1. Articles from Xiangzhao Wang

    1-18 of 18
    1. Denoising algorithm of OCT images via sparse representation based on noise estimation and global dictionary

      Denoising algorithm of OCT images via sparse representation based on noise estimation and global dictionary

      Optical coherence tomography (OCT) is a high-resolution and non-invasive optical imaging technology, which is widely used in many fields. Nevertheless, OCT images are disturbed by speckle noise due to the low-coherent interference properties of light, resulting in significant degradation of OCT image quality. Therefore, a denoising algorithm of OCT images via sparse representation based on noise estimation and global dictionary is proposed in this paper. To remove noise and improve image quality, the algorithm first constructs a global dictionary from high-quality OCT images as training samples and then estimates the noise intensity for each input image. Finally, the OCT images ...

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    2. A simple system of swept source optical coherence tomography for a large imaging depth range

      A simple system of swept source optical coherence tomography for a large imaging depth range

      In swept source optical coherence tomography (SSOCT), the imaging depth range sometimes limits its application, such as the whole eye measurement. The methods of extending depth range usually need to redesign the system or add some additional devices. In this paper, we propose a simple system of SSOCT for a large imaging depth range. The system is the same as the original SSOCT with using the swept source clock signal except for a slice glass in the reference arm. The large depth range is achieved by increasing the number of sampling point in every spectrum and wavenumber calibration. More sampling ...

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    3. Passively Driven Probe Based on Miniaturized Propeller for Intravascular Optical Coherence Tomography

      Passively Driven Probe Based on Miniaturized Propeller for Intravascular Optical Coherence Tomography

      Optical coherent tomography (OCT) has enabled clinical applications ranging from ophthalmology to cardiology that revolutionized in vivo medical diagnostics in the last few decades, and a variety of endoscopic probes have been developed in order to meet the needs of various endoscopic OCT imaging. We propose a passive driven intravascular optical coherent tomography (IV-OCT) probe in this paper. Instead of using any electrically driven scanning device, the probe makes use of the kinetic energy of the fluid that flushes away the blood during the intravascular optical coherence tomography imaging. The probe converts it into the rotational kinetic energy of the ...

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    4. Automatic spectral calibration for polarization-sensitive optical coherence tomography

      Automatic spectral calibration for polarization-sensitive optical coherence tomography

      Accurate wavelength assignment is important for Fourier domain polarizationsensitive optical coherence tomography. Incorrect wavelength mapping between the orthogonal horizontal (H) and vertical (V) polarization channels leads to broadening the axial point spread function and generating polarization artifacts. To solve the problem, we propose an automatic spectral calibration method by seeking the optimal calibration coefficient between wavenumber kH and kV. The method first performs a rough calibration to get the relationship between the wavelength λ and the pixel number x of the CCD for each channel. And then a precise calibration is taken to bring both polarization interferograms in the same k ...

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    5. Depth-dependent dispersion compensation for full-depth OCT image

      Depth-dependent dispersion compensation for full-depth OCT image

      A depth-dependent dispersion compensation algorithm for enhancing the image quality of the Fourier-domain optical coherence tomography (OCT) is presented. The dispersion related with depth in the sample is considered. Using the iterative method, an analytical formula for compensating the depth-dependent dispersion in the sample is obtained. We apply depth-dependent dispersion compensation algorithm to process the phantom images and in vivo images. Using sharpness metric based on variation coefficient to compare the results processed with different dispersion compensation algorithms, we find that the depth-dependent dispersion compensation algorithm can improve image quality at full depth.

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    6. Speckle reduction in optical coherence tomography by two-step image registration

      Speckle reduction in optical coherence tomography by two-step image registration

      The image quality of optical coherence tomography can be severely influenced by speckle noise (i.e., signal-degrading speckle). Averaging multiple B-scans can effectively suppress speckle noise. Because of sample motion, images subject to averaging must be aligned exactly. We propose a two-step image registration scheme that combines global and local registrations for speckle reduction by the averaging of multiple B-scans. The method begins with a global registration to compensate for overall motion, which is estimated based on the rigid transformation model involving translation and rotation. Then each A-scan is aligned by cross-correlation using a graph-based algorithm, followed by a pixel ...

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    7. Full-range Fourier domain polarization-sensitive optical coherence tomography using sinusoidal phase modulation

      Full-range Fourier domain polarization-sensitive optical coherence tomography using sinusoidal phase modulation

      We present a full-range Fourier domain polarization-sensitive optical coherence tomography technique which is able to obtain images of retardance, fast optical axis and intensity of sample. In this technique, the sinusoidal phase modulation is introduced into the spectral interferograms while the probe beam scans over the sample (B-scan). Then the complex horizontal and vertical signals are reconstructed by demodulation. By the Fourier transformation of the two interferograms, the full range images are obtained. Herein, the typical linear phase modulation is modified to sinusoidal phase modulation, which improves the system tolerance of sample movements and avoids sensitivity fall-off along the transverse ...

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    8. A novel method for speckle reduction in optical coherence tomography by image registration

      A novel method for speckle reduction in optical coherence tomography by image registration

      Speckle noise is a key factor that can influence the image quality of optical coherence tomography (OCT). The averaging of multiple B-scans can effectively suppress the speckle noise. Because of the sample motion, the images have to be exactly aligned before averaging. In this paper, we propose a new method for OCT image registration that combines global and local registration. The method is able to align the large global displacements in axial and lateral directions, as well as local displacements caused by non-linear deformation between images. Compared with other OCT image registration methods, our method improves the signal-to-noise ratio and ...

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    9. A method for obtaining scattering decomposed images in optical coherence tomography

      A method for obtaining scattering decomposed images in optical coherence tomography

      A method for obtaining scattering decomposed images in optical coherence tomography based on a multiple scattering model is proposed. Images of different scattering components can be obtained with this method. Employing the proposed method, scattering decomposed images of a biological sample are obtained. Then spatial mean filtering for denoising is performed on only the multiple scattering component, and the total signal is reconstructed. This method is useful for observing the images of different scattering components and has the potential to be applied to information extraction or signal processing on these components separately.

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    10. Full-range Fourier domain Doppler optical coherence tomography based on sinusoidal phase modulation

      Full-range Fourier domain Doppler optical coherence tomography based on sinusoidal phase modulation

      A novel full-range Fourier domain Doppler optical coherence tomography (full-range FD-DOCT) using sinusoidal phase modulation for B-M scan is proposed. In this sinusoidal B-M scan, zero optical path difference (OPD) position does not move corresponding to lateral scanning points in contrast to linear B-M scan. Since high phase sensitivity arises around the zero OPD position, the proposed full-range FD-DOCT can achieve easily high velocity sensitivity without mirror image around the zero OPD position. Velocity sensitivity dependent on the OPD and the interval of scanning points is examined, and flow velocity detection capability is verified through Doppler imaging of a flow ...

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    11. Scattering imaging of skin in Fourier domain optical coherence tomography

      Scattering imaging of skin in Fourier domain optical coherence tomography

      A scattering imaging method for skin tissue in Fourier domain optical coherence tomography is proposed. In this method, parameter F image is obtained from the intensity signal as a function of the depth. Since parameter F contains only the scattering coefficient and its first order derivative, the scattering coefficient image depending on depth can be calculated from the parameter F image. Two-dimensional (2D) scattering coefficient images of palm skin are calculated after extracting the tissue interfaces in the 2D parameter F images.

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    12. Full-range parallel Fourier-domain optical coherence tomography using a spatial carrier frequency

      Full-range parallel Fourier-domain optical coherence tomography using a spatial carrier frequency

      We propose a method of parallel full-range Fourier-domain optical coherence tomography (FDOCT) that is capable of acquiring an artifacts-free B-scan image by a single shot of a two-dimensional (2D) CCD camera. This method is based on a spatial carrier technique in which a spatial carrier-frequency is instantaneously introduced into the 2D spectral interferogram registered in parallel FDOCT by using a grating-generated line-reference beam. The spatial-carrier-contained 2D spectral interferogram is processed through Fourier transformation to obtain a complex 2D spectral interferogram, from which a full-range B-scan tomogram is reconstructed. The principle of our method is confirmed by imaging a tropical fish ...

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    13. Speckle reduction in parallel optical coherence tomography by spatial compounding

      Speckle reduction in parallel optical coherence tomography by spatial compounding

      In this paper, we propose a novel method for speckle reduction by combining spatial compounding technique with parallel Fourier-domain optical coherence tomography (FDOCT). Through a two-dimensional (2-D) CCD camera, multiple spectral interference fringes for a single lateral point are acquired with adjacent pixels in parallel detection plane simultaneously. By compounding these spatial-resolved images, we can obtain a speckle-suppressed B-scan tomogram in a single shot without sacrificing axial resolution and imaging speed. The principle of our method is demonstrated by imaging a shrimp's telson in vivo and a pearl. A signal-to-noise ratio improvement close to a factor of two was ...

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    14. Single-shot parallel full range complex Fourier-domain optical coherence tomography

      Single-shot parallel full range complex Fourier-domain optical coherence tomography

      We present a method of parallel full range complex Fourier-domain optical coherence tomography (FDOCT) that is capable of acquiring an artifacts-free two-dimensional (2-D) cross-sectional image, i.e. a full range B-scan tomogram, by a single shot of 2-D CCD camera. This method is based on a spatial carrier technique, in which the spatial carrier-frequency is instantaneously introduced into the 2-D spectral interferogram registered in parallel FDOCT by using a grating-generated reference beam. The spatial-carrier-contained 2-D spectral interferogram is processed through Fourier transformation to obtain a complex 2-D spectral interferogram. From the 2-D complex spectral interferomgram, a full range B-scan tomogram ...

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    15. A new spectral calibration method for Fourier domain optical coherence tomography

      Spectral calibration is important for a Fourier domain optical coherence tomography (FD-OCT) system. A new spectral calibration method for FD-OCT is presented. Through the iterated mapping of spectral interferograms detected by an optical spectrum analyzer and the CCD grating spectrometer, multiple groups of calibration coefficients are obtained. By comparing the effects of these coefficients on improving the amplitude of the axial point spread function (PSF), optimum coefficients are obtained. In this method, no additional calibration laser source is needed, reducing the complexity of the system. The cross-sectional images of a glass plate in milk are acquired, and the experimental results ...

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    16. One-shot parallel complex Fourier-domain optical coherence tomography using a spatial carrier frequency

      We propose a novel method of one-shot parallel complex Fourier-domain optical coherence tomography using a spatial carrier frequency for full range imaging. The spatial carrier frequency is introduced into the 2-D spectral interferogram in the lateral direction by using a tilted reference wavefront. This spatial-carrier-contained 2-D spectral interferogram is recorded with one shot of a 2-D CCD camera, and is Fourier-transformed in the lateral direction to obtain a 2-D complex spectral interferogram by a spatial-carrier technique. A full-range tomogram is reconstructed from the 2-D complex spectral interferogram. The principle of this method is confirmed by cross-sectional imaging of a glass ...

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    17. High-speed full range complex Fourier-domain optical coherence tomography using sinusoidal phase-modulating interferometry

      High-speed full-range complex Fourier domain optical coherence tomography (FDOCT) using sinusoidal phase-modulating interferometry is proposed. A high-rate two-dimensional (2-D) CCD camera is used to record time-sequential sinusoidally phase-modulated 2-D spectral interferograms, from which the complex 2-D spectral interferograms corresponding to each frame of the 2-D CCD camera are extracted by Fourier transform method. By taking inverse Fourier transform of the complex spectral interferograms, full-range B-scan images free of the complex conjugate ambiguity as well as dc and autocorrelation noises are obtained at intervals of the frame period of the 2-D CCD camera. Time-sequential cross-sectional imaging of human skin ex vivo ...

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    18. Dynamic full-range Fourier-domain optical coherence tomography using sinusoidal phase-modulating interferometry

      We propose a technique for dynamic full-range Fourier-domain optical coherence tomography by using sinusoidal phase-modulating interferometry, where both the full-range structural information and depth-resolved dynamic information are obtained. A novel frequency-domain filtering algorithm is proposed to reconstruct a time-dependent complex spectral interferogram from the sinusoidally phase-modulated interferogram detected with a high-rate CCD camera. By taking the amplitude and phase of the inverse Fourier transform of the complex spectral interferogram, a time-dependent full-range cross-sectional image and depth-resolved displacement are obtained. Displacement of a sinusoidally vibrating glass cover slip behind a fixed glass cover slip is measured with subwavelength sensitivity to demonstrate ...

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    1-18 of 18
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    Single-shot parallel full range complex Fourier-domain optical coherence tomography Speckle reduction in parallel optical coherence tomography by spatial compounding Full-range parallel Fourier-domain optical coherence tomography using a spatial carrier frequency Scattering imaging of skin in Fourier domain optical coherence tomography Full-range Fourier domain Doppler optical coherence tomography based on sinusoidal phase modulation A method for obtaining scattering decomposed images in optical coherence tomography The truth about invisible posterior vitreous structures Increased Macrophage-like Cell Density in Retinal Vein Occlusion as Characterized by en Face Optical Coherence Tomography The Influence of Eyelid Position and Environmental Conditions on the Corneal Changes in Early Postmortem Interval: A Prospective, Multicentric OCT Study The Use of Optical Coherence Tomography for Gross Examination and Sampling of Fixed Breast Specimens: A Pilot Study The Role of Widefield and Ultra Widefield Optical Coherence Tomography in the Diagnosis and Management of Vitreoretinal Diseases Acute Idiopathic Blind Spot Enlargement Syndrome-New Perspectives in the OCT Era