CN114209275A

CN114209275A - Opto-acoustic sensor compatible with OCT

Info

Publication number: CN114209275A
Application number: CN202111513505.4A
Authority: CN
Inventors: 张金英; 赵冬冬; 史亦凡; 李德芳
Original assignee: Beijing Institute of Technology BIT
Current assignee: Beijing Institute of Technology BIT
Priority date: 2021-12-10
Filing date: 2021-12-10
Publication date: 2022-03-22

Abstract

The invention relates to an OCT (optical coherence tomography) -compatible photoacoustic sensor, belonging to the technical field of photoacoustic imaging and ultrasonic sensors. The sensor is small in size and flexible, and can be directly attached to the surface of eyes like wearing contact lenses after eye drops are dripped in advance, so that the sensor can meet the requirements of clinical application. Moreover, the sensor has a central through hole, and does not cover the pupil when in use, so the sensor is compatible with ophthalmic OCT. Meanwhile, pulsed light of the photoacoustic imaging system can be transmitted to the interior of an eyeball through a central through hole of the sensor, a to-be-detected object at the eye bottom is stimulated to generate photoacoustic signals (ultrasonic waves), the ultrasonic waves are transmitted to the eye surface from the eye bottom, due to the fact that eye drops are dripped in advance, sound waves can be sufficiently coupled and transmitted to the photoacoustic sensor attached to the surface of the eye, and the sound waves are converted into electric signals after being collected by the sensor. The invention can conveniently acquire photoacoustic images under the condition of being compatible with an OCT imaging system, and is a new technology with great clinical application potential.

Description

Opto-acoustic sensor compatible with OCT

Technical Field

The invention relates to an OCT (optical coherence tomography) -compatible photoacoustic sensor, belonging to the technical field of photoacoustic imaging and ultrasonic sensors.

Background

Photoacoustic imaging is a new biomedical imaging technique. Compared with the traditional pure optical imaging technology, such as Optical Coherence Tomography (OCT) and the like, the photoacoustic imaging technology integrates the advantages of optical resolution and acoustic penetration depth, well avoids the limitation of small penetration depth caused by light scattering, and has deeper detection depth; compared with the traditional ultrasonic imaging technology, the contrast of the photoacoustic imaging technology is derived from the difference of the light absorption degrees of the objects to be measured, the imaging contrast is not high due to the fact that the acoustic impedance of the target objects is not large, the transverse resolution of the photoacoustic imaging depends on the optical focusing performance of the system, and therefore the photoacoustic imaging has higher resolution than the ultrasonic imaging. Therefore, the photoacoustic imaging technology with multiple advantages of no mark, no damage, no radiation, strong imaging specificity and the like has important application prospect for researching the morphological structure, physiological characteristics, pathological characteristics, metabolic function and the like of biological tissues.

Human ocular fundus retina and choroid blood vessels are observation windows of systemic vascular related diseases, and morphological changes of retinal blood vessels can be observed from the retinal blood vessels at an early stage, such as arteriosclerosis, hematopathy, retinal tumor, diabetes and the like. Due to the special physiological structure of the eyeball, laser light excited by a light probe in the photoacoustic system can pass through the pupil and is focused to the blood vessel of the fundus through the crystalline lens, and the human eye contains a large amount of soft tissue with good light absorption characteristics, so that the photoacoustic imaging system can well monitor and check the blood vessel of the fundus.

At present, items such as OCT, ophthalmic B-mode ultrasound, UBM and the like are mainly used in ophthalmic examination. Each of these imaging modalities has its advantages, but fails to provide high resolution examination of the retina deeper in the eye so that a timely diagnosis of certain vascular related diseases cannot be made. Photoacoustic imaging is expected to break this limitation due to its advantages described above. At present, a few scholars clearly image the eyes of animals through a photoacoustic imaging system, but the adopted method adopts an ultrasonic transducer with larger volume and a water tank to collect photoacoustic signals. Although images of the interior of the eyeball can also be obtained, such a system has the following disadvantages: firstly, the whole system is bulky; secondly, the detection sensitivity of the system is not high; third, it is difficult to apply to clinical applications due to the particularity of human eyes.

Disclosure of Invention

The invention aims to solve the problem that a small photoacoustic sensor is lacked in the clinical application of ophthalmology in the trend of photoacoustic imaging technology, and provides a photoacoustic sensor compatible with ophthalmic OCT. The sensor is small in size and flexible, and can be directly attached to the surface of eyes like wearing contact lenses after eye drops are dripped in advance, so that the sensor can meet the requirements of clinical application. Moreover, the sensor has a central through hole, and does not cover the pupil when in use, so the sensor is compatible with ophthalmic OCT. Meanwhile, pulsed light of the photoacoustic imaging system can be transmitted to the interior of an eyeball through a central through hole of the sensor, a to-be-detected object at the eye bottom is stimulated to generate photoacoustic signals (ultrasonic waves), the ultrasonic waves are transmitted to the eye surface from the eye bottom, due to the fact that eye drops are dripped in advance, sound waves can be sufficiently coupled and transmitted to the photoacoustic sensor attached to the surface of the eye, and the sound waves are converted into electric signals after being collected by the sensor. The photoacoustic sensor is closely attached to the surface of an eye and fixed, and the pulsed light of the photoacoustic imaging system is moved to perform scanning imaging, so that a photoacoustic image is obtained. The invention can conveniently acquire photoacoustic images under the condition of being compatible with an OCT imaging system, and is a new technology with great clinical application potential.

The purpose of the invention is realized by the following technical scheme.

An OCT compatible photoacoustic sensor, comprising: the probe comprises a probe shell, an upper electrode, a piezoelectric film, a lower electrode, an acoustic matching layer, an eye drop couplant, eyeballs and optical signals.

According to different actual requirements, the photoacoustic sensor compatible with the OCT has three structures of the internal piezoelectric film. The first structure is a bending self-focusing piezoelectric film, which enables the photoacoustic coaxial confocal to greatly improve the detection sensitivity and the system resolution, and can realize the imaging of a certain point with different depths in the center of the pupil of the human eye through the change of the curvature of the piezoelectric film. The second structure is a planar piezoelectric ultrasonic sensor, which can detect the maximum range signals on both sides of the fundus although the central area of the fundus cannot be detected due to the through hole with the same size as the pupil left in the center of the transducer of the present invention. The third piezoelectric film structure is a plane structure and is obliquely arranged according to a certain angle, so that an effective area of the flexible sensor with the structure, which can receive signals after being attached to the surface of the eye, can cover the retina and choroid blood vessels of the eye fundus in a large range, and the detection area is large.

The first structure: the probe shell is provided with a hole at the top end and is made of polymers such as PDMS; the upper electrode, the bent self-focusing piezoelectric film, the lower electrode and the acoustic matching layer are provided with holes in the centers and are sequentially attached to each other; attaching the acoustic matching layer to the surface of the eyeball through an eye drop couplant; the optical signal irradiates the eyeball through the central through hole of the probe shell, the upper electrode, the bending self-focusing piezoelectric film, the lower electrode and the acoustic matching layer. As in fig. 1.

The second structure: the probe shell is provided with a hole at the top end and is made of polymers such as PDMS; the upper electrode, the flat-field piezoelectric film, the lower electrode and the acoustic matching layer are provided with holes in the centers and are sequentially attached to each other; attaching the acoustic matching layer to the surface of the eyeball through an eye drop couplant; the optical signal irradiates the eyeball through the central through hole of the probe shell, the upper electrode, the flat-field piezoelectric film, the lower electrode and the acoustic matching layer. As shown in fig. 2.

The third structure: the probe shell is provided with a hole at the top end and is made of polymers such as PDMS; the upper electrode, the flat field inclined piezoelectric film, the lower electrode and the acoustic matching layer are provided with holes in the centers and are sequentially attached to each other; attaching the acoustic matching layer to the surface of the eyeball through an eye drop couplant; the optical signal irradiates the eyeball through the central through hole of the probe shell, the upper electrode, the flat field inclined piezoelectric film, the lower electrode and the acoustic matching layer. As shown in fig. 3.

The OCT-compatible photoacoustic sensor with the structure can be finally worn on eyes directly, and liquid such as eye drops is used as a coupling agent. The focused optical signal directly passes through the pupil to the bottom of the eye through the central through hole of the sensor, irradiates retina or choroid blood vessels to excite the photoacoustic signal, and is finally received by the OCT-compatible photoacoustic sensor. The photoacoustic sensor compatible with the OCT effectively avoids a water tank used when the traditional photoacoustic probe detects the photoacoustic signal of the fundus, can reduce the volume of the system, improves the detection sensitivity, and provides possibility for the photoacoustic imaging system to be applied to ophthalmology clinic.

When the photoacoustic sensor compatible with OCT is in a third structure, the piezoelectric film is in a plane structure and is obliquely arranged according to a certain angle, so that the photoacoustic sensor compatible with OCT is used for emitting the acoustic waves, and the acoustic waves at two sides are intersected at the bottom end. Because the sound waves on two sides of the intersection are transmitted by the same transducer, the same frequency, consistent vibration direction and fixed phase difference are satisfied, and sound wave interference is generated at the intersection part. When a certain area in the eyeball interferes with the acoustic wave, the tissue of the interference area is affected, so that the phase, the wavelength or the intensity of the optical signal emitted by the photoacoustic system and the OCT is modulated by the optical signal, and the system can obtain more obscure information in the eyeball. The inclination angle of the piezoelectric film of the OCT-compatible photoacoustic sensor not only determines the size of an acoustic wave intersection area, but also determines an interference pattern of the acoustic wave. The relationship between the fringe spacing in the interference pattern and the angle at which the piezoelectric film is tilted, as shown in fig. 4, can be obtained from equation 1:

in formula 1, λ is the acoustic wave wavelength, α is the inclination angle of the piezoelectric film, and Δ x is the fringe spacing. Different interference areas and interference patterns caused by different inclination angles of the piezoelectric film can obtain different blood vessel information in the eyeball.

The optoacoustic sensor compatible with OCT has the advantages that the structure of the central through hole enables optical signals of OCT in ophthalmology and pulse optical signals of an optoacoustic imaging system to be transmitted to the interior of eyeballs through pupils, the size of the central through hole is set to be consistent with the pupils of the eyeballs (the diameter is 2mm to 5mm), and the optoacoustic imaging system is photoacoustic coaxial due to the structure of the optoacoustic sensor, so that imaging resolution can be remarkably improved, and detection depth is greatly increased. When the photoacoustic sensor compatible with the OCT is attached to eyes, liquid coupling agents such as eye drops and the like need to be dripped in advance, a water tank used by the existing system is perfectly replaced, the volume of a detection system is greatly reduced, the comfort and the convenience of a patient during detection are improved, and the photoacoustic imaging system is possible to move to ophthalmology clinic. The OCT-compatible photoacoustic sensor adopts polymers such as PDMS (polydimethylsiloxane) as a backing and an outer protective layer, and has excellent biocompatibility, stability and formability; and piezoelectric films such as PZT, zinc oxide, aluminum nitride and PVDF are used as energy conversion materials, so that the bandwidth is large, the sensitivity is high, and the realization of high resolution is further ensured.

Advantageous effects

1. The photoacoustic sensor compatible with OCT adopts the flat field inclined piezoelectric film, so that the signal detection area of the photoacoustic sensor covers the blood vessel area of the fundus to the maximum extent.

2. The photoacoustic sensor compatible with the OCT adopts the bent self-focusing piezoelectric film, so that the photoacoustic coaxial confocal optical system has high detection sensitivity and high resolution, and can realize imaging of a certain point with different depths in the center of a pupil of a human eye through the change of the curvature of the piezoelectric film.

3. The photoacoustic sensor compatible with OCT adopts the flat field piezoelectric film, so that the signals of the photoacoustic sensor can detect the maximum range of two sides of the center of the fundus.

4. The photoacoustic sensor compatible with the OCT adopts the flat field inclined piezoelectric film to enable sound waves to intersect and interfere at the bottom, so that optical signals are modulated, and more eye information is acquired.

5. The photoacoustic sensor compatible with the OCT adopts the central through hole structure, so that not only can pulse light signals of a photoacoustic imaging system be directly transmitted to the eye ground through the central through hole, but also the photoacoustic sensor is compatible with an ophthalmic OCT system, so that the light signals can be directly transmitted to the eye ground through the central through hole, and the compatibility of the photoacoustic imaging system and the ophthalmic OCT is realized.

6. The photoacoustic sensor compatible with the OCT removes a water tank used by the traditional photoacoustic probe for acquiring photoacoustic signals, and directly drops coupling agents such as eye drops and the like on the surface of eyes, so that the bonding of the miniaturized photoacoustic sensor and the eyes is conveniently realized, and the photoacoustic imaging system becomes possible in ophthalmology clinic.

7. The photoacoustic sensor compatible with OCT adopts the piezoelectric film as the transduction material and adopts polymer materials such as PDMS (polydimethylsiloxane) as the backing and the outer protection layer, and has the advantages of small volume, high sensitivity, good flexibility, good biocompatibility and no harm to human eyes.

Drawings

FIG. 1 is a block diagram of an OCT-compatible photoacoustic sensor with a curved self-focusing piezoelectric film

FIG. 2 is a block diagram of an OCT-compatible photoacoustic sensor with a flat-field piezoelectric film

FIG. 3 is a block diagram of an OCT compatible photoacoustic sensor with flat field tilted piezoelectric film

FIG. 4 is a graph showing the relationship between the fringe spacing and the acoustic angle during acoustic interference

FIG. 5 is a simulation of an OCT-compatible photoacoustic sensor using a curved self-focusing piezoelectric film

FIG. 6 is a simulation of an OCT-compatible photoacoustic sensor using a flat field piezoelectric film

Figure 7 is a simulation of an OCT compatible photoacoustic sensor using a flat field tilted (5 ° tilt, 2mm central via diameter) piezoelectric film.

FIG. 8 is a simulation of an OCT compatible photoacoustic sensor using a flat field tilted (8 tilt, 5mm center via diameter) piezoelectric film.

The device comprises a probe shell 1, an upper electrode 2, a flat field inclined piezoelectric film 3, a lower electrode 4, an acoustic matching layer 5, an eye drop couplant 6, an eyeball 7 and an optical signal 8.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be further described in detail with reference to the following embodiments and accompanying drawings.

Example 1

As shown in fig. 1, an OCT compatible photoacoustic sensor includes: the probe comprises a probe shell 1, an upper electrode 2, a bending self-focusing piezoelectric film 3, a lower electrode 4, an acoustic matching layer 5, an eye drop couplant 6, an eyeball 7 and an optical signal 8.

The probe shell 1 is provided with a through hole at the top end, the size of the through hole is 2mm, the probe shell is made of PDMS materials and is positioned on the outer sides of the upper electrode 2, the bent self-focusing piezoelectric film 3, the lower electrode 4 and the acoustic matching layer 5; 2mm through holes are formed in the centers of the upper electrode 2, the bent self-focusing piezoelectric film 3, the lower electrode 4 and the acoustic matching layer 5; the upper electrode 2 is positioned between the probe shell 1 and the bending self-focusing piezoelectric film 3, and the thickness is 1 mu m; the thickness of the curved self-focusing piezoelectric film 3 is 100 μm, is a curved surface with the curvature radius of 25.4mm, and is arranged between the upper electrode 2 and the lower electrode 4; the thickness of the lower electrode 4 is 1 μm, and the lower electrode is positioned between the bending self-focusing piezoelectric film 3 and the acoustic matching layer 5; the acoustic matching layer 5 with the thickness of 24.1 μm is arranged below the lower electrode 4; the acoustic matching layer 5 is attached to an eyeball 7 through an eye drop couplant 6; the optical signal 8 enters the eyeball 7 through the central through hole of the probe shell 1, the upper electrode 2, the bent self-focusing piezoelectric film 3, the lower electrode 4 and the acoustic matching layer 5.

Because the sensor adopts the piezoelectric film as the transduction material, the performance of receiving the acoustic signal can be obtained by simulating the distribution of the transmitting sound field of the sensor based on the reciprocity of the piezoelectric effect and the inverse piezoelectric effect of the piezoelectric material. And carrying out simulation experiments on the designed structure to obtain the OCT-compatible photoacoustic sensor with the central working frequency of about 30 MHz. As shown in fig. 5, the OCT-compatible photoacoustic sensor has a good focusing effect at a certain point in the eyeball. The sensor for gaze imaging can greatly improve the detection sensitivity.

Example 2

On the basis of embodiment 1, only the curved arcs of the probe shell 1, the upper electrode 2, the curved arc piezoelectric film 3, the lower electrode 4 and the acoustic matching layer 5 are changed into a flat field, so that the transducer can detect information on two sides of the fundus oculi in the largest range, and the rest of the structure is the same as that of embodiment 1, as shown in fig. 2.

And carrying out simulation experiments on the designed structure to obtain the OCT-compatible photoacoustic sensor with the central working frequency of about 30 MHz. As shown in fig. 6, the area that can be detected by this OCT-compatible photoacoustic sensor covers the maximum range on both sides of the center of the fundus.

Example 3

On the basis of the embodiment 1, only the probe shell 1, the upper electrode 2, the curved arc piezoelectric film 3, the lower electrode 4 and the acoustic matching layer 5 are changed from a curved arc to an inclined flat field, the inclination angle of the flat field inclined piezoelectric film 3 is 5 degrees, and the rest of the structure is the same as that of the embodiment 1, as shown in fig. 3.

And carrying out simulation experiments on the designed structure to obtain the OCT-compatible photoacoustic sensor with the central working frequency of about 30 MHz. As shown in fig. 7, the region that can be detected by this OCT-compatible photoacoustic sensor covers a large range of fundus parts.

Example 4

On the basis of embodiment 3, only the inclination angles of the probe shell 1, the upper electrode 2, the flat-field inclined piezoelectric film 3, the lower electrode 4 and the acoustic matching layer 5 are changed from 5 ° to 8 °, and the diameters of the central through holes of the probe shell 1, the upper electrode 2, the flat-field inclined piezoelectric film 3, the lower electrode 4 and the acoustic matching layer 5 are changed from 2mm to 5mm, and the rest of the structure is the same as that of embodiment 3.

And carrying out simulation experiments on the designed structure to obtain the OCT-compatible photoacoustic sensor with the central working frequency of about 30 MHz. As shown in fig. 4, by changing the inclination angle, the region where the acoustic wave interference is obtained and the interference fringes change. As shown in fig. 8, the region that can be detected by this OCT-compatible photoacoustic sensor covers a large range of fundus parts.

The above detailed description is intended to illustrate the objects, aspects and advantages of the present invention, and it should be understood that the above detailed description is only exemplary of the present invention and is not intended to limit the scope of the present invention, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims

1. An OCT-compatible photoacoustic sensor, comprising: the middle of the sensor is provided with a light transmission hole, and the sensor can be attached to an eyeball; the sensor is placed on the eye, the light holes are ensured to correspond to the pupil, and the information of the fundus oculi optic nerve vessels is obtained through photoacoustic imaging and OCT dual-mode examination.

2. The OCT-compatible photoacoustic sensor of claim 1, wherein: the sensor comprises a piezoelectric film, a probe shell, an upper electrode, a lower electrode and an acoustic matching layer; the upper electrode, the piezoelectric film, the lower electrode and the acoustic matching layer are provided with holes in the centers and are sequentially attached to each other; the probe shell covers the probe.

3. The OCT-compatible photoacoustic sensor of claim 1, wherein: the piezoelectric film shape includes: curved self-focusing, flat field and flat field tilted shapes.

4. The OCT-compatible photoacoustic sensor of claim 3, wherein: the inclination angle of the piezoelectric film can determine the size of an intersecting area of the sound waves and can also determine an interference pattern of the sound waves; the relationship between the fringe spacing in the interference pattern and the inclination angle of the piezoelectric film is obtained by formula 1;

wherein, λ is the acoustic wave wavelength, α is the inclination angle of the piezoelectric film, and Δ x is the fringe spacing.

5. The OCT-compatible photoacoustic sensor of claim 1, wherein: the size of the light hole is the same as that of the pupil.

6. The OCT-compatible photoacoustic sensor of claim 1, wherein: the piezoelectric thin film material comprises PZT, zinc oxide, aluminum nitride and PVDF.

7. The OCT-compatible photoacoustic sensor of claim 2, wherein: the probe housing material comprises a polymer.

8. The OCT-compatible photoacoustic sensor of claim 7, wherein: polymers include PDMS, hydrogels.

9. The OCT-compatible photoacoustic sensor of claim 1, wherein: the inclined flat field piezoelectric film obtains the interference of sound waves in different areas and obtains different interference fringes to modulate optical signals in an OCT and photoacoustic system by adjusting the inclination angle of the inclined flat field piezoelectric film.

10. The OCT-compatible photoacoustic sensor of claim 1, wherein: the OCT-compatible photoacoustic sensor with the structure can be finally and directly worn on eyes, and liquid such as eye drops is used as a coupling agent; the focused optical signal directly passes through the pupil through the central through hole of the sensor to reach the bottom of the eye, irradiates retina or choroid blood vessels to excite the photoacoustic signal, and is finally received by the photoacoustic sensor compatible with OCT; the photoacoustic sensor compatible with the OCT effectively avoids a water tank used when the traditional photoacoustic probe detects fundus photoacoustic signals, can reduce the volume of the system, improves the detection sensitivity, and provides possibility for the photoacoustic imaging system to move to ophthalmic clinical application.