1. Articles from Wanrong Gao

    1-24 of 29 1 2 »
    1. Extended focus optical coherence tomography with Fresnel lens

      Extended focus optical coherence tomography with Fresnel lens

      We report a Fresnel lens based spectral domain optical coherence tomography (SDOCT) setup to overcome the trade-off between lateral resolution and focusing depth which is one of the main problems for OCT system. We demonstrated the feasibility of the Fresnel lens based SDOCT system by measuring the lateral resolution at different depth positions and compared these results with that obtained by conventional SDOCT illuminated with a light source of a central wavelength of 840 nm and a bandwidth of 50 nm. These results indicated that the Fresnel lens based SDOCT can maintain a constant lateral resolution (~ 6.2 μm or ...

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    2. Image contrast correction method in full-field optical coherence tomography

      Image contrast correction method in full-field optical coherence tomography

      An image contrast correction method is proposed for en face images obtained with full-field optical coherence tomography (FFOCT). First, the mechanism of image contrast decrease in FFOCT is considered and the theoretical models of main parameters that degrade image contrast are analyzed. Second, changes of contrast with depth are calculated under various conditions, from which the main parameters that affect contrast in tissue are identified. Then based on the analysis, the methods are proposed for correcting image contrast. Finally, the en face tomographic images of human liver tissue at different depths with and without contrast correction are presented to demonstrate ...

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    3. 2D MEMS-based high-speed beam-shifting technique for speckle noise reduction and flow rate measurement in optical coherence tomography

      2D MEMS-based high-speed beam-shifting technique for speckle noise reduction and flow rate measurement in optical coherence tomography

      In this manuscript, a two-dimensional (2D) micro-electro-mechanical system (MEMS)-based, high-speed beam-shifting spectral domain optical coherence tomography (MHB-SDOCT) is proposed for speckle noise reduction and absolute flow rate measurement. By combining a zigzag scanning protocol, the frame rates of 45.2 Hz for speckle reduction and 25.6 Hz for flow rate measurement are achieved for in-vivo tissue imaging. Phantom experimental results have shown that by setting the incident beam angle to ϕ = 4.76° (between optical axis of objective lens and beam axis) and rotating the beam about the optical axis in 17 discrete angular positions, 91% of speckle ...

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    4. Measurement and compensation of motion artifacts in spectral domain optical coherence tomography

      Measurement and compensation of motion artifacts in spectral domain optical coherence tomography

      Spectral domain optical coherence tomography (SDOCT) has the capability of generating optical sectioning images at high depth resolution in vivo, which is helpful for the diagnosis of various disease. But when the voluntary and involuntary movement of the sample occurs during the acquisition time, the real structure of the sample will be distorted. So it is valuable to compensate the motion artifacts in SDOCT imaging to obtain high quality images. We demonstrated a self-reference method of detecting and compensating the axial motion artifacts in which the axial motion is first detected by comparing the topology of different layers in tissue ...

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    5. All single-mode fiber-based polarization-sensitive spectral domain optical coherence tomography system

      All single-mode fiber-based polarization-sensitive spectral domain optical coherence tomography system

      We reported an all single-mode fiber (SMF)-based polarization sensitive spectral domain optical coherence tomography (PSSDOCT) system with single input polarization state (IPS). In our design, polarization state was modulated only by four polarization controllers (PC) and a polarization beam splitter. To extract the phase retardance and optical axis orientation of sample, the Mueller matrix of the fiber system and sample is transferred to a new retardar by employing PCs with the advantage that the effects of fiber birefringence of SMFs and SMF components are corrected. The contribution of the multibackscattering in tissues to the orthogonal polarization interference signals is ...

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    6. Single-shot wavelength-independent phase-shifting method for full-field optical coherence tomography

      Single-shot wavelength-independent phase-shifting method for full-field optical coherence tomography

      One limitation of a piezoelectric translator-based phase-shifting method in full-field optical coherence tomography (FF-OCT) is that there exist interference residuals because a light source with broadband is used. In this work, an achromatic phase-shifting method was proposed in which a linear polarizer and a quarter-wave plate were employed to generate the circularly polarized light in the reference arm of a basic Linnik interferometer. The light field reflected from the reference arm is supposed with the unpolarized light backscattered from the sample when the path difference is within the coherence length of the light source. A first phase difference of

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    7. Quantitative measurement of subsurface damage with self-referenced spectral domain optical coherence tomography

      Quantitative measurement of subsurface damage with self-referenced spectral domain optical coherence tomography

      In this work, we present the three-dimensional reconstruction of the subsurface damage (SSD) within the optical components at the level of several microns with a self-referenced spectral domain optical coherence tomography (SDOCT) system, from which the quantitative information, including the maximum depth, the cluster depth, the shape, the size and the damage density, can be acquired. First, to compare the actual maximum depths with the ones computed by the formulas for predicting the maximum depth, the theoretical and empirical formulas proposed so far were summarized. The values of the maximum depths of SSD within eight samples were then measured. It ...

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    8. Quantitative depth resolved microcirculation imaging with optical coherence tomography angiography (Part Ι): Blood flow velocity imaging

      Quantitative depth resolved microcirculation imaging with optical coherence tomography angiography (Part Ι): Blood flow velocity imaging

      The research goal of the microvascular network imaging with optical coherence tomography (OCT) angiography is to achieve depth resolved blood flow and vessel imaging in vivo in the clinical management of patents. In this review, we review the main phenomena that have been explored in OCT to image the blood flow velocity vector and the vessels of the microcirculation within living tissues. Parameters that limit the accurate measurements of blood flow velocity are then condisered. Finally, initial Clinic diagnosis applications of and future developments are discussed.

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    9. Quantitative depth resolved microcirculation imaging with optical coherence tomography angiography (Part ΙΙ): Microvascular network imaging

      Quantitative depth resolved microcirculation imaging with optical coherence tomography angiography (Part ΙΙ): Microvascular network imaging

      In this work, we review the main phenomena that have been explored in OCT angiography to image the vessels of the microcirculation within living tissues with the emphasis on how the different processing algorithms were derived to circumvent specific limitations. Parameters are then discussed that can quantitatively describe the depth-resolved microvascular network for possible clinic diagnosis applications. Finally,future directions in continuing OCT development are discussed.

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    10. High speed, wide velocity dynamic range Doppler optical coherence tomography (Part V): Optimal utilization of multi-beam scanning for Doppler and speckle variance microvascular imaging

      High speed, wide velocity dynamic range Doppler optical coherence tomography (Part V): Optimal utilization of multi-beam scanning for Doppler and speckle variance microvascular imaging

      In this paper, a multi-beam scanning technique is proposed to optimize the microvascular images of human skin obtained with Doppler effect based methods and speckle variance processing. Flow phantom experiments were performed to investigate the suitability for combining multi-beam data to achieve enhanced microvascular imaging. To our surprise, the highly variable spot sizes (ranging from 13 to 77 μm) encountered in high numerical aperture multi-beam OCT system imaging the same target provided reasonably uniform Doppler variance and speckle variance responses as functions of flow velocity, which formed the basis for combining them to obtain better microvascular imaging without scanning penalty ...

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    11. Multi-beam optical coherence tomography for microvascular imaging of human skin in vivo

      Multi-beam optical coherence tomography for microvascular imaging of human skin in vivo

      In this paper, a multi-beam optical coherence tomography (OCT) was used to reconstruct the microvascular image of human skin in vivo with phase resolved Doppler OCT (PRDOCT), phase resolved Doppler variance (PRDV) and speckle variance OCT (svOCT), in which the blood flow image was calculated by averaging the four blood flow images obtained by the four beams. In PRDOCT method, it is difficult to detect the blood flow perpendicular to optical axis of the probe beam for single beam OCT, but the multi-beam scanning method can solve this because the input angles of the four probe beams are slightly different ...

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    12. Differential standard deviation of log-scale intensity based optical coherence tomography angiography

      Differential standard deviation of log-scale intensity based optical coherence tomography angiography

      In this paper, a differential standard deviation of log-scale intensity (DSDLI) based optical coherence tomography angiography (OCTA) is presented for calculating microvascular images of human skin. The DSDLI algorithm calculates the variance in difference images of two consecutive log-scale intensity based structural images from the same position along depth direction to contrast blood flow. The en face microvascular images were then generated by calculating the standard deviation of the differential log-scale intensities within the specific depth range, resulting in an improvement in spatial resolution and SNR in microvascular images compared to speckle variance OCT and power intensity differential method. The ...

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    13. Dispersion analysis in micron resolution spectral domain optical coherence tomography

      Dispersion analysis in micron resolution spectral domain optical coherence tomography

      One of the main factors that limits the effective axial resolution of spectral domain optical coherence tomography in live tissue imaging is tissue-induced dispersion. In this work, first the methods are reviewed that have been proposed to compensate for the dispersion effects in various applications. Simple formulas are then derived that can be used to estimate the orders of the dispersion that may have significant influences. The formulas are then used to calculate relative contributions of various dispersion orders to the decrease of the axial resolution, in which the dispersion properties of water were employed as a first approximation to ...

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    14. Fractal analysis of en face tomographic images obtained with full field optical coherence tomography

      Fractal analysis of en face tomographic images obtained with full field optical coherence tomography

      The quantitative modeling of the imaging signal of pathological areas and healthy areas is necessary to improve the specificity of diagnosis with tomographic en face images obtained with full field optical coherence tomography (FFOCT). In this work, we propose to use the depth-resolved change in the fractal parameter as a quantitative specific biomarker of the stages of disease. The idea is based on the fact that tissue is a random medium and only statistical parameters that characterize tissue structure are appropriate. We successfully relate the imaging signal in FFOCT to the tissue structure in terms of the scattering function and ...

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    15. Imaginary part-based correlation mapping optical coherence tomography for imaging of blood vessels in vivo

      Imaginary part-based correlation mapping optical coherence tomography for imaging of blood vessels in vivo

      We present an imaginary part-based correlation mapping optical coherence tomography (IMcmOCT) technique for in vivo blood vessels imaging. In the conventional correlation mapping optical coherence tomography (cmOCT) method, two adjacent frames of intensity-based structural images are correlated to extract blood flow information and the size of correlation window has to be increased to improve the signal-to-noise ratio of microcirculation maps, which may cause image blur and miss the small blood vessels. In the IMcmOCT method, the imaginary part of a depth-resolved complex analytic signal in two adjacent B-scans is correlated to reconstruct microcirculation maps. Both phantom and in vivo experiments ...

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    16. Rapid and high-resolution imaging of human liver specimens by full-field optical coherence tomography

      Rapid and high-resolution imaging of human liver specimens by full-field optical coherence tomography

      We report rapid and high-resolution tomographic en face imaging of human liver specimens by full-field optical coherence tomography (FF-OCT). First, the arrangement of the FF-OCT system was described and the performance of the system was measured. The measured axial and lateral resolutions of the system are 0.8 and 0.9     μ m , respectively. The system has a sensitivity of ∼ 60     dB and can achieve an imaging rate of 7 fps and a penetration depth of ∼ 80     μ m . The histological structures of normal liver can be seen clearly in the en face tomographic images, including central veins, cords of hepatocytes separated ...

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    17. Image contrast reduction mechanism in full-field optical coherence tomography

      Image contrast reduction mechanism in full-field optical coherence tomography

      Correct interpretation of image contrast obtained with full-field optical coherence tomography (FFOCT) technique is required for accurate medical diagnosis applications. In this work, first, the characteristics of microscopic structures of tissue that generate the contrast in en-face tomographic image obtained with FFOCT are discussed. Then an overview is given of the parameters that affect image contrast. Finally, the contrast correction factor for correct image interpretation and the contrast limits to practical FFOCT systems are outlined.

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    18. Stage-based frequency-modulated full-range complex Fourier-domain optical coherence tomography

      Stage-based frequency-modulated full-range complex Fourier-domain optical coherence tomography

      We propose a simple method to modulate spatial interferogram to achieve full-range complex imaging in Fourier-domain optical coherence tomography, in which a sample stage is employed which can be adjusted to introduce a constant carrier frequency into the interference signal during the B-scan by adjusting the stage angle with respect to the normal to the object under test. An additional phase, which is linearly related to the lateral position, is then induced in the A-scan. The in vivo images of human skin were generated which demonstrate that the method proposed can generate the cross-sectional image with the same quality with ...

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    19. Fourier spectrum analysis of full-field optical coherence tomography for tissue imaging

      Fourier spectrum analysis of full-field optical coherence tomography for tissue imaging

      We propose a model of the full-field optical coherence tomography (FFOCT) technique for tissue imaging, in which the fractal model of the spatial correlation function of the refractive index of tissue is employed to approximate tissue structure. The results may be helpful for correctly interpreting en face tomographic images obtained with FFOCT.

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    20. Cube data correlation-based imaging of small blood vessels

      Cube data correlation-based imaging of small blood vessels

      We present a cube data correlation-based correlation mapping optical coherence tomography (cube-cmOCT) method to reconstruct small blood vessel maps. In the cube-cmOCT method, the two adjacent cube data are correlated to extract blood flow information. Both phantom experiments and in vivo experiments were performed to demonstrate the advantage of the proposed method in improving the SNR of blood vessel maps without increasing the window size in the x z plane and offering a clear image of the small blood vessels almost missed by the conventional cmOCT method.

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    21. High-resolution imaging of biological tissue with full-field optical coherence tomography

      High-resolution imaging of biological tissue with full-field optical coherence tomography

      A new full-field optical coherence tomography system with high-resolution has been developed for imaging of cells and tissues. Compared with other FF-OCT (Full-field optical coherence tomography, FF-OCT) systems illuminated with optical fiber bundle, the improved Köhler illumination arrangement with a halogen lamp was used in the proposed FF-OCT system. High numerical aperture microscopic objectives were used for imaging and a piezoelectric ceramic transducer (PZT) was used for phase-shifting. En-face tomographic images can be obtained by applying the five-step phase-shifting algorithm to a series of interferometric images which are recorded by a smart camera. Three-dimensional images can be generated from ...

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    22. The cross-correlation in spectral domain based Doppler optical coherence tomography

      The cross-correlation in spectral domain based Doppler optical coherence tomography

      We propose a cross-correlation method which is based on the cross-correlation of two adjacent A-scans of interferogram fringe for imaging the velocities of the blood flowing in vessels. The method was tested by measurements of the velocities of flowing particles within a glass capillary with known mean velocities. Mean standard deviations of flow velocities of the particles determined through the proposed method were compared to those by the conventional phase resolved method. I n vivo imaging of a mouse ear was performed and the Doppler flow velocity maps were reconstructed by both methods. The experimental results demonstrated that the proposed ...

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    23. Wavelet transform-based method of compensating dispersion for high-resolution imaging in SDOCT

      Wavelet transform-based method of compensating dispersion for high-resolution imaging in SDOCT

      The axial resolution is an important parameter in Optical Coherence Tomography (OCT). In OCT a broadband light source is used to achieve high axial resolution imaging. However the dispersion results in a broadening of the coherence envelope. The dispersion mismatch between reference and sample arms then needs to be minimized to achieve optimal axial resolution for OCT. In this work we propose a new numerical dispersion compensation method to obtain ultrahigh resolution in SDOCT, in which wavelet transform instead of Fourier transform is used to obtain the signal in different frequency domain. And a series of the phase signals of ...

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    24. Self-spectral calibration for spectral domain optical coherence tomography

      Self-spectral calibration for spectral domain optical coherence tomography

      A different real-time self-wavelength calibration method for spectral domain optical coherence tomography is presented in which interference spectra measured from two arbitrary points on the tissue surface are used for calibration. The method takes advantages of two favorable conditions of optical coherence tomography (OCT) signal. First, the signal back-scattered from the tissue surface is generally much stronger than that from positions in the tissue interior, so the spectral component of the surface interference could be extracted from the measured spectrum. Second, the tissue surface is not a plane and a phase difference exists between the light reflected from two different ...

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    1-24 of 29 1 2 »
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    1. (29 articles) Nanjing University of Science and Technology
    2. (25 articles) Wanrong Gao
    3. (4 articles) Ryerson University
    4. (4 articles) Victor X. D. Yang
    5. (3 articles) University of Toronto
    6. (2 articles) Sunnybrook Health Sciences Centre
    7. (2 articles) Joel Ramjist
    8. (1 articles) University of Lübeck
    9. (1 articles) University of Western Australia
    10. (1 articles) Erasmus University
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