CN116671860A - Full-eye imaging method and system based on polarization sensitive optical coherence tomography - Google Patents
Full-eye imaging method and system based on polarization sensitive optical coherence tomography Download PDFInfo
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Abstract
The application discloses a full-eye imaging method and a full-eye imaging system based on polarization sensitive optical coherence tomography, wherein the full-eye imaging method and the full-eye imaging system scan eyes through a polarization sensitive optical coherence tomography system to obtain two paths of interference signals with the polarization direction in the horizontal direction and the vertical direction, and the polarization state of light is represented by Stokes vectors so as to reconstruct a real-time image; full-eye imaging is realized based on polarization sensitive optical coherence tomography, the structure and polarization information of the full eye are provided without marks, the identification efficiency and accuracy of ophthalmic disease examination can be effectively improved, and a doctor is assisted in diagnosis. The dependent imaging system is simple and convenient to package, and has the advantages of non-invasiveness, high resolution and capability of detecting the internal structure and polarization characteristics of the whole eye tissue in real time in vivo.
Description
Technical Field
The application relates to a full-eye imaging method and system based on polarization sensitive optical coherence tomography, and belongs to the technical field of biological imaging.
Background
Ophthalmic diseases such as ametropia, cataracts, glaucoma, and ocular fundus lesions can affect the structure and function of the eye. In order to evaluate ophthalmic diseases and visual physiological changes caused by ophthalmic diseases, a technique for real-time high-resolution imaging of the eye is indispensable. As a non-invasive, high resolution, non-contact and real-time imaging technique, optical coherence tomography (Optical Coherence Tomography, OCT) has gradually become a conventional diagnostic technique in ophthalmology.
Full-eye range OCT imaging, which can measure anterior ocular segment and fundus information simultaneously, has important value in the ophthalmic clinical field, such as where some ophthalmic diseases involve physiological changes of anterior ocular segment and fundus simultaneously, myopia screening requires measurement of ocular axis length. In recent years, full-eye OCT imaging systems are mature, but traditional OCT can only detect biological sample structures through intensity information, and detailed characteristics of tissues are difficult to embody.
Polarization techniques can obtain more polarization information than structural information by detecting changes in the polarization state of light after reflection or scattering by biological tissue. On the basis of obtaining tissue structure information, polarization sensitive OCT (Polarization sensitive OCT, PS-OCT) combined with a polarization technology can distinguish tissues which cannot be distinguished in OCT structure images by analyzing the polarization characteristics of a sample. Various tissues in the eye can affect the polarization state of light, e.g., the melanin-containing retinal pigment epithelium and choroid can disrupt the polarization state of light, and can be identified as depolarizing tissue; sclera and retinal nerve fiber layers and the like having a fiber structure are birefringent. The use of PS-OCT can thus help doctors identify these tissues and make diagnoses.
In 2011, YIheng Lim et al proposed a PS-OCT system for imaging the cornea and anterior ocular segment, and studied the polarization properties of keratoconus and the blebs after trabeculectomy (Lim Y, yamanari M, fukuda S, et al Birefringence measurement of cornea and anterior segment by office-based polarization-sensitive optical coherence tomography [ J ]. Biomedical optics express,2011,2 (8): 2392-2402.). In 2014, boy Braaf et al developed a fundus PS-OCT system based on a fiber structure, exhibiting phase retardation and optical axis direction information of the retina of the human eye (Braaf B, vermeer K A, de Groot M, et al fiber-based polarization-sensitive OCT of the human retina with correction of system polarization distortions [ J ]. Biomedical optics express,2014,5 (8): 2736-2758.). Most of the subsequent studies have employed a similar dual input configuration, i.e., the sample was irradiated with two polarized light beams having orthogonal polarization states, and the polarization states of the two reflected light beams were obtained, respectively, to obtain the polarization characteristics of the sample. The method does not need to strictly control the polarization state of incident light, is easy to operate and maintain and has good stability, but the dual-input PS-OCT occupies more time cost or space cost, and the system light path and the imaging process are complex. In addition, there is currently no PS-OCT system that performs integrated measurement and imaging of the whole eye.
Therefore, there is a need for a PS-OCT-based whole-eye imaging method and system that can realize real-time imaging of the whole eye with high resolution, non-contact, and non-invasiveness, and provide information on the tissue structure and polarization of the eye.
Disclosure of Invention
The application aims to overcome the defects of the prior art and provide a full-eye imaging method and a full-eye imaging system based on PS-OCT, which can provide structural and polarization function information of the full eye without marks.
The specific technical scheme is that the full-eye imaging method based on polarization sensitive optical coherence tomography PS-OCT is provided, a PS-OCT imaging system scans eyes to obtain two paths of interference signals with the polarization direction in the horizontal direction and the vertical direction, and a Stokes vector is used for representing the polarization state of light to reconstruct a real-time image;
the method comprises the following specific steps:
step one, collecting the polarization direction to be in the horizontal direction I H (k) And vertical direction I V (k) Is a two-way interference signal;
step two, preprocessing the two interference signals after removing background light and zero padding to obtain I H (k) And I V (k) Wave number domain signals of (2); performing inverse Fourier transform on the wave number domain signals to obtain complex amplitudes of two paths of interference signals in the horizontal direction and the vertical direction, wherein the complex amplitudes are expressed as follows:
wherein the parameter z represents the depth coordinate in the axial direction, A andrespectively representing the amplitude and phase of the interference signal; subscripts H and V represent horizontal and vertical directions, respectively; eye information related to depth z can be obtained from the interference signals measured by the two orthogonal polarization channels according to the above formula;
step three, calculating Stokes vectorDescribing the polarization state of light: calculating polarized image based on PS-OCT imaging principle, and calculating corresponding Stokes vector +.>
Wherein, the stokes vector is an expression form describing polarization, and I, Q, U, V is a parameter of the stokes vector; phase differenceThe phase difference of the interference light measured in two orthogonal polarization channels is described;
step four, four parameters including the reflection intensity I, the accumulated phase delay delta, the accumulated optical axis theta and the polarization uniformity (Degree of Polarization Uniformity, DOPU) are further calculated according to Stokes vector quantity, and are respectively shown as follows:
I(z)＝|A H (z) 2 |+|A V (z) 2
wherein the measurement ranges of δ and θ are [0, pi/2 ] and [ -pi/2, pi/2 ], respectively, for describing the change in the cumulative polarization state of the eye from the surface to the measurement depth, DOPU represents the overall degree of polarization within the selected window for describing the depolarization characteristics of the eye.
In the above method, the PS-OCT imaging system is fiber-optic OCT or space-optical OCT.
In the above method, the PS-OCT imaging system is time domain OCT, spectral domain OCT, or swept source OCT.
Optionally, the PS-OCT imaging system may be a swept source PS-OCT imaging system, including a broad spectrum light source, a polarization controller, a circulator, a polarization beam splitter, a polarization maintaining coupler, a collimator one, a quarter wave plate one, a dispersion compensator, a diaphragm, a mirror, a collimator two, a quarter wave plate two, an eye scanning module, a polarization beam splitter two, a balance detector one, a balance detector two, and a signal processing device;
the light output by the wide-spectrum light source is output into linearly polarized light along the vertical direction after passing through the polarization controller, the linearly polarized light enters the circulator, and the light emitted from the circulator passes through the first polarizing beam splitter and the first polarizing beam splitter 50:50, equally dividing the polarization maintaining coupler into a reference beam and a sample beam after the end a of the polarization maintaining coupler; the reference beam passes through a first collimator, a first quarter wave plate with an included angle of 22.5 degrees between the fast axis direction and the vertical direction, a dispersion compensator and a diaphragm, and is reflected back to the c end of the polarization maintaining coupler by the original path of the reflector; the sample beam passes through a second collimator and a second quarter wave plate with an included angle of 45 degrees between the fast axis direction and the vertical direction, so that the sample beam is converted from a linear polarization state to a circular polarization state; the sample beam irradiates the eyes through the eye scanning module, and light scattered back from the eyes returns to the d end of the polarization maintaining coupler along the original path; the reference light entering the c end of the polarization maintaining coupler interferes with the sample light at the d end, and the interfered light exits from the polarization maintaining coupler; after light emitted from the end a of the polarization maintaining coupler enters the first polarization beam splitter, light in the vertical direction enters the first balance detector through the circulator, and light in the horizontal direction enters the second balance detector; after the light emitted from the b end of the polarization maintaining coupler passes through the second polarization beam splitter, the light in the vertical direction enters the first balance detector, and the light in the horizontal direction enters the second balance detector; the balance detector I and the balance detector II receive light and then convert the light into an electric signal to be transmitted to the signal processing device.
Alternatively, the PS-OCT imaging system may be a spectral domain PS-OCT imaging system comprising: the device comprises a wide-spectrum light source, a linear polaroid, a non-polarized beam splitter, a first quarter wave plate, a dispersion compensator, a diaphragm, a reflecting mirror, a second quarter wave plate, an eye scanning module, a polarized beam splitter, a first signal detector, a second signal detector and a signal processing device;
the light output by the broad spectrum light source is output into linearly polarized light along the vertical direction after passing through the linear polaroid, and the linearly polarized light enters 50:50 is divided into a reference beam and a sample beam after the non-polarizing beam splitter; the reference beam passes through a first quarter wave plate, a dispersion compensator and a diaphragm, wherein the included angle between the fast axis direction and the vertical direction is 22.5 degrees, and is reflected back to the non-polarizing beam splitter by the original path of the reflector; the sample beam passes through a second quarter wave plate with an included angle of 45 degrees between the fast axis direction and the vertical direction, so that the sample beam is converted from a linear polarization state to a circular polarization state; the sample beam irradiates the eyes through the eye scanning module, and light scattered back from the eyes returns to the non-polarized beam splitter along the original path; the reference light and the sample light entering the non-polarizing beam splitter interfere, the polarized beam splitter is utilized to divide the interfered light into two beams of light with vertical and horizontal polarization directions, and the two beams of light are respectively received by the first signal detector and the second signal detector; the first signal detector and the second signal detector receive light and convert the light into electric signals to be transmitted to the signal processing device.
In the spectrum domain PS-OCT imaging system, the signal detector comprises a spectrometer and a linear array camera, and the spectrometer splits light and the linear array camera receives the light.
Alternatively, the PS-OCT imaging system may be a time domain PS-OCT imaging system comprising: the device comprises a wide-spectrum light source, a linear polaroid, a non-polarized beam splitter, a first quarter wave plate, a dispersion compensator, a diaphragm, a reflecting mirror, a second quarter wave plate, an eye scanning module, a polarized beam splitter, a first signal detector, a second signal detector and a signal processing device;
the light output by the broad spectrum light source is output into linearly polarized light along the vertical direction after passing through the linear polaroid, and the linearly polarized light enters 50:50 is divided into a reference beam and a sample beam after the non-polarizing beam splitter; the reference beam passes through a first quarter wave plate, a dispersion compensator and a diaphragm, wherein the included angle between the fast axis direction and the vertical direction is 22.5 degrees, and is reflected back to the non-polarizing beam splitter by the original path of the reflector; the sample beam passes through a second quarter wave plate with an included angle of 45 degrees between the fast axis direction and the vertical direction, so that the sample beam is converted from a linear polarization state to a circular polarization state; the sample beam irradiates the eyes through the eye scanning module, and light scattered back from the eyes returns to the non-polarized beam splitter along the original path; the reference light and the sample light entering the non-polarizing beam splitter interfere, the polarized beam splitter is utilized to divide the interfered light into two beams of light with vertical and horizontal polarization directions, and the two beams of light are respectively received by a first signal detector and a second signal detector; the first signal detector and the second signal detector receive light and convert the light into electric signals to be transmitted to the signal processing device.
In the time domain PS-OCT imaging system, the signal detector is a point detector, and the reflecting mirror moves longitudinally to realize depth scanning.
Preferably, the eye scanning module is used for realizing focusing and scanning of the sample light beam at different positions of the whole eye, including a fundus imaging mode and an anterior ocular segment imaging mode.
Furthermore, the eye scanning module switches between fundus and anterior ocular segment imaging modes through switching of lenses to realize whole-eye imaging; the eye scanning module sequentially comprises a scanning galvanometer, a first convex lens and a second convex lens to an eye to be detected along an optical path when a fundus imaging mode is executed; the sample beam is focused on the fundus after passing through the eye scanning module, so as to realize fundus imaging; the structure of the eye scanning module in the anterior ocular segment imaging mode sequentially comprises a scanning galvanometer, a first convex lens, a third concave lens, a fourth convex lens and a second convex lens along an optical path to an eye to be detected; the sample beam is focused to the anterior ocular segment after passing through the eye scanning module, so as to realize anterior ocular segment imaging.
The application realizes full-eye imaging based on polarization sensitive optical coherence tomography, provides full-eye structure and polarization information without marks, can effectively improve the identification efficiency and accuracy of ophthalmic disease examination, and assists doctors in diagnosis. The dependent imaging system is simple and convenient to package, and has the advantages of non-invasiveness, high resolution and capability of detecting the internal structure and polarization characteristics of the whole eye tissue in real time in vivo.
Drawings
FIG. 1 is a flow chart of a PS-OCT whole-eye imaging method provided by the application;
FIG. 2 is a schematic diagram of a swept source PS-OCT imaging system according to an embodiment of the application;
in the figure, a 101-broad spectrum light source, a 102-polarization controller, a 103-circulator, a 104-polarization beam splitter I, a 105-polarization maintaining coupler, a 106-collimator I, a 107-quarter wave plate I, a 108-dispersion compensator, a 109-diaphragm, a 110-reflecting mirror, a 111-collimator II, a 112-quarter wave plate II, a 400-eye scanning module, a 113-polarization beam splitter II, a 114-balance detector I, a 115-balance detector II and a 116-signal processing device;
FIG. 3 is a schematic diagram of a spectral domain PS-OCT imaging system according to an embodiment of the present application;
in the figure, a 201-broad spectrum light source, a 202-linear polaroid, a 203-non-polarized beam splitter, a 204-first quarter wave plate, a 205-dispersion compensator, a 206-diaphragm, a 207-reflecting mirror, a 208-second quarter wave plate, a 400-eye scanning module, a 209-polarized beam splitter, a 210-signal detector I, a 211-signal detector II and a 212-signal processing device;
FIG. 4 is a schematic diagram of a time domain PS-OCT imaging system according to an embodiment of the present application;
in the figure, 301-broad spectrum light source, 302-linear polarizer, 303-non-polarizing beam splitter, 304-first quarter wave plate, 305-dispersion compensator, 306-diaphragm, 307-mirror, 308-second quarter wave plate, 400-eye scanning module, 309-polarizing beam splitter, 310-first signal detector, 311-second signal detector, 312-signal processing device;
FIGS. 5-1 and 5-2 are schematic diagrams of an eye scanning module; wherein, fig. 5-1 is a schematic diagram of an eye scanning module fundus imaging mode; FIG. 5-2 is a schematic diagram of an anterior ocular segment imaging mode of the eye scan module;
in the figure, 401-scanning galvanometer, 402-first convex lens, 403-second convex lens, 404-eye to be tested, 405-third concave lens, 406-fourth convex lens.
Detailed Description
In order to make the application more comprehensible, preferred embodiments accompanied with figures are described in detail below.
The application provides a full-eye imaging method and a full-eye imaging system based on PS-OCT, wherein a PS-OCT imaging system scans eyes to obtain two paths of interference signals with polarization directions in a horizontal direction and a vertical direction, and a Stokes vector is used for representing the polarization state of light to reconstruct a real-time image.
The flow chart of the PS-OCT full-eye imaging method provided by the application is shown in figure 1, and the specific steps are as follows:
step one, collecting the polarization direction to be in the horizontal direction I H (k) And vertical direction I V (k) Is a two-way interference signal;
step two, the two interference signals are subjected to pretreatment after background light removal and zero paddingAfter being treated, obtain I H (k) And I V (k) Wave number domain signals of (2); performing inverse Fourier transform on the wave number domain signal to obtain complex amplitudes of two paths of interference signals in the horizontal direction and the vertical direction, wherein the complex amplitudes can be expressed as follows:
wherein the parameter z represents the depth coordinate in the axial direction, A andrespectively representing the amplitude and phase of the interference signal; subscripts H and V represent horizontal and vertical directions, respectively; eye information related to depth z can be obtained from the interference signals measured by the two orthogonal polarization channels according to the above formula;
step three, calculating Stokes vectorDescribing the polarization state of light: calculating polarized image based on PS-OCT principle, and calculating corresponding Stokes vector +.>
Wherein, the stokes vector is an expression form describing polarization, and I, Q, U, V is a parameter of the stokes vector; phase differenceThe phase difference of the interference light measured in two orthogonal polarization channels is described;
and step four, further calculating four parameters of reflection intensity I, accumulated phase delay delta, accumulated optical axis theta and polarization uniformity DOPU according to Stokes vector, wherein the four parameters are respectively as follows:
I(z)＝|A H (z) 2 |+|A V (z) 2
wherein the measurement ranges of δ and θ are [0, pi/2 ] and [ -pi/2, pi/2 ], respectively, for describing the change in the cumulative polarization state of the eye from the surface to the measurement depth, DOPU represents the overall degree of polarization within the selected window for describing the depolarization characteristics of the eye.
According to the full-eye imaging method based on the PS-OCT, input information is two paths of interference signals with the polarization directions in the horizontal direction and the vertical direction, which are obtained by scanning eyes through the PS-OCT imaging system, the specific PS-OCT imaging system is not limited, and full-optical fiber transmission and space optical transmission can be adopted; the method is simple, the system is light and handy, and real-time image reconstruction can be realized.
Scanning an eye by adopting a PS-OCT imaging system, wherein the PS-OCT imaging system can be optical fiber OCT or space optical OCT; can be time domain OCT, spectral domain OCT or sweep frequency light source OCT; see the examples below.
Example 1
In one embodiment, a swept source PS-OCT system is employed, see FIG. 2, comprising: a broad spectrum light source 101, a polarization controller 102, a circulator 103, a polarization beam splitter I104, a polarization maintaining coupler 105, a collimator I106, a quarter wave plate I107, a dispersion compensator 108, a diaphragm 109, a reflecting mirror 110, a collimator II 111, a quarter wave plate II 112, an eye scanning module 400, a polarization beam splitter II 113, a balance detector I114, a balance detector II 115 and a signal processing device 116. Specifically, the broad spectrum light source 101 employs a 1060nm or 1310nm swept light source.
For the swept source PS-OCT imaging system shown in fig. 2, the light output from the broad spectrum light source 101 is output as linearly polarized light in the vertical direction after passing through the polarization controller 102, the linearly polarized light enters the circulator 103, and the light exiting from the circulator 103 passes through the polarization beam splitters one 104, 50:50 are split equally into a reference beam and a sample beam after the polarization maintaining coupler 105a end. The reference beam passes through a collimator I106, a quarter wave plate I107 with an included angle of 22.5 degrees between the fast axis direction and the vertical direction, a dispersion compensator 108 and a diaphragm 109, and is reflected back to the end of the polarization maintaining coupler 105c by a reflector 110. The sample beam passes through the second collimator 111 and the second quarter-wave plate 112 with an included angle of 45 ° between the fast axis direction and the vertical direction, so that the sample beam is converted from linear polarization state to circular polarization state. The sample beam irradiates the eye through the eye scan module 400 and light scattered back from the eye returns along the way to the end of the polarization maintaining coupler 105 d. The reference light entering the polarization maintaining coupler 105c end interferes with the sample light at the d end, and the interfered light exits from the polarization maintaining coupler 105. After the light emitted from the polarization maintaining coupler 105a enters the first polarization beam splitter 104, the light in the vertical direction enters the first balance detector 114 through the circulator 103, and the light in the horizontal direction enters the second balance detector 115. After the light emitted from the end of the polarization maintaining coupler 105b passes through the second polarization beam splitter 113, the light along the vertical direction enters the first balance detector 114, and the light along the horizontal direction enters the second balance detector 115. The first balance detector 114 and the second balance detector 115 receive light and convert the light into an electric signal, and the electric signal is transmitted to the signal processing device 116 for calculation.
The eye scanning module 400 provided in this embodiment, referring to fig. 5-1 and 5-2, includes two imaging modes, a fundus imaging mode and a anterior ocular segment imaging mode. The eye scanning module 400 performs switching between fundus imaging and anterior ocular segment imaging modes by switching of lenses, and achieves whole-eye imaging. Fundus imaging mode referring to fig. 5-1, including scanning galvanometer 401, first convex lens 402, second convex lens 403, and eye 404 under test; in the embodiment, the sample beam is focused on the fundus after passing through the eye scanning module, so that fundus imaging is realized. Anterior ocular segment imaging mode referring to fig. 5-2, includes scanning galvanometer 401, first convex lens 402, third concave lens 405, fourth convex lens 406, second convex lens 403, and eye 404 under test. In the embodiment, the sample beam is focused to the anterior ocular segment after passing through the eye scanning module, so that anterior ocular segment imaging is realized.
The signal processing device 116 in this embodiment is a computing device such as a computer or engineering machine equipped with a high-speed acquisition card, and performs a full-eye imaging method based on PS-OCT to calculate a polarized image of the eye.
Example 2
In yet another embodiment, a spectral domain PS-OCT system is employed, see FIG. 3, comprising: a broad spectrum light source 201, a linear polarizer 202, a non-polarizing beam splitter 203, a first quarter wave plate 204, a dispersion compensator 205, a diaphragm 206, a mirror 207, a second quarter wave plate 208, an eye scanning module 400, a polarizing beam splitter 209, a first signal detector 210, a second signal detector 211, and a signal processing device 212. Specifically, the broad spectrum light source 201 adopts a broad spectrum light source of 830nm or 1060 nm.
For a spectral domain PS-OCT imaging system, light output from a broad spectrum light source 201 passes through a linear polarizer 202 and is output as linearly polarized light in the vertical direction, which enters one 50:50 are then split equally into a reference beam and a sample beam. The reference beam passes through a first quarter wave plate 204 with a fast axis direction at an angle of 22.5 deg. to the vertical, a dispersion compensator 205 and diaphragm 206, and is reflected back to the non-polarizing beam splitter 203 by mirror 207. The sample beam passes through a second quarter wave plate 208 with an angle of 45 ° between the fast axis and the vertical direction, so that the sample beam is converted from linear polarization to circular polarization. The sample beam irradiates the eye through the eye scan module 400 and light scattered back from the eye returns to the non-polarizing beam splitter 203 along the original path. The reference light and the sample light entering the non-polarizing beam splitter 203 interfere, the polarized beam splitter 209 is used to split the interfered light into two beams of light with vertical and horizontal polarization directions, and the two beams of light are received by a first signal detector 210 and a second signal detector 211 respectively, and the signal detector adopted in the embodiment is composed of a spectrometer and a line camera. The first signal detector 210 and the second signal detector 211 receive the light, and convert the light into an electrical signal, and transmit the electrical signal to the signal processing device 212 for calculation.
The eye scanning module 400 in this embodiment is the same as the eye scanning module 400 of the first embodiment.
The signal processing device 212 in this embodiment is a computing device such as a computer or engineering machine equipped with a high-speed acquisition card, and performs a full-eye imaging method based on PS-OCT to calculate a polarized image of the eye.
In the spectral domain OCT system, a signal detector is used for light splitting by a spectrometer and is received by a linear array camera, so that the eye depth scanning is realized.
Example 3
In yet another embodiment, a time domain PS-OCT system is employed, see fig. 4, comprising a broad spectrum light source 301, a linear polarizer 302, a non-polarizing beam splitter 303, a first quarter wave plate 304, a dispersion compensator 305, a stop 306, a mirror 307, a second quarter wave plate 308, an eye scanning module 400, a polarizing beam splitter 309, a first signal detector 310, a second signal detector 311, a signal processing device 312. Specifically, the broad spectrum light source 301 is a 830nm or 1060nm broad spectrum light source.
Light output from the broad spectrum light source 301 passes through the linear polarizing plate 302 and is output as linearly polarized light in the vertical direction, and the linearly polarized light enters one 50:50 are then split equally into a reference beam and a sample beam. The reference beam passes through a first quarter wave plate 304 with a fast axis direction at an angle of 22.5 ° to the vertical, a dispersion compensator 305 and a diaphragm 306, and is reflected back to the non-polarizing beam splitter 303 by a mirror 307. The sample beam passes through a second quarter wave plate 308 having an angle of 45 ° between the fast axis and the vertical direction, so that the sample beam is converted from linear polarization to circular polarization. The sample beam irradiates the eye through the eye scan module 400 and light scattered back from the eye returns to the non-polarizing beam splitter 303 along the original path. The reference light and the sample light entering the non-polarizing beam splitter 303 interfere, and the interfered light is split into two light beams with vertical and horizontal polarization directions by the polarizing beam splitter 309 and received by the first signal detector 310 and the second signal detector 311, which are point detectors in the embodiment. The first signal detector 310 and the second signal detector 311 receive light, convert the light into an electrical signal, and transmit the electrical signal to the signal processing device 312 for calculation.
The eye scanning module 400 in this embodiment is the same as the eye scanning module 400 of the first embodiment.
The signal processing device 312 in this embodiment is a computing device such as a computer or engineering machine equipped with a high-speed acquisition card, and performs a full-eye imaging method of PS-OCT to calculate a polarized image of the eye.
In time domain OCT systems, the signal detector is a point detector and the mirror is moved longitudinally to effect a depth scan of the eye.
Claims (10)
1. A full-eye imaging method based on polarization sensitive optical coherence tomography (PS-OCT) is characterized in that a PS-OCT imaging system scans eyes to obtain two paths of interference signals with polarization directions in a horizontal direction and a vertical direction, and a Stokes vector is used for representing the polarization state of light so as to reconstruct a real-time image;
the method comprises the following specific steps:
step one, collecting the polarization direction to be in the horizontal direction I H (k) And vertical direction I V (k) Is a two-way interference signal;
step two, preprocessing the two interference signals after removing background light and zero padding to obtain I H (k) And I V (k) Wave number domain signals of (2); performing inverse Fourier transform on the wave number domain signals to obtain complex amplitudes of two paths of interference signals in the horizontal direction and the vertical direction, wherein the complex amplitudes are expressed as follows:
wherein the parameter z represents the depth coordinate in the axial direction, A andrespectively representing the amplitude and phase of the interference signal; subscripts H and V represent horizontal and vertical directions, respectively; eye information related to depth z can be obtained from the interference signals measured by the two orthogonal polarization channels according to the above formula;
step three, calculating Stokes vectorDescribing the polarization state of light: calculating polarized image based on polarization sensitive optical coherence tomography imaging principle, and calculating corresponding Stokes vector +.>
Wherein, the stokes vector is an expression form describing polarization, and I, Q, U, V is a parameter of the stokes vector; phase differenceThe phase difference of the interference light measured in two orthogonal polarization channels is described;
and step four, further calculating four parameters of reflection intensity I, accumulated phase delay delta, accumulated optical axis theta and polarization uniformity DOPU according to Stokes vector, wherein the four parameters are respectively as follows:
I(z)＝A H (z) 2 +A V (z) 2
wherein the measurement ranges of δ and θ are [0, pi/2 ] and [ -pi/2, pi/2 ], respectively, for describing the change in the cumulative polarization state of the eye from the surface to the measurement depth, DOPU represents the overall degree of polarization within the selected window for describing the depolarization characteristics of the eye.
2. A method of whole-eye imaging based on polarization-sensitive optical coherence tomography as recited in claim 1, wherein the PS-OCT imaging system is fiber OCT or space-optical OCT.
3. A method of full-eye imaging based on polarization-sensitive optical coherence tomography as recited in claim 1, wherein the PS-OCT imaging system is time domain OCT, spectral domain OCT, or swept source OCT.
4. The full-eye imaging method based on polarization sensitive optical coherence tomography of claim 1, wherein the PS-OCT imaging system is configured as a swept-source PS-OCT system, and comprises a broad-spectrum light source, a polarization controller, a circulator, a polarization beam splitter, a polarization maintaining coupler, a collimator one, a quarter-wave plate one, a dispersion compensator, a diaphragm, a mirror, a collimator two, a quarter-wave plate two, an eye scanning module, a polarization beam splitter two, a balance detector one, a balance detector two, and a signal processing device; the light output by the wide-spectrum light source is output into linearly polarized light along the vertical direction after passing through the polarization controller, the linearly polarized light enters the circulator, and the light emitted from the circulator passes through the first polarizing beam splitter and the first polarizing beam splitter 50:50, equally dividing the polarization maintaining coupler into a reference beam and a sample beam after the end a of the polarization maintaining coupler; the reference beam passes through a first collimator, a first quarter wave plate with an included angle of 22.5 degrees between the fast axis direction and the vertical direction, a dispersion compensator and a diaphragm, and is reflected back to the c end of the polarization maintaining coupler by the original path of the reflector; the sample beam passes through a second collimator and a second quarter wave plate with an included angle of 45 degrees between the fast axis direction and the vertical direction, so that the sample beam is converted from a linear polarization state to a circular polarization state; the sample beam irradiates the eyes through the eye scanning module, and light scattered back from the eyes returns to the d end of the polarization maintaining coupler along the original path; the reference light entering the c end of the polarization maintaining coupler interferes with the sample light at the d end, and the interfered light exits from the polarization maintaining coupler; after light emitted from the end a of the polarization maintaining coupler enters the first polarization beam splitter, light in the vertical direction enters the first balance detector through the circulator, and light in the horizontal direction enters the second balance detector; after the light emitted from the b end of the polarization maintaining coupler passes through the second polarization beam splitter, the light in the vertical direction enters the first balance detector, and the light in the horizontal direction enters the second balance detector; the balance detector I and the balance detector II receive light and then convert the light into an electric signal to be transmitted to the signal processing device.
5. A method of full-eye imaging based on polarization-sensitive optical coherence tomography as recited in claim 1, wherein the PS-OCT imaging system is configured as a spectral domain PS-OCT imaging system comprising: the device comprises a wide-spectrum light source, a linear polaroid, a non-polarized beam splitter, a first quarter wave plate, a dispersion compensator, a diaphragm, a reflecting mirror, a second quarter wave plate, an eye scanning module, a polarized beam splitter, a first signal detector, a second signal detector and a signal processing device;
the light output by the broad spectrum light source is output into linearly polarized light along the vertical direction after passing through the linear polaroid, and the linearly polarized light enters 50:50 is divided into a reference beam and a sample beam after the non-polarizing beam splitter; the reference beam passes through a first quarter wave plate, a dispersion compensator and a diaphragm, wherein the included angle between the fast axis direction and the vertical direction is 22.5 degrees, and is reflected back to the non-polarizing beam splitter by the original path of the reflector; the sample beam passes through a second quarter wave plate with an included angle of 45 degrees between the fast axis direction and the vertical direction, so that the sample beam is converted from a linear polarization state to a circular polarization state; the sample beam irradiates the eyes through the eye scanning module, and light scattered back from the eyes returns to the non-polarized beam splitter along the original path; the reference light and the sample light entering the non-polarizing beam splitter interfere, the polarized beam splitter is utilized to divide the interfered light into two beams of light with vertical and horizontal polarization directions, and the two beams of light are respectively received by the first signal detector and the second signal detector; the first signal detector and the second signal detector receive light and convert the light into electric signals to be transmitted to the signal processing device.
6. A method of full-eye imaging based on polarization-sensitive optical coherence tomography as recited in claim 5, wherein the signal detector comprises a spectrometer and a line camera, the spectrometer splitting light, the line camera receiving.
7. A method of full-eye imaging based on polarization-sensitive optical coherence tomography as recited in claim 1, wherein the PS-OCT imaging system is configured as a time domain PS-OCT imaging system comprising: the device comprises a wide-spectrum light source, a linear polaroid, a non-polarized beam splitter, a first quarter wave plate, a dispersion compensator, a diaphragm, a reflecting mirror, a second quarter wave plate, an eye scanning module, a polarized beam splitter, a first signal detector, a second signal detector and a signal processing device;
the light output by the broad spectrum light source is output into linearly polarized light along the vertical direction after passing through the linear polaroid, and the linearly polarized light enters 50:50 is divided into a reference beam and a sample beam after the non-polarizing beam splitter; the reference beam passes through a first quarter wave plate, a dispersion compensator and a diaphragm, wherein the included angle between the fast axis direction and the vertical direction is 22.5 degrees, and is reflected back to the non-polarizing beam splitter by the original path of the reflector; the sample beam passes through a second quarter wave plate with an included angle of 45 degrees between the fast axis direction and the vertical direction, so that the sample beam is converted from a linear polarization state to a circular polarization state; the sample beam irradiates the eyes through the eye scanning module, and light scattered back from the eyes returns to the non-polarized beam splitter along the original path; the reference light and the sample light entering the non-polarizing beam splitter interfere, the polarized beam splitter is utilized to divide the interfered light into two beams of light with vertical and horizontal polarization directions, and the two beams of light are respectively received by a first signal detector and a second signal detector; the first signal detector and the second signal detector receive light and convert the light into electric signals to be transmitted to the signal processing device.
8. A method of full-eye imaging based on polarization-sensitive optical coherence tomography as recited in claim 7, wherein the signal detector is configured as a point detector and the mirror is moved longitudinally to effect depth scanning.
9. A method of whole-eye imaging based on polarization-sensitive optical coherence tomography according to claim 4,5 or 7, wherein the eye scanning module is adapted to effect focusing and scanning of the sample beam at different positions of the whole eye, including fundus imaging mode and anterior ocular segment imaging mode.
10. A method of whole-eye imaging based on polarization-sensitive optical coherence tomography as recited in claim 9, wherein the eye scanning module switches between fundus and anterior ocular segment imaging modes by switching lenses to effect whole-eye imaging; the eye scanning module sequentially comprises a scanning galvanometer, a first convex lens and a second convex lens to an eye to be detected along an optical path when a fundus imaging mode is executed; the sample beam is focused on the fundus after passing through the eye scanning module, so as to realize fundus imaging; the structure of the eye scanning module in the anterior ocular segment imaging mode sequentially comprises a scanning galvanometer, a first convex lens, a third concave lens, a fourth convex lens and a second convex lens along an optical path to an eye to be detected; the sample beam is focused to the anterior ocular segment after passing through the eye scanning module, so as to realize anterior ocular segment imaging.
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| CN117462073B (en) * | 2023-12-25 | 2024-04-19 | 西北工业大学宁波研究院 | Hand-held polarization imaging intraocular pressure detection device and method |
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