bluuebunny/crossref_metadata_2025 huggingface dataset:
Ultrasound B-Scanner with Multi-Line Array
Authors: Hassler D. , Hönig D. , Schwarz R.
Published: March 2013

Linear phased array scanners employ dynamic focusing in the plane of the array and either no focusing or fixed lens focusing perpendicular to this plane. In this paper, we describe a simple and inexpensive method for improving the resolution in the perpendicular direction. The system is based on a transducer assembly consisting of three parallel lines, each containing 80 transducers, and custom monolithic integrated circuits. Sound field measurements and standardized B-scan images of phantoms were obtained with the system. An image interlacing technique is proposed in order to avoid the need for parallel processing channels.
An Experimental Investigation of the Cross-Coupling between Elements of an Acoustic Imaging Array Transducer
Authors: Dias J. Fleming
Published: March 2013

In a phased array acoustic imaging transducer, the cross coupling between elements of the array can lead to a loss in range resolution, cause an increase in rolloff with angle of the sector scan, and increase the ringdown time.

In this paper, we present results of an experimental investigation of an acoustic mode that couples the elements through the propagation of surface waves on the surface of the acoustic absorber. These results indicate that the strength of the mode is enhanced by the coherent reflections from adjacent neighbor elements which act as efficient reflectors of the surface waves. We also demonstrate a technique whereby reflections can be made to interact destructively to reduce the strength of that coupling mode. A further reduction can be obtained by stiffening the structure by bonding to the tops of the elements a thick brass foil and by using it as a common ground connection.
Effects of Phase-Cancellation on Scattering Measurements
Authors: Shung K. K. , Dzierzanowski J. M.
Published: March 2013

Piezoelectric transducers are sensitive to the phase of the incident pressure. When measuring the transmission properties of inhomogeneous materials which distort the shape of the wave front, a substantive error results if a phase-sensitive transducer is used as a receiver due to the phase-cancellation effect. This artifact has been found also to exist for reflected and scattered waves. A computer model has been used to quantify the influence of this artifact on backscattered waves by examining the average pressure received by a phase-sensitive transducer for point, linear, rectangular, and random arrays and random volume distributions of scatterers as a function of transducer diameter, the distance between the transducer and the scatterers, and the number of scatterers, at several frequencies.
Behavior of Arterial Grafts at the Hip and Knee Joints
Authors: Clifford P. C. , Skidmore R. , Woodcock J. P. , Baird R. N.
Published: March 2013

Real time ultrasonic scanning with a Duplex scanner (A.T.L.) was used to study Dacron arterial grafts crossing the hip and knee joints in 27 patients (25 males, 2 females), mean age 61 years. Ultrasonic imaging of the grafts was rapid and demonstrated kinking during knee flexion in 83 percent of grafts anastomosed to the distal popliteal artery. Only 7 percent of grafts crossing the inguinal ligament kinked during 60° of hip flexion.

Graft kinking during knee flexion may be a factor in acute thrombosis associated with long periods of immobility, such as during air travel.
Compound Scanning with a Phased Array
Authors: Shattuck David P. , von Ramm Olaf T.
Published: March 2013

Compound scans made with a dynamically focussed phased array system have been produced in real time. The scanner, intended for abdominal imaging, has a large field of view. The compounding improves the acquisition of echoes from specular targets by changing the orientation of the insonifying beam and also reduces the speckle noise in grey scale images. These gains are achieved while maintaining the high resolution and flexibility of a computer controlled phased array sector scanner. The configuration of the compound scanner is described, and in vivo abdominal scans are presented.
Frequency Compounding for Speckle Contrast Reduction in Phased Array Images
Authors: Magnin Paul A. , von Ramm Olaf T. , Thurstone Frederick L.
Published: March 2013

Frequency compounding is investigated as one technique for reducing the speckle contrast in phased array ultrasonic images. The degree of speckle contrast reduction was found to be inversely proportional to the bandwidth of the transmitted acoustic burst. The speckle pattern was also found to be anisotropic in its response to frequency compounding. Increases in the speckle pattern signal-to-noise ratios of 26 percent were found in B-mode images and increases as high as 84 percent were found in A-mode images.
Ultrasonic Attenuation Measurements of in Vivo Human Muscle
Authors: Ophir J. , Maklad N. F. , Bigelow R. H.
Published: March 2013

Attenuation measurements were performed on the quadriceps femoris muscle of 10 normal volunteers. The measurements were made using a statistical narrowband pulse echo method operating at 4.3 MHz. The results show a normal range of 4.71 ± 0.44 dB cm-1 (mean ± S.D.). A one-way analysis of variance was performed on the data which concluded that the populations of attenuation coefficients among the subjects were indeed distinct at the p < 0.0005 level.
Moiré Undersampling Artifacts in Digital Ultrasound Images
Authors: Ophir Jonathan , Brinch Johan M.
Published: March 2013

In modern ultrasonic digital sector scanners, the interaction between angulated line-of-sight vectors and a square pixel matrix results in Moiré artifacts in the image. These artifacts are a result of non-sampling of some pixels under certain conditions. The conditions which govern the appearance and progression of these artifacts are discussed, and an actual hardware demonstration is given.
Phase-Insensitive Pulse-Echo Imaging
Authors: O'Donnell M.
Published: March 2013

A method for reducing speckle in B-scan images using phase-insensitive detection is presented. This technique is based on the nonlinear processing of the detected output of an array of transducers. Using this method, phase-insensitive images of tissue phantoms have been compared to conventional phase-sensitive images of the same objects. The results of this comparison suggest that phase-insensitive imaging can reduce speckle in B-scan images.
Multifrequency and Nonuniformly-Spaced Arrays: Effects on Grating Lobe Amplitude
Authors: Bardsley B. G. , Christensen D. A. , Pryor T. A.
Published: March 2013

A computer simulation study on the effects of multifrequency and aperiodic ultrasonic transducer arrays has shown that both methods improve grating lobe response when compared to a periodic array of the same aperture and element spacing. The multifrequency array produces a better beam pattern than either the aperiodic or combination aperiodic/multifrequency array. Both the aperiodic and multifrequency arrays have a narrower main lobe and higher side lobe response than a periodic array with reduced element spacing and an equal number of elements.
Annular Arrays for Quantitative Pulsed Doppler Ultrasonic Flowmeters
Authors: Fu Chong-Cheng , Gerzberg Levy
Published: March 2013

A theory, based on the Fourier-Bessel series expansion, is developed to synthesize circularly symmetric field patterns by means of concentric annular arrays. The application of this theory to the formation of variable-width uniform sector beams is studied in detail and results in a canonical design procedure. Calculated beam patterns are compared to the actual measured patterns obtained from a prototype array suitable for transcutaneous investigation of the central blood-flow system and are observed to be in good agreement. The implementation of such arrays in the compensated-first-moment flowmeter is described. Methods of beam-pattern improvement are also discussed.
A Closed Form Method for the Measurement of Attenuation in Nonlinearly Dispersive Media
Authors: Narayana P. A. , Ophir J.
Published: March 2013

A closed form solution of the equation describing the spectrum of a Gaussian pulse propagating in a medium with nonlinear frequency dependence of attenuation is presented. This solution suggests that in general the spectrum remains Gaussian, subject only to center frequency downshift and bandwidth reduction. The possibility of experimentally determining the two nonlinear material parameters from the measurement of the center frequency downshift and the reduced bandwidth is proposed.
Spectral Shifts of Ultrasonic Propagation: A Study of Theoretical and Experimental Models
Authors: Narayana P. A. , Ophir J.
Published: March 2013

The theoretical relationship between center frequency downshift and the spectral bandwidth was investigated for pulses with a sinc (x) spectrum propagating through lossy media. Power law and exponential models for frequency dependence of attenuation were used. Six target materials encompassing a range of attenuation parameters were used to verify the theoretical model. The frequency downshift data from these materials was used to calculate their respective attenuation parameters. It was shown theoretically and verified experimentally that for small frequency downshifts, the sinc (x) model yields the same material parameters as the Gaussian model. The choice of the model for the attenuation of the material was found to be inconsequential.
Ultrasonic Signal Processing for

in Vivo

Attenuation Measurement: Short Time Fourier Analysis
Authors: Fink M. , Hottier F. , Cardoso J.F.
Published: March 2013

Short-time Fourier analysis is well suited for processing tissue echographic signals which are nonstationary. We have investigated the use of short-time Fourier analysis to provide an estimation of the echographic spectral composition as a function of time. It will be shown that the time dependence of the spectral centroid of this representation allows one to deduce easily the frequency-dependent attenuation. A simple correction of the noninvariant filtering effect due to diffraction is used to unbias the attenuation slope estimation. This new signal processing technique was first tested on simulated echographic data from a 1-D tissue model. Experimental results obtained from echo signals on a tissue-like phantom and on in vivo liver tissue show the influence of diffraction and attenuation respectively.
A Beam Corrected Estimation of the Frequency Dependent Attenuation of Biological Tissues from Backscattered Ultrasound
Authors: Cloostermans M.J.T.M. , Thijssen J.M.
Published: March 2013

A practical and highly accurate method of estimation of the frequency-dependent slope of the acoustic attenuation coefficient, α1, using backscattered ultrasound energy is presented. The influence or the focused ultrasound beam is experimentally measured and a simple method for incorporating the field effects in the estimate of α1 is described. The accuracy of the estimate of α1in vitro which appears to be of the order of 10 percent, demonstrates the feasibility of in vivo applications of the technique.
Changes in Myocardial Backscatter Throughout the Cardiac Cycle
Authors: Madaras E. I. , Barzilai B. , Perez J. E. , Sobel B. E. , Miller J. G.
Published: March 2013

This investigation was performed to identify and quantify systematic variations of myocardial ultrasonic backscatter throughout the cardiac cycle. Using a broadband 5 MHz focused transducer coupled to the epicardial surface of the left ventricle in dogs, backscatter measurements were obtained from each of 7 intervals (windows) of 34 milliseconds duration evenly distributed throughout the cardiac cycle and referenced to backscatter from a steel reflector. Values of integrated backscatter obtained demonstrated a consistent and reproducible pattern throughout the cardiac cycle characterized by elevated values at end-diastole and significantly lower values at end-systole. The average maximum difference was 3.5 dB.
Estimation of Ultrasonic Attenuation and Mean Backscatterer Size via Digital Signal Processing
Authors: Meyer C. R. , Herron D. S. , Carson P. L. , Banjavic R. A. , Thieme G. A. , Bookstein F. L. , Johnson M. L.
Published: March 2013

The backscattered rf signals from the lungs of fetal sheep during their last trimester of development were digitized and processed in an attempt to correlate ultrasonic parameters with measured functional parameters related to lung maturation. The broadband, post-TGC, rf signal of a commercial B-mode ultrasonic scanner was digitized at a sampling rate of 25 MHz. Sorting excluded data from regions of rib shadowing and other nonlung structures from analysis. The sorted data were used to estimate the slope of the ultrasonic attenuation coefficient with respect to frequency via linear regression on the average difference of the logarithm of power spectra from separated data segments. The power spectra were also corrected for attenuation, averaged and used to compute the power cepstrum of the backscattered signal which can be related to mean backscatterer radius. Results are presented for eight fetal sheep.
Inverse Scattering Solutions by a Sinc Basis, Multiple Source, Moment Method -- Part III: Fast Algorithms
Authors: Johnson S. A. , Zhou Y. , Tracy M. K. , Berggren M. J. , Stenger F.
Published: March 2013

Solving the inverse scattering problem for the Helmholtz wave equation without employing the Born or Rytov approximations is a challenging problem, but some slow iterative methods have been proposed. One such method suggested by us is based on solving systems of nonlinear algebraic equations that are derived by applying the method of moments to a sinc basis function expansion of the fields and scattering potential. In the past, we have solved these equations for a 2-D object of n by n pixels in a time proportional to n5. In the present paper, we demonstrate a new method based on FFT convolution and the concept of backprojection which solves these equations in time proportional to n3 • log(n). Several numerical examples are given for images up to 7 by 7 pixels in size. Analogous algorithms to solve the Riccati wave equation in n3 • log(n) time are also suggested, but not verified. A method is suggested for interpolating measurements from one detector geometry to a new perturbed detector geometry whose measurement points fall on a FFT accessible, rectangular grid and thereby render many detector geometrics compatible for use by our fast methods.
An Improved Stochastic Approach to RF Amplitude Analysis in Ultrasonic Cardiac Tissue Characterization
Authors: Vieli August , Heiserman Joseph , Schnittger Ingela , Popp Richard L.
Published: March 2013

We carried out a series of studies to improve the reproducibility of methods for ultrasonic myocardial tissue characterization using a stochastic approach to amplitude analysis of radiofrequency signals previously reported from our laboratory. Analysis of transducer scanner characteristics, data acquisition and processing, and data display from studies in tissue phantoms permit us to define some features of a parameter for expression of tissue character. The ratio of mean to standard deviation of the amplitude histogram from our system is explored as now implemented in our laboratory for reproducible measurements. The theoretical basis for understanding the utility of this method in defining tissue architecture and pathologic conditions requires further work.
A-Mode Speckle Reduction with Compound Frequencies and Compound Bandwidths
Authors: Melton H.E. , Magnin P.A.
Published: March 2013

A simple model for predicting the degree of speckle reduction in A-mode images via the correlation coefficient was tested experimentally. The model appeared to account correctly for the influence of image system bandwidth on frequency separations required for nearly independent sampling in compound frequency imaging. Moreover, the notion of compound bandwidth imaging was tested; the correlation between samples at different bandwidths decreased as the ratio of bandwidths decreased.
Diffraction Tomography Using Arbitrary Transmitter and Receiver Surfaces
Authors: Devaney A. J. , Beylkin G.
Published: March 2013

The theory of diffraction tomography for two-dimensional objects within the Born approximation is presented for cases where the scattered field is measured over arbitrarily shaped boundaries surrounding the object. Reconstruction algorithms are presented for both plane wave (parallel beam) and cylindrical wave (fan beam) insonification. Special attention is devoted to cases where the measurement and source boundaries are either lines or circles. The theory and algorithms presented are shown to be readily extended to the case of three-dimensional objects.
Frequency Domain Processing for Ultrasonic Attenuation Measurement in Liver
Authors: Wilson L.S. , Robinson D.E. , Doust B.D.
Published: March 2013

A frequency domain signal processing scheme is developed for measuring attenuation and attenuation slope in vivo, using equally spaced depth samples and linear regression techniques. The algorithm may be expressed in terms of linear, commuting operators acting on an array of log power spectra. By interchanging operators, a computationally efficient scheme may be developed, and the accuracy of the result assessed in terms of tissue uniformity and frequency linearity. Corresponding algorithms are demonstrated for measurement of attenuation at particular frequencies and attenuation in focal lesions. Measurements have been made using an Octoson water-delay echoscope on both normal and pathological livers. Variation of attenuation with a number of disease states has been found.
Angular Distribution of Scattered Ultrasound from a Single Steel Sphere in Agar Gelatin: A Comparison between Theory and Experiment
Authors: Burke Thomas M. , Goodsitt Mitch M. , Madsen Ernest L. , Zagzebski James A.
Published: March 2013

Experimental results for the angular distribution of scattered ultrasound in water from a 0.635 mm diameter steel sphere embedded in agar were obtained for interrogating frequencies of 1.0, 2.25, 3.5 and 5.0 MHz. The experimental results compared favorably with theoretical predictions based on the work of Faran. The results for both theory and experiment are presented in the form of the Differential Scattering Cross Section (DSC) for scattering angles from 170° to 44°. The implications of this study on calculating the expected scattering behavior of gelatin based ultrasound phantoms are briefly discussed.
High Frequency Ultrasonic Imaging of Skin: Experimental Results
Authors: Dines K. A. , Sheets P. W. , Brink J. A. , Hanke C. W. , Condra K. A. , Clendenon J. L. , Goss S. A. , Smith D. J. , Franklin T. D.
Published: March 2013

Experimental results are presented demonstrating the application of pulse echo ultrasound to imaging the skin. A laboratory prototype B-mode mechanical scanner was employed to obtain images of human skin, both in vitro and in vivo, using broadband pulsed ultrasound at 25 MHz. Images were formed by processing digitized A-mode waveforms and displaying the resulting two-dimensional cross sections using a digital imaging system. Images obtained by rectifying the A-modes are compared to those derived using a software-based cross-correlation technique. Scans of test targets demonstrate that an axial resolution of 100 m can be achieved at 25 MHz when the digital correlation method is employed. Lateral resolution is limited by the 0.25 mm half-power focal beamwidth of the transducer.

Seventeen in vitro ultrasonic scans of human skin were compared to frozen section histology. Average skin depth was well correlated between the two techniques (= 0.99, p < 0.001). Application of cross-correlated processing to 25 MHz in vivo images produced good delineation of epidermis, papillary, and reticular dermis. Conversion to a 50 MHz transducer did not delineate skin layers as well as the 25 MHz transducer due to inherent difficulties with transducer reverberations.
Two-Dimensional Echocardiographic Image Texture Analysis: Reduction of Regional Variability Using Polar Coordinates
Authors: Aylward Philip F. , Knosp Boyd N. , McPherson David D. , Eltoft Doug A. , Yurkonis Charles E. , Bean Judith A. , Skorton David J. , Collins Steve M.
Published: March 2013

Factors inherent to the ultrasound imaging system can influence quantitative ultrasound image texture and may produce changes that mask or mimic those due to alterations in tissue structure. In this study, we assessed the effect of the method of image data acquisition and analysis on the variations in quantitative texture measures that occurred solely due to the position of a region of interest (ROI) within the field of view. When ROI's, which varied in range and azimuth within the image of a tissue equivalent phantom (of uniform composition), were assessed by conventional analysis of scan-converted (rectangular coordinate) data, over 50 percent of all texture measures showed significant differences. Pseudo polar analysis reduced the number of texture measures showing regional variation by 80 percent (p < 0.01) and true polar coordinate data analysis reduced the number by 74 percent (p < 0.01). True polar analysis completely abolished differences in texture measures between ROI's separated in azimuth. Acquisition and analysis of tissue texture data using polar coordinates should allow a more definitive identification of abnormal tissue.
Generalized Description and Tracking Estimation of the Frequency Dependent Attenuation of Ultrasound in Biological Tissues
Authors: Cloostermans M.J. , Verhoef W.A. , Thijssen J.M.
Published: March 2013

In this paper a general model for the attenuation in biological tissues is proposed. The model consists of a series expansion of the attenuation coefficient, thereby covering the whole range of frequency dependencies from zero to four. Therefore, effects like pure specular reflections and negligible absorption at one extreme, as well as attenuation due to Rayleigh scattering, at the other extreme, are incorporated. A technique is described to estimate the attenuation in the range of frequency powers in a sampled depth ranging form. The applicability of the technique is illustrated by the results of a Simulation.
Texture of B-Mode Echograms: 3-D Simulations and Experiments of the Effects of Diffraction and Scatterer Density
Authors: Oosterveld B.J. , Thijssen J.M. , Verhoef W.A.
Published: March 2013

B-mode echograms were simulated by employing the impulse response method in transmission and reception using a discrete scatterer tissue model, with and without attenuation. The analytic signal approach was used for demodulation of the RF A-mode lines. The simulations were performed in 3-D space and compared to B-mode echograms obtained from experiments with scattering tissue phantoms. The average echo amplitude appeared to increase towards the focus and to decrease beyond it. In the focal zone, the average amplitude increased proportionally to the square root of the scatterer density. The signal to noise ratio (SNR) was found to be independent of depth, i.e., 1.91 as predicted for a Rayleigh distribution of gray levels, although a minimum was found in the focal zone at relatively low scatterer densities. The SNR continuously increased with increasing scatterer density and reached the limit of 1.91 at relatively high densities (>104 cm-3). The lateral full width at half maximum (FWHM) of the two dimensional autocovariance function of the speckle increased continuously from the transducer face to far beyond the focus and decreased thereafter due to the diffraction effect. The lateral FWHM decreased proportionally to the logarithm of the scatterer density at low densities and reached a limit at high densities. Introduction of attenuation in the simulated tissue resulted in a much more pronounced depth dependence of the texture. The axial FWHM was independent of the distance to the transducer to a first approximation and decreased slightly with increasing scatterer density until a limit was reached at densities larger than 103 cm-3. This limit was in agreement with theory. The experiments confirmed the simulations and it can be concluded that the presented results are of great importance to the understanding of B-mode echograms and to the potential use of the analysis of B-mode texture for tissue characterization.
Lipid Emulsions as Contrast Agents for Hepatic Sonography: An Experimental Study in Rabbits
Authors: Fink Ira J. , Miller Donald L. , Shawker Thomas H. , Girton Mary , Morrish Kathleen
Published: March 2013

An ultrasound contrast agent capable of increasing hepatic echogenicity would be useful for the detection of hepatic tumors and metastases. Fatty liver is known to produce increased liver echogenicity. Intravenously administered lipid emulsions are phagocytosed by cells of the reticuloendothelial system the liver with transient hepatic lipid accumulation. We examined the effectiveness of three lipid emulsions of differing particle size as potential ultrasound contrast agents using a rabbit liver model. None of the tested emulsions showed any consistent ability to alter liver echogenicity at maximum tolerable doses. Lipid emulsions do not appear to have potential as contrast agents for ultrasound examination of the liver.
Comment on Vaknine, R. and Lorenz, W.J. Lateral Filtering of Medical Ultrasonic B-Scans before Image Generation,

Ultrasonic Imaging 6

, 152–158 (1984)
Authors: Dickinson R. J.
Published: March 2013

In a recent paper, Vaknine and Lorenz [1] discuss the merits of lateral deconvolution of demodulated B-scans. While this technique will decrease the lateral blurring of single discrete targets, such as the diaphragm in their figure 3, it is inappropriate to apply the method to the echoes arising from inhomogeneous structures such as soft tissue. In this latter case, the echoes from individual scatterers within the resolution cell of the transducer interfere to give random fluctuations in received echo amplitude termed speckle [2]. Although his process can be modeled as a linear convolution similar to that of conventional image formation theory [3], the process of demodulation is a nonlinear process which loses the all-important phase information, and prevents the subsequent restoration of the image by Wiener filtering, itself a linear process.
Response to Comment on Vaknine, R. and Lorenz, W.J. Lateral Filtering of Medical Ultrasonic B-Scans before Image Generation,

Ultrasonic Imaging 6

, 152–158 (1984)
Authors: Vaknine R.
Published: March 2013

The technique presented in our paper was not intended to process the random fluctuations in received echo amplitudes nor the effect of the demodulation process on B-scan image resolution. It is a method which deconvolves the B-scan image data only in the lateral direction, before image generation, with the assumptions that led to Eq. (1) in our paper. The axial resolution is assumed to be good compared to the poor lateral resolution and the point spread function considered has a form of the normal distribution function [1].

As Dr. Dickinson mentions in his comment, the speckle process can be modeled as a linear convolution similar to that of conventional image formation and the low contrast resolution is not improved if the deconvolution in the lateral direction is performed before or after demodulation.

I agree that the low contrast resolution in B-scan images can be improved if a deconvolution in the axial direction is followed by lateral deconvolution. It would be inappropriate to perform an axial deconvolution without taking into consideration the deconvolution in the lateral direction to improve the poor lateral resolution. Our lateral filtering method has been applied to B-scan image data which were not previously processed by axial deconvolution. It can certainly be applied after axial deconvolution and elimination of the demodulation process.
Analysis of a System for Ultrasonic Imaging of Attenuation and Texture in Soft Tissue
Authors: Salomonsson Göran , Löfström Benny
Published: March 2013

Attenuation in tissue decreases both the amplitude and the bandwidth of a reflected ultrasonic signal. Only the amplitude is restored in conventional ultrasonic equipment by amplifying the signal in a time-gain-compensator.

This paper describes a method for restoring both the amplitude and bandwidth of the signal and an implemention of this method is proposed. This consists of two main parts: a device for estimating the attenuation and a time-variable circuit. The time-variable circuit is controlled by the estimated attenuation such that its transfer function approximates the inverse of the transfer function of the attenuation within the transducer passband. Its output is then almost independent of the attenuation and contains information on the texture of the tissue. Both the texture and attenuation estimates are displayed graphically. The quality of the image of the texture can be improved by choosing a wideband transducer, since it is almost exclusively dependent of transducer bandwidth.

The performance of the method is studied using both simulated signals and signals measured in vitro.
Reduced-Order Autoregressive Modeling for Center-Frequency Estimation
Authors: Kuc Roman , Li Hilda
Published: March 2013

The center frequency of a narrowband, discrete-time random process, such as a reflected ultrasound signal, is estimated from the parameter values of a reduced, second-order autoregressive (AR) model. This approach is proposed as a fast estimator that performs better than the zero-crossing count estimate for determining the center-frequency location. The parameter values are obtained through a linear prediction analysis on the correlated random process, which in this case is identical to the maximum entropy method for spectral estimation. The frequency of the maximum of the second-order model spectrum is determined from these parameters and is used as the center-frequency estimate. This estimate can be computed very efficiently, requiring only the estimates of the first three terms of the process autocorrelation function. The bias and variance properties of this estimator are determined for a random process having a Gaussian-shaped spectrum and compared to those of the ideal FM frequency discriminator, zero-crossing count estimator and a correlation estimator. It is found that the variance values for the reduced-order AR model center-frequency estimator lie between those for the ideal FM frequency discriminator and the zero-crossing count estimator.
Quantitative Tests of a Three-Dimensional Gray Scale Texture Model
Authors: Zagzebski J. A. , Madsen E. L. , Goodsitt M. M.
Published: March 2013

A three-dimensional model for gray scale texture in ultrasound B-mode images has been extended to enable absolute quantitative predictions of echo signal levels and texture characteristics. The quantitative aspects of the model are tested with a phantom in which the ultrasonic scattering properties as well as the ultrasonic attenuation coefficient and the speed of sound are known as functions of frequency. Good agreement between theoretical predictions and experimental results was found in the overall brightness of B-mode images, in pixel value histograms, and in an autocorrelation function analysis of images. Passing quantitative tests is additional evidence that the model is a reliable tool for computer simulations involving many important facets of ultrasound B-mode imaging and tissue characterization.
Generalized Projection-Slice Theorem for Fan Beam Diffraction Tomography
Authors: Devaney Anthony J.
Published: March 2013

A generalized projection-slice theorem is derived for transmission fan beam diffraction tomography within the Born or Rytov approximations. The development is based on the use of the so-called paraxial approximation which requires that the object being probed subtend a small angle relative to the source point and to the measurement plane. Within this approximation it is shown that the transmitted field measured over a plane surface located on the opposite side of the object from the insonifying point source determines the three-dimensional spatial Fourier transform of the object profile over the surface of an ellipsoid of revolution in Fourier space. In the special case where the point source is in the far field of the object the semiaxes of the ellipsoid become equal and the surface degenerates to a sphere and the result reduces to the usual projection-slice theorem of plane beam diffraction tomography.
Modelling and Restoration of Ultrasonic Phased-Array B-Scan Images
Authors: Ardouin Jean-Pierre , Venetsanopoulos A. N.
Published: March 2013

A model is presented for the radio-frequency image produced by a B-scan (pulse-echo) ultrasound imaging system using a phased-array transducer. This type of scanner is widely used for real-time heart imaging. The model allows for dynamic focusing as well as an acoustic lens focusing the beam in the elevation plane. A result of the model is an expression to compute the space-variant point spread function (PSF) of the system. This is made possible by the use of a combination of Fresnel and Fraunhoffer approximations which are valid in the range of interest for practical applications. The PSF is used to design restoration filters in order to improve image resolution. The filters are then applied to experimental images of wires.
Time Domain Formulation of Pulse-Doppler Ultrasound and Blood Velocity Estimation by Cross Correlation
Authors: Bonnefous O. , Pesqué P.
Published: March 2013

The Doppler effect is usually described as a frequency shift of the backscattered signals from moving targets with respect to the frequency transmitted. Recently, real-time blood flow imaging has become possible thanks to the development of a new velocity estimator based on phase-shift measurements of successive echoes. However, this method suffers from the well-known limitations of pulse-Doppler instruments. A new formulation is presented which describes the pulse-Doppler effect on the successive echoes from a cloud of moving targets as a progressive translation in time due to the displacement of the scatterers between two excitations. This approach allows us to generate efficiently computer-simulated data in order to evaluate accurately the various processing techniques. Furthermore, it leads to a novel class of velocity estimators in the time domain which measure the time shifts which are proportional to the local blood velocity. Among them, the cross correlation of the received rf signals turns out to be well suited. A local cross-correlation function is first calculated from a consecutive pair of range-gated echoes and the time shift is then determined by searching for the time position with the maximum correlation. The time-correlation technique is shown to provide accurate velocity profiles with broadband transducers. Moreover, the classical velocity limitation of pulse-Doppler is overcome because there is no ambiguity in measuring a time shift instead of a phase shift. These major advantages should make quantitative flow mapping possible and more reliable.
Attenuation Correction in Echocardiography
Authors: Pincu Madeleine , Schwartz Gary , Corday Stephen R. , Fujibayashi Yozo , Meerbaum Samuel
Published: March 2013

A commercial two-dimensional echo unit, modified to permit digital acquisition (2.2 MHz) of echo signals prior to time-gain-compensation (TGC), was ratiometrically calibrated. Simulating the TGC in software, we demonstrated improvements in image quality as compared to conventional video methods. A path-dependent attenuation correction (PDAC) algorithm, utilizing the gray level image statistics to assign one of three attenuation coefficients (for chest, myocardium or blood) to each image pixel, was then developed. Using it on left ventricular (LV) short axis images obtained in nine healthy closed chest dogs, we demonstrated that the backscatter intensity at end diastole (ED) was 2.0 ± 0.5 dB (mean ± SEM) higher (p>0.01) than at end systole (ES), in circumferential segments of the myocardium oriented anteriorly and posteriorly, relative to the transducer. In seven of the dogs, subsequently occluded for one hour in the anterior descending branch of the left coronary artery (LAD), this normal phasic myocardial backscatter (PMB) variation decreased or was reversed in ischemic segments, relative to preocclusion values, suggesting utility of the method for sequential study of myocardial ischemia and its treatment.
The Effect of Focusing on Ultrasonic Backscatter Measurements
Authors: Yuan Y. W. , Shung K. K.
Published: March 2013

In this paper, the effect of transducer focusing on the integrity of ultrasonic backscattering measurements is examined. The rationale for this study stems from our observation that the calculated values of backscattering coefficients from data obtained with nonfocused transducers are always substantially lower than those obtained with focused transducers when the standard substitution method is used for backscattering measurements. It is postulated that this discrepancy is caused by the extremely complicated beam behavior of a focused transducer. This hypothesis is verified experimentally. It is therefore concluded that focused transducer could yield misleading results when a standard substitution method is used for absolute backscattering measurements.
An Interactive Processing System for Ultrasonic Compound Imaging, Real-Time Image Processing and Textile Analysis
Authors: Schuster E. , Knoflach P. , Huber K. , Grabner G.
Published: March 2013

An interactive processing system for ultrasonic imaging, real-time image processing and texture analysis was developed and has been used under real clinical conditions at the 2nd Department of Gastroenterology and Hepatology, Vienna, since 1983. The major goal of this system is to determine what digital approaches to ultrasonic imaging, aided by computer processing, can contribute to ultrasonic diagnosis and whether clinically-relevant information can be extracted which is not obtained by conventional approaches.
Presence of Cepstral Peak in Random Reflected Ultrasound Signals
Authors: Kuc Roman , Haghkerdar Kiafar , O'Donnell Matt
Published: March 2013

A peak in the power cepstrum, or the squared magnitude of the Fourier transform of the data log-power spectrum, is commonly observed when processing reflections from plate-like structures, such as membranes. In this case, the cepstral peak at the smallest nonzero time lag, or quefrency, value can be used to determine the thickness of the plate. For reflections from a medium composed of randomly distributed scatterers, such as liver tissue, a cepstral peak is also commonly observed, but cannot be so intuitively explained as in the deterministic case above. In this paper, it is demonstrated that the presence of a cepstral peak depends on the form of the probability density function (pdf) of the separation between reflectors. In the case where the pdf is uniform from 0 to SM, the cepstral peak is found to occur at the quefrency corresponding to SM. For simple unimodal pdfs, a cepstral peak will occur at the location of the maximum probability. These observations are shown analytically and verified through simulations. The diagnostic value of these results lies in the interpretation of the relation of the cepstral peak location to the spacing of the scattering elements in the tissue.
Ultrasound Characterization of Acute Myocardial Ischemia by Quantitative Texture Analysis
Authors: McPherson David D. , Aylward Philip E. , Knosp Boyd M. , Bean Judy A. , Kerber Richard E. , Collins Steve M. , Skorton David J.
Published: March 2013

In this study we tested the efficacy of quantitative texture analysis in the identification of acute myocardial ischemia using an ultrasound data acquisition system that digitizes and stores echocardiographic data in polar format. In nine closed-chest dogs, data were acquired before and after coronary occlusion using a 2.4 MHz echocardiographic system. Regions of interest were analyzed at end-diastole and end-systole from the ischemic area and normal area at the same depth of field. Ultrasound data were evaluated using previously reported quantitative gray level texture measures. After occlusion, texture changes indicative of ischemia were found in systolic images. The directional component of the data analysis was important; analysis in the azimuthal direction was more accurate than in the axial direction. Six texture measures exhibited significant changes in the ischemic region from control to occlusion when analyzing data in the azimuthal direction. One false positive result occurred (significant texture change in the normal region from control to occlusion) in the azimuthal direction. Several false positive alterations in the normal regions from control to occlusion were found when the texture was evaluated in the axial direction. For accurate assessment of ischemic changes, preocclusion image data were required. We conclude that quantitative echocardiographic texture analysis using polar format data can identify subtle changes in myocardial texture such as that due to acute ischemia, using data acquired through the Chest Wall.
Signal-to-Clutter Ratio in Pseudo Random Doppler Flowmeter
Authors: Cathignol Dominique Jean
Published: March 2013

In order to increase the signal-to-noise ratio of Doppler velocimeters, several authors have proposed to use the emission of a sine wave phase modulated by a pseudorandom binary sequence with an on/off ratio equal to unity. The velocity measurement of the scatterers located in the range cell volume may be perturbed by all the other reflecting clutter targets which are moving in the ultrasonic field. The ratio between the Doppler signal issuing from the range cell and that from the mobile clutter targets will be defined as the signal-to-mobile clutter ratio (SCR)m. We have evaluated the (SCR)m by computing the ambiguity function of the pseudorandom binary sequence as a function of the vessel diameter, the number of phase states and the normalized particle velocity. The results show: (i) for high velocities, the (SCR)m decreases rapidly. (ii) an increase of the number of states of the code does not entail a proportional improvement in the (SCR)m because of the simultaneous decrease of the range cell;(iii) it is confirmed that pseudorandom flowmeters perform better than pulsed Doppler systems for small, even deep-lying, vessels. However, they do not allow for a precise velocity measurement in the case of vessel diameters larger than three Centimeters.
Correlations of Sound Speed with Tissue Constituents in Normal and Diffuse Liver Disease
Authors: Lin T. , Ophir J. , Potter G.
Published: March 2013

The speed of sound in normal and diffusely-diseased liver specimens was measured. There were four experimental groups, consisting of normal (n=21), fatty (n=7), fibrotic (n=7) and mixed fatty and fibrotic (n=9). These classifications were based on histological grading. We found that the results corroborate and extend most of the results of Bamber and coworkers. Specifically, no significant correlation was found between speed of sound and fibrosis score; a moderate correlation was found between speed of sound and tissue water content; and a relatively good correlation (r = −0.670, p<0.1%) was found between the speed of sound and the histological fat score, which increased to r = −0.819 (p<0.1%) when a correction for variations in water content was used.
Evaluation of Ultrasonic Attenuation in Diffuse Diseases of Spleen and Liver
Authors: Wilson L.S. , Robinson D.E. , Griffiths K.A. , Manoharan A. , Doust B.D.
Published: March 2013

Ultrasonic attenuation has been measured using frequency domain signal processing in clinical trials of patients with liver and spleen diseases. By comparing the variance encountered in local measurements and in measurements at a number of adjoining sites, the need for averaging over large volumes of tissue to avoid the effects of large fluctuations is established. In spleens of patients with myelofibrosis, no correlation between fibrosis and attenuation was found. However it was found that variations in splenic volume were accompanied by inverse changes in attenuation, most likely due to blood pooling. A correlation was found between splenic blood flow per unit organ volume and attenuation. In cirrhotic livers, attenuation was significantly increased with fatty infiltration, but only slightly increased in livers containing minimal fat. These findings tend to reduce the probability of finding successful clinical applications for attenuation slope measurements.
Diffraction Correction for Focused Transducers in Attenuation Measurements

in Vivo
Authors: Laugier P. , Berger G. , Fink M. , Perrin J.
Published: March 2013

Diffraction effects are a cause of error when estimating the frequency dependent attenuation of ultrasound in biological tissues in the reflection mode. Comparison of attenuation values estimated in vivo by different investigators using different types of transducers makes calibration and correction for diffraction necessary. In this paper, we present experimental results for in vivo calibration and correction for the diffraction effect for focused transducers. We also study numerically the diffraction filter in a time-frequency representation, and show that for a focused probe, there is a region in the time-frequency domain where the frequency slope of the diffraction filter does not vary with time. The main consequence for in vivo estimation is that for a given probe, it is possible to select both the distance between the region of interest and the probe, and the frequency limits, such that the attenuation thus estimated is unbiased by the diffraction effect. This result, obtained by numerical calculations, is confirmed by experimental calibration of a foam phantom and in vivo muscle.
An Improved Ultrasound Simulation Model: Use in Evaluating Log versus Linear Processing for Lesion Detection
Authors: Goodsitt Mitchell M. , Bleier Alan R. , Barber Frank E.
Published: March 2013

This paper reports the development of an improved three-dimensional computer simulation model for evaluation of ultrasonic imaging systems. This model was used to successfully evaluate a signal processing method for improving lesion detection in ultrasound imaging. Linear processing of the rf signal amplitudes from a limited region of tissue was compared with the logarithmic compression employed by most commercial scanners. Two lesions were simulated by spherical distributions of scatterers having backscatter coefficients greater than the scatterers in the surrounding medium. Linear processing improved the differential contrast by a factor of about two.

The simulation is based on the three-dimensional distribution of acoustic frequency spectra in a transducer beam and integration of scattered pulses from a corresponding three-dimensional array of scatterers. The simulation reported in previous papers depended upon physical measurement of the impulse response of a transducer. An original contribution described briefly herein, and in more detail in a companion article, is the addition of a model of the transducer's pulse waveform generation. Another new addition is the definition of a specific lesion detection task for objective assessment of a change in image quality following perturbation of some system parameter.
Phase Aberration Measurements in Medical Ultrasound: Human Studies
Authors: O'Donnell M. , Flax S.W.
Published: March 2013

Using a modified real-time phased array sector scanner, phase aberrations and amplitude fluctuations across the imaging aperture have been measured in a number of human subjects. Data from these subjects were classified into two categories based on the quality of conventional longitudinal images of the liver. Measured phase aberrations were very small in all subjects exhibiting high quality images. In contrast, large phase aberrations were measured in subjects producing low quality images. However, there were no significant amplitude variations across the array for all subjects studied. These results suggest that the absence of significant phase aberrations is a necessary condition for high quality phased array imaging. If so, improvements in clinical image quality in Such Subjects may be possible.