1. Articles from Anant Agrawal

    1-12 of 12
    1. Variations in optical coherence tomography resolution and uniformity: a multi-system performance comparison

      Variations in optical coherence tomography resolution and uniformity: a multi-system performance comparison

      Point spread function (PSF) phantoms based on unstructured distributions of sub-resolution particles in a transparent matrix have been demonstrated as a useful tool for evaluating resolution and its spatial variation across image volumes in optical coherence tomography (OCT) systems. Measurements based on PSF phantoms have the potential to become a standard test method for consistent, objective and quantitative inter-comparison of OCT system performance. Towards this end, we have evaluated three PSF phantoms and investigated their ability to compare the performance of four OCT systems. The phantoms are based on 260-nm-diameter gold nanoshells, 400-nm-diameter iron oxide particles and 1.5-micron-diameter silica ...

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    2. Quantitative analysis of low contrast detectability in optical coherence tomography

      Quantitative analysis of low contrast detectability in optical coherence tomography

      Optical coherence tomography (OCT) is a high resolution imaging technology that is rapidly being adopted as the standard of care for medical applications such as ocular and intravascular imaging. However, clinical translation has been hampered by the lack of standardized test methods for performance evaluation as well as consensus standards analogous to those that have been developed for established medical imaging modalities (e.g., ultrasound). In this study, we address low contrast detectability, specifically, the ability of systems to differentiate between regions exhibiting small differences in scattering coefficient. Based on standard test methods for established medical imaging modalities, we have ...

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    3. Retina-simulating phantom for optical coherence tomography

      Retina-simulating phantom for optical coherence tomography

      Optical coherence tomography (OCT) is a rapidly growing imaging modality, particularly in the field of ophthalmology. Accurate early diagnosis of diseases requires consistent and validated imaging performance. In contrast to more well-established medical imaging modalities, no standardized test methods currently exist for OCT quality assurance. We developed a retinal phantom which mimics the thickness and near-infrared optical properties of each anatomical retinal layer as well as the surface topography of the foveal pit. The fabrication process involves layer-by-layer spin coating of nanoparticle-embedded silicone films followed by laser micro-etching to modify the surface topography. The thickness of each layer and dimensions ...

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    4. Multilayer thin-film phantoms for axial contrast transfer function measurement in optical coherence tomography

      Multilayer thin-film phantoms for axial contrast transfer function measurement in optical coherence tomography

      In optical coherence tomography (OCT), axial resolution is one of the most critical parameters impacting image quality. It is commonly measured by determining the point spread function (PSF) based on a specular surface reflection. The contrast transfer function (CTF) provides more insights into an imaging system’s resolving characteristics and can be readily generated in a system-independent manner, without consideration for image pixel size. In this study, we developed a test method for determination of CTF based on multi-layer, thin-film phantoms, evaluated using spectral- and time-domain OCT platforms with different axial resolution values. Phantoms representing six spatial frequencies were fabricated ...

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    5. Multi-system comparison of optical coherence tomography performance with point spread function phantoms

      Multi-system comparison of optical coherence tomography performance with point spread function phantoms

      Point spread function (PSF) phantoms based on unstructured distributions of sub-resolution particles in a transparent matrix have proven effective for evaluating resolution and its spatial variation in optical coherence tomography (OCT) systems. Measurements based on PSF phantoms have the potential to become a standard test method for consistent, objective and quantitative inter-comparison of OCT system performance. Towards this end, we have evaluated three PSF phantoms and investigated their ability to compare the performance of four OCT systems. The phantoms are based on 260-nm-diameter gold nanoshells, submicron-diameter iron oxide particles and 1.5-micron-diameter silica particles. The OCT systems included spectral-domain and ...

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    6. OCT Phantoms Survey: Please share your opinions!

      OCT Phantoms Survey: Please share your opinions!

      Earlier this year, the OCT Phantoms Initiative began by posting a survey to better understand the interests and needs for phantoms (controlled test objects) in the OCT community. We thank everyone for all the responses thus far. But if you haven’t had a chance to fill out the survey, we would be grateful to hear from you. It should only take about 5 minutes of your time. We will be presenting our findings from this survey at the 2013 Photonics West BiOS symposium in San Francisco. Thanks again! Anant Agrawal Brendan Kennedy Guy Lamouche  Pete Tomlins

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    7. Invitation to Join and Participate in a Optical Coherence Tomography Phantoms Initiative Forum

      Invitation to Join and Participate in a Optical Coherence Tomography Phantoms Initiative Forum

      Anant Agrawal from the US Food and Drug Administration, Brendan Kennedy from the University of Western Australia, Guy Lamouche of the National Research Council Canada, and Pete Tomlins from Queen Mary, University of London invite your participation in the Optical Coherence Tomography Phantoms Initiative Forum. To sign up or to find out more details please click this LINK.

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    8. Characterizing the point spread function of retinal OCT devices with a model eye-based phantom

      Characterizing the point spread function of retinal OCT devices with a model eye-based phantom

      We have designed, fabricated, and tested a nanoparticle-embedded phantom (NEP) incorporated into a model eye in order to characterize the point spread function (PSF) of retinal optical coherence tomography (OCT) devices in three dimensions under realistic imaging conditions. The NEP comprises a sparse distribution of highly backscattering silica-gold nanoshells embedded in a transparent UV-curing epoxy. The commercially-available model eye replicates the key optical structures and focusing power of the human eye. We imaged the model eye-NEP combination with a research-grade spectral domain OCT system designed for in vivo retinal imaging and quantified the lateral and axial PSF dimensions across the ...

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    9. A review of consensus test methods for established medical imaging modalities and their implications for optical coherence tomography

      A review of consensus test methods for established medical imaging modalities and their implications for optical coherence tomography

      In recent years there has been increasing interest in development of consensus, tissue-phantom-based approaches for assessment of biophotonic imaging systems, with the primary goal of facilitating clinical translation of novel optical technologies. Well-characterized test methods based on tissue phantoms can provide useful tools for performance assessment, thus enabling standardization and device inter-comparison during preclinical development as well as quality assurance and re-calibration in the clinical setting. In this review, we study the role of phantom-based test methods as described in consensus documents such as international standards for established imaging modalities including X-ray CT, MRI and ultrasound. Specifically, we focus on ...

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      Mentions: FDA Anant Agrawal
    10. OCT Phantoms Initiative: A new effort to bring standardized tools for OCT system characterization and validation to the community

      OCT Phantoms Initiative: A new effort to bring standardized tools for OCT system characterization and validation to the community
      Over the past two decades, the capabilities, applications, and usage of OCT have advanced remarkably. Given the maturity of OCT, there is an imminent need for widely available and standardized tools to benchmark OCT device performance. Controlled test objects, generally known as phantoms, are essential to satisfy this need by serving as a stable, well-characterized reference which is periodically imaged. The proper phantom can ensure data accuracy and consistency over time, among multiple instruments, and across device manufacturers. This is a key step towards standardization and quality assurance on par with the most established medical imaging modalities. The OCT Phantoms ...
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    11. Optical coherence tomography imaging of retinal damage in real time under a stimulus electrode

      Optical coherence tomography imaging of retinal damage in real time under a stimulus electrode
      We have developed a novel method to study the effects of electrical stimulation of the local retina directly under an epiretinal stimulus electrode in real time. Using optical coherence tomography (OCT) and a superfused retinal eyecup preparation, we obtained high-resolution images of the rabbit retina directly under an optically transparent saline-filled fluoropolymer stimulation tube electrode. During OCT imaging, 50 Hz trains of biphasic current pulses 1 ms/phase (23–749 µC cm−2 ph−1) were applied to the retinal surface for 5 min. After imaging, the stimulated regions were stained with the dye propidium iodide (PI) to reveal cytotoxic ...
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    12. Three-dimensional characterization of optical coherence tomography point spread functions with a nanoparticle-embedded phantom

      Three-dimensional characterization of optical coherence tomography point spread functions with a nanoparticle-embedded phantom
      We present a novel (to our knowledge) approach for measurement of the three-dimensional point spread function (PSF) of optical coherence tomography (OCT) systems using a nanoparticle-embedded phantom (NEP), toward development of standardized test methods for biophotonic imaging. The NEP comprises highly reflective plasmonic nanoparticles, homogeneously distributed in a transparent silicone matrix. OCT image volumes were analyzed to characterize PSFs in axial and lateral directions at a variety of locations in the NEP. Results indicate submicrometer agreement with conventional approaches to measure dimensions of the PSF. The NEP offers a robust approach for validating and comparing imaging performance of OCT devices.
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    1-12 of 12
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  2. Topics in the News

    1. (12 articles) FDA
    2. (12 articles) Anant Agrawal
    3. (6 articles) University of Maryland
    4. (5 articles) Yu Chen
    5. (5 articles) Pete H. Tomlins
    6. (4 articles) University of London
    7. (4 articles) Rice University
    8. (3 articles) University of Western Australia
    9. (3 articles) National Research Council Canada
    10. (3 articles) Guy Lamouche
    11. (2 articles) Chang Gung University
    12. (2 articles) Meng-Tsan Tsai
    13. (2 articles) Cheng-Kuang Lee
    14. (2 articles) Tanja Maier
    15. (1 articles) Korea Advanced Institute of Science and Technology
    16. (1 articles) Yasushi Ino
    17. (1 articles) Feng-Yu Chang
    18. (1 articles) Thilo Gambichler
    19. (1 articles) AGFA Healthcare
    20. (1 articles) Optovue
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    Three-dimensional characterization of optical coherence tomography point spread functions with a nanoparticle-embedded phantom Optical coherence tomography imaging of retinal damage in real time under a stimulus electrode OCT Phantoms Initiative: A new effort to bring standardized tools for OCT system characterization and validation to the community A review of consensus test methods for established medical imaging modalities and their implications for optical coherence tomography Characterizing the point spread function of retinal OCT devices with a model eye-based phantom Invitation to Join and Participate in a Optical Coherence Tomography Phantoms Initiative Forum OCT Phantoms Survey: Please share your opinions! Multi-system comparison of optical coherence tomography performance with point spread function phantoms Multilayer thin-film phantoms for axial contrast transfer function measurement in optical coherence tomography Retina-simulating phantom for optical coherence tomography Handheld Micromanipulator for Robot-Assisted Microsurgery (Thesis) MACULAR AND PERIPAPILLARY SPECTRAL DOMAIN OPTICAL COHERENCE TOMOGRAPHY CHANGES IN SICKLE CELL RETINOPATHY