant literature also introduced a linear transducer detection array composed of 128 detectors (center frequency 7MHz, bandwidth 5MHz), which is used for photoacoustic tomography of mice in vitro, achieving a lateral resolution better than 130um and an axial resolution of 330um, with an imaging depth of about 7.5mm and an imaging time of about 1.5 hours. Generally speaking, the detection efficiency is highest when the normal direction of the ultrasonic wavefront is perpendicular to the detection surface of the detector. Obviously, the above-mentioned linear array detector does not meet this requirement. Brecht et al. described an arc-shaped detection array with a center frequency of 3.1MHz, a focal length of 65mm, and composed of 64 transducers for imaging the internal organs and blood vessels of mice. The imaging time is 8 minutes and the spatial resolution is 500um. Xia et al. proposed a ring transducer array with a center frequency of 5MHz and a diameter of 50mm composed of 512 detectors for imaging living mice. It can image an area with a diameter of 20mm and a thickness of 1mm in just 1.6s, with a resolution of up to 100um. Lin et al. disclosed a hemispherical detector array consisting of 4 arc-shaped transducers, with 256 detectors in each channel. A complete scan and imaging takes only 5 seconds, with an imaging resolution of 390 μm and an imaging depth of 10 mm for the mouse brain.

[0024] Most photoacoustic imaging systems integrate detectors, such as piezoelectric transducers (PZTs), micromachined piezoelectric ultrasound transducers (PMUTs), and capacitive micromachined ultrasonic transducers (CMUTs). However, these detectors all suffer from limited bandwidth, large size, and a narrow acceptance angle. This results in low image resolution, large imaging systems, slow imaging speed, and low sound source localization accuracy.

[0025] Therefore, in order to solve the technical problems of large imaging system size and slow imaging speed in related technologies, please refer to Figure 1An embodiment of the present invention provides a photoacoustic imaging system 1 , which includes a light source 10 , a microring resonator detector array 20 , and a signal processing unit 30 .

[0026] The light source 10 refers to a device capable of generating a laser signal, such as a wavelength-tunable continuous wave laser. The continuous wave laser can continuously emit a laser signal with a wavelength range of 1530-1565 nm.

[0027] The micro-ring resonant cavity detector array 20 includes at least two detector arrays, each detector array includes at least two micro-ring resonant cavities ( Figure 1 The two microring resonators on the left form one detector array, and the two microring resonators on the right form another detector array. That is, the number of detector arrays is n, and the corresponding number of microring resonators is m, where n and m are both integers greater than or equal to 2. The microring resonator detector array is manufactured using semiconductor processing technology.

[0028] Through the photoacoustic imaging system of this embodiment, the light source, the microring resonant cavity detector array and the signal processing unit constitute the photoacoustic imaging system, and the microring resonant cavity detector array includes at least two detector arrays, and each detector array includes at least two microring resonant cavities. During the imaging process, the light source emits a laser signal, each microring resonant cavity generates a corresponding resonance signal according to the laser signal, and the signal processing unit outputs an image signal according to each resonance signal. Based on the small size, high on-chip integration, high sensitivity, large bandwidth, and large receiving angle (~75°) of the microring resonant cavity detector array, it is incomparable to traditional detectors PZT, PMUTs and CMUTs, and can realize the miniaturization of the imaging system. At the same time, the photoacoustic detector array based on the microring resonant cavity can achieve high-resolution rapid imaging, precise positioning of the sound source, and deep and large field of view imaging, which can be further approached to clinical applications.

[0029] See also Figure 2 The signal processing unit 30 includes a photoelectric balance detector 301, an amplifier 302, a data acquisition card 303, and a control display 304. The photoelectric balance detector is electrically connected to the control display via the amplifier and the data acquisition card. Specifically, the output of the photoelectric balance detector is electrically connected to the input of the amplifier, the output of the amplifier is electrically connected to the input of the data acquisition card, and the output of the data acquisition card is electrically connected to the input of the control display. Specifically, when the microring resonator generates a resonant signal, the photoelectric balance detector converts the resonant signal into an electrical signal. The amplifier amplifies the electrical signal to generate an amplified signal. The data acquisition card collects the amplified signal, and the control display outputs an image signal based on the amplified signal.

[0030] In an actual application scenario, when a continuous-wave laser continuously emits a laser signal with a wavelength range of 1530-1565nm, each microring resonant cavity in the microring resonant cavity detector array generates a corresponding resonance signal based on the laser signal. The photoelectric balance detector in the signal processing unit receives the resonance signal and converts it into an electrical signal. The amplifier performs low-noise amplification on the electrical signal (increases the signal strength) to obtain an amplified signal. The data acquisition card collects data on the amplified signal changing over time, and controls the display based on a pre-installed image reconstruction program to reconstruct the data collected by the data acquisition card and display the reconstruction result (output image signal).

[0031] See also Figure 3 The photoacoustic imaging system also includes an optical fiber and a coupler, which are arranged between the light source and the microring resonator. The optical fiber has two sections (subsequently labeled as optical fiber 1 and optical fiber 2) and two couplers (labeled as couplers 1 and 2). Light is input from port 1 for transmission through optical fiber 1 and coupler 1 (the coupler is designed to improve coupling efficiency with the optical fiber). It is then coupled to the microring resonator via the evanescent field in coupling region 1. After a cycle of transmission within the microring resonator, the light returns to coupling region 1, where it constructively interferes with the light transmitted from port 1 to that region, increasing the light intensity within the cavity. Simultaneously, the light within the resonant cavity is output to port 2 via the evanescent field in coupling region 2, decreasing the light intensity within the cavity. As light is continuously input and output in coupling regions 1 and 2, the light intensity within the resonant cavity dynamically balances, and the light intensity output from port 2 stabilizes. Specifically, during imaging, optical (or ultrasonic) acoustic waves act as mechanical waves on the microring cavity, squeezing and deforming its waveguide, thereby changing the effective refractive index (neff) of the waveguide for 1550nm light. This causes the resonance of light of this wavelength to weaken in the microring cavity, making the light intensity in the microring cavity unstable and causing fluctuations in the light intensity output from port 2. Coupler 2 and optical fiber 2 transmit the optical signal output from port 2 to a photoelectric balanced detector, where it is converted into an electrical signal. After amplification by an amplifier, the data is recorded on an acquisition card and finally processed and displayed on a control display.

[0032] In an alternative embodiment of this embodiment, the data acquisition card is configured with a number of acquisition channels equal to the number of microring resonators, with each acquisition channel used to collect the amplified signal corresponding to a corresponding microring resonator. Specifically, the n lines of the microring cavity detection array correspond to n channels of the acquisition card, and the n*m ​​detectors in the array collectively receive optical (ultrasound) waves. (The spatial distribution of the microring cavities in the same line is designed so that the optical signal output interval between adjacent microring cavities is greater than the sampling interval of the photoelectrically balanced detectors, thereby preventing signal aliasing and image distortion.) Different image reconstruction algorithms are employed depending on the detector arrangement (linear, arcuate, annular, spherical, etc.).

[0033] The following further describes the technical effects achieved by this embodiment: The present invention utilizes semiconductor processing technology to manufacture microring resonant cavities based on SOI materials for photoacoustic imaging; utilizes a 1550nm wavelength continuous wave laser as a detection light source to realize all-optical detection of photoacoustics (ultrasounds) by the microring cavity; and adjusts the number and arraying method of the microring resonant cavities according to the different states of the imaging object (arraying the microring cavities for photoacoustic (ultrasound) imaging). That is, the microring cavity used in the present invention is smaller in size, has a larger bandwidth, and has a higher sensitivity per unit detection area than existing high-performance ultrasonic detectors, and can be integrated on a chip for mass production. The arraying method of the microring cavity can be changed according to the shape and size of the imaging sample to achieve higher ultrasonic detection efficiency and realize accurate imaging of the sample. The microring cavities that make up the detection array can adjust the structural size according to the application scenario to meet different detection requirements.

[0034] In a practical application scenario, photoacoustic imaging contrast can reveal the absorption differences of a sample's internal absorber to a specific wavelength of light. The photoacoustic signal is a series of ultrasonic waves with a sound pressure ranging from ~10Pa to ~KPa and a frequency ranging from ~KHz to ~GHz, which carries information about the absorber. Microring resonators have a detection sensitivity of mPa / √Hz and a bandwidth of ~100MHz, making them suitable for use as ultrasonic detectors in photoacoustic imaging. Furthermore, their small size, large detection angle, and ease of arraying make it easy to achieve high resolution and high absorber positioning accuracy when used in photoacoustic tomography.

[0035] In the several embodiments provided in this application, it should be understood that the disclosed devices can be implemented in other ways. For example, the device embodiments described above are merely illustrative. For example, the division of modules is only a logical function division. In actual implementation, there may be other division methods, such as multiple modules or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, indirect coupling or communication connection of devices or modules, which can be electrical, mechanical or other forms.

[0036] Modules described as separate components may or may not be physically separate, and components shown as modules may or may not be physical modules, that is, they may be located in one place or distributed across multiple network modules. Some or all of these modules may be selected to achieve the purpose of this embodiment based on actual needs.

[0037] In addition, the functional modules in the various embodiments of the present application may be integrated into a processing module, or each module may exist physically separately, or two or more modules may be integrated into a single module. The above-mentioned integrated modules may be implemented in the form of hardware or software functional modules.

[0038] If the integrated module is implemented in the form of a software functional module and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present application, or the part that contributes to the prior art, or all or part of the technical solution can be embodied in the form of a software product, which is stored in a readable storage medium and includes several instructions for enabling a computer device (which can be a personal computer, server, or network device, etc.) to execute all or part of the steps of the various embodiments of the present application. The aforementioned readable storage medium includes various media that can store program codes, such as a USB flash drive, a mobile hard disk, a ROM, a RAM, a magnetic disk, or an optical disk.

[0039] In the above embodiments, the description of each embodiment has its own focus. For parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0040] The above are only preferred embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention description and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A photoacoustic imaging system, characterized in that: The photoacoustic imaging system includes a light source, a microring resonator detector array and a signal processing unit; The microring resonant cavity detector array includes at least two detector arrays, and each detector array includes at least two microring resonant cavities; The photoacoustic imaging system further includes an optical fiber and a coupler; The optical fiber has two sections, and the number of the couplers is two; A section of the optical fiber and a coupler are both arranged between the light source and the microring resonator, and another section of the optical fiber and another coupler are both arranged between the microring resonator and the signal processing unit; The light source is used to emit a laser signal, each of the microring resonators is used to generate a corresponding resonance signal according to the laser signal, and the signal processing unit is used to output an image signal according to each of the resonance signals; the resonance signal includes a laser signal that reaches dynamic equilibrium; The laser signal enters the microring resonant cavity through a section of the optical fiber and a coupling region of one of the couplers. When the light intensity in the microring resonant cavity reaches dynamic equilibrium, the laser signal that has reached dynamic equilibrium in the microring resonant cavity is transmitted to the signal processing unit through another coupling region of another coupler and another section of the optical fiber. One coupling region and the other coupling region are respectively located on opposite sides of the microring resonant cavity. The signal processing unit includes a photoelectric balance detector, an amplifier, a data acquisition card and a control display; The photoelectric balance detector is electrically connected to the control display via the amplifier and the data acquisition card; The photoelectric balance detector is used to convert the resonant signal into an electrical signal, the amplifier is used to amplify the electrical signal to obtain an amplified signal, the data acquisition card is used to acquire the amplified signal, and the control display is used to output an image signal according to the amplified signal.

2. The photoacoustic imaging system according to claim 1, wherein: The light source is a wavelength-tunable continuous wave laser, which is used to continuously emit laser signals with a wavelength range of 1530-1565 nm.

3. The photoacoustic imaging system according to claim 1, wherein: The data acquisition card is configured with acquisition channels having the same number as the number of the microring resonant cavities, and each acquisition channel is used to acquire the amplified signal corresponding to a corresponding microring resonant cavity.

4. The photoacoustic imaging system according to claim 1, wherein: The optical signal output interval of adjacent micro-ring resonators is greater than the sampling interval of the photoelectric balance detector.

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