Journal Article•
Mathematical Analysis of Random Noise-Conclusion
About: This article is published in Bell System Technical Journal.The article was published on 1945-01-01 and is currently open access. It has received 807 citations till now.
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TL;DR: In this paper, typical examples of QUS techniques for evaluating attenuation, speed of sound, amplitude envelope characteristics, and backscatter coefficient in living tissues are introduced, and initiatives currently being undertaken to establish the QUS method as a true tissue characterization technology, are also discussed.
Abstract: In the field of clinical ultrasound, the full digitalization of diagnostic equipment in the 2000s enabled the technological development of quantitative ultrasound (QUS), followed by multiple diagnostic technologies that have been put into practical use in recent years. In QUS, tissue characteristics are quantified and parameters are calculated by analyzing the radiofrequency (RF) echo signals returning to the transducer. However, the physical properties (and pathological level structure) of the biological tissues responsible for the imaging features and QUS parameters have not been sufficiently verified as there are various conditions for observing living tissue with ultrasound and inevitable discrepancies between theoretical and actual measurements. A major issue of QUS in clinical application is that the evaluation results depend on the acquisition conditions of the RF echo signal as the source of the image information, and also vary according to the model of the diagnostic device. In this paper, typical examples of QUS techniques for evaluating attenuation, speed of sound, amplitude envelope characteristics, and backscatter coefficient in living tissues are introduced. Exemplary basic research and clinical applications related to these technologies, and initiatives currently being undertaken to establish the QUS method as a true tissue characterization technology, are also discussed.
4 citations
TL;DR: In this paper, a discrete non-stationary gust model is proposed, consisting of a series of stationary processes, having different gust intensities and spectrum parameters, and the response covariances of the plunging velocity and acceleration have been computed.
4 citations
15 Oct 1990-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: In this paper, the effects of compensation magnets, general spatial forms which are more realistic models of experimental wigglers and statistical correlations of the field errors are compared with a quantitative means of measuring the relative merit of these experimental techniques for reducing wiggler field-error effects.
Abstract: There have been extensive studies on the effects of intrinsic field errors on the operation and performance of free electron lasers (FELs) based predominately on simple models for the spatial form and statistical properties of the field errors. In some cases, the effects of compensation magnets or steering coils have been included as a method of reducing the deletrious effects of field errors. In the present study we consider the effects of (i) compensation magnets, (ii) general spatial forms which are more realistic models of experimental wigglers and (iii) statistical correlations of the field errors. This theoretical study has resulted in a quantitative means of measuring the relative merit of these experimental techniques for reducing wiggler field-error effects. These means of comparative analysis yield important criteria for experimental design and modeling.
4 citations
Dissertation•
01 Jan 2006
TL;DR: In this paper, a series of NMR experiments intended to probe diffusion of 3He gas within a restricted geometry and in very low magnetic fields are described, and data from these experiments show clear evidence for the perturbing influence of concomitant gradients.
Abstract: Linear magnetic field gradients are used in conventional magnetic resonance (MR) imaging in order to spatially encode andlor resolve nuclear spin distributions. These gradients are normally thought of as being unidirectional, but are always accompanied by orthogonal field components and gradients. These concomitant gradients can largely be ignored as long as the curvature they induce in magnetic field lines is small compared to inverse dimensions of the field of view. Recent attempts to acquire MR images in milliTesla magnetic fields have sparked interest in trying to understand the potential influence of concomitant field gradients. In this thesis a series of NMR experiments intended to probe diffusion of 3He gas within a restricted geometry and in very-low magnetic fields are described. Data from these experiments show clear evidence for the perturbing influence of concomitant gradients, and can be qualitatively understood in terms of a simple model that ignores diffusion.
3 citations