技术领域technical field
本发明涉及活体人眼视网膜的光学高分辨率成像仪器，尤其是涉及一种采用轴锥镜实现贝塞尔环带照明的长焦深暗场视网膜OCT成像仪器。The invention relates to an optical high-resolution imaging device for living human retina, in particular to a telephoto deep dark-field retinal OCT imaging device which adopts an axicon to realize Bessel annular zone illumination.
背景技术Background technique
视网膜成像方法，主要包括眼底相机、荧光造影术、共焦扫描激光检眼镜、和光学相干层析(Opticalcoherencetomography，OCT)成像仪等。其中，只有OCT技术的横向和纵向分辨率是相互独立的，分别由光束的聚集条件和光源的带宽决定，故有可能同时获得高横向和高纵向分辨率。采用宽带、甚至超宽带光谱光源，很容易获得10μm以下、甚至达到细胞级(视细胞尺寸约2-4μm)的纵向分辨率。因此视网膜OCT成像技术获得了迅猛发展，并已有众多商用化仪器在眼科临床实践中获得应用。Retinal imaging methods mainly include fundus camera, fluorescein angiography, confocal scanning laser ophthalmoscope, and optical coherence tomography (Optical coherencetomography, OCT) imager, etc. Among them, only the horizontal and vertical resolutions of OCT technology are independent of each other, which are respectively determined by the focusing conditions of the beam and the bandwidth of the light source, so it is possible to obtain high horizontal and high vertical resolutions at the same time. Using a broadband or even ultra-broadband spectral light source, it is easy to obtain a longitudinal resolution below 10 μm, or even reach the cell level (depending on the cell size of about 2-4 μm). Therefore, retinal OCT imaging technology has developed rapidly, and many commercial instruments have been applied in ophthalmology clinical practice.
但目前的常规视网膜OCT技术，仍难以获得视网膜的高横向分辨率δr和高对比度图像，这是由于：1)视网膜是半透明组织，上皮细胞吸收了入射光信号中的大部分，被反射至探测器用于成像的光信号非常微弱。活体人眼成像有曝光剂量的限制，仅靠提高照明光强来改善成像质量的方法不可取；2)理论上增大入瞳光束直径Φ能提高δr，但人眼在大瞳孔时存在着复杂、动态变化的像差，反而会极大地降低δr。自适应光学(Adaptiveoptics，AO)技术被引入眼科领域而形成的视网膜AO-OCT技术，利用AO技术来矫正大瞳孔成像时存在的人眼像差，才实现了视网膜的横向细胞级分辨成像。但AO-OCT技术的高成本、高复杂度、和大体积等因素，制约了它的实际应用。因此，常规视网膜OCT技术简单、但δr低；而视网膜AO-OCT技术有极高的δr(细胞级)、但付出的代价极大。如果有一种新型视网膜OCT技术，其δr远高于常规视网膜OCT、但又无需付出视网膜AO-OCT技术的代价，这必将成为眼科基础研究和临床应用的有力工具。遗憾的是，目前还未见这样技术的报道。However, the current conventional retinal OCT technology is still difficult to obtain high lateral resolution δr and high contrast images of the retina, because: 1) the retina is a translucent tissue, and epithelial cells absorb most of the incident light signal and are reflected to The light signal that the detector uses for imaging is very weak. In vivo human eye imaging is limited by the exposure dose, and it is not advisable to improve the imaging quality only by increasing the illumination intensity; 2) In theory, increasing the diameter of the entrance pupil beam Φ can increase δr, but the human eye has complex problems when the pupil is large. , Dynamically changing aberrations will greatly reduce δr. Adaptive optics (AO) technology was introduced into the field of ophthalmology to form the AO-OCT technology of the retina. AO technology is used to correct the human eye aberrations that exist in large pupil imaging, and to achieve horizontal cell-level resolution imaging of the retina. However, the high cost, high complexity, and large volume of AO-OCT technology restrict its practical application. Therefore, conventional retinal OCT technology is simple, but δr is low; while retinal AO-OCT technology has extremely high δr (cell level), but the price paid is extremely high. If there is a new retinal OCT technology whose δr is much higher than conventional retinal OCT without paying the price of retinal AO-OCT technology, it will surely become a powerful tool for ophthalmology basic research and clinical application. Unfortunately, there are no reports of such technology at present.
常规光学成像技术的横向分辨率δr和焦深l是一对矛盾，高δr会导致短l。如中心波长λ0＝1060nm时：δr＝8.6μm、l＝284μmΦ2.5mm(不受像差影响的最大入瞳光束直径)；δr＝3.6μm、l＝49.3μmΦ6mm(视网膜AO-OCT系统常用的入瞳光束直径)。视网膜厚度约350μm，因此高δr成像时，l不能覆盖视网膜厚度。作为当前OCT技术主流的傅里叶域(Fourier-domain)OCT技术，包括谱域(Spectral-domain)OCT和扫频(Swept-source)OCT技术，均无需参考光束的纵向扫描就能获取样品深度方向的全部信息，故不能采用动态调焦技术以对不同深度的组织进行高分辨观察。因此，在保持高δr的同时，又使系统具有足够长的l，是视网膜成像亟待解决的问题。贝塞尔(Bessel)照明技术是解决这一问题的有效方法，其δr由照明环带光束的直径Φ决定、且相对常规照明方式(通常为高斯型照明)δr在同等条件下要提高约37％；l则由照明环带的厚度H和入瞳光束直径Φ共同决定，通过合理的光学设计可极大地扩展l，但需权衡由于l扩展导致的光能密度下降问题。所以贝塞尔照明有可能同时获得高δr(相对常规视网膜OCT系统)和长l、且δr在长l范围内保持不变，这些特点使其成为视网膜成像的最佳手段，但目前未见相关报道。The lateral resolution δr and depth of focus l of conventional optical imaging technology are a pair of contradictions, high δr will lead to short l. For example, when the central wavelength λ0 =1060nm: δr=8.6μm, l=284μmΦ2.5mm (maximum entrance pupil beam diameter not affected by aberration); pupil beam diameter). The thickness of the retina is about 350 μm, so when imaging with high δr, l cannot cover the thickness of the retina. As the current mainstream of OCT technology, Fourier-domain OCT technology, including Spectral-domain OCT and Swept-source OCT technology, can obtain the depth of the sample without longitudinal scanning of the reference beam Therefore, dynamic focusing technology cannot be used for high-resolution observation of tissues at different depths. Therefore, making the system have a sufficiently long l while maintaining a high δr is an urgent problem to be solved in retinal imaging. Bessel (Bessel) lighting technology is an effective method to solve this problem. Its δr is determined by the diameter Φ of the lighting ring beam, and compared with conventional lighting (usually Gaussian lighting) δr is about 37% higher under the same conditions. %; l is determined by the thickness H of the illumination ring and the diameter of the entrance pupil beam Φ, and l can be greatly expanded through reasonable optical design, but the problem of the decrease of light energy density caused by the expansion of l needs to be weighed. Therefore, it is possible to obtain high δr (compared to the conventional retinal OCT system) and long l at the same time with Bessel illumination, and δr remains unchanged in the range of long l. These characteristics make it the best means for retinal imaging, but there is no correlation reports.
视网膜图像的信噪比和对比度低，这是由于：1)视网膜是半透明组织，其后向反射光信号非常微弱；2)光路上的光学器件和角膜界面均存在着后向反射杂散光、以及照明光束入射视网膜时存在着镜面反射光信号，它们会形成很强的背景信号，占据了探测器的动态范围，使得来自视网膜微小变化的光信号不能被探测。这一问题可采用暗场(Dark-field)成像技术来解决：通过把来自视网膜的有用暗场光信号与上述强背景信号相分离、而只探测前者，就可实现在低背景信号下的大动态范围成像，就有可能观察到组织结构的微小变化和更深层的结构信息。现有的暗场成像技术，通常采用中心遮挡的方式来形成暗场照明，并在探测端进行边缘遮挡来滤除照明光束的后向反射光信号。由于照明光束大多为高斯型能量分布，其总能量的86.5％分布在光束中心32％的区域内，可见中心遮挡会极大地降低光能利用率。轴锥镜(Axicon)是实现暗场照明的最佳器件，平行光束通过轴锥镜并传输到远场后成为圆锥型环带光束、经过光学系统传输后，以环带形式入射角膜，在视网膜上形成暗场照明，且无光能利用率低的问题。The signal-to-noise ratio and contrast of the retinal image are low, which is due to: 1) the retina is a translucent tissue, and its retroreflected light signal is very weak; 2) there are retroreflected stray light, And when the illumination beam enters the retina, there are specular reflection light signals, which will form a strong background signal and occupy the dynamic range of the detector, so that the light signal from the small change of the retina cannot be detected. This problem can be solved by using dark-field imaging technology: by separating the useful dark-field light signal from the retina from the above-mentioned strong background signal and only detecting the former, large-scale imaging under low background signal can be achieved. With dynamic range imaging, it is possible to observe small changes in tissue structure and deeper structural information. The existing dark-field imaging technology usually adopts a central shading method to form dark-field illumination, and performs edge shading at the detection end to filter out the back-reflected light signal of the illumination beam. Since most of the illumination beams have a Gaussian energy distribution, 86.5% of the total energy is distributed in the area of 32% of the center of the beam, so it can be seen that the central occlusion will greatly reduce the utilization rate of light energy. Axicon is the best device for dark-field illumination. The parallel light beam passes through the axicon and is transmitted to the far field to become a conical ring-shaped beam. After being transmitted by the optical system, it enters the cornea in the form of a ring. Dark field illumination is formed on the surface, and there is no problem of low utilization rate of light energy.
在中科院光电所杨亚良等人提出的视网膜暗场OCT系统里(杨亚良等，连续可调环带照明视网膜暗视场光学相干层析成像仪，发明专利：ZL201410066927.5)，利用一对锥顶相对安装的轴锥镜来形成暗场照明，其显著特点有：1)照明环带的大小和厚度可连续调节、以满足不同被测对象的需求；2)具有横向超分辨效果，但δr在l范围内不能保持不变。该系统为传统的高斯照明、而不是贝塞尔照明方式，不具有提高δr和扩展l的能力。In the retinal dark-field OCT system proposed by Yang Yaliang et al. from the Institute of Optoelectronics, Chinese Academy of Sciences (Yang Yaliang et al., continuous adjustable ring-illuminated retinal dark-field optical coherence tomography, invention patent: ZL201410066927.5), using a pair of cone tops facing each other The installed axicon mirror is used to form dark-field illumination, and its salient features are: 1) The size and thickness of the illumination ring can be adjusted continuously to meet the needs of different measured objects; 2) It has a horizontal super-resolution effect, but δr is in l The range cannot remain constant. The system is traditional Gaussian lighting, not Bezier lighting, and does not have the ability to increase δr and expand l.
总之，目前还未见同时具有以下三个特点的视网膜OCT成像技术的报道：1)显著提高δr，以填补常规视网膜OCT和视网膜AO-OCT技术之间的δr空隙；2)保持高δr的同时、仍具有足够长的l，以便对视网膜深度范围内的全部组织进行高分辨成像；3)暗场成像以提高图像的信噪比、对比度、和立体感。In conclusion, there is no report on a retinal OCT imaging technique that simultaneously has the following three characteristics: 1) Significantly increase δr to fill the δr gap between conventional retinal OCT and retinal AO-OCT techniques; 2) Maintain high δr while maintaining high δr , still have a long enough l, so that high-resolution imaging is performed on all tissues within the depth range of the retina; 3) dark field imaging to improve the signal-to-noise ratio, contrast, and stereoscopic effect of the image.
发明内容Contents of the invention
本发明要解决的技术问题是：克服现有技术的不足，提供一种活体人眼视网膜的长焦深高分辨率暗场OCT成像系统，该系统采用一个轴锥镜来形成贝塞尔环带暗场照明，以实现扩展焦深的同时、极大地提高横向分辨率并在长焦深范围内保持不变、和提高图像的信噪比、对比度、和立体感。The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a long focal depth and high resolution dark-field OCT imaging system for the living human retina, which uses an axicon to form a Bessel ring Dark field illumination, in order to realize the expansion of the focal depth, greatly improve the lateral resolution and keep it unchanged in the long focal depth range, and improve the signal-to-noise ratio, contrast, and stereoscopic effect of the image.
本发明解决其技术问题所采用的技术方案是：采用贝塞尔环带照明方式的长焦深暗场视网膜OCT系统，包括：光源、光纤耦合器、第一准直器、第二准直器、第一可变光阑(5)、第二可变光阑、轴锥镜、第一透镜、第二透镜、第三透镜、分光镜、水平扫描器、垂直扫描器、第一耦合镜、第二耦合镜、色散补偿片、水盒、平移台、第一偏振控制器、第二偏振控制器、探测端、第一单模光纤、第二单模光纤、第三单模光纤、第四单模光纤、第五单模光纤、函数发生卡、数据采集卡和计算机；The technical solution adopted by the present invention to solve the technical problems is: a telephoto deep dark-field retinal OCT system adopting the Bessel ring illumination mode, comprising: a light source, an optical fiber coupler, a first collimator, and a second collimator , the first iris diaphragm (5), the second iris diaphragm, the axicon, the first lens, the second lens, the third lens, the beam splitter, the horizontal scanner, the vertical scanner, the first coupling mirror, The second coupling mirror, the dispersion compensation film, the water box, the translation stage, the first polarization controller, the second polarization controller, the detection end, the first single-mode fiber, the second single-mode fiber, the third single-mode fiber, the fourth Single-mode optical fiber, fifth single-mode optical fiber, function generation card, data acquisition card and computer;
光源发出的光信号，经第一单模光纤传输至光纤耦合器后分成两路，分别经第二单模光纤和第三单模光纤传输至样品臂和参考臂；The optical signal sent by the light source is transmitted to the fiber coupler through the first single-mode fiber and then divided into two paths, which are respectively transmitted to the sample arm and the reference arm through the second single-mode fiber and the third single-mode fiber;
在样品臂中，从第二单模光纤输出的光束，被第一准直器准直和通过第一可变光阑后，平行入射轴锥镜；光束通过轴锥镜并传播到远场后形成圆锥型环带光束，然后依次经过第一透镜、分光镜、水平扫描器、垂直扫描器、第二透镜和第三透镜后，以环带方式入射人眼、并被人眼屈光系统聚焦在视网膜上，形成贝塞尔环带暗场照明；被视网膜后向反射或散射的样品光信号，沿原路返回至分光镜；被分光镜反射的样品光信号中、通过第二可变光阑的部分，被第一耦合镜耦合进第四单模光纤中、并传输至探测端；第一偏振控制器安装在第四单模光纤上；In the sample arm, the light beam output from the second single-mode fiber is collimated by the first collimator and passes through the first iris diaphragm, and is parallel to the incident axicon; the light beam passes through the axicon and propagates to the far field Form a conical ring-shaped light beam, and then pass through the first lens, the beam splitter, the horizontal scanner, the vertical scanner, the second lens and the third lens in sequence, enter the human eye in the form of a ring, and be focused by the human eye refractive system On the retina, dark-field illumination of the Bessel ring is formed; the sample light signal reflected or scattered by the retina returns to the spectroscope along the original path; the sample light signal reflected by the spectroscope passes through the second variable light The part of the diaphragm is coupled into the fourth single-mode fiber by the first coupling mirror and transmitted to the detection end; the first polarization controller is installed on the fourth single-mode fiber;
在参考臂中，从第三单模光纤输出的参考光信号，被第二准直器准直后，依次经过色散补偿片和水盒，然后被第二耦合镜耦合进第五单模光纤中、并传输至探测端；第二耦合镜固定在平移台上；第二偏振控制器安装在第五单模光纤上；In the reference arm, the reference optical signal output from the third single-mode fiber is collimated by the second collimator, passes through the dispersion compensation plate and the water box in turn, and then is coupled into the fifth single-mode fiber by the second coupling mirror , and transmitted to the detection end; the second coupling mirror is fixed on the translation stage; the second polarization controller is installed on the fifth single-mode fiber;
由平移台带着第二耦合镜作轴向移动，用于匹配样品臂和参考臂之间的光程，直至样品光信号和参考光信号在探测端形成干涉光谱信号；通过调节第一偏振控制器和第二偏振控制器，来匹配样品光信号和参考光信号的偏振态；The translation stage moves the second coupling mirror axially to match the optical path between the sample arm and the reference arm until the sample optical signal and the reference optical signal form an interference spectrum signal at the detection end; by adjusting the first polarization control and a second polarization controller to match the polarization states of the sample optical signal and the reference optical signal;
光源、水平扫描器和垂直扫描器、以及对干涉光谱信号的采样，需同步控制；光源发出光束的同时，还发出同步触发信号，去控制计算机同步发出开始扫描和对干涉光谱信号进行采样的触发信号；由函数发生卡产生所需的扫描信号，分别去驱动水平扫描器和垂直扫描器，使聚焦在视网膜上的光斑进行横向二维扫描；干涉光谱信号被探测端接收并转换成模拟电信号，再被数据采集卡同步触发采样并转换成数字信号，然后传输至计算机进行处理，以获得视网膜的图像。The light source, horizontal scanner and vertical scanner, and the sampling of the interference spectrum signal need to be controlled synchronously; while the light source sends out the beam, it also sends out a synchronous trigger signal to control the computer to simultaneously send out the trigger to start scanning and sample the interference spectrum signal Signal; the required scanning signal is generated by the function generation card to drive the horizontal scanner and the vertical scanner respectively, so that the light spot focused on the retina can be scanned in two dimensions horizontally; the interference spectrum signal is received by the detection end and converted into an analog electrical signal , which is then synchronously triggered by the data acquisition card to be sampled and converted into a digital signal, and then transmitted to a computer for processing to obtain retinal images.
所述的光源可以是超连续发光二极管即SLD、或锁模飞秒激光光源等近红外波段宽光谱光源，此时的探测端采用光谱探测方式，即：干涉光谱信号被色散器件按波长色散开来、再用线阵探测器接收，这一方式构成了谱域OCT成像模式；光源也可以是波长随时间快速扫描的近红外波段宽光谱扫频光源，此时的探测端采用平衡探测方式，具体由分光比为50:50的光纤耦合器和平衡探测器实现，这一方式构成了扫频OCT成像模式；谱域OCT和扫频OCT为傅里叶域OCT的两种成像模式，均不需参考光的轴向扫描就能获得视网膜整个成像深度范围内的图像。The light source can be a near-infrared band wide-spectrum light source such as a supercontinuous light-emitting diode (SLD), or a mode-locked femtosecond laser light source. At this time, the detection end adopts a spectral detection method, that is, the interference spectrum signal is dispersed by the dispersion device according to the wavelength. Open, and then receive with a linear array detector, this method constitutes a spectral domain OCT imaging mode; the light source can also be a near-infrared band wide-spectrum frequency-sweeping light source whose wavelength quickly scans over time, and the detection end at this time adopts a balanced detection method , specifically implemented by a fiber coupler with a splitting ratio of 50:50 and a balanced detector. This method constitutes a swept-frequency OCT imaging mode; spectral domain OCT and frequency-swept OCT are two imaging modes of Fourier domain OCT, both Axial scans without a reference beam can acquire images across the entire imaging depth of the retina.
所述的第一可变光阑用于调节入射角膜的环带照明的厚度；第二可变光阑用于遮挡从视网膜返回样品光信号中对应于照明环带部分的光信号，以实现暗场OCT成像。The first iris diaphragm is used to adjust the thickness of the annulus illumination of the incident cornea; the second iris diaphragm is used to block the light signal corresponding to the part of the illumination annulus in the sample light signal returned from the retina to achieve dark Field OCT imaging.
所述的第一透镜的后焦面和前焦面，分别与轴锥镜的主焦面和第二透镜的后焦面重合；第二透镜的前焦面与第三透镜的后焦面重合，二者构成一个缩束系统。The rear focal plane and the front focal plane of the first lens coincide with the main focal plane of the axicon and the rear focal plane of the second lens respectively; the front focal plane of the second lens coincides with the rear focal plane of the third lens , the two form a contraction system.
所述的分光镜具有高反射/透射比，使从视网膜返回样品光信号中的大部分用于OCT成像，以提高图像信噪比。The spectroscope has a high reflectance/transmittance ratio, so that most of the sample light signals returned from the retina are used for OCT imaging, so as to improve the signal-to-noise ratio of the image.
所述的第一耦合镜和第二耦合镜，可以是对光源输出的宽光谱波段进行消色差设计的透射式器件、也可以是反射式器件，以使样品光信号中的各光谱分量均能被第一耦合镜耦合进第四单模光纤中、和使参考光信号中的各光谱分量均能被第二耦合镜耦合进第五单模光纤中。The first coupling mirror and the second coupling mirror can be transmissive devices with achromatic design for the wide spectral band output by the light source, or reflective devices, so that each spectral component in the sample optical signal can be coupled into the fourth single-mode optical fiber by the first coupling mirror, and enable each spectral component in the reference optical signal to be coupled into the fifth single-mode optical fiber by the second coupling mirror.
所述的水盒用于补偿由人眼引起的色散；色散补偿片和水盒两端的密封窗口片，用于补偿样品臂中轴锥镜、第一透镜、第二透镜、第三透镜和分光镜引起的色散。The water box is used to compensate for the dispersion caused by the human eye; the dispersion compensation plate and the sealing windows at both ends of the water box are used to compensate the axicon, the first lens, the second lens, the third lens and the beam splitter in the sample arm. Dispersion caused by the mirror.
本发明与现有技术相比的有益效果是：The beneficial effect of the present invention compared with prior art is:
1)相对于常规的高斯照明，本发明采用的贝塞尔照明方式具有横向超分辨的效果，在同等条件下可观察到更多组织细节。本发明能够获得高于常规视网膜OCT系统约37％的横向分辨率、但又无需付出诸如视网膜AO-OCT系统的代价，因此是一种填补常规视网膜OCT与视网膜AO-OCT系统之间横向分辨率空隙的新型、简单技术。横向超分辨的原因有：(1)环带照明本身就具有一定的超分辨效果；(2)高斯能量分布的准直光束通过轴锥镜后，能量较高的中心区域光线被转换到环带的外侧、而能量较低的边缘区域光线被转换到环带的内侧，这一反转的能量分布比高斯能量分布更能充分利用聚焦物镜(人眼屈光系统)的数值孔径；(3)接收从样品返回光信号的单模光纤的芯径较小(小于10μm)，其包层具有针孔滤波的作用，可滤除贝塞尔环带照明存在的旁瓣信号和各种杂散光信号。1) Compared with conventional Gaussian lighting, the Bessel lighting method adopted in the present invention has the effect of lateral super-resolution, and more tissue details can be observed under the same conditions. The present invention can obtain about 37% higher lateral resolution than the conventional retinal OCT system without paying the price of the retinal AO-OCT system, so it is a method to fill the lateral resolution between conventional retinal OCT and retinal AO-OCT systems A new, simple technique for voiding. The reasons for lateral super-resolution are as follows: (1) the annular zone illumination itself has a certain super-resolution effect; (2) after the collimated beam of Gaussian energy distribution passes through the axicon, the light in the central area with higher energy is converted to the annular zone , and the light in the edge region with lower energy is converted to the inner side of the annulus. This inverted energy distribution can make full use of the numerical aperture of the focusing objective lens (the refractive system of the human eye) than the Gaussian energy distribution; (3) The core diameter of the single-mode optical fiber that receives the light signal returned from the sample is small (less than 10 μm), and its cladding has the function of pinhole filtering, which can filter out the side lobe signal and various stray light signals existing in Bessel ring illumination .
2)本发明采用的贝塞尔照明成像方式，极大地扩展了焦深范围、并使横向分辨率在长焦深范围内保持不变，避免了常规光学成像系统固有的横向分辨率和焦深的矛盾。这是由于贝塞尔照明成像技术的横向分辨率由环带光束的直径、焦深由环带光束的直径和厚度决定。因此通过合理的光学设计，有可能同时获得高横向分辨率和长焦深，从而能够对视网膜深度范围内的全部组织进行高横向分辨率观察。长焦深还有利于对屈光不正眼的成像、而无需进行离焦矫正。2) The Bessel illumination imaging method adopted in the present invention greatly expands the focal depth range, and keeps the lateral resolution unchanged in the long focal depth range, avoiding the inherent lateral resolution and focal depth of conventional optical imaging systems contradiction. This is because the lateral resolution of Bessel illumination imaging technology is determined by the diameter of the annular beam, and the depth of focus is determined by the diameter and thickness of the annular beam. Therefore, through reasonable optical design, it is possible to obtain high lateral resolution and long focal depth at the same time, thus enabling high lateral resolution observation of all tissues within the depth range of the retina. A long depth of focus also facilitates imaging of ametropic eyes without defocus correction.
3)本发明采用轴锥镜来形成环带暗场照明，克服了通常采用中心遮挡方式导致的光能损失过大问题。虽然本发明采用对入射轴锥镜的准直光束进行边缘遮挡来调节环带照明的厚度，但入射轴锥镜的光束为高斯能量分布，其边缘光线的能量极低，故不会造成太大的光能损失。3) The present invention uses an axicon mirror to form annular dark-field illumination, which overcomes the problem of excessive loss of light energy caused by the usual central blocking method. Although the present invention adopts the edge shielding of the collimated light beam of the incident axicon to adjust the thickness of the ring illumination, the light beam of the incident axicon is Gaussian energy distribution, and the energy of its edge light is extremely low, so it will not cause too much damage. loss of light energy.
4)本发明提出的暗场视网膜OCT成像系统，能够获得高信噪比、高对比度、和强立体感的视网膜图像。由于光路上所有的光学器件和角膜界面均存在着后向反射杂散光信号、以及照明光束入射视网膜时存在着镜面反射光信号，它们形成了很强的背景信号，占据了探测器的动态范围，使得视网膜结构微小变化的光信号不能被探测到。本发明采用可变光阑来滤除强背景信号，而只接收来自视网膜的暗场光信号，从而释放了探测器的动态范围，使得视网膜结构的微小变化以及更深层结构的信息均能被探测。4) The dark-field retinal OCT imaging system proposed by the present invention can obtain retinal images with high signal-to-noise ratio, high contrast, and strong stereoscopic effect. Since there are back-reflected stray light signals in all the optical devices and the corneal interface on the optical path, and specularly reflected light signals exist when the illumination beam enters the retina, they form a strong background signal and occupy the dynamic range of the detector. Light signals that cause small changes in retinal structure cannot be detected. The present invention uses variable aperture to filter out strong background signals, and only receives dark-field light signals from the retina, thereby releasing the dynamic range of the detector, so that small changes in the retinal structure and information of deeper structures can be detected .
附图说明Description of drawings
图1是本发明的系统结构示意图；Fig. 1 is a schematic diagram of the system structure of the present invention;
图2是本发明的控制系统示意图；Fig. 2 is a schematic diagram of a control system of the present invention;
图3是贝塞尔环带照明的光路示意图；Fig. 3 is a schematic diagram of the optical path of the Bessel ring illumination;
图4是贝塞尔环带照明和常规高斯环带照明的对比示意图，其中：图4(a)为贝塞尔环带照明示意图，图4(b)为常规高斯环带照明示意图。Fig. 4 is a schematic diagram of comparison between Bessel ring lighting and conventional Gauss ring lighting, wherein: Fig. 4(a) is a schematic diagram of Bessel ring lighting, and Fig. 4(b) is a schematic diagram of conventional Gauss ring lighting.
图中：1.光源，2.光纤耦合器，3.第一准直器，4.第二准直器，5.第一可变光阑，6.第二可变光阑，7.轴锥镜，8.第一透镜，9.第二透镜，10.第三透镜，11.分光镜，12.水平扫描器，13.垂直扫描器，14.人眼屈光系统，15.视网膜，16.第一耦合镜，17.第二耦合镜，18色散补偿片，19水盒，20.平移台，21.第一偏振控制器，22.第二偏振控制器，23.探测端，24.第一单模光纤，25.第二单模光纤，26.第三单模光纤，27.第四单模光纤，28.第五单模光纤，29.函数发生卡，30.数据采集卡，31计算机。In the figure: 1. Light source, 2. Fiber coupler, 3. First collimator, 4. Second collimator, 5. First iris diaphragm, 6. Second iris diaphragm, 7. Axis Axicon, 8. First lens, 9. Second lens, 10. Third lens, 11. Beam splitter, 12. Horizontal scanner, 13. Vertical scanner, 14. Human eye refractive system, 15. Retina, 16. First coupling mirror, 17. Second coupling mirror, 18 Dispersion compensation film, 19 Water box, 20. Translation stage, 21. First polarization controller, 22. Second polarization controller, 23. Detection end, 24 .First single-mode optical fiber, 25. Second single-mode optical fiber, 26. Third single-mode optical fiber, 27. Fourth single-mode optical fiber, 28. Fifth single-mode optical fiber, 29. Function generation card, 30. Data acquisition card , 31 computers.
具体实施方式detailed description
下面结合附图以及具体实施例进一步说明本发明。The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.
本发明提出的采用贝塞尔环带照明方式的长焦深暗场视网膜OCT系统的结构如图1示，包括：光源1、光纤耦合器2、第一和第二准直器3-4、第一和第二可变光阑5-6、轴锥镜7、第一至第三透镜8-10、分光镜11、水平和垂直扫描器12-13、第一和第二耦合镜16-17、色散补偿片18、水盒19、平移台20、第一和第二偏振控制器21-22、探测端23、第一至第五单模光纤24-28、函数发生卡29、数据采集卡30和计算机31。The structure of the telephoto deep dark-field retinal OCT system that adopts the Bessel ring illumination mode proposed by the present invention is shown in Figure 1, including: a light source 1, an optical fiber coupler 2, a first and a second collimator 3-4, First and second iris 5-6, axicon 7, first to third lens 8-10, beam splitter 11, horizontal and vertical scanner 12-13, first and second coupling mirror 16- 17. Dispersion compensation sheet 18, water box 19, translation stage 20, first and second polarization controllers 21-22, detection end 23, first to fifth single-mode optical fibers 24-28, function generation card 29, data acquisition card 30 and computer 31 .
光源1发出的光信号，经第一单模光纤24传输至光纤耦合器2后分成两路，分别经第二和第三单模光纤25-26传输至样品臂和参考臂。在样品臂中，从第二单模光纤25输出的光束，被第一准直器3准直和通过第一可变光阑5后，平行入射轴锥镜7。光束通过轴锥镜7并传播到远场后成为圆锥型环带光束，然后依次经过第一透镜8、分光镜11、水平和垂直扫描器12-13、第二和第三透镜9-10后，以环带方式入射人眼、并被人眼屈光系统14聚焦在视网膜15上，形成贝塞尔环带暗场照明。被视网膜15后向反射或散射的样品光信号，沿原路返回至分光镜11。被分光镜11反射的样品光信号中、通过第二可变光阑6的部分，被第一耦合镜16耦合进第四单模光纤27中、并传输至探测端23。其中，第一可变光阑5用于调节入射角膜的环带照明光束的厚度，第二可变光阑6用于遮挡从视网膜15返回样品光信号中对应于照明环带部分的光信号、以实现暗场OCT成像。第一透镜8的后焦面和前焦面，分别与轴锥镜7的主焦面和第二透镜9的后焦面重合；第二透镜9的前焦面与第三透镜10的后焦面重合，二者构成一个缩束系统。分光镜11具有高反射/透射比、如高于70/30，使从视网膜15返回样品光信号中的大部分用于OCT成像，以提高图像信噪比。The optical signal emitted by the light source 1 is transmitted to the fiber coupler 2 through the first single-mode optical fiber 24 and then divided into two paths, which are respectively transmitted to the sample arm and the reference arm through the second and third single-mode optical fibers 25-26. In the sample arm, the light beam output from the second single-mode fiber 25 is collimated by the first collimator 3 and passes through the first variable diaphragm 5 , and is incident parallel to the axicon 7 . The light beam passes through the axicon mirror 7 and propagates to the far field to become a conical annular beam, and then passes through the first lens 8, the beam splitter 11, the horizontal and vertical scanners 12-13, the second and the third lens 9-10 in sequence , enters the human eye in an annular manner, and is focused on the retina 15 by the human eye refractive system 14 to form a Bessel annular dark field illumination. The light signal of the sample back reflected or scattered by the retina 15 returns to the spectroscope 11 along the original path. Among the sample light signals reflected by the beam splitter 11 , the part passing through the second iris diaphragm 6 is coupled into the fourth single-mode optical fiber 27 by the first coupling mirror 16 and transmitted to the detection end 23 . Wherein, the first iris diaphragm 5 is used to adjust the thickness of the annulus illumination light beam incident on the cornea, and the second iris diaphragm 6 is used to block the light signal corresponding to the illuminated annulus part of the sample light signal returned from the retina 15, To achieve dark-field OCT imaging. The back focal plane and the front focal plane of the first lens 8 coincide with the main focal plane of the axicon 7 and the back focal plane of the second lens 9 respectively; The planes coincide, and the two form a attenuator system. The spectroscope 11 has a high reflectance/transmittance ratio, such as higher than 70/30, so that most of the sample light signal returned from the retina 15 is used for OCT imaging, so as to improve the signal-to-noise ratio of the image.
在参考臂中，从第三单模光纤26输出的参考光信号，被第二准直器4准直后，依次经过色散补偿片18和水盒19，然后被固定在平移台20上的第二耦合镜17耦合进第五单模光纤28中、并传输至探测端23。其中，水盒19用于补偿由人眼引起的色散；色散补偿片18和水盒19两端的密封窗口片，用于补偿样品臂中轴锥镜7、第一至第三透镜8-10、和分光镜11引起的色散。由平移台20带着第二耦合镜17作轴向移动，用于匹配样品臂和参考臂之间的光程，直至样品光信号和参考光信号在探测端23形成干涉光谱信号。第一和第二耦合镜16-17，可以是对光源1输出的宽光谱波段进行消色差设计的透射式器件，也可以是反射式器件、如90°离轴抛物面反射式准直器，以使样品光信号中的各光谱分量均能被第一耦合镜16耦合进第四单模光纤27中、和使参考光信号中的各光谱分量均能被第二耦合镜17耦合进第五单模光纤28中。第一和第二偏振控制器21-22分别安装在第四和第五单模光纤27-28上，通过调节第一和第二偏振控制器21-22来匹配样品光信号和参考光信号的偏振态。In the reference arm, the reference optical signal output from the third single-mode optical fiber 26 is collimated by the second collimator 4, passes through the dispersion compensation plate 18 and the water box 19 in sequence, and is then fixed on the first The second coupling mirror 17 is coupled into the fifth single-mode fiber 28 and transmitted to the detection end 23 . Wherein, the water box 19 is used to compensate the dispersion caused by the human eye; the sealing windows at the two ends of the dispersion compensation sheet 18 and the water box 19 are used to compensate the sample arm axis axicon 7, the first to the third lens 8-10, and the dispersion caused by the beam splitter 11. The second coupling mirror 17 is moved axially by the translation stage 20 to match the optical path between the sample arm and the reference arm until the sample light signal and the reference light signal form an interference spectrum signal at the detection end 23 . The first and second coupling mirrors 16-17 can be transmissive devices with achromatic design for the wide spectral band output by the light source 1, or reflective devices, such as 90° off-axis parabolic reflective collimator, to Each spectral component in the sample optical signal can be coupled into the fourth single-mode optical fiber 27 by the first coupling mirror 16, and each spectral component in the reference optical signal can be coupled into the fifth single-mode optical fiber by the second coupling mirror 17. mode fiber 28. The first and second polarization controllers 21-22 are installed on the fourth and fifth single-mode optical fibers 27-28 respectively, and the first and second polarization controllers 21-22 are adjusted to match the polarity of the sample optical signal and the reference optical signal polarization state.
本发明采用傅里叶域、也叫频率域OCT技术，具体包含谱域OCT和扫频OCT两种模式，无需参考光的轴向扫描就能获得视网膜15整个成像深度范围内的图像，因此具有成像速度快、信噪比高等优点。谱域OCT成像时：光源1为超连续发光二极管即SLD、或锁模飞秒激光光源等近红外波段宽光谱光源；探测端23采用光谱探测方式，即：干涉光谱信号被色散器件按波长色散开来、再用线阵探测器接收。扫频OCT成像时：光源1为波长随时间快速扫描的近红外波段宽光谱扫频光源；探测端23采用平衡探测方式，具体由分光比为50:50的光纤耦合器和平衡探测器实现。The present invention adopts Fourier domain, which is also called frequency domain OCT technology, specifically includes two modes of spectral domain OCT and frequency sweep OCT, and can obtain images within the entire imaging depth range of the retina 15 without axial scanning of reference light, so it has the advantages of It has the advantages of fast imaging speed and high signal-to-noise ratio. In spectral domain OCT imaging: the light source 1 is a near-infrared band wide-spectrum light source such as a supercontinuum light-emitting diode (SLD), or a mode-locked femtosecond laser light source; Spread out and then receive with a line array detector. During frequency-sweeping OCT imaging: the light source 1 is a near-infrared band wide-spectrum frequency-sweeping light source whose wavelength rapidly scans over time; the detection end 23 adopts a balanced detection method, which is specifically realized by a fiber coupler and a balanced detector with a splitting ratio of 50:50.
本发明的控制系统如图2示。光源1、水平和垂直扫描器12-13、和对干涉光谱信号的采样，需实现同步控制。光源1发出光束的同时，还发出同步触发信号，去控制计算机31同步发出开始扫描和对干涉光谱信号进行采样的触发信号：由函数发生卡29产生所需的扫描信号，分别去驱动水平和垂直扫描器12-13，使聚焦在视网膜15上的光斑进行横向二维扫描；干涉光谱信号被探测端23接收并转换成模拟电信号，再被数据采集卡30同步触发采样并转换成数字信号，然后传输至计算机31进行处理，以获得视网膜15的图像。The control system of the present invention is shown in Figure 2. The light source 1, the horizontal and vertical scanners 12-13, and the sampling of the interference spectrum signal need to be controlled synchronously. When the light source 1 emits the light beam, it also sends out a synchronous trigger signal to control the computer 31 to synchronously send out a trigger signal to start scanning and sample the interference spectrum signal: the function generation card 29 generates the required scanning signal to drive the horizontal and vertical signals respectively. The scanners 12-13 enable the light spot focused on the retina 15 to scan horizontally and two-dimensionally; the interference spectrum signal is received by the detection terminal 23 and converted into an analog electrical signal, and is then synchronously triggered by the data acquisition card 30 to sample and convert into a digital signal. Then it is transmitted to the computer 31 for processing to obtain the image of the retina 15 .
图3是本发明用于说明贝塞尔环带照明的光路示意图。为使光路简洁易懂，把本应被水平和垂直扫描器12-13反射的光束作透射处理、以拉直光路，但光路原理和相互关系仍不变。设可变光阑5的孔径为d，轴锥镜7的折射率为n、锥面底角为θ，光源1输出光谱的中心波长为λ0，这些参数均已知。平行光束通过轴锥镜7并传输到远场后形成圆锥型环带光束，其与光轴的夹角为βa，由Snell定律可得：βa＝arcsin(n·sinθ)-θ。光束通过轴锥镜7后形成的近场贝塞尔光斑的横向分辨率δra和焦深la分别由式(1)和式(2)求得：Fig. 3 is a schematic diagram of the light path used to illustrate the Bezier ring illumination in the present invention. In order to make the light path simple and easy to understand, the light beams that should be reflected by the horizontal and vertical scanners 12-13 are transmitted to straighten the light path, but the principle and mutual relationship of the light path remain unchanged. Let the aperture of the iris 5 be d, the refractive index of the axicon 7 be n, the base angle of the cone surface be θ, and the central wavelength of the output spectrum of the light source 1 be λ0 , these parameters are known. The parallel light beam passes through the axicon mirror 7 and is transmitted to the far field to form a conical annular beam. The angle between it and the optical axis is βa . According to Snell's law: βa =arcsin(n·sinθ)-θ. The lateral resolution δra and depth of focusla of the near-field Bessel spot formed after the beam passes through the axicon 7 are obtained by formula (1) and formula (2) respectively:
其中H为入射人眼环带光束的厚度。Where H is the thickness of the beam incident on the annulus of the human eye.
圆锥型环带光束依次经过第一至第三透镜8-10(焦距分别为f1、f2、f3)传输后，被焦距为fe的人眼屈光系统14聚焦在视网膜15上，形成贝塞尔环带暗场照明。从轴锥镜7的近场光斑到视网膜15上的聚焦光斑，光学系统放大率为M＝(f2·fe)/(f1·f3)。环带光束被聚焦在视网膜15上的孔径角为βe＝arctan(tanβa/M)，在视网膜15上的贝塞尔照明光斑的横向分辨率δre和焦深le分别由式(3)和式(4)求得：After being transmitted through the first to third lenses 8-10 (with focal lengths of f1 , f2 , and f3 ) successively, the conical annular light beams are focused on the retina 15 by the human eye refractive system 14 with the focal length of fe , Form a Bezier ring with darkfield illumination. From the near-field light spot of the axicon 7 to the focused light spot on the retina 15, the magnification of the optical system is M=(f2 ·fe )/(f1 ·f3 ). The aperture angle at which the annular light beam is focused on the retina 15 is βe =arctan(tan βa /M), and the lateral resolution δre and focal depth le of the Bessel illumination spot on the retina 15 are respectively given by the formula (3 ) and formula (4) to obtain:
le＝M2·la，(4)le =M2 ·la , (4)
图4是本发明用于比较说明贝塞尔环带照明和常规高斯环带照明的示意图。由图4(a)上图所示的贝塞尔环带照明光路可知：入射人眼的环带光束的主光线与光轴平行、光线在人眼屈光系统14的后焦面上是汇聚的；通过人眼屈光系统14后成为圆锥形环带光束，圆锥内外侧的光线相互平行。在视网膜15上形成沿轴向z扩展的聚焦光斑，即系统的焦深le获得了扩展，如图4(a)中图所示；该聚焦光斑为贝塞尔型光强I分布，如图4(a)下图所示，其主瓣的半高全宽(FWHM)δre表示系统的横向分辨率，δre在扩展的焦深范围内保持不变；旁瓣信号由接收样品光信号的第四单模光纤27的芯径包层(芯径尺寸小于10μm，包层起着针孔的作用)滤除。需注意的是，聚焦光斑沿轴向z的过度扩展(有利于屈光不正眼成像)，会导致在视网膜15上的照明光功率密度的下降，因此在扩展焦深的同时需权衡考虑照明光功率密度。好在本系统为暗场成像技术，即使在相对较低的照明光功率密度条件下，也有可能获得高信噪比、高对比度、和强立体感图像。Fig. 4 is a schematic diagram of the present invention for comparing Bezier ring illumination and conventional Gaussian ring illumination. It can be known from the Bessel annular illumination optical path shown in the upper figure of Fig. 4(a): the chief ray of the annular light beam incident on the human eye is parallel to the optical axis, and the light rays converge on the back focal plane of the refractive system 14 of the human eye. After passing through the refractive system 14 of the human eye, it becomes a conical annular light beam, and the light rays inside and outside the cone are parallel to each other. A focal spot extending along the axis z is formed on the retina 15, that is, the focal depth le of the system is expanded, as shown in the figure in Fig. 4(a); the focal spot is a Bessel-type light intensity I distribution, as As shown in the lower figure of Figure 4(a), the full width at half maximum (FWHM) δre of the main lobe represents the lateral resolution of the system, and δre remains constant in the extended focal depth range; the side lobe signal is determined by the received sample optical signal The core cladding of the fourth single-mode optical fiber 27 (the core diameter is smaller than 10 μm, and the cladding acts as a pinhole) is filtered out. It should be noted that the excessive expansion of the focal spot along the axis z (beneficial to the imaging of ametropic eyes) will lead to a decrease in the power density of the illumination light on the retina 15, so it is necessary to balance the consideration of the illumination light while expanding the depth of focus power density. Fortunately, this system is a dark-field imaging technology, and it is possible to obtain images with high signal-to-noise ratio, high contrast, and strong stereoscopic effect even under the condition of relatively low illumination light power density.
由图4(b)上图所示的常规高斯环带照明光路可知：入射人眼的环带光束为平行光(光线在人眼屈光系统14的后焦面上不汇聚)；通过人眼屈光系统14后成为圆锥形环带光束，但光线在锥顶、即焦点处是汇聚的。在视网膜15上的聚焦光斑为高斯型能量分布，其沿轴向z的光斑分布如图4(b)中图所示，沿径向r的光强I分布如图4(b)下图所示，可知横向分辨率δrG在焦深lG范围内有所下降。From the conventional Gaussian annular illumination optical path shown in the upper figure of Fig. 4 (b), it can be seen that the annular light beam incident on the human eye is parallel light (the light does not converge on the back focal plane of the refractive system 14 of the human eye); After the refractive system 14, it becomes a conical ring-shaped light beam, but the light rays converge at the apex of the cone, that is, at the focal point. The focused light spot on the retina 15 has a Gaussian energy distribution, the light spot distribution along the axis z is shown in the middle figure of Figure 4(b), and the light intensity I distribution along the radial direction r is shown in the lower figure of Figure 4(b) It can be seen that the lateral resolution δrG decreases in the range of focal depth lG.
相对于常规高斯照明，贝塞尔照明具有提高横向分辨率δr和扩展焦深l的能力。高斯照明时的横向分辨率δrG和焦深lG计算公式分别为：δrG＝1.22λ0(fe/Φ)、lG＝6λ0(fe/Φ)2，其中Φ为入瞳光束直径；而贝塞尔照明时的横向分辨率δre和焦深le分别由式(3)和式(4)给出。横向分辨率和焦深的提高量，分别由式(5)和式(6)给出：Compared with conventional Gaussian lighting, Bessel lighting has the ability to improve the lateral resolution δr and expand the depth of focus l. The calculation formulas of lateral resolution δrG and depth of focus lG under Gaussian illumination are: δrG = 1.22λ0 (fe /Φ), lG = 6λ0 (fe /Φ)2 , where Φ is the entrance pupil The beam diameter; while the lateral resolution δre and focal depth le during Bessel illumination are given by formula (3) and formula (4), respectively. The improvement of lateral resolution and depth of focus are given by Equation (5) and Equation (6) respectively:
可见与高斯照明相比，贝塞尔照明的横向分辨率提高了约37％；或者说，要达到相同的横向分辨率，贝塞尔照明的入瞳光束直径Φ可减小约37％，Φ减小意味着受人眼像差的影响下降。It can be seen that compared with Gaussian lighting, the lateral resolution of Bessel lighting is increased by about 37%; or in other words, to achieve the same lateral resolution, the entrance pupil beam diameter Φ of Bessel lighting can be reduced by about 37%, Φ Reduction means less influence from human eye aberrations.
人眼屈光系统14的有效焦距fe≈16.7mm、视网膜OCT成像的中心波长λ0通常为1060nm、设照明环带光束的厚度H＝0.5mm。当入瞳光束直径Φ取不受像差影响的最大尺寸2.5mm时：δrG＝8.6μm、lG＝0.28mm；δre＝5.4μm、le≈6.7mm(扩展约23.5倍)。本发明也适用于视网膜AO-OCT系统，入瞳光束直径Φ取6mm时：δrG＝3.6μm、lG＝0.05mm；δre＝2.3μm(超高分辨率)、le＝2.8mm(扩展约56.5倍)。因此，本发明提出的采用贝塞尔环带照明方式的长焦深暗场视网膜OCT系统，其横向分辨率填补了常规视网膜OCT和视网膜AO-OCT之间的空隙；焦深获得了极大扩展，能对视网膜全部深度内的组织高分辨成像，甚至无需离焦像差矫正就能直接对屈光不正眼成像。The effective focal length fe ≈16.7 mm of the refractive system 14 of the human eye, the central wavelength λ0 of the retinal OCT imaging is usually 1060 nm, and the thickness H of the illumination ring beam is assumed to be 0.5 mm. When the diameter of the entrance pupil beam Φ is 2.5 mm, which is the maximum size not affected by aberration: δrG =8.6 μm, lG =0.28 mm; δre =5.4 μm, le ≈6.7 mm (expansion is about 23.5 times). The present invention is also applicable to the retinal AO-OCT system. When the entrance pupil beam diameter Φ is 6 mm: δrG =3.6 μm, lG =0.05 mm; δre =2.3 μm (ultra-high resolution), le =2.8 mm ( expanded about 56.5 times). Therefore, the long-focus deep dark-field retinal OCT system proposed by the present invention adopts the Bessel ring illumination method, and its lateral resolution fills the gap between conventional retinal OCT and retinal AO-OCT; the depth of focus has been greatly expanded , capable of high-resolution imaging of tissues within the full depth of the retina, and can even directly image ametropic eyes without defocus aberration correction.
上述具体实施方式用来解释说明本发明，而不是对本发明进行限制。在本发明的精神和权利要求的保护范围内，对本发明作出的任何修改和改变，都落入本发明的保护范围。The specific embodiments above are used to explain the present invention, but not to limit the present invention. Within the spirit of the present invention and the protection scope of the claims, any modification and change made to the present invention will fall into the protection scope of the present invention.
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| CN201610179161.0ACN105615824A (en) | 2016-03-25 | 2016-03-25 | Long-focus deep dark field retina OCT system adopting Bessel ring band illumination mode |
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| CN201610179161.0APendingCN105615824A (en) | 2016-03-25 | 2016-03-25 | Long-focus deep dark field retina OCT system adopting Bessel ring band illumination mode |
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