Photoacoustic liquid viscosity detection device and method based on spectrum resolution

Abstract

The invention relates to a photoacoustic liquid viscosity detection device and method based on spectrum resolution, and belongs to the field of photoacoustic detection and liquid physical property analysis. The device comprises a solid-state laser, a collimating lens, a plane mirror, a plate-type semitransparent mirror, a microscope objective lens, a photodiode, a photoacoustic coupling cavity, a rectangular prism group, an ultrasonic transducer, a pre-signal amplifier, a digital oscilloscope and a computer. Pulse laser is focused to a liquid sample after being processed by an optical path to excite a photoacoustic effect, an ultrasonic transducer receives a signal and converts the signal into an electric signal, after a digital oscilloscope synchronously samples, a computer extracts a frequency spectrum full width at half maximum (FWHM) through fast Fourier transform, and non-contact detection is realized based on a negative correlation between the frequency spectrum full width at half maximum and viscosity. The method can overcome the defects of large sample size, mechanical contact and the like of a traditional method, and is suitable for high-precision viscosity detection of biological tissues and industrial samples in the field of biomedicine.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of photoacoustic technology and its application in liquid viscosity detection, and in particular to a device and method for real-time and non-invasive detection of liquid viscosity (especially biological liquid) based on the negative correlation between the full width at half maximum (FWHM) of the photoacoustic signal spectrum generated by laser excitation of the liquid and the viscosity of the liquid. BACKGROUND

[0002] Liquid viscosity is an important physical quantity for measuring the internal friction and flow behavior of the liquid, and is widely used in chemical engineering, pharmaceutical processes, biomedical research, material research and clinical diagnosis. For example, the viscosity changes of human blood and other physiological liquids are often closely related to the development of diseases, and therefore, accurate measurement of liquid viscosity is of great significance for early warning and treatment strategy of diseases.

[0003] The conventional viscosity measurement methods widely used at present usually require a large sample volume, such as a rotary viscometer, a capillary viscometer or a falling ball method. Such methods often have many limitations, such as errors caused by mechanical contact, deviations caused by unstable temperature, and cross-contamination problems of samples during the measurement process, especially when dealing with high-value or difficult-to-obtain biological samples, the application range is obviously restricted.

[0004] With the development of microfluidic and micro-rheological technology, low-volume viscosity measurement methods have gradually emerged (the sample volume can be reduced to nanoliter level), but the results are easily affected by factors such as liquid flow rate, micro-channel surface state and wettability, resulting in insufficient measurement consistency and long-term stability; at the same time, the complex microstructure manufacturing process also increases the system cost, limiting its wide application.

[0005] As a new non-contact detection method, the full width at half maximum (FWHM) in the signal spectrum of photoacoustic technology is closely related to the distribution of high-frequency components of the signal. Photoacoustic effect usually refers to the process of ultrasonic field excited by optical radiation. When using pulsed light source or modulated light source, the fluctuation of local temperature in the object will cause the expansion and contraction of its volume, so it can radiate sound waves. Different types of signals will be generated under the same excitation conditions for tissues or pathological states with different mechanical properties. The viscosity of the liquid will affect the high-frequency attenuation characteristics of the sound wave during its propagation in the medium. Theoretical analysis shows that with the increase of the viscosity of the liquid, the high-frequency signal component is attenuated to a greater extent, resulting in a decrease in the FWHM of the photoacoustic signal. This physical mechanism lays a theoretical foundation for the application of photoacoustic spectrum analysis in liquid viscosity detection.

[0006] In view of the problems of large sample consumption, complex operation, poor repeatability and inability to realize non-invasive detection in the prior art, the present application provides a kind of liquid viscosity detection device and method based on frequency spectrum resolution of photoacoustic.The scheme excites the liquid to be measured to generate photoacoustic response signal by pulsed laser, and extracts signal frequency domain characteristics by combining fast Fourier transform.Using the negative correlation between FWHM and liquid viscosity, real-time, high-precision, non-invasive detection of viscosity is realized.The present application has significant advantages in reducing sample consumption, improving measurement stability and adapting to micro-biological sample detection, and is suitable for biomedical and industrial applications. SUMMARY

[0007] The present application aims to provide a kind of liquid viscosity detection device and method based on frequency spectrum resolution of photoacoustic, which excites liquid to generate local photoacoustic effect by pulsed laser, and realizes real-time, non-contact measurement of liquid viscosity by using the negative correlation between FWHM in photoacoustic signal spectrum and liquid viscosity, so as to overcome the shortcomings of large sample requirement, mechanical contact and environmental interference in traditional methods.

[0008] According to the first aspect of the present application, a kind of liquid viscosity detection device based on frequency spectrum resolution of photoacoustic is provided, comprising: solid-state laser, for emitting pulsed laser to the liquid to be measured, so that it generates photoacoustic effect in predetermined area;Collimating lens ensures that the light beam enters the subsequent optical path in parallel state;Plane mirror is used for turning the light path;Plate-shaped half lens is used for splitting light to provide reference light beam for photodiode;Microscope objective focuses laser on local area of sample to obtain high energy density photoacoustic excitation;Photodiode receives laser signal and converts it into electrical signal, which is used to assist time alignment and normalize laser intensity;Photoacoustic coupling cavity is a closed structure, which provides a stable environment for the generation and reception of photoacoustic signals and reduces sound interference;Right-angle prism group does not affect the transmission of the outgoing laser along the original path, while it is used to realize the turning transmission of the return sound wave;Ultrasonic transducer is used to receive the photoacoustic signal generated by the excitation area and convert it into an electrical signal;Pre-amplifier amplifies the received photoacoustic signal;Digital oscilloscope samples the amplified photoacoustic signal and the signal output by photodiode;Computer carries out frequency spectrum analysis on photoacoustic signal by fast Fourier transform, and obtains FWHM of photoacoustic signal spectrum, which is used to characterize the viscosity of liquid.

[0009] The wavelength range of the laser emitted by the solid-state laser is 500nm to 900nm.

[0010] The solid-state laser, collimating lens, plane mirror, plate-shaped half lens and microscope objective are placed in sequence.The plane mirror is placed at an angle of 45 degrees, with an angle of 135 degrees between its mirror surface and the horizontal direction, and the plate-shaped half lens is placed at an angle of 45 degrees, with an angle of 45 degrees between its incident surface and the horizontal direction.

[0011] The photoelectric diode is placed on a light splitting path of the laser beam, used for receiving a laser pulse signal, converting the light signal into an electric signal, and outputting into a digital oscilloscope.

[0012] The microscope objective is mounted on a three-dimensional electric translation stage, and the focal point position can be adjusted by adjusting X / Y / Z axes.

[0013] The photoacoustic coupling cavity is a closed structure, the shell material is polymethyl methacrylate, the top is provided with a laser incidence port, the incidence port is covered with a light-transmitting protective film; the bottom is provided with a detection interface, which is covered with a light-transmitting protective film, and the outer side of the light-transmitting protective film is tightly attached to the sample to be measured. The light-transmitting protective film can transmit laser and allow photoacoustic signals to transmit out, and the two layers of films are made of polystyrene film materials with good light-transmitting property and flexibility. The polyurethane-based wave-absorbing material is attached to the inner wall of the cavity to reduce signal interference caused by multiple reflections of sound waves.

[0014] The right-angle prism group is close to the inner side of the light-transmitting protective film at the bottom, and comprises two right-angle prisms with mutually attached oblique reflection sections, the attached surfaces are at 45 degrees to the propagation direction of sound waves and at 135 degrees to the axial direction of the ultrasonic transducer, the attached surfaces are coated with a light-transmitting sound reflection layer, and the material of the sound reflection layer is silicone oil.

[0015] The ultrasonic transducer is placed on one side of the right-angle prism group, the volume is adapted to the coupling cavity design, a coupling gel is coated on the receiving port of the ultrasonic transducer close to the right-angle prism group, and the coupling gel can maintain the acoustic transmission path. The distance between the ultrasonic transducer and the focal point of laser in the sample is fixed as L (L is the position distance of the transducer and the focal point of laser), the output end of the ultrasonic transducer is electrically connected with a preamplifier, the excited sound waves are converted into electric signals after being received by the ultrasonic transducer, and the ultrasonic transducer outputs the electric signals to the preamplifier.

[0016] The digital oscilloscope is electrically connected with the output end of the preamplifier and the output end of the photoelectric diode, and the output end of the digital oscilloscope is electrically connected with a computer.

[0017] The application also provides a method of the photoacoustic liquid viscosity detection device based on spectrum resolution.

[0018] Step S1: a solid-state laser emits pulse laser, and the laser sequentially passes through a collimating lens, a plane mirror and a plate-shaped half lens.

[0019] Step S2: a photoelectric diode receives part of the laser passing through the plate-shaped half lens on a light splitting path, and the laser on a main light path passes through a microscope objective, sequentially passes through an upper light-transmitting protective film of a photoacoustic coupling cavity, a right-angle prism group and a lower light-transmitting protective film, is focused on a sample and excites an ultrasonic field.

[0020] Step S3: the excited acoustic wave is reflected by the right-angle prism group and received by the ultrasonic transducer in the photoacoustic coupling cavity, the preamplifier connected to the ultrasonic transducer amplifies the electrical signal output by the ultrasonic transducer, and the digital oscilloscope samples and amplifies the signal and the signal output by the photodiode.

[0021] Step S4: the digital oscilloscope sends the collected data to the computer for storage, and the computer performs frequency spectrum analysis on the photoacoustic signal through fast Fourier transform.

[0022] Step S5: the full width at half maximum (FWHM) parameter is extracted from the obtained signal spectrum to represent the viscosity of the liquid.

[0023] The solid-state laser emits laser, and the pulsed laser first passes through a collimating lens to ensure that the light beam enters the subsequent optical path in a parallel state. Then the light path is turned 90 degrees at a plane mirror, and when the laser passes through a plate-shaped semi-transmissive lens, the transmitted part of the laser is the main light beam, and the reflected part of the light beam is the reference light beam.

[0024] The signal output by the photodiode and the photoacoustic signal collected by the ultrasonic transducer are connected to the digital oscilloscope for synchronous sampling. The digital oscilloscope is set to a free sampling mode, and all data including the laser reference signal and the photoacoustic signal are continuously recorded. The output signal data are transmitted to the computer.

[0025] The computer receives and processes the signal data output by the oscilloscope, determines the starting time of each excitation by extracting the rising edge of the photodiode signal, and aligns the photoacoustic signal in time with the starting time as a reference. The computer also detects the amplitude of the photodiode signal to normalize the intensity of the collected photoacoustic signal. By using the photodiode signal to realize unified reference time and laser intensity normalization, the stability of photoacoustic signal acquisition and the accuracy of frequency spectrum analysis are significantly improved.

[0026] The computer uses MATLAB software to perform fast Fourier transform analysis on the signal data output by the digital oscilloscope, obtains the corresponding frequency spectrum, and extracts the full width at half maximum (FWHM) in the frequency spectrum to represent the viscosity of the liquid.

[0027] Preferably, to establish the relationship between the photoacoustic signal spectrum parameters and the viscosity of the liquid, the internal mechanism of the present application is derived in detail, and each step is specifically described as follows:

[0028] Step A1, constructing the basic equation and performing linearization processing:

[0029] First, consider that the liquid locally expands and generates pressure disturbance under the excitation of pulsed laser, and the mechanical movement related to this becomes the source of acoustic wave. The velocity field in the liquid satisfies the traditional Navier-Stokes equation:

[0030]

[0031] where, is the liquid density, is the pressure, and is the shear viscosity and bulk viscosity.

[0032] At the same time, it is assumed that the light incident on the medium is generated by a pulsed light source, and the duration of the pulse is very short compared to the time scale of thermal diffusion. In addition, the mass density satisfies the continuity equation:

[0033]

[0034] where is the constant pressure heat capacity per unit mass, is the volumetric thermal expansion coefficient, is the absorption coefficient, is the instantaneous radiation intensity of the laser.

[0035] If the light source power is small enough, the fluctuations in density and pressure will be δρ << ρ and δp << p, so linearization of the above Navier-Stokes equation and continuity equation can be obtained:

[0036]

[0037]

[0038] Step A2, establish the acoustic pressure fluctuation equation:

[0039] Using the above results, the velocity field can be eliminated and a single equation containing only and can be obtained:

[0040]

[0041] Using the relationship δp = c s 2 δρ, where c s is the acoustic velocity, the fluctuation equation of the photoacoustic (PA) pressure can be obtained:

[0042]

[0043] The Gruneisen constant and the viscosity coefficient are introduced:

[0044]

[0045]

[0046] For simplicity, our current analysis is limited to the plane wave model. In this case, the acoustic wave varies with time along one of the Cartesian coordinates, x, and the wave equation is expressed in the form of the Laplacian operator

[0047]

[0048] A PA pressure of the form is set to be generated at a location in a homogeneous medium where is the propagation phase constant, the variable can be eliminated and a second-order differential equation for the variable is obtained. The PA wave is obtained using a short laser pulse, so the light intensity can be assumed to be an incremental function. Considering the light attenuation described by the Beer's law approximation, the time irradiance of the laser can be expressed as

[0049]

[0050] is the time interval between laser pulses, is the effective attenuation coefficient, and Ω is the angular frequency of the laser.

[0051] Thus the wave equation is finally

[0052]

[0053] Step A3, from time domain to frequency domain - Analyzing the FWHM and viscosity relationship:

[0054] where and the solution of the above equation is obtained:

[0055]

[0056] where A and B are constants determined by the initial conditions, is the impedance of the system. The first term is the transient vibration, and the second term is the response synchronized with the external driving force. The synchronization indicates that the vibration frequency is consistent with the laser angular frequency Ω. Since the stimulated photoacoustic signal has a wide frequency range, the full width at half maximum (FWHM) of the photoacoustic spectrum can be proportional to the frequency of the photoacoustic signal:

[0057] , the FWHM is negatively correlated with the viscosity of the liquid.

[0058] ​We can conclude that the liquid viscosity will cause the loss of high frequency components than low frequency components. Therefore, we finally get the relationship between the FWHM of photoacoustic spectrum and the viscosity coefficient, the negative correlation between the full width at half maximum (FWHM) of photoacoustic signal spectrum and the liquid viscosity coefficient.

[0059] The beneficial effects of the present application are:

[0060] The non-contact laser excitation and ultrasonic detection are adopted, the generation and collection of the local photoacoustic signal in the liquid are realized, the sample requirement is effectively reduced, and the influence of mechanical contact on the measurement accuracy is eliminated.

[0061] The frequency spectrum parameters of the photoacoustic signal are obtained by using fast Fourier transform, especially the FWHM at the main peak, so that the detection result has high robustness and repeatability.

[0062] The empirical model established by combining detailed theoretical derivation and experimental calibration can realize real-time and high-precision inversion of the liquid viscosity, and is suitable for viscosity monitoring of biomedical liquids, industrial samples and new drugs.

[0063] The system has compact overall structure and simple operation, and is easy to integrate into a microfluidic platform or an online detection system, and has wide application prospects in the fields of medical diagnosis, material science and precision chemical industry. BRIEF DESCRIPTION OF DRAWINGS

[0064] Figure 1 It is a structural schematic diagram of the device of the present application.

[0065] Figure 2 It is a structural schematic diagram of the photoacoustic coupling cavity.

[0066] Figure 3 It is a flowchart of the method of the present application.

[0067] Figure 4 It is a comparison diagram of photoacoustic signals of glycerol-ink solutions with different glycerol concentrations changing with time.

[0068] Figure 5 It is a normalized photoacoustic signal spectrum diagram of glycerol-ink solutions with different glycerol concentrations.

[0069] Figure 6 It is a relationship diagram of the photoacoustic signal characteristics of glycerol-ink solutions with different viscosity coefficients changing with viscosity.

[0070] Figure 7 It is a spectrum comparison diagram of photoacoustic signals at different blood vessel branches (V1, V2).

[0071] Figure 8 It is a curve diagram of the amplitude distribution of microvessel photoacoustic signals along the scanning position.

[0072] Figure 9 This is a comparison of the full width at half maximum (FWHM) of the photoacoustic signal spectrum of arteries (A) and veins (V) over time.

[0073] The reference numerals in the attached figures represent the following meanings: 1. Solid-state laser; 2. Collimating lens; 3. Plane mirror; 4. Plate semi-transparent mirror; 5. Microscope objective lens; 6. Photodiode; 7. Preamplifier; 8. Digital oscilloscope; 9. Computer; 10. Light-transmitting protective film; 11. Opto-acoustic coupling cavity; 12. Laser; 13. Polyurethane-based absorbing material; 14. Sample; 15. Right-angle prism assembly; 16. Ultrasonic transducer; 17. Ultrasonic wave. Detailed Implementation

[0074] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0075] Unless otherwise stated, the raw materials and samples used in the following examples are commercially available products or can be prepared by known methods.

[0076] Example 1

[0077] like Figures 1-2 As shown, the photoacoustic liquid viscosity detection device based on spectrum resolution provided in this embodiment includes: a solid-state laser 1, a collimating lens 2, a plane mirror 3, a plate semi-transparent mirror 4, a microscope objective lens 5, a photodiode 6, a preamplifier 7, a digital oscilloscope 8, a computer 9, a light-transmitting protective film 10, a photoacoustic coupling cavity 11, a polyurethane-based absorbing material 13, a right-angle prism group 15, and an ultrasonic transducer 16.

[0078] In this embodiment, the solid-state laser 1 operates at a wavelength of 532nm and a frequency of 10Hz.

[0079] In this embodiment, the solid-state laser 1, collimating lens 2, plane mirror 3, plate semi-transparent mirror 4, and microscope objective lens 5 are placed sequentially. The plane mirror 3 is placed at a 45-degree angle, with its mirror surface forming an angle of 135 degrees with the horizontal direction. The plate semi-transparent mirror 4 is placed at a 45-degree angle, with the laser incident surface forming an angle of 45 degrees with the horizontal direction.

[0080] In this embodiment, the photodiode 6 is placed on the beam splitter of the laser beam to receive the signal of the pulsed laser 12, convert the optical signal into an electrical signal, and the output terminal is electrically connected to the digital oscilloscope 8.

[0081] In this embodiment, the microscope objective 5 is mounted on a three-dimensional motorized translation stage, and the focal position is adjusted by adjusting the X / Y / Z axes to accurately position the laser 12 focal point on the sample 14. The microscope objective 5 uses a 4x magnification (NA = 0.1) to focus the laser 12 transmitted through the plate-shaped half lens 4, which can effectively focus the laser 12 on the target sample 14.

[0082] In this embodiment, the center frequency of the ultrasonic transducer 16 is 75 MHz.

[0083] In this embodiment, the photoacoustic coupling cavity 11 is a closed structure, the shell material is polymethyl methacrylate, the top is provided with a laser incidence opening, the incidence opening is covered with a light-transmitting protective film 10 for transmitting laser 12; the bottom is provided with a detection interface for adhering to the sample to be measured, which is covered with a light-transmitting protective film 10, which can transmit laser and allow photoacoustic signals to pass through. Both films are made of polystyrene film material with good light transmission and flexibility. The polyurethane-based wave-absorbing material 13 is attached to the inner wall of the cavity to reduce signal interference caused by multiple reflections of sound waves, suppress standing wave effects, and improve spectral resolution. The inside of the bottom light-transmitting protective film 10 is tightly attached to the right-angle prism group 15, and the outside is tightly attached to the sample to be measured 14. The right-angle prism group 15 is tightly attached to the bottom light-transmitting protective film 10, including two right-angle prisms with mutually adhered inclined reflection sections, the adhered surface is at 45 degrees to the propagation direction of the sound wave and at 135 degrees to the axial direction of the ultrasonic transducer 16, the adhered surface is coated with a light-transmitting sound reflection layer, and the material of the sound reflection layer is silicone oil. The ultrasonic transducer 16 is placed on one side of the right-angle prism group 15, and its volume is adapted to the coupling cavity design, and a layer of coupling gel is coated on the receiving port of the ultrasonic transducer 16 to tightly adhere to the right-angle prism group 15, and the coupling gel can maintain the acoustic transmission path. The output end of the ultrasonic transducer 16 is electrically connected to the preamplifier 7, and the excited ultrasonic wave 17 is converted into an electrical signal by the ultrasonic transducer 16 after being received, and the output electrical signal is output to the preamplifier 7.

[0084] The digital oscilloscope 8 is electrically connected to the output end of the preamplifier 7 and the output end of the photodiode 6, and the output end is electrically connected to the computer 9.

[0085] As shown in Figures 1-3 The method for detecting the viscosity of a liquid based on spectral resolution photoacoustic liquid viscosity detection includes the following steps:

[0086] Step S1: The solid-state laser 1 emits pulsed laser 12, and the laser 12 passes through the collimating lens 2, the plane mirror 3, and the plate-shaped half lens 4 in turn.

[0087] Step S2: The photoelectric diode 6 receives the partial laser 12 passing through the plate-shaped half lens 4 in the light splitting path. The laser 12 in the main light path passes through the upper light-transmitting protective film 10, the right-angle prism group 15 and the lower light-transmitting protective film 10 of the photoacoustic coupling cavity 11 in turn after passing through the microscope objective 5, is focused on the sample 14 and excites the ultrasonic wave 17.

[0088] Step S3: The excited ultrasonic wave 17 is reflected by the right-angle prism group 15 and is received by the ultrasonic transducer 16 in the photoacoustic coupling cavity 11. The preamplifier 7 electrically connected to the ultrasonic transducer 16 amplifies the electrical signal output by the ultrasonic transducer 16, and the digital oscilloscope 8 samples the amplified signal and the signal output by the photoelectric diode 6.

[0089] Step S4: The digital oscilloscope 8 sends the collected data to the computer 9 for storage, and the computer 9 performs spectral analysis on the photoacoustic signal through fast Fourier transform.

[0090] Step S5: The full width at half maximum (FWHM) parameter is extracted from the obtained signal spectrum to characterize the viscosity of the liquid.

[0091] In this embodiment, the laser 12 first passes through the collimating lens 2 to ensure that the light beam enters the subsequent light path in a parallel state; then the light path is turned 90 degrees at the plane mirror 3, and after being split by the plate-shaped half lens 4, part of the light beam is shot at the photoelectric diode 6, and the main light beam continues to propagate.

[0092] In this embodiment, the signal output by the photoelectric diode 6 and the photoacoustic signal collected by the ultrasonic transducer 16 are connected to the digital oscilloscope 8 for synchronous sampling. The oscilloscope is set to free sampling mode to continuously record all data including the laser reference signal and the photoacoustic signal.

[0093] In this embodiment, the signal data output by the digital oscilloscope 8 is transmitted to the computer 9. The computer 9 receives and processes the signal data output by the digital oscilloscope 8, determines the starting time of each excitation by extracting the rising edge of the photoelectric diode 6 signal, and aligns the photoacoustic signal in time with the starting time as the reference. The computer 9 also detects the amplitude of the photoelectric diode 6 signal to normalize the intensity of each collected photoacoustic signal. By using the photoelectric diode 6 signal to realize unified reference time and laser intensity normalization, the stability of photoacoustic signal acquisition and the accuracy of spectral analysis are significantly improved. The computer 9 uses MATLAB software to perform fast Fourier transform analysis on the photoacoustic signal to obtain the corresponding spectrum.

[0094] In this embodiment, the sample 14 is a glycerol-ink mixture. The ink volume concentration is fixed at 4%, and the glycerol volume concentration is set at 20%, 30%, 40%, and 50% in sequence. The viscosity coefficients of the solutions are 1.31 cP, 1.76 cP, 2.5 cP, and 3.72 cP, respectively. The distance from the sound wave transmission to the transducer 16 is fixed at "l" (l is the actual propagation path length of the sound wave).

[0095] In this embodiment, the photoacoustic signal amplitude and the normalized spectrum are obtained by detecting the above sample 14, as shown in Figure 4 、 Figure 5 The full width at half maximum is extracted to obtain the negative correlation between the full width at half maximum (FWHM) of the photoacoustic signal spectrum and the liquid viscosity coefficient, as shown in Figure 6 The experimental results show that under the same absorption coefficient and fixed transmission distance, the amplitude of the photoacoustic signal changes little, but the full width at half maximum (FWHM) of the spectrum significantly decreases with the increase of the solution viscosity, verifying the theory that the FWHM is negatively correlated with the liquid viscosity coefficient, which is consistent with the theoretical relationship.

[0096] Embodiment 2

[0097] On the basis of the disclosure of the above embodiments, the present embodiment further discloses the following:

[0098] In this embodiment, the present technology is applied to the biomedical field, and a device and method for photoacoustic liquid viscosity detection based on spectrum resolution are used to measure the blood viscosity in the mouse ear microvessels:

[0099] In this embodiment, the device and method in Embodiment 1 are used to perform viscosity detection through the following steps:

[0100] The capillary blood vessels of the ear skin of BALB / c mice are selected as the sample 14. After the mouse is removed of the ear hair, the detection points V1 and V2 are selected at different parts of the uniform skin. Pentobarbital sodium (40 mg / kg, supplemented with 10 mg / kg / h) is used for anesthesia treatment to ensure that the mouse remains relatively still during the detection process.

[0101] The pulsed laser emitted by the solid-state laser 1 passes through the collimating lens 2, the plane mirror 3, and the plate-shaped half lens 4.

[0102] The photodiode 6 receives part of the laser passing through the plate-shaped half lens 4 in the light splitting path. The laser 12 in the main light path passes through the microscope objective 5, the upper layer of light-transmitting protective film 10, the right-angle prism group 15, and the lower layer of light-transmitting protective film 10 of the photoacoustic coupling cavity 11 in sequence, and is focused on the sample 14 to excite the ultrasonic wave 17.

[0103] The ultrasonic transducer 16 in the photoacoustic coupling cavity 11 receives the generated photoacoustic signal, the front signal amplifier 7 electrically connected to the ultrasonic transducer 16 amplifies the electrical signal, and the digital oscilloscope 8 samples and amplifies the signal and the signal output by the photodiode 6.

[0104] The data collected by the digital oscilloscope 8 is transmitted to the computer 9, and the computer 9 uses MATLAB software to perform fast Fourier transform on the photoacoustic signal to obtain the corresponding frequency spectrum.

[0105] The full width at half maximum (FWHM) is extracted from the obtained signal spectrum, and the viscosity of the liquid is characterized according to the relationship between the FWHM and the liquid viscosity.

[0106] The frequency spectrum of the photoacoustic signal obtained at V1 and V2 is shown in Figure 7 The full width at half maximum is extracted, and the full width at half maximum of the frequency spectrum at V1 and V2 is 28.7 MHz and 29.3 MHz, respectively. According to the negative correlation between the FWHM and the viscosity, the viscosity of the blood can be characterized.

[0107] The results show that the frequency-resolved photoacoustic measurement can simultaneously provide absorption and viscosity information of different vascular branches, and can be used for dual-parameter morphological and functional imaging of microcirculation.

[0108] In this embodiment, the viscosity change caused by metabolism in the microvessels of the mouse is also monitored by the device and method in Example 1, and the steps are as follows:

[0109] First, the photoacoustic image containing different vascular branches is obtained, and a scanning path crossing the vascular branches is selected from the photoacoustic image, the path covering the artery (A), the vein (V) and the surrounding tissue area, and according to Figure 7 The dashed curve of the maximum amplitude projection of the photoacoustic signal on the scanning line is shown in the figure, and the artery and vein blood vessels on the scanning line are distinguished. At the same time, the FWHM of the photoacoustic spectrum is used to separate the artery and vein, which reflects the difference between the vein and artery blood in physiology. The FWHM of the photoacoustic signal of the artery (A) is measured to be 33.0 MHz, and the FWHM of the photoacoustic signal of the vein (V) is measured to be 31.3 MHz.

[0110] Further, a series of FWHM values at a fixed time point are collected, and the viscosity change trend of the artery and vein is analyzed. As shown in Figure 9 The FWHM value of the photoacoustic signal of the artery is much higher than that of the photoacoustic signal of the vein, which indicates that the viscosity of the artery blood is much lower than that of the vein blood, and the frequency-resolved photoacoustic measurement can be used to monitor the change of the viscosity of the liquid in the blood vessel in real time, and has good resolution and physiological consistency.

[0111] This embodiment shows that the device and method described in the application can not only be used to distinguish different types of blood vessels, but also can be used to track the viscosity change in real time during the microcirculation process, and has biomedical application prospect.

[0112] The above merely provides the preferred embodiment of the present application, and not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall fall within the protection scope of the present application.

Claims

1. A frequency resolution based optoacoustic liquid viscosity detection apparatus, characterized by, The application relates to a liquid viscosity detection device. The device comprises: a solid-state laser for emitting pulsed laser light with a wavelength ranging from 500 nm to 900 nm; a collimating lens for collimating the laser light into a parallel light beam; a plane mirror placed at an angle of 45 degrees, with the mirror surface being at an angle of 135 degrees with the horizontal direction, for turning the light path by 90 degrees; a plate-shaped half mirror placed at an angle of 45 degrees, with the incident surface being at an angle of 45 degrees with the horizontal direction, for splitting the light and providing a reference light beam for a photodiode; a microscope objective installed on a three-dimensional electric translation stage, for accurately focusing the laser light on a local area of a sample; a photodiode arranged on the light splitting path, for receiving part of the laser light and converting the laser light into an electric signal, for assisting in time alignment and normalizing the laser intensity; a photoacoustic coupling cavity with a closed structure, an internal laser entrance and a detection interface, and a wave-absorbing material coated on the inner wall of the cavity, and a light-transmitting protective film arranged on the top and the bottom of the cavity; a right-angle prism group closely arranged on the upper side of the laser exit of the photoacoustic coupling cavity, without affecting the transmission of the outgoing laser light along the original path, and capable of realizing the transmission of the return sound wave; an ultrasonic transducer arranged in the coupling cavity, for receiving the photoacoustic signal generated by the sample; a preamplifier electrically connected to the ultrasonic transducer, for amplifying the received photoacoustic electric signal; a digital oscilloscope for synchronously sampling the electric signals output by the ultrasonic transducer and the photodiode; 2. The apparatus of claim 1, wherein: a computer for receiving and processing the sampling data, extracting the full width at half maximum (FWHM) in the photoacoustic signal spectrum through fast Fourier transform, and representing the liquid viscosity.

3. The apparatus of claim 1, wherein: The shell of the photoacoustic coupling cavity is made of polymethyl methacrylate, the inner wall is coated with a polyurethane wave-absorbing material, the top and the bottom are covered with light-transmitting protective films made of polystyrene, the inner side of the light-transmitting protective film on the bottom is closely attached to the right-angle prism group, and the outer side of the light-transmitting protective film is closely attached to the sample to be detected; the light entrance, the right-angle prism group and the light exit are arranged in sequence on a straight line in the photoacoustic coupling cavity, and the laser light propagates along the original direction after passing through the right-angle prism group; the laser light exit, the right-angle prism group and the ultrasonic transducer are arranged in sequence along the propagation direction of the sound wave in the photoacoustic coupling cavity, and the sound wave is turned after passing through the light-transmitting protective film and the right-angle prism group and is transmitted to the ultrasonic transducer.

4. The apparatus of claim 1, wherein: The right-angle prism group is closely arranged at the laser light exit and comprises two right-angle prisms with mutually attached oblique reflection sections, the attached surface is at an angle of 45 degrees with the propagation direction of the sound wave and at an angle of 135 degrees with the axial direction of the ultrasonic transducer, the attached surface is coated with a light-transmitting sound reflection layer, and the material of the sound reflection layer is silicon oil.

5. The apparatus of claim 1, wherein: The ultrasonic transducer is closely arranged beside the right-angle prism group through a coupling liquid and is electrically connected to the preamplifier.

6. The apparatus of claim 1, wherein: The signal output by the photodiode is used for determining the starting time of each pulsed laser excitation and is used for time alignment and laser intensity normalization processing of the collected photoacoustic signal.

7. The apparatus of claim 1, wherein: The digital oscilloscope is used for high-speed sampling and is electrically connected to the preamplifier and the photodiode, synchronously samples the electric signals at two positions, and is connected to the computer at the output end. The computer receives and stores the data of the digital oscilloscope, performs fast Fourier transform analysis by using MATLAB software, obtains the corresponding spectrum, extracts the full width at half maximum (FWHM) in the spectrum, and represents the liquid viscosity.

8. The apparatus of claim 1, wherein: The relationship model that the full width at half maximum in the photoacoustic signal spectrum characterizes the liquid viscosity is established on the basis of theoretical derivation of photoacoustic wave equation obtained by using linearized Navier-Stokes equation and continuity equation in the process of laser exciting liquid, which shows that liquid viscosity will make high frequency component loss more obvious than low frequency component, thereby leading to reduction of photoacoustic signal spectrum FWHM.

9. A method of spectrally resolved optoacoustic liquid viscosity detection, characterized in that The method comprises the following steps: Step S1: the solid-state laser emits pulsed laser, and the laser passes through a collimating lens, a plane mirror and a plate-shaped half lens in sequence; Step S2: the photodiode receives part of the laser passing through the plate-shaped half lens at a light splitting path, and the laser at a main light path passes through a microscope objective, an upper light-transmitting protective film, a right-angle prism group and a lower light-transmitting protective film of a photoacoustic coupling cavity in sequence, is focused on a sample and excites an ultrasonic field; Step S3: the excited sound wave is reflected by the right-angle prism group, the ultrasonic transducer in the photoacoustic coupling cavity receives the sound wave, a preamplifier electrically connected amplifies the electrical signal output by the ultrasonic transducer, and a digital oscilloscope samples and amplifies the signal output by the photodiode; Step S4: the digital oscilloscope sends the collected data to a computer for storage, and the computer performs spectrum analysis on the photoacoustic signal by fast Fourier transform; Step S5: the full width at half maximum (FWHM) parameter is extracted from the obtained signal spectrum to characterize the liquid viscosity.

10. The method of claim 9, wherein, The photoacoustic signal generated by laser pulse excitation is obtained by fast Fourier transform, and it is known from theoretical derivation that liquid viscosity will make high frequency component attenuate more obviously than low frequency component, thereby making the full width at half maximum (FWHM) of the photoacoustic signal spectrum negatively correlated with the liquid viscosity, that is, the greater the viscosity, the smaller the FWHM, a mathematical model between FWHM and liquid viscosity is established to characterize the viscosity of the liquid to be measured.

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