Bimodal optical coherence elastography device and method

Abstract

The invention discloses a bimodal optical coherence elastography device and method, and the device comprises an excitation unit which is used for generating a sound field; the imaging unit is an optical coherence tomography system and is used for detecting vibration of the sample to be detected, namely strain response and elastic wave response; and the coupling unit is provided with a sound reflecting surface with a middle through hole and is used for reflecting the sound field generated by the excitation unit, so that the detection light beam emitted by the imaging unit and the sound field emitted by the excitation unit are coupled and irradiated on the same side of the to-be-detected sample. According to the invention, the multi-beam optical coherence tomography system is utilized to emit two or more detection beams to carry out bimodal elastic imaging, high-resolution strain information and quantitative elastic information of the sample to be detected can be obtained at the same time, and the problem that strain imaging and elastic wave imaging cannot be carried out at the same time in the prior art is solved.

Description

Technical Field

[0001] The present invention relates to the field of elastic imaging, and in particular to a dual-modality optical coherence elastic imaging device and method. Background Art

[0002] Physiological and pathological changes in tissues are often accompanied by changes in biomechanical properties such as tissue elasticity. For example, skin diseases such as systemic sclerosis and melanoma can cause patients' skin to become hard and thick. Tissue elasticity testing is an important auxiliary means for disease detection and treatment, and can be used for clinical diagnosis of diseases.

[0003] As a visual elasticity measurement method, elasticity imaging technology uses an imaging system to measure the mechanical response of tissues such as deformation and mechanical wave propagation under stimulation, thereby obtaining the elastic modulus of tissues. Among the many elasticity imaging technologies, Optical Coherence Elastography (OCE) is an elasticity detection technology based on Optical Coherence Tomography (OCT), which has the advantages of non-invasiveness, high resolution and high displacement sensitivity, and is widely used in the characterization of mechanical properties of biological soft tissues.

[0004] OCE technology often uses acoustic radiation force (ARF) as an excitation source. Unlike piezoelectric transducers, laser pulses and other excitation methods, ARF can stimulate the mechanical response of deep tissues. In order to meet the requirements of clinical disease detection, the sound beam of the ultrasonic transducer in the OCE device and the detection beam of OCT must be emitted on the same side of the tissue. At present, there are two main installation methods that can meet the requirements that the ARF and the detection light are on the same side and both are perpendicular to the sample surface: one method is to use a circular ultrasonic focusing transducer, and the OCT detection beam passes through the middle through hole of the circular ultrasonic transducer for detection. However, in this method, the lateral scanning distance of the OCT detection light is limited by the size of the central hole of the transducer (see the prior art [1] Yueqiao Qu, Youmin He, Yi Zhang, et al. Quantified elasticity mapping of retinal layers using synchronized acoustic radiation force optical coherence elastography [J]. Biomedical Optics Express, 2018, 9 (9): 4054-4063); the other method is to use a coupling unit (such as a glass slide) to achieve the ARF and OCT detection light on the same side of the sample, in a parallel or approximately parallel direction. In this method, the OCT detection light will be partially reflected by the glass slide, resulting in a decrease in the OCT signal-to-noise ratio. In the phase-sensitive displacement detection algorithm commonly used in OCE, the displacement sensitivity is proportional to the OCT signal-to-noise ratio. Therefore, this method reduces the sensitivity of displacement measurement. (See prior art [2] Chongyang Wang, Fan Fan, Jiawei Ma, et al. Opticalcoherence elastography under homolateral parallel acoustic radiation forceexcitation for ocular elasticity quantification [J]. Optics Letters, 2024, 49(10): 2817-2820)

[0005] On the other hand, there are elastic imaging methods of different modalities in OCE technology, such as strain imaging and elastic wave imaging. The strain imaging method is easy to obtain high-resolution elasticity maps, while the elastic wave imaging method is easy to obtain quantitative elastic results. These two modal elastic imaging methods have their own advantages, but the existing OCE technology cannot obtain high-resolution strain imaging results and quantitative elastic wave imaging results at the same time. Summary of the invention

[0006] The purpose of the present invention is to overcome the shortcomings of the above-mentioned prior art and provide a dual-modality optical coherence elastic imaging device and method. The technical solution of the present invention is briefly described below, and more details will be described in specific embodiments in conjunction with the accompanying drawings later.

[0007] The technical solution of the present invention is as follows:

[0008] A dual-modality optical coherence elastic imaging device, characterized in that it comprises:

[0009] An excitation unit, for generating a sound field;

[0010] An imaging unit, which is an optical coherence tomography system, is used to detect the vibration of the sample to be tested, namely, the strain response and the elastic wave response;

[0011] A coupling unit having an acoustic reflection surface with a middle through hole, which is used to reflect the acoustic field generated by the excitation unit, so as to couple the detection beam emitted by the imaging unit with the acoustic field emitted by the excitation unit; wherein the detection beam irradiates the sample to be tested through the middle through hole of the coupling unit and the area outside the edge of the coupling unit, and the acoustic field emitted by the excitation unit is reflected by the acoustic reflection surface of the coupling unit and then transmitted to the sample to be tested along the same direction or a similar direction as the detection beam, thereby forming an acoustic radiation force field.

[0012] An excitation unit is used to generate an acoustic field, an ARF is formed in the sample to be tested and vibration is induced, and an imaging unit is used to measure the vibration in the sample to be tested. The coupling unit is used to achieve coupling between the detection light beam emitted by the imaging unit and the acoustic field generated by the excitation unit. Specifically, the detection light beam can irradiate the sample to be tested through the middle through hole of the coupling unit or through the area outside the edge of the coupling unit, and the acoustic field is reflected by the acoustic reflection surface of the coupling unit and then irradiates the sample to be tested in the same direction as the detection light beam, thereby achieving the purpose of the acoustic beam and the detection light beam being incident on the sample to be tested on the same side of the sample. In addition, since the detection light beam passes through the middle through hole of the coupling unit or the area outside the edge of the coupling unit and does not pass through the acoustic reflection structure of the coupling unit, there will be no loss of light energy in the detection light beam during the process of passing through the coupling unit.

[0013] Optionally, the light source in the imaging unit may be a swept-frequency light source or a broadband low-coherence light source.

[0014] Optionally, the imaging unit can emit two or more probe lights at the same time; through the method of optical fiber delay or spatial delay, each probe light can have a different phase delay, so as to obtain structural information obtained by different probe lights at different depth positions in a structural image.

[0015] A dual-modality optical coherence elastic imaging method, characterized in that the method comprises the following:

[0016] The acoustic field emitted by the excitation unit is used to form an acoustic radiation force field in the sample to be tested, inducing deformation and elastic waves in the sample to be tested; the OCT system emits two or more detection light signals, wherein one or more detection light beams illuminate the sample to be tested through the middle through hole of the coupling unit, and the remaining detection light illuminates the sample to be tested through the area outside the edge of the coupling unit; different beams of detection light have different optical paths, and data collected by different detection lights can be obtained at different depth areas of the OCT image; the data collected by the detection light through the middle through hole of the coupling unit (the first group of data) is used to measure the strain information of the sample, and the data collected by the detection light that does not pass through the middle through hole of the coupling unit (the second group of data) is used to measure the elastic wave information of the sample.

[0017] Optionally, the signal transmitted to the ultrasonic transducer is a pulse modulation signal or a continuous wave modulation signal, or may be a chirp modulation signal.

[0018] Optionally, the processing step of the first set of data specifically includes: calculating the displacement between two moments of each position of the sample to be tested, thereby obtaining strain parameters and strain images. The processing step of the first set of data includes but is not limited to any method of calculating the displacement or deformation of the sample to be tested from the data.

[0019] Optionally, the processing step of the second set of data specifically includes: calculating the displacement of each position of the sample to be tested over time, thereby calculating the propagation speed of the elastic wave, and then obtaining viscoelastic parameters (such as Young's modulus) and viscoelastic images. The processing step of the second set of data includes but is not limited to any method of deriving the viscoelasticity of the sample to be tested from the properties of the elastic wave.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1. Using a multi-beam optical coherence tomography system for dual-modal elastic imaging can simultaneously obtain high-resolution strain information and quantitative elastic information of the sample to be tested, thus solving the problem that the existing technology cannot simultaneously perform strain imaging and elastic wave imaging.

[0022] 2. Compared with the prior art [1], the device of the present invention is not limited by the middle through hole of the annular ultrasonic transducer and can perform lateral scanning over a longer range.

[0023] 3. Compared with the prior art [2], the OCT detection light in the device of the present invention does not lose energy due to reflection from the coupling unit, thereby having a higher displacement detection sensitivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1It is a schematic structural diagram of an optical coherence elastic imaging system using a ring-shaped ultrasonic transducer in the prior art;

[0025] Figure 2 It is a schematic structural diagram of an optical coherence elastic imaging system using a coupling unit in the prior art;

[0026] Figure 3 is a schematic structural diagram of an optical coherence elastic imaging system provided by an embodiment of the present invention;

[0027] Figure 4 is a schematic diagram of the structure of an excitation unit provided in an embodiment of the present invention;

[0028] Figure 5 is a schematic structural diagram of a fiber-optic imaging unit provided in an embodiment of the present invention;

[0029] Figure 6 is a schematic structural diagram of a spatial imaging unit provided by an embodiment of the present invention;

[0030] Figure 7 is a flow chart of a dual-modality optical coherence elastic imaging method provided by an embodiment of the present invention;

[0031] Figure 8 It is a timing diagram of the MB scanning mode provided by an embodiment of the present invention.

[0032] Figure numerals: 011 - a beam of detection light, 012 - a second beam of detection light, 02 - a ring-shaped ultrasonic transducer, 03 - an ultrasonic coupling agent, 04 - a coupling unit, 051 - an optical fiber coupler, 052 - a 50:50 optical fiber coupler, 06 - a circulator, 07 - a polarization controller, 08 - a collimator, 09 - a focusing mirror, 10 - a reflector, 11 - a galvanometer, 12 - a beam splitter, 13 - a depolarizer, 14 - a dispersion compensator, 15 - a non-polarizing beam splitter, 16 - a Rochon prism. DETAILED DESCRIPTION

[0033] The present invention will be further described below in conjunction with embodiments and drawings, but the protection scope of the present invention should not be limited by these embodiments.

[0034] The dual-modal optical coherence elastic imaging device provided in this embodiment can simultaneously obtain the strain information and elasticity information of the sample to be tested.

[0035] A dual-mode optical coherence elastic imaging device includes an excitation unit, an imaging unit and a coupling unit. The excitation unit is used to generate an acoustic radiation force (ARF) to induce vibration of the sample to be tested. Figure 4As shown, it includes a signal generator, a power amplifier and an ultrasonic transducer. The signal generator generates a sine wave signal, which drives the ultrasonic transducer to generate an acoustic field after power amplification. This acoustic field forms an ARF in the sample to be tested after passing through a specific design (such as a ring coupling unit).

[0036] The imaging unit is used to detect the vibration of the sample to be tested, that is, the strain response and the elastic wave response. The imaging unit of this embodiment adopts an OCT system based on a swept frequency light source, such as Figure 5 As shown, the light output by the swept frequency light source is split by the fiber coupler 051, and a part of the light enters the reference arm as the reference light, and the other part of the light enters the sample arm as the detection light. The reference light passes through the circulator 06, the polarization controller 07, the collimator 08 and the focusing mirror 09 and is reflected by the reflector 10. The detection light is divided into two beams of detection light after passing through the circulator 06 and the beam splitter 12. These two beams of detection light pass through optical fibers of different lengths and have different phase delays. They are focused on the sample after passing through the collimator 08, the galvanometer 11 and the focusing mirror 09. The light returned from the sample and the light returned from the reference arm interfere in the 50:50 fiber coupler 052 and are detected by a balanced detector. After signal processing, the complex structural information of the sample to be tested can be obtained. The detection light 011 and the detection light 012 display their obtained structural information at different depths of the structural image because they have different phase delays. The imaging unit can be an optical coherence tomography system based on a broadband low-coherence light source, such as Figure 6 As shown, the light output by the superluminescent diode passes through the collimator 08 and the depolarizer 13 and is then split in the non-polarizing beam splitter 15. One part of the light enters the reference arm as the reference light, and the other part of the light enters the sample arm as the detection light. The reference light passes through the dispersion compensator 14 and the focusing mirror 09 and is reflected by the reflector 10. The detection light passes through the galvanometer 11 and is split into two beams of detection light by the Rochon prism 16. The two beams of detection light pass through the focusing mirror 09 and are focused onto the sample. The light returned by the sample and the light returned by the reference arm interfere in the non-polarizing beam splitter 15 and are detected by the spectrometer. After signal processing, the complex structural information of the sample to be tested can be obtained. The detection light 011 and the detection light 012 separated by the Rochon prism 16 have different phase delays because they pass through different paths, so that the obtained structural information can be displayed at different depths of the structural image.

[0037] Coupling units, such as Figure 3 As shown, there is an annular acoustic reflection surface for reflecting the acoustic field, so that the acoustic beam and the detection beam are incident on the same side of the sample. The detection light 011 irradiates the sample to be tested through the middle through hole of the annular coupling unit 04; the detection light 012 irradiates the sample to be tested through the area outside the edge of the annular coupling unit 04; after the acoustic field is reflected by the acoustic reflection surface of the annular coupling unit 04, it irradiates the sample to be tested along the same direction as the two detection lights, thereby achieving the acoustic beam and the detection beam incident on the sample on the same side of the sample.

[0038] The following describes the dual-modality optical coherence elastic imaging method provided in the embodiment of the present application. Figure 7 is a schematic flow chart of a dual-modality optical coherence elastography method in an embodiment, comprising the following steps:

[0039] -Emitting sound field: The sound field is emitted by the excitation unit. After being reflected by the annular coupling unit, the sound field forms an acoustic radiation force field in the sample to be tested, inducing the sample to be tested to vibrate.

[0040] -Data collection: The OCT system is used to simultaneously collect the strain response and elastic wave response of the sample under test.

[0041] The OCT system simultaneously emits two beams of detection light signals, one beam of detection light 01 illuminates the sample to be tested through the middle through hole of the annular coupling unit 04, and the other beam of detection light 012 illuminates the sample to be tested through the area outside the edge of the annular coupling unit 04. The data obtained by the detection light 01 passing through the middle through hole of the annular coupling unit 04 is the first set of data, which is used to measure the strain information of the sample. The data obtained by the detection light 012 that does not pass through the middle through hole of the coupling unit 04 is the second set of data, which is used to measure the elastic wave information of the sample. Because the two beams of detection light have different optical paths, the signals obtained by the two beams of detection light can be distinguished from the depth in the OCT structure diagram.

[0042] -Data processing: Process the collected data and convert the strain information and quantitative elastic information of the sample to be tested from the OCT data.

[0043] In this embodiment, both the first set of data and the second set of data can use a phase-based displacement detection algorithm. First, the interference signals of different wave numbers acquired by the OCT system are transformed into complex signals that vary with depth using a fast Fourier transform. Among them, A, The OCT complex signal can be used to obtain the phase change of the sample at the same position along the beam direction (i.e. axial direction) at adjacent moments: Among them, F m and F m-1 are the complex OCT signals of the same position of the sample under test at adjacent moments, Im() and Re() are the operators for extracting the imaginary and real parts of the signal respectively. * is the conjugate complex number of F. According to the Doppler principle, the axial displacement of the sample to be tested between two consecutive acquisition moments at a given position can be obtained: Where λ0 is the central wavelength of the light source and n is the refractive index of the sample.

[0044] The first set of data is used to calculate strain based on data from at least two moments. By comparing the data from the two moments, the displacement of the current frame of the sample to be tested relative to the reference frame is calculated, and the strain of the sample to be tested is calculated based on the displacement information. In this embodiment, an area with uniform acoustic radiation force is selected, and the axial displacement within a certain custom time window is calculated. The axial strain can be obtained Where z0 is the original thickness of the sample before excitation.

[0045] For the second set of data, the displacement of each position of the sample under test over time is calculated, and then the propagation speed of the elastic wave can be calculated. In this embodiment, a two-dimensional Fourier transform can be used to convert the time-space displacement diagram of each depth of the sample under test into a frequency-wave number diagram; by selecting each frequency f e The wave number k of maximum intensity m According to the formula c(f e )=2πf e / k m Specifically, the surface Rayleigh wave velocity c obtained from the surface of the sample to be tested is used. R The Young's modulus of the sample can be obtained Among them, ρ is the concentration of the sample to be tested, ν is the Poisson's ratio, and the shear wave velocity c obtained inside the sample to be tested is used. s The Young's modulus of the sample can also be obtained: E = 2ρ(1+v)c s 2 .

[0046] Optionally, the OCT system can collect data in MB scanning mode or BM scanning mode. MB scanning mode collects M-scan data at different lateral positions to form a set of data. BM scanning mode collects B-scan data at different times to form a set of data. The OCT system can obtain an A-scan signal of the sample reflectivity changing with depth after a single acquisition and data processing. The B-scan data is composed of a group of A-scan signals at different positions obtained by transverse scanning of the light beam in a direction perpendicular to the optical axis; while the M-scan data is composed of A-scan signals at the same lateral position collected at different times.

[0047] Taking MB scanning mode as an example, in one sampling period, by x The entire data set consists of M scan data collected at each lateral position, where each M scan data consists of N A The excitation trigger signal is composed of A scan data and sent at each lateral position in synchronization with an M scan trigger signal. Figure 8 1 is a timing diagram of the MB scanning mode in this embodiment. x =512,N A =512.

[0048] Based on the above description, this embodiment can simultaneously display the strain image of the sample to be tested and the elastic image calculated based on elastic waves in real time, thereby achieving high-resolution qualitative judgment and quantitative measurement of the elasticity of the sample to be tested.

Claims

1. A dual-modality optical coherence elastic imaging device, characterized in that: include: An excitation unit, for generating a sound field; An imaging unit, which is an optical coherence tomography system, is used to detect the vibration of the sample to be tested, namely, the strain response and the elastic wave response; A coupling unit having an acoustic reflection surface with a middle through hole, which is used to reflect the acoustic field generated by the excitation unit, so as to couple the detection beam emitted by the imaging unit with the acoustic field emitted by the excitation unit; wherein the detection beam irradiates the sample to be tested through the middle through hole of the coupling unit and the area outside the edge of the coupling unit, and the acoustic field emitted by the excitation unit is reflected by the acoustic reflection surface of the coupling unit and then transmitted to the sample to be tested along the same direction or a similar direction as the detection beam, thereby forming an acoustic radiation force field.

2. The dual-modality optical coherence elastic imaging device according to claim 1, characterized in that: The imaging unit emits at least two beams of detection light simultaneously, and each beam of detection light has a different phase delay, so that structural information acquired by different beams of detection light can be obtained simultaneously at different depth regions in an optical coherence tomography image.

3. The dual-modality optical coherence elastic imaging device according to claim 1, characterized in that: The excitation unit includes a signal generator, a power amplifier and an ultrasonic transducer. The signal generator generates a sine wave signal, which is amplified by the power amplifier and then drives the ultrasonic transducer to generate a sound field.

4. A method for performing dual-modality optical coherence elastic imaging using the device according to any one of claims 1 to 3, characterized in that: The method comprises the following steps: Step 1. The acoustic field is emitted by the excitation unit. After being reflected by the annular coupling unit, the ARF is formed in the sample to be tested, inducing the sample to be tested to vibrate; Step 2. Use an imaging unit to simultaneously collect strain response and elastic wave response in the sample to be tested: the imaging unit sends out two or more detection light signals, which respectively illuminate the sample to be tested through different areas of the annular coupling unit, the first detection light passes through the middle through hole of the annular coupling unit to obtain data for measuring the strain information of the sample, and the second detection light passes through the area outside the edge of the annular coupling unit to obtain data for measuring the elastic wave information of the sample; Step 3. Process the collected data and convert the strain information and quantitative elastic information of the sample to be tested from the OCT data; the data obtained by coupling the detection light of the middle through hole of the unit is used to measure the strain information of the sample; the data obtained by coupling the detection light of the area outside the edge of the unit is used to measure the elastic wave information of the sample.

5. The dual-modality optical coherence elastic imaging method according to claim 4, characterized in that: The method also includes step 4 of displaying the strain image of the sample to be tested and the elastic image calculated based on the elastic wave in real time.

6. The dual-modality optical coherence elastic imaging method according to claim 4, characterized in that: The strain information is based on data analysis at two or more consecutive acquisition moments to calculate the strain size of the sample to be tested; the elastic wave information is calculated by calculating the displacement of each position of the sample to be tested over time, and then calculating the propagation speed or attenuation coefficient of the elastic wave, and the viscoelastic parameters of the sample are obtained using the elastic wave speed or attenuation coefficient.

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