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Full-Text Articles in Engineering
Statistics Of Local Speckle Contrast, Donald D. Duncan, Sean J. Kirkpatrick, Ruikang K. Wang
Statistics Of Local Speckle Contrast, Donald D. Duncan, Sean J. Kirkpatrick, Ruikang K. Wang
Electrical and Computer Engineering Faculty Publications and Presentations
In describing the first-order properties of laser speckle under polarized illumination conditions, it is almost an article of faith that the contrast is unity. In many processing schemes, however, the contrast defined as the quotient of the standard deviation and the mean is calculated over a localized spatial region. In such cases, this local contrast displays a distribution of values that can depart substantially from unity. Properties of this distribution depend on details of the data acquisition and on the size of the local neighborhood over which the contrast is calculated. We demonstrate that this local contrast can be characterized …
Can Laser Speckle Flowmetry Be Made A Quantitative Tool?, Donald D. Duncan, Sean J. Kirkpatrick
Can Laser Speckle Flowmetry Be Made A Quantitative Tool?, Donald D. Duncan, Sean J. Kirkpatrick
Electrical and Computer Engineering Faculty Publications and Presentations
The ultimate objective of laser speckle flowmetry (and a host of specific implementations such as laser speckle contrast analysis, LASCA or LSCA; laser speckle spatial contrast analysis, LSSCA; laser speckle temporal contrast analysis, LSTCA; etc.) is to infer flow velocity from the observed speckle contrast. Despite numerous demonstrations over the past 25 years of such a qualitative relationship, no convincing quantitative relationship has been proven. One reason is a persistent mathematical error that has been propagated by a host of workers; another is a misconception about the proper autocorrelation function for ordered flow. Still another hindrance has been uncertainty in …
The Copula: A Tool For Simulating Speckle Dynamics, Donald D. Duncan, Sean J. Kirkpatrick
The Copula: A Tool For Simulating Speckle Dynamics, Donald D. Duncan, Sean J. Kirkpatrick
Electrical and Computer Engineering Faculty Publications and Presentations
Use of a copula for generating a sequence of correlated speckle patterns is introduced. The chief characteristic of this algorithm is that it generates a continuous speckle sequence with a specified evolution of the correlation and does so with just two arrays of random numbers. Thus, physically realistic temporally varying speckle patterns with proper first- and second-order statistics are easily realized. We illustrate use of the algorithm for generating sequences with prescribed Gaussian, exponential, and equal-interval correlations and demonstrate how correlation times can be specified independently. This approach to generating sequences of random realizations with prescribed correlations should prove useful …
Oct-Based Elastography For Large And Small Deformations, Donald D. Duncan, Sean J. Kirkpatrick, Ruikang K. Wang
Oct-Based Elastography For Large And Small Deformations, Donald D. Duncan, Sean J. Kirkpatrick, Ruikang K. Wang
Electrical and Computer Engineering Faculty Publications and Presentations
We present two approaches to speckle tracking for optical coherence tomography (OCT)-based elastography, one appropriate for small speckle motions and the other for large, rapid speckle motions. Both approaches have certain advantages over traditional cross-correlation based motion algorithms. We apply our algorithms to quantifying the strain response of a mechanically inhomogeneous, bi-layered polyvinyl alcohol tissue phantom that is subjected to either small or large dynamic compressive forces while being imaged with a spectral domain OCT system. In both the small and large deformation scenarios, the algorithms performed well, clearly identifying the two mechanically disparate regions of the phantom. The stiffness …
Imaging The Mechanical Stiffness Of Skin Lesions By In Vivo Acousto-Optical Elastography, Sean J. Kirkpatrick, Donald D. Duncan, Ruikang K. Wang, Molly Kulesz-Martin, Ken Lee
Imaging The Mechanical Stiffness Of Skin Lesions By In Vivo Acousto-Optical Elastography, Sean J. Kirkpatrick, Donald D. Duncan, Ruikang K. Wang, Molly Kulesz-Martin, Ken Lee
Electrical and Computer Engineering Faculty Publications and Presentations
Optical elastography is an imaging modality that relies on variations in the local mechanical properties of biological tissues as the contrast mechanism for image formation. Skin lesions, such as melanomas and other invasive conditions, are known to alter the arrangement of collagen fibers in the skin and thus should lead to alterations in local skin mechanical properties. We report on an acousto-optical elastography (AOE) imaging modality for quantifying the mechanical behavior of skin lesions. The method relies upon stimulating the tissue with a low frequency acoustic force and imaging the resulting strains in the tissue by means of quantifying the …
Performance Analysis Of A Maximum-Likelihood Speckle Motion Estimator, Donald D. Duncan, Sean J. Kirkpatrick
Performance Analysis Of A Maximum-Likelihood Speckle Motion Estimator, Donald D. Duncan, Sean J. Kirkpatrick
Electrical and Computer Engineering Faculty Publications and Presentations
Presented herein is a performance analysis of a maximum likelihood estimator for calculating small speckle motions. Such estimators are important in a variety of speckle techniques used in non-destructive evaluation. The analysis characterizes the performance (bias and RMS deviation) of the estimator as a function of the signal-to-noise ratio. This SNR parameter is a convenient surrogate for decorrelation of sequential speckle patterns such as are seen in biological tissues. Although the particular estimator is predicated on speckle motions that are a small fraction of a pixel, accurate performance is demonstrated for instantaneous motions of up to ±0.8 pixel/record. Beyond this …