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CN109276229B - Rapid focusing system and method for photoacoustic microscopic imaging - Google Patents

Rapid focusing system and method for photoacoustic microscopic imaging Download PDF

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CN109276229B
CN109276229B CN201810927962.XA CN201810927962A CN109276229B CN 109276229 B CN109276229 B CN 109276229B CN 201810927962 A CN201810927962 A CN 201810927962A CN 109276229 B CN109276229 B CN 109276229B
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CN109276229A (en
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骆清铭
杨孝全
宋贤林
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Hust-Suzhou Institute For Brainsmatics
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Abstract

The invention relates to a rapid focusing method and a rapid focusing system for photoacoustic microscopic imaging, wherein a laser beam is focused and then irradiated on a sample to be detected to generate a photoacoustic signal, the photoacoustic signal is received by an ultrasonic probe and transmitted to a collecting card, and a B-type scanning image is formed by scanning; when the signal position of the sample is in the far focus area, adjusting the distance between the sample and the ultrasonic probe according to the first further distance until the signal position of the sample is in the near focus area; or judging that the position of the sample signal is in a near-focus area, judging that the image definition value reaches the maximum value in the image definition evaluation values for a plurality of times, and taking the sample position corresponding to the maximum value as an observation position. The rapid focusing method provided by the invention continuously and automatically adjusts the distance between the sample and the ultrasonic probe by utilizing the position of the sample signal reflected in the photoacoustic B-type scanning image in the photoacoustic signal and the image definition, and realizes that the sample is automatically and rapidly adjusted to the focal plane of the laser beam, thereby rapidly realizing focusing and greatly improving the experimental efficiency.

Description

Rapid focusing system and method for photoacoustic microscopic imaging
Technical Field
The invention relates to the field of photoacoustic microscopic imaging, in particular to a rapid focusing system and a rapid focusing method for photoacoustic microscopic imaging.
Background
The recently appeared photoacoustic microscopic imaging technology is a novel nondestructive medical imaging technology, and organically combines the advantages of high contrast of pure optical imaging and high resolution of pure ultrasonic imaging. Photoacoustic imaging technology has been widely used in biological research, such as structural imaging of vasculature, imaging of brain structure and function, tumor detection, and the like. In consideration of lateral resolution, photoacoustic microscopy imaging systems can be classified into optical resolution photoacoustic microscopy imaging systems (OR-PAM) and acoustic photoacoustic microscopy imaging systems (AR-PAM). In AR-PAM the spot size is large because the light focused on the sample is weakly focused and the lateral resolution of the system depends on the acoustic focus with a small focus, whereas in OR-PAM the spot size can typically reach several microns, much smaller than the acoustic focus, because the incident light is strongly focused. In general, in OR-PAM, the incident optical axis and the detection acoustic axis are kept coaxial and confocal, and the highest resolution and signal-to-noise ratio can be obtained by placing the imaging sample at the focal point of the system. The incident light needs to be focused by a large numerical aperture condenser, which results in a small imaging depth of field (DoF) of the imaging system (typically on the order of tens of microns). In the imaging process, an experiment operator needs to manually control the lifting platform to adjust the distance between the sample and the imaging probe, so that the sample is placed at the focus as much as possible and then imaging is started. However, manual focusing is highly dependent on the experience of the experimental operator, and the problems of poor imaging quality, time and labor consumption for focusing and the like due to inaccurate focusing may occur.
The imaging quality of photoacoustic microscopic imaging is a key problem for subsequent researches on biological structures, functions and the like, and images with poor imaging quality can directly obstruct subsequent analysis and research works. The image obtained is clearest and has more detail only when the object to be imaged is in focus. When the object to be imaged deviates from the focal plane, the imaging blur and the definition are reduced, so that whether the sample to be imaged can be accurately and quickly positioned on the focal plane of the imaging system becomes an urgent problem to be solved.
Disclosure of Invention
In view of the above, it is desirable to provide a fast focusing system and method for photoacoustic microscopy imaging, which addresses at least one of the above-mentioned problems.
A fast focusing method for photoacoustic microscopy imaging comprises the following steps:
s100: focusing a laser beam, irradiating the laser beam on a sample to be detected to generate a photoacoustic signal, receiving the photoacoustic signal through an ultrasonic probe, transmitting the photoacoustic signal to a collection card, and scanning to form a B-type scanning image; defining an interval with the distance from the focal plane of the laser beam within a preset numerical range as a near-focus area, and defining an interval with the distance from the focal plane of the laser beam outside the preset numerical range as a far-focus area;
s200: judging that the position of the sample signal is located in the far focus area according to the position information on the B-type scanning image, adjusting the distance between the sample and the ultrasonic probe according to a first further distance until the position of the sample signal is located in the near focus area, and executing the step S300;
or, judging that the position of the sample signal is in the near-focus area, and executing the step S300;
s300: and scanning the photoacoustic signal on the acquisition card to acquire a photoacoustic B-type scanning image, judging that the image definition value reaches the maximum value in the image definition evaluation values for a plurality of times, and finishing focusing of the sample to be detected by taking the sample position corresponding to the maximum value as an observation position.
In one embodiment, the step of adjusting the distance between the sample and the ultrasonic probe until the image resolution reaches the maximum value specifically includes:
s310: judging that the position of the sample signal is in the near-focus area, and reducing the distance between the sample and the ultrasonic probe by a second step distance;
s320: judging that the image definition value is larger than the definition value before the distance between the sample and the ultrasonic probe is adjusted, and executing the step S310; or,
and judging that the image definition is smaller than the definition before the adjustment of the distance between the sample and the ultrasonic probe, and increasing the distance between the sample and the ultrasonic probe to a value before the adjustment of the distance corresponding to the image definition.
In one embodiment, the first step pitch is greater than the second step pitch.
In one embodiment, the image definition evaluation of the photoacoustic B-mode scan is performed by using an image evaluation function, which uses a variance function.
The invention also provides a rapid focusing system for photoacoustic microscopic imaging, which is used for executing the rapid focusing method for photoacoustic microscopic imaging, and comprises the following steps:
the laser module is used for generating a laser beam and focusing the laser beam and comprises a laser, an objective lens, an optical fiber and a condenser lens;
the acquisition module is used for transmitting the focused laser beam generated by the laser module to a sample and acquiring a photoacoustic signal generated on the sample, and comprises an ultrasonic probe, a signal amplifier and an acquisition card;
the focusing module is used for adjusting the distance between the ultrasonic probe and the sample and comprises a three-dimensional scanner and an object stage;
and the control module is electrically connected with the laser module, the acquisition module and the focusing module.
In one embodiment, the objective lens comprises a first objective lens and a second objective lens, and the optical fiber is a single-mode optical fiber; after the laser beam emitted by the laser passes through the first objective lens, the laser beam is transmitted by the optical fiber, passes through the condenser lens and then is incident on a sample through the second objective lens.
In one embodiment, the ultrasound probe comprises an ultrasound transducer and an acoustic lens having a numerical aperture of 0.5.
In one embodiment, the collection module further comprises a water tank disposed between the ultrasound probe and the sample.
In one embodiment, the three-dimensional detector comprises an elevating platform, a translation platform and a two-dimensional grating scanner, wherein the two-dimensional grating scanner is arranged on the translation platform, and the ultrasonic probe is arranged on the elevating platform.
The rapid focusing method of the photoacoustic microimaging provided by the invention continuously and automatically adjusts the distance between the sample and the ultrasonic probe by analyzing and feeding back the photoacoustic signal generated by the laser on the surface of the sample and utilizing the position and the image definition of the sample signal reflected in the photoacoustic B-type scanning image in the photoacoustic signal, so that the sample is automatically and rapidly adjusted to the focal plane of the laser beam, thereby rapidly realizing focusing, lightening the operation burden of experimenters and greatly improving the experimental efficiency.
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FIG. 1 is a schematic structural diagram of a fast focusing system for photoacoustic microscopy in an embodiment of the present invention;
FIG. 2 is a flow chart of a fast focusing method for photoacoustic microscopy in an embodiment of the present invention;
FIG. 3 is a flowchart of the method of step S3 according to an embodiment of the present invention;
fig. 4 is a flowchart illustrating the step S3 according to an embodiment of the present invention.
Detailed Description
To facilitate an understanding of the invention, the invention will now be described more fully with reference to the accompanying drawings. Preferred embodiments of the present invention are shown in the drawings. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.
It will be understood that when an element is referred to as being "secured to" another element, it can be directly on the other element or intervening elements may also be present. When an element is referred to as being "connected" to another element, it can be directly connected to the other element or intervening elements may also be present.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.
In an embodiment of the present invention, a fast focusing system for photoacoustic microscopy is provided, as shown in fig. 1, components of the system mainly include: the device comprises a laser module, an acquisition module, a focusing module and a control module. The laser module is used for generating laser beams and focusing the laser beams, and comprises a laser, an objective lens, an optical fiber and a collecting lens, wherein the laser generates a laser beam and then generates a focal plane through the focusing of the objective lens and the collecting lens, the optical fiber is used for conducting the laser beams, the optical fiber is preferable, the objective lens comprises a first objective lens and a second objective lens, the optical fiber is a single-mode optical fiber, the laser beam emitted by the laser sequentially passes through the first objective lens, the single-mode optical fiber, the collecting lens and the second objective lens, and the laser beam enters the acquisition module after being focused. The acquisition module is used for transmitting the laser beam generated by the laser module and focused onto a sample, the laser beam irradiates on the sample and generates a photoacoustic signal due to a photoacoustic effect, the photoacoustic effect is a phenomenon that when a substance is irradiated by light with periodic intensity modulation, an acoustic signal is generated, when a certain medium is irradiated by the light, the temperature inside the medium is changed due to the absorption of the medium to change the structure and the volume of certain areas in the medium, and when a pulse light source or a modulation light source is adopted, the volume expansion and contraction of the medium can be caused by the temperature rise and fall of the medium, so that the acoustic wave can be radiated outwards. The photoacoustic signal acquisition device comprises an ultrasonic probe, a signal amplifier and an acquisition card, wherein the ultrasonic probe is used for detecting and receiving the photoacoustic signal generated on the surface of a sample, the ultrasonic probe receives the photoacoustic signal, then the photoacoustic signal is processed and amplified by the signal amplifier and transmitted to the acquisition card, and the acquisition card records and stores the amplified photoacoustic signal for subsequent processing. Preferably, the ultrasonic probe comprises an ultrasonic transducer and an acoustic lens, wherein the center frequency of the ultrasonic transducer is 50MHz, and the numerical aperture of the acoustic lens is 0.5. The focusing module is used for adjusting the distance between the ultrasonic probe and the sample and comprises a three-dimensional scanner and an object stage, the distance between the ultrasonic probe and the sample can be achieved by adjusting the position of the ultrasonic probe and/or the position of the sample, the ultrasonic probe is preferably adjusted by adopting the position adjusting method, the ultrasonic probe is arranged in the three-dimensional scanner, the three-dimensional scanner comprises a lifting table, a translation table and a two-dimensional grating scanner, the ultrasonic probe is specifically arranged on the lifting table, and the two-dimensional grating scanner is arranged on the translation table. Obviously, the ultrasonic probe faces the sample, and the sample is loaded on the stage, which usually adopts a three-dimensional translation stage, and can adjust the position in three-dimensional space, so as to fix the sample loading at a specific position, and preferably, the acquisition module further comprises a water tank, and a certain amount of pure water is contained in the water tank and can be used for coupling the photoacoustic signals. The control module comprises a calculation processing unit for controlling the operation of the laser module, the acquisition module and the focusing module and is electrically connected with the laser module, the acquisition module and the focusing module. The rapid focusing system provided by the invention is driven by a stepping motor, the stepping motor is connected with a relevant unit in a control module, and the operation of the stepping motor is automatically controlled according to the feedback of information acquired by the system, so that the automatic lifting of the lifting platform and the translation platform, particularly the lifting platform, is realized.
The invention provides a fast focusing method for photoacoustic microscopic imaging, which adopts the fast focusing system for photoacoustic microscopic imaging to quickly adjust a sample to the focal plane position of a focused laser beam, and as shown in figure 2, the fast focusing method comprises the following steps:
step S100: focusing a laser beam, irradiating the laser beam on a sample to be detected to generate a photoacoustic signal, receiving the photoacoustic signal through an ultrasonic probe, transmitting the photoacoustic signal to a collection card, and scanning to form a B-type scanning image; an interval within a predetermined numerical range from the focal plane of the laser beam, in which photoacoustic signals generated on the surface of the sample can be detected, is defined as a near-focus region, and an interval outside the predetermined numerical range from the focal plane of the laser beam is defined as a far-focus region. The laser beam can form focal plane after focusing, if can place the position to be measured of sample on focal plane, then the sample position to be measured image information that can acquire is most clear or most accurate, however the concrete condition of sample position to be measured can't learn, consequently can't directly place it on focal plane, need make sample position to be measured be close to focal plane through gradually adjusting. For the convenience of describing the technical scheme of the invention, the spatial position within a certain range of the focal plane is defined as a near-focus area, and otherwise, the spatial position is defined as a far-focus area.
Step S200: and judging that the signal position of the sample is in a far focus area through position information on the B-type scanning image, and adjusting the distance between the sample and the ultrasonic probe according to the first further distance until the signal position of the sample is in the near focus area. The sample signal position can be known by the system through measuring the position information on the B-type scanogram, the sample signal position directly reflects the actual sample position, the relative position relation between the sample and the focal plane can also be judged, and when the sample signal position is judged to be in a far-focus area, a larger adjustment amplitude can be adopted to draw the distance between the ultrasonic probe and the sample, so that the focusing efficiency is improved. The same distance is adopted for each adjustment amplitude, namely, the first further distance is adopted, and multiple times of adjustment and judgment are possibly needed to adjust the position of the sample signal to be in the near-focus area. And generating a photoacoustic signal at a new position every time the position of the ultrasonic probe is adjusted, and scanning to obtain a new B-type scanning image so as to obtain a new sample signal position and judge whether the sample signal position is in a near-focus area.
Step S300: and scanning the photoacoustic signals on the acquisition card to acquire a photoacoustic B-type scanning image, judging that the image definition value reaches the maximum value in the image definition evaluation values for a plurality of times, and finishing focusing of the sample to be detected by taking the sample signal position corresponding to the maximum value as an observation position. When the signal position of the sample is located in the near-focus area, the acquisition card is continuously scanned, a new photoacoustic B-type scanning image is acquired, and the image definition of the photoacoustic B-type scanning image is evaluated, wherein the evaluation is continuously carried out for multiple times.
In other words, no matter whether the position of the sample signal is in the near-focus area or the image definition of the photoacoustic B-type scan is judged to be the maximum, the distance between the ultrasonic probe and the sample is adjusted, and it is assumed that when the position to be measured of the sample is at the focal plane, the definition of the acquired B-type scan is the maximum, the focusing is completed, the position of the focal plane is naturally determined by the laser beam, the objective lens for processing the laser beam and the condenser lens, and is a known parameter, but the microscopic appearance of the sample is not a plane, and the specific situation of the microscopic appearance is an unknown quantity, so that it is impossible to always place the micro area to be observed on the sample on the focal plane, and always the micro area is in a certain range, and in the normal situation, when the sample is automatically focused, the distance between the ultrasonic probe and the sample shows a change trend from large to small, and a position interval near the focal plane is set as [ a-B, a + b ], which is a near focus region, and b is a set value, which can be set according to the type of sample or the parameters of the laser. When the signal position is outside the interval, namely in a far-focus area, the lifting platform moves rapidly to enable the sample position to be in the interval, and the image quality of the photoacoustic B-type scanning image is inevitably not high enough, so that the evaluation of the image definition of the B-type scanning image by the system can be correspondingly reduced and even stopped, and the efficiency is improved; when the photoacoustic signal of the sample enters the interval, the focusing condition of the sample is judged mainly through image definition evaluation, so that focusing can be accurately realized.
As a preferable scheme, as shown in fig. 3, the step of adjusting the distance between the sample and the ultrasonic probe until the image sharpness reaches the maximum value specifically includes:
step S310: and judging that the position of the sample signal is in a near-focus area, and reducing the distance between the sample and the ultrasonic probe by a second step distance. The distance between the ultrasonic probe and the sample is usually adjusted from far to near, and when the position of the ultrasonic probe is adjusted, the focal plane position of the laser beam is also changed to be continuously close to the sample, so that the signal position of the sample is gradually changed into a near-focus area.
S320: judging that the image definition is larger than the definition before the distance between the sample and the ultrasonic probe is adjusted, and executing the step S310; or judging that the image definition is smaller than the definition before the adjustment of the distance between the sample and the ultrasonic probe, and adjusting the distance between the sample and the ultrasonic probe to be a value before the adjustment of the distance corresponding to the image definition. Because the distance between the ultrasonic probe and the sample is from far to near, the sample is gradually close to the focal plane, so that the definition of the obtained B-type scanning image is continuously improved, and the definition of the B-type scanning image is smaller than that of the B-type scanning image before adjustment in the last adjustment, which indicates that the sample crosses the focal plane, so that the distance between the ultrasonic probe and the sample is adjusted back to the previous position.
In summary, as shown in fig. 4, the process of automatic fast focusing can be described as follows: firstly, scanning and obtaining a B-type scanning image at the same position on a sample, obtaining an average position Z1 of a sample signal corresponding to the B-type scanning image, and judging whether Z1 is in a parameter range of [ a-B, a + B ], wherein a is the height of a theoretical focal plane of a laser signal, B reflects the effective detection range of the system, and a parameter value set according to the focal depth of a self-made acoustic lens of the system, the focal depth of the acoustic lens is the response range of the acoustic lens for collecting the acoustic signal, the acoustic signal can be effectively detected in the range, and the detection efficiency is low outside the range, so that the sample signal value cannot be clearly obtained. When the Z1 is more than a-b or the Z1 is more than a + b, the defocusing plane of the sample is far away, the control module drives the lifting platform and drives the ultrasonic probe to translate and adjust according to the first step distance d1, so that the ultrasonic probe is further close to the sample, and the process is circulated for a plurality of times until the condition that the a-b is more than Z1 and more than a + b is met; when a-B < Z1 < a + B, it indicates that the sample is very close to the focal plane, and then it starts to evaluate whether the sharpness of the B-scan reaches the maximum to determine whether the sample is at the focal plane or is closest to the focal plane, preferably, a variance (variance) function is used as the image quality evaluation function, the variance function is to use the difference between the gray value of the current pixel and the mean value of the gray value of the image to sum up the squares to characterize the image sharpness, and assuming that the gray value of a certain point (x, y) of the image is g (x, y), the variance function is as follows:
Figure BDA0001765858180000081
wherein,
Figure BDA0001765858180000082
m, N are the number of pixels in the horizontal and vertical directions of an image, i.e. the length and width of the image, respectively. The obtained evaluation values are stored as an array s [ i ]](i denotes the i-th cycle, array s stores evaluation function values, s [ i ]]The image definition of the B-type scanning image of the ith cycle), the lifting platform drives the ultrasonic probe to be close to the sample according to the second stepping distance d2 to enter the next cycle, the B-type scanning image is obtained, and the image definition evaluation value s [ i +1] is obtained]Comparing s [ i ]]And s [ i +1]]:
If s [ i +1] is larger than s [ i ], the definition evaluation value is not the maximum value, and the sample is still at a certain distance from the focal plane, so that the lifting platform is driven to continuously approach the sample according to the second stepping distance, and the next cycle is carried out, namely s [ i +2] is obtained.
If s [ i +1] < s [ i ], the definition evaluation value exceeds the maximum definition value, the distance between the sample and the focal plane is too small, and the lifting platform is driven, so that the second step of distance drives the ultrasonic probe to return to the position corresponding to the previous cycle, and the definition evaluation value of the position is s [ i ]. Of course, the second step distance may be further adjusted, for example, the lifting stage drives the ultrasonic probe to approach the sample by half of the second step distance, and the adjustment of the distance between the ultrasonic probe and the sample is repeated according to the aforementioned determining and adjusting steps until the sample is focused to the position closest to the focal plane with a certain precision.
In summary, it is preferable that the first step distance d1 is greater than the second step distance d2, so that the method can ensure focusing efficiency and obtain high focusing accuracy.
In order to further understand the fast focusing method for photoacoustic microscopy provided by the present invention, the practical operation process of a certain case is illustrated:
the method comprises the steps of placing a sample to be measured on an objective table, enabling the sample to be measured to be located below an ultrasonic probe, starting a system focusing button, enabling the system to send a focused laser beam to the surface of the sample, enabling the distance between the ultrasonic probe and the sample to be continuously reduced by a specific frequency and a step distance, further reducing the distance to a certain range by another specific frequency and another step distance, finally adjusting the distance to be increased once (the adjustment range is possibly very small so that a human eye cannot perceive the distance), completing focusing of a certain region to be measured of the sample to be measured, and automatically executing the whole focusing process by the system according to a preset quick focusing method.
The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.
The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.

Claims (7)

1. A fast focusing method for photoacoustic microscopy imaging is characterized by comprising the following steps:
s100: focusing a laser beam, irradiating the laser beam on a sample to be detected to generate a photoacoustic signal, receiving the photoacoustic signal through an ultrasonic probe, transmitting the photoacoustic signal to a collection card, and scanning to form a B-type scanning image; defining an interval within a predetermined numerical range [ a-b, a + b ] from the focal plane of the laser beam as a near-focus area, and an interval outside the predetermined numerical range [ a-b, a + b ] from the focal plane of the laser beam as a far-focus area;
s200: judging that the position of a sample signal is in the far focus area through position information on a B-type scanning image, wherein the position of the sample signal is obtained by measuring the position information on the B-type scanning image, the position of the sample signal directly reflects the actual position of the sample, the distance between the sample and the ultrasonic probe is adjusted according to a first further distance until the position of the sample signal is in the near focus area, and executing the step S300;
or, judging that the position of the sample signal is in the near-focus area, and executing the step S300;
s300: scanning a photoacoustic signal on the acquisition card to acquire a photoacoustic B-type scanning image, judging that the image definition value reaches the maximum value in the image definition evaluation values for a plurality of times, and finishing focusing of the sample to be detected by taking the sample position corresponding to the maximum value as an observation position;
wherein, the specific steps of judging that the position of the sample signal is in the near-focus area are as follows:
scanning to obtain a B-type scanning diagram at the same position on a sample, obtaining an average position Z1 of a sample signal corresponding to the B-type scanning diagram, and judging whether Z1 is in a range of [ a-B, a + B ], wherein a is the height of a theoretical focal plane of a laser signal, and B reflects the effective detection range of a system;
the step of adjusting the distance between the sample and the ultrasonic probe until the image definition reaches the maximum value specifically comprises:
s310: judging that the position of the sample signal is in the near-focus area, and reducing the distance between the sample and the ultrasonic probe by a second step distance;
s320: judging that the image definition value is larger than the definition value before the distance between the sample and the ultrasonic probe is adjusted, and executing the step S310; or,
judging that the image definition is smaller than the definition before adjusting the distance between the sample and the ultrasonic probe, and increasing the distance between the sample and the ultrasonic probe to a value before adjusting the distance corresponding to the image definition;
the first step pitch is greater than the second step pitch.
2. The fast focusing method for photoacoustic microscopy according to claim 1, wherein the evaluation of the image sharpness of the photoacoustic B-scan is performed using an image evaluation function that uses a variance function.
3. A fast focusing system for photoacoustic microscopy, characterized in that it is used to execute the fast focusing method for photoacoustic microscopy as claimed in any one of claims 1-2, comprising:
the laser module is used for generating a laser beam and focusing the laser beam and comprises a laser, an objective lens, an optical fiber and a condenser lens;
the acquisition module is used for transmitting the focused laser beam generated by the laser module to a sample and acquiring a photoacoustic signal generated on the sample, and comprises an ultrasonic probe, a signal amplifier and an acquisition card;
the focusing module is used for adjusting the distance between the ultrasonic probe and the sample and comprises a three-dimensional scanner and an object stage;
and the control module is electrically connected with the laser module, the acquisition module and the focusing module.
4. The fast focusing system for photoacoustic microscopy according to claim 3, wherein the objective lens comprises a first objective lens and a second objective lens, and the optical fiber is a single mode optical fiber; after the laser beam emitted by the laser passes through the first objective lens, the laser beam is transmitted by the optical fiber, passes through the condenser lens and then is incident on a sample through the second objective lens.
5. The fast focusing system for photoacoustic microscopy according to claim 3, wherein the ultrasound probe comprises an ultrasound transducer and an acoustic lens, the acoustic lens having a numerical aperture of 0.5.
6. The fast focusing system for photoacoustic microscopy imaging according to claim 3, further comprising a water tank in the acquisition module, the water tank being disposed between the ultrasound probe and the sample.
7. The fast focusing system for photoacoustic microscopy imaging according to claim 3, wherein the three-dimensional scanner comprises a lift table, a translation table, and a two-dimensional raster scanner disposed on the translation table, the ultrasound probe being disposed on the lift table.
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