Photo-thermal imaging method and system based on photo-thermal modulation speckles

Abstract

The invention discloses a photo-thermal imaging method and system based on photo-thermal modulation speckles. The method comprises the steps that a pump light source is selected, and a spectral domain OCT unit is constructed; performing cross-section diagram scanning on the sample based on a spectral domain OCT unit and a large-step sectional scanning protocol, and synchronously irradiating the sample through a pump light source to obtain a scanning data set; on the basis of the scanning data set, performing inverse fast Fourier transform along the wave number direction to obtain a speckle signal; the change integral of the speckle signal within the irradiation time of the pump light is used as an imaging parameter, and an effective A line of the photo-thermal OCT is generated; according to a large-step segmented scanning protocol, the effective A lines are arranged, and photo-thermal OCT imaging is achieved. The system comprises a pump light source, a detection light source, a sample arm light path, a reference arm light path, an optical fiber coupler and a spectrograph. By means of the method, the problems that in an existing photo-thermal OCT method, the imaging speed is low, and sensitivity is insufficient can be solved. The method can be widely applied to the field of optical detection.

Description

Technical Field

[0001] The present invention relates to the field of optical detection, and in particular to a photothermal imaging method and system based on photothermal modulation speckle. Background Art

[0002] Photothermal optical coherence tomography (Photothermal OCT) is one of the important functional extensions of optical coherence tomography (OCT). Photothermal OCT has high sensitivity and specificity for certain contrast agents and certain components in tissues. It has high potential application value in the fields of biomedical imaging and photothermal therapy.

[0003] Imaging speed is one of the important topics in the field of biomedical imaging. To obtain the optical absorption characteristics of biological samples, traditional photothermal OCT technology uses the method of periodically modulating the pump light source, and obtains enough data samples through long-time sampling in the time dimension to recover the photothermal signal at the modulation frequency. However, this method sacrifices imaging speed and seriously hinders the research development and clinical transformation of photothermal OCT.

[0004] Therefore, there is an urgent need for a faster photothermal OCT imaging method that is more suitable for the market. Summary of the Invention

[0005] In view of this, in order to solve the problem that most existing photothermal OCT methods use the method of periodically modulating the pump light source, which in turn leads to slow imaging speed, on the one hand, the present invention proposes a photothermal imaging method based on photothermal modulation speckle, and the method includes the following steps:

[0006] Select a pump light source and perform short-time rapid illumination to avoid long-time pump light irradiation and sampling of the sample after reaching thermal equilibrium;

[0007] Construct a spectral domain OCT unit, wherein the pump light and the probe light in the spectral domain OCT unit are coaxially irradiated on the sample through the same optical path, inducing a photothermal response in a local area of the sample and ensuring that the photothermal response area is consistent with the OCT detection area;

[0008] In the spectral domain OCT unit, perform cross-sectional scanning on the sample based on a large-step segmented scanning protocol, collect interference spectral data, and obtain a scanning data set; in addition, while scanning, the pump light source irradiates the sample synchronously;

[0009] Perform an inverse fast Fourier transform on the interference spectral data in the scanning data set along the wavenumber direction, transform the sampled spectral domain signal into the spatial domain, and obtain the speckle signal of OCT;

[0010] Integrate the change of the speckle signal within the pump light irradiation time as a quantization parameter of the photothermal response to generate an effective A-line of photothermal OCT.

[0011] According to the large-step segmented scanning protocol, rearrange the distribution of the effective A-lines of the cross-sectional image to achieve fast photothermal OCT imaging.

[0012] In some embodiments, the process of performing cross-sectional scanning on the sample based on the large-step segmented scanning protocol aims to ensure that the sampling at two adjacent positions is not affected by the thermal relaxation process at the previous position, and specifically includes:

[0013] Set a distance step size greater than the laser spot diameter.

[0014] Move the optical probe to the starting position of the sample cross-section for scanning and sampling. According to the set distance step size, control the optical probe to move to the next position, repeat the above sampling steps, collect and store the interference spectral data until the optical probe moves to the termination position of the sample cross-section.

[0015] In a second aspect, the present invention also proposes a photothermal imaging system based on photothermal modulation speckle, and the system includes:

[0016] A pump light source, which is modulated by time, illuminates the sample, and induces a photothermal response in a local area of the sample.

[0017] A detection light source, a low-coherence light source, which is used to output low-coherence light to detect the sample.

[0018] The sample arm optical path, the light of the sample arm irradiates the sample, generates backscattered light and returns to the fiber coupler.

[0019] The reference arm optical path, the light of the reference arm is reflected by the reference mirror and then returns to the fiber coupler.

[0020] A fiber coupler, which is used to interfere the backscattered light and the reference light.

[0021] A spectrometer, which is used to receive the signal after interference by the fiber coupler.

[0022] Based on the above solution, the present invention provides a photoacoustic imaging method and system based on photo-thermal modulation speckle, which utilizes the rapid heat accumulation of the sample caused by the rapid illumination of the pump light, rather than periodically modulating the pump light to induce a periodic photo-thermal response of the sample. Compared with the previous photoacoustic OCT technology, the imaging speed has been greatly improved; during the imaging process, the speckle signal of OCT, that is, the amplitude term of the OCT interference spectrum, is used for imaging. Compared with the previous photoacoustic imaging using the phase term, the sensitivity to the edges of the region of interest and samples with weak absorption characteristics is higher; in addition, a large-step segmented scanning protocol is also used for cross-sectional scanning, avoiding the interference of the thermal relaxation process at the previous position on the occurrence process of the photo-thermal effect at the next position and interfering with the next sampling in the traditional point-by-point scanning. Description of the Drawings

[0023] Figure 1 is the flowchart of the steps of a photoacoustic imaging method based on photo-thermal modulation speckle according to the present invention;

[0024] Figure 2 is the schematic diagram of the large-step segmented scanning protocol adopted by the present invention. (a) Influence of the photo-thermal effect on the scanning of adjacent positions A; (b) Fast-axis galvanometer control timing of the large-step segmented scanning; (c) Control timing of the CCD and the pump light when the voltage of the control galvanometer is at the value corresponding to the blue ellipse; (d) A-line distribution of the fast-axis scanning under the new scanning protocol;

[0025] Figure 3 are the speckle signal change curves of the strongly absorbing region, weakly absorbing region, and background under the irradiation of pump light with different durations;

[0026] Figure 4 are the simulated imaging experiments of black and white hair samples by various photoacoustic OCT methods. Scale = 100μm. (a) and (b) OCT projection results and cross-sectional views at the green dotted line, as the control group; (c)-(f) Photoacoustic OCT frontal view results corresponding to the speckle signals; (g)-(j) are the cross-sectional views at the green line of (c)-(f); (k)-(n) correspond to the phase experiment results; (o)-(r) are the cross-sectional views at the green line of (k)-(n); the corresponding pump light control signals are placed at the bottom of the results, such as (s)-(v). Among them, (f) and (j) are the imaging results of the method provided by this patent;

[0027] Figure 5 are the fast photoacoustic OCT imaging results based on photo-thermal modulation speckle of black and white hair samples under different pump light irradiation durations. Scale = 100μm. (d)-(f) and (j)-(l) are the normalized results of (a)-(c) and (g)-(i);

[0028] Figure 6To compare the sensitivity of the method provided by this patent and the phase extraction-based photoacoustic OCT method for in vitro mouse ear blood vessel images. Scale bar = 150 μm. (a) Projection result of OMAG angiography; (b) Projection map of mouse ear based on phase imaging photoacoustic OCT; (c) Projection map of mouse ear of the method provided by this patent; (g) Top view of the sample, the red box area indicates the scanning range; (d)-(f) Cross-sectional views corresponding to the green dashed lines in (a)-(c) respectively; (h)-(i) Signal maps corresponding to the positions indicated by the red and blue arrows in (e)-(f) respectively, the black arrow indicates the moment when the pump light starts to work;

[0029] Figure 7 For rapid photoacoustic OCT thermography of damaged mouse ears. Scale bar = 200 μm. (a) Angiography result of the OMAG method with motion contrast, as the control group; (b) Projection result without photoacoustic excitation; (c) Projection result with photoacoustic excitation; (d)-(f) Corresponding parts to the green dashed lines in (a)-(c) respectively. Detailed implementation manners

[0030] In addition to the technical problem of slow imaging speed of the traditional methods mentioned in the background art, the phase signals extracted by the traditional methods lack sensitivity to weak photoacoustic responses because the phase signals are only sensitive to the axial photoacoustic responses and most of the photoacoustic response information is lost; on the other hand, long-time sampling in the time dimension means that the system needs to continue sampling for a period of time after the sample reaches thermal equilibrium, and the long-time incomplete thermal relaxation of the sample will increase the possibility of damage. In past studies, optically locked photoacoustic OCT was considered a potential solution. However, this method has not got rid of the modulation form of periodically modulating the pump light. Although in principle, the CCD camera of this method acts as a filter function and can remove the background and retain the absorption information. But the signal-to-noise ratio of the image is still related to the number of sampling periods, so the problem of long-time acquisition in the time dimension has not been well solved. The slow imaging speed, long-time pump light irradiation and lack of high sensitivity to weak photoacoustic responses seriously hinder the research development and clinical transformation of photoacoustic OCT.

[0031] Aiming at the technical problem in the background art that the artifacts of the zero-order image, conjugate image and defocus information in the hologram cannot be eliminated simultaneously, which leads to low resolution of image reconstruction. With the development of machine learning / deep learning, the present invention is based on Fresnel incoherent correlation holography and combines the intelligent technology of deep learning to train the sample data to obtain a more reliable elimination network for generating focused images.

[0032] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative efforts shall fall within the protection scope of the present application.

[0033] It should be noted that for the convenience of description, only the parts related to the relevant invention are shown in the drawings. Without conflict, the embodiments in the present application and the features in the embodiments can be combined with each other.

[0034] It should be understood that the "system", "device", "unit" and / or "module" used in the present application are a method for distinguishing different components, elements, parts, portions or assemblies at different levels. However, if other words can achieve the same purpose, the word can be replaced by other expressions.

[0035] As shown in the present application and the claims, unless the context clearly indicates an exceptional situation, words such as "a", "an", "one" and / or "the" do not specifically refer to the singular and may also include the plural. Generally speaking, the terms "comprising" and "including" only indicate the inclusion of the clearly identified steps and elements, and these steps and elements do not constitute an exclusive list. The method or device may also include other steps or elements. Elements defined by the statement "including one..." do not exclude the existence of other identical elements in the process, method, commodity or device including the element.

[0036] In the description of the embodiments of the present application, "a plurality" means two or more than two. The following terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features.

[0037] In addition, flowcharts are used in the present application to illustrate the operations performed by the system according to the embodiments of the present application. It should be understood that the previous or subsequent operations do not necessarily need to be executed precisely in sequence. On the contrary, the operations can be executed in reverse order or simultaneously. At the same time, other operations can also be added to these processes, or one or several operations can be removed from these processes.

[0038] Refer to Figure 1 , which is a schematic flowchart of an optional example of the photoacoustic imaging method based on photoacoustic modulation speckle proposed by the present invention. This method can be applied to a computer device. The photoacoustic imaging method proposed in this embodiment may include but is not limited to the following steps:

[0039] Step S1: Select a 532 nm pump light source that can be time - modulated. In the way of rapid illumination of the pump light, when the probe light samples the sample, irradiate the sample synchronously.

[0040] Step S2: Construct a spectral - domain OCT unit.

[0041] Step S3: In the spectral - domain OCT unit, based on the large - step segmented scanning protocol, cooperate with a high - speed scanning galvanometer to scan the cross - sectional image of the sample. At the same time, irradiate the sample synchronously through the pump light source to obtain a scanning data set.

[0042] Step S4: Based on the scanning data set, perform an inverse fast Fourier transform on the interference spectral data in the wavenumber direction to obtain the speckle signal of OCT.

[0043] Step S5: Integrate the change of the speckle signal within the pump light irradiation time as the imaging parameter to obtain the effective A - line of photo - thermal OCT.

[0044] Step S6: According to the large - step segmented scanning protocol, rearrange the A - line distribution of the cross - sectional image to achieve photo - thermal OCT imaging.

[0045] The imaging speed of photo - thermal OCT does not depend on the scanning rate of the OCT system used, but on the physical process of the photo - thermal effect occurring between the sample and light. The speed and amplitude of heat accumulation determine the rate and sensitivity of photo - thermal OCT to obtain the photo - thermal tomography information (A - line) at a position.

[0046] Therefore, the key to achieving fast photo - thermal OCT lies in avoiding repeated photo - thermal modulation and making the best use of the photo - thermal response generated by a single heat accumulation as much as possible. Both the speckle (amplitude) and phase signals can respond to this fast photo - thermal effect. However, the phase signal of OCT does not have enough sensitivity to detect weak photo - thermal signals because it is only sensitive to part of the changes (i.e., axial changes) caused by the photo - thermal effect and is highly sensitive to noise. To solve the problems existing in the traditional photo - thermal OCT method, the fast photo - thermal OCT based on photo - thermal modulation speckle provided in this patent adopts three strategies to improve the imaging speed: (1) Use rapid illumination instead of the method of periodically modulating the pump light to induce the occurrence of the photo - thermal effect, that is, Step S1; (2) Propose a large - step segmented scanning protocol to avoid waiting for the heat relaxation process, that is, Step S3; (3) Use the speckle signal instead of the phase signal to extract the photo - thermal signal, which has higher sensitivity, that is, Steps S4 and S5.

[0047] In some feasible embodiments, in Step S1:

[0048] The working timing of the pump light satisfies:

[0049]

[0050] Among them, t 0 represents the moment when the pump light starts to work, and t max represents the moment when the pump light ends to work.

[0051] The pump light does not require periodic modulation, but adopts short-time rapid illumination, which avoids long-time pump light irradiation and sampling of the sample after reaching thermal equilibrium.

[0052] To avoid long-time irradiation of the sample and reduce the sampling time, the pump light only realizes short-time rapid illumination, and the illumination time is consistent with the sampling time of the effective A-line of photoacoustic OCT. In this embodiment, t max -t 0 = 1 ms of rapid pump light irradiation is adopted.

[0053] In some feasible embodiments, step S2 specifically includes:

[0054] The spectral domain OCT unit includes a detection light source, an optical fiber coupler, a reference arm, a sample arm and a spectrometer. Among them, the spectrometer includes a spectral grating and a linear array CCD camera.

[0055] Its working process is as follows: The detection light source is a low-coherence light source with a central wavelength of 1310 nm and a bandwidth of 55 nm; after passing through a 2×2 optical fiber coupler, the low-coherence light is split into the reference arm and the sample arm at a ratio of 50:50. The backscattered light of the sample and the reference light of the reference mirror return to the optical fiber coupler for interference, and then are received by the spectrometer composed of a spectral grating and a linear array CCD camera. The acquisition rate of the linear array CCD camera is 46.816 kHz, and it cooperates with a high-speed scanning galvanometer to perform fast-axis scanning (B-scan) on the sample in the X direction, and the cross-sectional tomography information of the sample can be obtained. A 532 nm time-modulated continuous laser is used as the pump light source to co-axially irradiate the sample with the low-coherence light, inducing a photo-thermal response in a local area of the sample.

[0056] Since photoacoustic OCT depends on the photo-thermal effect caused by the interaction between the sample and light, and the development of the photo-thermal effect requires a certain amount of time, therefore, the data acquisition of photoacoustic OCT needs to perform delayed sampling (M-scan) at the same position of the sample. A set of M-scan data sets contains multiple A-lines, that is, I OCT (k, N) is obtained, where k is the wave number of light, and its value is related to the wavelength of the light wave used for OCT imaging. I OCT (k, N) reflects the photo-thermal response of each depth at a certain position of the sample.

[0057] To extract as much photo-thermal response information detected by the system as possible, after performing an inverse Fourier transform along the wave number k direction, the modulus is taken to obtain the OCT speckle signal I OCT(z,N), since N represents the number of repeated samplings, thus I OCT (z,N) varies with time, see Figure 3 , Figure 3 which shows the variation of the OCT speckle signal at a certain depth of an analog sample with time. Step S6 is performed to calculate the integral of the variation of the OCT speckle signal during the pump light irradiation time as an imaging parameter, and the effective A-line I PT (z) of photoacoustic OCT is obtained. The specific formula for calculating I PT (z) is as follows:

[0058]

[0059] What the present invention solves is the two-dimensional and three-dimensional photoacoustic OCT rapid imaging of a sample. Therefore, after the sampling of the M-scan data set at one position is completed, the optical probe will move to the next position. It has been found through research that since the light spot of the pump light focused on the sample has a certain size, it is not an ideal point irradiation. Therefore, the sampling at adjacent positions may be affected by the relaxation process, see Figure 2 (a) the left image. To prevent the influence of adjacent two pump light irradiations and acquisitions on the sampling at adjacent positions, during the data acquisition stage, the optimization of the fast-axis scanning protocol is carried out, and increasing the distance step between adjacent two M-scans is an ideal solution, see Figure 2 (a) the right image. Finally, a large-step segmented scanning protocol is used to replace the traditional B-scanning protocol, see Figure 2 (b) and Figure 2 (c). That is, step S3 is performed during data sampling.

[0060] See Figure 2 (c), the pump light only works continuously for a very short time, and there is no need to wait for the sample to relax subsequently. Although this sampling protocol will disrupt the A-line order of the cross-sectional view, see Figure 2 (d), its restoration is easy, that is, step S6 is performed. The two-dimensional cross-sectional rapid photoacoustic OCT image of biological tissue can be obtained, such as Figure 6 (f) and Figure 7 (f).

[0061] By repeating the operations of S2 to S6 at different positions in the slow-axis direction (Y direction), the three-dimensional rapid photoacoustic OCT image of the biological sample can be obtained. Such as Figure 6 (c) and Figure 7 (c).

[0062] In the present invention, the experimental results of the generated black and white hair simulation are as shown in Figure 4 and Figure 5 shown, Figure 4The imaging speed and imaging quality of the previous photo-thermal OCT method with periodically modulated pump light and the fast photo-thermal OCT method based on photo-thermal modulation speckles provided by this patent were compared. In all photo-thermal images, black hair and white hair can be distinguished, demonstrating the feasibility of all photo-thermal OCT methods. In the photo-thermal OCT images with modulated pump light, such as the front projection images Figure 4 (c)-4(e) and Figure 4 (k)-4(m); cross-sectional images Figure 4 (g)-4(i) and Figure 4 (o)-4(q). As the number of repeated scans decreases, the photo-thermal signal contrast between white hair and black hair gradually decreases, indicating that there is a trade-off between the acquisition time and imaging quality of the photo-thermal OCT with modulated pump light. In addition, although the phase signal can distinguish black hair and white hair with higher contrast, there are the following problems: one is that it shows strong random noise in the background area, which leads to the morphological recognition of the region of interest relying only on ordinary OCT; the other is that the imaging effect of the morphological integrity of the hair Figure 4 (k)-4(n) is not as good as that of the image with the speckle signal as the imaging parameter Figure 4 (c)-4(f). This shows that the phase signal is not sensitive to weak photo-thermal responses. In the images of the method provided by this patent Figure 4 (f) and Figure 4 (j), it can be seen that the fast photo-thermal OCT method based on photo-thermal modulation speckles not only has a fast imaging speed, but also has a higher image contrast than the result of using the traditional large sampling period modulation method Figure 4 (c) and Figure 4 (g). In addition, compared with the results of the method using the phase term as the imaging parameter Figure 4 (n) and Figure 4 (r), at the same imaging speed, the image of the method provided by this patent has better morphological integrity of black hair, indicating that its intensity signal is more sensitive to weak photo-thermal responses.

[0063] Figure 5 The imaging results with different pump light irradiation durations were compared. By observing the normalized results, it can be found that increasing the pump light irradiation duration can enhance the image contrast and improve the signal-to-noise ratio of the image within a certain range, and the edge region gradually becomes visible, but the improvement is limited beyond a certain range. This is because the imaging speed and sensitivity of photo-thermal OCT do not depend on the scanning speed of the OCT system, but on the physical process of the photo-thermal effect. The method provided by this patent utilizes the rapid heat accumulation of the sample after the pump light starts to work. Since this process reaches thermal equilibrium after a period of time, long-term pump light irradiation and system sampling are unnecessary. Different samples have an optimal irradiation and acquisition time interval, within which the speckle signal changes during one heat accumulation can be efficiently utilized, and subsequent sampling is redundant.

[0064] Figure 6 The photoacoustic OCT imaging experiment on the mouse ear blood vessels verified again that, under the same imaging speed, the fast photoacoustic OCT method based on photoacoustic modulation speckle provided by this patent can provide better imaging performance by improving sensitivity and signal-to-noise ratio. Compared with the method of motion contrast OCT, this method does not lose the ability of static specific molecular imaging, such as Figure 7 shown.

[0065] In summary, the fast photoacoustic OCT imaging method based on photoacoustic modulation speckle provided by the present invention utilizes the rapid heat accumulation of the sample caused by the rapid illumination of the pump light, rather than periodically modulating the pump light to induce a periodic photoacoustic response of the sample. Compared with the previous photoacoustic OCT technology of periodically modulating the pump light, the imaging speed has been greatly improved. The fast photoacoustic OCT imaging method based on photoacoustic modulation speckle provided by the present invention uses the speckle signal of OCT, that is, the amplitude term of the OCT interference spectrum for imaging. Compared with the previous photoacoustic imaging using the phase term, it has higher sensitivity to the edges of the region of interest and samples with weak absorption characteristics. The fast photoacoustic OCT imaging method based on photoacoustic modulation speckle provided by the present invention uses a large-step segmented scanning protocol for cross-sectional scanning, avoiding the interference of the thermal relaxation process at the previous position on the photoacoustic effect occurrence process and the next sampling during point-by-point scanning. The method proposed by the present invention improves the imaging speed of photoacoustic OCT and the sensitivity to photoacoustic response. It can provide technical references for targeted photoacoustic probe contrast imaging, the diagnosis field of ischemic diseases, etc.

[0066] A photoacoustic imaging system based on photoacoustic modulation speckle, comprising:

[0067] A pump light source, which is modulated by time to illuminate the sample and induce a photoacoustic response in a local area of the sample;

[0068] A detection light source for outputting low-coherence light to detect the sample;

[0069] The sample arm optical path that generates the backscattered light of the sample and returns it to the fiber coupler;

[0070] The reference arm optical path that generates the reference light and returns it to the fiber coupler;

[0071] A fiber coupler for interfering the backscattered light and the reference light;

[0072] A spectrometer for receiving the signal interfered by the fiber coupler.

[0073] The content in the above method embodiments is applicable to the system embodiments of the present invention. The functions specifically implemented in the system embodiments of the present invention are the same as those in the above method embodiments, and the beneficial effects achieved are also the same as those in the above method embodiments.

[0074] A storage medium storing instructions executable by a processor, the instructions executable by the processor being used to implement the above-described method for photothermal imaging based on photothermal modulation speckles when executed by the processor.

[0075] The content in the above method embodiments is applicable to the storage medium embodiments of the present invention. The functions specifically implemented in the storage medium embodiments of the present invention are the same as those in the above method embodiments, and the beneficial effects achieved are also the same as those in the above method embodiments.

[0076] The above is a specific description of the preferred embodiments of the present invention, but the present invention is not limited to the described embodiments. Those skilled in the art can make various equivalent deformations or substitutions without departing from the spirit of the present invention, and these equivalent deformations or substitutions are all included within the scope defined by the claims of this application.

Claims

1. A photothermal imaging method based on photothermal modulation speckle, characterized in that: The following steps are involved: Select the pump source and build the spectral domain OCT unit; Scanning a cross-sectional image of the sample based on the spectral domain OCT unit and the large-step segmented scanning protocol, and irradiating the sample synchronously through the pump light source to obtain a scanning data set; Based on the scanning data set, performing an inverse fast Fourier transform along a wavenumber direction to obtain a speckle signal; The integral of the speckle signal change during the pump light irradiation time is used as an imaging parameter to generate the effective A-line of photothermal OCT. According to the large-step segmented scanning protocol, the effective A-lines are arranged to achieve photothermal OCT imaging.

2. The photothermal imaging method based on photothermal modulation speckle according to claim 1, characterized in that: The spectral domain OCT unit includes a detection light source, a fiber coupler, a reference arm optical path, a sample arm optical path and a spectrometer.

3. The photothermal imaging method based on photothermal modulation speckle according to claim 2, characterized in that: The step of scanning the sample in cross-section based on the spectral domain OCT unit and the large-step segmented scanning protocol, and synchronously irradiating the sample with the pump light source to obtain a scan data set is specifically: Outputting low-coherence light based on the detection light source; The low-coherence light passes through the optical fiber coupler and is split into the reference arm optical path and the sample arm optical path in a preset ratio; In the sample arm optical path, a cross-sectional image scanning is performed on the sample based on a large-step segmented scanning protocol to generate backscattered light of the sample and return it to the optical fiber coupler; When scanning the sample, the sample is synchronously irradiated by the pump light source; After passing through the reference arm optical path, a reference light is generated and returned to the optical fiber coupler; The backscattered light of the sample and the reference light interfere in the optical fiber coupler and are received by the spectrometer to obtain a scanning data set.

4. The photothermal imaging method based on photothermal modulation speckle according to claim 3, characterized in that: The process of scanning the cross-section of the sample based on the large-step segmented scanning protocol specifically includes: Set the distance step; After completing the scanning sampling at the current position, the optical probe moves to the next position for pump light irradiation and scanning sampling in combination with the distance step until the scanning sampling of the entire cross section of the sample is completed.

5. The photothermal imaging method based on photothermal modulation speckle according to claim 4, characterized in that: The distance step length is greater than the spot diameter.

6. The photothermal imaging method based on photothermal modulation speckle according to claim 1, characterized in that: The pump light source uses rapid illumination of less than a preset duration.

7. The photothermal imaging method based on photothermal modulation speckle according to claim 1, characterized in that: The formula for the integral of the change of the speckle signal during the pump light irradiation time is expressed as follows: Among them, I PT (z) represents the effective A-line that constitutes the photothermal OCT image, and N represents the total number of sampling at the same position of the sample.

8. A photothermal imaging system based on photothermal modulation speckle, characterized in that: include: The pump light source is modulated in time to illuminate the sample, inducing a photothermal response in a local area of ​​the sample; A detection light source, used for outputting low-coherence light to detect samples; The sample arm optical path generates the backscattered light of the sample and returns it to the fiber coupler; Reference arm optical path, generating reference light and returning it to the fiber coupler; A fiber coupler for interfering the backscattered light with the reference light; The spectrometer is used to receive the signal after interference through the optical fiber coupler.

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