bluuebunny/crossref_metadata_2025 huggingface dataset:
A Simulation Study and Theoretical Comparison of Various Processing Techniques Used in Ultrasonic Bloodflow Measurement
Authors: Olinger M. , Siegel M.
Published: March 2013

In the past, several ultrasonic bloodflow imaging systems have been proposed. Those of most interest to us have been the pulsed sinusoid system, the random noise system, and the pseudo noise system. In this paper, some advantages and disadvantages of each are discussed.

This paper begins with a brief review of signal processing as it applies to blood flow measuring systems in general. Next each of the above systems are discussed and related to the general theory. A system which combines some of the advantages of each is introduced at this point. Finally, the results of a sophisticated simulation developed specifically to compare these systems is presented.
Compound Scanning with an Electrically Steered Beam
Authors: Berson M. , Roncin A. , Pourcelot L.
Published: March 2013

Compound scanning using electronic steering of an array of transducers makes it possible to widen the area being explored and to increase the amount of information contained in an ultrasonic image. The principle and the operating characteristics of the method are described and its effectiveness demonstrated by in vitro and in vivo experiments. Possible improvements and applications are discussed.
Time Series Analysis of Ultrasonic Observations of Gross Fetal Body Movements during the Last 10 Weeks of Pregnancy
Authors: Campbell Karen , MacNeill Ian , Patrick John
Published: March 2013

Thirty fetuses were observed for 24 hours and one fetus was observed for 20 hours during the last 10 weeks of gestation. Observations were made of the amount of gross fetal body movement in each successive 5 minute observation epoch, thus resulting in 30 time series of 288 observations and one time series of 240 observations. Spectral analysis of these time series demonstrated the presence of significant power in the frequency range of 0.002 to 0.0175 cpm. Application of Box-Jenkins techniques to the time series resulted in the choice of a first-order auto-regression model to fit the data. It was concluded that the incidence of episodes of gross fetal body movements were non-random and were, in fact, pseudoperiodic.
Ultrasonic Transmission Speckle Imaging
Authors: Bates R. H. T. , Robinson B. S.
Published: March 2013

Speckle interferometry, as developed during the past decade for optical astronomy, is adapted to ultrasonic imaging through water and animal tissue. Experimental results are presented illustrating not only Labeyrie's original idea, but also speckle holography and our recently devised shift-and-add technique. Both incoherent and coherent processing are investigated (only the former is feasible in astronomy since the sources are spatially incoherent). The results demonstrate that image quality can be improved dramatically when coherent processing is used.
A Filtered Backpropagation Algorithm for Diffraction Tomography
Authors: Devaney A. J.
Published: March 2013

A reconstruction algorithm is derived for parallel beam transmission computed tomography through two-dimensional structures in which diffraction of the insonifying beam must be taken into account. The algorithm is found to be completely analogous to the filtered backprojection algorithm of conventional transmission tomography with the exception that the backprojection operation has to be replaced by a back propagation process whereby the complex phase of a field measured over a line outside the object is made to propagate back through the object space. The algorithm is applicable to diffraction tomography within either the first Born or Rytov approximations. Application of the algorithm to three-dimensional structures is also discussed.
A Dispersive Model for the Propagation of Ultrasound in Soft Tissue
Authors: Gurumurthy K. V. , Arthur R. Martin
Published: March 2013

Although the dispersion of tissue is small and difficult to measure, it can be calculated from a knowledge of the tissue's attenuation. A minimum-phase function, which characterizes tissue dispersion was derived using the Hilbert transform. This function was incorporated into a tissue model which has a causal impulse response and from which accurate estimates of the slope of attenuation times path length can be extracted. Predictions of phase velocity closely match available dispersion measurements. The model suggests that phase velocity measurements must be much more accurate than attenuation measurements for a comparable description of tissue.
Application of Pattern Recognition Techniques to Breast Cancer Detection: Ultrasonic Analysis of 100 Pathologically Confirmed Tissue Areas
Authors: Good Morris S. , Rose Joseph L. , Goldberg Barry B.
Published: March 2013

Ultrasonic pulse-echo rf waveform analysis and selected pattern recognition methods were applied to classification of breast tissue. Emphasis was placed on the classification of solid tissue areas since fluid areas are easily identified by present B-scan techniques.

Pattern recognition techniques such as the Fisher Linear Discriminant (FLD), Probability Density Function (PDF) curves, jackknife estimate and committee vote were used to construct and evaluate a two class algorithm, malignant versus benign tissue areas. A data base consisting of frequency domain features from 100 pathologically confirmed tissue areas from 87 patients were used to train the algorithm. Algorithm performance was acquired via the generalized jackknife procedure to significantly reduce the bias frequently encountered in algorithm evaluation. Estimated values of algorithm performance are sensitivity and specificity values of 96 percent and 68 percent, respectively.
Lateral Inverse Filtering of Ultrasonic B-Scan Images
Authors: Schomberg H. , Vollmann W. , Mahnke G.
Published: March 2013

The formation of ultrasonic B-scan images using parallel beams may be modelled as a lateral, one-dimensional convolution of the beam profile and an unknown but wanted reflection coefficient. Lateral inverse filtering, or deconvolution, might therefore be used to improve the image quality. Two different deconvolution techniques are applied to both an image of a tissue mimicking phantom and a human liver. An enhancement of the resolution (defined as the reciprocal of the half-width of the image of a point reflector) of about 1.4 is achieved. This is in good agreement with the previously derived formula R = [Formula: see text], which relates the signal-to-noise ratio, SNR, to the resolution enhancement, R. However, each method also creates artifacts, and despite the slight resolution enhancement, the deconvolved liver images do not exhibit more information nor are they more appealing. So it is felt that the computational effort is wasted. This failure is not a fault of the special deconvolution techniques tried here, but rather caused by the logarithmic dependence of R on SNR and by the noise level, which is largely due to macro- and microscopic inhomogeneities of the tissue and cannot be made arbitrarily small.
Breast Tissue Classification Using Diagnostic Ultrasound and Pattern Recognition Techniques: II. Experimental Results
Authors: Finette Steven , Bleier Alan R. , Swindell William , Haber Kai
Published: March 2013

The methods of statistical pattern recognition have been applied to the problem of in vivo ultrasonic characterization of breast disease in humans. Backscattered A-mode signals obtained from a commercial pulse imaging system were used to generate a large set of potentially useful features. Using statistical tests, a small subset of discriminatory features was selected to design a Bayes decision rule for each of two tissue classification schemes: malignant disease vs. benign disease, and malignant disease vs. (benign disease + normal tissue). Classification results obtained by the rotation method included sensitivities of 88 percent and 76 percent for the two schemes, based on data obtained from 32 women. These results are encouraging, though a definitive statement concerning the extrapolation of these numbers to the general population should only be made after obtaining results with a large data base.
Rational Gain Compensation for Attenuation in Cardiac Ultrasonography
Authors: Melton Hewlett E. , Skorton David J.
Published: March 2013

A new method of compensating for the attenuation of ultrasound by chest wall, myocardium and blood has been devised by using an optimum threshold to distinguish between blood and myocardium. This allows changing receiver gain at rates suitable for either blood or myocardium for each line-of-sight forming a real-time image. Compensation artifacts arising from the effects of speckle or phase cancellation are minimized by using a one-bit digital filter after threshold detection. This method of compensation is a necessary first step toward quantitative two-dimensional echocardiography.
Modeling Acoustic Attenuation of Soft Tissue with a Minimum-Phase Filter
Authors: Kuc Roman
Published: March 2013

Soft biological tissue has been observed to exhibit an acoustic attenuation log-magnitude characteristic which increases as an approximately linear function of frequency. This paper describes the implementation of a finite-impulse-response (FIR) digital filter model for simulating this behavior on a digital computer. To insure that the filter is causal, the minimum-phase constraint is imposed. For minimum-phase filters, the log-magnitude and phase characteristics form a Hilbert Transform pair. The discrete-time Hilbert Transform of the linear log-magnitude characteristic was evaluated to determine the phase of the filter. The inverse Fourier Transform of the resulting real and imaginary components of the frequency transform produces the finite-duration unit-sample response of the digital filter model. Experimental results using plexiglas material, which has a linear-with-frequency loss characteristic, indicate that the minimum-phase model is more accurate than the linearphase model, resulting in a rms error between predicted and observed time waveforms that is 3 times smaller. The effects of varying the sampling period and the size of the FIR filter are discussed. A FORTRAN program to calculate the minimum-phase unit-sample response from the slope of the log-magnitude characteristic is included in the Appendix.
Characterization of Tongue Shape
Authors: Morrish K.A. , Stone M. , Sonies B.C. , Kurtz D. , Shawker T.
Published: March 2013

Mathematical techniques are described for analyzing tongue shapes obtained with ultrasound images. The surface of the mid-sagittal section of the tongue was approximated by discrete points. In turn, these points were used to approximate position, slope and curvature of the tongue surface at a fixed time during speech. Two approaches were employed. The first method involved the use of finite difference approximations to derivatives of the function of tongue position. The second utilized a curve fit. Both methods were examined for reliability. Results of these analyses on a simple, single speech sound are discussed.
Computerized Three-Dimensional Finite Element Reconstruction of the Left Ventricle from Cross-Sectional Echocardiograms
Authors: Nikravesh P. E. , Skorton D. J. , Chandran K. B. , Attarwala Y. M. , Pandian N. , Kerber R. E.
Published: March 2013

A computerized method for the generation of a three-dimensional finite element mesh of left ventricular geometry is presented. The technique employs two dimensional echocardiographic images of the left ventricle. The echocardiographic transducer is attached to an articulated, computerassisted, position registration arm with six degrees-of-freedom. These six degrees-of-freedom record the location and orientation of the transducer, when images are obtained, referenced to an external point. Eence, the images are digitized and aligned relative to one another, then several interpolation and curve fitting steps are used to reconstruct a threedimensional finite element model of the left ventricle. The finite element model can be used for volume determination, stress analysis, material property identification, and other applications.
Diffraction Tomography Using Beam Waves: Z-Average Reconstruction
Authors: Lu Z. Q. , Kaveh M. , Mueller R. K.
Published: March 2013

This paper discusses the problem of diffraction tomography, when a general bean wave is used as the excitation and the three-dimensional structure of the object is considered. The special case of a zero-order beam wave with measurements of the average of the scattered field in the z direction is detailed. It is shown that in this case a reconstruction algorithm identical to the two-dimensional geometry yields a z-averaged tomogram of the inhomogeneity.
Texture Analysis of Ultrasound B-Mode Images by Segmentation
Authors: Mailloux Guy E. , Bertrand Michel , Stampfler Robert , Ethier Serge
Published: March 2013

B-mode texture characterization by supervised methods of pattern recognition is subject to the following drawbacks: precise localization of the lesion to characterize is often difficult and, even when the lesion is well isolated, its texture can be corrupted by the presence of tumor non specific structures. These structures are not easily discernable and introduce a bias in the statistical measures. The results presented in this paper show that these problems can be circumvented by the use of an unsupervised method of image segmentation. The method enhances the B-mode image and partitions the non specific structures and the lesion texture in different regions which can be characterized independently by statistical methods. The unsupervised approach also facilitates the clinical diagnosis done by visual inspection, by revealing subtle characteristics of the B-mode textures.
Transfer Function Analysis of a Quasioptical Ultrasonic Imaging System
Authors: Oppelt R. , Ermert H.
Published: March 2013

The imaging properties of lenses have been well analyzed in the optical regime. However, most of these analyses have been confined to two cases: illumination of the object with ideal coherent or ideal incoherent light. In ultrasonics, imaging systems with lenses also are known. But in contrast to the optical case, the object can be easily insonified with waves of variable frequency or with a noise source of adjustable bandwidth. In this paper, the influence of the broad frequency bandwidth in an ultrasonic imaging system is emphasized. A so called “imaging channel transfer function” (ICTF) is introduced to describe all nonelectrical system properties. It is shown that the ICTF is part of a temporal frequency transfer function. This transfer function has a frequency dependence which is not readily attainable with well-known active or passive RLC-networks. Finally, it is demonstrated how to use the ICTF for calculating the image response in a wideband imaging system with ultrasonic sources emitting either deterministic or stochastic signals of a certain bandwidth.
Improved Mirror Systems for High Resolution Ultrasonic Imaging
Authors: Nicoll J. J. , Piggins J. M. , McDicken W. N. , Borthwick R.
Published: March 2013

High resolution ultrasonic imaging in a water bath, for example breast imaging, demands a transducer of large aperture. Such an aperture is most easily achieved by the use of mirrors. Previous such mirror systems suffered problems from reverberations between and within their component parts. Changes in the design of the system, and the use of thin metal reflectors, reduce these reverberations to an acceptable level. There is no sacrifice in the focusing performance, and losses in the system are minimized.
Scatterer-Induced Frequency Variations in Reflected Acoustic Pulses: Implications for Tissue Characterization
Authors: Gehlbach S.M. , Sommer F.G. , Stern R.A.
Published: March 2013

A Hilbert transform approach to the detection of the instantaneous center frequency of reflected ultrasonic pulses was performed for simulated reflected ultrasonic pulses, and digitized ultrasonic waveforms from tissue phantoms. Considerable center frequency modulation was observed for both simulated and recorded ultrasonic waveforms. This phenomenon of frequency modulation can be explained with the aid of a phasor model, in which variations in instantaneous frequency results from the interaction of a multitude of overlapping ultrasonic pulses arising from different scattering centers in tissue. The observed frequency modulation of ultrasonic signals has important implications for tissue characterization techniques, including the measurement of attenuation by the determination of the shift in ultrasonic center frequency.
Quantitative Assessment of in Vivo Backscatter Enhancement from Gelatin Microspheres
Authors: Ophir J. , Gobuty A. , Maklad N. , Tyler T. , Jaeger P. , McWhirt R.
Published: March 2013

Experimental work using a quantitative C-scan technique to measure in situ enhancement of hepatic backscatter resulting from the administration of gelatin microspheres to dogs is reported. We have found that (1) reproducible enhancement of hepatic backscatter on the order of 2 dB followed the peripheral administration of gelatin within minutes, (2) the magnitude of the effect was not sensitive to the rate of infusion, but was likely to be dose dependent, (3) changes in the overlying tissue attenuation had a pronounced effect on the measurement, and (4) the effect was sustained for up to one half hour or longer.
Multifrequency Holography Using Backpropagation
Authors: Teo Tat-Jin , Reid John M.
Published: March 2013

The technique of wavefield backpropagation has been used quite extensively in the literature. We report on an analytical study of the resolution properties of this technique. Backpropagation as a form of holographic reconstruction suffers from poor axial resolution. We derive expressions for both the axial and the lateral resolutions. We also show that the axial resolution can be substantially improved by the use of multiple frequencies. We derive an expression relating the resolution and bandwidth.
Two-Dimensional Ultrasonic Variation in Myocardium Throughout the Cardiac Cycle
Authors: Fitzgerald Peter J. , McDaniel Martha M. , Rolett Ellis L. , James Douglas H. , Strohbehn John W.
Published: March 2013

This study was performed to investigate the two-dimensional unprocessed radiofrequency (rf) ultrasonic backscatter from myocardium throughout the cardiac cycle. Eleven mongrel dogs underwent left lateral thoracotomy and had two-dimensional echocardiographic studies performed using a 5 MHz transducer. Regions of interest, selected to encompass a portion of the myocardium, were transported at 33 ms intervals to a host computer and disc. Results show a reproducible cyclic variation in backscatter power throughout the cardiac cycle for the anterior wall. The backscatter power was highest during diastolic relaxation and lowest during systolic contraction. The average change was 4.5 dB.
The Instantaneous Frequency of a Sinewave Squelched Bandlimited Signal
Authors: Komaili Jaleh , Sankar P. V. , Ferrari Leonard A. , Leeman S.
Published: March 2013

We study the instantaneous frequency of a signal which is formed by the summation of a sinewave and a bandlimited signal. We refer to the composite signal as a sinewave squelched or simply a squelched signal. We study the behavior of the squelched signal at its real zeros and extrema.

In particular when the sinewave frequency is equal to the largest frequency in the signal's spectrum and its amplitude is greater than the signal's maximum amplitude, the analytic signal corresponding to this resultant signal (hereafter abbreviated as RZ signal) has only real zeros which contain all of the bandlimited signal's information.

FM systems often use zero crossing techniques in the demodulation process. For a process with a normal amplitude distribution, we derive a relationship between the zero crossing density of an RZ converted signal and that of the original signal.

One application of these analyses is in ultrasonic FM imaging. We give an explanation for the behavior of the FM imaging system as a function of amplitude and frequency of the added cosine.
Frequency Diversity Speckle Processing
Authors: Gehlbach Steve M. , Sommer F. Graham
Published: March 2013

Ultrasonic waveform data from a tissue-mimicking phantom containing low contrast targets was digitized, stored and processed prior to creating and displaying ultrasonic images. Speckle reduction was performed by digital filtering of the waveform data with appropriately spaced and weighted digital filters, prior to both coherent and incoherent image averaging. The resultant images showed increased signal-to-noise ratios, consistent with theory. Better definition of low contrast target boundaries was noted in the processed, compared to unprocessed, images. Incoherent and coherent processing were investigated, and appeared to be equivalent.
A Method to Improve the Accuracy of Ultrasound Geometrical Measurements of Boundaries in Soft Tissue
Authors: Goldberg V. , Pryor A.T. , Parker D.L.
Published: March 2013

The geometric distortion due to the neglect of refraction in existing ultrasound scanners is demonstrated. An iterative technique to correct for refraction errors in B-mode ultrasound, denoted Second Order Refraction Transposition (SORT), is presented. In vitro experiments were performed that confirm the calculated results.
A Preliminary Study on the Angular Distribution of Scattered Ultrasound from Bovine Liver and Myocardium
Authors: Burke Thomas M. , Madsen Ernest L. , Zagzebski James A.
Published: March 2013

Measurements were performed on freshly-excised bovine liver and myocardium to determine the ultrasonic scattering nature of the tissues under a variety of experimental conditions. Results for the angular distribution of the differential scattering cross section per unit volume of tissue are reported for scattering angles spanning 170 to 44 degrees for interrogating frequencies of 1.0, 2.25, 3.5 and 5.0 MHz. Fresh and aged tissues, some with abnormally high connective tissue content were analyzed. The results are compared to previously-published works.
Phase-Derivative Imaging I: Methods and Stabilization Analysis
Authors: Romijn R.L. , Oosterveld B.J. , Thijssen J.M.
Published: March 2013

The potential of using the phase derivative (PD) for echographic imaging was investigated. The PD data were calculated by four methods: zero crossing (ZCS) with squelch addition, analytic signal either with squelch addition (ASS) or with employment of a Wiener kernel (ASW), and unwrapped phase (UWP). The large peaks which occur in an unprocessed PD signal were “stabilized” by some kind of smoothing algorithm. The effects of the amplitude of the squelch signal and of the degree of smoothing were systematically investigated for experimental and simulated 1-D and 2-D rf echograms. The optimal pictures obtained for all four PD estimation methods were compared to the amplitude modulated (AM) image obtained from the same rf data. It is concluded that three different PD images can be derived: AM dominated (ZCS, ASS), mixed AM-PD (ASW) and pure PD (UWP) images. Some preliminary conclusions regarding the potential of PD imaging for medical diagnostics were drawn. These conclusions were based on quantitative 1st order statistics and on a qualitative assessment of 2nd order statistics of the PD image texture.
Optimization of the Lateral Resolution of a Transducer
Authors: Salomonsson Göran , Mandersson Bengt
Published: March 2013

This paper deals with the problem of optimizing the lateral resolution with respect to the velocity distribution of the transducer surface. In order to determine the acoustic field, the transducer is divided into circular annuli with a predetermined shape of the velocity distribution. The acoustic field from the transducer is a weighted sum of the fields from the annuli. The lateral resolution is optimized with respect to these weights. Examples are given to illustrate the method.
A Wavefield Extrapolation Method for Simulating B-Scan Images
Authors: Finette S.
Published: March 2013

We describe an algorithm which improves the efficiency of simulations of B-scan images involving water path acoustical imaging systems. The method is a hybrid approach in which Rayleigh-Sommerfeld diffraction theory is used to extrapolate the propagated part of the acoustic pressure field back to the transducer while the scattered field produced by the tissue is obtained using a time-domain scattering algorithm. Considerable savings in both CPU time and array storage are achieved by elimination of discrete time updates on the computational grid between the source and the tissue.
Dependence of Ultrasonic Nonlinear Parameter B/A on Fat
Authors: Errabolu R. L. , Sehgal C. M. , Greenleaf J. F.
Published: March 2013

This study deals with the relationship between the magnitude of acoustic nonlinearity, sound speed of tissues and the amount of fat present in them. A two-component model, i.e., nonfat and fat, has been assumed and equations that relate the nonlinear parameter (B/A) of a medium to the properties of its components have been derived for two cases. In the first case, the density and sound speed are the same for the two components; B/A is a linear function of fat concentration. To represent this case, mixtures of egg white and yolk were studied. Even though the differences in density and sound speed of the two egg components were within 1 percent of each other, B/A showed a deviation from linearity. In the second case, i.e., when the density and sound speed of the two components are not equal, a quadratic equation has been derived using mixture laws. Livers, fats, egg mixtures, and oil data were used to represent this case. B/A increased quadratically with fat concentration. The presence of proteins on the binary aqueous/fat mixtures modified the quadratic rule.
Ultrasonography for Fetal Weight Estimation: The Birnholz Equation
Authors: Acker David B. , Sachs Benjamin P. , Ransil Bernard J. , Friedman Emanuel A.
Published: March 2013

In the population of 563 normal live births, subject to the selection criteria of this study, the mean ultrasonographically-estimated fetal weight calculated using the Birnholz equation accurately predicts the mean true birth weight with less than 1 percent error. However, on a pairwise basis, the error was found to be systematic (rather than random) with a large standard error of the estimate (± 300 g). The equation consistently underestimated the mean birth weight between 1500–3750 g and consistently overestimated it thereafter.
Digital Simulation of Pulsed Ultrasonic Waveforms
Authors: Barber Frank E. , Goodsitt Mitchell M.
Published: March 2013

When modeling or simulating an ultrasonic pulse-echo system it is necessary to know the transducer waveforms that are the input to the system. In general, accurate transducer modeling is complex and waveform calculation is computationally intensive. Because of this, investigators often assume these waveforms to be simple sinusoids, modulated by Gaussian or exponential envelopes. However, these latter type pulses do not properly represent the complex resoponse of modern piezoelectric transducers. In this paper, a simple set of equations is presented which can approximate the behavior of a number of common transducer configurations. In the first step of the procedure, a simple but accurate model is employed to calculate the step responses of quarter-wave-matched and backed piezoelectric transducers, assuming open circuit conditions. Effects of electrical terminations and transmit/receive bandwidth limitations are accounted for, approximately, by cascaded filtering. Emitted pressure waveforms and echo voltage waveforms synthesized by this simple procedure are very similar to measured waveforms from real transducers. Under most conditions, the method is only an approximation because the model erroneously assumes isolation between the electrical and acoustic networks. However, under many conditions the model is sufficiently accurate to predict actual transducer performance.
Deviations from Rayleigh Statistics in Ultrasonic Speckle
Authors: Tuthill T.A. , Sperry R.H. , Parker K.J.
Published: March 2013

The statistics of speckle patterns in ultrasound images have potential for tissue characterization. In “fully developed speckle” from many random scatterers, the amplitude is widely recognized as possessing a Rayleigh distribution. This study examines how scattering populations and signal processing can produce non-Rayleigh distributions. The first order speckle statistics are shown to depend on random scatterer density and the amplitude and spacing of added periodic scatterers. Envelope detection, amplifier compression, and signal bandwidth are also shown to cause distinct changes in the Signal distribution.
Computation of Local Directivity, Speed of Sound and Attenuation from Ultrasonic Reflection Tomography Data
Authors: Bartelt H.
Published: March 2013

Ultrasound reflection tomography based on the compound scan principle, allows one to produce reflectivity images with high quality and reproducibility. In this paper, methods are discussed on how to extract additional physical parameters from the same set of reflection data for medical applications. Experimental results from a phantom object and in-vivo measurements illustrate the capabilities of such tomographic reflection Systems.
Elimination of Diffraction Error in Acoustic Attenuation Estimation via Axial Beam Translation
Authors: Ophir J. , Mehta D.
Published: March 2013

Optimized wideband attenuation estimations were performed on a tissue mimicking phantom in a water tank with and without axial beam translation (ABT), and the results were compared to those from standard substitution measurements. A −17 percent discrepancy between the results of the substitution method and the optimized estimation without ABT was noted in the far field. This discrepancy was eliminated when ABT was utilized.
Gray Level Transforms and Lesion Detectability in Echographic Images
Authors: Thijssen J.M. , Oosterveld B.J. , Wagner R.F.
Published: March 2013

In search of the optimal display of echographic information for the detection of focal lesions, a systematic study was performed considering a wide range of gray level transforms (i.e., lookup tables). This range comprised power functions of the echo envelope signal (1/8 ≤ n ≤ 8), power functions of the logarithmic transform and a sigmoid function. The implications of the transforms on the first order statistics (histogram, “point signal-to-noise ratio” SNRp) and on the second order statistics (autocorrelation function) could be derived both analytically, and from the analysis of simulated and experimentally obtained echograms of homogeneously scattering tissue models. These results were employed to estimate the lesion signal-to-noise ratio SNRQ, which specifies the detectability of a lesion by an ideal observer. It was found, both theoretically and practically, that the intensity display corresponds to the optimal transform (i.e., n=2) for a low contrast lesion. When the data were first logarithmically compressed, the lesion SNR appeared to increase with increasing power (1/8 ≤ n ≤ 8). A logarithmic transform followed by a sigmoid compression did not produce much improvement. These effects of gray level transforms on the SNRQ were shown to be relatively small, with the exception of powers n > 2 when applied to linear (i.e. amplitude) data. In the case of high lesion contrast, the sequence of log compression, followed by a square law produced the optimum SNRQ. This sequence is equivalent to the processing within echographic equipment, where the TV monitor has a gamma of the order of 2.
A Ray Tracing Method for Calculating the Speed of Sound in a Nonparallel Layered Model Using Pulse Echo Ultrasound
Authors: Lockwood G. R. , Foster F. S. , Hunt J. W.
Published: March 2013

A method of calculating the speed of sound in a nonparallel layered model is presented. A focussed ultrasound source and receiver are used to locate the angle and position of an incident pulse and the reflected pulses at the surface of the model. Triangulation is used to calculate the speed of sound in the first layer and points on the first interface for a number of source positions and angles. For subsequent layers, ray tracing is used to eliminate the effect of the overlying layers. A computer simulation in which images of the speed of sound are reconstructed from data generated by ray tracing through two models is presented. Ways in which this method could be implemented are proposed.
Bias and Variance in the Estimate of the Doppler Frequency Induced by a Wall Motion Filter
Authors: Willemetz J.C. , Nowicki A. , Meister J.J. , De Palma F. , Pante G.
Published: March 2013

In pulsed Doppler flowmeters, processing of the Doppler signals is often done digitally. The first step in the analysis of the echoes is the filtering which is needed to remove stationary components and low frequency shifts induced by wall motion. This preliminary step is of utmost importance. The influence of uncorrelated noise on the measurement of Doppler signals at the input of this filter is analysed. The frequencies of the Doppler signals are extracted by an algorithm based on correlation techniques. We observed that the filter induces a correlated noise term, which results in an overestimation of the frequency. An effect similar to frequency aliasing may appear. The level of the bias is dependent on filter characteristics and noise level. Our study was carried out on simulated Doppler signals using first and second order filters. An especially desirable solution in flow mapping is proposed in order to decrease this error.
Quasi-Paraxial Acoustic Field Approximation for Phased Arrays
Authors: Peng Ke-Ou , de la Fonteijne Marcel R.
Published: March 2013

The quasi-paraxial theory for phased arrays presented here can be used to estimate and analyze the acoustic field in the focal plane for a large scanning angle. The transient acoustic field is considered as the product of two terms that describe the time characteristics of the acoustic vibration over the array and the geometrical characteristics of the array, respectively. This method requires little computation time. The influence of special element shapes and functions that modulate the amplitude of the element vibration on the field distribution is also investigated.
A New Digital Phased Array System for Dynamic Focusing and Steering with Reduced Sampling Rate
Authors: Song Tai K. , Park Song B.
Published: March 2013

In order to enhance the resolution of the ultrasonic B-mode image, digital techniques for dynamic focusing and steering have been receiving a great deal of attention for a long time. In this paper, we present the theory and preliminary experimental results for a new architecture of a fully digital B-mode imaging system with this desired feature. The system employs the Pipelined-Sampled-Delay-Focusing (PSDF) scheme to eliminate the bulky memory addressing and interpolation circuits which are needed in conventional digital imaging systems. To reduce hardware requirements and the bandwidth required for digital processings, we describe an efficient method to generate the sampling clocks for dynamic focusing and steering and some modified bandwidth sampling techniques to reduce the sampling rate for signal digitization. Using these methods, it is possible to achieve dynamic focusing and steering in real-time sector imaging using a linear phased array.
Parametric Ultrasound Imaging from Backscatter Coefficient Measurements: Image Formation and Interpretation
Authors: Insana Michael F. , Hall Timothy J.
Published: March 2013

A broadband method for measuring backscatter coefficients σ b and other acoustic parameters is described. From the σ b measurements, using a commercially-available imaging system, four high-resolution parametric ultrasound images are formed in a C-scan image plane. Scatterer size images are computed from the frequency dependence of σ b and a correlation model function that describes the structure and elastic properties of the medium. Scattering strength images are computed from the absolute magnitude of σ b. Chi-square images are generated to display how well the correlation model represents the interrogated medium. Integrated backscatter coefficient images are formed over the transducer bandwidth. All four images are generated simultaneously and compared with the corresponding B-mode image. Test samples with known physical properties were used to demonstrate experimentally that accurate parametric images are possible if an accurate correlation model is used. Local variations in attenuation, the center frequency and bandwidth of the transducer, and the distribution of scatterer sizes greatly influence the accuracy of estimates and the appearance of the image, thus demonstrating the importance of these factors in parametric image interpretation.
Ultrasonic Differentiation of Intraocular Melanomas: Parameters and Estimation Methods
Authors: Romijn R.L. , Thijssen J.M. , Oosterveld B.J. , Verbeek A.M.
Published: March 2013

In this study, the estimation of ultrasound parameters is evaluated for in vivo differentiation of intraocular melanomas. For this purpose, both tissue and image parameters of the ultrasound signal are considered. These parameters comprised, respectively, the frequency dependent attenuation and backscattering coefficient of the melanoma tissue, and the first and second-order statistics of the amplitude-modulated and phase-derivative images of the melanomas.

A diffraction correction procedure has been applied prior to the estimation of the parameters to correct the ultrasound signals for the echographic equipment used and for the various distances of the region-of-interest to the transducer. In addition, a preprocessing to select a homogeneous region from the tumours was implemented to obtain consistent estimates of the ultrasound parameters, because the accuracy and the precision of the parameters would be greatly reduced by the inhomogeneity of the melanoma tissue.

The estimation methods are evaluated by means of the accuracy and precision of the parameters estimated from simulated ultrasound data and data obtained from a tissue-mimicking phantom. The mutual correlations of the parameters are discussed for the ultrasound data obtained from the melanomas.

This study enabled a preselection of the indepedent ultrasound parameters that could be used in a discriminant analysis to perform a differentiation of intraocular melanomas. The sensitivity and specificity of differentiating spindle cell type from mixed-epitheloid meleanomas were 92 and 89 percent, respectively.
Experimental Evaluation of the Correlation Interpolation Technique to Measure Regional Tissue Velocity
Authors: de Jong P.G.M. , Arts T. , Hoeks A.P.G. , Reneman R.S.
Published: March 2013

A newly developed correlation interpolation method to measure the regional velocity of moving tissue is evaluated in an experimental setup. Pulsed ultrasound echo signals (center frequency 3.5 MHz) are received from a rotating Agar disk containing scattering particles. When averaging over a depth range of 2.2 mm at a pulse repetition frequency (PRF) of 930 Hz, the standard deviation of the measured displacement between 2 successive pulses was found to be ±6 μm. In a second series of experiments, the angular velocity of the disk is estimated from the displacement, as measured simultaneously in two different regions located on separate echo lines (PRF = 465 Hz per line). The exact position of both regions in respect to the center of rotation was found to be irrelevant. The accuracy of the calculated angular velocity was found to be better for large angles between the two lines of observation than for small angles.
Potential and Limitations of Angle-Independent Flow Detection Algorithms Using Radio-Frequency and Detected Echo Signals
Authors: Ramamurthy Bhaskar S. , Trahey Gregg E.
Published: March 2013

New techniques to estimate local blood and tissue velocities have been developed by several groups, including our own. The performance of these techniques is ultimately limited by the characteristics of ultrasonic imaging systems that determine the second-order statistics of speckle. These statistical parameters vary widely depending on the dimension of analysis in the image plane (lateral or axial) and on the echo input signal (radio-frequency or detected data). We use experiments and theory to examine these factors and describe their impact on the performance of our correlation-based technique for angle-independent tracking of blood or tissue motion. The results indicate that the second-order statistics determine the performance of our correlation-based algorithm and can be used to predict the performance of other angle-independent flow detection techniques.
A Single Transducer Transaxial Compression Technique for the Estimation of Sound Speed in Biological Tissues
Authors: Ophir J. , Moriya T. , Yazdi Y.
Published: March 2013

In this paper we report an extension to the TACT method for the estimation of sound speed with a single transducer to any depth. This method is based on the hypothesis that the displacement of the tissue caused by transaxial compression follows a theoretical function which we derive analytically. In this method, as in the original TACT, a transducer imparts an accurate transaxial compression to the tissue, and the corresponding change in the arrival time of an echo at a range of interest is measured. This procedure results in a biased speed estimate whose value is range dependent. The theoretical function is fitted to the experimental estimates, from which the unbiased sound speed is then computed.
Apparatus for Ultrasound Tissue Characterization of Excised Specimens
Authors: Arditi M. , Edmonds P. D. , Jensen J. F. , Mortensen C. L. , Ross W. C. , Schattner P. , Stephens D. N. , Vinzant W.
Published: March 2013

Apparatus is described for measurement of sound speed and ultrasound attenuation coefficients by the substitution technique in the frequency range 3 to 8 MHz. Phase-cancellation artifacts leading to overestimation of attenuation coefficients are avoided by use of an acoustoelectric transducer. Specimens confined by polystyrene windows can be interrogated by focused ultrasound beams at selected locations spaced on a grid of 3 × 3 mm voxels. Pulse time of flight is measured with an accuracy of 30 ns, yielding sound speeds accurate to ±6.7 m/s, for samples 10 mm thick. Uncertainties in measured insertion losses range from 0.1 dB in low-loss (10 dB) specimens to 0.5 dB in high-loss (25 dB) specimens.
Deconvolution of Ultrasound Images
Authors: Jensen Jørgen Arendt
Published: March 2013

Based on physical models, it is indicated that the received pressure field in ultrasound B-mode images can be described by a convolution between a tissue reflection signal and the emitted pressure field. This result is used in a description of current image formation and in formulating a new processing scheme. The suggested estimator can take into account the dispersive attenuation, the temporal and spatial variation of the pulse, and the change in reflection strength and signal-to-noise ratio. Details of the algorithm and the estimation of parameters to be used are given. The performance is indicated by two examples. One is for a synthetic signal and the other is for data measured from a tissue mimicking phantom. The last example shows a finer speckle pattern, giving an increased resolution.
Reconstruction of the Acoustical Impedance Profile of a Multilayer Medium
Authors: Lifshitz Ilan , Pedersen Peder C. , Lewin Peter A.
Published: March 2013

The recovery of the acoustical reflectivity function and impedance profile of a layered medium from bandlimited and noisy pulse-echo ultrasonic data is considered. The effects of the transducer and the noise are reduced using Wiener filtering. With further signal processing and a priori knowledge of the attenuation and the velocity profiles, the compensated coefficients of the reflectivity function and the impedance profile are recovered. The reconstruction techniques are presented analytically, and are also evaluated in an experimental setup composed of a conventional pulse echo system, a data acquisition and a data processing system. Under experimental conditions, the RMS errors in the estimation of the compensated acoustical discrete impedance profile were within 3% of the calculated values.
Nonperturbative Diffraction Tomography via Gauss-Newton Iteration Applied to the Scattering Integral Equation
Authors: Borup D. T. , Johnson S. A. , Kim W. W. , Berggren M. J.
Published: March 2013

A nonperturbational inverse scattering solution for the scattering integral equation (SIE) is presented. The numerical discretization of the SIE is performed by the moment method (MM) using sine basis functions. Previous algorithms using the alternating variable (AV) nonlinear iteration with algebraic reconstruction technique (ART) solution of the linearizations are shown to diverge for high contrast/large size acoustic scatterers. This deficiency is alleviated by the use of the Gauss-Newton (GN) nonlinear iteration with conjugate gradient (CG) solution of the linearizations. Further numerical efficiency is attained by use of the biconjugate gradient (BCG) algorithm to solve the forward scattering problems. Test problem reconstructions of circular cylinders, using the Bessel series analytic solution to generate the scattering data, demonstrate the accuracy of the method. Inhomogeneous models of human cross-sections verify the high spatial resolution and high speed of sound contrast capability of the method.
Ultrasonic Characterization of Mycelial Morphology as a Fractal Structure
Authors: Patankar Dhananjay , Oolman Timothy , Johnson Steven , Berggren Michael
Published: March 2013

Preliminary measurements of scattering of ultrasound from filamentous microorganisms in aqueous-medium suspensions are reported. The data are used to characterize the structuring (morphology) between the organisms quantitatively by modelling the morphology in terms of fractal structures and obtaining the fractal dimension as the characteristic parameter. The fractal dimension is calculated from the slope of a log-log plot of scattered intensity versus the scattering vector magnitude. The intensity is measured over a range of magnitudes of the scattering vector by varying the scattering angle as well as the ultrasonic frequency. Results from microbial suspensions of different species and different morphologies indicate that the fractal dimension can be used to quantify the morphological state of a suspension. The fractal dimension ranges from around 1.5 for suspensions with pelletous morphology to around 2.5 for suspensions with filamentous morphology.
Microscopic Mechanism of Attenuation of Compressional Ultrasonic Waves in Tissue-Mimicking Phantom Materials
Authors: Wu Ed X. , Goodsitt Mitchell M. , Madsen Ernest L.
Published: March 2013

An investigation was performed to determine whether the sound-attenuation-in-suspensions theory of Allegra and Hawley can be used to explain the compressional (longitudinal wave) attenuation of ultrasonically tissue-mimicking materials commonly used in phantoms for testing the performance of medical ultrasound systems. These materials are composed of microscopic graphite particles suspended in a gel. The theory was first tested using materials containing spherical glass beads instead of graphite particles because these materials more closely fit the geometric conditions assumed in the theory. For the glass bead type materials as well as the graphite particle type materials, the attenuation coefficients predicted using the Allegra and Hawley model agreed rather well with experimental measurements over the diagnostic frequency range.