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Real-time pixelwise phasor analysis for video-rate two-photon fluorescence lifetime imaging microscopy

BIOMEDICAL OPTICS EXPRESS 2021年第7期12卷 4003-4019页

作者： Sorrells, Janet E. Iyer, Rishyashring R. Yang, Lingxiao Bower, Andrew J. Spillman, Darold R. Chaney, Eric J. Tu, Haohua Boppart, Stephen A. Univ Illinois Beckman Inst Adv Sci & Technol Urbana IL 61801 USA Univ Illinois Dept Bioengn Urbana IL 61801 USA Univ Illinois Dept Elect & Comp Engn Urbana IL 61801 USA Canc Ctr Illinois Urbana IL 61801 USA Univ Illinois Carle Illinois Coll Med Urbana IL 61801 USA

Two-photon fluorescence lifetime imaging microscopy (FLIM) is a widely used technique in biomedical optical imaging. Presently, many two-photon time-domain FLIM setups are limited by long acquisition and postprocessing times that decrease data throughput and inhibit the ability to image fast sub-second processes. Here, we present a versatile two-photon FLIM setup capable of video-rate (up to 25 fps) imaging with graphics processing unit (GPU)accelerated pixelwise phasor analysis displayed and saved simultaneously with acquisition. The system uses an analog output photomultiplier tube in conjunction with 12-bit digitization at 3.2 GHz to overcome the limited maximum acceptable photon rate associated with the photon counting electronics in many FLIM systems. This allows for higher throughput FLIM acquisition and analysis, and additionally enables the user to assess sample fluorescence lifetime in real-time. We further explore the capabilities of the system to examine the kinetics of Rhodamine B uptake by human breast cancer cells and characterize the effect of pixel dwell time on the reduced nicotinamide adenine dinucleotide and reduced nicotinamide adenine dinucleotide phosphate (NAD(P)H) autofluorescence lifetime estimation accuracy. (c) 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

关键词： image processing image processing algorithms Medical imaging Phase shift Photon counting Visible light

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Reducing speckle in anterior segment optical coherence tomography images based on a convolutional neural network

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APPLIED OPTICS 2021年第35期60卷 10964-10974页

作者： Liu, Liansheng Zhai, Zuopan Zhang, Ting Fan, Licheng Soochow Univ Sch Mech & Elect Engn Suzhou 215137 Peoples R China Soochow Univ Res Ctr Robot & Microsyst Suzhou 215137 Peoples R China

Speckle noise is ubiquitous in the optical coherence tomography (OCT) image of the anterior segment, which greatly affects the image quality and destroys the relevant structural information. In order to reduce the influence of speckle noise in OCT images, a denoising algorithm based on a convolutional neural network is proposed in this paper. Unlike traditional algorithms that directly obtain denoised images, the algorithm model proposed in this paper learns the speckle noise distribution through the constructed trainable OCT dataset and indirectly obtains the denoised result image. In order to verify the performance of the model, we compare the denoising results of the algorithm proposed in this paper with several state-of-the-art algorithms from three perspectives: qualitative evaluation from the subjective visual perspective, quantitative evaluation from objective parameter indicators, and running time. The experimental results show that the proposed algorithm has a good denoising effect on different OCT images of the anterior segment and has good generalization ability. Besides, it retains the relevant details and texture information in the image, and it has strong edge preserving ability. The image of OCT speckle removal can be obtained within 0.4 s, which meets the time limit requirement of clinical application. (C) 2021 Optical Society of America

关键词： image metrics image processing image processing algorithms image quality Speckle noise Speckle patterns

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Color three-dimensional imaging based on patterned illumination using a negative pinhole array

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OPTICS EXPRESS 2021年第5期29卷 6509-6522页

作者： Kim, Chang-Soo Kim, Junyoung Yoo, Hongki Korea Res Inst Stand & Sci KRISS Adv Instrumentat Inst Opt Imaging & Metrol Team Sci Town 34113 Daejeon South Korea Harvard Med Sch Wellman Ctr Photomed 55 Fruit St Boston MA 02114 USA Massachusetts Gen Hosp 55 Fruit St Boston MA 02114 USA Korea Adv Inst Sci & Technol Dept Mech Engn 291 Daehak Ro Daejeon 34141 South Korea

Reflectance confocal microscopy is widely used for non-destructive optical three-dimensional (3D) imaging. In confocal microscopy, a stack of sequential two-dimensional (2D) images with respect to the axial position is typically needed to reconstruct a 3D image. As a result, in conventional confocal microscopy, acquisition speed is often limited by the rate of mechanical scanning in both the transverse and axial directions. We previously reported a high-speed parallel confocal detection method using a pinhole array for color 3D imaging without any mechanical scanners. Here, we report a high-speed color 3D imaging method based on patterned illumination employing a negative pinhole array, whose optical characteristics are the reverse of the conventional pinhole array for transmitting light. The negative pinhole array solves the inherent limitation of a conventional pinhole array, i.e., low transmittance, meaning brighter color images with abundant color information can be acquired. We also propose a 3D image processing algorithm based on the 2D cross-correlation between the acquired image and filtering masks, to produce an axial response. By using four-different filtering masks, we were able to increase the sampling points in calculation of height and enhance the lateral resolution of the color acquisition by a factor of four. The feasibility of high-speed non-contact color 3D measurement with the improved lateral resolution and brightness provided by the negative pinhole array was demonstrated by imaging various specimens. We anticipate that this high-speed color 3D measurement technology with negative pinhole array will be a useful tool in a variety of fields where rapid and accurate non-contact measurement are required, such as industrial inspection and dental scanning. (C) 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

关键词： Brightness Confocal microscopy image processing algorithms Spatial light modulators Three dimensional image processing Three dimensional imaging

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Robust optical axis control of monocular active gazing based on pan-tilt mirrors for high dynamic targets

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OPTICS EXPRESS 2021年第24期29卷 40214-40230页

作者： Cao, Ruimin Fu, Jian Yang, Hui Wang, Lihui Ishikawa, Masatoshi Guangdong Acad Sci Inst Semicond Guangzhou 510650 Peoples R China Univ Tokyo Informat Technol Ctr Data Sci Res Div Tokyo 1138656 Japan

The real-time and stability performance are both crucial for the active vision system (AVS) to gaze the high dynamic targets (HDTs). This study focused on the robust optical axis control mechanism of monocular AVS based on pan-tilt mirrors. We proposed an adaptive selfwindow to accommodate the HDTs within the region of interest. The minimum-envelope-ellipse and unscented-Kalman-filter methods were proposed to compensate and predict the angle of optical axis when the HDTs were blocked. The static and dynamic compensation error rates were less than 1.46% and 2.71%, prediction error rate was less than 13.88%, improving the gazing stability while ensuring real-time performance. (C) 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

关键词： High speed photography image processing image processing algorithms Liquid lenses Optical design Parallel processing

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Open-top axially swept light-sheet microscopy

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BIOMEDICAL OPTICS EXPRESS 2021年第4期12卷 2328-2338页

作者： Kim, Bumju Na, Myeongsu Park, Soohyun Kim, Kitae Park, Jung-Hoon Chung, Euiheon Chang, Sunghoe Kim, Ki Hean Pohang Univ Sci & Technol Div Integrat Biosci & Biotechnol 77 Cheongam Ro Pohang 37673 Gyeongbuk South Korea Seoul Natl Univ Dept Physiol & Biomed Sci Med Res Ctr Coll Med 103 Daehak Ro Seoul 03080 South Korea Pohang Univ Sci & Technol Dept Mech Engn 77 Cheongam Ro Pohang 37673 Gyeoungbuk South Korea Ulsan Natl Inst Sci & Technol UNIST Dept Biomed Engn Ulsan 44919 South Korea Gwangju Inst Sci & Technol Dept Biomed Sci & Engn Gwangju 61005 South Korea

Open-top light-sheet microscopy (OT-LSM) is a specialized microscopic technique for high throughput cellular imaging of large tissue specimens including optically cleared tissues by having the entire optical setup below the sample stage. Current OT-LSM systems had relatively low axial resolutions by using weakly focused light sheets to cover the imaging field of view (FOV). In this report, open-top axially swept LSM (OTAS-LSM) was developed for high-throughput cellular imaging with improved axial resolution. OTAS-LSM swept a tightly focused excitation light sheet across the imaging FOV using an electro tunable lens (ETL) and collected emission light at the focus of the light sheet with a camera in the rolling shutter mode. OTAS-LSM was developed by using air objective lenses and a liquid prism and it had on-axis optical aberration associated with the mismatch of refractive indices between air and immersion medium. The effects of optical aberration were analyzed by both simulation and experiment, and the image resolutions were under 1.6 & micro;m in all directions. The newly developed OTAS-LSM was applied to the imaging of optically cleared mouse brain and small intestine, and it demonstrated the single-cell resolution imaging of neuronal networks. OTAS-LSM might be useful for the high-throughput cellular examination of optically cleared large tissues. (c) 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

关键词： image processing image processing algorithms image resolution Light sheet microscopy Tunable lenses Wave front sensing

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Flexible foveated imaging using a single Risley-prism imaging system

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OPTICS EXPRESS 2021年第24期29卷 40072-40090页

作者： Huang, Feng Ren, He Wu, Xianyu Wang, Pengfei Fuzhou Univ Sch Mech Engn & Automat Fuzhou 350108 Peoples R China

Foveated imaging, which has the ability to provide overall situational awareness over a large field of view and high-resolution perception of local details, has significant advantages in many specific applications. However, existing artificially foveated imaging systems are complex, bulky, and expensive, and the flexibility of the fovea specifically has many limitations. To overcome these deficiencies, this paper proposes a method for foveated imaging by collecting multiple partially overlapping sub-fields of view. To capture the above special sub-fields of view, we propose a high-efficiency algorithm based on the characteristics of the field of view deflected by the Risley-prism and aimed at solving the prism rotation angles. In addition, we prove the reliability of the proposed algorithm by cross-validation with the particle swarm optimization algorithm. The experimental results show that the proposed method can achieve flexible foveated imaging using a single Risley-prism imaging system. (C) 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

关键词： Digital image processing image processing algorithms image quality Imaging systems Liquid crystal lenses Spatial light modulators

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FMCW lidar multitarget detection based on skeleton tree waveform matching

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APPLIED OPTICS 2021年第27期60卷 8328-8335页

作者： Li, Bingchen Mo, Di Wang, Peisi Gan, Nan Lin, Miao Wang, Ran Li, Shiqiang Chinese Acad Sci Aerosp Informat Res Inst Beijing 100190 Peoples R China Univ Chinese Acad Sci Beijing 100049 Peoples R China

Frequency-modulated continuous-wave lidar realizes 4D (three-dimensional space and velocity) imaging of the scene by emitting positive and negative frequency sweep laser signals. The premise of it is to identify the frequency points corresponding to the same target in the positive and negative sweep echo signals. For dechirp receiving, there is usually one peak in the frequency spectrum of the positive and negative sweep signals, respectively. Therefore, it is easy to identify and match the peaks. But in a complex environment, the laser beam will irradiate multiple targets at the same time. In addition, beam scanning and target motion cause the echo spectrum to broaden. The above reasons make it extremely difficult to identify and match peaks in practice. To solve this problem, the waveform matching algorithm based on the skeleton tree is first applied to multitarget echo pairing. The basic idea of the algorithm is to quantify the target echo hierarchically to generate a skeleton tree. The generation of nodes is based on the relative amplitude of waveform peaks and reflects the characteristics of wave crests nesting. Then the similarity of the signal is determined by comparing the distance between the two signal waveform feature trees. Finally, the waveforms are matched in terms of similarity. To further substantiate the role of the proposed algorithm, imaging experiments and related comparative data for different targets have been completed. The results show that the accuracy of matching processed by the algorithm exceeds 90%, which is improved by about 50% compared with not using the algorithm for the target whose overlapping part accounts for a large proportion of itself. (C) 2021 Optical Society of America

关键词： Fast Fourier transforms Frequency modulation image processing image processing algorithms Laser beams Modulation techniques

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High accuracy indoor visible light positioning using a long short term memory-fully connected network based algorithm

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OPTICS EXPRESS 2021年第25期29卷 41109-41120页

作者： Chen, Hongyao Han, Wei Wang, Jianping Lu, Huimin Chen, Danyang Jin, Jianli Feng, Lifang Univ Sci & Technol Being Shunde Grad Sch Foshan 528000 Peoples R China Univ Sci & Technol Beijing Sch Comp & Commun Engn Beijing 100083 Peoples R China

In this work, a novel positioning algorithm based on a long short term memory-fully connected network (LSTM-FCN) is proposed to improve the performance of an indoor visible light positioning (VLP) system. Using the proposed LSTM-FCN based positioning algorithm, the VLP system with a single light emitting diode (LED) and multiple photodetectors (PDs) was implemented. On this basis, the positioning performance of the established VLP system using proposed LSTM-FCN, traditional FCN and support vector regression (SVR) based algorithm is investigated and compared. It is demonstrated that the VLP system using the proposed LSTM-FCN based algorithm has better performance than that using other machine learning algorithms. As a result, an average positioning error of 0.92 cm and a maximum positioning error of less than 5 cm can be obtained for the established VLP system. (C) 2021 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

关键词： image processing algorithms Phase measurement Photodetectors Power spectral density Visible light Visible light communications

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Optical-image communication through random-phase propagation channels using phase-shifting coding

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APPLIED OPTICS 2021年第11期60卷 3162-3169页

作者： Servin, Manuel Padilla, Moises Ctr Invest Opt AC Loma Bosque 115 Guanajuato 37150 Mexico

We propose an optical-image communication system robust to random-phase propagation using phase-shifting (PS) image coding. That is, this optical-image communication system is based on digital PS interferometry principles. Each pixel of the parallel transmitted image is coded as the phase of a sequence of N phase-shifted fringe patterns. The temporal fringe patterns may be displayed on a TV screen (or a multimedia projector) for transmission through the random-phase channel. At the receiver, the PS fringe patterns are digitized with a telescopic digital camera. The received fringes are phase-demodulated using an N-steps least-squares PS algorithm (LS-PSA). We show that the received, phase-demodulated images are less blurred and have better contrast than any received image without PS coding. We propose and analyze a mathematical model for the received PS fringes degraded by random-phase propagation. This PS communication system can also be used for robust optical communications through random refractive media such as underwater, air-water, or random-thickness textured glass. In particular, we show experiments for LS-PSA imaging through textured-glass, obtaining sharper images. As far as we know, this is the first time that PS interferometry has been used for parallel optical-image communication through random-phase channels. (C) 2021 Optical Society of America

关键词： Atmospheric turbulence Free space optics image processing image processing algorithms Optical imaging Underwater imaging

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Characterizing and correcting camera noise in back-illuminated sCMOS cameras

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OPTICS EXPRESS 2021年第5期29卷 6668-6690页

作者： Zhang, Zhaoning Wang, Yujie Piestun, Rafael Huang, Zhen-li Huazhong Univ Sci & Technol Britton Chance Ctr Biomed Photon Wuhan Natl Lab Optoelect Wuhan 430074 Hubei Peoples R China Huazhong Univ Sci & Technol Sch Engn Sci MoE Key Lab Biomed Photon Wuhan 430074 Hubei Peoples R China Univ Colorado Dept Elect Comp & Energy Engn Boulder CO 80309 USA Hainan Univ Sch Biomed Engn Haikou 570228 Hainan Peoples R China

With promising properties of fast imaging speed, large field-of-view, relative low cost and many others, back-illuminated sCMOS cameras have been receiving intensive attention for low light level imaging in the past several years. However, due to the pixel-to-pixel difference of camera noise (called noise non-uniformity) in sCMOS cameras, researchers may hesitate to use them in some application fields, and sometimes wonder whether they should optimize the noise non-uniformity of their sCMOS cameras before using them in a specific application scenario. In this paper, we systematically characterize the impact of different types of sCMOS noise on image quality and perform corrections to these types of sCMOS noise using three representative algorithms (PURE, NCS and MLEsCMOS). We verify that it is possible to use appropriate correction methods to push the non-uniformity of major types of camera noise, including readout noise, offset, and photon response, to a satisfactory level for conventional microscopy and single molecule localization microscopy. We further find out that, after these corrections, global read noise becomes a major concern that limits the imaging performance of back-illuminated sCMOS cameras. We believe this study provides new insights into the understanding of camera noise in back-illuminated sCMOS cameras, and also provides useful information for future development of this promising camera technology. (C) 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

关键词： Charge coupled devices Complementary metal oxide semiconductors High speed photography image processing algorithms image quality Low light levels

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