1. Articles from timothy r. hillman

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    1. Speckle reduction in optical coherence tomography images using tissue viscoelasticity

      Speckle reduction in optical coherence tomography images using tissue viscoelasticity
      We present a technique to reduce speckle in optical coherence tomography images of soft tissues. An average is formed over a set of B-scans that have been decorrelated by viscoelastic creep strain. The necessary correction for the deformation-induced spatial distortions between B-scans is achieved through geometrical co-registration using an affine transformation. Speckle reduction by up to a factor of 1.65 is shown in images of tissue-mimicking soft fibrin phantoms and excised human lymph node tissue with no observable loss of spatial resolution.
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    2. Speckle reduction in optical coherence tomography by strain compounding

      Speckle reduction in optical coherence tomography by strain compounding
      We present a speckle reduction technique for optical coherence tomography based on strain compounding. Decorrelation is introduced between B-scans by altering the sample’s strain. A theoretical description of the technique, based on a transfer-function formalism, and experimental results on silicone phantoms are presented. Nearly complete decorrelation between successive B-scan speckle patterns was observed for a variation in strain of 0.045. Strain compounding by averaging nine B-scans, with 0.003 strain increments between them, resulted in a 1.5-fold reduction in speckle contrast ratio.
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    3. Detection of multiple scattering in optical coherence tomography by speckle correlation of angle-dependent B-scans

      Detection of multiple scattering in optical coherence tomography by speckle correlation of angle-dependent B-scans
      Angular diversity is a successful speckle-reduction technique in optical coherence tomography (OCT). We employ angle-dependent detection for a different purpose: to distinguish the singly backscattered and multiply scattered signal components. Single backscattering is highly correlated over a large range of detection angles; multiple scattering rapidly decorrelates as the angle is varied. Theoretical justification is provided using a linear-systems description of the OCT imaging process; detection of multiple scattering is corroborated experimentally.
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    4. In vivo dynamic optical coherence elastography using a ring actuator

      In vivo dynamic optical coherence elastography using a ring actuator
      We present a novel sample arm arrangement for dynamic optical coherence elastography based on excitation by a ring actuator. The actuator enables coincident excitation and imaging to be performed on a sample, facilitating in vivo operation. Sub-micrometer vibrations in the audio frequency range were coupled to samples that were imaged using optical coherence tomography. The resulting vibration amplitude and microstrain maps are presented for bilayer silicone phantoms and multiple skin sites on a human subject. Contrast based on the differing elastic properties is shown, notably between the epidermis and dermis. The results constitute the first demonstration of a practical means ...
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    5. Detection of multiple scattering in optical coherence tomography using the spatial distribution of Stokes vectors

      Steven G. Adie, Timothy R. Hillman, David D. Sampson. Multiple scattering is one of the main degrading influences in optical coherence tomography, but to date its presence in an image can only be indirectly inferred. We present a polarization-sensitive method that shows the potential to detect it more directly, based on the degree to which the ... [Opt. Express 15, 18033-18049 (2007)]
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    6. Microstructural information beyond the resolution limit: studies in two coherent, wide-field biomedical imaging systems (Thesis)

      Microstructural information beyond the resolution limit: studies in two coherent, wide-field biomedical imaging systems (Thesis)
      In this thesis, we describe and analyse the characteristics of two different coherence optical microscopic imaging modalities, with a particular emphasis on their principles of operation and their respective resolution limits. By coherent, we mean that each detects a signal on an optical field basis; they are therefore sensitive to both the amplitude and phase of the light detected after interaction with a sample. This information is obtained interferometerically, by isolating the cross-term associated with detecting the intensity (squared modulus) of the sum of the sample field and a coherent reference wave. Both modalities have advanced rapidly in the last ...
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    1-6 of 6
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    1. (6 articles) University of Western Australia
    2. (1 articles) Sir Charles Gairdner Hospital
    3. (1 articles) Massachusetts Institute of Technology
    4. (1 articles) Northwestern University
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    In vivo dynamic optical coherence elastography using a ring actuator Microstructural information beyond the resolution limit: studies in two coherent, wide-field biomedical imaging systems (Thesis) Detection of multiple scattering in optical coherence tomography by speckle correlation of angle-dependent B-scans Speckle reduction in optical coherence tomography by strain compounding Speckle reduction in optical coherence tomography images using tissue viscoelasticity Influence of scan direction on subfoveal choroidal vascularity index using optical coherence tomography Subthreshold Nanosecond Laser for Non-resolving Central Serous Chorioretinopathy: A Double-masked Sham-controlled Randomised Trial Optical Coherence Tomography Angiography (OCTA) to Assess Cardiac Output and Cerebral Perfusion at the Time of Children's Cardiac Surgery Recent advances in optical coherence tomography for anterior segment imaging in small animals and their clinical implications Intraoperative optical coherence tomography-guided donor corneal tissue assessment and preparation Peripapillary and fovea avascular zone optical coherence tomography angiography parameters in exfoliation glaucoma versus primary open-angle glaucoma versus healthy eyes Comparison of the proposed DCNN model with standard CNN architectures for retinal diseases classification