1. Articles from Aaron C. Chan

    1-8 of 8
    1. Noise-bias and polarization-artifact corrected optical coherence tomography by maximum a-posteriori intensity estimation

      Noise-bias and polarization-artifact corrected optical coherence tomography by maximum a-posteriori intensity estimation

      We propose using maximum a-posteriori (MAP) estimation to improve the image signal-to-noise ratio (SNR) in polarization diversity (PD) optical coherence tomography. PD-detection removes polarization artifacts, which are common when imaging highly birefringent tissue or when using a flexible fiber catheter. However, dividing the probe power to two polarization detection channels inevitably reduces the SNR. Applying MAP estimation to PD-OCT allows for the removal of polarization artifacts while maintaining and improving image SNR. The effectiveness of the MAP-PD method is evaluated by comparing it with MAP-non-PD, intensity averaged PD, and intensity averaged non-PD methods. Evaluation was conducted in vivo with human ...

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    2. High contrast and polarization-artifact-free optical coherence tomography by maximum a-posteriori estimation

      High contrast and polarization-artifact-free optical coherence tomography by maximum a-posteriori estimation

      We propose a maximum a-posteriori (MAP) intensity estimator to improve the image contrast of polarization diversity (PD)-OCT imaging to achieve high contrast polarization-artifact-free images. The MAP estimator compensates for the inevitable reduction of signal-to-noise ratio (SNR) in PD-OCT caused by the splitting of power into two polarization detection channels. It also has low noise-offset in low intensity regions such as the vitreous. This method is applied to posterior eye images, and shows high-contrast, polarization-artifact-free images. This method also enables attenuation coefficient imaging with finer differentiation of attenuation levels.

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    3. Quantitative optical coherence tomography by maximum a-posteriori estimation of signal intensity

      Quantitative optical coherence tomography by maximum a-posteriori estimation of signal intensity

      A maximum a-posteriori (MAP) estimator for signal amplitude of optical coherence tomography (OCT) is presented. This estimator provides an accurate and low bias estimation of the correct OCT signal amplitude even at very low signal-tonoise ratios. As a result, contrast improvement of retinal OCT images is demonstrated. In addition, this estimation method allows for an estimation reliability to be calculated. By combining the MAP estimator with a previously demonstrated attenuation imaging algorithm, we present attenuation coefficient images of the retina. From the reliability derived from the MAP image one can also determine which regions of the attenuation images are unreliable ...

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    4. Maximum a posteriori estimator for high-contrast image composition of optical coherence tomography

      Maximum a posteriori estimator for high-contrast image composition of optical coherence tomography

      A quantitative signal amplitude estimator for optical coherence tomography (OCT) is presented. It is based on a statistical model of OCT signal and noise, using a Bayesian maximum a posteriori (MAP) estimation framework. Multiple OCT images are used for estimation, similar to the widely utilized intensity averaging method. The estimator is less biased especially at low-intensity regions, where intensity averaging approaches the noise power and hence is biased. The estimator is applied to posterior ocular OCT images and provides high-contrast visualization of pathologies. In addition, histogram analysis objectively shows the superior performance of the estimator compared with intensity averaging.

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    5. Maximum Likelihood Doppler Frequency Estimation under Decorrelation Noise for Quantifying Flow in Optical Coherence Tomography

      Maximum Likelihood Doppler Frequency Estimation under Decorrelation Noise for Quantifying Flow in Optical Coherence Tomography

      Recent hardware advances in optical coherence tomography (OCT) have led to ever higher A-scan rates. However, the estimation of blood flow axial velocities is limited by the presence and type of noise. Higher acquisition rates alone do not necessarily enable precise quantification of Doppler velocities, particularly if the estimator is sub-optimal. In previous work, we have shown that the Kasai autocorrelation estimator is statistically sub-optimal under conditions of additive white Gaussian noise. In addition, for practical OCT measurements of flow, decorrelation noise affects Doppler frequency estimation by broadening the signal spectrum. Here we derive a general maximum likelihood estimator (MLE ...

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    6. Optimal doppler frequency estimators for ultrasound and optical coherence tomography

      Optimal doppler frequency estimators for ultrasound and optical coherence tomography

      The Kasai autocorrelation estimator is widely used in Doppler optical coherence tomography and ultrasound to determine blood velocities. However, as a non-parametric estimator, it may not be optimal. Assuming an additive white Gaussian noise (AWGN) model, we show that the Kasai estimator variance is far from the Cramer-Rao lower bound. Moreover, paradoxically, the Kasai estimator performance degrades as the acquisition rate is increased. By contrast, the additive white Gaussian noise maximum likelihood estimator (AWGN MLE) variance asymptotically approaches the Cramer-Rao lower bound, making it a better estimator at high acquisition rates. Nevertheless, the Kasai estimator outperforms the AWGN MLE under ...

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    7. Feature Of The Week 7/29/12: Researchers From The University of Hong Kong Use Optical Parametric Wavelength Conversion for Dual-Wavelength Spectroscopic OCT

      Feature Of The Week 7/29/12: Researchers From The University of Hong Kong Use Optical Parametric Wavelength Conversion for Dual-Wavelength Spectroscopic OCT

      Researchers from the University of Hong Kong recently reported on a high-speed time-multiplexing dual wavelength band swept laser source based on an optical parametric amplifier. A dual-band swept-source optical coherence tomography (OCT) system is implemented to demonstrate the advantage of a second wavelength band for fast spectroscopic OCT (SOCT). The innovative time-multiplexing architecture greatly reduces the complexity of the coupling and detecting configuration in comparison with the previous dual-band swept-source setup. We demonstrate the optical parametric amplification’s characteristics as a dual-band generator and applied the source to firstly achieve the SOCT around 1550 nm.For more information see recent ...

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    8. Dual-Band Time-Multiplexing Swept-Source Optical Coherence Tomography Based on Optical Parametric Amplification

      Dual-Band Time-Multiplexing Swept-Source Optical Coherence Tomography Based on Optical Parametric Amplification

      We report a high-speed time-multiplexing dual wavelength band swept laser source based on an optical parametric amplifier. A dual-band swept-source optical coherence tomography (OCT) system is implemented to demonstrate the advantage of a second wavelength band for fast spectroscopic OCT (SOCT). The innovative time-multiplexing architecture greatly reduces the complexity of the coupling and detecting configuration in comparison with the previous dual-band swept-source setup. We demonstrate the optical parametric amplification’s characteristics as a dual-band generator and applied the source to firstly achieve the SOCT around 1550 nm.

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    1-8 of 8
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  2. Topics in the News

    1. (5 articles) National Institutes of Health
    2. (4 articles) University of Tsukuba
    3. (4 articles) University of Hong Kong
    4. (4 articles) Masahiro Miura
    5. (4 articles) Shuichi Makita
    6. (4 articles) Yoshiaki Yasuno
    7. (2 articles) Vivek J. Srinivasan
    8. (2 articles) Kenneth K. Y. Wong
    9. (1 articles) Harvard University
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    11. (1 articles) Massachusetts Institute of Technology
    12. (1 articles) University of Houston
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    15. (1 articles) Yale University
    16. (1 articles) Massachusetts Institute of Technology
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    Dual-Band Time-Multiplexing Swept-Source Optical Coherence Tomography Based on Optical Parametric Amplification Feature Of The Week 7/29/12: Researchers From The University of Hong Kong Use Optical Parametric Wavelength Conversion for Dual-Wavelength Spectroscopic OCT Optimal doppler frequency estimators for ultrasound and optical coherence tomography Maximum Likelihood Doppler Frequency Estimation under Decorrelation Noise for Quantifying Flow in Optical Coherence Tomography Maximum a posteriori estimator for high-contrast image composition of optical coherence tomography Quantitative optical coherence tomography by maximum a-posteriori estimation of signal intensity High contrast and polarization-artifact-free optical coherence tomography by maximum a-posteriori estimation Noise-bias and polarization-artifact corrected optical coherence tomography by maximum a-posteriori intensity estimation Indiana University Receives NIH Grant for Imaging Spatial and Temporal Dynamics of Retinal Ganglion Cells University of Houston Receives NIH Grant for Structural and Molecular Phenotyping of Embryonic Development Through Multi-Modal Optical Imaging. Massachusetts Institute of Technology Receives NIH Grant for Novel Optical Diagnostics with Optical Coherence Tomography Yale University Receives a NIH Grant for Xenopus As A Model System for Hydrocephaly and Ependymal Ciliogenesis