A method for adaptively positioning acoustic focus in photoacoustic microscopy and its application

Abstract

The purpose of the present invention is to adaptively adjust the relative distance between the subject and the probe during the scanning process of photoacoustic microscopy. In order to achieve the above purpose, one technical solution of the present invention is to provide a method for adaptively positioning the acoustic focus in photoacoustic microscopy. Another technical solution of the present invention is to provide the application of the above-mentioned method for adaptively positioning the acoustic focus in photoacoustic microscopy in photoacoustic microscopy. The present invention can adaptively adjust the relative distance between the subject and the probe during the scanning process to change the position of the transducer focal area in the depth direction, improve the detection sensitivity of the photoacoustic signal, and ultimately improve the imaging resolution of the photoacoustic image.

Description

Technical Field

[0001] The invention relates to a method for adaptively positioning an acoustic focus, and also relates to an application of the method for adaptively positioning an acoustic focus in photoacoustic microscopy imaging. Background Art

[0002] Photoacoustic Microscopy (PAM) is a new type of medical imaging modality. This imaging technology uses the photoacoustic effect to perform non-invasive, quantitative and high-resolution imaging (μm level) of biological tissues. At present, photoacoustic microscopy has made a lot of progress in subcutaneous microvascular network imaging, diagnosis of benign and malignant tumors, etc., and has great clinical value.

[0003] Different from photoacoustic tomography, photoacoustic microscopy uses an ultrasonic focusing transducer as the signal receiving end. The detection sound field of the ultrasonic focusing transducer is as follows: Figure 1 As shown. The acoustic focal length of the ultrasonic focusing transducer depends on the model and process parameters of the probe and is generally a fixed value. When the sound source is located in the acoustic focal area of ​​the ultrasonic focusing transducer, the probe has the highest detection sensitivity for photoacoustic signals; on the contrary, when the sound source is located in the acoustic defocusing area (near field and far field) of the ultrasonic focusing transducer, the probe's sensitivity to detecting photoacoustic signals decreases.

[0004] When users or experimenters use existing photoacoustic microscopy imaging systems, they need to manually adjust the distance between the sample and the probe. During an experiment, after the position of the probe and the sample is fixed, the acoustic focus position no longer changes. However, due to the special internal structure and complexity of the sample, the endogenous absorber of the sample may be in the out-of-focus area of ​​the ultrasonic focusing transducer. The photoacoustic signal detection sensitivity generated in this area is low, which affects the imaging contrast and resolution. Summary of the invention

[0005] The purpose of the present invention is to adaptively adjust the relative distance between the test object and the probe during the scanning process of photoacoustic microscopy imaging.

[0006] In order to achieve the above object, a technical solution of the present invention is to provide a method for adaptively positioning the acoustic focus in photoacoustic microscopy imaging, wherein the depth direction is defined as the Z-axis direction, and the plane where the length direction and the width direction are located is defined as the XOY plane. In the photoacoustic microscopy imaging system, the distance between the probe and the test object is the value in the Z-axis direction, and the method is characterized in that it includes the following steps:

[0007] Step 1: When the scanning component of the photoacoustic microscopy imaging system is at the starting position (x0, y0), the PC sends a command to the Z-axis motor, and the Z-axis motor drives the scanning component to move the target distance in the Z-axis direction with a set step length;

[0008] Step 2: After the scanning component moves a set step length each time, the ultrasonic focusing transducer receives the photoacoustic signal excited in the test object, and then uses the low-noise amplifier module to amplify the weak photoacoustic signal collected by the ultrasonic focusing transducer while only introducing low noise, and then the data acquisition card converts the amplified photoacoustic signal into an electro-photoacoustic signal and stores it on the PC;

[0009] Step 3, the PC records all electro-optical acoustic signals obtained by the data acquisition card during the movement of the scanning component along the Z-axis direction and the depth value corresponding to each electro-optical acoustic signal, and calculates the signal-to-noise ratio of each electro-optical acoustic signal;

[0010] Step 4: The PC traverses the signal-to-noise ratios of all electro-optical acoustic signals obtained in step 3, obtains the electro-optical acoustic signal with the highest signal-to-noise ratio, and then obtains the depth value Z corresponding to the electro-optical acoustic signal. optimized The photoacoustic microscopy system is based on the depth value Z optimized Determine the distance between the test sample and the probe corresponding to the current starting position (x0, y0) to achieve the acoustic focus positioning at the current starting position (x0, y0).

[0011] Preferably, in step 3, for the i-th electro-optical acoustic signal, the PC terminal calculates its signal-to-noise ratio SNR using the following formula: i :

[0012]

[0013] In the formula, represents the effective value of the amplitude of the ith electro-optical-acoustic signal, Represents the effective value of the noise voltage amplitude corresponding to the i-th electro-optical acoustic signal.

[0014] Another technical solution of the present invention is to provide an application of the above-mentioned method for adaptively positioning the acoustic focus in photoacoustic microscopy in photoacoustic microscopy, characterized in that before the photoacoustic microscopy system scans the ROI (Region of Interest) area line by line and point by point in the XOY plane, the scanning starting point of the entire ROI area is used as the current starting position (x0, y0) of the above-mentioned method for adaptively positioning the acoustic focus in photoacoustic microscopy, and the distance between the test sample and the probe corresponding to the scanning starting point of the entire ROI area is obtained, so as to realize the acoustic focus positioning at the current scanning starting point.

[0015] Another technical solution of the present invention is to provide an application of the above-mentioned method for adaptively positioning the acoustic focus in photoacoustic microscopy in photoacoustic microscopy, characterized in that the ROI area is divided into different units, and the photoacoustic microscopy system scans each unit of the ROI area line by line and point by point in the XOY plane; before the photoacoustic microscopy system scans the current unit line by line and point by point, the unit scanning starting point of the current unit is used as the current starting position (x0, y0) of the above-mentioned method for adaptively positioning the acoustic focus in photoacoustic microscopy, and the distance between the test sample and the probe corresponding to the current unit scanning starting point is obtained, so as to realize the acoustic focus positioning at the current unit scanning starting point.

[0016] Another technical solution of the present invention is to provide the application of the above-mentioned method for adaptively positioning the acoustic focus in photoacoustic microscopy in photoacoustic microscopy, characterized in that the photoacoustic microscopy system scans the ROI area line by line and point by point in the XOY plane. Before the photoacoustic microscopy system scans the current pixel point position, the current pixel point position is used as the current starting position (x0, y0) of the above-mentioned method for adaptively positioning the acoustic focus in photoacoustic microscopy, and the distance between the test sample and the probe corresponding to the current pixel point position is obtained to realize the acoustic focus positioning at the current pixel point position.

[0017] The present invention can adaptively adjust the relative distance between the test object and the probe during scanning to change the position of the transducer focusing area in the depth direction, improve the detection sensitivity of the photoacoustic signal, and ultimately improve the imaging resolution of the photoacoustic image. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The detection sound field of the ultrasonic focusing transducer is illustrated;

[0019] Figure 2 The workflow of adaptive positioning acoustic focal plane is illustrated;

[0020] Figure 3 It shows the scanning method of PAM system;

[0021] Figure 4 The pseudo code flow of adaptive positioning acoustic focal plane is shown;

[0022] Figure 5 The scanning method with the minimum unit being N rows (global) is shown;

[0023] Figure 6 It shows the scanning mode in which the minimum unit is a row;

[0024] Figure 7 The scanning method in which the minimum unit is a single step is illustrated. DETAILED DESCRIPTION

[0025] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0026] The present invention proposes a method for adaptively positioning the acoustic focus in photoacoustic microscopy imaging, and the workflow is as follows: Figure 2 As shown. The present invention can change the acoustic focus position by adjusting the distance between the transducer and the object under test, so as to obtain the best imaging result. In the present invention, the depth direction is defined as the Z-axis direction, and the plane where the length direction and the width direction are located is defined as the XOY plane. In the photoacoustic microscopy imaging system (hereinafter referred to as the PAM system), the distance between the probe and the object under test is the value in the Z-axis direction. The present invention specifically includes the following steps:

[0027] Step 1: When the scanning component of the PAM system is at the starting position (x0, y0), the PC sends a command to the Z-axis motor, and the Z-axis motor drives the scanning component to move the target distance in the Z-axis direction with a set step length. In this embodiment, the step length is set to the minimum distance unit that the scanning component can move under the drive of the Z-axis motor. The scanning component is a conventional component of the PAM system, which usually includes an ultrasonic focusing transducer, a lens module, a multimode optical fiber, etc.

[0028] Step 2: After the scanning component moves a set step length each time, the ultrasonic focusing transducer receives the photoacoustic signal excited in the test object, and then uses the low-noise amplifier module to amplify the weak photoacoustic signal collected by the ultrasonic focusing transducer while only introducing low noise, and then the data acquisition card converts the amplified photoacoustic signal into an electro-photoacoustic signal and stores it on the PC;

[0029] Step 3: The PC records all electro-optical acoustic signals obtained by the data acquisition card during the movement of the scanning component along the Z-axis direction and the depth value corresponding to each electro-optical acoustic signal, and calculates the signal-to-noise ratio (SNR) of each electro-optical acoustic signal.

[0030] For the i-th electro-optical acoustic signal, the PC uses the following formula to calculate its signal-to-noise ratio SNR i :

[0031]

[0032] In the formula, represents the effective value of the amplitude of the ith electro-optical-acoustic signal, Represents the effective value of the noise voltage amplitude corresponding to the i-th electro-optical acoustic signal.

[0033] Step 4: The PC traverses the signal-to-noise ratios of all electro-optical acoustic signals obtained in step 3, obtains the electro-optical acoustic signal with the highest signal-to-noise ratio, and then obtains the depth value Z corresponding to the electro-optical acoustic signal. optimized , the PAM system is based on the depth value Z optimized Determine the distance between the test sample and the probe corresponding to the current starting position (x0, y0) to achieve the acoustic focus positioning at the current starting position (x0, y0).

[0034] After the adaptive positioning of the acoustic focus is completed by the above method, the PAM system can scan the ROI area line by line and point by point in the XOY plane to perform photoacoustic microscopy imaging. Figure 4 As shown in the figure, according to the complexity of the sample under test, the acoustic focal plane can be adjusted and scanned according to different units. The entire sample can be scanned according to the optimal acoustic focal plane obtained at the starting point, or each row can be scanned along the Y axis toward the starting point, or the acoustic focal plane can be positioned in a single step and the optimal acoustic focal plane obtained at each sampling point (X, Y) can be used to complete the scanning and data collection of the point.

[0035] Example 1

[0036] In this embodiment, the ROI area is regarded as a whole, and the current starting position (x0, y0) in the above method of adaptively positioning the acoustic focus is the starting position of the entire ROI area. After obtaining the distance between the test sample and the probe at the starting position by the above method, the PAM system keeps the distance value unchanged when scanning the ROI area line by line and point by point in the XOY plane, that is, the optimal acoustic focal plane obtained at the starting position is applied to the whole, which can preliminarily improve the sensitivity of photoacoustic signal detection in the ROI area, and can perform high-resolution imaging of the ROI area tissue, which is suitable for detecting test objects with simple endogenous absorbent structures and application scenarios with high time cost requirements. For example, in clinical in vivo detection of subcutaneous microvascular networks, a photoacoustic microscopy scan can be completed after the system adaptively calibrates the acoustic focal plane.

[0037] Example 2

[0038] In this embodiment, the ROI area is divided into different units (for example, each scanning behavior can be a unit), each unit is a whole, and each unit has a different scanning starting point. Before the PAM system scans the current unit in the XOY plane, the current starting position (x0, y0) in the above-mentioned method of adaptively positioning the acoustic focus is set as the scanning starting point of the current unit, and then the distance between the test sample and the probe corresponding to the current scanning starting point is obtained, so as to realize the acoustic focus positioning at the current scanning starting point. That is, in this embodiment, the optimal acoustic focal plane obtained based on the scanning starting point of each unit is only applied to the current unit. The method disclosed in this embodiment can further improve the sensitivity of photoacoustic signal detection in the ROI area, and is suitable for detecting test objects with more complex structures of endogenous absorbers and application scenarios with low time cost requirements. For example, in small animal live anesthesia experiments, the resolution of photoacoustic images and time cost are well balanced.

[0039] Example 3

[0040] In this embodiment, before the PAM system scans the ROI area each time, the position of the current pixel point in the XOY plane is used as the current starting position (x0, y0) in the above-mentioned method of adaptively positioning the acoustic focus, and then the distance between the test sample and the probe corresponding to the current pixel point is obtained to achieve the acoustic focus positioning at the current pixel point position. That is, the above-mentioned method of adaptively positioning the acoustic focus is used to obtain the optimal focal plane position of each pixel point in the XOY plane. The method disclosed in this embodiment can greatly improve the sensitivity of photoacoustic signal detection in the ROI area and improve the quality of photoacoustic microscopy images, which is suitable for scientific research on complex or unknown structures of endogenous absorbers. For example, in vitro pathological detection of tissue sections has a high time cost, but the photoacoustic image resolution of the ROI scanning area is the best and the judgment is the most accurate.

Claims

1. A method for adaptively locating the acoustic focus in photoacoustic microscopy imaging, wherein the depth direction is defined as the Z-axis direction, the plane where the length direction and the width direction are located is defined as the XOY plane, and in the photoacoustic microscopy imaging system, the distance between the probe and the test object is the value in the Z-axis direction, characterized in that: The following steps are involved: Step 1: When the scanning component of the photoacoustic microscopy imaging system is at the starting position (x0, y0), the PC sends a command to the Z-axis motor, and the Z-axis motor drives the scanning component to move the target distance in the Z-axis direction with a set step length; Step 2: After the scanning component moves a set step length each time, the ultrasonic focusing transducer receives the photoacoustic signal excited in the test object, and then uses the low-noise amplifier module to amplify the weak photoacoustic signal collected by the ultrasonic focusing transducer while only introducing low noise, and then the data acquisition card converts the amplified photoacoustic signal into an electro-photoacoustic signal and stores it on the PC; Step 3, the PC records all electro-optical acoustic signals obtained by the data acquisition card during the movement of the scanning component along the Z-axis direction and the depth value corresponding to each electro-optical acoustic signal, and calculates the signal-to-noise ratio of each electro-optical acoustic signal; Step 4: The PC traverses the signal-to-noise ratios of all electro-optical acoustic signals obtained in step 3, obtains the electro-optical acoustic signal with the highest signal-to-noise ratio, and then obtains the depth value Z corresponding to the electro-optical acoustic signal. optimized The photoacoustic microscopy system is based on the depth value Z optimized The distance between the test sample and the probe corresponding to the current starting position (x0, y0) is determined to achieve the acoustic focus positioning at the current starting position (x0, y0).

2. A method for adaptively locating acoustic focus in photoacoustic microscopy imaging according to claim 1, characterized in that: In step 3, for the i-th electro-optical acoustic signal, the PC uses the following formula to calculate its signal-to-noise ratio SNR: i : In the formula, represents the effective value of the amplitude of the ith electro-optical-acoustic signal, Represents the effective value of the noise voltage amplitude corresponding to the i-th electro-optical acoustic signal.

3. Application of the method for adaptively positioning acoustic focus in photoacoustic microscopy as claimed in claim 1 in photoacoustic microscopy, characterized in that: Before the photoacoustic microscopy imaging system scans the ROI area line by line and point by point in the XOY plane, the scanning starting point of the entire ROI area is used as the current starting position (x0, y0) of the method for adaptively positioning the acoustic focus in photoacoustic microscopy imaging as described in claim 1, and the distance between the test sample and the probe corresponding to the scanning starting point of the entire ROI area is obtained to achieve acoustic focus positioning at the current scanning starting point.

4. Application of the method for adaptively positioning acoustic focus in photoacoustic microscopy as claimed in claim 1 in photoacoustic microscopy, characterized in that: The ROI area is divided into different units, and the photoacoustic microscopy imaging system scans each unit of the ROI area line by line and point by point in the XOY plane; before the photoacoustic microscopy imaging system scans the current unit line by line and point by point, the unit scanning starting point of the current unit is used as the current starting position (x0, y0) of the method for adaptively positioning the acoustic focus in photoacoustic microscopy imaging as described in claim 1, and the distance between the test sample and the probe corresponding to the current unit scanning starting point is obtained, so as to realize the acoustic focus positioning at the current unit scanning starting point.

5. Application of the method for adaptively positioning acoustic focus in photoacoustic microscopy as claimed in claim 1 in photoacoustic microscopy, characterized in that: The photoacoustic microscopy system scans the ROI area line by line and point by point in the XOY plane. Before the photoacoustic microscopy system scans the current pixel point position, the current pixel point position is used as the current starting position (x0, y0) of the method for adaptively locating the acoustic focus in photoacoustic microscopy as described in claim 1, and the distance between the test sample and the probe corresponding to the current pixel point position is obtained to realize the acoustic focus positioning at the current pixel point position.

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