CN212698854U - Photoacoustic Doppler blood flow velocity and blood oxygen content measuring system - Google Patents
Photoacoustic Doppler blood flow velocity and blood oxygen content measuring system Download PDFInfo
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Abstract
The utility model discloses a photoacoustic Doppler blood flow velocity and blood oxygen content measuring system, which comprises a pulse light filtering and collimating unit, a pulse laser amplitude modulation unit, a sample unit, a collecting and amplifying unit, a signal demodulation unit and a spectrum analysis unit; the utility model discloses simultaneously disclose the measuring method who adopts above-mentioned measurement system. The utility model discloses a photoacoustic Doppler blood flow velocity and blood oxygen content measurement system and measuring method have measurement accuracy height, measurable velocity of flow scope big, measurable degree of depth is big, the spectrum broadening is little, spectral resolution is high, the wavelength selective range is big, the detection bandwidth is high, the characteristics that system sensitivity is high.
Description
Technical Field
The utility model relates to a velocity of flow measurement technical field specifically indicates a photoacoustic Doppler blood flow velocity and blood oxygen content measurement system.
Background
The photoacoustic doppler effect refers to a phenomenon in which when a light absorbing substance sample moving relative to an ultrasonic transducer absorbs light, an acoustic wave detected by the ultrasonic transducer has a doppler shift due to the photoacoustic effect and the doppler effect under illumination. Obtaining the average Doppler shift f by measurementdThe average flow velocity can be obtained by calculation
Where θ is the angle between the direction of blood flow and the axis of the ultrasound transducer, caIs the propagation velocity of the acoustic wave, f0The intensity modulation frequency of the continuous light wave.
The existing photoacoustic blood flow velocity measurement technology mainly comprises continuous wave photoacoustic Doppler flow velocity measurement, sine pulse wave photoacoustic Doppler flow velocity measurement, pulse wave photoacoustic Doppler flow velocity measurement and the like.
The laser source in the continuous wave photoacoustic Doppler flow velocity measurement is a sine continuous modulation wave, the used light source is the sine modulation continuous wave, and the Doppler frequency shift is extracted by demodulating an photoacoustic Doppler frequency shift signal and a reference signal through a phase-locked amplifier. And finally, storing the time domain signal into a computer through signal acquisition software, and carrying out FFT (fast Fourier transform) processing on the computer to obtain a photoacoustic Doppler frequency shift signal so as to calculate the flow velocity and the direction.
The laser source in the flow velocity measurement of the sine pulse wave photoacoustic Doppler is a sine pulse continuous modulation wave, a relatively flexible external modulation mode and high-sensitivity heterodyne detection are utilized, so that the range of measurable flow velocity is enlarged, the flow velocity and the position can be measured simultaneously, the compromise problem of measuring the axial position and the detectable maximum velocity can be relieved, and compared with a phase-locked measurement mechanism, the central frequency of the signal receiver can be changed and is not limited to direct current.
Pulsed wave photoacoustic doppler flow velocity measurements are excited with a pulsed laser. A pulse laser acoustic Doppler flow velocity measurement technique is excited by several optical pulse pairs, and the time frequency shift of the optical acoustic waveform pair is obtained by using a cross-correlation method, so that the velocity is estimated. Another pulse laser photoacoustic Doppler flow velocity measurement provides a new method for measuring the transverse flow velocity based on photoacoustic Doppler bandwidth broadening, the transverse flow velocity is determined by the geometric shape and the velocity of a probe beam, a three-dimensional structure and the flow velocity can be simultaneously carried out by utilizing pulse laser excitation and raster motor scanning, the Doppler bandwidth depends on the linear correlation of the flow velocity, and the flow velocity can be accurately measured.
In the continuous wave photoacoustic Doppler flow velocity measurement, due to the fact that photoacoustic signals are weak, the flow velocity which can be measured cannot be too fast, the Doppler frequency spectrum is widened and the peak value is increased along with the increase of the flow velocity, the measurement sensitivity is affected, and depth information between an ultrasonic transducer and particles cannot be obtained. The flow velocity measurement of the sine pulse wave photoacoustic Doppler uses sine pulse signals to modulate the light intensity of continuous waves, performs external modulation and heterodyne detection, uses lower laser power, generates weaker photoacoustic signals, has lower spectral resolution and poorer signal-to-noise ratio. A pulsed laser acoustic Doppler flow velocity measurement technique is excited by several optical pulse pairs, and the time shift of the optical acoustic waveform pair is obtained by using a cross-correlation method to estimate the velocity, however, the higher concentration of particles and the non-linear motion of the particles (turbulence and eddy) cause poor correlation, and the poorer the accuracy and precision of the velocity measurement. Another pulse laser photoacoustic Doppler flow velocity measurement provides a new method for measuring the transverse flow velocity based on photoacoustic Doppler bandwidth broadening, the transverse flow velocity is determined by the geometric shape and the velocity of a probe beam, the Doppler bandwidth depends on the linear correlation of the flow velocity by utilizing pulse laser excitation and raster motor scanning, the measurement precision of the flow velocity can be greatly influenced due to the low signal-to-noise ratio of tissues and flowing turbulence, and the measurement precision can be improved by correcting a model. If the difference between the photoacoustic signal and the noise is not large or the photoacoustic signal is smaller than the noise, the advantages of the digital signal processing and the phase locking technology cannot be fully utilized to accurately extract the required signal, so that it is difficult to accurately measure the flow velocity of blood and photoacoustic doppler flow velocity measurement of multiple wavelengths cannot be performed.
SUMMERY OF THE UTILITY MODEL
The utility model aims at providing a photoacoustic Doppler blood flow velocity and blood oxygen content measurement system has that measurement accuracy is high, measurable velocity of flow scope is big, measurable degree of depth is big, the spectrum broadens for a short time, spectral resolution is high, wavelength selective range is big, the detection bandwidth is high, the characteristics that system sensitivity is high.
The utility model discloses a realize through following method:
the utility model discloses a photoacoustic Doppler blood flow velocity and blood oxygen content measurement system, include:
the pulse light filtering and collimating unit is used for filtering and collimating to obtain collimated laser;
a pulse laser amplitude modulation unit of a Glan prism and 1/4 wave plates which are used for carrying out amplitude modulation on the collimated laser and have mutually vertical polarization directions;
a sample unit for inserting a blood vessel sample;
the collecting and amplifying unit is used for collecting and amplifying pulse laser acoustic wave signals generated by irradiating the sample unit;
a signal demodulation unit for demodulating the amplified photoacoustic signal and the reference signal;
and the spectrum analysis unit is used for processing Doppler analysis on the signals obtained by the collection amplification unit and the signal demodulation unit to obtain the blood flow velocity and the blood oxygen content of the sample.
The utility model discloses in, the flow measurement technique based on optoacoustic Doppler effect has utilized the light absorption characteristic of spike granule, is different from laser Doppler flow measurement technique and supersound Doppler flow measurement technique and has utilized the light scattering or the sound scattering characteristic of spike granule, and the red blood cell is the granule that an endogenous light absorption performance is good moreover, and its light absorption coefficient is than general biological tissue will be high nearly 2 orders of magnitude. For blood flow velocity measurement, the photoacoustic doppler technology has the advantages of large detection depth relative to the laser doppler flow measurement technology and high detection sensitivity relative to the ultrasonic doppler flow measurement technology.
Furthermore, the pulse light filtering and collimating unit comprises a supercontinuum laser, a filter and a coupling collimating lens, and the pulse laser generated by the supercontinuum laser is transmitted to the coupling collimating lens through the filter and the single-mode fiber in sequence to be coupled and collimated to obtain collimated laser.
Further, the pulse laser amplitude modulation unit comprises a horizontal polarization Glan prism, an 1/4 wave plate with the polarization direction forming 45 degrees with the direction of the horizontal polarization Glan prism, an electro-optic crystal and a vertical polarization Glan prism, and the pulse laser is changed into the sine wave amplitude modulated pulse laser through the horizontal polarization Glan prism, the 1/4 wave plate, the electro-optic modulator and the vertical polarization Glan prism in sequence.
Furthermore, the signal demodulation unit comprises a waveform generator and a phase-locked amplifier, and the phase-locked amplifier is connected with the spectrum analysis unit.
Further, the collecting and amplifying unit comprises a broadband focusing ultrasonic transducer for collecting frequency-shifted photoacoustic waves after the sample is irradiated, a three-dimensional precise displacement platform for enabling a focal spot of the ultrasonic transducer to coincide with a light spot of laser to generate a photoacoustic signal, and a preamplifier for amplifying the photoacoustic signal.
Further, the spectrum analysis unit comprises a phase-locked amplifier for performing phase-locked processing on the photoacoustic signal output by the preamplifier and the reference signal output by the waveform generator to extract the photoacoustic wave frequency shift, and a digital oscilloscope for observing and storing the photoacoustic wave signal after the frequency shift. The mode-locked laser with high repetition frequency is added with light intensity frequency modulation, and then the phase-sensitive phase-locked detection technology is combined, so that the method has obvious advantages in coherent nonlinear optical imaging.
Further, the spectrum analyzing unit further includes an electronic computer for performing data processing on the demodulated signal of the lock-in amplifier and the frequency-shifted photoacoustic signal of the digital oscilloscope, the data processing including fourier transform processing.
Furthermore, the filter screens the pulse laser generated by the supercontinuum laser to form 532nm pulse laser with 20MHz repetition frequency.
Further, the ultrasonic transducer is arranged on the three-dimensional precise displacement platform, and the center frequency of the ultrasonic transducer is 1 MHz.
Another object of the present invention is to protect the measurement method using the above photoacoustic doppler blood flow velocity and blood oxygen content measurement system.
The utility model relates to a photoacoustic Doppler blood flow velocity and blood oxygen content measurement system has following beneficial effect:
the utility model discloses combine together high frequency pulse laser and sine wave intensity modulation to obtain velocity of flow measurement accuracy height, measurable velocity of flow scope big, measurable degree of depth is big, the spectrum broadening is little, spectral resolution is high, the wavelength selective range is big from visible light to infrared, the detection bandwidth is high, the high measurable absorption spectrum's of system sensitivity optoacoustic Doppler blood flow velocity of flow measurement system, thereby the realization is to the accurate measurement of the red blood cell velocity of flow of blood vessel and to the differentiation of arteriovenous blood.
Drawings
FIG. 1 is a schematic diagram of the system components of a photoacoustic Doppler blood flow velocity and blood oxygen content measurement system according to the present invention;
FIG. 2 is a schematic diagram of the simulated connection relationship of the photoacoustic Doppler blood flow velocity and blood oxygen content measurement system of the present invention;
FIG. 3 is a schematic diagram showing the relationship between the sample and the light path in the simulation connection relationship of the photoacoustic Doppler blood flow velocity and blood oxygen content measurement system of the present invention;
FIG. 4 is a graph of the spectrum of a photoacoustic signal excited by an unmodulated 10MHz pulsed laser;
FIG. 5 is a graph of the spectrum of a portion of the area of an unmodulated photoacoustic signal excited by a 10MHz pulsed laser;
FIG. 6 is a graph of the spectrum of a photoacoustic signal excited by a 10MHz pulsed laser modulated by a 1MHz sinusoidal signal intensity;
FIG. 7 is a graph of a spectrum of a portion of a photoacoustic signal excited by a 10MHz pulsed laser modulated by a 1MHz sinusoidal signal intensity;
FIG. 8 is a frequency domain plot and a time domain plot of the demodulated signal corresponding to +0.2 mm/s; wherein, (a) is a frequency domain diagram, and (b) is a time domain diagram;
FIG. 9 is a frequency domain plot and a time domain plot of the demodulated signal corresponding to-0.2 mm/s; wherein, (a) is a frequency domain diagram, and (b) is a time domain diagram;
FIG. 10 is a frequency domain plot and a time domain plot of a demodulated signal corresponding to +1.6 mm/s; wherein, (a) is a frequency domain diagram, and (b) is a time domain diagram;
FIG. 11 is a frequency domain plot and a time domain plot of a demodulated signal corresponding to-1.6 mm/s; wherein, (a) is a frequency domain diagram, and (b) is a time domain diagram;
FIG. 12 shows measured frequency shift values and theoretical frequency shift values in the range of-1.6 mm/s to 1.6 mm/s;
FIG. 13 is a graph of the absorption spectrum of a 100nm graphene layer at 0.2mm/s under quiescent conditions;
FIG. 14 is a graph of the absorption spectra of 100 micron red particles and 100 micron black particles and their ratio of absorption spectra;
the reference numbers in the drawings include: 1. a supercontinuum laser; 2. a filter; 3. a single mode optical fiber; 4. a coupling collimating lens; 5. a horizontally polarizing glan prism; 6. 1/4 a wave plate; 7. an electro-optic crystal; 8. a horizontally polarizing glan prism; 9. a waveform generator; 10. a broadband focusing ultrasonic transducer; 11. a preamplifier; 12. A phase-locked amplifier; 13. a digital oscilloscope; 14. a liquid pipe; 15. a sample measurement chamber; 16. an injector; 17. A microflow pump; 18. a liquid collecting container; 19. a three-dimensional precision displacement platform; 20. an electronic computer.
Detailed Description
In order to make those skilled in the art better understand the technical solution of the present invention, the following provides a detailed description of the product of the present invention with reference to the embodiments and the accompanying drawings.
Example 1
As shown in fig. 1, the utility model discloses a photoacoustic doppler blood flow velocity and blood oxygen content measurement system, include:
the pulse light filtering and collimating unit is used for filtering and collimating to obtain collimated laser;
a pulse laser amplitude modulation unit of a Glan prism and 1/4 wave plates which are used for carrying out amplitude modulation on the collimated laser and have mutually vertical polarization directions;
a sample unit for inserting a blood vessel sample;
the collecting and amplifying unit is used for collecting and amplifying pulse laser acoustic wave signals generated by irradiating the sample unit;
a signal demodulation unit for demodulating the amplified photoacoustic signal and the reference signal;
and the spectrum analysis unit is used for processing Doppler analysis on the signals obtained by the collection amplification unit and the signal demodulation unit to obtain the blood flow velocity and the blood oxygen content of the sample.
Example 2
As shown in fig. 2, the utility model discloses a photoacoustic doppler blood flow velocity and blood oxygen content measuring system, wherein each constitutional unit introduces as follows:
the pulse light filtering and collimating unit comprises a supercontinuum laser 1, a filter 2 and a coupling collimating lens 4, and the pulse laser generated by the supercontinuum laser 1 is transmitted to the coupling collimating lens 4 through the filter 2 and the single-mode fiber 3 in sequence to be coupled and collimated to obtain collimated laser. The filter 2 screens the pulse laser generated by the supercontinuum laser 1 to form pulse laser with the repetition frequency of 532nm and 20 MHz.
The pulse laser amplitude modulation unit comprises a horizontal polarization Glan prism 5, an 1/4 wave plate 6 with the polarization direction forming 45 degrees with the direction of the horizontal polarization Glan prism 5, an electro-optical crystal 7 and a vertical polarization Glan prism 8, and the pulse laser is changed into the pulse laser with sine wave amplitude modulation through the horizontal polarization Glan prism, the 1/4 wave plate 6, the electro-optical modulator and the vertical polarization Glan prism 8 in sequence.
The signal demodulation unit comprises a waveform generator 9 and a lock-in amplifier 12, and the lock-in amplifier 12 is connected with the spectrum analysis unit.
The collecting and amplifying unit comprises a broadband focusing ultrasonic transducer 10 for collecting frequency-shifted photoacoustic waves after irradiating a sample, a three-dimensional precise displacement platform 19 for enabling a focal spot of the ultrasonic transducer 10 to coincide with a light spot of laser to generate a photoacoustic signal, and a preamplifier 11 for amplifying the photoacoustic signal. The ultrasonic transducer 10 is arranged on the three-dimensional precise displacement platform 19, and the center frequency of the ultrasonic transducer 10 is 1 MHz.
The spectrum analysis unit comprises a phase-locked amplifier 12 for performing phase-locked processing on the photoacoustic signal amplified and output by the preamplifier 11 and the reference signal output by the waveform generator 9 to extract the frequency shift of the photoacoustic wave, and a digital oscilloscope 13 for observing and storing the frequency-shifted photoacoustic wave signal. The spectral analysis unit further comprises an electronic computer 20 for data processing of the demodulated signal of the lock-in amplifier 12 and the photoacoustic signal of the digital oscilloscope 13, the data processing including fourier transform processing.
In fig. 2 and 3, the present embodiment uses the liquid tube 14 to simulate a blood vessel, and the signal irradiating the liquid tube 14 is transduced by the ultrasonic transducer 10.
The utility model discloses an electro-optical modulator carries out outside nimble amplitude modulation to the pulse laser of high frequency (MHz), and the optoacoustic signal ratio that produces like this is stronger for the detectable degree of depth is big, uses lock-in amplifier demodulation optoacoustic Doppler signal simultaneously, can improve the resolution ratio of system, sensitivity, adopts the absorption spectrum that the different samples can be measured to the super continuous spectrum laser instrument.
Example 3
Another object of the present invention is to protect the measurement method using the above photoacoustic doppler blood flow velocity and blood oxygen content measurement system.
The utility model discloses in using optoacoustic Doppler blood flow velocity of flow to optoacoustic Doppler laser instrument, carry out sine wave intensity modulation to pulse laser under 1 megahertz frequency, laser direct irradiation transparent hose after using the modulation at present the optoacoustic signal that the granule of flow produced is stronger, then respectively with ultrasonic transducer, preamplifier, the phase-locked amplifier is collected, enlarge, demodulation and processing signal, it is high to form one set of velocity of flow measurement precision, measurable velocity of flow scope is big, measurable depth is big, the spectrum broadening is little, spectral resolution is high, the wavelength selective range is big from the visible light to infrared, the detection bandwidth is high, optoacoustic Doppler blood flow velocity of flow measurement system that system sensitivity is high. The method can be used for measuring blood flow in blood vessels, and meanwhile, the distinction of the arterial venous blood can be realized according to the optical acoustic response of the absorption spectrum.
Example 4
The utility model discloses an adopt above-mentioned optoacoustic Doppler blood flow velocity and blood oxygen content measurement system's measuring method, its concrete step is:
the laser generated by a supercontinuum laser passes through a filter and a single-mode fiber to generate pulse laser with the repetition frequency of 20MHz and the wavelength of 532nm, and the pulse laser firstly passes through a coupling collimating lens;
then sequentially passing through a Glan prism with a horizontal polarization direction, an 1/4 wave plate with an included angle of 45 degrees between the polarization direction and the horizontal polarization Glan prism, and a 1MHz sine wave signal generated by a waveform generator to drive an electro-optical modulator to modulate the crystal inside, and then vertically irradiating the blood vessel through the Glan prism with a vertical polarization direction;
the photoacoustic Doppler effect can generate photoacoustic Doppler frequency shift signals which are received by a water immersion type broadband focusing ultrasonic transducer arranged on a three-dimensional precise displacement platform, in the receiving process, the three-dimensional precise displacement platform is adjusted to adjust the light spot of laser to coincide with the focus of the ultrasonic transducer, and the axis of the ultrasonic transducer is vertical to the flowing direction of particles) the ultrasonic transducer converts the received photoacoustic signals into electric signals;
the electric signal is amplified by a preamplifier, then is connected to a digital oscilloscope to observe a photoacoustic Doppler frequency shift signal, and then is connected to a phase-locked amplifier; the other path of the same sine wave signal of the waveform generator is taken as a reference signal and is connected to the phase-locked amplifier; and the Doppler frequency shift signal obtained by demodulation is connected to an electronic computer for Fourier transform processing.
Example 5
For effective simulation the utility model discloses measuring device's measurement process, the utility model discloses a liquid pipe simulation blood vessel specifically is shown in fig. 2. In fig. 2, a liquid tube 14 is placed in a sample measuring chamber 15, a syringe 16 driven by a micro-flow pump 17 is connected to the other end of the liquid tube 14, the syringe 16 contains a particle suspension of 50 microns, the micro-flow pump 17 regulates different flow rates of the liquid in the liquid tube 14, and the liquid discharged from the liquid tube 14 is placed in a liquid collecting container 18. The tube was then used to simulate the vessel for specific performance tests.
The utility model discloses through the analog verification, to the optoacoustic Doppler who has carried out the amplitude modulation of pulse laser measurement, after the time domain is modulated, the corresponding Fourier transform of optoacoustic signal discovers whole spectrum respectively and moves 1 megahertz fundamental frequency unit of a sinusoidal modulation signal left and right, because sample motion, the corresponding frequency shift is removed again to whole spectrum, can utilize lock-in amplifier to demodulate the part of optoacoustic Doppler frequency shift and obtain to calculate the velocity of flow. The results of the specific simulation verification are shown in FIGS. 4 to 14.
From a comparison of fig. 5 and fig. 7, it is apparent that there is a 1MHz spectral component near zero frequency; when the sample is moving at a constant rate, a photoacoustic doppler shift is added at a frequency of 1MHz, thus demonstrating the feasibility of amplitude intensity modulated pulsed laser acoustic doppler flow velocity measurements from simulations.
In a pulse modulation type photoacoustic Doppler blood flow velocity experiment, photoacoustic Doppler flow velocity measurement with velocities of +/-0.2 mm/s and +/-1.6 mm/s is carried out, a moving photoacoustic signal and a reference signal are demodulated to obtain a Doppler frequency shift signal, and finally Fourier transform is carried out, wherein the method comprises the following steps:
wherein f0 is the frequency of the sine wave modulation signal, v0 is the flow rate of the particles, and vc is 1500m/s is the sound velocity in the medium.
From FIG. 8 to FIG. 11, it can be seen that the Doppler shifts of +0.2, -0.2mm/s, +1.6mm/s and-1.6 mm/s correspond to +0.1277Hz, -0.1277Hz, +1.098Hz and-1.098 Hz, respectively; the theoretical calculated frequency shifts were +0.1916mm/s, -0.1916mm/s, +1.647mm/s, -1.647mm/s, respectively. The corresponding errors are 4.2%, 4.2%, 2.9%, 2.9%. Unlike continuous wave photoacoustic doppler flow velocity measurements, doppler shift does not broaden, and one velocity corresponds to only one doppler shift. Whether the noise is stronger than the photoacoustic signal or not, the photoacoustic signal can be accurately demodulated. The signal near zero frequency is noise generated by the waveform generator.
From FIG. 12, it can be seen that the measured frequency shift values agree well with the theoretical frequency shift values over the rate range of 0.1-1.6 mm/s; it can be seen from figure 13 that the normalized absorption spectra of the graphene layers at rest and at a rate of 0.2mm/s, measured after 100nm respectively, are substantially close. Therefore, the utility model discloses a strategic system not only can be accurate measurement absorption flow velocity information, but also can measure the absorption spectrum of sample simultaneously. The absorption spectra of different samples are different, and different samples can be separated by measuring the absorption spectra.
From fig. 14, it can be seen that the absorption spectra of the 100 micron red particles and the 100 micron black particles are substantially the same in the range of 500nm to 600nm, and from 600nm to 700nm, the absorption spectrum of the red particles drops faster than the black particles, with the absorption at 650nm being the smallest, so that the absorption spectra of different samples can be measured to distinguish different samples.
The above embodiments are only specific embodiments of the present invention, and the description thereof is specific and detailed, but not construed as limiting the scope of the present invention. It should be noted that, for a person skilled in the art, many variations and modifications are possible without departing from the inventive concept, and such obvious alternatives fall within the scope of the invention.
Claims (9)
1. A photoacoustic doppler blood flow rate and blood oxygen content measurement system comprising:
the pulse light filtering and collimating unit is used for filtering and collimating to obtain collimated laser;
a pulse laser amplitude modulation unit of a Glan prism and 1/4 wave plates which are used for carrying out amplitude modulation on the collimated laser and have mutually vertical polarization directions;
a sample unit for inserting a blood vessel sample;
the collecting and amplifying unit is used for collecting and amplifying pulse laser acoustic wave signals generated by irradiating the sample unit;
a signal demodulation unit for demodulating the amplified photoacoustic signal and the reference signal;
and the spectrum analysis unit is used for processing Doppler analysis on the signals obtained by the collection amplification unit and the signal demodulation unit to obtain the blood flow velocity and the blood oxygen content of the sample.
2. The photoacoustic doppler blood flow rate and blood oxygen content measurement system of claim 1, wherein: the pulse light filtering and collimating unit comprises a supercontinuum laser, a filter and a coupling collimating lens, and the pulse laser generated by the supercontinuum laser is transmitted to the coupling collimating lens through the filter and the single-mode fiber in sequence to be coupled and collimated to obtain collimated laser.
3. The photoacoustic doppler blood flow rate and blood oxygen content measurement system of claim 2, wherein: the pulse laser amplitude modulation unit comprises a horizontal polarization Glan prism, an 1/4 wave plate, an electro-optic crystal and a vertical polarization Glan prism, wherein the polarization direction of the 1/4 wave plate and the direction of the horizontal polarization Glan prism form 45 degrees, and the pulse laser is changed into the sine wave amplitude modulated pulse laser through the horizontal polarization Glan prism, the 1/4 wave plate, the electro-optic modulator and the vertical polarization Glan prism in sequence.
4. The photoacoustic doppler blood flow rate and blood oxygen content measurement system of claim 3, wherein: the signal demodulation unit comprises a waveform generator and a phase-locked amplifier, and the phase-locked amplifier is connected with the spectrum analysis unit.
5. The photoacoustic doppler blood flow rate and blood oxygen content measurement system of claim 4, wherein: the collecting and amplifying unit comprises a broadband focusing ultrasonic transducer for collecting frequency-shifted photoacoustic waves after a sample is irradiated, a three-dimensional precise displacement platform for enabling a focal spot of the ultrasonic transducer to coincide with a light spot of laser to generate a photoacoustic signal, and a preamplifier for amplifying the photoacoustic signal.
6. The photoacoustic doppler blood flow rate and blood oxygen content measurement system of claim 5, wherein: the spectrum analysis unit comprises a phase-locked amplifier and a digital oscilloscope, wherein the phase-locked amplifier is used for performing phase-locked processing on the photoacoustic signal amplified and output by the preamplifier and the reference signal output by the waveform generator to extract photoacoustic wave frequency shift, and the digital oscilloscope is used for observing and storing the photoacoustic wave signal after frequency shift.
7. The photoacoustic doppler blood flow rate and blood oxygen content measurement system of claim 6, wherein: the frequency spectrum analysis unit also comprises an electronic computer for carrying out data processing on the demodulation signal of the phase-locked amplifier and the photoacoustic signal of the digital oscilloscope frequency, and the data processing process comprises Fourier transform processing.
8. The photoacoustic doppler blood flow rate and blood oxygen content measurement system of claim 7, wherein: the filter screens the pulse laser generated by the supercontinuum laser to form pulse laser with the repetition frequency of 532nm and 20 MHz.
9. The photoacoustic doppler blood flow rate and blood oxygen content measurement system of claim 8, wherein: the ultrasonic transducer is arranged on the three-dimensional precise displacement platform, and the center frequency of the ultrasonic transducer is 1 MHz.
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