CN113406008B - Photoacoustic imaging device and method based on white light interference - Google Patents

Abstract

A photoacoustic imaging device and method based on white light interference, the device comprises an optical interference detection system, a photoacoustic excitation system, a scanning system and a computer; one end of the optical interference detection system is electrically connected with the computer, and the other end of the optical interference detection system is connected with the scanning system Optical connection is performed; one end of the photoacoustic excitation system is electrically connected to the computer, and the other end of the photoacoustic excitation system is optically connected to the scanning system; the scanning system is optically connected to the sample. The white light interference-based photoacoustic imaging method of the present invention uses the white light interference to detect the reflected light intensity change of the excitation point of the photoacoustic signal in the sample, and can obtain the photoacoustic signals from different depths of the sample at the same time, and has a certain depth resolution capability, And using Fourier transform to demodulate the signal, compared with the time domain demodulation method currently used, can effectively improve the detection sensitivity.

Description

A photoacoustic imaging device and method based on white light interference

technical field

The invention belongs to the technical field of photoacoustic imaging, and in particular relates to a photoacoustic imaging device and method based on white light interference.

Background technique

Photoacoustic imaging (PAI) is a rapidly developing medical imaging technology in recent years. PAI combines the high contrast of pure optical imaging and the deep penetration of pure ultrasound imaging. It is a non-invasive imaging mode that can be used for Structural and functional imaging of biological tissues. The principle of PAI is the photoacoustic effect. When the pulsed laser is irradiated to the biological tissue, the tissue absorbs the light energy and generates thermoelastic expansion, and thus generates the corresponding ultrasonic wave. The absorption distribution image of the tissue can be obtained by detecting the ultrasonic wave.

At present, contact photoacoustic imaging technology based on piezoelectric transducers is widely used as a relatively mature technology. This technology uses piezoelectric transducers to directly detect photoacoustic signals, but due to the acoustic impedance of ultrasonic waves in different media Differently, this also makes the ultrasound produce strong reflection on the two medium surfaces, so in order to improve the sensitivity and reduce the loss, an acoustic coupling medium is necessary, which also limits the scope of application of this technology in principle.

For the inspection of special cases such as burns and brain diseases, a non-contact detection method is required. Therefore, a non-contact detection method based on optical interference is proposed as an optimization method of piezoelectric transducers. This method can realize non-contact and obtain sample information. Compared with piezoelectric transducers, optical interference detection has the characteristics of non-contact, miniaturization and high sensitivity.

For example, the Chinese patent application with the application number of 201510881786.7 discloses a non-contact photoacoustic detection method and device based on optical interferometry, and proposes a detection method based on optical interference, but the photoacoustic imaging of the optical interference The method still has flaws. In order to solve the weak and random variation in the intensity and phase of the reflected probe light caused by the rough surface of the tissue sample, this method applies a water layer on the surface of the sample, and the water layer produces a uniform reflection surface, but this method adds a layer of water on the surface of the sample. The method of the water layer is not completely non-contact in essence, and there are also inconveniences in application.

In addition, the application number is 201910587193.8 Chinese patent application, which discloses a non-contact photoacoustic imaging device and method, and proposes a non-contact photoacoustic imaging system and method based on 3×3 fiber coupler demodulation, using optical The interference method directly detects the change of the reflected light intensity of the excitation point of the photoacoustic signal in the sample, and makes the focus of the excitation light and the sample light coincide with the inside of the sample. The light intensity of the backscattered sample light increases, and the interferometric method of demodulation by a 3×3 fiber coupler is used to measure this light intensity change for imaging. Although this method solves the problem of water layer and improves the flexibility of the method, it still has defects, that is, the depth information inside the sample is ambiguous at the same time, so it is impossible to obtain the excitation position of the photoacoustic signal in the sample. depth information, and the demodulation result is overly dependent on the manufacturing accuracy of the 3×3 fiber coupler, otherwise there will be large errors.

SUMMARY OF THE INVENTION

In view of the problems existing in the prior art, the present invention provides a photoacoustic imaging device and method based on white light interference, which utilizes white light interference to detect changes in the reflected light intensity of the excitation point of the photoacoustic signal in the sample, and can obtain images from different depths of the sample at the same time. The photoacoustic signal has a certain depth resolution capability, and the Fourier transform is used for signal demodulation, which can effectively improve the detection sensitivity compared with the currently used time domain demodulation method.

In order to achieve the above purpose, the present invention adopts the following technical scheme: a photoacoustic imaging device based on white light interference, including an optical interference detection system, a photoacoustic excitation system, a scanning system and a computer; one end of the optical interference detection system is electrically connected to the computer. The other end of the optical interference detection system is optically connected to the scanning system; one end of the photoacoustic excitation system is electrically connected to the computer, and the other end of the photoacoustic excitation system is optically connected to the scanning system; the scanning system is optically connected to the sample .

The optical interference detection system includes a low-coherence light source, an optical fiber isolator, an optical switch, a 2×2 optical fiber coupler, a first collimator, a first lens, a first mirror and a spectrometer; the low-coherence light source is isolated by an optical fiber The first collimator is optically connected to the optical switch, one way of the optical switch is electrically connected to the computer, and the other way of the optical switch is connected to the 2×2 fiber optic coupler through an optical fiber; one end of the first collimator is connected to the 2×2 fiber optic coupler through an optical fiber For connection, the laser light emitted by the other end of the first collimator is directed to the first mirror through the first lens; one end of the spectrometer is electrically connected to the computer, and the other end of the spectrometer is connected to the 2×2 fiber coupler through optical fibers.

The photoacoustic excitation system includes an excitation light source and a second reflection mirror; the excitation light source is electrically connected to a computer, and the excitation light emitted by the excitation light source is directed toward the second reflection mirror.

The scanning system includes a second collimator, a dichroic mirror, a Y-direction scanning galvanometer, an X-direction scanning galvanometer and a second lens; one end of the second collimator is connected to a 2×2 fiber coupler through an optical fiber. connected, the laser light emitted from the other end of the second collimator is directed to the sample through the dichroic mirror, the Y-direction scanning galvanometer, the X-direction scanning galvanometer and the second lens in turn; the laser reflected by the second mirror directly irradiates the sample The dichroic mirror is directed to the sample through the Y-direction scanning galvanometer, the X-direction scanning galvanometer and the second lens in turn.

A photoacoustic imaging method based on white light interference adopts the photoacoustic imaging device based on white light interference, comprising the following steps:

Step 1: Start the low-coherence light source, and the detection laser emitted by the low-coherence light source enters the 2×2 fiber coupler through the fiber isolator and the optical switch in turn, and then outputs two paths through the 2×2 fiber coupler, and one path is used as the reference light in turn. After passing through the first collimator, the first lens and the first reflector, and returning to the 2×2 fiber coupler in the same way, the other way as the sample light passes through the second collimator, the dichroic mirror and the Y-direction scanning galvanometer in turn. , X-direction scanning galvanometer, second lens and sample and return to 2×2 fiber coupler in the same way;

Step 2: When the reference light and the sample light return to the 2×2 fiber coupler, they will directly enter the spectrometer through the 2×2 fiber coupler, and then the computer will perform spectral analysis;

Step 3: The computer sends a trigger signal to the excitation light source to prompt the excitation light source to start. When the excitation light trigger signal is at a high level, the excitation light is output from the excitation light source, and the excitation light passes through the second reflecting mirror, the dichroic mirror, and the Y direction in turn. The scanning galvanometer, X-direction scanning galvanometer and the second lens are directed to the sample, and converge with the sample light at a point inside the sample. After the sample absorbs the laser energy, a photoacoustic pressure will be generated, and the photoacoustic pressure will stimulate the excitation point inside the sample. The optical index of refraction increases, which in turn increases the reflected light intensity and generates a photoacoustic signal; on the contrary, when the excitation light trigger signal is at a low level, the excitation light source stops outputting the excitation light;

Step 4: Send a trigger signal to the optical switch by the computer. When the trigger signal of the optical switch is at a high level, the detection laser emitted by the low-coherence light source can directly reach the sample through the optical switch; on the contrary, when the trigger signal of the optical switch is at a low level The detection laser emitted by the low-coherence light source cannot pass through the optical switch;

Step 5: When the excitation light trigger signal is in the low level period and the optical switch trigger signal is in the high level period, the detected photoacoustic signal is recorded as S0(K); in addition, when the excitation light trigger signal and the optical switch trigger signal are When both are in the high-level period, the detected photoacoustic signal is recorded as S1(K); wherein, K represents the wavenumber coordinate of the spectrometer;

Step 6: Preprocess the photoacoustic signal S0(K) and the photoacoustic signal S1(K), eliminate the DC component and normalize the intensity, and then perform fast Fourier transform to obtain the amplitude of the photoacoustic signal S0(K) The spectrum F0(u) and the amplitude spectrum F1(u) of the photoacoustic signal S1(K), where u represents the frequency, the frequency u is proportional to the depth z, and z=au, where a is the proportionality coefficient, and the proportionality coefficient a is a known quantity, which can be determined by measuring a sample with a known depth; finally, the reflected light intensity distributions F0(z) and F1(z) of samples at different depths can be obtained by the formula z=au, where F0(z ) is the reflected light intensity of the sample when the excitation light source stops outputting the excitation light, and F1(z) is the reflected light intensity of the sample when the excitation light source outputs the excitation light;

Step 7: Calculate the photoacoustic signal P(z) at different depths of the sample, the calculation formula is P(z)=F1(z)-F0(z);

Step 8: realize two-dimensional scanning through the X-direction scanning galvanometer and the Y-direction scanning galvanometer, and realize two-dimensional imaging in the computer.

Beneficial effects of the present invention:

The white light interference-based photoacoustic imaging device and method of the present invention utilizes the white light interference to detect the reflected light intensity change of the excitation point of the photoacoustic signal in the sample, and can obtain the photoacoustic signals from different depths of the sample at the same time, and has a certain depth resolution. Compared with the current time domain demodulation method, the detection sensitivity can be effectively improved.

Description of drawings

1 is a schematic structural diagram of a photoacoustic imaging device based on white light interference of the present invention;

2 is a waveform diagram of an excitation light trigger signal and an optical switch trigger signal in an embodiment;

In the figure, I—optical interference detection system, II—photoacoustic excitation system, III—scanning system, 1—computer, 2—sample, 3—low coherence light source, 4—fiber isolator, 5—optical switch, 6—2 ×2 fiber coupler, 7—first collimator, 8—first lens, 9—first reflector, 10—spectroscope, 11—excitation light source, 12—second reflector, 13—second collimator , 14—dichroic mirror, 15—Y scanning galvanometer, 16—X scanning galvanometer, 17—second lens.

Detailed ways

The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

As shown in FIG. 1, a photoacoustic imaging device based on white light interference includes an optical interference detection system I, a photoacoustic excitation system II, a scanning system III and a computer 1; one end of the optical interference detection system I is electrically connected to the computer 1. connected, the other end of the optical interference detection system I is optically connected with the scanning system III; one end of the photoacoustic excitation system II is electrically connected with the computer 1, and the other end of the photoacoustic excitation system II is optically connected with the scanning system III; the scanning System III was optically connected to Sample 2.

The optical interference detection system 1 includes a low-coherence light source 3, an optical fiber isolator 4, an optical switch 5, a 2×2 optical fiber coupler 6, a first collimator 7, a first lens 8, a first reflector 9 and a spectrometer 10 ; The low-coherence light source 3 is optically connected to the optical switch 5 through the optical fiber isolator 4, the optical switch 5 is electrically connected to the computer 1, and the other optical switch 5 is connected to the 2 × 2 optical fiber coupler 6 through optical fibers; One end of the first collimator 7 is connected to the 2×2 fiber coupler 6 through optical fibers, and the laser light emitted by the other end of the first collimator 7 is directed to the first mirror 9 through the first lens 8; one end of the spectrometer 10 is It is electrically connected to the computer 1 , and the other end of the spectrometer 10 is connected to the 2×2 fiber coupler 6 through an optical fiber.

The photoacoustic excitation system II includes an excitation light source 11 and a second reflection mirror 12 ; the excitation light source 11 is electrically connected to the computer 1 , and the excitation light emitted by the excitation light source 11 is directed toward the second reflection mirror 12 .

The scanning system III includes a second collimator 13 , a dichroic mirror 14 , a Y-direction scanning galvanometer 15 , an X-direction scanning galvanometer 16 and a second lens 17 ; one end of the second collimator 13 is connected to 2× 2. The optical fiber coupler 6 is connected by an optical fiber, and the laser light emitted from the other end of the second collimator 13 is directed to the sample through the dichroic mirror 14, the Y-direction scanning galvanometer 15, the X-direction scanning galvanometer 16 and the second lens 17 in turn. 2. The laser light reflected by the second reflecting mirror 12 is directed toward the dichroic mirror 14, and then directed toward the sample 2 through the Y-direction scanning galvanometer 15, the X-direction scanning galvanometer 16 and the second lens 17 in sequence.

A photoacoustic imaging method based on white light interference adopts the photoacoustic imaging device based on white light interference, comprising the following steps:

Step 1: Start the low-coherence light source 3, and the detection laser emitted by the low-coherence light source 3 enters the 2×2 fiber coupler 6 through the fiber isolator 4 and the optical switch 5 in turn, and then outputs two channels through the 2×2 fiber coupler 6 , one way as the reference light passes through the first collimator 7, the first lens 8 and the first reflector 9 in turn and returns to the 2×2 fiber coupler 6 in the same way, and the other way as the sample light passes through the second collimator 13 in sequence , the dichroic mirror 14, the Y-direction scanning galvanometer 15, the X-direction scanning galvanometer 16, the second lens 17 and the sample 2 and return to the 2×2 fiber coupler 6 in the same way;

Step 2: After the reference light and the sample light return to the 2×2 fiber coupler 6, they will directly enter the spectrometer 10 through the 2×2 fiber coupler 6, and then the computer 1 will perform spectral analysis;

Step 3: The computer 1 sends a trigger signal to the excitation light source 11 to prompt the excitation light source 11 to start up. When the excitation light trigger signal is at a high level, the excitation light source 11 outputs the excitation light, and the excitation light passes through the second reflecting mirror 12 and the two-way in turn. The chromatic mirror 14, the Y-direction scanning galvanometer 15, the X-direction scanning galvanometer 16 and the second lens 17 are directed towards the sample 2, and converge with the sample light at a point inside the sample 2, and the sample 2 will generate photoacoustics after absorbing the laser energy The photoacoustic pressure will increase the optical refractive index of the excitation point inside the sample 2, thereby increasing the reflected light intensity and generating a photoacoustic signal; on the contrary, when the excitation light trigger signal is low, the excitation light source 11 Pause the output excitation light;

Step 4: The computer 1 sends a trigger signal to the optical switch 5. When the optical switch trigger signal is at a high level, the detection laser emitted by the low-coherence light source 3 can reach the sample 2 directly through the optical switch 5; on the contrary, when the optical switch trigger signal is When the level is low, the detection laser emitted by the low-coherence light source 3 cannot pass through the optical switch 5;

Step 5: When the excitation light trigger signal is in the low level period and the optical switch trigger signal is in the high level period, the detected photoacoustic signal is recorded as S0(K); in addition, when the excitation light trigger signal and the optical switch trigger signal are When both are in the high-level period, the detected photoacoustic signal is recorded as S1(K); wherein, K represents the wave number coordinate of the spectrometer 10; in this embodiment, as shown in FIG. The time-length ratio of the flat period to the low-level period is 1:1 and occurs alternately, while the time-length ratio of the high-level period to the low-level period of the excitation light trigger signal is 1:3 and alternately occurs;

Step 6: Preprocess the photoacoustic signal S0(K) and the photoacoustic signal S1(K), eliminate the DC component and normalize the intensity, and then perform fast Fourier transform to obtain the amplitude of the photoacoustic signal S0(K) The spectrum F0(u) and the amplitude spectrum F1(u) of the photoacoustic signal S1(K), where u represents the frequency, the frequency u is proportional to the depth z, and z=au, where a is the scale factor, and the scale factor a is a known quantity, which can be determined by measuring a sample 2 with a known depth; finally, through the formula z=au, the reflected light intensity distributions F0(z) and F1(z) of sample 2 at different depths can be obtained, where F0 (z) is the reflected light intensity of the sample 2 when the excitation light source 11 stops outputting the excitation light, and F1(z) is the reflected light intensity of the sample 2 when the excitation light source 11 outputs the excitation light;

Step 7: Calculate the photoacoustic signal P(z) of sample 2 at different depths, and the calculation formula is P(z)=F1(z)-F0(z);

Step 8: Two-dimensional scanning is realized by the X-direction scanning galvanometer 16 and the Y-direction scanning galvanometer 15 , and two-dimensional imaging is realized in the computer 1 .

The solutions in the embodiments are not intended to limit the scope of the patent protection of the present invention, and all equivalent implementations or modifications that do not depart from the present invention are included in the scope of the patent of this case.

Claims (1)

1. A photoacoustic imaging method based on white light interference adopts a photoacoustic imaging device based on white light interference, and the device comprises an optical interference detection system, a photoacoustic excitation system, a scanning system and a computer; one end of the optical interference detection system is electrically connected with the computer, and the other end of the optical interference detection system is optically connected with the scanning system; one end of the photoacoustic excitation system is electrically connected with the computer, and the other end of the photoacoustic excitation system is optically connected with the scanning system; the scanning system is optically connected with the sample; the optical interference detection system comprises a low-coherence light source, an optical fiber isolator, an optical switch, a 2 x 2 optical fiber coupler, a first collimator, a first lens, a first reflector and a spectrometer; the low-coherence light source is optically connected with the optical switch through the optical fiber isolator, one path of the optical switch is electrically connected with the computer, and the other path of the optical switch is connected with the 2 x 2 optical fiber coupler through the optical fiber; one end of the first collimator is connected with the 2 x 2 optical fiber coupler through an optical fiber, and laser emitted by the other end of the first collimator is emitted to the first reflector through the first lens; one end of the spectrometer is electrically connected with the computer, and the other end of the spectrometer is connected with the 2 x 2 optical fiber coupler through an optical fiber; the photoacoustic excitation system comprises an excitation light source and a second reflecting mirror; the excitation light source is electrically connected with the computer, and the excitation light emitted by the excitation light source directly irradiates the second reflecting mirror; the scanning system comprises a second collimator, a dichroic mirror, a Y-direction scanning galvanometer, an X-direction scanning galvanometer and a second lens; one end of the second collimator is connected with the 2X 2 optical fiber coupler through an optical fiber, and laser emitted by the other end of the second collimator sequentially passes through the dichroic mirror, the Y-direction scanning galvanometer, the X-direction scanning galvanometer and the second lens and is emitted to the sample; the laser reflected by the second reflecting mirror directly irradiates to the dichroic mirror and irradiates to a sample through the Y-direction scanning vibrating mirror, the X-direction scanning vibrating mirror and the second lens in sequence; the method is characterized in that: the method comprises the following steps:

the method comprises the following steps: starting a low-coherence light source, enabling detection laser emitted by the low-coherence light source to enter a 2X 2 optical fiber coupler through an optical fiber isolator and an optical switch in sequence, outputting the detection laser in two paths through the 2X 2 optical fiber coupler, enabling one path of the detection laser to serve as reference light to pass through a first collimator, a first lens and a first reflector in sequence and return to the 2X 2 optical fiber coupler in the original path, enabling the other path of the detection laser to serve as sample light to pass through a second collimator, a dichroic mirror, a Y-direction scanning vibration mirror, an X-direction scanning vibration mirror, a second lens and a sample in sequence and return to the 2X 2 optical fiber coupler in the original path;

step two: when the reference light and the sample light original path return to the 2 x 2 optical fiber coupler, the reference light and the sample light directly enter the spectrometer through the 2 x 2 optical fiber coupler, and then the spectral analysis is carried out by the computer;

step three: the computer sends a trigger signal to the excitation light source to prompt the excitation light source to start, when the trigger signal of the excitation light is at a high level, the excitation light source outputs the excitation light, the excitation light sequentially passes through the second reflecting mirror, the dichroic mirror, the Y-direction scanning vibrating mirror, the X-direction scanning vibrating mirror and the second lens to emit to the sample, and is converged at one point with the sample light inside the sample, the sample can generate light sound pressure after absorbing laser energy, and the light sound pressure can prompt the optical refractive index of an excitation point inside the sample to be increased, so that the reflected light intensity is increased, and a light sound signal is generated; on the contrary, when the exciting light trigger signal is at a low level, the exciting light source stops outputting exciting light;

step four: sending a trigger signal to the optical switch by the computer, and when the trigger signal of the optical switch is at a high level, directly sending detection laser sent by the low-coherence light source to the sample through the optical switch; on the contrary, when the trigger signal of the optical switch is at a low level, the detection laser emitted by the low-coherence light source cannot pass through the optical switch;

step five: when the excitation light trigger signal is in a low level period and the optical switch trigger signal is in a high level period, recording the detected photoacoustic signal as S0 (K); further, when both the excitation light trigger signal and the optical switch trigger signal are in the high level period, the detected photoacoustic signal is denoted as S1 (K); wherein K represents the wave number coordinate of the spectrometer;

step six: preprocessing a photoacoustic signal S0(K) and a photoacoustic signal S1(K), eliminating a direct current component and normalizing the intensity, and then performing fast Fourier transform to obtain an amplitude spectrum F0(u) of the photoacoustic signal S0(K) and an amplitude spectrum F1(u) of the photoacoustic signal S1(K), wherein u represents frequency, the frequency u is in direct proportion to a depth z, and the z is au, wherein a is a proportionality coefficient, and a is a known quantity, which is determined by measuring a sample with a known depth; finally, the reflected light intensity distributions F0(z) and F1(z) of the samples at different depths are obtained by the formula z au, wherein F0(z) is the reflected light intensity of the sample when the excitation light source stops outputting the excitation light, and F1(z) is the reflected light intensity of the sample when the excitation light source outputs the excitation light;

step seven: calculating photoacoustic signals P (z) of different depths of the sample, wherein the calculation formula is P (z) ═ F1(z) -F0 (z);

step eight: two-dimensional scanning is realized through the X-direction scanning galvanometer and the Y-direction scanning galvanometer, and two-dimensional imaging is realized in a computer.

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