Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 20 of 48 for “"Fourier Domain"”.
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Spectral/ Fourier domain Doppler Optical Coherence Tomography in the rodent retina
… unprecedented detail. However, conventional time domain OCT systems are limited by low imaging speeds. Conventional time domain OCT systems use a mechanically scanned reference mirror to adjust the reference arm path length in time. Spectral / Fourier domain OCT systems use a spectrometer to …
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Applications of Fourier Domain Mode Locked lasers for optical coherence tomography imaging
… the spectrum of the interference signal in the Fourier domain. In "swept source OCT" implementations, the interference spectra are generated with a wavelength-swept laser and photodetector. Axial image lines are obtained via Fourier transformation of the spectra. Fourier domain techniques have …
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Accelerated image reconstruction for a cylindrical positron tomograph using Fourier domain methods
Thesis (Ph. D.)--Harvard University--Massachusetts Institute of Technology Division of Health Sciences and Technology, Program in Medical Engineering and Medical Physics, 1990.
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High-speed Fourier domain Optical Coherence Tomography for structural and functional imaging of the retina
… limited by low imaging speeds. Recently, new Fourier domain OCT detection methods have enabled speeds of ~20,000-40,000 axial scans per second, which are ~50-100x faster than conventional OCT. These methods are called "Fourier domain" because they detect the interference spectrum and do not …
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Development of a Fourier Domain Low Coherence Interferometry Optical System for Applications in Early Cancer Detection
… the development of one such technique called Fourier domain low coherence interferometry (fLCI). </p><p>The presented work first describes a detailed analysis of temporal and spatial coherence. The study shows that temporal coherence information in time frequency distributions contains …
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Structural and functional imaging of the human and small animal eyes using ultrahigh speed Fourier domain optical coherence tomography
… of retinal diseases. Although current commercial Fourier domain OCT systems have high imaging speeds of 20-100kHz A-scan rates, these imaging speeds are not sufficient for more advanced structural and functional imaging techniques. Current state-of-the-art spectral domain and swept source OCT …
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Imaging applications of the sparse FFT
The sparse Fourier transform leverages the intrinsic sparsity of the frequency spectrum in many natural applications to compute the discrete Fourier Transform (DFT) in sub-linear time. Consequently, it has the potential to enable Big Data applications. In this thesis, we focus on extending the …
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Ultrahigh speed optical coherence tomography for ophthalmic imaging applications
… a standard clinical tool in ophthalmology. Fourier domain OCT detection methods have enabled higher sensitivity and imaging speeds compared to previous generation timedomain OCT. Spectral / Fourier domain OCT (SD-OCT) detects the interference spectrum using a broadband light source and …
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Parkinson's Disease Automated Hand Tremor Analysis from Spiral Images
… hand tremors. This work presents a novel Fourier Domain analysis technique that transforms the pencil content of hand-drawn spiral images into frequency features. Our technique is applied to an image dataset consisting of spirals drawn by healthy individuals and people with Parkinson’s …
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Segmented Mirror Telescope model and simulation
… for future spacebased telescopes. A discrete Fourier transform wavefront reconstruction technique developed at Lawrence Livermore National Laboratory is discussed in this thesis as applied to a hexagonal aperture. A Fourier domain implementation of a spatial-frequency modal controller for a …
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Enhancing land seismic data with compressive sensing and processing
… variant. I establish that complex wavelet domain is an optimal choice for sparsifying highly non-stationary land wavefields for single-channel compressive sensing and develop thresholding techniques that can be used for a sparsity-promoting data reconstruction and for interpolation beyond …
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Frequency Analysis and Sheared Filtering for Multidimensional Effects in Rendering
… the sparse structure of these signals in the Fourier domain. We then leverage this information to design a sheared filter that is customized to each pixel's frequency content. We finally present practical algorithms that share samples between pixels, reduce sampling requirements by an order of …
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A systematic periodicity and time-variable modulation search in RXTE ASM data : methods, findings, and implications for astrophysical X-ray sources
… used to enhance the signal-to-noise ratio in the Fourier domain for many sources.
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Estimation of Intrinsic Gravity Wave Parameters From Multiple, Ground-Based Observations of a Single Mesopheric Airglow Emission
… Next, a tomography scheme that works in the Fourier domain is developed to take advantage of the wave perturbation's Fourier sparseness. Then, a parameter estimation (PE) technique is developed to infer the key AGW parameters directly from the data, followed by an in-depth analysis of the …
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Swept source optical coherence microscopy for pathological assessment of cancerous tissues
… of OCT systems have been focused on time domain and spectral/Fourier domain methods which offer high axial resolution and imaging speeds. However, recent advances in the OCT technology have pushed the development into the direction of swept source OCT technologies, and development of the …
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Scanning-free compressive reconstruction of object motion with sub-pixel accuracy
… compressive holography. Together with spectrum domain zero-padding, our compressive algorithm allows for sub-pixel accuracy edge localization. The extension to the 2D case is not trivial. It has been shown that the spiral phase mask can serve as an approximate 2D derivative operator in the …
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Testing New Weak Lensing Measurement Techniques With The Dark Energy Survey
… shear using an implementation of the Bayesian Fourier Domain (BFD) method, proposed by \cite{BA14}, extended to correct for selection biases. The BFD formalism is rigorously correct for Nyquist-sampled, background-limited, uncrowded image of background galaxies. We conduct initial tests of this …
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Improving reconstructions of digital holograms
… to a technique that filters in the Fourier domain of the reconstructed DH. We have also investigated the most commonly used industrial speckle reduction technique - wavelet filters. In Part B, we investigate the nature of opaque and non-opaque partial occlusions. We motivate this …
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A signal processing approach to ultrasound localization microscopy
… filtering operation in three-dimensional (3D) Fourier domain and provide rigorous theoretical analysis on the performance of the filtering operation. Numerical experiments validate that the proposed filtering method is able to separate the microbubbles with respect to the speed and direction of …
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Numerical analysis and visualization of the ionospheric Kelvin-Helmholtz instability
Fourier spectral and pseudospectral methods are used in the numerical modeling of processes that produce ionospheric irregularities; namely the evolution of the Kelvin-Helmholtz instability (KHI) is studied. The simulation model consists of two-dimensional, electrostatic, nonlinear, and time …
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