1. Articles from Gangjun Liu

    1-24 of 57 1 2 3 »
    1. Weakly Supervised Deep Learning-Based Optical Coherence Tomography Angiography

      Weakly Supervised Deep Learning-Based Optical Coherence Tomography Angiography

      Optical coherence tomography angiography (OCTA) is a promising imaging modality for microvasculature studies. Deep learning networks have been widely applied in the field of OCTA reconstruction, benefiting from its powerful mapping capability among images. However, these existing deep learning-based methods depend on high-quality labels, which are hard to acquire considering imaging hardware limitations and practical data acquisition conditions. In this article, we proposed an unprecedented weakly supervised deep learning-based pipeline for OCTA reconstruction task, in the absence of high-quality training labels. The proposed pipeline was investigated on an in vivo animal dataset and a human eye dataset by a cross-validation ...

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    2. Weakly Supervised Deep Learning Based Optical Coherence Tomography Angiography

      Weakly Supervised Deep Learning Based Optical Coherence Tomography Angiography

      Optical coherence tomography angiography (OCTA) is a promising imaging modality for microvasculature studies. Deep learning networks have been widely applied in the field of OCTA reconstruction, benefiting from its powerful mapping capability among images. However, these existing deep learning-based methods depend on high-quality labels, which are hard to acquire considering imaging hardware limitations and practical data acquisition conditions. In this paper, we proposed an unprecedented weakly supervised deep learning-based pipeline for OCTA reconstruction task, in the absence of high-quality training labels. The proposed pipeline was investigated on an in vivo animal dataset and a human eye dataset by a cross-validation ...

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    3. N2NSR‐OCT: Simultaneous denoising and super‐resolution in optical coherence tomography images using semi‐supervised deep learning

      N2NSR‐OCT: Simultaneous denoising and super‐resolution in optical coherence tomography images using semi‐supervised deep learning

      Optical coherence tomography (OCT) imaging shows a significant potential in clinical routines due to its noninvasive property. However, the quality of OCT images is generally limited by inherent speckle noise of OCT imaging and low sampling rate. To obtain high signal‐to‐noise ratio (SNR) and high‐resolution (HR) OCT images within a short scanning time, we presented a learning‐based method to recover high‐quality OCT images from noisy and low‐resolution OCT images. We proposed a semi‐supervised learning approach named N2NSR‐OCT, to generate denoised and super‐resolved OCT images simultaneously using up‐ and down‐sampling networks ...

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    4. Retinal choroidal vessel imaging based on multi-wavelength fundus imaging with the guidance of optical coherence tomography

      Retinal choroidal vessel imaging based on multi-wavelength fundus imaging with the guidance of optical coherence tomography

      A multispectral fundus camera (MSFC), as a novel noninvasive technology, uses an extensive range of monochromatic light sources that enable the view of different sectional planes of the retinal and choroidal structures. However, MSFC imaging involves complex processes affected by various factors, and the recognized theory based on light absorption above the choroid is not sufficient. In an attempt to supplement the relevant explanations, in this study, we used optical coherence tomography (OCT), a three-dimensional tomography modality, to analyze MSFC results at the retina and choroid. The swept-source OCT system at 1060 nm wavelength with a 200 kHz A-scan rate ...

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    5. Comparative study of deep learning models for optical coherence tomography angiography

      Comparative study of deep learning models for optical coherence tomography angiography

      Optical coherence tomography angiography (OCTA) is a promising imaging modality for microvasculature studies. Meanwhile, deep learning has achieved rapid development in image-to-image translation tasks. Some studies have proposed applying deep learning models to OCTA reconstruction and have obtained preliminary results. However, current studies are mostly limited to a few specific deep neural networks. In this paper, we conducted a comparative study to investigate OCTA reconstruction using deep learning models. Four representative network architectures including single-path models, U-shaped models, generative adversarial network (GAN)-based models and multi-path models were investigated on a dataset of OCTA images acquired from rat brains. Three ...

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    6. Noise reduction in optical coherence tomography images using a deep neural network with perceptually-sensitive loss function

      Noise reduction in optical coherence tomography images using a deep neural network with perceptually-sensitive loss function

      Optical coherence tomography (OCT) is susceptible to the coherent noise, which is the speckle noise that deteriorates contrast and the detail structural information of OCT images, thus imposing significant limitations on the diagnostic capability of OCT. In this paper, we propose a novel OCT image denoising method by using an end-to-end deep learning network with a perceptually-sensitive loss function. The method has been validated on OCT images acquired from healthy volunteers’ eyes. The label images for training and evaluating OCT denoising deep learning models are images generated by averaging 50 frames of respective registered B-scans acquired from a region with ...

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    7. Post-processing reduction of fixed pattern artifacts and trigger jitter in swept-source optical coherence tomography

      Post-processing reduction of fixed pattern artifacts and trigger jitter in swept-source optical coherence tomography

      Disclosed herein are methods and systems for aligning swept-source optical coherence tomography (SS-OCT) spectral interferograms to a reference spectral interferogram based on signal information (e.g., amplitude or phase) at a fixed-pattern noise location to reduce residual fixed-pattern noise and improve the phase stability of SS-OCT systems.

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    8. Optical Coherence Tomography Angiography and UltraWidefield Optical Coherence Tomography in a Child With Incontinentia Pigmenti

      Optical Coherence Tomography Angiography and UltraWidefield Optical Coherence Tomography in a Child With Incontinentia Pigmenti

      Incontinentia pigmenti (IP) is a rare X-linked dominant disorder that can cause retinal nonperfusion, neovascularization, and retinal detachment. Evaluation of the peripheral retinal vasculature and appropriate treatment can reduce the risk of blindness. The authors report the use of a handheld prototype optical coherence tomography angiography (OCTA) and ultra-widefield OCT (UWF-OCT) during exam under anesthesia of a 2-year-old with a history of severe early onset IP. UWF-OCT and OCTA may be used as noninvasive imaging modalities for IP and similar retinal vascular disorders in supine young children.

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    9. Optical Coherence Tomography Angiography and Ultra-Widefield Optical Coherence Tomography in a Child With Incontinentia Pigmenti

      Optical Coherence Tomography Angiography and Ultra-Widefield Optical Coherence Tomography in a Child With Incontinentia Pigmenti

      Incontinentia pigmenti (IP) is a rare X-linked dominant disorder that can cause retinal nonperfusion, neovascularization, and retinal detachment. Evaluation of the peripheral retinal vasculature and appropriate treatment can reduce the risk of blindness. The authors report the use of a handheld prototype optical coherence tomography angiography (OCTA) and ultra-widefield OCT (UWF-OCT) during exam under anesthesia of a 2-year-old with a history of severe early onset IP. UWF-OCT and OCTA may be used as noninvasive imaging modalities for IP and similar retinal vascular disorders in supine young children.

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    10. A Postdoctoral Research Fellowship/Research Associate Position at OHSU

      A Postdoctoral Research Fellowship/Research Associate Position at OHSU

      A postdoctoral research fellowship/research associate position is immediately available in the Center for Ophthalmic Optics and Lasers, Casey Eye Institute, Oregon Health & Science University. The fellowship will focus on the development and clinical application of medical imaging system, especially OCT and related technologies (laser-tissue interaction). Ph.D in Optics, Biomedical Engineering, Electrical Engineering or a related field is required. Demonstrated excellence in one or more of the following area is required: optical system set-up, image acquisition, simulation using Zemax software and C++/GPU programming for real-time processing. Broad experience in optics, signal processing, and image processing are also desirable ...

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    11. Handheld OCT Angiography and Ultra–Wide-Field OCT in Retinopathy of Prematurity

      Handheld OCT Angiography and Ultra–Wide-Field OCT in Retinopathy of Prematurity

      Importance Retinopathy of prematurity (ROP) is a leading cause of childhood blindness worldwide. Optical coherence tomography (OCT) has improved the care of adults with vitreoretinal disease, and OCT angiography (OCTA) is demonstrating promise as a technique to visualize the retinal vasculature with lower risk and cost than fluorescein angiography. However, to date, there are no commercially available devices able to obtain ultra–wide-field OCT or OCTA images in neonates. Objective To obtain ultra–wide-field OCT and OCTA images in neonates with ROP using a prototype handheld OCT and OCTA device. Design, Setting, and Participants This observational case series was conducted ...

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    12. Regression-based algorithm for bulk motion subtraction in optical coherence tomography angiography

      Regression-based algorithm for bulk motion subtraction in optical coherence tomography angiography

      We developed an algorithm to remove decorrelation noise due to bulk motion in optical coherence tomography angiography (OCTA) of the posterior eye. In this algorithm, OCTA B-frames were divided into segments within which the bulk motion velocity could be assumed to be constant. This velocity was recovered using linear regression of decorrelation versus the logarithm of reflectance in axial lines (A-lines) identified as bulk tissue by percentile analysis. The fitting parameters were used to calculate a reflectance-adjusted upper bound threshold for bulk motion decorrelation. Below this threshold, voxels are identified as non-flow tissue, their flow values are set to zeros ...

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    13. Extended axial imaging range, widefield swept source optical coherence tomography angiography

      Extended axial imaging range, widefield swept source optical coherence tomography angiography

      We developed a high-speed, swept source OCT system for widefield OCT angiography (OCTA) imaging. The system has an extended axial imaging range of 6.6 mm. An electrical lens is used for fast, automatic focusing. The recently developed split-spectrum amplitude and phase-gradient angiography allow high-resolution OCTA imaging with only two B-scan repetitions. An improved post-processing algorithm effectively removed trigger jitter artifacts and reduced noise in the flow signal. We demonstrated high contrast 3 mm×3 mm OCTA image with 400×400 pixels acquired in 3 seconds and high-definition 8 mm×6 mm and 12 mm×6 mm OCTA images with ...

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    14. Handheld optical coherence tomography angiography

      Handheld optical coherence tomography angiography

      We developed a handheld optical coherence tomography angiography (OCTA) system using a 100-kHz swept-source laser. The handheld probe weighs 0.4 kg and measures 20.6 × 12.8 × 4.6 cm 3 . The system has dedicated features for handheld operation. The probe is equipped with a mini iris camera for easy alignment. Real-time display of the en face OCT and cross-sectional OCT images in the system allows accurately locating the imaging target. Fast automatic focusing was achieved by an electrically tunable lens controlled by a golden-section search algorithm. An extended axial imaging range of 6 mm allows easy alignment. A ...

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    15. Automated three-dimensional registration and volume rebuilding for wide-field angiographic and structural optical coherence tomography

      Automated three-dimensional registration and volume rebuilding for wide-field angiographic and structural optical coherence tomography

      We propose a three-dimensional (3-D) registration method to correct motion artifacts and construct the volume structure for angiographic and structural optical coherence tomography (OCT). This algorithm is particularly suitable for the nonorthogonal wide-field OCT scan acquired by a ultrahigh-speed swept-source system ( > 200    kHz >200  kHz A-scan rate). First, the transverse motion artifacts are corrected by the between-frame registration based on en face OCT angiography (OCTA). After A-scan transverse translation between B-frames, the axial motions are corrected based on the rebuilt boundary of inner limiting membrane. Finally, a within-frame registration is performed for local optimization based on cross-sectional OCTA. We evaluated ...

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    16. Hematocrit dependence of flow signal in optical coherence tomography angiography

      Hematocrit dependence of flow signal in optical coherence tomography angiography

      The hematocrit dependence of flow signal (split-spectrum amplitude decorrelation angiography-SSADA decorrelation value) was investigated in this paper. Based on the normalized field temporal correlation function and concentration dependent particle scattering properties, the relationship between hematocrit and flow signal was analytically derived. Experimental verification of the relationship was performed with custom-designed microfluidic chips and human blood with 45%, 40% and 32% hematocrit. It was found that, in large flow channels and blood vessels, the normal hematocrit is near the decorrelation saturation point and therefore a change in hematocrit has little effect on the SSADA decorrelation value (flow signal). However, in narrow ...

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    17. Selected Topics in Optical Coherence Tomography (Textbook)

      Selected Topics in Optical Coherence Tomography (Textbook)

      This book includes different exciting topics in the OCT fields, written by experts from all over the world. Technological developments, as well as clinical and industrial applications are covered. Some interesting topics like the ultrahigh resolution OCT, the functional extension of OCT and the full field OCT are reviewed, and the applications of OCT in ophthalmology, cardiology and dentistry are also addressed. I believe that a broad range of readers, such as students, researchers and physicians will benefit from this book.

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      Mentions: Gangjun Liu
    18. Calibration of optical coherence tomography angiography with a microfluidic chip

      Calibration of optical coherence tomography angiography with a microfluidic chip

      A microfluidic chip with microchannels ranging from 8 to 96    μ m 96  μm was used to mimic blood vessels down to the capillary level. Blood flow within the microfluidic channels was analyzed with split-spectrum amplitude-decorrelation angiography (SSADA)-based optical coherence tomography (OCT) angiography. It was found that the SSADA decorrelation value was related to both blood flow speed and channel width. SSADA could differentiate nonflowing blood inside the microfluidic channels from static paper. The SSADA decorrelation value was approximately linear with blood flow velocity up to a threshold V sat Vsat of 5.83 ± 1.33    mm / s 5.83 ...

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    19. Optical Coherence Tomography Angiography

      Optical Coherence Tomography Angiography

      Optical coherence tomography angiography (OCTA) is a noninvasive approach that can visualize blood vessels down to the capillary level. With the advent of high-speed OCT and efficient algorithms, practical OCTA of ocular circulation is now available to ophthalmologists. Clinical investigations that used OCTA have increased exponentially in the past few years. This review will cover the history of OCTA and survey its most important clinical applications. The salient problems in the interpretation and analysis of OCTA are described, and recent advances are highlighted.

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    20. Split-spectrum phase-gradient optical coherence tomography angiography

      Split-spectrum phase-gradient optical coherence tomography angiography

      A phase gradient angiography (PGA) method is proposed for optical coherence tomography (OCT). This method allows the use of phase information to map the microvasculature in tissue without the correction of bulk motion and laser trigger jitter induced phase artifacts. PGA can also be combined with the amplitude/intensity to improve the performance. Split-spectrum technique can further increase the signal to noise ratio by more than two times. In-vivo imaging of human retinal circulation is shown with a 70 kHz, 840 nm spectral domain OCT system and a 200 kHz, 1050 nm swept source OCT system. Four different OCT angiography ...

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    21. Apparatus and method for capturing a vital vascular fingerprint

      Apparatus and method for capturing a vital vascular fingerprint

      A method using optical coherence tomography to capture the microvascular network of the superficial layer of the finger skin for the purpose of fingerprint authentication and liveness detection. At the dermal papilla region, the vascular pattern follows the same pattern of the fingerprint and this vascular pattern forms a live vascular fingerprint. This live vascular fingerprint provides for ultrahigh security and a unique way for fingerprint-based personal verification. Because the system is based on blood flow, which only exists in a living person, the technique is robust against spoof attaching. After performing non-contact in-vivo imaging of a human fingertip, a ...

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    22. Imaging the anterior eye with dynamic-focus swept-source optical coherence tomography.

      Imaging the anterior eye with dynamic-focus swept-source optical coherence tomography.

      A custom-built dynamic-focus swept-source optical coherence tomography (SS-OCT) system with a central wavelength of 1310 nm was used to image the anterior eye from the cornea to the lens. An electrically tunable lens was utilized to dynamically control the positions of focusing planes over the imaging range of 10 mm. The B-scan images were acquired consecutively at the same position but with different focus settings. The B-scan images were then registered and averaged after filtering the out-of-focus regions using a Gaussian window. By fusing images obtained at different depth focus locations, high-resolution and high signal-strength images were obtained over the ...

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    23. Optimization of the split-spectrum amplitude-decorrelation angiography algorithm on a spectral optical coherence tomography system

      Optimization of the split-spectrum amplitude-decorrelation angiography algorithm on a spectral optical coherence tomography system

      The split-spectrum amplitude-decorrelation angiography algorithm was optimized on a spectral optical coherence tomography system using a flow phantom. The number of times the spectrum was split and the bandwidth of each split were adjusted to maximize the flow phantom decorrelation signal-to-noise ratio. The improvement in flow detection was then demonstrated with en face retinal angiograms. The optimized algorithm increased the detectable retinal microvascular flow and decreased the variability of the quantified vessel density in OCT retinal angiograms of healthy human subjects

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    24. Postdoctoral Positions in Biomedical Optics and Optical Coherence Tomography at the Center for Ophthalmic Optics & Lasers, Oregon Health & Science University

      Postdoctoral Positions in Biomedical Optics and Optical Coherence Tomography at the Center for Ophthalmic Optics & Lasers, Oregon Health & Science University

      Postdoctoral research opportunities are available in the area of biomedical optics at the Center for Ophthalmic Optics & Lasers ( www.COOLLab.net ) in the Casey Eye Institute, Oregon Health & Science University (OHSU). The COOL laboratory is a multidisciplinary team that incorporates optical scientists, image processing experts, ophthalmologists, statisticians, managers, and technicians. The group collaborates with several institutions to develop novel OCT technology, develop diagnostic and surgical planning software, and conduct clinical trials. The laboratory is well supported by the National Institutes of Health ( http://www.octnews.org/articles/2920025/optical-coherence-tomography-used-500m-of-federall/ ) and industry, and has brought many novel diagnostic technology into clinical ...

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    1-24 of 57 1 2 3 »
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    1. (54 articles) Gangjun Liu
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