1. Articles from I. Alex Vitkin

    1-24 of 30 1 2 »
    1. Analysis of low-scattering regions in optical coherence tomography: applications to neurography and lymphangiography

      Analysis of low-scattering regions in optical coherence tomography: applications to neurography and lymphangiography

      Analysis of semi-transparent low scattering biological structures in optical coherence tomography (OCT) has been actively pursued in the context of lymphatic imaging, with most approaches relying on the relative absence of signal as a means of detection. Here we present an alternate methodology based on spatial speckle statistics, utilizing the similarity of a distribution of given voxel intensities to the power distribution function of pure noise, to visualize the low-scattering biological structures of interest. In a human tumor xenograft murine model, we show that these correspond to lymphatic vessels and nerves; extensive histopathologic validation studies are reported to unequivocally establish ...

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    2. Analysis of low-scattering regions in optical coherence tomography

      Analysis of low-scattering regions in optical coherence tomography

      Analysis of semi-transparent low scattering biological structures in optical coherence tomography (OCT) has been actively pursued in the context of lymphatic imaging, with most approaches relying on the relative absence of signal as a means of detection. Here we present an alternate methodology based on spatial speckle statistics, utilizing the similarity of a distribution of given voxel intensities to the power distribution function of pure noise, to visualize the low-scattering biological structures of interest. In a human tumor xenograft murine model, we show that these correspond to lymphatic vessels and nerves; extensive histopathologic validation studies are reported to unequivocally establish ...

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    3. Preclinical quantitative in-vivo assessment of skin tissue vascularity in radiation-induced fibrosis with optical coherence tomography

      Preclinical quantitative in-vivo assessment of skin tissue vascularity in radiation-induced fibrosis with optical coherence tomography

      Radiation therapy (RT) is widely and effectively used for cancer treatment but can also cause deleterious side effects, such as a late-toxicity complication called radiation-induced fibrosis (RIF). Accurate diagnosis of RIF requires analysis of histological sections to assess extracellular matrix infiltration. This is invasive, prone to sampling limitations, and thus rarely used; instead, current practice relies on subjective clinical surrogates, including visual observation, palpation, and patient symptomatology questionnaires. This preclinical study demonstrates that functional optical coherence tomography (OCT) is a useful tool for objective noninvasive in-vivo assessment and quantification of fibrosis-associated microvascular changes in tissue. Data were collected from murine ...

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    4. Preclinical longitudinal imaging of tumor microvascular radiobiological response with functional optical coherence tomography

      Preclinical longitudinal imaging of tumor microvascular radiobiological response with functional optical coherence tomography

      Radiation therapy (RT) is widely used for cancer treatment, alone or in combination with other therapies. Recent RT advances have revived interest in delivering higher dose in fewer fractions, which may invoke both cellular and microvascular damage mechanisms. Microvasculature may thus be a potentially sensitive functional biomarker of RT early response, especially for such emerging RT treatments. However it is difficult to measure directly and non-invasively, and its time course, dose dependencies, and overall importance in tumor control are unclear. We use functional optical coherence tomography for quantitative longitudinal in vivo imaging in preclinical models of human tumor xenografts subjected ...

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    5. Polarization image segmentation of radiofrequency ablated porcine myocardial tissue

      Polarization image segmentation of radiofrequency ablated porcine myocardial tissue

      Optical polarimetry has previously imaged the spatial extent of a typical radiofrequency ablated (RFA) lesion in myocardial tissue, exhibiting significantly lower total depolarization at the necrotic core compared to healthy tissue, and intermediate values at the RFA rim region. Here, total depolarization in ablated myocardium was used to segment the total depolarization image into three (core, rim and healthy) zones. A local fuzzy thresholding algorithm was used for this multi-region segmentation, and then compared with a ground truth segmentation obtained from manual demarcation of RFA core and rim regions on the histopathology image. Quantitative comparison of the algorithm segmentation results ...

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    6. Statistical properties of dynamic speckles from flowing Brownian scatterers in the vicinity of the image plane in optical coherence tomography

      Statistical properties of dynamic speckles from flowing Brownian scatterers in the vicinity of the image plane in optical coherence tomography

      A closed-form analytical expression is obtained for the spatio-temporal correlation function of the scattered radiation detected in fiber-based optical coherence tomography (OCT), assuming a clean optical system arrangement in the OCT sample arm. It is shown that the transverse flow component causes purely translational speckle motion with the predicted speckle velocity 2x higher than the velocity of the flowing particles as would be observed in the image plane under incoherent illumination. It is also shown that both speckle velocity and speckle radius do not depend on the position of the scattering volume relative to the focal plane, hence the derived ...

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    7. Microvascular contrast enhancement in optical coherence tomography using microbubbles

      Microvascular contrast enhancement in optical coherence tomography using microbubbles

      Gas microbubbles (MBs) are investigated as intravascular optical coherence tomography (OCT) contrast agents. Agar + intralipid scattering tissue phantoms with two embedded microtubes were fabricated to model vascular blood flow. One was filled with human blood, and the other with a mixture of human blood + MB. Swept-source structural and speckle variance (sv) OCT images, as well as speckle decorrelation times, were evaluated under both no-flow and varying flow conditions. Faster decorrelation times and higher structural and svOCT image contrasts were detected in the presence of MB in all experiments. The effects were largest in the svOCT imaging mode, and uniformly diminished ...

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    8. Optical clearing of melanoma in vivo: characterization by diffuse reflectance spectroscopy and optical coherence tomography

      Optical clearing of melanoma in vivo: characterization by diffuse reflectance spectroscopy and optical coherence tomography

      Melanoma is the most aggressive type of skin cancer, with significant risk of fatality. Due to its pigmentation, light-based imaging and treatment techniques are limited to near the tumor surface, which is inadequate, for example, to evaluate the microvascular density that is associated with prognosis. White-light diffuse reflectance spectroscopy (DRS) and near-infrared optical coherence tomography (OCT) were used to evaluate the effect of a topically applied optical clearing agent (OCA) in melanoma in vivo and to image the microvascular network. DRS was performed using a contact fiber optic probe in the range from 450 to 650 nm. OCT imaging was ...

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    9. Blood flow contrast enhancement in optical coherence tomography using microbubbles: a phantom study

      Blood flow contrast enhancement in optical coherence tomography using microbubbles: a phantom study

      In this study gas microbubbles are investigated as intravascular OCT contrast agents. Agar+Intralipid scattering tissue-like phantoms with two embedded microtubes were fabricated to model vascular blood flow. One was filled with human blood, and the other with a mixture of human blood and microbubbles. Swept-source structural and speckle variance OCT images, as well as speckle decorrelation times, were evaluated under both stationary and flow conditions. Faster decorrelation times and higher image contrast were detected in the presence of microbubbles in all experiments, and the effect was largest for speckle variance OCT ~2.3x greater contrast under flow conditions. The ...

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    10. Quantitative assessment of oral microstructural and microvascular changes in late oral radiation toxicity, using noninvasive in-vivo optical coherence tomography

      Quantitative assessment of oral microstructural and microvascular changes in late oral radiation toxicity, using noninvasive in-vivo optical coherence tomography

      Background and objectives: About half of the head and neck cancer patients treated with radiotherapy suffer from late radiation effects months to years after the treatment. The most common diagnosis and monitoring methods for such oral toxicities are based on surface examination of the oral tissue, which is subjective. Therefore, subsurface imaging and image quantification tools can be highly useful for monitoring these late effects as these approaches are more robust and objective. In this study, we demonstrate the ability of optical coherence tomography (OCT) technology and its newly developed quantitative imaging platform to reveal subsurface microstructural and microvascular changes ...

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    11. Dynamic light scattering arising from flowing Brownian particles: analytical model in optical coherence tomography conditions

      Dynamic light scattering arising from flowing Brownian particles: analytical model in optical coherence tomography conditions

      The statistical model of scattered by flowing Brownian particles coherent radiation is suggested. The model includes the random Doppler shifts caused by particle Brownian motion and the speckle fluctuations caused primarily by the flow motion of particles. Analytical expressions are obtained for the correlation function, power spectrum, and spectral width of scattered radiation in the imaging geometry typically used in optical coherence tomography (OCT). It is shown that the spectral density has the Voigt shape, a well-known spectral profile from atomic and molecular spectroscopy. The approach enables the choice of the experimental regimes for the measurement of Brownian particle motion ...

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    12. Optical coherence tomography platform for microvascular imaging and quantification: initial experience in late oral radiation toxicity patients

      Optical coherence tomography platform for microvascular imaging and quantification: initial experience in late oral radiation toxicity patients

      An optical coherence tomography (OCT) microvascular imaging platform, consisting of Doppler (DOCT) and speckle variance (svOCT) modalities, and microvascular image quantification tools are developed. The quantification methods extract blood flow-related parameters from DOCT images and vessel morphological parameters from svOCT images. This platform is used to assess the microvascular (DOCT and svOCT) images obtained during a clinical study on late oral radiation toxicity. This specific pathology was considered a suitable scenario for verifying the performance of the developed quantification platform because late oral radiation toxicity is known to involve microvascular damage. The derived parameters are compared between several DOCT and ...

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    13. Feature Of The Week 4/21/13: University of Toronto Investigates Analysis of OCT Speckle to Differentiate Tissue Disease State

      Feature Of The Week 4/21/13: University of Toronto Investigates Analysis of OCT Speckle to Differentiate Tissue Disease State

      Optical coherence tomography is playing an increasingly important role in the differentiation between normal and diseased tissue states in situ. While OCT’s resolution is typically on the micrometer scale and is generally insufficient for direct visualization of cellular organelles and cellular level changes, as these are submicrometer in size. Recently researchers at the University of Toronto, Sunnybrook Health Sciences Center, University Health Network, and National Research Council Canada published some interesting results investigating speckle which is highly correlated with the underlying scatterers’ average properties, such as size, shape, and distribution. Such an approach may give important information on sub-micrometer ...

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    14. Texture analysis of optical coherence tomography speckle for characterizing biological tissues in vivo

      Texture analysis of optical coherence tomography speckle for characterizing biological tissues in vivo

      We demonstrate a method for differentiating tissue disease states using the intrinsic texture properties of speckle in optical coherence tomography (OCT) images of normal and tumor tissues obtained in vivo . This approach fits a gamma distribution function to the nonlog-compressed OCT image intensities, thus allowing differentiation of normal and tumor tissues in an ME-180 human cervical cancer mouse xenograft model. Quantitative speckle intensity distribution analysis thus shows promise for identifying tissue pathologies, with potential for early cancer detection in vivo .

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    15. Optical assessment of tissue anisotropy in ex vivo distended rat bladders

      Optical assessment of tissue anisotropy in ex vivo distended rat bladders

      Microstructural remodelling in epithelial layers of various hollow organs, including changes in tissue anisotropy, are known to occur under mechanical distension and during disease processes. In this paper, we analyze how bladder distension alters wall anisotropy using polarized light imaging (followed by Mueller matrix decomposition). Optical retardance values of different regions of normal rat bladders under different distension pressures are derived. Then optical coherence tomography is used to measure local bladder wall thicknesses, enabling the calculation of the tissue birefringence maps as a measure of the tissue anisotropy. Selected two-photon microscopy is also performed to better understand the compositional origins ...

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    16. Quantifying tissue microvasculature with speckle variance optical coherence tomography

      Quantifying tissue microvasculature with speckle variance optical coherence tomography

      In this Letter, we demonstrate high resolution, three-dimensional optical imaging of in vivo blood vessel networks using speckle variance optical coherence tomography, and the quantification of these images through the development of biologically relevant metrics using image processing and segmentation techniques. Extracted three-dimensional metrics include vascular density, vessel tortuosity, vascular network fractal dimension, and tissue vascularity. We demonstrate the ability of this quantitative imaging approach to characterize normal and tumor vascular networks in a preclinical animal model and the potential for quantitative, longitudinal vascular treatment response monitoring.

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    17. OCT monitoring of cosmetic creams in human skin in vivo

      OCT monitoring of cosmetic creams in human skin in vivo

      Optical coherence tomography (OCT) is a tool currently used for noninvasive diagnosis of human disease as well as for monitoring treatment during or after therapy. In this study, OCT was used to examine penetration and accumulation of cosmetic creams on human hand skin. The samples varied in collagen content with one formulation containing soluble collagen as its primary active ingredient. Collagen is a major connective tissue protein that is essential in maintaining health vitality and strength of many organs. The penetration and localization of collagen in cosmetic creams is thought to be the main determinant of the efficacy of new ...

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    18. Tissue polarimetry: concepts, challenges, applications, and outlook

      Tissue polarimetry: concepts, challenges, applications, and outlook
      Polarimetry has a long and successful history in various forms of clear media. Driven by their biomedical potential, the use of the polarimetric approaches for biological tissue assessment has also recently received considerable attention. Specifically, polarization can be used as an effective tool to discriminate against multiply scattered light (acting as a gating mechanism) in order to enhance contrast and to improve tissue imaging resolution. Moreover, the intrinsic tissue polarimetry characteristics contain a wealth of morphological and functional information of potential biomedical importance. However, in a complex random medium-like tissue, numerous complexities due to multiple scattering and simultaneous occurrences of ...
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    19. Simultaneous 6-channel optical coherence tomography using a high-power telescope-less polygon-based swept laser in dual amplifier configuration

      Simultaneous 6-channel optical coherence tomography using a high-power telescope-less polygon-based swept laser in dual amplifier configuration
      Multichannel optical coherence tomography (MOCT) imaging is demonstrated using a high-power wavelength-swept laser source. The main benefit of MOCT is faster image acquisition rates without a corresponding increase in the laser tuning speed. The wavelength-swept laser was constructed using a compact telescope-less polygon-based filter in Littman arrangement. High output power, necessary for MOCT, was achieved by incorporating two serial semiconductor optical amplifiers in a ring laser cavity in Fourier domain mode-locked configuration. The laser has a measured wavelength tuning range of 111 nm centered at 1329 nm, coherence length of 5.5 mm, and total average output power of 131 ...
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    20. Doppler optical coherence tomography for interventional cardiovascular guidance: in vivo feasibility and forward-viewing probe flow phantom demonstration

      Doppler optical coherence tomography for interventional cardiovascular guidance: in vivo feasibility and forward-viewing probe flow phantom demonstration
      We demonstrate the potential of a forward-looking Doppler optical coherence tomography (OCT) probe for color flow imaging in several commonly seen narrowed artery morphologies. As a proof of concept, we present imaging results of a surgically exposed thrombotic occlusion model that was imaged superficially to demonstrate that Doppler OCT can identify flow within the recanalization channels of a blocked artery. We present Doppler OCT images in which the flow is nearly antiparallel to the imaging direction. These images are acquired using a flexible 2.2-mm-diam catheter that used electrostatic actuation to scan up to 30 deg ahead of the distal ...
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    21. In vivo endoscopic multi-beam optical coherence tomography

      In vivo endoscopic multi-beam optical coherence tomography
      multichannel optical coherence tomography (multi-beam OCT) system and an in vivo endoscopic imaging probe were developed using a swept-source OCT system. The distal optics were micro-machined to produce a high numerical aperture, multi-focus fibre optic array. This combination resulted in a transverse design resolution of <10 µm full width half maximum (FWHM) throughout the entire imaging range, while also increasing the signal intensity within the focus of the individual channels. The system was used in a pre-clinical rabbit study to acquire in vivo structural images of the colon and ex vivo images of the oesophagus and trachea. A good correlation ...
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    22. High-power wavelength-swept laser in Littman telescope-less polygon filter and dual-amplifier configuration for multichannel optical coherence tomography

      High-power wavelength-swept laser in Littman telescope-less polygon filter and dual-amplifier configuration for multichannel optical coherence tomography
      We report a high-power wavelength-swept laser source for multichannel optical coherence tomography (OCT) imaging. Wavelength tuning is performed by a compact telescope-less polygon-based filter in Littman arrangement. High output power is achieved by incorporating two serial semiconductor optical amplifiers in the laser cavity in Fourier domain mode-locked configuration. The measured wavelength tuning range of the laser is 111 nm centered at 1329 nm, coherence length of 5.5 mm, and total average output power of 131 mW at 43 kHz sweeping rate. Multichannel simultaneous OCT imaging at an equivalent A-scan rate of 258 kHz is demonstrated. © 2009 Optical Society of ...
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    23. Oxygen-independent degradation of HIF- via bioengineered VHL tumour suppressor complex

      Tumour hypoxia promotes the accumulation of the otherwise oxygen-labile hypoxia-inducible factor (HIF)- subunit whose expression is associated with cancer progression, poor prognosis and resistance to conventional radiation and chemotherapy. The oxygen-dependent degradation of HIF- is carried out by the von Hippel-Lindau (VHL) protein-containing E3 that directly binds and ubiquitylates HIF- for subsequent proteasomal destruction. Thus, the cellular proteins involved in the VHL-HIF pathway have been recognized as attractive molecular targets for cancer therapy. However, the various compounds designed to inhibit HIF- or HIF-downstream targets, although promising, have shown limited success in the clinic. In the present study, we describe the ...
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    24. Interstitial Doppler Optical Coherence Tomography as a Local Tumor Necrosis Predictor in Photodynamic Therapy of Prostatic Carcinoma: An In vivo Study

      We have tested the feasibility of real-time localized blood flow measurements, obtained with interstitial (IS) Doppler optical coherence tomography (DOCT), to predict photodynamic therapy (PDT)-induced tumor necrosis deep within solid Dunning rat prostate tumors. IS-DOCT was used to quantify the PDT-induced microvascular shutdown rate in s.c. Dunning prostate tumors (n = 28). Photofrin (12.5 mg/kg) was administered 20 to 24 hours before tumor irradiation, with 635 nm surface irradiance of 8 to 133 mWcm–2 for 25 minutes. High frequency ultrasound and calipers were used to measure the thickness of the skin covering the tumor and the ...
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    1-24 of 30 1 2 »
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    1. (29 articles) University of Toronto
    2. (29 articles) I. Alex Vitkin
    3. (13 articles) Ontario Cancer Institute
    4. (9 articles) Ryerson University
    5. (9 articles) Adrian Mariampillai
    6. (9 articles) Victor X. D. Yang
    7. (8 articles) Nigel R. Munce
    8. (8 articles) Beau A. Standish
    9. (7 articles) Sunnybrook Health Sciences Centre
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    Speckle variance detection of microvasculature using swept-source optical coherence tomography High-power wavelength-swept laser in Littman telescope-less polygon filter and dual-amplifier configuration for multichannel optical coherence tomography In vivo endoscopic multi-beam optical coherence tomography Doppler optical coherence tomography for interventional cardiovascular guidance: in vivo feasibility and forward-viewing probe flow phantom demonstration Simultaneous 6-channel optical coherence tomography using a high-power telescope-less polygon-based swept laser in dual amplifier configuration Correlation of retinal sensitivity in microperimetry with vascular density in optical coherence tomography angiography in primary open-angle glaucoma Normal Reference Ranges of Optical Coherence Tomography Parameters in Children Optical coherence tomography angiography using the black-and-white pixel binarization histogram software: a new technique for evaluating healing of macular holes in two surgical techniques B-Scan Attentive CNN for the Classification of Retinal Optical Coherence Tomography Volumes The protective effect of astaxanthin on the ganglion cell complex in glutamate/aspartate transporter deficient mice, a model of normal tension glaucoma, analyzed by spectral domain-optical coherence tomography Small Symptomatic Unilateral Choroidal Osteoma Diagnosed with Enhanced-Depth Imaging Optical Coherence Tomography and Thin-Slice Computed Tomography: 2 Clinical Cases Reliability and Recommended Settings for Pediatric Circumpapillary Retinal Nerve Fiber Layer Imaging Using Hand-Held Optical Coherence Tomography