Coaxial common-optical-path optical coherence elastography probe

Abstract

The invention relates to the technology of medical instruments, in particular to a coaxial common-optical-path optical coherence elastography probe which is used for solving the problem that an existing probe is too large and not suitable for intravascular examination. According to the scheme, the transparent transducer and the lens are coaxially arranged, so that the sound beam and the light beam are coaxial, the probe structure is more compact, and the size of the probe is smaller; the transmitting surface of the transparent transducer is plated with an optical film, and the optical film enables the transmitting surface of the transparent transducer to serve as a reference surface for optical coherence elastography, so that a reference arm and a sample arm can share a part of light path under the condition that the reference arm is not additionally arranged; the problem of phase disturbance caused by system phase noise and piezoelectric material deformation when the transparent transducer works can be solved, and the phase stability is improved.

Description

Technical Field

[0001] The present invention relates to medical device technology, and in particular to a coaxial and co-optical path optical coherence elastic imaging probe. Background Art

[0002] Optical coherence elastography (OCE) uses the phase information of interfering light for imaging, and has the characteristics of high resolution, high displacement detection sensitivity and high accuracy. In the prior art, in order to improve the detection and excitation efficiency, the excitation beam and the detection beam are coaxially arranged. However, in order to achieve coaxial arrangement, it is usually necessary to design a complex optical path structure, such as adding a spectroscope and a reflector to make the light beam bypass the ultrasonic transducer; or design a special transducer structure, such as a hollow ultrasonic transducer, so that the light beam can pass through the middle of the transducer. These coaxial designs cause the problem of excessive probe volume, including both rigid length and probe diameter. Probes with long rigid length and large diameter are difficult to enter narrow lumens, such as small branches of the coronary artery, and cannot provide more detailed inspection results; large diameter probes will also cause compression to the lumen wall, so that the biological tissue is not imaged in its natural state, thereby affecting the accuracy of elasticity measurement.

[0003] Therefore, although there is an urgent need for endoscopic OCE technology for early diagnosis of vulnerable plaques in clinical practice, the current probes are too large and there are no products available for clinical use. Summary of the Invention

[0004] To address the aforementioned issues in the prior art, the present application aims to propose a coaxial, common optical path optical coherence elastography probe. This probe not only simplifies the optical path structure and offers the advantages of miniaturization, but also improves the accuracy of detecting sample deformation. To achieve this technical objective, the specific technical solution is as follows.

[0005] First, this case proposes a coaxial and common optical path optical coherence elastic imaging probe, which arranges a transparent transducer and a lens coaxially to achieve coaxiality between the acoustic beam and the optical beam; the optical coherence elastic imaging uses the emitting surface of the transparent transducer as a reference surface, so that the reference arm and the sample arm share a part of the optical path.

[0006] In one embodiment of the above technical solution, an optical film is coated on the emitting surface of the transparent transducer, and the thickness of the optical film is less than 1 / 4 of the wavelength of the emitted sound wave.

[0007] In one embodiment of the above technical solution, the optical film is made of a waterproof and insulating material.

[0008] In one embodiment of the above technical solution, the optical coherence elastography probe further includes a reflector for changing the propagation path of the light or sound waves emitted by the transparent transducer so that the light or sound waves reach the target sample.

[0009] In one embodiment of the above technical solution, the optical coherence elastic imaging probe also includes an optical fiber for transmitting light. After the light is converged by the lens, it is emitted through the transparent transducer; the output end face of the optical fiber, the front and rear end faces of the lens, and the incident surface of the light entering the transparent transducer are tilted, and the surfaces are parallel and there is a gap. The gap is filled with an optical refractive index matching medium to reduce the energy of the reflected light.

[0010] In one embodiment of the above technical solution, the outer diameter of the transparent transducer is not greater than the largest outer diameter of the optical fiber and the lens, and the height of the reflector is not greater than the largest outer diameter of the optical fiber, the lens and the transparent transducer.

[0011] In one embodiment of the above technical solution, a material that changes the optical refractive index is added to the layers where the front and rear end surfaces of the transparent transducer are located during production.

[0012] In one embodiment of the above technical solution, the optical coherence elastography probe further includes a base and a housing. The base is fixed in the housing. The base is used to place the wires of the transparent transducer. The base is used to fix the lens, transparent transducer and reflector.

[0013] The second method is to propose a transparent transducer, wherein the emitting surface of the transparent transducer is coated with an optical film. The optical film enables the emitting surface to partially transmit and partially reflect light, and enables the reference arm and the sample arm to share a part of the optical path without adding a reference arm.

[0014] The beneficial technical effects of this case are as follows: (1) A special transparent transducer is designed, and its emitting surface is coated with an optical film, so that the reference arm and the sample arm share a portion of the optical path; (2) An optical coherence elastic imaging probe is designed. By using the above-mentioned specially designed transparent transducer, the lens and the transparent transducer are arranged coaxially, so that the acoustic beam and the light beam are coaxial, making the optical coherence elastic imaging probe have the characteristics of simple optical path structure and small size compared with the existing technology. Moreover, the use of the above-mentioned specially designed transparent transducer makes the optical coherence elastic imaging probe have a common optical path structure, thereby overcoming the problems of system phase noise and phase disturbance caused by the deformation of the piezoelectric material when the transparent transducer is working, and making the optical coherence elastic imaging probe have phase stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following is a brief introduction to the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0016] Figure 1 , Schematic diagram of the coaxial structure of the sound beam and light beam using a hollow transducer.

[0017] Figure 2 、 one Schematic diagram of a transparent transducer structure in an embodiment.

[0018] Figure 3 ,use Figure 1 Schematic diagram of the interferometer principle of the common optical path of the transparent transducer. The red solid line in the figure is the path of the light beam in the reference arm, and the blue dotted line is the path of the light beam in the sample arm.

[0019] Figure 4 ,use Figure 1 Schematic diagram of the coaxial structure of the sound beam and light beam of the transparent transducer.

[0020] Figure 5 ,based on Figure 1 A schematic diagram of a structural embodiment of an optical coherence elastography probe with a transparent transducer. DETAILED DESCRIPTION

[0021] Cardiovascular disease causes more deaths than any other disease, with acute coronary syndrome (ACS) caused by ruptured atherosclerotic plaques being one of the leading causes of death. Early identification of vulnerable atherosclerotic plaques is crucial for effective therapeutic intervention. Endoscopic imaging is an important tool for diagnosing cardiovascular disease. Intravascular ultrasound (IVUS) and intravascular optical coherence tomography (OCT) have been widely used in clinical practice. They can visualize the morphology and thickness of intravascular plaques and assess their vulnerability from a morphological perspective, significantly advancing the identification of vulnerable atherosclerotic plaques. However, during the pathological process of atherosclerosis, significant changes in the elasticity of vascular wall tissue occur, such as fibrosis and calcification. These changes often precede visible morphological changes. Therefore, assessing the elastic properties of the vascular wall would be more beneficial for the early diagnosis of vulnerable plaques. However, existing IVUS and OCT techniques for assessing vascular morphology are unable to obtain information about the elasticity of biological tissues.

[0022] Optical coherence elastography, as an extension of phase-sensitive OCT (PS-OCT), is an emerging elasticity inspection technology. Its principle is to apply pressure to biological tissues through external excitation means, such as ultrasound, mechanical stimulation, air pulses, laser pulses, etc., to cause them to deform, and then use PS-OCT to detect the deformation. Under the same pressure, the deformation of the sample varies due to the difference in Young's modulus. The smaller the deformation, the larger the Young's modulus, and thus the harder the sample. Among them, the acoustic radiation force generated by ultrasonic excitation provides the excitation pressure, which has the advantage of being easy to control the force and speed, and is therefore very popular. Therefore, the OCE technology, which combines the fine excitation of ultrasound with the high-sensitivity displacement detection of PS-OCT, can quantify the elastic properties of biological tissues with high precision and is an important tool for elasticity inspection.

[0023] Based on the principle of OCE, the process involves applying an excitation to a sample and then detecting the resulting deformation. Therefore, the quality of OCE imaging is influenced by the performance of both the excitation and detection modules, and is also closely related to the coupling between the excitation and detection modules. Due to the Doppler principle, PS-OCT is most sensitive to displacement along the beam propagation direction. Therefore, applying a force in this direction to cause sample deformation maximizes both excitation and detection efficiency.

[0024] The existing technology arranges the excitation beam and the detection beam coaxially to improve the detection and excitation efficiency. However, the realization of the coaxial arrangement has a complex optical path structure, resulting in a problem of too large a probe volume, which is difficult to be used in clinical practice for early diagnosis of vulnerable plaques. For example, the OCE probe based on the hollow transducer consists of an optical fiber, a Green (gradient refractive index) lens and a hollow ultrasonic transducer. The acoustic beam and the optical beam are coaxial (see Figure 1 ), improving the efficiency of excitation and detection. The probe is capable of scanning OCE imaging, showing the elastic distribution image of the human carotid artery. However, the outer diameter of the probe is 3.5mm, which does not meet the requirement of a probe outer diameter of less than 1mm for intravascular imaging. In intravascular diagnosis scenarios, side-viewing probes are more conducive to examining the vessel wall because they can provide a more comprehensive field of view and a closer distance. However, this probe is a forward-viewing probe, and due to design limitations, it cannot achieve this purpose, so it has limitations in intravascular diagnosis.

[0025] Using optically transparent ultrasonic transducers (transparent transducers) for OCT allows the beam to pass through the transducer, eliminating the problem of the beam bypassing the transducer and achieving coaxial alignment, thereby miniaturizing the probe. However, currently, no technology or products exist for using transparent transducers for OCT. This is because placing a transparent transducer in the optical path of the OCT increases elastic quantization error. During transducer operation, the piezoelectric material deforms. Because the piezoelectric material is located in the optical path, the resulting thickness change can alter the phase of the OCT signal, thereby affecting the accurate detection of sample deformation. For example, lead magnesium niobate titanate (PMN-PT), a piezoelectric material commonly used in transparent transducers, has a thickness of approximately 300 μm at a center frequency of 10 MHz. During operation, the strain is 0.053%, corresponding to a thickness change of approximately 159 nm. Because PS-OCT has nanometer-scale displacement detection sensitivity, deformation of the piezoelectric material can cause significant phase perturbations, disrupting phase stability and significantly affecting the detection of sample deformation. Furthermore, the rotation of the endoscopic OCT probe during imaging can affect the phase stability of the OCT system, severely impacting diagnostic accuracy. On the one hand, the accuracy of OCT deformation detection is affected by phase stability. Insufficient phase stability can lead to inaccurate detected deformations, thus failing to accurately reflect the elasticity of the sample. On the other hand, poor phase stability can make it difficult to detect even small deformations. This reduces the maximum Young's modulus that the system can detect, limiting the dynamic range of tissue elasticity measurements and complicating diagnostic challenges for physicians.

[0026] This proposal proposes a coaxial, shared optical path optical coherence elastography probe. By coaxially arranging a transparent transducer and lens to achieve coaxiality between the acoustic and optical beams, the probe structure becomes more compact and its size is reduced. Furthermore, by coating the emitting surface of the transparent transducer with an optical film, the optical coherence elastography uses the emitting surface of the transparent transducer as a reference surface. This allows the reference arm and sample arm to share a portion of the optical path without adding a reference arm. This shared optical path structure eliminates phase perturbations introduced by transducer deformation and improves phase stability.

[0027] The following will be combined with the Figure 2 one Figure 5 The present invention clearly and completely describes how to implement the technical solution of this case. Obviously, the described implementation methods are only part of the implementation methods of this case, not all of them. Based on the implementation methods of this case, all other implementation methods obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of this application.

[0028] like Figure 2The transparent transducer in one embodiment shown includes a backing, a piezoelectric layer, and a matching layer. The interface between the backing and the outside world is surface ④, and the interface between the matching layer and the outside world is surface ⑤.

[0029] The optical refractive index of the transducer's backing material must be close to that of the piezoelectric material, and the optical refractive index of the matching layer must be close to that of the piezoelectric material. Close refractive index means the difference is within 20% of the larger refractive index. During fabrication of the backing and matching layers, materials that modify the optical refractive index may be added to adjust the refractive index. In one embodiment, the material is in the form of particles or granules.

[0030] The matching layer includes an acoustic matching layer and an optical matching layer. The acoustic matching layer is connected to the piezoelectric material and is a layer of thermoplastic plastic coating (such as polyparaxylene) or transparent glue. The function of the acoustic matching layer is to improve the energy transmission efficiency of sound waves between different media. The optical matching layer is an optical film coated on the acoustic matching layer, which is used to adjust the optical reflectivity of surface ⑤ to avoid signal saturation and meet the imaging signal-to-noise ratio requirements. In one embodiment, the optical film adjusts the optical reflectivity of the emitting surface to 10% or less.

[0031] In order to reduce the energy lost by the sound wave at surface ⑤, the effect of the optical film on surface ⑤ on the acoustic impedance difference of the media on both sides of surface ⑤ should be as small as possible. Therefore, the thickness of the optical film on surface ⑤ should be as thin as possible, preferably less than 1 / 4 of the wavelength of the emitted sound wave. In order to prevent the piezoelectric material from being damaged by water, the optical film on surface ⑤ is made of waterproof and insulating material. In this probe, the OCT reference arm and the sample arm share a part of the optical path. The reference arm is part of the sample arm, so there is no need to set up an additional reference arm, which has the advantages of simplifying the system, saving costs and improving adaptation efficiency. The schematic diagram of the common optical path structure is shown in Figure 3 As shown in the figure, the solid red line represents the path of the light beam in the reference arm, and the dashed blue line represents the path of the light beam in the sample arm. The common optical path structure avoids dispersion and polarization mismatch, improves the system's signal-to-noise ratio, and overcomes system phase noise and phase disturbances caused by piezoelectric material deformation during transparent transducer operation, thereby improving phase stability.

[0032] The transparent transducer is arranged coaxially with the lens so that the light is converged by the lens and then emitted from the transparent transducer, which can realize elastic imaging with the acoustic beam and the light beam coaxial (see Figure 4 ), that is, the propagation of the sound beam and the light beam is along the same axis, and the propagation paths overlap.

[0033] In a specific embodiment of an optical coherence elastography probe, its structure is as follows Figure 5 As shown in FIG, the probe is composed of an excitation module, an optical module, a reflector, a base, and a housing. The excitation module includes a transparent transducer and its wires, and the optical module includes an optical fiber, a lens, and a reflector.

[0034] Specifically, in the optical module, the optical fiber is used to transmit light to the probe. The lens is used to converge the light beam so that the light beam is focused on the target sample. The reflector is used to change the propagation path of the light beam so that the light beam reaches the target sample. The reflector is also used to change the propagation path of the sound wave so that the sound wave reaches the target sample. The reflecting surface of the reflector is the inclined surface of the triangular reflector, and the reflecting surface is coated with a material with strong optical reflectivity, such as aluminum, silver, gold, etc., and has the function of reflecting the 0CT light beam to the area to be imaged. The reflector is a hard material and is integrated with the base. It has the function of reflecting the sound wave to the area to be imaged, and the vibration and deformation are as small as possible. Optical fibers, lenses and reflectors are common optical components, all of which are small-sized miniature components.

[0035] In the excitation module, the wire is placed between the base and the shell and connected to the transparent transducer. The transparent transducer is used to emit excitation sound waves to drive the sample to deform. The transparent transducer includes a piezoelectric material, a backing and a matching layer. When voltage is applied to both ends of the piezoelectric material, the electrical energy generates mechanical vibrations, and the vibrations propagate in the form of sound waves, becoming a sound beam. However, the sound beam has energy distribution on both the front and back surfaces of the material. The function of the backing is to absorb the sound wave energy on the back and reduce the influence of interfering clutter. The matching layer is the emitting surface of the transparent transducer, and its outermost layer has an optical film that can adjust the surface to partially transmit and partially reflect light to achieve a common optical path structure.

[0036] In an optical coherence elastography probe, light travels through an optical fiber to a lens, where it converges and then exits through a transparent transducer. The coaxial arrangement of the lens and transparent transducer enables elastic imaging with the acoustic and optical beams coaxial, reducing the probe's size. To further enhance the probe's compactness and diameter, the outer diameter of the transparent transducer should be no larger than the largest of the optical fiber and lens, and the height of the reflector should be no greater than the largest of the three diameters.

[0037] To reduce light reflection and imaging artifacts, the fiber end face (surface ①), the front and rear end faces of the lens (surfaces ② and ③), and surface ④ are inclined surfaces, and the surfaces should be parallel to each other. For example, the inclination angle is 8°±5°. There is a gap between surfaces ① and ②, and there is a gap between surfaces ③ and ④, and the gap is filled with an optical refractive index matching medium material. Surface ④ can be made by forming the backing material in a mold with an inclined angle and then bonding it to the piezoelectric material.

[0038] In summary, this solution achieves coaxiality between the acoustic and optical beams, resulting in a more compact and smaller probe structure, making it more suitable for intravascular examinations. Furthermore, by coating the emitting surface of the transparent transducer with an optical film, the optical coherence elastography uses the emitting surface of the transparent transducer as a reference surface, enabling the reference arm and sample arm to share a portion of the optical path. This simplifies the system, saves costs, and improves adaptation efficiency. Furthermore, this solution improves phase stability without incorporating complex structures, resulting in more accurate deformation detection and a simpler structure for greater practicality.

[0039] Although the embodiments of the present invention have been described above with reference to the accompanying drawings, the present invention is not limited to the above-mentioned specific embodiments and application fields. The above-mentioned specific embodiments are merely illustrative and instructive, and are not restrictive. A person skilled in the art, guided by this specification and without departing from the scope of protection of the claims of the present invention, may also devise various forms, all of which fall within the scope of protection of the present invention.

Claims

1. A coaxial and co-optical optical coherence elastography probe, characterized by: The optical coherence elastic imaging probe realizes the coaxiality of the acoustic beam and the optical beam by coaxially arranging the transparent transducer and the lens; The optical coherence elastic imaging uses the emission surface of the transparent transducer as a reference surface, so that the reference arm and the sample arm share a part of the optical path.

2. The optical coherence elastography probe according to claim 1, wherein: An optical film is plated on the emission surface of the transparent transducer, and the thickness of the optical film is less than 1 / 4 of the wavelength of the emitted sound wave.

3. The optical coherence elastography probe according to claim 1, wherein: The optical film is made of waterproof and insulating material.

4. The optical coherence elastography probe according to claim 1, wherein: The optical coherence elastic imaging probe further includes a reflector for changing the propagation path of the light or sound waves emitted by the transparent transducer so that the light or sound waves reach the target sample.

5. The optical coherence elastography probe according to claim 4, characterized in that: The optical coherence elastic imaging probe further includes an optical fiber for transmitting light, which is converged by a lens and then emitted through a transparent transducer; The output end face of the optical fiber, the front and rear end faces of the lens, and the incident surface of the transparent transducer are tilted, and the surfaces are parallel and have gaps. The gaps are filled with an optical refractive index matching medium to reduce the energy of the reflected light.

6. The optical coherence elastography probe according to claim 5, characterized in that: The outer diameter of the transparent transducer is not greater than the largest outer diameter of the optical fiber and the lens, and the height of the reflector is not greater than the largest outer diameter of the optical fiber, the lens and the transparent transducer.

7. The optical coherence elastography probe according to claim 1, wherein: The difference in refractive index between the layers in the transparent transducer is within 20% of the larger refractive index.

8. The optical coherence elastography probe according to claim 1, wherein: When the layers of the front and rear end surfaces of the transparent transducer are manufactured, a material that changes the optical refractive index is added.

9. The optical coherence elastography probe according to claim 5, characterized in that: The optical coherence elastic imaging probe further comprises a base and a shell. The base is fixed in the shell. The base is used to place the wires of the transparent transducer. The base is used to fix the lens, the transparent transducer and the reflector.

10. A transparent transducer, characterized in that: The emitting surface of the transparent transducer is coated with an optical film, which enables the emitting surface to partially transmit and partially reflect light, so that the reference arm and the sample arm can share a part of the optical path without adding a reference arm.

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