1. Articles from Zhuolin Liu

    1-16 of 16
    1. Post-doctoral Adaptive Optics Research Fellow at U.S. Food and Drug Administration

      Post-doctoral Adaptive Optics Research Fellow at U.S. Food and Drug Administration

      Seeking a highly motivated post-doctoral Adaptive Optics Research Fellow to work at the U.S. Food and Drug Administration, Center for Devices and Radiological Health. The candidate will work in the Division of Biomedical Physics under the direction of Drs. Zhuolin Liu and Daniel X. Hammer and perform research with the FDA multimodal adaptive optics (mAO) imager. The FDA mAO imaging system allows visualization of different retinal cells, including ganglion cells, retinal pigment epithelial cells, and photoreceptors. The candidate will be expected to: conduct human imaging in healthy and diseased eyes, perform data processing, analysis and presentation, develop new and ...

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    2. 3-D printed photoreceptor phantoms for evaluating lateral resolution of adaptive optics imaging systems

      3-D printed photoreceptor phantoms for evaluating lateral resolution of adaptive optics imaging systems

      With adaptive optics (AO), optical coherence tomography and scanning laser ophthalmoscopy imaging systems can resolve individual photoreceptor cells in living eyes, due to enhanced lateral spatial resolution. However, no standard test method exists for experimentally quantifying this parameter in ophthalmic AO imagers. Here, we present three-dimensional (3-D) printed phantoms, which enable the measurement of lateral resolution in an anatomically relevant manner. We used two-photon polymerization to fabricate two phantoms, which mimic the mosaic of cone photoreceptor outer segments at multiple retinal eccentricities. With these phantoms, we demonstrated that the resolution of two multimodal AO systems is similar to theoretical predictions ...

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    3. Method to investigate temporal dynamics of ganglion and other retinal cells in the living human eye

      Method to investigate temporal dynamics of ganglion and other retinal cells in the living human eye

      The inner retina is critical for visual processing, but much remains unknown about its neural circuitry and vulnerability to disease. A major bottleneck has been our inability to observe the structure and function of the cells composing these retinal layers in the living human eye. Here, we present a noninvasive method to observe both structural and functional information. Adaptive optics optical coherence tomography (AO-OCT) is used to resolve the inner retinal cells in all three dimensions and novel post processing algorithms are applied to extract structure and physiology down to the cellular level. AO-OCT captured the 3D mosaic of individual ...

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    4. Imaging and quantifying ganglion cells and other transparent neurons in the living human retina [Engineering]

      Imaging and quantifying ganglion cells and other transparent neurons in the living human retina [Engineering]

      Ganglion cells (GCs) are fundamental to retinal neural circuitry, processing photoreceptor signals for transmission to the brain via their axons. However, much remains unknown about their role in vision and their vulnerability to disease leading to blindness. A major bottleneck has been our inability to observe GCs and their degeneration in the living human eye. Despite two decades of development of optical technologies to image cells in the living human retina, GCs remain elusive due to their high optical translucency. Failure of conventional imaging—using predominately singly scattered light—to reveal GCs has led to a focus on multiply-scattered, fluorescence ...

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    5. OPTICAL PROPERTIES OF PHOTORECEPTOR AND RETINAL PIGMENT EPITHELIUM CELLS INVESTIGATED WITH ADAPTIVE OPTICS OPTICAL COHERENCE TOMOGRAPHY (Thesis)

      OPTICAL PROPERTIES OF PHOTORECEPTOR AND RETINAL PIGMENT EPITHELIUM CELLS INVESTIGATED WITH ADAPTIVE OPTICS OPTICAL COHERENCE TOMOGRAPHY (Thesis)

      Human vision starts when photoreceptors collect and respond to light. Photoreceptors do not function in isolation though, but share close interdependence with neighboring photoreceptors and underlying retinal pigment epithelium (RPE) cells. These cellular interactions are essential for normal function of the photoreceptor-RPE complex, but methods to assess these in the living human eye are limited. One approach that has gained increased promise is highresolution retinal imaging that has undergone tremendous technological advances over the last two decades to probe the living retina at the cellular level. Pivotal in these advances has been adaptive optics (AO) and optical coherence tomography (OCT ...

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    6. Tracking dynamics of photoreceptor disc shedding with adaptive optics-optical coherence tomography

      Tracking dynamics of photoreceptor disc shedding with adaptive optics-optical coherence tomography

      Absorption of light by photoreceptors initiates vision, but also leads to accumulation of toxic photo-oxidative compounds in the photoreceptor outer segment (OS). To prevent this buildup, small packets of OS discs are periodically pruned from the distal end of the OS, a process called disc shedding. Unfortunately dysfunction in any part of the shedding event can lead to photoreceptor and RPE dystrophy, and has been implicated in numerous retinal diseases, including age related macular degeneration and retinitis pigmentosa. While much is known about the complex molecular and signaling pathways that underpin shedding, all of these advancements have occurred in animal ...

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    7. Adaptive optics optical coherence tomography angiography for morphometric analysis of choriocapillaris [Invited]

      Adaptive optics optical coherence tomography angiography for morphometric analysis of choriocapillaris [Invited]

      Histological studies have shown that morphometric changes at the microscopic level of choriocapillaris (CC) occur with aging and disease onset, and therefore may be sensitive biomarkers of outer retinal health. However, visualizing CC at this level in the living human eye is challenging because its microvascular is tightly interconnected and weakly reflecting. In this study, we address these challenges by developing and validating a method based on adaptive optics optical coherence tomography with angiography (AO-OCTA) that provides the necessary 3D resolution and image contrast to visualize and quantify these microscopic details. The complex network of anastomotic CC capillaries was successfully ...

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    8. Photoreceptor disc shedding in the living human eye

      Photoreceptor disc shedding in the living human eye

      Cone photoreceptors undergo a daily cycle of renewal and shedding of membranous discs in their outer segments (OS), the portion responsible for light capture. These physiological processes are fundamental to maintaining photoreceptor health, and their dysfunction is associated with numerous retinal diseases. While both processes have been extensively studied in animal models and postmortem eyes, little is known about them in the living eye, in particular human. In this study, we report discovery of the optical signature associated with disc shedding using a method based on adaptive optics optical coherence tomography (AO-OCT) in conjunction with post-processing methods to track and ...

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    9. A Review of Adaptive Optics Optical Coherence Tomography: Technical Advances, Scientific Applications, and the Future

      A Review of Adaptive Optics Optical Coherence Tomography: Technical Advances, Scientific Applications, and the Future

      Purpose : Optical coherence tomography (OCT) has enabled “virtual biopsy” of the living human retina, revolutionizing both basic retina research and clinical practice over the past 25 years. For most of those years, in parallel, adaptive optics (AO) has been used to improve the transverse resolution of ophthalmoscopes to foster in vivo study of the retina at the microscopic level. Here, we review work done over the last 15 years to combine the microscopic transverse resolution of AO with the microscopic axial resolution of OCT, building AO-OCT systems with the highest three-dimensional resolution of any existing retinal imaging modality. Methods : We ...

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    10. Imaging human retinal pigment epithelium cells using adaptive optics optical coherence tomography

      Imaging human retinal pigment epithelium cells using adaptive optics optical coherence tomography

      Retinal pigment epithelium (RPE) cells are vital to health of the outer retina, but are often compromised in ageing and major ocular diseases that lead to blindness. Early manifestation of RPE disruption occurs at the cellular level, and while biomarkers at this scale hold considerable promise, RPE cells have proven extremely challenging to image in the living human eye. We present a novel method based on optical coherence tomography (OCT) equipped with adaptive optics (AO) that overcomes the associated technical obstacles. The method takes advantage of the 3D resolution of AO-OCT, but more critically sub-cellular segmentation and registration that permit ...

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    11. Imaging modal content of cone photoreceptors using adaptive optics optical coherence tomography

      Imaging modal content of cone photoreceptors using adaptive optics optical coherence tomography

      It has been long established that photoreceptors capture light based on the principles of optical waveguiding. Yet after decades of experimental and theoretical investigations considerable uncertainty remains, even for the most basic prediction as to whether photoreceptors support more than a single waveguide mode. To test for modal behavior in human cone photoreceptors, we took advantage of adaptive-optics optical coherence tomography (AO-OCT, λc=785 nm) to noninvasively image in three dimensions the reflectance profiles generated in the inner and outer segments (IS, OS) of cones. Mode content was examined over a range of cone diameters by imaging cones from 0 ...

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    12. Feature Of The Week 01/11/15: Indiana University Demonstrates Adaptive Optics Optical Coherence Tomography at 1 MHz

      Feature Of The Week 01/11/15: Indiana University Demonstrates Adaptive Optics Optical Coherence Tomography at 1 MHz

      Since its first report in 1991, OCT has undergone tremendous advances in almost all aspects of its underlying technologies and methods. For ophthalmic imaging, one of the most impactful advances has been the substantial improvement in image acquisition speed. Increased speed has enabled larger fields of view (FOV) of the retina to be imaged faster and with finer spatial and temporal sampling than ever before. These have greatly expanded the scientific and clinical utility of OCT and have opened new directions into imaging both structure and function of the retina. In this paper, we demonstrate a novel quad-spectrometer adaptive optics ...

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    13. Adaptive-optics optical coherence tomography processing using a graphics processing unit

      Adaptive-optics optical coherence tomography processing using a graphics processing unit

      Graphics processing units are increasingly being used for scientific computing for their powerful parallel processing abilities, and moderate price compared to super computers and computing grids. In this paper we have used a general purpose graphics processing unit to process adaptive-optics optical coherence tomography (AOOCT) images in real time. Increasing the processing speed of AOOCT is an essential step in moving the super high resolution technology closer to clinical viability.

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    14. Adaptive optics optical coherence tomography at 1 MHz

      Adaptive optics optical coherence tomography at 1 MHz

      Image acquisition speed of optical coherence tomography (OCT) remains a fundamental barrier that limits its scientific and clinical utility. Here we demonstrate a novel multi-camera adaptive optics (AO-)OCT system for ophthalmologic use that operates at 1 million A-lines/s at a wavelength of 790 nm with 5.3 μm axial resolution in retinal tissue. Central to the spectral-domain design is a novel detection channel based on four high-speed spectrometers that receive light sequentially from a 1 × 4 optical switch assembly. Absence of moving parts enables ultra-fast (50ns) and precise switching with low insertion loss (−0.18 dB per channel ...

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    15. Adaptive optics optical coherence tomography with dynamic retinal tracking

      Adaptive optics optical coherence tomography with dynamic retinal tracking

      Adaptive optics optical coherence tomography (AO-OCT) is a highly sensitive and noninvasive method for three dimensional imaging of the microscopic retina. Like all in vivo retinal imaging techniques, however, it suffers the effects of involuntary eye movements that occur even under normal fixation. In this study we investigated dynamic retinal tracking to measure and correct eye motion at KHz rates for AO-OCT imaging. A customized retina tracking module was integrated into the sample arm of the 2nd-generation Indiana AO-OCT system and images were acquired on three subjects. Analyses were developed based on temporal amplitude and spatial power spectra in conjunction ...

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    16. Adaptive optics optical coherence tomography for measuring phase and reflectance dynamics of photoreceptors

      Adaptive optics optical coherence tomography for measuring phase and reflectance dynamics of photoreceptors

      Optical coherence tomography with adaptive optics (AO-OCT) is a noninvasive method for imaging the living retina at the microscopic level. We used AO-OCT technology to follow changes in cone photoreceptor outer segment (OS) length and reflectance. To substantially increase sensitivity of the length measurements, a novel phase retrieval technique was demonstrated, capable of detecting changes on a nanometer scale. We acquired volume videos of 0.65°x0.65° retinal patches at 1.5° temporal to the fovea over 75 and 105 minutes in two subjects. Volumes were dewarped and registered, after which the cone intensity, OS length, and referenced phase ...

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    1-16 of 16
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    1. (16 articles) Zhuolin Liu
    2. (13 articles) Indiana University
    3. (13 articles) Donald T. Miller
    4. (9 articles) Omer P. Kocaoglu
    5. (5 articles) Timothy L. Turner
    6. (4 articles) Ravi S. Jonnal
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    Adaptive optics optical coherence tomography for measuring phase and reflectance dynamics of photoreceptors Adaptive optics optical coherence tomography with dynamic retinal tracking Adaptive optics optical coherence tomography at 1 MHz Adaptive-optics optical coherence tomography processing using a graphics processing unit Feature Of The Week 01/11/15: Indiana University Demonstrates Adaptive Optics Optical Coherence Tomography at 1 MHz Imaging modal content of cone photoreceptors using adaptive optics optical coherence tomography Imaging human retinal pigment epithelium cells using adaptive optics optical coherence tomography A Review of Adaptive Optics Optical Coherence Tomography: Technical Advances, Scientific Applications, and the Future Photoreceptor disc shedding in the living human eye Post-doctoral Adaptive Optics Research Fellow at U.S. Food and Drug Administration WF and Pr OCTA in Diabetic Retinopathy Research Associate / Postdoctoral Fellow in Adaptive Optics and Optical Coherence Tomography at Indiana University