Bioacoustics Research Lab
University of Illinois at Urbana-Champaign | Department of Electrical and Computer Engineering | Department of Bioengineering
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Title Statement of Mammalian in vivo ultrasonic biological effects.
Author Bio-effects committee; chaired by Fry FJ.
Journal J Clin Ultrasound
Volume
Year 1977
Abstract In the low megahertz frequency range there have been (as of this date) no demonstrated significant biological effects in mammalian tissues exposed to intensities* below 100 mW/cm(^2). Furthermore, for ultrasonic exposure times** less than 500 seconds and greater than one second, such effects have not been demonstrated even at higher intensities when the product of intensity* and exposure time** is less than 50 joules/cm(^2)..*spatial peak, temporal average as measured in a free field in water.**total time; this includes off-time as well as on-time for repeated-pulse remgime.


Title Statement on the use of diagnostic ultrasound instrumentation on humans for training, demonstration, and research.
Author Carson PL.
Journal AAPM Science Council
Volume
Year 1975
Abstract No abstract available.


Title Statistical analysis of ultrasound echo envelope.
Author Dutt V.
Journal Thesis(PhD): The Mayo Graduate School
Volume
Year 1995
Abstract The ultrasound echo signal has a statistical nature because it is formed by summation of signals from randomly backscattering sites located randomly inside the medium being imaged. Therefore, the statistics of ultrasound echo signals should be useful for understanding the relationship between the medium parameters and the echo images, and thus for characterization of the scattering media. This thesis focuses on first order statistical analysis for general echo scattering situations. The Rayleigh distribution and its generalized forms, the K and Rice distributions, have been previously suggested to model the echo envelope signal. But these distributions have a very limited applicability. This thesis examines the K distribution and its more generalized version, the homodyned K distribution, which combines the K and Rice distribution features, to model and analyze the statistics of the echo envelope. The analysis shows that the K distribution can be used to model the variations in the statistics of the echo envelope due to variations in the scatterer number density. Also, the signal to noise ratio, SNR, is evaluated for its statistical properties and as a measure of scatterer density. This enables the use of signal-to-noise ratio (SNR) to be used as a statistical parameter for scatterer number density measurement. Also derived is an adaptive filter for speckle reduction based on the K distribution model using this model to quantitate the extent of speckle formation. One of the problems with the statistical analysis is the non-linear signal processing involved in clinical echo imaging systems which changes the statistics of the images acquired from clinical systems. This thesis also examines the log compression involved in the signal processing step of clinical systems and develops the statistics of such compressed images. This analysis shows that the variance of compressed images is a function of the scatterer density. This result could be used to design another speckle reduction filter which can filter the compressed clinical images without having to decompress the images first. Then the more general (and complex) model, the homodyned K distribution model, is examined for modeling any arbitrary backscattered echo signal. This model includes the possibility of a coherent component in the signal and thus is the most general model for the echo envelope. This model provides two parameters, k (the ratio of coherent signal to diffuse signal) and b (which characterizes the clustering of scatterers in the medium), which are useful for general media characterization. The model is used experimentally (and in simulations) to demonstrate the parameterization of scattering media. Various inversion techniques to solve for the parameters using the moments of the distribution are tested for efficacy.


Title Statistical parameter estimation in ultrasound backscattering from tissue mimicking media.
Author Chen JF.
Journal Thesis(PhD): Univ of Wisconsin-Madison
Volume
Year 1994
Abstract Several tissue characterization parameters, including the effective scatterer number density and the backscatter coefficient, were derived from the statistical properties of ultrasonic echo signals. The effective scatterer number density is the actual scatterer number density in a medium multiplied by a frequency-dependent factor that depends on the differential scattering cross-sections of all scatterers. The method described in this thesis for determining the scatterer number density explicitly retains both the temporal nature of the data acquisition and the properties of the ultrasound field in the data reduction. Moreover, it accounts for the possibility that different sets of scatterers may dominate the echo signal at different frequencies. The random processes involved in forming ultrasound echo signals from random media give rise to an uncertainty in the estimated effective scatterer number density. This uncertainty is evaluated using error propagation. The statistical uncertainty depends on the effective number of scatterers contributing to the segmented echo signal, increasing when the effective number of scatterers increases. Tests of the scatterer number density data reduction method and the statistical uncertainty estimator were done using phantoms with known ultrasound scattering properties. Good agreement was found between measured values and those calculated from first-principles. The properties of the non-Gaussian and non-Rayleigh parameters of ultrasound echo signals are also studied. Both parameters depend on the measurement system, including the transducer field and pulse frequency content, as well as on the medium?s properties. The latter is expressed in terms of the scatterer number density and the second and fourth moments of the medium?s scattering function. A simple relationship between the non-Gaussian and non-Rayleigh parameters is derived and verified experimentally. Finally, a reference phantom method is proposed for measuring the effective scatterer number density in vivo. Various groups are using the frequency dependent backscatter coefficient (or the spatial autocorrelation function) to characterize scatterer sizes in biological tissue. Generally, sparse scatterer concentrations are assumed in relating scattering parameters to this tissue property. For dense scattering media, we study whether the frequency dependent backscatter coefficient changes with the scatterer volume fraction. Two scattering models suggested by Debye and Yagi are reviewed. In these models, the spatial autocorrelation function describing mass density and compressibility fluctuations in the scattering medium has a characteristic length that depends on the scatterer volume fraction as well as the scatterer size. The models predict the frequency dependence of the backscatter coefficient will vary with the scatterer volume fraction. Qualitative agreement between the model predictions and experimental results are seen for sephadex-in-agar phantoms.


Title Statistical properties of radio-frequency and envelope-detected signals with applications to medical ultrasound.
Author Wagner RF, Insana MF, Brown DG.
Journal J Opt Soc Am
Volume
Year 1987
Abstract Both radio-frequency (rf) and envelope-detected signal analyses have lead to successful tissue discrimination in medical ultrasound. The extrapolation from tissue discrimination to a description of the tissue structure requires an analysis of the statistics of complex signals. To that end, first- and second-order statistics of complex random signals are reviewed, and an example is taken from rf signal analysis of the backscattered echoes from diffuse scatterers. In this case the scattering form factor of small scatterers can be easily separated from long-range structure and corrected for the transducer characteristics, thereby yielding an instrument-independent tissue signature. The statistics of the more economical envelope- and square-law-detected signals are derived next and found to be almost identical when normalized autocorrelation functions are used. Of the two nonlinear methods of detection, the square-law or intensity scheme gives rise to statistics that are more transparent to physical insight. Moreover, an analysis of the intensity-correlation structure indicates that the contributions to the total echo signal from the diffuse scatter and from the steady and variable components of coherent scatter can still be separated and used for tissue characterization. However, this analysis is not system independent. Finally, the statistical methods of this paper may be applied directly to envelope signals in nuclear-magnetic-resonance imaging because of the approximate equivalence of second-order statistics for magnitude and intensity.


Title Statistical properties of radio-frequency and envelope-detected signals with applications to medical ultrasound.
Author Wagner RF, Insana MF, Brown DG.
Journal J Opt Soc Am
Volume
Year 1987
Abstract Both radio-frequency (rf) and envelope-detected signal analyses have lead to successful tissue discrimination in medical ultrasound. The extrapolation from tissue discrimination to a description of the tissue structure requires an analysis of the statistics of complex signals. To that end, first- and second-order statistics of complex random signals are reviewed and an example is taken from rf signal analysis of the backscattered echoes from diffuse scatterers. In this case the scattering form factor of small scatterers can be easily separated from long-range structure and corrected for the transducer characteristics, thereby yielding an instrument-independent tissue signature. The statistics of the more economical envelope- and square-law-detected signals are derived next and found to be almost identical when normalized autocorrelation functions are used. Of the two nonlinear methods of detection, the square-law or intensity scheme gives rise to statistics that are more transparent to physical insight. Moreover, an analysis of the intensity-correlation structure indicates that the contributions to the total echo signal from the diffuse scatter and from the steady and variable components of coherent scatter can still be separated and used for tissue characterization. However, this analysis is not system independent. Finally, the statistical methods of this paper may be applied directly to envelop signals in nuclear-magnetic-resonance imaging because of the approximate equivalence of second-order statistics for magnitude and intensity.


Title Statistical uncertainty in estimates of an effective scatterer number density for ultrasound.
Author Chen JF, Zagzebski JA, Madsen EL.
Journal J Acoust Soc Am
Volume
Year 1994
Abstract In a previous paper [J. Acoust. Soc. Am. 95, 77-85 (1994)], a method for determining an effective scatterer number density in ultrasonography was presented. This is the actual number density multiplied by a frequency-dependent factor that depends on the differential scattering cross sections of all scatterers. This method involves evaluating the ratio of the fourth moment to the square of the second moment of echo signals scattered from the sample. The random processes involved in forming these echo signals give rise to an uncertainty in the estimated effective scatterer number density. This uncertainty is evaluated here using error propagation. The statistical uncertainty depends on the effective number of scatterers contributing to the segmented echo signal; it increases when the effective number of scatterers increases. Tests of the statistical uncertainty estimator were in good agreement with uncertainties computed from experimental data. ..


Title Statistical uncertainty in ultrasonic backscatter and attenuation coefficients determined with a reference phantom.
Author Yao LX, Zagzebski JA, Madsen EL.
Journal Ultrasound Med Biol
Volume
Year 1991
Abstract Uncertainties in measured attenuation and backscatter coefficients due to statistical fluctuations in echo signal data from a randomly scattering medium are estimated. The uncertainties are computed for the special case in which a reference phantom is employed to account for transducer and instrumentation factors when measuring attenuation and backscatter coefficients. The resultant uncertainty in the attenuation is inversely proportional to the 3/2 power of the depth range. The error in the backscatter coefficient arises both from the local fluctuation in the data and from the uncertainty in the attenuation estimate. The first of these is inversely proportional to the square root of the number of independent data points, while the second results in a contribution that is depth dependent. Predicted errors were tested by scanning tissue mimicking phantoms and estimating attenuation and backscatter coefficients for subsets of the digitized echo data. Standard deviations of the experimental results were in agreement with those predicted.


Title Statistics of speckle in ultrasound b-scans.
Author Wagner RF, Smith SW, Sandrik JM, Lopez H.
Journal IEEE Trans Sonics Ultrason
Volume
Year 1983
Abstract In the ultrasound imaging process, the complex summation at the transducer face is assumed to be linear. The envelope detection process in B-scanning is a nonlinear step which yields essentially the magnitude of the complex field or voltage.( A square law detector, as in the analogous laser case, yields the square of the magnitude, i.e., the intensity, of the field.) It is shown that Rayleigh statistics govern the fist-order behavior of the magnitude; and the auto correlation of the resulting image speckle is obtained by the method of Middleton. The corresponding power spectrum follows immediately by Fourier transformation.Theoretical and experimentally determined auto correlation functions and power spectra derived from B -scans of a scattering phantom containing many scatterers per resolution cell are presented. These functions lead naturally to the definition of the average speckle spot or cell sue, and this in turn is comparable to the resolution cell. Each independent speckle serves as a degree of freedom that determines the number of samples of tissue available over a target. As the speckle cell size decreases this number increases in a manner predictable from the physical parameters of the cell size. However, it is found that the speckle cell is broadened, the degrees of freedom diminished, when the object structure is correlated. This yields the possibility of deducing information about the object structure from the second-order statistics of the speckle texture, in addition to that obtainable from the first order statistics.


Title Statistics of the log-compressed echo envelope.
Author Dutt V, Greenleaf JF.
Journal J Acoust Soc Am
Volume
Year 1996
Abstract Log compression of A lines to produce B‐scan images in clinical ultrasound imaging systems is a standard procedure to control the dynamic range of the images. The statistics of such compressed images in terms of underlying scatterer statistics have not been derived. The statistics are analyzed for partially formed speckle using a general K distribution model of envelope statistics to derive the density function for the log‐compressed envelope. This density function is used to elucidate the relation between the moments of the compressed envelope, the compression parameters, and the statistics of the scatterers. The analysis shows that the mean of the log‐compressed envelope is an increasing function of both the backscattered energy and the effective scatterer density. The variance of the log‐compressed envelope is a decreasing function of the effective scatterer density and is independent of the backscattered energy.


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