1. A photoacoustic imaging apparatus based on white light interference, comprising: 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 to the sample.

2. A photoacoustic imaging apparatus based on white light interference as set forth in claim 1, wherein: 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.

3. A photoacoustic imaging apparatus based on white light interference as set forth in claim 2, wherein: 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.

4. A photoacoustic imaging apparatus based on white light interference as set forth in claim 3, wherein: 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 the sample through the Y-direction scanning vibrating mirror, the X-direction scanning vibrating mirror and the second lens in sequence.

5. A photoacoustic imaging method based on white light interference, which employs the photoacoustic imaging apparatus based on white light interference of claim 1, characterized by comprising the steps of:

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, then 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, wherein when the trigger signal of the optical switch is at a high level, the detection laser sent by the low-coherence light source can directly reach the sample through the optical switch; conversely, when the optical switch trigger signal 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, normalizing the direct current component and 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 and can be determined by measuring a sample with a known depth; finally, the sample reflected light intensity distributions F0(z) and F1(z) 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 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.

Background

The technology of Photoacoustic imaging (PAI) is a medical imaging technology rapidly developed in recent years, and PAI combines the high contrast of pure optical imaging and the deep penetration of pure ultrasonic imaging, and is a non-invasive imaging mode which can be used for structural and functional imaging of biological tissues. The principle of PAI is the photoacoustic effect, when pulsed laser light is irradiated to biological tissue, the tissue absorbs light energy and generates thermoelastic expansion, and thus generates corresponding ultrasonic waves, and the ultrasonic waves are detected to obtain an absorption distribution image of the tissue.

At present, a contact type photoacoustic imaging technology based on a piezoelectric transducer is widely used as a relatively mature technology, which uses the piezoelectric transducer to directly detect photoacoustic signals, but since the acoustic impedance of ultrasonic waves in different media is different, the ultrasonic waves are also strongly reflected on the surfaces of the two media, so that an acoustic coupling medium is necessary for improving sensitivity and reducing loss, which also limits the application range of the technology in principle.

For the examination of special cases such as burns and brains, a non-contact detection method is required, and therefore, a non-contact detection method based on optical interference is proposed as an optimization method of the piezoelectric transducer. The method can realize non-contact and obtain sample information, and compared with a piezoelectric transducer, the optical interference detection has the characteristics of non-contact, miniaturization, high sensitivity and the like.

For example, chinese patent application No. 201510881786.7 discloses a non-contact photoacoustic detection method and apparatus based on optical interference method, and proposes a detection method based on optical interference, but the photoacoustic imaging method based on optical interference still has defects. In order to solve the problem that the intensity and the phase of the reflected detection light are weak and randomly change due to the rough surface of the tissue sample, the method coats a water layer on the surface of the sample, and the water layer generates a uniform reflecting surface.

In addition, the application No. 201910587193.8, chinese patent application, discloses a non-contact photoacoustic imaging device and method, and provides a non-contact photoacoustic imaging system and method based on 3 × 3 fiber coupler demodulation, using an optical interference method to directly detect the reflected light intensity change of the photoacoustic signal excitation point in the sample, and making the focus of the excitation light and the sample light coincide inside the sample, the absorber at the focus absorbs the laser energy to cause the optical refractive index change at the position, and further cause the light intensity of the back-scattered sample light to increase, and then using the interference method of 3 × 3 fiber coupler demodulation to measure the light intensity change for imaging. Although the method solves the problem of the water layer and improves the flexibility of the method, the method still has the defects that the depth information of the interior of the sample is fuzzy at the same time, the depth information of the position excited by the photoacoustic signal in the sample cannot be obtained, the demodulation result excessively depends on the manufacturing precision of the 3 × 3 optical fiber coupler, and otherwise, a large error is generated.

Disclosure of Invention

The invention provides a photoacoustic imaging device and method based on white light interference, aiming at the problems in the prior art, the white light interference is utilized to detect the reflected light intensity change of a photoacoustic signal excitation point in a sample, photoacoustic signals from different depths of the sample at the same moment can be obtained, the photoacoustic imaging device has certain depth resolution capability, and Fourier change is adopted to demodulate the signals, so that the detection sensitivity can be effectively improved compared with the currently adopted time domain demodulation mode.

In order to achieve the purpose, the invention adopts the following technical scheme: a photoacoustic imaging device based on white light interference 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 to 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 the sample through the Y-direction scanning vibrating mirror, the X-direction scanning vibrating mirror and the second lens in sequence.

A photoacoustic imaging method based on white light interference adopts the photoacoustic imaging device based on white light interference, and 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, then 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, wherein when the trigger signal of the optical switch is at a high level, the detection laser sent by the low-coherence light source can directly reach the sample through the optical switch; conversely, when the optical switch trigger signal 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, normalizing the direct current component and 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 and can be determined by measuring a sample with a known depth; finally, the sample reflected light intensity distributions F0(z) and F1(z) 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 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.

The invention has the beneficial effects that:

the photoacoustic imaging device and method based on white light interference provided by the invention can obtain photoacoustic signals from different depths of a sample at the same time by detecting the reflected light intensity change of the photoacoustic signal excitation point in the sample through white light interference, have certain depth resolution capability, and adopt Fourier change to demodulate the signals, so that the detection sensitivity can be effectively improved compared with the currently adopted time domain demodulation mode.

Drawings

FIG. 1 is a schematic diagram of a photoacoustic imaging apparatus based on white light interference according to the present invention;

FIG. 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 coherent light source, 4-fiber isolator, 5-optical switch, 6-2 × 2 fiber coupler, 7-first collimator, 8-first lens, 9-first reflector, 10-spectrometer, 11-excitation light source, 12-second reflector, 13-second collimator, 14-dichroic mirror, 15-Y-direction scanning galvanometer, 16-X-direction scanning galvanometer, 17-second lens.

Detailed Description

The invention is described in further detail below with reference to the figures and the specific embodiments.

As shown in fig. 1, a photoacoustic imaging apparatus 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 with the computer 1, and 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 is optically connected to the sample 2.

The optical interference detection system I comprises a low-coherence light source 3, an optical fiber isolator 4, an optical switch 5, a 2 x 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 with an optical switch 5 through an optical fiber isolator 4, one path of the optical switch 5 is electrically connected with the computer 1, and the other path of the optical switch 5 is connected with a 2 x 2 optical fiber coupler 6 through an optical fiber; one end of the first collimator 7 is connected with the 2 x 2 optical fiber coupler 6 through an optical fiber, and laser emitted by the other end of the first collimator 7 is emitted to the first reflector 9 through the first lens 8; one end of the spectrometer 10 is electrically connected with the computer 1, and the other end of the spectrometer 10 is connected with the 2 x 2 optical fiber coupler 6 through an optical fiber.

The photoacoustic excitation system II comprises an excitation light source 11 and a second reflecting mirror 12; the excitation light source 11 is electrically connected with the computer 1, and the excitation light emitted by the excitation light source 11 directly irradiates the second reflecting mirror 12.

The scanning system III comprises 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 with the 2 × 2 optical fiber coupler 6 through an optical fiber, and laser emitted from the other end of the second collimator 13 sequentially passes through the dichroic mirror 14, the Y-direction scanning galvanometer 15, the X-direction scanning galvanometer 16 and the second lens 17 to be emitted to the sample 2; the laser beam reflected by the second reflecting mirror 12 is directed to a dichroic mirror 14, and is directed to the sample 2 through a Y-direction scanning mirror 15, an X-direction scanning mirror 16, and a second lens 17 in this order.

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

the method comprises the following steps: starting a low-coherence light source 3, enabling detection laser emitted by the low-coherence light source 3 to enter a 2X 2 optical fiber coupler 6 through an optical fiber isolator 4 and an optical switch 5 in sequence, then outputting the detection laser in two paths through the 2X 2 optical fiber coupler 6, enabling one path as reference light to pass through a first collimator 7, a first lens 8 and a first reflector 9 in sequence and return to the 2X 2 optical fiber coupler 6 in the original path, enabling the other path as sample light to pass through a second collimator 13, a dichroic mirror 14, a Y-direction scanning vibration mirror 15, an X-direction scanning vibration mirror 16, a second lens 17 and a sample 2 in sequence and return to the 2X 2 optical fiber coupler 6 in the original path;

step two: when the reference light and the sample light original path return to the 2 × 2 optical fiber coupler 6, the reference light and the sample light directly enter the spectrometer 10 through the 2 × 2 optical fiber coupler 6, and then the computer 1 performs spectral analysis;

step three: the computer 1 sends a trigger signal to the excitation light source 11 to prompt the excitation light source 11 to start, when the trigger signal of the excitation light is at a high level, the excitation light is output by the excitation light source 11, the excitation light sequentially passes through the second reflecting mirror 12, the dichroic mirror 14, the Y-direction scanning vibrating mirror 15, the X-direction scanning vibrating mirror 16 and the second lens 17 to irradiate the sample 2, and is converged at one point with the sample light inside the sample 2, the sample 2 generates optical sound pressure after absorbing laser energy, and the optical sound pressure prompts the optical refractive index of an excitation point inside the sample 2 to increase, so that the reflected light intensity is increased, and an optical sound signal is generated; on the contrary, when the excitation light trigger signal is at a low level, the excitation light source 11 stops outputting the excitation light;

step four: the computer 1 sends a trigger signal to the optical switch 5, and when the trigger signal of the optical switch is at a high level, the detection laser sent by the low-coherence light source 3 can directly reach the sample 2 through the optical switch 5; on the contrary, when the optical switch trigger signal is at a low level, the detection laser emitted by the low coherent light source 3 cannot pass through the optical switch 5;

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); where K represents the wavenumber coordinate of the spectrometer 10; in this embodiment, as shown in fig. 2, the high level period and the low level period of the optical switch trigger signal have a time length ratio of 1:1 and appear alternately, and the high level period and the low level period of the excitation light trigger signal have a time length ratio of 1:3 and appear alternately;

step six: preprocessing a photoacoustic signal S0(K) and a photoacoustic signal S1(K), eliminating a direct current component, normalizing the intensities, 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 directly proportional to a depth z, and the z is au, wherein a is a proportionality coefficient, and a is a known quantity, and can be determined by measuring a sample 2 with a known depth; finally, the reflected light intensity distributions F0(z) and F1(z) of the sample 2 at different depths can be obtained by the formula z ═ au, 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 seven: calculating photoacoustic signals P (z) of different depths of the sample 2, wherein the calculation formula is P (z) ═ F1(z) -F0 (z);

step eight: two-dimensional scanning is realized through the X-direction scanning galvanometer 16 and the Y-direction scanning galvanometer 15, and two-dimensional imaging is realized in the computer 1.

The embodiments are not intended to limit the scope of the present invention, and all equivalent implementations or modifications without departing from the scope of the present invention are intended to be included in the scope of the present invention.