CN111938581A - Axial high-resolution photoacoustic imaging method and system using high-frequency and low-frequency probe matching - Google Patents
Axial high-resolution photoacoustic imaging method and system using high-frequency and low-frequency probe matching Download PDFInfo
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- CN111938581A CN111938581A CN202010641077.2A CN202010641077A CN111938581A CN 111938581 A CN111938581 A CN 111938581A CN 202010641077 A CN202010641077 A CN 202010641077A CN 111938581 A CN111938581 A CN 111938581A
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- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/0093—Detecting, measuring or recording by applying one single type of energy and measuring its conversion into another type of energy
- A61B5/0095—Detecting, measuring or recording by applying one single type of energy and measuring its conversion into another type of energy by applying light and detecting acoustic waves, i.e. photoacoustic measurements
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/72—Signal processing specially adapted for physiological signals or for diagnostic purposes
Abstract
An axial high-resolution photoacoustic imaging method and device system using high-frequency and low-frequency probes to cooperate comprises a laser generator, an objective lens, two focusing ultrasonic probes with different center frequencies, a three-dimensional scanner, a signal acquisition card and a workstation. The requirement of axial high-resolution imaging of the photoacoustic microscopic imaging system is met. The axial high-resolution photoacoustic imaging method using the high-frequency probe and the low-frequency probe to be matched mainly uses two focusing ultrasonic probes with different central frequencies, and because the ultrasonic probes with different central frequencies can detect different frequency spectrum ranges, photoacoustic signal frequency spectrums acquired by the probes with two different central frequencies are fused to obtain expanded photoacoustic signal frequency spectrums, so that the axial resolution of the system is improved. The method can enable the system to reflect the three-dimensional structure information of the sample more truly, and expand the application range of photoacoustic microscopic imaging.
Description
Technical Field
The invention relates to the field of photoacoustic microscopic imaging, in particular to an axial high-resolution photoacoustic imaging method and system using high-low frequency probe matching.
Background
Over the course of more than 20 years, photoacoustic imaging has become one of the fastest growing biological imaging technologies. Depending on the form of optical excitation and acoustic detection, there are two main types of photoacoustic imaging: photoacoustic tomography (PAT) and photoacoustic microscopy (PAM). PAT provides relatively low spatial resolution (on the order of hundreds of microns) and deep imaging depth (several centimeters) using wide field illumination and ultrasound detection at multiple locations; PAM provides high spatial resolution (from a few microns to tens of microns) and relatively shallow imaging depth (one to a few millimeters) using either strongly or weakly focused illumination and focused ultrasound detection. Photoacoustic microscopy has been widely used in biological research, such as structural imaging of vasculature, imaging of brain structure and function, tumor detection, and the like. As an important branch of photoacoustic imaging, photoacoustic microscopic imaging meets the requirement of high-resolution imaging in biological imaging, and can realize multi-scale photoacoustic imaging from single cells to tissues. Photoacoustic microscopy generally uses a focused laser beam or a focused ultrasound probe to obtain better spatial resolution. Photoacoustic microscopy generally employs a point-scan method, with lateral resolution determined by both optical and acoustic foci. When the laser beam is strongly focused, the optical focus is smaller than the acoustic focus, the photoacoustic signal is only excited in the optical focus area, the transverse resolution of the system depends on the size of the optical focus, and the imaging system is called an optical resolution photoacoustic microscopic imaging system, and is called an acoustic resolution photoacoustic microscopic imaging system in contrast. In photoacoustic imaging, lateral resolution is easily achieved on the order of a few microns or even hundreds of nanometers by focusing with a high numerical aperture objective lens. In the axial direction, however, the axial resolution of the system is determined by the bandwidth of the ultrasound transducer. Due to its narrow bandwidth (on the order of tens of megahertz), ultrasonic transducers can provide axial resolution on the order of tens of microns and are difficult to scale further to better than 10 microns. The low axial resolution causes the non-uniform three-dimensional spatial resolution, the imaging cannot correctly reflect the real structure of the sample, and the real structure information is the basis for the subsequent analysis of functions and the like. Therefore, it is necessary to develop a method for improving the axial resolution while ensuring the original performance of the system.
Disclosure of Invention
The invention aims to solve the technical problem of low axial resolution in a photoacoustic microscopic imaging system in the prior art, and provides a photoacoustic microscopic imaging method and system which can obtain high axial resolution and are matched by using a high-low frequency probe.
An axial high-resolution photoacoustic imaging method using a high-frequency and low-frequency probe, comprising the steps of:
s1: the pump laser emits laser, a light beam is coupled into the single-mode optical fiber through the first objective lens, the light beam is collimated through the first condenser lens after coming out of the optical fiber, and then is focused on a sample through the second objective lens to generate a photoacoustic signal;
s2: the method comprises the steps that two focusing ultrasonic probes with different central frequencies are used, a first focusing ultrasonic probe and a second focusing ultrasonic probe respectively acquire photoacoustic signals, and due to the fact that the central frequencies of the ultrasonic probes are different, the obtained photoacoustic signals are different in frequency spectrum range, and the signals are amplified by a signal amplifier and then acquired by a signal acquisition card;
s3: performing Fourier transform on the two acquired photoacoustic signals respectively to obtain photoacoustic signal frequency spectrums, fusing the two photoacoustic signal frequency spectrums to obtain expanded photoacoustic signal frequency spectrums, and finally performing inverse Fourier transform or axial high-resolution image on the fused photoacoustic signal frequency spectrums;
s4: and performing two-dimensional raster scanning to acquire three-dimensional data.
Preferably, the second objective lens of S1 is vertically disposed so that the laser beam is focused from top to bottom.
Preferably, the two focusing ultrasonic probes with different center frequencies in S2 include a first focusing ultrasonic probe and a second focusing ultrasonic probe, which are symmetrically disposed on both sides of the second objective lens and form an included angle of 45 degrees with the second objective lens, and the focus of the ultrasonic probe coincides with the optical focus of the second objective lens to obtain a better signal-to-noise ratio. The center frequencies f1, f2 of the two ultrasound probes are selected to take into account the bandwidths (pass frequency ranges) of the two ultrasound probes, and the pass frequency ranges of the two probes should not overlap and be contiguous.
Preferably, the fusing of the photoacoustic signal spectrums acquired by the two ultrasound probes in S3 means that the photoacoustic signal spectrums acquired by the two ultrasound probes are directly added.
Preferably, the optical fiber in S1 is a single mode optical fiber.
An axial high resolution photoacoustic imaging system using a high and low frequency probe cooperation, comprising: the device comprises a laser module, a time delay module, an acquisition module, a focusing module and a control module.
The laser module is used for generating a laser beam and focusing the laser beam and comprises a pumping laser, a first objective lens, an optical fiber, a first condenser lens and a second objective 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 a first focused ultrasonic probe, a second focused ultrasonic probe, a signal amplifier and a signal 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 the control module is electrically connected with the laser module, the acquisition module and the focusing module.
Preferably, the numerical aperture of the first focused ultrasonic probe and the second focused ultrasonic probe of the two focusing ultrasonic probes is 0.5.
Preferably, the collection module further comprises a water tank disposed between the ultrasonic probe and the sample.
The invention has the advantages and beneficial effects that:
the invention mainly uses two focusing ultrasonic probes with different central frequencies, and because the ultrasonic probes with different central frequencies can detect different frequency spectrum ranges, the photoacoustic signal frequency spectrums acquired by the two probes with different central frequencies are fused to obtain an expanded photoacoustic signal frequency spectrum, thereby improving the axial resolution of the system. The method can enable the system to reflect the three-dimensional structure information of the sample more truly, and expand the application range of photoacoustic microscopic imaging.
Drawings
Fig. 1 is a schematic structural diagram of an axial high-resolution photoacoustic imaging system using a high-frequency probe and a low-frequency probe in an embodiment of the present invention.
In the figure: 1. a pump laser; 2. a first objective lens; 3. an optical fiber; 4. a first condenser lens; 5. a second objective lens; 6. a first focused ultrasound probe; 7. a second focused ultrasound probe; 8. a water tank; 9. a sample; 10. A three-dimensional scanner; 11. a signal amplifier; 12. a signal acquisition card; 13. a workstation.
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.
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.
Example 1
Fig. 1 is a schematic structural diagram of the whole set of imaging system of the present invention. The main components of the system comprise a pump laser 1, a first objective lens 2, an optical fiber 3, a first condenser lens 4, a first second objective lens 5, a first focused ultrasonic probe 6, a second focused ultrasonic probe 7, a three-dimensional scanner 10, a signal amplifier 11, a signal acquisition card 12 and a workstation 13. The pump laser 1 is used for emitting laser beams, the laser beams are coupled into the optical fiber 3 through the first objective lens 2 after being emitted, are collimated after passing through the first condenser lens 4, and are focused on the sample 9 by the second objective lens 5 to be excited to generate photoacoustic signals. The first focused ultrasonic probe 6 and the second focused ultrasonic probe 7 with the center frequencies of 25MHz and 50MHz (the bandwidth is 80%) are symmetrically arranged at the two sides of the second objective lens at an inclination angle of 45 degrees to receive the photoacoustic signals. Both ultrasound probes are confocal with the second objective lens 5 to ensure a better signal-to-noise ratio. The signals are received by the two focusing ultrasonic probes, then sent to the signal amplifier 11 to be amplified, and collected by the signal acquisition card 12. The sample 9 is placed on a three-dimensional scanner 10, and the three-dimensional scanner 10 is used for sample position adjustment and two-dimensional raster scanning. The workstation 13 is responsible for timing control of the entire system.
The axial resolution is according to the formula 0.88v/B, where v-1500 m/s is the speed of sound in water and B is the bandwidth of the ultrasound probe. Ultrasonic transducers (with 80% bandwidth) with center frequencies of 25MHz and 50MHz, respectively, can provide axial resolutions of 66 microns and 33 microns, respectively. The method comprises the steps of performing Fourier transform on two acquired photoacoustic signals respectively to obtain photoacoustic signal frequency spectrums, fusing the two photoacoustic signal frequency spectrums to obtain expanded photoacoustic signal frequency spectrums, and finally performing inverse Fourier transform or axial high-resolution image on the fused photoacoustic signal frequency spectrums. Theoretically, the frequency spectrum bandwidth of the fused photoacoustic signal is about 52.5MHz, the axial resolution provided by the fused photoacoustic signal is about 25 microns, and the axial resolution is improved by 1.32 times.
While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the spirit and scope of the invention. The present invention is not to be limited by the specific embodiments disclosed herein, and other embodiments that fall within the scope of the claims of the present application are intended to be within the scope of the present invention.
Claims (8)
1. An axial high-resolution photoacoustic imaging method using a high-frequency and low-frequency probe, comprising the steps of:
s1: the pump laser (1) emits laser, a light beam is coupled into the optical fiber (3) through the first objective lens (2), the light beam is collimated through the first condenser lens (4) after coming out of the optical fiber (3), and then is focused on a sample through the second objective lens (5) to generate a photoacoustic signal;
s2: the method comprises the steps that two focusing ultrasonic probes with different central frequencies, namely a first focusing ultrasonic probe (6) and a second focusing ultrasonic probe (7), are used for respectively acquiring photoacoustic signals, and due to the fact that the spectral ranges of the photoacoustic signals acquired by the ultrasonic probes are different, the signals are acquired by a signal acquisition card (12) after being amplified by a signal amplifier (11);
s3: performing Fourier transform on the two acquired photoacoustic signals respectively to obtain photoacoustic signal frequency spectrums, fusing the two photoacoustic signal frequency spectrums to obtain expanded photoacoustic signal frequency spectrums, and finally performing inverse Fourier transform or axial high-resolution image on the fused photoacoustic signal frequency spectrums;
s4: and performing two-dimensional raster scanning to acquire three-dimensional data.
2. The method of claim 1, wherein the second objective lens (5) is vertically disposed in S1 to focus the laser beam from top to bottom.
3. The method according to claim 1, wherein the two focused ultrasound probes with different center frequencies in S2, the first focused ultrasound probe (6) and the second focused ultrasound probe (7) are symmetrically disposed on both sides of the second objective lens (5) and form an angle of 45 degrees with the second objective lens (5), the focal points of the first focused ultrasound probe (6) and the second focused ultrasound probe (7) coincide with the optical focal point of the second objective lens (5) to obtain a better signal-to-noise ratio, the center frequencies f1 and f2 of the first focused ultrasound probe (6) and the second focused ultrasound probe (7) are selected to take into account the bandwidths (pass frequency ranges) of the two ultrasound probes, and the pass frequency ranges of the two probes should not overlap and be continuous.
4. The axial high-resolution photoacoustic imaging method using the high-frequency and low-frequency probe matching according to claim 1, wherein the step S3 of fusing the photoacoustic signal spectrums acquired by the first focused ultrasound probe (6) and the second focused ultrasound probe (7) is to directly add the photoacoustic signal spectrums acquired by the first focused ultrasound probe (6) and the second focused ultrasound probe (7).
5. The method according to claim 1, wherein the optical fiber in S1 is a single mode optical fiber.
6. An axial high resolution photoacoustic imaging system using a high and low frequency probe cooperation, comprising:
the laser module is used for generating laser beams and focusing the laser beams and comprises a pumping laser (1), a first objective lens (2), an optical fiber (3), a first condenser lens (4) and a second objective lens (5);
the acquisition module is used for transmitting the focused laser beam generated by the laser module to a sample (9) and acquiring a photoacoustic signal generated on the sample (9), and comprises a first focused ultrasonic probe (6), a second focused ultrasonic probe (7), a signal amplifier (11) and a signal acquisition card (12);
the focusing module is used for adjusting the distance between the ultrasonic probe and the sample and comprises a three-dimensional scanner (10);
and the control module is electrically connected with the laser module, the acquisition module and the focusing module.
7. An axial high resolution photoacoustic imaging system using a high and low frequency probe to mate as in claim 6, characterized in that the numerical aperture of the first focused ultrasound probe (6) and the second focused ultrasound probe (7) is 0.5.
8. The axial high-resolution photoacoustic imaging system matched with the high-frequency and low-frequency probes according to claim 6, wherein the acquisition module further comprises a water tank (8), the first focused ultrasound probe (6) and the second focused ultrasound probe (7) are respectively arranged on two sides of the water tank (8), and a sample (9) is arranged below the water tank (8).
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Cited By (2)
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| CN112504926A (en) * | 2020-11-25 | 2021-03-16 | 长江水利委员会长江科学院 | Ultrasonic suspended load measurement system and method based on multi-frequency backscattering principle |
| CN113654993A (en) * | 2021-07-14 | 2021-11-16 | 华中科技大学 | Coaxial axial modulation high-resolution photoacoustic microscopic imaging method and imaging system |
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Cited By (3)
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| CN112504926A (en) * | 2020-11-25 | 2021-03-16 | 长江水利委员会长江科学院 | Ultrasonic suspended load measurement system and method based on multi-frequency backscattering principle |
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| CN113654993A (en) * | 2021-07-14 | 2021-11-16 | 华中科技大学 | Coaxial axial modulation high-resolution photoacoustic microscopic imaging method and imaging system |
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Application publication date: 20201117 |