1. Articles from Dan P. Popescu

    1-12 of 12
    1. Maximization of signal-to-noise ratio in optical coherence tomography using a depth-dependent matched filter

      Maximization of signal-to-noise ratio in optical coherence tomography using a depth-dependent matched filter

      We discuss and demonstrate the dependence of noise on the signal in time-domain optical coherence tomography (TDOCT). We then derive a depth-dependent matched filter to maximize the signal-to-noise ratio at every pixel in a depth scan (A-scan). We use an empirical estimate of the second order statistics of the noise in OCT images of vascular tissue to implement a depth-dependent filter that is matched to these images. The application of our filter results in an average increase of signal-to-noise ratio of about 7 dB compared to a simple averaging operation. Our filter is not specific to time-domain OCT, but it ...

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    2. Optical coherence tomography: fundamental principles, instrumental designs and biomedical applications

      Optical coherence tomography: fundamental principles, instrumental designs and biomedical applications
      The advances made in the last two decades in interference technologies, optical instrumentation, catheter technology, optical detectors, speed of data acquisition and processing as well as light sources have facilitated the transformation of optical coherence tomography from an optical method used mainly in research laboratories into a valuable tool applied in various areas of medicine and health sciences. This review paper highlights the place occupied by optical coherence tomography in relation to other imaging methods that are used in medical and life science areas such as ophthalmology, cardiology, dentistry and gastrointestinal endoscopy. Together with the basic principles that lay behind ...
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    3. A comparison of methods using optical coherence tomography to detect demineralized regions in teeth

      A comparison of methods using optical coherence tomography to detect demineralized regions in teeth
      Optical coherence tomography (OCT) is a three- dimensional optical imaging technique that can be used to identify areas of early caries formation in dental enamel. The OCT signal at 850 nm back-reflected from sound enamel is attenuated stronger than the signal back-reflected from demineralized regions. To quantify this observation, the OCT signal as a function of depth into the enamel (also known as the A-scan intensity), the histogram of the A-scan intensities and three summary parameters derived from the A-scan are defined and their diagnostic potential compared. A total of 754 OCT A-scans were analyzed. The three summary parameters derived ...
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    4. Performance analysis of a swept-source optical coherence tomography system with a quadrature interferometer and optical amplification

      Performance analysis of a swept-source optical coherence tomography system with a quadrature interferometer and optical amplification
      A performance analysis of signal to noise ratio for an optical coherence tomography system with quadrature detection and a semiconductor optical amplifier in the sample arm is discussed. The results are compared and discussed in relation to a conventional OCT system (without optical amplification). An increase of the signal to noise ratio up to 14 dB at a depth of 0.5 mm is obtained compared to the system without the optical amplifier. Overall, an improvement was demonstrated for signal coming from deeper regions within the samples. Arterial plaque from a myocardial infarction-prone Watanabe heritable hyperlipidemic (WHHLMI) rabbit is visualized ...
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    5. Signal attenuation and box-counting
fractal analysis of optical coherence
tomography images of arterial tissue

      Signal attenuation and box-counting
fractal analysis of optical coherence
tomography images of arterial tissue
      The sensitivity of optical coherence tomography images to sample morphology is tested by two methods. The first method estimates the attenuation of the OCT signal from various regions of the probed tissue. The second method uses a box-counting algorithm to calculate the fractal dimensions in the regions of interest identified in the images. Although both the attenuation coefficient as well as the fractal dimension correlate very well with the anatomical features of the probed samples; the attenuation method provides a better sensitivity. Two types of samples are used in this study: segments of arteries collected from atherosclerosis–prone Watanabe rabbits ...
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    6. Extracting information from optical coherence tomography images of tissues: signal attenuation and fractal analysis of speckle pattern

      Extracting information from optical coherence tomography images of tissues: signal attenuation and fractal analysis of speckle pattern
      Two methods for analyzing OCT images of arterial tissues are tested. These methods are applied toward two types of samples: segments of arteries collected from atherosclerosis-prone Watanabe heritable hyper-lipidemic rabbits and pieces of porcine left descending coronary arteries without atherosclerosis. The first method is based on finding the attenuation coefficients for the OCT signal that propagates through various regions of the tissue. The second method involves calculating the fractal dimensions of the OCT signal textures in the regions of interest identified within the acquired images. A box-counting algorithm is used for calculating the fractal dimensions. Both parameters, the attenuation coefficient ...
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    7. Characteristics of time-domain optical coherence tomography profiles generated from blood–saline mixtures

      Abstract. Time-domain optical coherence tomography (OCT) employing a 1300 nm broadband source is used to study flowing blood–saline mixtures with blood concentration ranging from 20% to 100%. The study emphasizes the characteristics of the recorded OCT signal and its connection with the properties of the corresponding fluids. There are three regions with distinct properties along the compounded OCT profiles showing the signal dependence on depth. The recorded OCT signal increases for the first 80 µm into the fluid. The flow characteristics of the solution and the average spatial orientation of the blood cells can be extracted from this region ...
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    8. Flow of blood-saline mixtures studied by time-domain optical coherence tomography

      In-vitro analysis of flowing blood-saline mixtures is performed by time-domain optical coherence tomography imaging. The mixtures contain blood in concentrations ranging from 100% to 20%. For each image, a corresponding compounded profile is obtained by adding one thousand adjacent A-scans. The compounded profiles are used for characterizing the optical coherence tomography signal as it propagates within the studied blood-saline mixtures. The results obtained point toward the possibility of acquiring intra-vascular images of arterial tissue that is located behind slabs of flowing blood-saline. A threshold in the propagation distance beyond which the recorded signal becomes dominated by its multiple scattered components ...
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    9. Assessment of early demineralization in teeth using the signal attenuation in optical coherence tomography images

      Dan P. Popescu, Michael G. Sowa, Mark D. Hewko et al. Optical coherence tomography imaging is used to improve the detection of incipient carious lesions in dental enamel. Measurements of signal attenuation in images acquired with an 850-nm light source were performed on 21 extracted molars from eight human volunteers. Stronger attenuation was observed ... [J. Biomed. Opt. 13, 054053 (2008)] published Mon Oct 6, 2008.
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    10. In Vitro Assessment of Optical Properties of Blood by Applying the Extended Huygens-Fresnel Principle to Time-Domain Optical Coherence Tomography Signal at 1300 nm

      A direct method for the measurement of the optical attenuation coefficient and the scattering anisotropy parameter based on applying the extended Huygens-Fresnel principle to optical coherence tomography images of blood is demonstrated. The images are acquired with a low-power probing beam at the wavelength of 1300 nm. Values of 12.15 mm−1 and 0.95 are found for the total attenuation coefficient and the scattering anisotropy factor, respectively. Also, as a preliminary step, the optical refraction index is determined with a precision of two decimal numbers directly from optical coherence images. The total attenuation coefficient and the scattering anisotropy ...
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    11. Propagation properties of 1300-nm light in blood-saline mixtures determined through optical coherence tomography

      Dan P. Popescu, Bernhard Schattka, Mark D. Hewko et al. Establishing when the amount of recorded multiple scattered signal becomes dominant is important for various clinical applications that require optical coherence tomography imaging through a turbid environment such as blood. The profiles of detected signals obtained by compounding coherence tomograp ... [Proc. SPIE Int. Soc. Opt. Eng. 6864, 686408 (2008)] published Fri Feb 15, 2008.
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    1-12 of 12
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  2. Topics in the News

    1. (12 articles) National Research Council Canada
    2. (2 articles) University of Manitoba
    3. (1 articles) Northwestern University
    4. (1 articles) University College London
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    Extracting information from optical coherence tomography images of tissues: signal attenuation and fractal analysis of speckle pattern Signal attenuation and box-counting
fractal analysis of optical coherence
tomography images of arterial tissue Performance analysis of a swept-source optical coherence tomography system with a quadrature interferometer and optical amplification Optical coherence tomography: fundamental principles, instrumental designs and biomedical applications A comparison of methods using optical coherence tomography to detect demineralized regions in teeth 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