Methods for Estimation of Subsample Time Delays of Digitized Echo Signals

Céspedes, I.; Huang, Yijun; Ophir, Jonathan; Spratt, S.C.

doi:10.1177/016173469501700204

Cited by 334 publications

(167 citation statements)

References 24 publications

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“…In this study, we employed a cosine fitting method to estimate sub-sample delay time in time domain [18][19] . Given the largest sample of the correlation function, cc(0), and its two neighbours cc(-1) and cc(1), the estimated sub-sample shift is given by following expression:…”

Section: Sub-sample Delay Time Estimate (Dte)mentioning

confidence: 99%

Preseismic velocity changes observed from active source monitoring at the Parkfield SAFOD drill site

Niu

Silver

Daley

et al. 2008

Nature

234

185

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Measuring stress changes within seismically active fault zones has been a longsought goal of seismology. Here we show that such stress changes are measurable by exploiting the stress dependence of seismic wave speed from an active source cross-well experiment conducted at the SAFOD drill site. Over a two-month period we observed an excellent anti-correlation between changes in the time required for an S wave to travel through the rock along a fixed pathway -a few microseconds--and variations in barometric pressure. We also observed two large excursions in the traveltime data that are coincident with two earthquakes that are among those predicted to produce the largest coseismic stress changes at SAFOD. Interestingly, the two excursions started approximately 10 and 2 hours before the events, respectively, suggesting that they may be related to pre-rupture stress induced changes in crack properties, as observed in early laboratory studies [1][2] .It is well known from laboratory experiments that seismic velocities vary with the level of applied stress [3][4][5] . Such dependence is attributed to the opening/closing of microcracks due to changes in the stress normal to the crack surface [6][7][8] . In principle, this dependence constitutes a stress meter, provided the induced velocity changes can be 2 measured precisely and continuously. Indeed, there were several attempts in the 1970s to accomplish this goal using either explosive or non explosive surface sources 9-11 . The source repeatability and the precision in traveltime measurement appeared to be the main challenges in making conclusive observations.With the availability of highly repeatable sources, modern data acquisition systems, and advanced computational capability, Yamamura et al. 12 showed compelling evidence that seismic velocity along a baseline in a vault near the coast of Miura Bay, Japan, responds regularly to tidal stress changes. Silver et al. 13 found an unambiguous dependence of seismic velocity on barometric pressure from a series of cross-well experiments at two test sites in California. The stress sensitivity depends primarily on crack density and has a strong nonlinear dependence on confining pressure.Consequently, crack density is expected to decrease rapidly with depth as should stress sensitivity. It is thus unclear whether the stress-induced velocity variations observed at shallow depths [12][13] are still detectable at seismogenic depth.To explore stress sensitivity at seismogenic depth, we have conducted an experiment at Parkfield where adjacent deep wells, the SAFOD (San Andreas Fault Observatory at Depth) pilot and main holes (Figure 1), are available. Accurately located seismicity together with the availability of high-quality geophysical data in the Parkfield region make it one of the best areas to detect temporal changes related to the earthquake cycle.A specially-designed 18-element piezoelectric source and a three-component accelerometer were deployed inside the pilot and main holes, respectively, at ~1 km depth (see methods)...

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Section: Sub-sample Delay Time Estimate (Dte)mentioning

confidence: 99%

Preseismic velocity changes observed from active source monitoring at the Parkfield SAFOD drill site

Niu

Silver

Daley

et al. 2008

Nature

234

185

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“…The rate of deformation (strain) of the tissue is directly related to the mechanical properties. The tissue under inspection is deformed, and the strain between pairs of ultrasound signals with and without deformation is determined [17]. For intravascular purposes, the compression can be obtained from the pressure difference in the artery.…”

Section: Intravascular Palpographymentioning

confidence: 99%

Intravascular Palpography for High-Risk Vulnerable Plaque Assessment

Schaar

Korte

Mastik³

et al. 2003

Herz

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Background:The composition of an atherosclerotic plaque is considered more important than the degree of stenosis. An unstable lesion may rupture and cause an acute thrombotic reaction. Most of these lesions contain a large lipid pool covered by an inflamed thin fibrous cap. The stress in the cap increases with decreasing cap thickness and increasing macrophage infiltration. Intravascular ultrasound (IVUS) palpography might be an ideal technique to assess the mechanical properties of high-risk plaques. Technique: Palpography assesses the local mechanical properties of tissue using its deformation caused by the intraluminal pressure. In Vitro Validation:The technique was validated in vitro using diseased human coronary and femoral arteries. Especially between fibrous and fatty tissue, a highly significant difference in strain (p = 0.0012) was found. Additionally, the predictive value to identify the vulnerable plaque was investigated. A high-strain region at the lumen-vessel wall boundary has an Intravaskuläre Palpographie zur Erfassung vulnerabler Hochrisikoplaques

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“…One of the few papers to address lateral interpolation is [9], in which the grid slopes algorithm is shown to be relatively unbiased in comparison with other techniques. More prone to bias are cosine [3,5,6], cubic spline [9] and parabolic interpolation [2,3,7]. Fourier reconstruction [3] has been shown to work well in the axial direction, provided the signal is bandlimited and the sampling frequency above the Nyquist limit.…”

Section: Introductionmentioning

confidence: 99%

Subsample interpolation strategies for sensorless freehand 3D ultrasound

Housden

Gee

Treece

et al. 2006

Ultrasound in Medicine & Biology

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Freehand 3D ultrasound can be acquired without a position sensor by deducing the elevational probe motion from the inter-frame speckle decorrelation. However, a freehand scan involves lateral and axial, as well as elevational, probe motion. The lateral sampling is determined by the A-line separation and is relatively sparse: lateral motion tracking therefore requires sub-sample interpolation. In this paper, we investigate the resilience of lateral interpolation techniques to simultaneous lateral and elevational probe motion. We propose a novel interpolation strategy and, through a series of in vitro experiments, compare its performance with that of established alternatives. The new technique is shown to be superior, limiting interpolation errors to around 5% of the length of the freehand reconstruction.

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Methods for Estimation of Subsample Time Delays of Digitized Echo Signals

Cited by 334 publications

References 24 publications

Preseismic velocity changes observed from active source monitoring at the Parkfield SAFOD drill site

Preseismic velocity changes observed from active source monitoring at the Parkfield SAFOD drill site

Intravascular Palpography for High-Risk Vulnerable Plaque Assessment

Subsample interpolation strategies for sensorless freehand 3D ultrasound

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