bluuebunny/crossref_metadata_2025 huggingface dataset:
Improvements in the Spectral Difference Method for Measuring Ultrasonic Attenuation
Authors: Insana Michael , Zagzebski James , Madsen Ernest
Published: March 2013

The accuracy of the spectral difference method for measuring ultrasonic attenuation has been investigated using tissue-mimicking phantoms. Attenuation coefficients of the phantom materials were measured using a narrow-band substitution technique and compared with the results of the spectral difference method. Agreement within ±10 percent was typical for measurements in homogeneous materials. The best agreement between the spectral difference and substitution techniques was obtained when effects due to transducer beam diffraction were taken into account in the analysis. This was found for two types of homogeneous tissue-mimicking materials, both having speed of sound and attenuation properties similar to human liver but each with different backscatter properties. The effects of inhomogeneous tissues interposed between the transducer and the interrogated volume were also studied by simulating these conditions in phantoms. Experimental techniques which minimize the effects of perturbations introduced by these inhomogeneities are suggested.
Classification of Scattering Objects by Regular Arrays of Scatterers Using Fourier Analysis
Authors: Koch Ingeborg
Published: March 2013

For a class of scattering objects the mean separation between the scatterers is determined. Over a range of frequencies, ultrasonic back-scattered pressure signals are recorded. It is suggested to derive the mean spacing of an unknown scattering object by employing Fourier analysis and comparing the signal with signals from known regular arrays of scatterers. In a computer simulation it is shown that this approach determines the mean spacing very well for random arrays consisting of three-dimensional spherical scatterers.
Lateral Deconvolution of Ultrasonic Beams
Authors: Robinson D. E. , Wing M.
Published: March 2013

A number of papers have appeared recently describing methods of lateral resolution improvement in ultrasonic images by deconvolution of the amplitude detected cross-beam characteristic. It is the intention of this paper to demonstrate that such methods of resolution improvement are appropriate only for a limited class of targets. In general, the effect of interference between the r.f. signals from multiple targets at differing distances is such that the amplitude beam width obtained for these targets cannot be considered as the linear combination of shifted replicas of the amplitude beam width for an individual target. This is a consequence of the non-linear character of the detection process. In these cases the method of deconvolving the detected responses, although capable of giving reduced spot sizes, makes errors in the position of the images and is susceptible to false images and sidelobes. The phenomenon is demonstrated with computer and experimental data on point targets.
Scattering of Ultrasound by Tissues
Authors: Sehgal Chandra M. , Greenleaf James F.
Published: March 2013

Scattering of ultrasound by biological tissues (continuous-inhomogeneous media) is discussed. An analytical expression for the attenuation due to scattering (αTSC) and backscatter coefficients (σT) of tissues are obtained. The results explain the variation of (αTSC) and σT with frequency for a number of tissues. The study also provides two statistical parameters, velocity fluctuation coefficient and correlation length, in terms of which the scattering of tissues can be defined quantitatively.
Simultaneous Algebraic Reconstruction Technique (SART): A Superior Implementation of the Art Algorithm
Authors: Andersen A. H. , Kak A. C.
Published: March 2013

In this paper we have discussed what appears to be a superior implementation of the Algebraic Reconstruction Technique (ART). The method is based on 1) simultaneous application of the error correction terms as computed by ART for all rays in a given projection; 2) longitudinal weighting of the correction terms back-distributed along the rays; and 3) using bilinear elements for discrete approximation to the ray integrals of a continuous image. Since this implementation generates a good reconstruction in only one iteration, it also appears to have a computational advantage over the more traditional implementation of ART. Potential applications of this implementation include image reconstruction in conjunction with ray tracing for ultrasound and microwave tomography in which the curved nature of the rays leads to a non-uniform ray density across the image.
Attenuation of Ultrasound in Normal Liver and Diffuse Liver Disease in Vivo
Authors: Maklad N. F. , Ophir J. , Balsara V.
Published: March 2013

Preliminary results of in vivo attenuation measurements of the liver have been obtained in 39 normal patients and in 35 patients with diffuse liver disease. A modified real-time sector scanner incorporating an online attenuation measurement method was used. The value of attenuation in normal liver was estimated as 0.52 ± 0.03 dB/cm/MHz, measured at 3 MHz. Significantly higher attenuation values were obtained from patients with alcoholic and cardiac cirrhosis, and following hepatic artery infusion with chemotherapeutic agents. Lower values were obtained from patients with biliary cirrhosis, chronic active hepatitis, and diffuse infiltration by lymphoma or leukemia. Fatty infiltrated livers showed a wide range of values of 0.37 − 0.66 dB/cm/MHz. The results suggest that estimates of attenuation coefficients are useful in detecting the presence of diffuse liver disease.
Estimation of the Slope of the Acoustic Attenuation Coefficient
Authors: Shaffer Shmuel , Pettibone D. W. , Havlice J. F. , Nassi M.
Published: March 2013

In this paper, a theoretical framework is developed which removes the Gaussian assumption commonly used in ultrasonic attenuation estimation based on mean frequency shift. The theory is developed for general non-Gaussian spectra and for media whose attenuation coefficient is nonlinear with frequency. Then, a linear approximation in the estimation of the attenuation coefficient's slope is examined. It is shown that the error due to the linear approximation is negligibly small.
Lateral Filtering of Medical Ultrasonic B-Scans before Image Generation
Authors: Vaknine R. , Lorenz W.J.
Published: March 2013

A method is presented for improving the lateral resolution of diagnostic B-scan images. Wiener filtering is applied on sequences of A-scan echo amplitudes acquired during B-scanning, using a simple scanning action. The first applications to clinical B-scan data show an improvement in the image quality. The filtered images obtained by this technique may provide an improvement in the performance of pattern recognition methods on medical ultrasonic image data.
Ultrasound Speckle Size and Lesion Signal to Noise Ratio: Verification of Theory
Authors: Smith S.W. , Wagner R.F.
Published: March 2013

We compare predictions from our published theory of speckle cell size with recently published experimental results and a three dimensional computer simulation for the case of Gaussian pulses from spherically focused transducers in random media. The agreement is very good. We also compare our published theoretical predictions of the signal-to-noise ratio for a circular lesion in a speckle background with published “contrast to speckle ratio” data for anechoic cylindrical lesions in tissue mimicking material. Again, agreement is very good. The verification of these theoretical predictions has important implications for the evaluation of B-scan image quality and the study of tissue characterization.
Analysis of Random Backscatter in the Presence of Static Reflection Components
Authors: Rhyne T. L. , Sagar K. B.
Published: March 2013

The problem of analysis of random ultrasonic backscatter is treated using linear time-varying channel theory. The backscatter is modeled to have random and deterministic echo components, where the emphasis is on the estimation of the random component in the presence of the deterministic component. A tissue characterizing mechanism is modeled as the range correlation of the random backscatter component, which gives rise to a frequency signature function. Finally, the statistics of the resulting backscatter are given as non-central Chi Squared.
The Ultrasound Macroscope: Initial Studies of Breast Tissue
Authors: Foster F.S. , Strban M. , Austin G.
Published: March 2013

A system called the ultrasound macroscope has been developed to measure the ultrasonic properties of tissues. Based on the concept of the scanning acoustic microscope, it is capable of generating quantitative images of ultrasound velocity, attenuation and backscatter for macroscopic slices of tissue. By maintaining high resolution (∼ 120 μm at 13 MHz) the morphology of complex tissues is well delineated. Data from regions of interest in the tissue are transformed into three dimensional probability distributions representative of the tissue's ultrasonic characteristics. Sets of two dimensional projections of these distributions are used to display the information. As an initial study, the properties of breast tissues are analyzed. Examples of both normal and abnormal pathology are presented and the relevance of the results to clinical imaging are discussed.
Beam Pattern (Diffraction) Correction for Ultrasonic Attenuation Measurement
Authors: Robinson D.E. , Wilson L.S. , Bianchi T.
Published: March 2013

The measurement of tissue attenuation from pulse-echo data has been widely investigated. This paper examines correction of the measurements for the effect of the transducer beam. Computer and experimental studies are performed on a number of reflectors including smooth and rough planes, ideal point scatterers, T.M. material and liver and spleen tissue. It is shown that the corrections obtained from T.M. phantom material differ from those obtained using in vivo tissue as the reflector and corrections for liver and spleen differ markedly. Comment is made on the possibility of using “beam correction” itself as a tissue characterization parameter.
Signal-to-Noise Ratio and Bandwidth for Pseudo-Random Codes in an Ultrasonic Imaging System
Authors: Kim Won K. , Park Song B. , Johnson Steven A.
Published: March 2013

Signal-to-noise ratio and image resolution in an ultrasonic imaging system are compared for four kinds of excitation signals, namely, a single pulse, an unmodulated pseudo-random code, a modulated pseudorandom code and a deconvolved pseudo-random code, all for a given length and amplitude. It was predicted and found from measurements that the best S/N and resolution are obtainable with the deconvolved pseudorandom code.
Attenuation Estimation in Reflection: Progress and Prospects
Authors: Ophir J. , Shawker T. H. , Maklad N. F. , Miller J. G. , Flax S. W. , Narayana P. A. , Jones J. P.
Published: March 2013

This monograph presents a tutorial review of the current state-of-the-art in ultrasonic attenuation estimation in reflection. Clinical indications which provide the motivation for attempting in vivo attenuation estimation are discussed. Frequency and time domain techniques and their respective tradeoffs and problems are presented. Finally, current clinical results obtained with the various techniques are summarized and further areas of study are suggested.
Ultrasound Attenuation Measurements of the Liver in Vivo Using a Commercial Sector Scanner
Authors: Garra Brian S. , Shawker Thomas H. , Nassi Menahem , Russell Mary Ann
Published: March 2013

Attenuation measurements of various tissue minicking phantoms and three different groups of patients were obtained using a modified commercial sector scanner. Estimates of attenuation were made using the spectral shift method with mean frequencies at different depths of a region of interest being obtained by both zero crossing and fast Fourier transform techniques. The accuracy and precision of both techiques was compared in phantoms and it was found that the FFT technique yielded less day-to-day variation (SD=3 percent) than the zero crossing technique (5 percent). For larger regions of interest, the range of variation in both techniques was more similar. Day-to-day variation in livers of normal patients was much larger than that seen in phantoms (10 to 15 percent) suggesting that in vivo measurements may be less precise due to actual daily changes in patients' livers. Attenuation estimates of phantoms were high by approximately 0.16 dB/Mllz/cm compared to values obtained by transmission techniques. The attenuation values of livers in a group of 31 normal patients ranged from 0.214 dB/cm/MHz to 0.849 dB/cm/MHz with a mean of 0.627 ± 0.126 dB/cm/MHz for the zero crossing technique while the mean value using the FFT technique was 0.86 ± 0.168 dB/cm/MHz. A group of 26 Gauchers disease patients also showed wide variation with a mean attenuation value of 0.768 ± 0.21 dB/cm/MHz using the FFT technique. This was significantly different than that of the normal group (p<.05). Also, a group of 22 chronic B hepatitis patients was examined, having a mean attenuation value of 0.823 ± 0.21 dB/cm/MHz, not significantly different from those of the normal patients. Highly significant differences were found between the three groups when the power spectrum bandwidths of signals received were compared. These differences may be due to differences in the dependence of attenuation as a function of frequency between the groups and may represent a useful tissue characterization parameter.
Range Resolution Improvement by a Fast Deconvolution Method
Authors: Demoment G. , Reynaud R. , Herment A.
Published: March 2013

Range resolution improvement in ultrasonic echography is considered as an estimation problem which is solved using a new fast minimum variance de-convolution algorithm specially designed for a microprocessor-based on-line processing. This method is used to accurately study the lenses and fundus of the eye and to follow variations of an arterial wall thickness during the cardiac cycle.
An Analytical Study of Doppler Ultrasound Systems
Authors: Azimi Mani , Kak A. C.
Published: March 2013

The past theoretical contributions in Doppler ultrasonic imaging have borrowed heavily from the electromagnetic case. In these contributions, most points of departure between the ultrasonic and electromagnetic cases were taken care of by heuristic incorporation of factors in the derived formulas. A theory is presented that is more complete in the sense that it specifically accounts for the diffracted fields of the transducer aperture (assumed to be a source of a Gaussian focussed beam), the interaction of these fields with the scattering sites, and the interaction of the transducer aperture with the back scattered fields. The theoretical formulation was used to perform a series of computer simulation studies on Doppler ultrasound. The control afforded by the theory over different parameters of the system has allowed us to study the effect of the different signal bandwidths, tissue attenuation constants, and the role of transducer design in the ultrasound Doppler systems.
Nonlinear Parameter Tomography System Using Counterpropagating Probe and Pump Waves
Authors: Sato Takuso , Fukusima Akira , Ichida Nobuyuki , Ishikawa Hiroyuki , Miwa Hirohide , Igarashi Yutaka , Shimura Takaki , Murakami Keiichi
Published: March 2013

In this paper, a novel tomographic system for imaging the nonlinear parameter (B/A) of biological objects is described. This parameter is closely related to the detailed properties of tissue, and may well provide a new powerful tool for ultrasonic tissue characterization.

In our new system, an impulsive, relatively high power (10 mW/cm2), low frequency pump wave is applied from the opposite direction of a cw low intensity probe wave of high frequency (5 MHz) so that the phase of the probe wave is modulated sequentially by the product of the nonlinear parameter (B/A) along the beam (x axis) and the pressure of the impulsive pump wave. This modulated probe wave is detected and demodulated to derive the distribution of (B/A) along the x axis. Many responses are averaged to increase the S/N ratio. Inverse or other filtering operations are applied to widen the frequency bandwidth of the pump wave. The entire system is realized in hardware. The counterbeam orientation makes the imaging system compact, with easy access to many parts of the human body. Its resolution is two times that of the perpendicular system proposed previously by us and the attenuation of the pump wave can also be compensated for easily.

A practical system aimed at breast and liver diagnosis is described. The principle of the method and the system construction are described. B/A images of several objects are given.
Attenuation Estimation with the Zero-Crossing Technique: Phantom Studies
Authors: Ophir J. , Ghouse M. A. , Ferrari L. A.
Published: March 2013

Global and local attenuation coefficient estimations were performed in a phantom using a pulse echo method based on the rate of decay of zero crossing density. Focussed and unfocussed 3.5 MHz transducers were used. It was found that good global estimates could be made with either transducer over a 2:1 range of attenuation coefficient. Local estimates exhibit large bias errors and a high degree of variability. This variability diminishes in the focal zone of the focussed transducer and in the far field of the unfocussed transducer.
Estimation of Scatterer Volume Density near a Concentration Gradient
Authors: Newhouse V.L. , Amir Israel
Published: March 2013

A general formulation of the echo received from a random scatterer ensemble illuminated by a short electromagnetic or sonic signal is developed. It is shown theoretically and confirmed experimentally with ultrasound, that a gradient in scatterer density will return an echo which is partially spatially coherent (i.e. specular). The surface of a random ensemble of uniform scatterers is shown to produce an echo from whose degree of coherence, the scatterer density and cross section can be calculated.
Prior Inverse Filtering for the Improvement of Axial Resolution
Authors: Kim Jin H. , Lee Bum S. , Park Song B.
Published: March 2013

A prior inverse filtering technique is applied to improve the axial resolution in ultrasonic imaging. The ultrasound transducer is excited by a synthesized signal corresponding to the impulse response of the inverse filter. The diffraction effects of the transducer and the observed scatterer, which limit the performance of the inverse filter, are examined experimentally as well as theoretically. Using a B-scan image of a tissue-equivalent phantom, we demonstrate the possibility of applying the prior inverse filtering method to improve medical ultrasound images.
Ultrasonic Reflex Transmission Imaging
Authors: Green Philip S. , Arditi Marcel
Published: March 2013

Reflex Transmission Imaging (RTI) is a new imaging method by which orthographic transmission images can be made using augmented B-mode equipment. Conventional transmission imaging requires acoustic coupling to large areas on both sides of the body, whereas RTI can be performed from one side with a single, small transducer probe. In this mode, transmission images in a plane normal to the beam are made by integrating the reverberations from beyond the focal zone of the transducer. These reverberations provide, in essence, a source of incoherent insonification from behind the focal plane.

Preliminary in-vitro images have been made using a computer-interfaced rectilinear scanner with a 1-inch diameter f/2.8 transducer. The images have good resolution and signal-to-noise ratio, and a short depth-of-field. Backscatterer inhomogeneity is well smoothed.

Transmission images provide information that is complementary to B-scans. RTI will allow both to be made with the same instrument and presented on the same display. A time-gated reflection C-scan could be generated simultaneously. Other RTI modes, including an attenuation B-mode, also are discussed.
Specular Reflector Noise: Effect and Correction for in Vivo Attenuation Estimation
Authors: Laugier P. , Berger G. , Fink M. , Perrin J.
Published: March 2013

After reviewing the usual models proposed for the echo-graphic response of soft tissues, we discuss the interaction between the ultrasonic wave and large size obstacles. Structures of this size, specular reflectors, can be found in tissues. The influence of such reflectors on in vivo attenuation measurements is detailed. We point out the importance of the specular echo noise originating from two kinds of reflectors: planelike and vessel-like reflectors. We present a complete study of their influence on two different algorithms for attenuation estimates: the spectral centroid shift and the narrow band methods. Results are presented on stimulated data, a tissue-mimicking phantom and in vivo muscle data. Different procedures for minimizing the specular echo noise are also discussed.
Reflection Mode Diffraction Tomography
Authors: Roberts B.A. , Kak A.C.
Published: March 2013

A reconstruction algorithm is presented which possesses a simple scanning geometry and promises higher resolution than conventional transmission mode diffraction tomography algorithms. This broad-band reflection mode algorithm inherently lacks a certain amount of low frequency information but an estimate of the information is recovered by spectral extrapolation. The resolution of the algorithm will be shown to be limited by the bandwidth and physical size of the single plane wave transducer, as well as the Born approximation.
Attenuation Estimation on Phantoms - A Stability Test
Authors: He P. , Greenleaf J. F.
Published: March 2013

Global and local attenuation coefficient estimates were calculated using three methods: the envelope peak method, the central-frequency-downshift method, and the zero-crossing method. The results show that for each method the error of the local estimate with respect to the global estimate is increased as the sample volume is decreased. While the performances of the latter two methods are comparable, the performance of the envelope peak method is significantly superior.
Speckle Reduction in Pulse Echo Imaging Using Phase Insensitive and Phase Sensitive Signal Processing Techniques
Authors: Kerr A.T. , Patterson M.S. , Foster F.S. , Hunt J.W.
Published: March 2013

In conventional B-scan imaging, speckle often distorts the true representation of small structures and lesions and hence reduces the diagnostic potential of the technique. Considerable speckle reduction has been achieved with an f/2.4, cone hybrid system by cutting the large aperture transducers into sectors, and using either phase insensitive sector addition (PISA), phase insensitive sector multiplication (PISM), or an rf multiplicative processing technique. We have compared two modes of operation with the hybrid system. In the first, the cone acts as transmitter, and each sector of the f/2.4 spherical aperture is a receiver. In the second mode, the f/2.4 sphere acts as transmitter, and each sector of the cone is a receiver. Quantitative assessment using the contrast to speckle ratio developed by Patterson et al, indicates that processing under both modes results in reduced speckle noise and improved image quality, with the cone sector receive (rx) geometry offering the greatest improvement.
The Myocardial Signature: Absolute Backscatter, Cyclical Variation, Frequency Variation, and Statistics
Authors: Rhyne T. L. , Sagar K. B. , Wann S. L. , Haasler G.
Published: March 2013

This paper studies the absolute myocardial backscatter as a function of the frequency and phase of the cardiac cycle. This was achieved by calibration of the ultrasonic instrumentation and the random diffraction process. We have discovered a first-order model in which the scattering from the myocardium is Rayleigh scattering with a cardiac cycle variation in the scattering cross section. Furthermore, the statistics are approximately those of a radio frequency waveform with two independent Gaussian components (Rayleigh envelope). Deviations from the first-order model suggest measurable fine structure related to myocardial ultrastructure. This model has profound effects on the choice of optimal radiation patterns and signal processing schemes for preparing diagnostic parameters (e.g., integrated backscatter).
A Quantitative Approach to Speckle Reduction via Frequency Compounding
Authors: Trahey G.E. , Allison J.W. , Smith S.W. , von Ramm O.T.
Published: March 2013

Coherent speckle is a source of image noise in ultrasonic B-mode imaging. The use of multiple imaging frequencies has been suggested as a technique for speckle contrast reduction. This technique involves the averaging of images whose speckle patterns have been modified by a change in the spectrum of the transmitted or received acoustical pulse. We have measured the rate of this speckle pattern change in ultrasonic images as a function of the change in center frequency of the transmitted acoustical pulse. This data is used to quantitatively describe the trade-off of resolution loss versus speckle reduction encountered when frequency compounding is employed and to derive the optimal method of frequency compounding. These results are then used as a basis for describing the overall advisability of frequency compounding in ultrasonic imaging systems. Our analysis indicates that simple frequency compounding is counterproductive in improving image quality.
Pattern Recognition Methods for Optimizing Multivariate Tissue Signatures in Diagnostic Ultrasound
Authors: Insana Michael F. , Wagner Robert F. , Garra Brian S. , Momenan Reza , Shawker Thomas H.
Published: March 2013

Described is a supervised parametric approach to the detection and classification of disease from acoustic data. Statistical pattern recognition techniques are implemented to design the best ultrasonic tissue signature from a set of measurements and for a given task, and to rate its performance in a way that can be compared with other diagnostic tools. In this paper, we considered combinations of four ultrasonic tissue parameters to discriminate, in vivo, between normal liver and chronic active hepatitis. The separation between normal and diseased samples was made by application of the Bayes decision rule for minimum risk which includes the prior probability for the presence of disease and the cost of misclassification. Large differences in classification performance of various tissue parameter combinations were demonstrated using the Hotelling trace criterion (HTC) and receiver operating characteristic (ROC) analysis. The ability of additional measurements to increase or decrease discriminability, even measurements from other diagnostic modalities, can be evaluated directly in this manner.
Simulation of Real-Time Frequency Estimators for Pulsed Doppler Systems
Authors: van Leeuwen G.H. , Hoeks A.P.G. , Reneman R.S.
Published: March 2013

Four time-domain oriented, real-time frequency estimators, based on the detection of phase, zero-crossings, instantaneous frequency or autocorrelation, were simulated on a digital computer and subjected to computer generated Doppler signals, enabling the investigation of the influence of spectral shape, filtering, frequency shift, noise and quantization. Three estimators, the autocorrelator as well as the instantaneous frequency detector and the autocorrelator, both with extended frequency range, appeared to be very accurate. They exhibit a bias in the estimator output of less than 2 percent over a wide frequency range, the former up to nearly the Nyquist frequency, the latter two beyond, even for skew spectra and under poor signal conditions regarding bandwidth and noise.
Optimal Precision in Ultrasound Attenuation Estimation and Application to the Detection of Duchenne Muscular Dystrophy Carriers
Authors: Berger G. , Laugier P. , Fink M. , Perrin J.
Published: March 2013

This paper deals with the measurement of the attenuation of ultrasound in muscle and its application to the detection of Duchenne Muscular Dystrophy (DMD) carriers. The precision obtained when measuring the attenuation is an important parameter to be considered. A statistical approach is taken on simulated data and compared to in vivo results. The results allow discussion for the minimum tissue volume needed for the estimation. Variations in muscle attenuation between normals were obtained from studies on 27 volunteers. These attenuation values were compared to those obtained from 19 carriers of DMD. Attenuation appears to be a potential clinical indicator of DMD carriers.
Modification of Spectra of Pulses from Ultrasonic Transducers by Scatterers in Non-Attenuating and in Attenuating Media
Authors: Round W.H. , Bates R.H.T.
Published: March 2013

When an ultrasonic pulse is scattered off a particle, the spectrum of the scattered pulse differs from that which was transmitted. A mathematical analysis is presented to show that the center frequency of the backscattered pulse is greater than that of the transmitted pulse and that the bandwidth decreases slightly when the spectrum of the pulse is Gaussian in shape. The results of measurements designed to test the theory are presented. The magnitude of the shift in center frequency for pulses backscattered off subwavelength-diameter wires is found to be similar to that predicted by the analysis. It is shown that characteristics of the spectra of the backscattered pulses can differ from those predicted if the shape of the spectrum is not truly Gaussian (as is assumed in most published analyses, including that introduced here). In medical ultrasonic imaging, the pulses are modified by scattering and absorption. The analysis is extended to account for the effects of both interactions. This allows the bandwidth and center frequency of pulses backscattered from tissues and received by medical ultrasonic scanners to be predicted.
Pipelined Sampled-Delay Focusing in Ultrasound Imaging Systems
Authors: Kim Joo Han , Song Tae Kyong , Park Song Bai
Published: March 2013

A sampled-delay focusing technique was recently proposed by the authors which completely eliminates the use of analog L-C delay lines for beam focusing in ultrasound B-mode imaging systems. With this approach, the product of sampling rate and maximum time delay is required to be less than unity. To remove this constraint, we propose in this paper a first-in-first-out pipelining technique. This allows one to perform beam steering and dynamic focusing simultaneously on a resolution-cell basis and in a completely digital fashion without the use Of analog L-C delay lines.
The Practical Significance of Two-Dimensional Deconvolution in Echography
Authors: Jeurens T.J.M. , Somer J.C. , Smeets F.A.M. , Hoeks A.P.G.
Published: March 2013

This paper evaluates deconvolution (inverse filtering) as applied to ultrasonic imaging systems, and discusses the obstacles which are encountered employing the technique in practice. A minicomputer is used to generate artifical echo signals, simulating rf signals resulting from a set of point reflectors in a homogeneous medium, as recorded by an electronically focused group-steered linear array scanner. Two-dimensional deconvolution in combination with a Wiener noise reduction filter (i.e., a Wiener-Inverse filter) is applied to these simulated rf signals, which were contaminated with white noise. The efficacy of the Wiener-Inverse filter is defined in terms of its ability to resolve two point reflectors with a lateral spacing equal to the local −6 dB width of the ultrasonic beam. In favorable circumstances, the targets are resolved at signal-to-noise ratios (SNR) better than 20 dB, where SNR is defined as the maximum signal power divided by the average noise power level. Nonlinear effects due to quantization or signal clipping are investigated. In order to improve the resolution of an rf signal with a dynamic range of 40 dB, the input signal should be digitized at a minimum of 12 bits. The problem of signal clipping can be circumvented by oversampling. The two-dimensional Wiener-Inverse filter is defined in terms of both temporal and spatial properties of the insonification. Effects of wave diffraction give rise to a depth-dependent ultrasonic beam. As a result of a misfit of the Wiener-Inverse filter and the local properties of the ultrasonic beam, erroneous noisy texture arises in the image. Adaptation of the Wiener-Inverse filter with respect to the beam properties gives acceptable results, at the expense of a rather large computational effort.
A Taylor Series Expansion for Time Savings in Accurate Computation of Focused Ultrasound Pressure Fields
Authors: Hall Timothy J. , Madsen Ernest L. , Zagzebski James A.
Published: March 2013

A model for the continuous wave (cw) pressure beam distribution of a focused axially symmetric ultrasonic radiator with constant radius of curvature involves integration of eikr/r over the surface of the radiator. ( k is the complex wave number and r is the distance from a radiating area element to the field point.) A single integral form exists, and it is this form that is expanded in a Taylor series in frequency. Thus, when representing a pulse as a superposition of cw beams, the need to do numerical integrations for each one of a large number of frequencies is eliminated. Accuracy of the truncated Taylor series depends on the coordinates of the field point as well as on the difference between the frequency of interest and the reference frequency. Accuracy criteria for a particular application are also presented. The computer time savings for our applications correspond to a factor of about 60 with accuracy being maintained.
Clinical Sound Speed Measurement in Liver and Spleen

in Vivo
Authors: Chen C.F. , Robinson D.E. , Wilson L.S. , Griffiths K.A. , Manoharan A. , Doust B.D.
Published: March 2013

The paper describes an implementation of clinical sound speed measurement using either a commercial water path scanner or a specially developed dual transducer real time scanner, each interfaced to a general purpose minicomputer for off-line analysis. It describes the examination technique to obtain suitable in vivo clinical data from the liver and the spleen. It develops signal processing methods to achieve clinical confidence in individual measurements. Forty-five liver patients and 46 spleen patients were examined. Sound speed was found to correlate closely with fibrosis content in both the liver and the spleen with an increase in fibrosis resulting in a decrease in sound speed. Sound speed in various pathological conditions are discussed. Clinical results of sequential examinations on patients under treatment are presented and successful monitoring of the disease status is demonstrated. The potential clinical role of sound speed measurement is suggested.
Properties of Acoustical Speckle in the Presence of Phase Aberration Part II: Correlation Lengths
Authors: Smith Stephen W. , Trahey Gregg E. , Hubbard Sylvia M. , Wagner Robert F.
Published: March 2013

In recent years, analysis of the second order statistics of ultrasound speckle has led to accurate prediction and measurements of the average speckle size in the transducer focal zone. In this paper, that work has been extended to the average speckle size as determined by the normalized autocovariance in the presence of transducer phase aberrations. In general, a phase aberration causes a narrowing of the main lobe of the normalized autocovariance in the lateral direction. However, the lateral speckle autocovariance also showed significant side lobes in the presence of phase aberrations, indicating that individual speckles in a region of interest are not independent but are correlated so that less information is present for the task of signal detection when a transducer phase aberration exists. The same evidence of correlated speckle was found in the near field of a transducer in the region of fine speckle texture. This explanation satisfies the quandary of poor detectability in the near field region where the speckle is fine but the lateral resolution is quite degraded. The axial speckle in the presence of phase aberrations showed a small increase in main lobe widths and no evidence of side lobes. Beginning in 1978, the analysis of the second order statistics of speckle images for the purpose of spatial compounding led to accurate measurement and prediction of the cross-correlation curve as a function of transducer aperture translation for purposes of spatial compounding. In this paper, that work has been extended to the presence of transducer phase aberrations. The existence of transducer phase aberrations causes significant increases in the rate of decorrelation of speckle interference patterns as a transducer is translated. This indicates that spatial compounding will result in quite significant improvements in area-wise SNR and low contrast lesion detection for the case of severe random aberrators or focal point errors.
Diffraction Tomography by a Method of Image Projections
Authors: Rouseff Daniel , Tsang Leung , Porter Robert P.
Published: March 2013

A method of three-dimensional diffraction tomography based on image projections is derived. Inversion methods based on projections generally are inaccurate due to the spreading nature of the scattered wave. By backpropagating the field onto a single plane in the image region, diffraction effects are reduced and a projection of the weakly scattering object is generated. Consequently, conventional X-ray inversion techniques may be used to image the object The relationship between the backpropagated field and the projection is derived both for high frequency incident waves and low spatial frequency scatterers. The generalized image kernel allows the use of curved or misaligned recording surfaces. Numerical results are included.
Statistical Relationship between Ultrasound Echo Envelope and Envelope Peak
Authors: He Ping
Published: March 2013

This study shows that the amplitude information of ultrasound echoes is carried mainly by the envelope peaks (EPs). It is first shown that the EPs in an A-line represent the maximum number of independent amplitude data. It is then demonstrated that the entire envelope could be approximately reconstructed from the EPs. Finally, using the echo data from a tissue-mimicking phantom, it is found that there are no significant differences among the attenuation coefficients estimated from the EPs, the original envelope samples, and the reconstructed envelope samples. The results of this study indicate that, in the time domain, the attenuation coefficient can be most efficiently estimated from the envelope peaks.
A Concave Annular Array Design, Based on Phasor Summation — Part I: Design Methodology
Authors: Yuan Weiquan , Johnson Steven A. , Berggren Michael J. , Eidens Richard S.
Published: March 2013

A detailed method for the design of anular arrays based on phasor summation is developed. The net phase shift across each annulus obtained by phasor summation is a very important factor in the design of an annular array, and determines the strength of the signal received. The method presented in this paper allows the designer to evaluate the trade-offs in parameters such as the strength of the signal from each annulus, the efficiency of each annulus, and the depth of focus that would be achievable. A concave annular array has been fabricated according to this design method. A set of graphs are given for an actual design to illustrate how one may readily evaluate these trade-offs.
A Concave Annular Array Design, Based on Phasor Summation — Part II: Beam Profiles and Resultant Images by B-Scan and Synthetic Focus Methods
Authors: Yuan Weiquan , Johnson Steven A. , Berggren Michael J. , Eidens Richard S.
Published: March 2013

A brief review of the synthetic focusing method is given. The theoretical limit of resolution that may be achieved with the synthetic focusing methods is demonstrated using experimental results on a thin thread obtained with an annular array whose design was given in Part I. The advantage of large aperture arrays is illustrated by an in vitro reflection image of a dog artery, made with this array, that has at least four times the spatial resolution of present clinical B-scanners operating in the same frequency range.
High-Resolution, Reflection Mode Tomographic Imaging Part II: Application to Echography
Authors: Herment A. , Guglielmi J.P. , Péronneau P. , Dumée Ph.
Published: March 2013

Principles of high-resolution, ultrasonic imaging using data acquisition by a compound scanning with a sector echograph are presented. The signal processing is based on both deconvolution and reflection mode tomography. Three of the methods that can be derived from these principles are selected due to their lower computation costs. Applications of these methods to synthetic data and test targets demonstrate that, with respect to 2D deconvolution, they offer: a gain in computation time of more than 8, an improvement in resolution of the order of 10 and an increase of S/N ratio of the order of 4. Finally, both the effects of limited acquisition angular window and of a variable propagation speed are illustrated.
The Design and Fabrication of High Frequency Poly(Vinylidene Fluoride) Transducers
Authors: Sherar M.D. , Foster F.S.
Published: March 2013

Poly(vinylidene fluoride) (PVDF) transducers are well suited for use in high frequency pulse-echo ultrasound systems because of their high bandwidth. We analyze the design parameters of PVDF transducers operating in the 100 MHz range using the KLM transducer model. The effect of backing layers, electrode configuration, transducer surface area and tuning circuits on the insertion loss and pulse-echo response of the transducers are investigated. Using this design procedure, an experimental PVDF transducer is proposed for applications in the 100 MHz range. The transducer is built into a high frequency SMA electrical connector. Insertion loss and pulse-echo response measurements are compared with theoretical predictions.
A 100 MHz B-Scan Ultrasound Backscatter Microscope
Authors: Sherar M.D. , Starkoski B.G. , Taylor W.B. , Foster F.S.
Published: March 2013

The construction and operation of a 100 MHz B-mode ultrasound backscatter microscope are described. The powerful B-mode technique is extended into the domain of microscopy allowing the imaging of internal structure in living specimens on a microscopic scale. A frame rate of 5 frames per second is achieved which gives rapid feedback to the operator. Specially designed components of the scanner are described in detail, including the transducer, motion system and scan converter. An f/2 transducer is employed, leading to a scanner resolution of approximately 36 μm in both the lateral and axial directions. The benefits of such high resolution are demonstrated in preliminary images of multicellular spheroids and intact human ocular tissue.
Phase-Derivative Imaging II: Effects of Beam Diffraction and Scatterer Density
Authors: Oosterveld B.J. , Romijn R.L. , Thijssen J.M.
Published: March 2013

The potential of using the phase derivative (PD) of the radio-frequency echograms for producing 2-dimensional grey scale images was further investigated. The PD images were produced by five different algorithms, which according to the results described in the companion paper yield PD images dominated by the amplitude (envelope, ENV), mixed PD-AM images and pure PD images. These images are termed according to their algorithms: ZCS, zero crossing counter with squelch; ASS, analytic signal with squelch; ASW, analytic signal with Wiener kernel; UNP, unwrapped phase; and SAS, smoothed analytic signal. The rf data were obtained from simulations and from experiments with a tissue mimicking phantom. PD images were analysed by calculation of the first and second order grey level statistics: mean level, signal-to-noise ratio (SNR) and the full width at half maximum (FWHM) of the autocovariance functions (ACVF). These parameters were systematically investigated for a range of depths with respect to the transducer and a range of scatterer densities of the insonated medium. The UNP and SAS images do not suffer much from the diffraction effect but do not display much information about the scatterer density either. The ASW and ASS images qualitatively display beam diffraction effects similar to those of the AM images, with the exception of the mean value which is at the minimum in the focus, where the AM yields a sharp maximum at that depth. The mean and the SNR of the ASW and ASS images increase with increasing scatterer density and saturate at a density of 5000 cm-3. The mean value of the envelope, however, displays a square root dependency over the whole range. The axial and lateral FWHM of the ACVF of the UNP and SAS methods are not significantly dependent on the scatterer density and decrease with increasing density for the ASW and ASS images, as was observed in the envelope images. It may be concluded that ASW and ASS methods produce PD grey scale images which are equally well suited for the diagnosis of diffuse diseases of parenchymal tissues as conventional AM images. The smaller “speckle” size of the ASW images might be advantageous, for the detection of focal lesions, but the lesion contrast is found to be much lower than for the ENV.
Modeling of Doppler Signal considering Sample Volume and Field Distribution
Authors: Kim Yeong M. , Park Song B.
Published: March 2013

The ultrasound Doppler amplitude spectrum for a single scatterer and the power spectrum for multiple scatterers were calculated in terms of the echo signal from scatterers crossing the sample volume, defined by the transmitted pulse and the diffracted field distribution for cw. The observation time for the Doppler signal is also considered. Statistical parameters such as mean and variance of the Doppler power spectrum are studied as continuous functions of the intersection angle between the beam axis and the flow direction, the pulse length and the viewing position. The derived equations are valid whether the transit time is governed by the pulse length, or beam geometry, or both. It is shown that the Doppler power spectra calculated by the proposed model and by the Doppler signal obtained from field theory are in good agreement. It is also shown that, when the Doppler signal broadening due to the transmitted pulse and beam geometry is constant without regard to the intersection angle, the degree of spread of the velocity distribution can be estimated from the variance of the Doppler power spectrum measured by the Doppler system once the intersection angle is known.
A New Aliasing Extension Method for Ultrasonic 2-Dimensional Pulsed Doppler Systems
Authors: Baek K. R. , Bae M. H. , Park S. B.
Published: March 2013

The mean frequency aliasing problem originating from the pulse repetition frequency is one of major limitations in ultrasound pulsed Doppler systems. A conventional approach to resolving this problem is to track the mean frequencies close to and beyond the Nyquist frequency along the temporal axis. In this paper, a new concept of tracking the mean frequencies along the spatial axis is proposed for the same problem. The technique is fault tolerable and more suitable for multigate and 2-D Doppler systems than conventional methods. Simulation and experimental results show that the proposed system has improved performance compared with that of the conventional systems.