A dual-modality optical coherence elastography device and method

Abstract

The application discloses a dual-mode optical coherence elastography device and method. The device comprises an excitation unit for generating an acoustic field; an imaging unit which is an optical coherence tomography system and is used for detecting the vibration of a sample, i.e. a strain response and an elastic wave response; and a coupling unit which has an acoustic reflection surface with a middle through hole and is used for reflecting the acoustic field generated by the excitation unit so that the coupling between a probe light beam emitted by the imaging unit and the acoustic field emitted by the excitation unit is on the same side of the sample. The application uses a multi-beam optical coherence tomography system to emit two or more probe light beams for dual-mode elastography, and can simultaneously obtain high-resolution strain information and quantitative elastic information of the sample, thereby solving the problem that the prior art cannot simultaneously perform strain imaging and elastic wave imaging.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of elastic imaging, in particular to a dual-mode optical coherence elastography device and method. BACKGROUND

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

[0003] As a visualized elasticity measurement method, the elastic imaging technology measures the mechanical response of the deformation and mechanical wave propagation of the tissue under excitation by using an imaging system, so as to obtain the elastic modulus of the tissue. Among the numerous elastic imaging technologies, the optical coherence elastography (OCE) is an elasticity detection technology based on optical coherence tomography (OCT), and has the advantages of non-invasiveness, high resolution and high displacement sensitivity, and is widely used in the characterization of the mechanical properties of biological soft tissues.

[0004] OCE technology often uses acoustic radiation force (ARF) as an excitation source. Unlike piezoelectric transducers and laser pulses, acoustic radiation force can stimulate the mechanical response of deep tissue. To meet the requirements of clinical disease detection, the acoustic beam of the ultrasonic transducer and the detection beam of the OCT must be emitted on the same side of the tissue. Currently, there are two main installation methods that can meet the requirements of ARF and detection light on the same side and perpendicular to the sample surface: one method uses a ring-shaped ultrasonic focusing transducer, and the OCT detection beam passes through the central hole of the ring-shaped ultrasonic transducer for detection, but the lateral scanning distance of the OCT detection light is limited by the size of the transducer center hole (see 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 realize the ARF and OCT detection light on the same side of the sample through a coupling unit (such as a glass slide) to transmit in a parallel or approximately parallel direction. In this method, the detection light of the OCT will reflect part of the energy, resulting in a decrease in the OCT signal-to-noise ratio. In the commonly used phase-sensitive displacement detection algorithm 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. Optical coherence elastography under homolateral parallel acoustic radiation force excitation for ocular elasticity quantification [J]. Optics Letters, 2024, 49(10):2817-2820)

[0005] On the other hand, there are different modalities of elastic imaging methods in OCE technology, such as strain imaging methods and elastic wave imaging methods. Strain imaging methods are easy to obtain high-resolution elastic images, while elastic wave imaging methods are easy to obtain quantitative elastic results. These two modalities of elastic imaging methods have their own advantages, but existing OCE technology cannot simultaneously obtain high-resolution strain imaging results and quantitative elastic wave imaging results. SUMMARY

[0006] The present application aims to overcome the deficiencies of the prior art, and provide a dual-mode optical coherence elastography device and method. The technical solution of the present application is described briefly below, and more details will be described in the specific embodiments below with reference to the drawings.

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

[0008] A dual-mode optical coherence elastography device, characterized in that it comprises:

[0009] An excitation unit for generating an acoustic field;

[0010] An imaging unit, which is an optical coherence tomography system, for detecting the vibration of a sample to be measured, i.e. the strain response and the elastic wave response;

[0011] A coupling unit having an acoustic reflecting surface with a central through hole, for reflecting the acoustic field generated by the excitation unit, so that the coupling between the probe light beam emitted by the imaging unit and the acoustic field emitted by the excitation unit is achieved; wherein the probe light beam irradiates the sample to be measured through the central 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 reflecting surface of the coupling unit and then transmitted into the sample to be measured along the same direction or a similar direction of the probe light beam, forming an acoustic radiation force field.

[0012] The excitation unit generates an acoustic field, which forms an ARF and induces vibration in the sample to be measured, while the imaging unit measures the vibration in the sample to be measured. The coupling unit achieves the coupling between the probe light beam emitted by the imaging unit and the acoustic field generated by the excitation unit. Specifically, the probe light beam can irradiate the sample to be measured through the central through hole of the coupling unit or through the area outside the edge of the coupling unit, while the acoustic field is reflected by the acoustic reflecting surface of the coupling unit and then irradiates the sample to be measured along the same direction as the probe light beam, so as to achieve the purpose of the acoustic beam and the probe light beam being incident into the sample to be measured on the same side of the sample. In addition, since the probe light beam passes through the central through hole of the coupling unit or the area outside the edge of the coupling unit without passing through the acoustic reflecting structure of the coupling unit, the probe light beam will not lose light energy during the process of passing through the coupling unit.

[0013] Optionally, the light source in the imaging unit can 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; the method of optical fiber delay or spatial delay can make each probe light have different phase delay, so as to obtain structural information at different depth positions in one structural image.

[0015] A bimodal optical coherence elastography method, characterized in that the method comprises the following steps:

[0016] The sound field emitted by the excitation unit forms a sound radiation force field in the sample to be measured, and induces the sample to be measured to produce deformation and elastic waves; the OCT system emits two or more probe light signals, wherein one or more probe lights irradiate the sample to be measured through the middle hole of the coupling unit, and the remaining probe lights irradiate the sample to be measured through the area outside the edge of the coupling unit; the probe lights of different beams have different optical paths, and the data collected by different probe lights can be obtained in different depth regions of the OCT image; the data collected by the probe light through the middle hole of the coupling unit (first group of data) is used to measure the strain information of the sample, and the data collected by the probe light not through the middle hole of the coupling unit (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, and can also be a chirp modulation signal.

[0018] Optionally, the processing steps of the first group of data specifically include: calculating the displacement between two time instants at each position of the sample to be measured, and then obtaining the strain parameter and the strain image. The processing steps of the first group of data include but are not limited to any method of calculating the displacement or deformation of the sample to be measured from the data.

[0019] Optionally, the processing steps of the second group of data specifically include: calculating the propagation speed of the elastic wave by calculating the displacement of each position of the sample to be measured with time, and then obtaining the viscoelastic parameter (such as Young's modulus) and the viscoelastic image. The processing steps of the second group of data include but are not limited to any method of deriving the viscoelasticity of the sample to be measured from the properties of the elastic wave.

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

[0021] 1. The bimodal elastic imaging is carried out by using the multi-beam optical coherence tomography system, so that the high-resolution strain information and the quantitative elastic information of the sample to be measured can be obtained at the same time, thereby solving the problem that the prior art cannot simultaneously perform strain imaging and elastic wave imaging.

[0022] 2. Compared with the prior art [1], the device of the present application can perform long-range lateral scanning without being limited by the middle hole of the annular ultrasonic transducer.

[0023] 3. Compared with the prior art [2], the OCT probe light in the device of the present application will not lose energy due to reflection of the coupling unit, so that the device has higher displacement detection sensitivity. BRIEF DESCRIPTION OF DRAWINGS

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

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

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

[0027] Figure 4 is a structural schematic diagram of an excitation unit provided by an embodiment of the present application;

[0028] Figure 5 is a structural schematic diagram of a fiber type imaging unit provided by an embodiment of the present application;

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

[0030] Figure 7 is a flow chart of a dual-mode optical coherence elastography method provided by an embodiment of the present application;

[0031] Figure 8 is a timing schematic diagram of an M-B scanning mode provided by an embodiment of the present application.

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

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

[0034] The dual-mode optical coherence elastography device provided by the embodiment can simultaneously acquire strain information and elasticity information of a sample to be measured.

[0035] A dual-mode optical coherence elastography device includes an excitation unit, an imaging unit and a coupling unit. The excitation unit is used to form acoustic radiation force (ARF) to induce a sample to be measured to vibrate, such as Figure 4As shown, it includes a signal generator, a power amplifier and an ultrasonic transducer. The signal generator generates a sinusoidal signal, which drives the ultrasonic transducer to generate an acoustic field after power amplification. This acoustic field, after passing through a specially designed coupling unit (such as a ring-shaped coupling unit), forms an ARF in the sample to be measured.

[0036] An imaging unit is used to detect the vibration of the sample to be measured, i.e. the strain response and the elastic wave response. The imaging unit of the present embodiment uses an OCT system based on a swept source, such as Figure 5 As shown, the light output by the swept source is split by the fiber coupler 051, with part of the light entering the reference arm as reference light and the other part of the light entering the sample arm as probe light. The reference light is reflected by the mirror 10 after passing through the circulator 06, the polarization controller 07, the collimator 08 and the focusing lens 09. The probe light is split into two beams of probe light after passing through the circulator 06 and the beam splitter 12. The two beams of probe light pass through optical fibers of different lengths and have different phase delay amounts, and are focused onto the sample by the collimator 08, the galvanometer 11 and the focusing lens 09. The light returned by the sample and the light returned by the reference arm interfere in the 50:50 fiber coupler 052, and are detected by the balanced detector. After signal processing, the complex structural information of the sample to be measured can be obtained. The probe light 011 and the probe light 012 display the structural information obtained at different depths of the structural image due to the different phase delay amounts. 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 split in the non-polarization beam splitter 15, with part of the light entering the reference arm as reference light and the other part of the light entering the sample arm as probe light. The reference light is reflected by the mirror 10 after passing through the dispersion compensator 14 and the focusing lens 09. The probe light is split into two beams of probe light by the Rochon prism 16 after passing through the galvanometer 11. The two beams of probe light are focused onto the sample by the focusing lens 09. The light returned by the sample and the light returned by the reference arm interfere in the non-polarization beam splitter 15, and are detected by the spectrometer. After signal processing, the complex structural information of the sample to be measured can be obtained. The probe light 011 and the probe light 012 have different phase delay amounts due to the different paths, so that the structural information obtained can be displayed at different depths of the structural image.

[0037] A coupling unit, such as Figure 3 As shown, the coupling unit has a ring-shaped acoustic reflecting surface for reflecting the acoustic field so that the acoustic beam and the probe beam are incident on the sample on the same side. The probe light 011 irradiates the sample to be measured through the middle through hole of the ring-shaped coupling unit 04; the probe light 012 irradiates the sample to be measured through the area outside the edge of the ring-shaped coupling unit 04; and the acoustic field, after being reflected by the acoustic reflecting surface of the ring-shaped coupling unit 04, irradiates the sample to be measured along the same direction as the two beams of probe light, so that the acoustic beam and the probe beam are incident on the sample on the same side.

[0038] The dual-mode optical coherence elastography method provided by the embodiment of the present application is described below. Referring to Figure 7 is a schematic flowchart of the dual-mode optical coherence elastography method in an embodiment, including the following steps:

[0039] - Emitting a sound field: Emitting a sound field by using an excitation unit, and the sound field forms an acoustic radiation force field in the sample to be measured after being reflected by the annular coupling unit, thereby inducing the sample to be measured to vibrate.

[0040] - Collecting data: Collecting the strain response and the elastic wave response in the sample to be measured simultaneously by using the OCT system.

[0041] The OCT system simultaneously emits two probe light signals, one of which, probe light 01, irradiates the sample to be measured through the middle through hole of the annular coupling unit 04, and the other, probe light 012, irradiates the sample to be measured through the area outside the edge of the annular coupling unit 04. The data obtained by the probe light 01 through the middle through hole of the annular coupling unit 04 is the first group of data, which is used to measure the strain information of the sample. The data obtained by the probe light 012 not through the middle through hole of the coupling unit 04 is the second group of data, which is used to measure the elastic wave information of the sample. Because the two probe lights pass through different optical paths, the signals obtained by the two probe lights can be distinguished in depth in the OCT structure diagram.

[0042] - Processing data: Processing the collected data to calculate the strain information and quantitative elastic information of the sample to be measured from the OCT data.

[0043] In the embodiment, both the first group of data and the second group of data can use a phase-based displacement detection algorithm. First, the interference signals of different wave numbers obtained by the OCT system are transformed into complex signals varying with depth by using fast Fourier transform wherein A, are the amplitude and phase components of the signal, respectively. The phase change of the sample to be measured at the same position and adjacent time along the beam direction (i.e., the axial direction) can be obtained from the OCT complex signal: wherein F m and F m-1 are the complex OCT signals of the sample to be measured at the same position and adjacent time, and Im() and Re() are the operators for extracting the imaginary part and the real part of the signal, respectively. F * is the conjugate complex of F. According to the Doppler principle, the axial displacement of the sample to be measured between two continuous acquisition times at a given position can be obtained: wherein λ0 is the center wavelength of the light source, and n is the refractive index of the sample.

[0044] The first group of data is used to calculate the strain of the sample based on the data at at least two time points. By comparing the data at two time points, the displacement of the sample at the current frame relative to the reference frame is calculated, and the strain of the sample is calculated based on the displacement information. In this embodiment, a region with uniform acoustic radiation force is selected, and the axial displacement in 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 group of data, the propagation speed of the elastic wave can be calculated by calculating the displacement of each position of the sample over time. In this embodiment, two-dimensional Fourier transform can be used to convert the time-space displacement map of each depth of the sample into a frequency-wave number map; by selecting the wave number k e with the maximum intensity at each frequency f m , the elastic wave speed can be obtained according to the formula c(f e ) = 2pf e / k m . Specifically, the surface Rayleigh wave speed c R obtained from the surface of the sample can be used to obtain the Young's modulus of the sample where p is the concentration of the sample, and v is the Poisson's ratio; the shear wave speed c s obtained from the interior of the sample can also be used to obtain the Young's modulus of the sample E = 2p(1 + v)c s 2 .

[0046] Optionally, the OCT system can collect data in M-B scanning mode or B-M scanning mode. The M-B scanning mode is to collect M scanning data at different lateral positions to form a group of data. The B-M scanning mode is to collect B scanning data at different time points to form a group of data. The OCT system can obtain an A scanning signal of the sample reflectivity varying with depth after single collection and data processing. The B scanning data is composed of a group of A scanning signals at different positions obtained by lateral scanning of the light beam perpendicular to the optical axis; and the M scanning data is composed of A scanning signals at the same lateral position collected at different time points.

[0047] Taking the M-B scanning mode as an example, in a sampling period, M scanning data is collected at N x lateral positions to form the entire data set, wherein each M scanning data is composed of N A A scanning data, and the excitation trigger signal sent at each lateral position is synchronized with the M scanning trigger signal. Figure 8 is a timing diagram of the M-B scanning mode in this embodiment. In this embodiment, N x = 512, and N A = 512.

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

Claims

1. A dual modality optical coherence elastography apparatus, characterized in that, The application relates to a method for measuring strain and elastic wave information of a sample, comprising the following steps: An excitation unit is used to generate an acoustic field; An imaging unit is an optical coherence tomography system used to detect the vibration of a sample, i.e. the strain response and the elastic wave response; the optical coherence tomography system emits two or more probe light signals, wherein one or more probe lights irradiate the sample through the middle hole of a coupling unit, and the rest of the probe lights irradiate the sample through the area outside the edge of the coupling unit; the probe lights of different beams have different optical paths, and the data collected by the different probe lights can be obtained at different depth regions of the optical coherence tomographic image; the data collected by the probe light through the middle hole of the coupling unit are used to measure the strain information of the sample, and the data collected by the probe light not through the middle hole of the coupling unit are used to measure the elastic wave information of the sample; A coupling unit has a sound reflection surface with a middle hole, which is used to reflect the acoustic field generated by the excitation unit, so that the coupling between the probe light beams emitted by the imaging unit and the acoustic field emitted by the excitation unit is realized; wherein the probe light beams irradiate the sample through the middle hole and the area outside the edge of the coupling unit, and the acoustic field emitted by the excitation unit is reflected by the sound reflection surface of the coupling unit and then transmitted into the sample along the same direction or a similar direction of the probe light beams, thereby forming an acoustic radiation force field.

2. The dual modality optical coherence elastography device of claim 1, wherein, The imaging unit emits at least two probe lights at the same time, and each probe light has a different phase delay amount, so that the structural information obtained by the different probe lights can be obtained at different depth regions of an optical coherence tomographic image at the same time.

3. The dual modality optical coherence elastography device of claim 1, wherein, The excitation unit comprises 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 an acoustic field.

4. A method for dual-mode optical coherence elastography using the apparatus of any one of claims 1-3, wherein, The method comprises the following steps: Step 1: emitting an acoustic field by the excitation unit, and forming an ARF in the sample after the acoustic field is reflected by the ring-shaped coupling unit, so as to induce the sample to vibrate; Step 2: collecting the strain response and the elastic wave response of the sample by the imaging unit at the same time; the imaging unit emits two or more probe light signals, which irradiate the sample through different areas of the ring-shaped coupling unit; the first probe light obtains the data for measuring the strain information of the sample through the middle hole of the ring-shaped coupling unit, and the second probe light obtains the data for measuring the elastic wave information of the sample through the area outside the edge of the ring-shaped coupling unit; Step 3: processing the collected data to calculate the strain information and the quantitative elastic information of the sample from the optical coherence tomographic imaging data; the data obtained by the probe light through the middle hole of the coupling unit are used to measure the strain information of the sample, and the data obtained by the probe light through the area outside the edge of the coupling unit are used to measure the elastic wave information of the sample.

5. The dual modality optical coherence elastography method of claim 4, wherein, Step 4: displaying the strain image and the elastic image calculated based on the elastic wave of the sample in real time.

6. The dual modality optical coherence elastography method of claim 4, wherein, The strain information is calculated based on data analysis from two or more consecutive acquisition times to determine the strain magnitude of the sample under test. The elastic wave information is obtained by calculating the displacement of each position of the sample under test over time, thereby determining the propagation velocity or attenuation coefficient of the elastic wave, and using the elastic wave velocity or attenuation coefficient to obtain the viscoelastic parameters of the sample.

Images