CN111948145A - Bessel beam large-depth-of-field photoacoustic microscopic imaging device and method based on ultrasonic modulation - Google Patents

Abstract

A Bessel beam photoacoustic microscopy imaging device with large depth of field based on ultrasonic modulation, including a pulsed laser, a piezoelectric ceramic circular tube, a three-dimensional scanner, a function generator, a digital pulse delayer, and a synchronization device composed of a D-type flip-flop circuit. The pulse laser emits laser pulses, which are incident on the piezoelectric ceramic circular tube filled with liquid. The function generator applies a sinusoidal RF signal to the piezoelectric ceramic circular tube. The piezoelectric ceramic circular tube vibrates in the radial direction to generate ultrasonic waves. The refractive index of the liquid in the radial direction shows The zero-order Bessel function distribution, the synchronization circuit synchronizes the laser light output and the refractive index change of the piezoelectric ceramic tube, so that the pulsed laser emits light when the refractive index change of the piezoelectric ceramic tube is positive and maximum. The beam coming out of the ceramic tube is a Bessel beam, which is focused on the sample by the fifth lens. The invention uses ultrasonic modulation to generate Bessel beams, realizes the expansion of the imaging depth of photoacoustic microscopic imaging, and is beneficial to the rapid and large-scale monitoring of physiological activities.

Description

A Bessel beam photoacoustic microscopy imaging device with large depth of field based on ultrasonic modulation and method

technical field

The invention relates to the field of optical imaging, in particular to a large-depth-of-field Bessel beam photoacoustic microscopic imaging device and method based on ultrasonic modulation.

Background technique

Photoacoustic imaging technology is a biomedical imaging technology that has developed rapidly in recent years. It combines the high contrast of optical imaging with the high penetrability and high resolution of acoustic imaging, and has biomedical imaging with deep imaging depth and high spatial resolution. Way. In recent years, it has been widely used in various fields of biomedicine, such as vascular structure, tumor detection, brain structure and functional imaging. Photoacoustic microscopy is an important branch of photoacoustic imaging with high spatial resolution, enabling multi-scale imaging from cells to tissues. In photoacoustic microscopy imaging, the optical focus and the acoustic focus are usually co-axial and confocal, and the lateral resolution is determined by the optical focus and the acoustic focus. Micro imaging system. In the acoustically resolved photoacoustic microscopy imaging system, the incident light is weakly focused, and the size of the light focus is much larger than the size of the acoustic focus. Therefore, the lateral resolution is determined by the smaller acoustic focus. In an optically resolved photoacoustic microscopy imaging system, an objective lens with a high numerical aperture is usually used to focus the incident light strongly, and the size of the optical focus is much smaller than that of the acoustic focus, and the lateral resolution depends on the size of the optical focus. However, in optically resolved photoacoustic microscopy imaging systems, strong focusing of the beam to achieve high resolution results in a small imaging depth of field, and lateral resolution deteriorates rapidly outside the optical focus. The small imaging depth of field results in the limited volume imaging speed of the system, which makes it impossible to quickly and widely monitor physiological activities.

To solve this problem, many researchers have proposed different methods. A relatively common and simple method is to use mechanical scanning, but this method has problems such as slow scanning speed, limited accuracy, and introduction of mechanical vibration. Some researchers also use illumination from the upper and lower directions to obtain twice the imaging depth of field, but this method can only be transmissive, and can only image transparent or thinner samples with a large depth of field. Some researchers also use the chromatic aberration characteristics of non-achromatic objectives to use multi-wavelength lasers to generate multiple foci along the axial direction, thereby improving the axial imaging range of the system, but this method sacrifices the functional imaging of the system.

SUMMARY OF THE INVENTION

Based on this, it is necessary to provide a large-depth-of-field Bessel beam photoacoustic microscopy imaging device and method based on ultrasonic modulation for the above-mentioned problems.

A large-depth-of-field Bessel beam photoacoustic microscopic imaging device based on ultrasonic modulation, characterized in that: the large-depth-of-field Bessel beam photoacoustic microscopic imaging device based on ultrasonic modulation mainly includes pulsed lasers, piezoelectric ceramics Round tubes, 3D scanners and function generators, digital pulse delayers.

A method for photoacoustic microscopy imaging of Bessel beams with large depth of field based on ultrasonic modulation, comprising:

S1: The pulsed laser emits laser pulses, and the beam expander system reshapes the spot size to be equivalent to the diameter of the piezoelectric ceramic circular tube, and then injects it into the piezoelectric ceramic circular tube filled with optically transparent liquid;

S2: Use a function generator to apply a sinusoidal RF signal to the piezoelectric ceramic tube, the inner and outer walls of the piezoelectric ceramic tube vibrate and generate ultrasonic waves. The ultrasonic waves will periodically modulate the density of the local optically transparent liquid, thereby changing the refractive index distribution of the optically transparent liquid. , the refractive index distribution of the optically transparent liquid in the radial direction exhibits a zero-order Bessel function distribution, and changes synchronously with the sinusoidal RF signal;

S3: Use a synchronous circuit to synchronize the laser light output and the change of the refractive index of the liquid in the piezoelectric ceramic tube, so that the laser is fixed at a phase of the refractive index change to emit light;

By controlling the delay of the digital pulse delay device, the pulsed laser can emit light when the refractive index of the liquid in the piezoelectric ceramic tube becomes the maximum positive, and the radial refractive index distribution of the liquid in the piezoelectric ceramic tube is zero-order Bessel. function distribution. In this way, the beam coming out of the piezoelectric ceramic tube after ultrasonic modulation is a Bessel beam.

S4: Focus the obtained Bessel beam onto the sample through the fifth condenser lens. The generated photoacoustic signal is detected by the acoustic lens, amplified by the amplifier, and finally collected by the acquisition card.

S5: Use a 3D scanner to perform 2D raster scanning to obtain 3D data

The beam expander system in S1 consists of a first condenser lens and a second condenser lens.

Preferably, the piezoelectric ceramic tube is polarized and plated on the inner and outer walls to form an inner electrode and an outer electrode, the inner electrode extends from one end to the outer wall, and the inner electrode and the outer electrode are on the outer wall and the other end. The end faces form two gaps.

Preferably, the laser pulse is vertically incident on the piezoelectric ceramic tube, and the piezoelectric ceramic tube is placed vertically, in order to avoid asymmetric radial refractive index distribution due to gravity when placed laterally.

Preferably, the optically transparent liquid is silicone oil, and the silicone oil has a kinematic viscosity of 50-150 cSt, a refractive index of 1-2, and a sound velocity of 800-1200 m/s.

其中n₀为介质的静态折射率，c_s为介质中的声速，ω为驱动信号的频率，r和t分别表示位置和时间，J₀为零阶贝塞尔函数，n_a是与ω、声介质物理特性有关的常数，折射率分布表现为零阶贝塞尔函数，且随时间与驱动信号同步变化。The refractive index distribution of the optically transparent liquid after ultrasonic modulation described in S2 is:

where n ₀ is the static refractive index of the medium, c _s is the speed of sound in the medium, ω is the frequency of the driving signal, r and t represent the position and time, respectively, J ₀ is _a zero-order Bessel function, and na is the relationship between ω, A constant related to the physical properties of the acoustic medium, the refractive index distribution behaves as a zero-order Bessel function and changes in synchrony with the driving signal over time.

Preferably, the synchronization circuit described in S3 is composed of a three-dimensional scanner, a function generator, a D-type flip-flop, and a digital pulse delay device. The function generator is used to output a sinusoidal radio frequency signal to drive the piezoelectric ceramic circular tube, and the synchronization of the sinusoidal radio frequency signal is used. The signal is connected to the clock end of the D-type flip-flop, and the 3D scanner will output a position synchronization signal every time it moves horizontally. Several kilohertz) connected to the D terminal of the D-type flip-flop;

According to the characteristic equation of the D-type flip-flop, the D-type flip-flop is triggered only when the synchronization signal rises, and the output signal is equal to the input signal; the output of the D-type flip-flop is connected to a digital pulse delayer, and the digital pulse delays The output of the device is used to trigger the pulsed laser;

By adjusting the delay time of the digital pulse delay device, the pulse laser can emit light when the refractive index of the liquid in the piezoelectric ceramic tube changes to the positive maximum. At this time, the beam coming out of the piezoelectric ceramic tube is the Bessel beam.

Preferably, the acoustic lens in S4 is composed of an ultrasonic transducer and an acousto-optic coupling prism, and the numerical aperture of the acousto-optic coupling prism is 0.5.

The advantages and beneficial effects of the present invention are:

The advantage of the invention is that the piezoelectric ceramic tube is driven by a sinusoidal radio frequency signal to generate ultrasonic waves, and the ultrasonic waves modulate the radial refractive index distribution of the optically transparent liquid to a zero-order Bessel function distribution, thereby obtaining a Bessel beam. Compared with Gaussian beams, Bessel beams are non-diffractive and have a greater depth of field. The device will increase the depth of field of the photoacoustic microscopy imaging system, thereby increasing its volume imaging speed, enabling better rapid, large-scale, high-resolution monitoring of physiological activities and expanding its application in biomedicine.

Description of drawings

1 is a schematic diagram of a photoacoustic microscopic imaging device for Bessel beams with a large depth of field based on ultrasonic modulation according to an embodiment of the present invention;

Figure 2 shows the radial distribution when the refractive index of the liquid filled in the piezoelectric ceramic tube changes to a positive maximum.

In the figure: 1, pulsed laser; 2, the first condenser lens; 3, the second condenser lens; 4, the first reflector; 5, the second reflector; 6, the piezoelectric ceramic tube; 7, the third Condensing lens; 8. Fourth condensing lens; 9. Fifth condensing lens; 10. Function generator; 11. D-type trigger; 12. Digital pulse delay device; 13. Ultrasonic transducer; 14. Acousto-optic coupling prism; 15, water tank; 16, sample; 17, three-dimensional scanner; 18, amplifier; 19, acquisition card; 20, workstation.

Detailed ways

In order to facilitate understanding of the present invention, the present invention will be described more fully hereinafter with reference to the related drawings. Preferred embodiments of the invention are shown in the accompanying drawings. However, the present invention may be embodied in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that a thorough and complete understanding of the present disclosure is provided.

Unless otherwise defined, 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 terms used herein in the description of the present invention are for the purpose of describing specific embodiments only, and are not intended to limit the present invention.

Example 1

Apparatus and method of the present invention: FIG. 1 is a schematic structural diagram of the entire imaging apparatus of the present invention. The laser light source is a Nd:YLF pulsed laser 1, and the pulsed laser 1 emits a laser with a pulse frequency of 1 KHz, a wavelength of 523 nanoseconds, and a pulse width of 9 nanoseconds. After the laser is emitted, it is shaped to a spot diameter of 20mm by the beam expansion system composed of the first condenser lens 2 and the second condenser lens 3, and then the beam is converted from horizontal to vertical by the first reflector 4, and then vertically incident into the beam. Piezoelectric ceramic round tube 6. The laser light from the piezoelectric ceramic tube passes through the third condenser lens 7, is reflected by the second mirror 5, enters the fourth condenser lens 8, and is finally focused on the sample 16 through the fifth condenser lens 9. The focal region produces a Bessel beam and is excited to produce a photoacoustic signal. The generated photoacoustic signal is detected and received by the acousto-optic coupling prism (numerical aperture is 0.5) 14 and the ultrasonic transducer 13 (center frequency 50MHz, Olympus), and after being amplified by the amplifier 18, it is collected by a signal acquisition card with a sampling rate of 500MHz. 19 acquisitions (number of samples: 1024). The collected signals are transmitted to the workstation 20 for analysis. The function of the water tank 15 is to couple the photoacoustic signal. The three-dimensional scanner 17 is used to adjust the position of the sample 16 in the lateral and axial directions.

Piezoelectric ceramic round tube 6 (PZT-8) is filled with silicone oil (100 cSt). The inner diameter of the piezoelectric ceramic circular tube is 16mm, the outer diameter is 20mm, and the length is 20mm. The refractive index of silicone oil is 1.403 and the speed of sound is 1000m/s. When the piezoelectric ceramic tube is driven by a sinusoidal RF drive signal, the refractive index of the silicone oil appears to change synchronously with the drive signal.

The piezoelectric ceramic tube 6 is driven by a sinusoidal drive signal with a frequency of 707kHz and a peak-to-peak voltage of 10V _pp from the function generator 10 . The three-dimensional scanner 17 will output a position synchronization signal to connect to the D end of the D-type flip-flop every time it moves horizontally. kilohertz). The output end of the D-type flip-flop is connected to a digital pulse delay device 12, and the output signal of the digital pulse delay device 12 is used as the trigger signal of the pulse laser 1, so that the pulse laser 1 is synchronized with the driving signal of the piezoelectric ceramic tube 6, and the laser The pulses are synchronized with a certain vibrational force of the piezoelectric ceramic circular tube 6 . In this way, by adjusting the delay of the digital pulse delay device 12, the laser can emit light when the refractive index of the piezoelectric ceramic tube changes to the positive maximum. At this time, the radial refractive index distribution of the liquid in the piezoelectric ceramic tube is zero-order Bessel. function distribution, as shown in Figure 2. In this way, the beam coming out of the piezoelectric ceramic tube after ultrasonic modulation is a Bessel beam.

The present invention has been described in terms of preferred embodiments, and those skilled in the art will appreciate that various changes or equivalent substitutions may be made to these features and embodiments without departing from the spirit and scope of the present invention. The present invention is not limited by the specific embodiments disclosed herein, and other embodiments falling within the claims of the present application all belong to the protection scope of the present invention.

Claims (6)

1. A large-depth-of-field Bessel beam photoacoustic microscopic imaging device based on ultrasonic modulation comprises: the device comprises a pulse laser (1), a piezoelectric ceramic round tube (6), a three-dimensional scanner (17), a digital pulse delayer (12) and a function generator (10);

the pulse laser (1) is electrically connected with the digital pulse delayer (12) and the workstation (20);

the function generator (10) is electrically connected with the D-type trigger (11) and the piezoelectric ceramic round tube (6);

the workstation (20) is electrically connected with the pulse laser (1), the acquisition card (19) and the three-dimensional scanner (17).

2. A large-depth-of-field Bessel beam photoacoustic microscopic imaging method based on ultrasonic modulation comprises the following steps:

s1: the pulse laser (1) emits laser pulses, the size of a light spot is shaped to be equal to the caliber of the piezoelectric ceramic round tube (6) through the beam expanding system, and then the laser pulses are incident to the piezoelectric ceramic round tube (6) filled with optical transparent liquid;

s2: a function generator (10) is used for applying a sine radio frequency signal to the piezoelectric ceramic circular tube (6), the inner wall and the outer wall of the piezoelectric ceramic circular tube (6) vibrate and generate ultrasonic waves, the ultrasonic waves can periodically modulate the density of local optical transparent liquid, so that the refractive index distribution of the optical transparent liquid is changed, and the refractive index distribution of the optical transparent liquid in the radial direction is represented as zero-order Bessel function distribution and is synchronously changed with the sine radio frequency signal;

s3: the synchronous circuit is used for synchronizing the light emission of the pulse laser (1) and the change of the refractive index of liquid in the piezoelectric ceramic round tube (6), so that the pulse laser (1) emits light on a phase of the change of the refractive index;

the pulse laser (1) emits light when the refractive index of liquid in the piezoelectric ceramic round tube (6) is changed to be positive and maximum by controlling the time delay of the digital pulse time delay device (12), the radial refractive index distribution of the liquid in the piezoelectric ceramic round tube (6) is zero-order Bessel function distribution at the moment, and thus, a light beam which is subjected to ultrasonic modulation and then comes out of the piezoelectric ceramic round tube (6) is a Bessel light beam;

s4, focusing the acquired Bessel light beam on a sample (16) through a fifth condenser lens (9), detecting the generated photoacoustic signal through an acoustic lens, amplifying the photoacoustic signal through an amplifier (18), and finally acquiring the photoacoustic signal by an acquisition card (19);

s5, using the three-dimensional scanner (17) to perform two-dimensional raster scanning to acquire three-dimensional data.

3. The large-depth-of-field Bessel beam photoacoustic microscopy method based on ultrasonic modulation according to claim 2, characterized in that:

the beam expanding system in S1 is composed of a first condenser lens (2) and a second condenser lens (3),

the piezoelectric ceramic round tube (6) is polarized and then is plated on the inner wall and the outer wall to form an inner electrode and an outer electrode, the inner electrode extends from one end to the outer wall, the inner electrode and the outer electrode form two gaps on the outer wall and the end face of the other end,

the laser pulse vertically enters the piezoelectric ceramic round tube (6), in order to avoid asymmetric radial refractive index distribution caused by gravity when the piezoelectric ceramic round tube is horizontally placed, the piezoelectric ceramic round tube (6) is vertically placed, the optical transparent liquid is silicone oil, and the silicone oil has the kinematic viscosity of 50-150cSt, the refractive index of 1-2 and the sound velocity of 800-1200 m/s.

4. The large-depth-of-field Bessel beam photoacoustic microscopy method based on ultrasonic modulation according to claim 2, characterized in that:

s2, the refractive index distribution of the optically transparent liquid after being subjected to ultrasonic modulation is

Wherein n is₀Is the static refractive index of the medium, c_sIs the speed of sound in the medium, ω is the frequency of the drive signal, r and t denote position and time, respectively, J₀Is a zero order Bessel function, n_aIs a constant related to omega, the physical properties of the acoustic medium, and the refractive index distribution behaves as a zero order bessel function and changes synchronously with the drive signal over time.

5. The large-depth-of-field Bessel beam photoacoustic microscopy method based on ultrasonic modulation according to claim 2, characterized in that:

the synchronous circuit of S3 is composed of a three-dimensional scanner (17), a function generator (10), a D-type trigger (11) and a digital pulse delayer (12), wherein the function generator (10) is used for outputting sine radio frequency signals to drive the piezoelectric ceramic round tube (6), the synchronous signals of the sine radio frequency signals are accessed to the clock end of the D-type trigger (11), the three-dimensional scanner (17) outputs position synchronous signals to be accessed to the D end of the D-type trigger (11) every step of horizontal movement, and the position synchronous signals are TTL square wave signals;

according to the characteristic equation of the D-type flip-flop (11), the D-type flip-flop (11) is triggered only when the synchronous signal rises, and the output signal is equal to the input signal; the output end of the D-type trigger (11) is connected with a digital pulse delayer (12), and the output end of the digital pulse delayer (12) is used for triggering the pulse laser (1).

6. The large-depth-of-field Bessel beam photoacoustic microscopy method based on ultrasonic modulation according to claim 2, characterized in that:

s4, the acoustic lens is composed of an ultrasonic transducer (13) and an acoustic-optical coupling prism (14),

the numerical aperture of the acousto-optic coupling prism is 0.5.

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