CN102608036B - Three-dimensional opto-acoustic imaging system based on acoustic lens and sensor array and method - Google Patents

Abstract

The invention relates to a three-dimensional photoacoustic imaging system and method based on an acoustic lens and a sensor array. The system is a cube test bench, which mainly includes a laser, a beam expander, a phononic crystal lens, a photoacoustic sensor array, a data bus, and a frosted glass vessel. , a data acquisition module and a computer for image processing; the laser light is used to irradiate the center points of the four sides of the cube frosted glass container, so that the sample is evenly irradiated through the ground glass, so that the sample is heated and expanded evenly, so that the acoustic signal generated by the sample expansion is focused The beam is formed, and the three-dimensional data of photoacoustic imaging is collected and recorded in real time through the photoacoustic sensor array, data acquisition module and computer used for image processing. After image processing, the three-dimensional image of the light absorption distribution of the test sample can be directly seen on the display. It has the advantages of complete functions, stable performance, low cost, etc., and can be widely used in the fields of biology, medicine, and material analysis.

Description

Three-dimensional photoacoustic imaging system and method based on acoustic lens and sensor array

technical field

The invention belongs to the technical field of photoacoustic imaging, in particular to a three-dimensional photoacoustic imaging method and device based on an acoustic lens and a sensor array.

Background technique

Photoacoustic imaging technology is a non-destructive medical imaging method developed in recent years. It combines the high contrast characteristics of pure optical imaging and the high penetration depth characteristics of pure ultrasound imaging to provide high-resolution and high-contrast tissue imaging. Photoacoustic imaging technology is a new imaging technology using "light excitation-ultrasonic imaging". Photoacoustic imaging technology is a detection technology with strong adaptability and high sensitivity, especially suitable for non-destructive detection of strong scattering and non-transparent samples, and is widely used in biology, medicine, material analysis and other fields.

At present, photoacoustic imaging technology can be classified into three modes: phase-controlled focusing method, Radon inversion-based filtered back-projection imaging method and acoustic lens imaging method. Based on the principle of phased focusing, Xing et al. used a 320-element transducer linear array to realize fast photoacoustic imaging. Wang L.V. developed the Radon inversion algorithm into a high-resolution photoacoustic imaging method. Both of these imaging methods avoid the limitation of the acoustic diffraction effect, so high-resolution imaging can be achieved, but due to the need to scan the imaging object And data averaging processing, etc., takes a long time, and may also cause reconstruction artifacts.

There have been many reports on photoacoustic imaging and in vivo functional imaging of simulated tissues, but the experimental equipment is complex, the data acquisition time is long, and the imaging algorithm is complex, the calculation is large, and the time to obtain a complete reconstructed image is often It takes several minutes to tens of minutes, which cannot meet the requirements of actual clinical application. At the same time, due to the mechanical scanning of hundreds of angles and the long-term data acquisition process, unstable factors such as mechanical vibration and random parameter drift caused by long-term operation of the instrument will inevitably bring random errors to the research results, thus seriously affecting the quality of imaging. and the reliability and stability of the research results.

There are still some deficiencies in the existing photoacoustic imaging system. The general light source uses a pulsed laser, which is relatively bulky and expensive. In addition, the image effect is not up to the level of other imaging technologies, especially the imaging of deep tissues is affected by the absorption of tissues. More serious. Moreover, most of the existing photoacoustic imaging systems use hydrophones to realize two-dimensional imaging, and few use arrays to realize three-dimensional high-resolution photoacoustic imaging systems. Furthermore, existing photoacoustic imaging systems rarely take sample irregularities into account.

Contents of the invention

The purpose of the present invention is to overcome the deficiencies and shortcomings of the existing photoacoustic imaging technology, provide a method that reduces system errors, can receive and accurately record the three-dimensional data of photoacoustic imaging in real time, and can be directly displayed on the display after image processing. A three-dimensional photoacoustic imaging method and system based on an acoustic lens and a sensor array for viewing a three-dimensional image of light absorption distribution of a detection sample.

For realizing above-mentioned purpose of the invention, technical scheme of the present invention is:

The three-dimensional photoacoustic imaging system based on acoustic lenses and sensor arrays is a cube experimental platform, including lasers, beam expanders, phononic crystal lenses, photoacoustic sensor arrays, data buses, frosted glass vessels, data acquisition modules and image processing tools. computer; it is characterized in that: each of the four lasers and the beam expander, the ground glass vessel is placed at the center of the inner bottom of the cube; the four lasers are located at the bottom of the four vertical surfaces of the cube test bench, and It is perpendicular to the ground glass vessel inside; the four beam expanders are attached to the outer wall of the ground glass vessel, and the spatial position corresponds to the laser; the acoustic lens made of phononic crystal is directly above the ground glass vessel, and the photoacoustic sensor array is located in the acoustic The lens is directly above the focal point of the acoustic lens, and the photoacoustic sensor is connected with the data acquisition module and the computer through the data bus. The computer used for image processing includes image processing, display module and image processing software, which can perform photoacoustic image noise reduction and enhancement processing on the received three-dimensional photoacoustic data, so as to obtain a three-dimensional image of the light absorption distribution of the test sample , and can display two-dimensional or three-dimensional images on the monitor.

The acoustic lens is composed of a phononic crystal, wherein: the phononic crystal is composed of a lead ball with a diameter of about 0.78 cm uniformly coated with 0.02 cm soft rubber, and then embedded in an epoxy resin cube.

A method for three-dimensional photoacoustic imaging based on an acoustic lens and a sensor array, characterized in that:

(1) The laser irradiates the sample to expand and emit acoustic signals: the four sides of the frosted glass container are irradiated by the laser, so that the sample is evenly heated and expanded to emit acoustic signals, and the timing control circuit realizes the parameter control and time recording of the laser signal emission; record the initial time t ₀ , the center of the container is irradiated by the laser at the same time, so that the sample is heated and expands to emit an acoustic signal;

(2) Acoustic lens focusing: the acoustic lens is composed of phononic crystals, which receive the acoustic waves emitted by the sample and focus them; the imaging position of the sample in the photoacoustic sensor array is drawn up according to the acoustic lens imaging model, and the reflected photoacoustic signal is generated by the phonon crystal focus;

(3) Acoustic signal reception and conditioning: the photoacoustic sensor array receives the emitted photoacoustic signal at the focal position of each photoacoustic sensor, and collects, receives and records the three-dimensional data of photoacoustic imaging in real time through the data acquisition module; wherein:

When the photoacoustic sensor array has an acoustic wave signal, record the time at this time as t ₁ and store it in the data memory RAM of the computer; at the same time, the photoacoustic sensor array converts the weak photoacoustic signal into an electrical signal, and the value of the electrical signal is The energy E of the reflected sound wave;

According to the negative refraction law of the acoustic lens, the two-dimensional imaging data f(x, y) of the sample imaging area can be obtained; the distance L from the sound source of the detection sample to the receiving array can be calculated by using the traveling time T of the sound wave. This distance L, That is, the third-dimensional coordinate data z of the imaging area of the sample, where: T=t ₁ -t ₀ , L=T*sound velocity in the scattering liquid, (z=L); using the coordinate data z combined with the two-dimensional imaging data f(x , y) can obtain the three-dimensional imaging data f(x, y, z) of the photoacoustic image of the imaging area of the sample, and the energy E of the reflected acoustic wave is the three-dimensional imaging data f(x, y) of the photoacoustic image of the imaging area of the sample , z), namely E=f (x, y, z);

(4) Photoacoustic image processing and display: the three-dimensional imaging data f(x, y, z) of the photoacoustic image, wherein the two-dimensional imaging data f(x, y) is obtained by the acoustic lens imaging model, and the other dimension The coordinate data f(z) is determined by the travel time T in the scattering liquid, and E is the photoacoustic pressure of the sample, which is the gray value of the photoacoustic image; the received three-dimensional imaging data is enhanced and feature extracted from the photoacoustic image , classification and identification, input the obtained 3D imaging data into a computer or a single chip microcomputer, and realize the 3D display and analysis of the detection samples through image processing.

Beneficial effects of the present invention:

In the present invention, the laser light is used to irradiate the center points of the four sides of the cube frosted glass container, so that the sample is evenly irradiated through the frosted glass, so that the sample is evenly heated and expanded, and the system error is reduced as little as possible. In addition, using the characteristics of the perfect lens of the phononic crystal, the acoustic signal generated by the sample expansion is focused to form a beam, and the acoustic signal receiving array is placed at the focal position of the acoustic lens. The receiving array can receive and accurately record the three-dimensional data of photoacoustic imaging in real time. After image processing, the three-dimensional image of the light absorption distribution of the test sample can be directly seen on the display, and the three-dimensional image of the light absorption distribution of the sample can be obtained.

The system provided by the present invention has the advantages of complete functions, stable performance, low cost, etc., and can be widely used in the fields of biology, medicine, material analysis, etc., and has great significance in the imaging of cancerous tissues and the detection of tumors.

Description of drawings

Figure 1 is a schematic diagram of the structure of the photoacoustic imaging system.

Figure 2 is a diagram of the structure of the phononic crystal.

Figure 3 is a picture of the focused imaging of sound waves through the acoustic lens.

Fig. 4 is a configuration diagram of a single photoacoustic sensor.

Fig. 5 is a configuration diagram of a photoacoustic sensor array.

Figure 6 shows the work of data collection and processing.

Figure 7 is the flow of image processing.

Fig. 8 is a three-dimensional rendering after image processing.

Reference numerals in Fig. 1: 1 is a laser, 2 is a beam expander, 3 is a phononic crystal lens, 4 is a sensor array, 5 is a data bus, 6 is a glass container, 7 is a (cell) sample, 8 is after beam expansion Laser, 9 is the radiated sound wave, 10 is the two-dimensional image of the detection sample, 11 is the induction fiber, 12 the bridge circuit, 13 the energy-gathering cavity, 14 is 256 analog signals, 15 is the 16-bit data acquisition board, 16 is the control Board, 17 is a RAM memory 18 is a three-dimensional image of the detected (cell) sample.

Detailed ways

The present invention will be described in detail below in conjunction with the accompanying drawings.

As shown in Figure 1, the three-dimensional photoacoustic imaging system based on the acoustic lens and sensor array is a cube test bench, and a three-dimensional photoacoustic imaging system based on the acoustic lens and sensor array is a cube test bench; including laser 1, beam expander mirror 2, phononic crystal lens 3, photoacoustic sensor array 4, data bus 5, frosted glass vessel 6, data acquisition module and computer for image processing; it is characterized in that: the laser and the beam expander each have four , the frosted glass vessel is placed at the center of the inner bottom of the cube; the four lasers are located at the bottom of the four vertical surfaces of the cube test bench, and are in a vertical state with the ground glass vessel inside; the four beam expanders are attached to the The outer wall of the frosted glass vessel corresponds to the spatial position of the laser; the acoustic lens composed of phononic crystals is directly above the ground glass vessel, the photoacoustic sensor array is located directly above the acoustic lens, at the focal position of the acoustic lens, and the photoacoustic sensor passes through the data bus It is connected with the data acquisition module and the computer.

1. Laser excitation ultrasound.

First, the initial time t ₀ of the excitation is recorded by the single-chip microcomputer control circuit and stored in the data memory RAM. At this time, four lasers of the same type irradiate the centers of the four sides of the ground glass container at the same time, so that the (cell) sample 7 is evenly heated and expanded emit a sonic signal.

2. Sound wave focusing.

As shown in Figure 2, the excited acoustic signal is focused through the acoustic lens composed of phononic crystals, and the transmitted acoustic waves at different positions in the sample are respectively focused on different focal points, and the elements on the receiving array are arranged according to these focal positions. The focal plane is formed, and the receiving array coincides with the focal plane. As shown in FIG. 3 , the acoustic wave emitted by the sample is refracted by the phononic crystal lens and focused on the receiving array to form a two-dimensional image 10 of the illuminated surface. The detected target is divided into multiple primitives in the field of view. The division of primitives determines the resolution of the focal plane. The receiving array of this system is 16*16 256 focal planes of primitives. The more detailed the matrix division, The received 2D image is clearer.

3. Sound wave reception.

As shown in Figure 4, the photoacoustic sensor array is a receiving module, which is a mesoscopic piezoresistive acoustic sensor, wherein: the photoacoustic sensor array is made of MEMS. It consists of the same four varistors connected into two full-bridge circuits. When an acoustic signal along the Z-axis acts on the energy-gathering cavity, the energy-gathering cavity is excited by the sound pressure and vibrates, and the bottom of the energy-gathering cavity is connected to the piezoresistor through the fiber, because the piezoresistor passes through the Wheatstone bridge Connected, when external excitation can generate analog current. The sound energy received by the energy-gathering cavity is different, the size of the excitation is different, the value of the varistor is different, and the current generated is different.

In the photoacoustic imaging system, many photoacoustic sensors are arranged in an array according to the imaging law and focus distribution, which is called the receiving matrix, and each photoacoustic sensor is called the array element or primitive. The sound wave in a certain direction is focused on a point (focus) through the acoustic lens, and a receiving element is placed here to realize beam reception in that direction. Arranging a receiving array composed of multiple primitives (as shown in Figure 5) on the focal plane can receive incident sound waves from different directions, and different sampling moments correspond to different distances. The photoacoustic sensor array receives the emitted photoacoustic signal at the focal position of each photoacoustic sensor, and calculates the time when the photoacoustic signal reaches the array through the single-chip microcomputer control circuit and counting circuit, records the time at this time as t ₁ , and stores it in the data memory RAM In , because the sample structure and three-dimensional profile are inconsistent, the time t ₁ for the excited ultrasonic wave to reach the receiving array is inconsistent, so the travel time T of the sound wave in the scattering liquid can be obtained by using the receiving array time t ₁ (T=t ₁ -t ₀ ), combined with the travel time T[T=t ₁ -t ₀ ] of the sound wave, the distance L from the detection sample sound source to the receiving array can be calculated [L=T*sound velocity in the scattering liquid], and this distance L is the imaging of the sample The third-dimensional coordinate number z (z=L) of the region, combined with the two-dimensional imaging data f(x, y) of the image obtained by the above-mentioned negative refraction law of the acoustic lens, can obtain the three-dimensional coordinates (x, y) of the photoacoustic image , z), and because the photoacoustic sensor converts the weak photoacoustic signal into an electrical signal, the value of the electrical signal is the size (amplitude) of the photoacoustic pressure of the sample, which is recorded as E, which is the gray value of the photoacoustic image. In summary, the three-dimensional coordinate data of the photoacoustic image can be obtained as E=f(x, y, z), where the coordinate value of (x, y) is obtained by the acoustic lens imaging model, and the coordinate value of (z) is obtained by the scattering liquid The travel time T is decided.

4. Data reception.

As shown in Figure 6, the data receiving system is composed of a control board and 16 data acquisition boards that collect data in units of 16 channels, collect and process 256 analog signals received by the acoustic wave receiving array, and The 3D photoacoustic data is stored in RAM for later image processing. The data acquisition board receives 256 channels of analog signals from the receiving array. The basic structure of each channel is the same and can be designed in a modular manner. Each acquisition board has 16 channels of analog input, 16 analog signal processing units, and 1 control processing unit with FPGA and DSP as the core device, so that each data acquisition board completes the acquisition, processing and transmission of 16 channels of signals, a total of 16 acquisition boards are required to work simultaneously. The specific workflow is as follows: when the central control board starts the transmitting module, it will send working parameters and start collection commands to the data receiving system, and this part of the control board will set the sampling time of the A/D converter according to the corresponding working parameters. When receiving the module, the control board will start 16 data acquisition boards at the same time to collect data. When all the data is collected, the control board will interrupt the reception and generate a chip selection signal. The chip selects the units with analog signals for signal conditioning. After the analog signal conditioning The amplification, filtering, envelope detection and other processing of the circuit are converted into signals that meet the requirements of the A/D converter and then sampled. The control board saves the data in RAM to prepare for post-processing.

5. Image processing and display.

Import the three-dimensional photoacoustic data in the data acquisition module into the computer (single chip or PC) for image processing and display. As shown in Figure 7, the classic image is denoised and enhanced in the image processing, and finally the open source visualization program library VTK is used to develop a photoacoustic three-dimensional data visualization platform, which can obtain a three-dimensional image of the light absorption distribution of the detected (cell) sample 18, as shown in Figure 8.

The working principle of the sensor-based measurement system for the launch height of the flare is as follows: first, the laser irradiation makes the sample uniformly heated and expanded to emit an acoustic signal, and the sound wave excited by the sample is focused at the focal point through the acoustic lens; The array receives the photoacoustic signal emitted by the sample. The photoacoustic signal receiving array is mainly composed of a photoacoustic sensor based on the mesoscopic piezoresistive effect; the sensor converts the received weak acoustic signal into an electrical signal, and then the signal conditioning circuit The electrical signal is pre-amplified and filtered, and then the analog signal is converted into a digital signal, so as to record and store the time-domain characteristics and amplitude characteristics of the ultrasonic signal received by each sensor in real time, and use the sound wave to travel time in the liquid while combining The two-dimensional imaging data obtained by the acoustic lens imaging model can be used to obtain three-dimensional photoacoustic imaging data, which is stored and transmitted to the image processing and display module for photoacoustic image noise reduction and enhancement, so as to obtain the light absorption distribution of the test sample 3D image.

The imaging principle of the system is scientific, the circuit structure is simple, the hardware scale of the system is reduced, and the cost of the system is greatly reduced. It adopts a reasonable laser distribution, an acoustic lens composed of advanced phononic crystals, and a photoacoustic sensor array. The photoacoustic data acquisition and three-dimensional acoustic image data processing realize the display and analysis of the three-dimensional high-resolution image of the test sample.

The specific operation steps of the application of the present invention in lesion cell tissue imaging:

(1) Place the diseased cell tissue in a ground glass vessel on the laboratory bench.

(2) Turn on the lasers in four directions, emit laser light, and expand the beam through the beam expander and ground glass, so that the laser light can be evenly irradiated on the diseased tissue.

(3) The diseased cells irradiated by the laser will heat up and expand and emit sound waves outward. These sound waves are focused by the phononic crystal to the photoacoustic sensor array consisting of 16*16 256 primitives located on the focal plane.

(4) The photoacoustic sensor converts the acoustic signal emitted by the diseased cells into an electrical signal, and obtains an analog signal through filtering and amplifying the signal, and the analog signal is converted into a digital signal through a data acquisition card. The imaging model of the two-dimensional image of the diseased cells is obtained according to the law of negative refraction.

(5) The time-domain characteristics and amplitude characteristics of the ultrasonic signals received by each photoacoustic sensor are transmitted to the RAM, and combined with the imaging model of the acoustic lens, the three-dimensional photoacoustic imaging data can be obtained.

(6) The computer (single chip or PC) stores and transmits the data to the image processing and display module for photoacoustic image noise reduction and enhancement, so as to obtain the three-dimensional image data of the light absorption distribution of the test sample.

(7) Three-dimensional data processing and imaging technologies include:

Option 1: The three-dimensional data is processed by the embedded system and then displayed on the monitor.

Option two: the three-dimensional data is processed by a peripheral computer and displayed as an image.

Finally, it should be noted that: the above examples are only examples for clearly illustrating the present invention, and are not intended to limit the implementation. In terms of technology, other changes or changes in different forms can also be made to the above description. It is not possible to exhaustively list all the implementation manners here. However, obvious changes or changes derived therefrom still fall within the protection scope of the present invention.

Claims (3)

1. the three-dimensional photoacoustic imaging system based on acoustic lens and sensor array is square experiment table; Comprise laser instrument (1), beam expanding lens (2), phonon crystal lens (3), photoacoustic sensors array (4), data bus (5), frosted glass vessel (6), data acquisition module and the computing machine for image processing; It is characterized in that: described laser instrument and beam expanding lens respectively have four, described frosted glass vessel are placed on square inner bottom surface center position; Four laser instrument portions are in the bottom at four vertical planes of square experiment table, and become spatial vertical state with inner frosted glass vessel; Four beam expanding lenss are close to the outer wall of frosted glass vessel, and locus and laser relative should; Phonon crystal lens are the acoustic lenses that are made up of phonon crystal, directly over frosted glass vessel, photoacoustic sensors array be positioned at acoustic lens directly over, in acoustic lens focal position, and photoacoustic sensors is connected with data acquisition module and computing machine by data bus; Wherein: the described computing machine for image processing contains image processing, display module and image processing software, the three-dimensional optoacoustic data that receive can be carried out to photoacoustic image noise reduction, strengthen and process, to obtain detecting the light absorption distribution 3-D view of sample, and can on display, show two dimension or 3-D view.

2. the three-dimensional photoacoustic imaging system based on acoustic lens and sensor array according to claim 1, it is characterized in that: described acoustic lens is made up of phonon crystal, wherein: phonon crystal is about the evenly coated soft rubber of 0.02cm in shot outside of 0.78cm by diameter, then be embedded in epoxy resin cube and form.

3. a formation method for the three-dimensional photoacoustic imaging system based on acoustic lens and sensor array claimed in claim 1, is characterized in that:

(1) Ear Mucosa Treated by He Ne Laser Irradiation sample expanded by heating utilizing emitted light acoustical signal: by four sides of Ear Mucosa Treated by He Ne Laser Irradiation frosted glass vessel, make the even expanded by heating utilizing emitted light of sample acoustical signal, realized the timely interocclusal record of parameter control of laser signal transmitting by sequential control circuit; Record initial time t ₀, irradiated the center of frosted glass vessel surrounding by laser instrument simultaneously, make sample expanded by heating utilizing emitted light acoustical signal;

(2) acoustic lens focuses on: form acoustic lens by phonon crystal, receive the photoacoustic signal of sample transmitting, focus on; Draft the image space of sample in photoacoustic sensors array according to acoustic lens imaging model, the photoacoustic signal of sample transmitting is focused on by phonon crystal;

(3) reception of photoacoustic signal, conditioning: photoacoustic sensors array also receives the photoacoustic signal of sample transmitting in the focal position of photoacoustic sensors separately, by the three-dimensional data of data acquisition module Real-time Collection, reception and recording light acoustic imaging; Wherein:

In the time that photoacoustic sensors array has photoacoustic signal, recording the now moment is t ₁, be stored in the data-carrier store RAM of computing machine; Photoacoustic sensors array changes faint photoacoustic signal into electric signal simultaneously, and the value of electric signal, is the acoustic pressure E of sample utilizing emitted light acoustical signal;

According to the negative refraction rule of acoustic lens, can obtain the two-dimensional imaging data f (x, y) in imaging samples region; Utilize travelling time T and can calculating and detect the sample sound source distance L to receiving array of photoacoustic signal, this distance L, is the third dimension coordinate data z of the imaging region of sample, wherein: T=t ₁-t ₀, the velocity of sound in L=T* scattering liquid, z=L; Utilize coordinate data z in conjunction with two-dimensional imaging data f (x, y) just can obtain the three-dimensional imaging data f (x of the photoacoustic image of the imaging region of sample, y, three-dimensional imaging data f (x, the y of the photoacoustic image of the imaging region that z), the acoustic pressure E of sample utilizing emitted light acoustical signal is sample, z), be E=f (x, y, z);

(4) photoacoustic image is processed and is shown: the three-dimensional imaging data f (x of described photoacoustic image, y, z), wherein two-dimensional imaging data f (x, y) obtained by acoustic lens imaging model, another dimension coordinate data z is determined by the time T of travelling in scattering liquid, the namely gray-scale value of photoacoustic image of size of sample utilizing emitted light acoustical signal acoustic pressure E; The three-dimensional imaging data receiving is carried out to enhancing, feature extraction, classification and the identification of photoacoustic image, by the three-dimensional imaging data input computing machine or the single-chip microcomputer that obtain, process and realize the 3-D display and the analysis that detect sample through image.