bluuebunny/crossref_metadata_2025 huggingface dataset:
Properties of Acoustical Speckle in the Presence of Phase Aberration Part I: First Order Statistics
Authors: Trahey Gregg E. , Smith Stephen W.
Published: March 2013

The first order statistical properties of acoustical speckle patterns are studied as a function of several types of random and structured phase error. Such errors may arise from tissue velocity inhomogeneities or limitations in the acoustical imaging system. In this paper, we review the theory describing the statistical properties of speckle, describe a computer model which predicts the mean speckle brightness in the presence of phase aberrations, and report experiments in which we measure the effect of these aberrations on speckle brightness and variance. We find that the average speckle brightness is significantly reduced by even mild phase aberrations. The phase aberrations studied include focal point errors, random phase errors, and structured errors. Good agreement is found between experiment and computer simulation. We then discuss the implications of these results for imaging through aberrating media, tissue characterization and phase compensation methods.
Instrument-Independent Acoustic Backscatter Coefficient Imaging
Authors: Boote Evan J. , Zagzebski James A. , Madsen Ernest L. , Hall Timothy J.
Published: March 2013

This paper presents an adaptation of a method for determining acoustic backscatter coefficients to produce quantitative ultrasound images. Backscattered echo signals are recorded from a region to be imaged and backscatter coefficients are determined and related to spatial position. The values of the backscatter coefficients are then translated into a gray scale image. Testing of this imaging technique has been performed using tissue-mimicking phantoms which contain sections having backscatter coefficients different from that of the surrounding material. The technique has also been tested using a phantom in which a fat-mimicking layer is interposed between the acoustic window and the main body of the phantom. The images produced were found to be quantitatively accurate throughout the phantom, including the sections with differing backscatter. Quantitative accuracy did not suffer when the fat-mimicking layer was present.
The Maltese Cross Processor: Speckle Reduction for Circular Transducers
Authors: Smith S.W. , von Ramm O.T.
Published: March 2013

A new online signal processing technique is described to reduce speckle noise in ultrasound images. In the imaging system, a focused piston transducer is divided into thirty-two sectors. In the receive mode, parallel signal processing arranges the sectors into eight maltese crosses. The rf signals of the perpendicular arms of each cross are multiplied in a phase sensitive process. The orthogonal receive mode multiplication is designed to reduce side lobes resulting from the sector shapes while maintaining lateral resolution through the use of the full aperture diameter. The signals from the crosses are then combined via postdetection summation. Six of the eight crosses perform successfully. The six maltese crosses show decorrelated signals equivalent to four independent samples of the speckle noise which decreases noise contrast by a factor of two with no measureable loss of spatial resolution. Post summation compression is included to retain the conventional signal dynamic range. Parallel signal processing maintains the normal image line rate. Images of tissue-mimicking phantoms including speckle targets show improved detectability of simulated lesions.
Synthetic B-Scan Images by Numerical Solution of a Wave Equation
Authors: Finette S.
Published: March 2013

We describe an efficient method for obtaining model sector-scan images by direct solution of a linear wave equation characterizing pulse scattering from spatially varying bulk modulus and density distributions. Using a pseudospectral approach, the wave equation is solved numerically for each transducer orientation to obtain a set of A-line signals. After preprocessing the raw data, sector-scan images are constructed and displayed. Examples are given for several scattering object configurations, illustrating both specular and diffractive scattering in inhomogeneous media and demonstrating the utility of the model.
Ultrasound Attenuation Estimation in Soft Tissue Using the Entropy Difference of Pulsed Echoes between Two Adjacent Envelope Segments
Authors: Jang Heung S. , Song Tai K. , Park Song B.
Published: March 2013

In this paper, we describe a new method of estimating the ultrasound attenuation coefficient of soft tissue based on the entropy difference between two adjacent envelope segments of narrowband ultrasound pulse echoes. Assuming uniform attenuation in the region under investigation, the attenuation is estimated by minimizing the difference of entropies in the two segments as the attenuation is continuously compensated for. The simulation and experimental results with a tissue equivalent (TE) phantom show that the proposed estimator is quite robust to receiver noise and requires considerably less data length as compared with conventional methods. At present, an experimental result with a TE phantom shows that a resolution of 10 mm × 10 mm can be attained with echoes from a depth of 3 cm using a 2.25 MHz transducer.
High-Resolution, Reflection Mode Tomographic Imaging Part I: Principles and Methods
Authors: Herment A. , Guglielmi J.P. , Péronneau P. , Dumée Ph.
Published: March 2013

A general method for improving image resolution is derived and applied to ultrasound signals; it combines the principles of both reflection mode tomography and deconvolution. The different possibilities of applying these principles allow two types of approaches to be defined, depending upon whether image reconstruction is achieved on radiofrequency or detected signals. A thorough description of three methods that are of particular interest due to their lower computation costs is presented, and their results quantified. They permit a gain in resolution of the order of ten with respect to two-dimensional deconvolution of images, as well as an improvement of the S/N ratio, which is related to the square root of the number of projections used in the reconstruction process, and a decrease of about four in computation time.
Numerical Study of Higher-Order Diffraction Tomography via the Sinc Basis Moment Method
Authors: Cavicchi Thomas J. , O'Brien William D.
Published: March 2013

Behavior and limitations of the sinc basis method have been discovered during simulation studies. An iterative row-action method (ART) is compared with a full-matrix, least-squares solution (QR decomposition) and the problem of multiple solutions is discussed. Knowledge of the spatial distribution of scattered field energy can be used to speed up convergence. The first iteration is shown to be equivalent to the first Born solution. A fundamental limitation of present diffraction tomography algorithms, concerning phase shift through the scatterer, is found and related to clinical values. Effects of improvements on the initial guesses for the object function and internal field are studied. Lossy cylinder and contrived multicomponent reconstructions yield additional understanding of the phase shift problem. A sequence of simulations investigates estimated solution movement in hyperspace.
Optimum Focusing in an Ultrasonic Annular Array Imaging System Using a Nonspherical Lens
Authors: Song Tai K. , Park Song B.
Published: March 2013

In this paper, a new focusing method for ultrasonic annular array imaging systems is presented. The technique minimizes the lateral resolution for a specified sidelobe suppression over the depth of interest, using a nonspherical lens for line focusing in transmit in combination with continuous dynamic focusing in receive. For this purpose, an effective analysis model is developed for calculating the impulse response of an annulus with an arbitrarily-shaped lens in the whole imaging plane. Using this analysis method, an iterative technique is then applied to obtain an optimum transmit delay profile when continuous receive focusing is employed at all imaging points along the depth of view. The delay profile is optimum in the sense that the lateral beam width is minimized under a specified sidelobe suppression at three depths of the imaging field. The continuous receive focusing is realized in a new digital focusing system which enables arbitrary control of transmit time delays and dynamic focusing in the receive mode. In the proposed system, focusing is achieved by adjusting the sampling time for each array element according to the arrival time differences among array elements for a given focal point. Experimental results show the validity of the analysis model and the optimum lens design.
The Performance of Mechanically Scanned Color Flow Mapping
Authors: Burckhardt C.B.
Published: March 2013

The performance of mechanically scanned Color Flow Mapping is analysed. It is shown that the Doppler spectrum is convolved with a scaled version of the Fourier transform of the two-way point spread function of the transducer. This spectral broadening is no larger than the inherent limit of the method if the point spread function shows smooth amplitude variation and little phase variation. The spectral broadening can cause clutter from stationary objects to fall outside the MTI filter stopband and, thereby, alter the estimates of the mean velocity and turbulence. Mechanically scanned and electronically stepped Color Flow Mapping are compared.
Backscatter Coefficient Measurements Using a Reference Phantom to Extract Depth-Dependent Instrumentation Factors
Authors: Yao Lin Xin , Zagzebski James A. , Madsen Ernest L.
Published: March 2013

In previous work, we demonstrated that accurate backscatter coefficient measurements are obtained with a data reduction method that explicitly accounts for experimental factors involved in recording echo data. An alternative, relative processing method for determining the backscatter coefficient and the attenuation coefficient is presented here. This method involves comparison of echo data from a sample with data recorded from a reference phantom whose backscatter and attenuation coefficients are known. A time domain processing technique is used to extract depth and frequency dependent signal ratios for the sample and the reference phantom. The attenuation coefficient and backscatter coefficient of the sample are found from these ratios. The method is tested using tissue-mimicking phantoms with known scattering and attenuation properties.
Determination of Tissue Motion Velocity by Correlation Interpolation of Pulsed Ultrasonic Echo Signals
Authors: de Jong P.G.M. , Arts T. , Hoeks A.P.G. , Reneman R.S.
Published: March 2013

Correlation interpolation is introduced as a method to determine the displacement of moving biological tissue on the basis of a sequence of ultrasonic echo signals. The echo signal is sampled along the echo depth with approximately 4 samples per average high frequency period. Sampling in time occurs with the pulse repetition frequency. The necessary information is extracted from a crosscorrelation function between successive signals, which is modelled using four parameters. The parameters are estimated from five calculated correlation sums and the shift with maximum correlation is determined. In contrast to existing techniques, the performance of this method is determined mainly by the number of samples used, while the ratio of the number of samples in depth and time is irrelevant. Using 64 samples at a signal-to-noise power ratio of 10, the standard deviation of the error in the determination of the shift in depth is 0.08 sampling intervals. As in many other methods, the width of the aliasing interval equals the mean frequency period.
Computerized Ultrasound B-Scan Texture Analysis of Experimental Fatty Liver Disease: Influence of Total Lipid Content and Fat Deposit Distribution
Authors: Layer G. , Zuna I. , Lorenz A. , Zerban H. , Haberkorn U. , Bannasch P. , van Kaick G. , Räth U.
Published: March 2013

Statistical pattern recognition procedures allow a quantitative description of ultrasound-B-scan image texture. According to well-established animal models, different types of fatty liver disease were induced in female Wistar rats. For the correlation of the computerized ultrasound image with its underlying histology a variable tissue model based on histomorphological data, texture analysis of the histological image and biochemical measurements of total lipid, water and hydroxyprolin content was created.

Whereas a regional arrangement of large fat deposits leads to a significant increase in the “mean grey level” (measure of image brightness) of the ultrasound-B-scan image, there is no difference in image brightness between normal liver tissue and liver steatosis for the tissue model with diffuse homogeneous fatty infiltration. It is demonstrated by multiple linear regression analysis that the “mean grey level” of the ultrasound-B-scan image depends not only on total lipid content but even more on the histomorphological fat deposit distribution.
Partially Coherent Transducers: The Random Phase Transducer Approach
Authors: Mallart R. , Fink M. , Laugier P. , Abouelkaram S.
Published: March 2013

Ultrasound speckle is a consequence of the stochastic nature of the reflectivity of scattering media (e.g., biological tissue) and of the coherent nature of piezoelectric transducers. This speckle noise can be reduced by the use of incoherent processing techniques (e.g., spatial compounding, incoherent summation, random phase and phase insensitive transducers.).

We present a unified framework that explains the limitations of incoherent processing in terms of the information grain theory. This theory predicts the gains in SNR as well as the losses in directivity. We also present the random phase transducer approach to incoherent processing. This approach allows continuous control of the coherence from total incoherence to total coherence. We present applications to speckle reduction, detection of specular reflectors, attenuation estimation and ultrasound imaging. We show that totally incoherent transducers completely remove diffraction effects. They might be used in attenuation estimation, in which case, correction for diffraction is no longer required, in order to obtain unbiased estimates. Partially coherent transducers might also be useful in imaging to reduce speckle noise.
Statistics of the Physiologic Phase of Integrated Backscatter from Canine Myocardium with Normal and Reduced Coronary Circulation
Authors: Kumar K. N. , Reisner S. , Ernst Alexander , Gottlieb Shmuel , Meltzer R. S. , Mottley J. G.
Published: March 2013

The phase, relative to the arterial pressure, of cyclically varying integrated backscatter from canine myocardium was measured at normal and reduced coronary blood flow levels and was found to become more randomized with decreasing flow. The phase, modeled as a von Mises distribution on a unit circle which is very similar to the normal distribution on the line, is characterized by a mean (μ0) and a concentration or width parameter (κ). κ is used to characterize the degree of randomization. The von Mises distribution provides an excellent fit to measured data (p < 0.01). Hypothesis tests performed on the data for various coronary flow levels indicate that the phase distribution for normal coronary flow level is significantly different from the distributions at other flow levels (p < 0.05). The results suggest that the parameter κ may be used for differentiating normal and ischemic myocardium.
Inverse Scattering Scheme Based on the Moment Method in the Spectral Domain, Part I: Theory
Authors: Kim Se-Yun , Choi Hyun-Chul , Lee Jae-Min , Ra Jung-Woong
Published: March 2013

Recently, electromagnetic and ultrasonic imaging of inhomogeneous objects by applying the moment-method procedures of forward scattering problems in the reverse sequence have been developed. In this paper, the inverse scattering formulation has been modified to be applicable in the spectral domain. Compared to previous schemes, the suggested formulation illustrates clearly the actual mechanism of the inverse scattering process by explicit separation of the contributions from several variables, such as the measurement location, basis function, and geometry of objects. The ill-posedness inherent in inverse scattering problems was also explained easily in this spectral scheme by the exponentially-decaying behavior of high-frequency spectral components of the scattered field. It implies that enlargement of the discretized cell size is a key factor in regularizing the ill-posedness. In particular, since the singular kernel to be integrated on each cell became regular in the modified scheme, various types of basis functions instead of pulse function were adopted without additional difficulties. This advantage is expected to play an important role in regularizing the noise effect by selecting polynomial basis function on the enlarged cells of discretization in the spectral inverse scattering scheme.
Phase Aberration Correction Using Echo Signals from Moving Targets II: Experimental System and Results
Authors: Bohs L.N. , Zhao D. , Trahey G.E.
Published: March 2013

A method for correcting errors due to near-field tissue inhomogeneities in phased array ultrasound images is evaluated experimentally. The method uses the brightness of a moving speckle-generating target, such as blood, as a quality factor to correct for unknown phase aberrations. A real time experimental system utilizing the technique has been constructed and is described. Initial results from in vitro studies using a flow phantom are compared to theoretical predictions. The results indicate that the technique can provide significant improvements in image quality when imaging through aberrating media, and may find application in clinical imaging through skull and fatty layers.
Optimum Nonlinear Signal Detection and Estimation in the Presence of Ultrasonic Speckle
Authors: Kotropoulos Constantine , Pitas Ioannis
Published: March 2013

A unified approach to the design of nonlinear filters for speckle suppression in ultrasound B-mode images is presented. The detection of the (lesion) signal is formulated as a binary hypothesis-testing problem. The structure of the optimal decision rules is derived both in the case where the lesion signal is assumed either a constant or random variable. In the case of a constant signal, the maximum likelihood (ML) estimator and the optimal L-estimator are derived. In the case of a random lesion signal, the maximum a posteriori probability estimator of the lesion signal has also been found. Experimental results verify the superiority of the proposed ML-estimator and the L-estimator over the straightforward choice of an arithmetic mean for speckle filtering in simulated tissue mimicking phantom ultrasound B-mode images.
Large-Transducer Measurements of Wavefront Distortion in the Female Breast
Authors: Zhu Qing , Steinberg Bernard D.
Published: March 2013

Ultrasonic waves propagating through soft tissue experience wavefront distortion. Refraction occurs at boundaries between tissue beds having different sound speeds; scattering occurs within a tissue bed, caused by local impedance variations. This paper describes measurements of wavefront distortion in the human female breast that indicate that refraction is the dominant distortion mechanism when the ultrasonic phased array is very large.

The determination that refraction dominates the wavefront distortion is based upon studies of multiple image artifacts that result from a single source radiated through in vivo breasts and breast phantoms. The receiving apertures used were 4.65 and 9.6 cm. Such image artifacts are repeatedly observed in the 10 young subjects reported in this paper, and also in older subjects. An understanding of the in vivo observations is obtained by phantom studies.
Simulation of B-Scan Images from Two-Dimensional Transducer Arrays: Part I - Methods and Quantitative Contrast Measurements
Authors: Turnbull Daniel H. , Lum Paul K. , Kerr Andrew T. , Foster F. Stuart
Published: March 2013

Recently, theoretical investigations of the beamforming capability of two-dimensional (2-D) transducer arrays have characterized the array parameters required to steer a symmetrically focused ultrasound beam up to 45° off-axis. These investigations have also shown that the number of elements in a steered 2-D array can be dramatically reduced by using a sparse set of elements, randomly distributed throughout the aperture of the transducer. The penalty paid for the use of a sparse array is the development of a “pedestal” sidelobe in the beam profile, the amplitude of which increases as the number of elements in the array decreases. In this paper the potential of 2-D arrays for medical imaging is assessed by simulating B-scan images of spherical lesions, both cystic and scattering, embedded in a large random scattering volume. Similar contrast characteristics over a range of cyst sizes are demonstrated for a dense 2-D array and a sparse array with 1/8th the number of elements, both operating at 5 MHz. A 32nd order sparse array is shown to perform at a reduced level, producing unacceptable artifactual echoes within images of cysts. The 8th order sparse array pattern has been fabricated on a fixed-focus poly(vinylidene difluoride) transducer using photolithographic, techniques. Experimental images from this transducer are used to verify some of the theoretical predictions made in this paper. Comparisons between simulated B-scan images from linear and 2-D phased arrays are presented in a companion paper.
A Discussion of Two Wavefront Aberration Correction Procedures
Authors: Steinberg Bernard D.
Published: March 2013

This review paper discusses the basic properties of two adaptive signal processing procedures for dealing with weak scattering in a phased array transducer system. A fundamental improvement in the lateral resolution of ultrasonic echo scanners will result if the weight vector of a large phased array transducer can be modified to account for distortion in the propagation medium. Lateral resolution in most tissue is limited to a few mm by wavefront-distortion-induced sound-speed variations. One important wavefront-distortion source is scattering from local speed variations within large and reasonably homogeneous tissue beds such as the liver. Scattering disperses some energy from the beam and perturbs the wavefront, thereby distorting the image and limiting the resolution to the scale of the distortion. Often, such scattering is weak, meaning that most of the energy in the beam is unscattered. The total field at the receiving transducer is the vector sum of the unscattered and scattered fields. In weak scattering the unscattered field is dominant and the resultant field can be treated as the unscattered field plus a perturbation. The net effect is primarily a distorted phasefront, while the ampitude or modulus of the wavefront remains reasonably intact. Refraction and strong scattering affect the wavefront more severely and are less responsive to these algorithms.
A 45 TO 55 Mhz Needle-Based Ultrasound System for Invasive Imaging
Authors: Lockwood G. R. , Ryan L. K. , Foster F. S.
Published: March 2013

The design, construction and fabrication of a high frequency needle-based ultrasound imaging system is described. A miniature lead zirconate titanate transducer was mounted opposite a parabolic mirror in a stainless steel needle. By inserting the needle into a tissue, a cross section image of the tissue can be made. Two needle probes were built, a 45 MHz 2.8 mm diameter probe with 125 μm lateral, 55 μm axial resolution and a 55 MHz 1.6 mm diameter probe with 105 μm lateral, 40 μm axial resolution. Preliminary phantom and in vitro tissue images demonstrate the feasibility of high frequency needle-based imaging.
Assessment of Echography as a Monitoring Technique for Cryosurgery
Authors: Laugier P. , Berger G.
Published: March 2013

One of the principal difficulties encountered in cryosurgery is to know the extent and depth of the frozen tissue boundary during the freezing process and the extent of the cryonecrosis in the postfreezing period. These problems have to be solved for cryosurgery to be a controlled therapeutic method and to avoid injuries to tissues adjacent to the tumor. The aim of this study was to evaluate echographic possibilities in monitoring the freezing process during cryotherapy in dermatology. In this paper, we describe the first experimental results of ultrasound monitoring of the freezing process with a 15 MHz transducer on pig skin in vitro. We show that it is possible to easily detect the depth boundary of the frozen region Conventional linear filtering of the echographic signals can be very useful for SNR enhancement in the detection of a target signal drowned in speckle noise. Measurement of the kinetics of the freeze-thaw cycle (thickness of the frozen region versus time) is also measurable, which is of major importance as it allows the exact adjustment of the freezing time as a function the extent of tumor depth. Cryotherapy monotoring by ultrasound, added to the new diagnostic possibilities of high frequency ultrasound transducers, makes it an interesting controlled therapeutic method in such clinical fields as dermatology.
The Lack of Effect of Hemodilution, Myocardial Water Content, and Increased Coronary Artery Blood Flow on Integrated Myocardial Ultrasonic Backscatter in the Beating Canine Heart
Authors: Haasler George B. , Rhyne Theodore L. , Komorowski Richard , Boerboom Lawrence E. , Sagar Kiran B.
Published: March 2013

The effects of coronary blood flow, tissue water content and hematocrit variation on the Integrated Myocardial Backscatter Rayleigh 5 (IBR5) and Fourier coefficient of amplitude modulation (FAM, an index of cardiac cylce-dependent variation in IBR5) were measured in five open chest dogs. Data were obtained at baseline, during adenosine infusion and after two hours of crystalloid hemodilution (Hct 15%). IBR5 of −46.4 ± .94 dB at baseline did not change significantly during adenosine infusion (−45 ± .85 dB) and after hemodilution (−46.4 ± 2.0 dB). FAM at baseline was (4.0 ± 1.0 dB) (3.8 ± −1.0 dB) during adenosine infusion and after hemodilution (5.0 ± 1.8 dB). Myocardial water content increased significantly (p < .05) from 78 ± .20% at baseline to 80.7 ± .17% after hemodilution. Coronary blood flow demonstrated a three-fold increase with adenosine and two-fold increase with hemodilution. Electronmicroscopy demonstrated an increase in intracellular and extracellular water content. In conclusion, IBR5 and FAM did not change significantly despite significant increases in coronary blood flow and myocardial water content. Myocardial cellular derangements seen with nonischemic cell swelling, increased blood flow and a fall in hematocrit are insufficient to affect integrated backscatter.
Application of An Art Algorithm in an Experimental Study of Ultrasonic Diffraction Tomography
Authors: Ladas K. T. , Devaney A. J.
Published: March 2013

This paper describes results obtained using a recently developed Algebraic Reconstruction Technique (ART) for diffraction tomography on experimental data obtained from an ultrasound scanner built by Norwave Development A.S. of Oslo, Norway. The test objects (phantoms) employed in the study are low contrast cylindrical rods made out of agar with dimensions comparable to the wavelength of the incident wavefield. The reconstructions obtained from the ART algorithm are compared to the ones obtained from the filtered backpropagation algorithm. It is determined that the ART algorithm out performs the filtered backpropagation algorithm for cases where data from only a small number of tomographic experiments are available.
Texture Analysis of Ultrasonic Images of the Prostate by Means of Co-Occurrence Matrices
Authors: Basset O. , Sun Z. , Mestas J.L. , Gimenez G.
Published: March 2013

As speckle on ultrasonic B-scan may reveal information relative to tissue structure, the present work attempts to discriminate the various prostatic tissues (normal tissue, benign prostatic hypertrophy and cancer) by means of texture analysis. We select regions of interest by their homogeneous appearance. A pre-processing stage is required to obtain stationary samples. The method used measures the second-order statistics, namely co-occurrence matrices. Fairly good tissue signatures have been obtained with parameters derived from these matrices. Of 37 images processed, 78 percent of the samples were classified with success, which is a high score considering that the images cannot be discriminated visually. However, while such results are obtained when wide regions of interest are investigated (64 × 64 pixels), they are not as good with smaller sample sizes, i.e., when the pathological area is very small.
Variable Density Linear Acoustic Inverse Problem
Authors: Moghaddam M. , Chew W.C.
Published: March 2013

The linear acoustic inverse problem is solved simultaneously for density (ρ) and compressibility (κ) using the basic ideas of diffraction tomography (DT). The key to solving this problem is to utilize frequency diversity to obtain the required independent measurements. The receivers are assumed to be in the far field of the object, and plane wave incidence is also assumed. The Born approximation is used to arrive at a relationship between the measured pressure field and two terms related to the spatial Fourier transform of the two unknowns, ρ and κ. The term involving compressibility corresponds to monopole scattering and that for density to dipole scattering. Measurements at several frequencies are used and a least squares problem is solved to reconstruct ρ and κ at the same time. It is observed that the low spatial frequencies in the spectra of ρ and κ produce inaccuracies in the results. Hence, a regularization method is devised to remove this problem. Several results are shown. Low contrast objects for which the above analysis holds are used to show that good reconstructions are obtained for both density and compressibility after regularization is applied.
Improving the Distinction between Benign and Malignant Breast Lesions: The Value of Sonographic Texture Analysis
Authors: Garra Brian S. , Krasner Brian H. , Horii Steven C. , Ascher Susan , Mun Seong K. , Zeman Robert K.
Published: March 2013

To improve the ability of ultrasound to distinguish benign from malignant breast lesions, we used quantitative analysis of ultrasound image texture. Eight cancers, 22 cysts, 28 fibroadenomata, and 22 fibrocystic nodules were studied. The true nature of each lesion was determined by aspiration (for some cysts) or by open biopsy. Analysis of image texture was performed on digitized video output from the ultrasound scanner using fractal analysis and statistical texture analysis methods. The most useful features were those derived from co-occurrence matrices of the images. Using two features together (contrast of a co-occurrence matrix taken in an oblique direction, and correlation of a co-occurrence matrix taken in the horizontal direction), it was possible to exclude 78% of fibroadenomata, 73% of cysts, and 91% of fibrocystic nodules while maintaining 100% sensitivity for cancer. These findings suggest that ultrasonic image texture analysis is a simple way to markedly reduce the number of benign lesion biopsies without missing additional cancers.
Potential of Fractal Analysis for Lesion Detection in Echographic Images
Authors: Verhoeven J.T.M. , Thijssen J.M.
Published: March 2013

The application of fractal analysis to parametric imaging of B-mode echograms and to differentation of echographic speckle textures was investigated. Echograms were obtained from realistic simulations and from a clinical study on diffuse liver disease. The simulations comprised tissue models with randomly positioned scatterers in a 3-D volume in which the number density was varied over a range from 0.5 to 25 mm–3. The clinical echograms comprised both normals and patients with liver cirrhosis. Three methods of estimating the fractal dimension were investigated, two in the spatial image domain and one in the spatial frequency domain. The results of these methods are compared and the applicability and the limitations of texture differentiation using fractal analysis is discussed. The main conclusion is that fractal analysis offers no obvious advantage over statistical analysis of the texture of echographic images. Its use for parametric imaging is further limited by the need to use relatively large windows for local estimation of the fractal dimension.
Quantitative Ultrasound Imaging: in Vivo Results in Normal Liver
Authors: Zagzebski J.A. , Lu Z.F. , Yao L.X.
Published: March 2013

A method for quantitative imaging of ultrasonic backscatter levels has been implemented on a clinical imager. The method is based on comparing echo signal data from a sample or patient to echo data processed in the same way but acquired from a reference phantom. The attenuation coefficient and the backscatter coefficient of the reference phantom are known, permitting these quantities to be estimated for the sample. In the present paper, the spatial location of echo data acquisition is retained in the backscatter data analysis; quantitative “backscatter estimator” images are constructed, from which the backscatter coefficient over a region of interest may be obtained. When applied to human liver images, backscatter coefficients determined in 10 normal subjects were in approximate agreement with in vitro liver backscatter coefficients reported by previous Workers.
An Efficient Real Time Focusing Delay Calculation in Ultrasonic Imaging Systems
Authors: Jeon Ki , Bae Moo H. , Park Song B. , Kim Seong D.
Published: March 2013

An efficient real time focusing delay calculation algorithm is proposed for variable sampling clock generation (SCG) with high accuracy needed in digital focusing in ultrasonic imaging systems. The proposed algorithm is an extension of the midpoint drawing algorithm that is well known in the computer graphics area. It can be implemented with simple hardware amenable to VLSI realization, without using a large amount of look-up memory to store the sampling clock information otherwise required.
Ultrasound Echo Envelope Analysis Using a Homodyned K Distribution Signal Model
Authors: Dutt Vinayak , Greenleaf James F.
Published: March 2013

The statistics of ultrasound echo envelope signals can be used to characterize scattering media. The Rayleigh distribution and its generalized forms, the K and Rice distributions, have been previously used to model the echo signal. A more generalized statistical model, the homodyned K distribution, combines the K and Rice distribution features to better account for the statistics of the echo signal. We show that this model can give two parameters that are useful for media characterization: k, the ratio of coherent to diffuse signals, and, β, which characterizes the clustering of scatterers in the medium.
An Adaptive Approach to Computing the Spectrum and Mean Frequency of Doppler Signals
Authors: Herment A. , Giovannelli J.F.
Published: March 2013

Modern ultrasound Doppler systems are facing the problem of processing increasingly shorter data sets. Spectral analysis of the strongly nonstationary Doppler signal needs to shorten the analysis window while maintaining a low variance and high resolution spectrum. Color flow imaging requires estimation of the Doppler mean frequency from even shorter Doppler data sets to obtain both a high frame rate and high spatial resolution. We reconsider these two estimation problems in light of adaptive methods. A regularized parametric method for spectral analysis as well as an adapted mean frequency estimator are developed. The choice of the adaptive criterion is then addressed and adaptive spectral and mean frequency estimators are developed to minimize the mean square error on estimation in the presence of noise. Two suboptimal spectral and mean-frequency estimators are then derived for real-time applications. Finally, their performance is compared to that of both the FFT based periodogram and the AR parametric spectral analysis for the spectral estimator, and, to both the correlation angle and the Kristoffersen's [8] estimators for the mean frequency estimator using Doppler data recorded in vitro.
Experimental Studies on an Efficient Catheter Array Imaging System
Authors: O'Donnell M. , Shapo B.M. , Eberle M.J. , Stephens D.N.
Published: March 2013

A new synthetic aperture system for intraluminal imaging has been tested using a 32 element, 20 MHz circular array wrapped around the surface of a catheter appropriate for coronary artery applications. This system is based on an optimal reconstruction method that has been extended to reduce grating lobes using a slight modification to classic synthetic aperture data acquisition. Optimal reconstruction filters have been derived for two different operating modes based on this new data acquisition strategy. Imaging results on a wire target phantom show that spatial resolution is a simple linear function of depth, reaching a minimum 6 dB beam width of approximately 2.2 wavelengths. Sidelobe levels are inherently high for this system because of the small number of firings used to synthesize an aperture. Optimal reconstruction filters, however, can reduce these sidelobes to at least −20 dB in all cases. Finally, images of an excised segment of porcine femoral artery demonstrate the overall performance of the system as an intraluminal imager.
Experimental Point Spread Function of Fm Pulse Imaging Scheme
Authors: Rao N.A.H.K. , Mehra S. , Bridges J. , Venkatraman S.
Published: March 2013

In this paper, we have examined the possibility of incorporating pulse compression techniques into a conventional medical B-scan imaging scheme. Linear frequency modulation fm, one form of pulse coding among many others, has been used in this study. With this approach, one can overcome current peak intensity limitations. A theoretical framework that includes medium propagation effects, transducer bandwidth and diffraction effects is presented, which could be used to examine the system point spread function under this imaging scheme. A prototype experimental set-up and signal processing are described and used for simple imaging tasks in attenuating and nonattenuating media. Analysis of the experimental point spread functions shows that resolution similar to conventional short pulse imaging can be achieved. However, the existence of large range side lobe levels usually associated with pulse compression processing can degrade contrast resolution in medical ultrasound. We have considered various different factors that can affect the range side lobe levels and examined their effect either experimentally or through simulations. The technique has the potential for improving signal-to-noise ratio (SNR), maximum penetration depth and resolution without exceeding peak intensity limitations. Some possible applications are discussed that merit further evaluation. Our work demonstrates the feasibility of this technique and presents a theoretical framework that can be used in future studies aimed at evaluating image quality, system performance, and possible artifacts under such an imaging scheme.
Improved Lesion Detection by Level-Dependent Spatial Summation
Authors: Collaris R.J. , Hoeks A.P.G.
Published: March 2013

A novel signal postprocessing method has been developed for application in lesion detection. A signal distribution, directly related to the 2-dimensional envelope distribution comprising a B-mode image, is convolved with a block shaped kernel of which both base area (i.e., window size) and height are modulated by the local signal level. A theoretical analysis shows that the output includes information regarding the local mean brightness in the original image. This information can be displayed as a gray scale image. The predicted behavior agrees with experimental observations. On the basis of twenty simulated lesion images, it is demonstrated that the present algorithm is superior to the conventional L2-mean filter in lesion detection problems, whereby the performance is quantified by the area AROC under the Receiver Operating Characteristic. An improvement in the median value of AROC of the order of 0.1 was observed. Two parameters are used for adjustment. The total number of summations involved in the processing of a frame is comparable to the number required by the arithmetic mean filter, allowing real-time implementation.
Multiple Resolution Bayesian Segmentation of Ultrasound Images
Authors: Ashton Edward A. , Parker Kevin J.
Published: March 2013

We propose a novel method for obtaining the maximum a posteriori (MAP) probabilistic segmentation of speckle-laden ultrasound images. Our technique is multiple-resolution based, and relies on the conversion of speckle images with Rayleigh statistics to subsampled images with Gaussian statistics. This conversion reduces computation time, as well as allowing accurate parameter estimation for a probabilistic segmentation algorithm. Results appear to provide improvements over previous techniques in terms of low-contrast detail and accuracy.
Time Reversal Focusing Applied to Lithotripsy
Authors: Thomas Jean-Louis , Wu François , Fink Mathias
Published: March 2013

Time reversal of ultrasonic field allows a very efficient approach to focusing pulsed ultrasonic waves through lossless inhomogeneous media. Time reversal mirrors (TRM) are made of large transducer arrays, allowing the incident acoustic field to be sampled, time reversed and re-emitted. Time reversal processing permits a choice of any temporal window to be time reversed, allowing operation in an iterative mode. In multitarget media, this process converges on the most reflective target, i.e., the dominant scatterer. In this paper, the time reversal process is applied to track, in real time, a moving gall bladder or kidney stone embedded in its surrounding medium. We investigate the feasibility of a piezoelectric shock wave generator in which the focal zone is moved electronically to track the stone during a lithotripsy treatment. We show that TRM allows us to obtain sharp focusing on one bright point of the stone. The time of flight profile is then determined and used in a least-mean-square method to calculate the spatial coordinates of the stone.
A Real-Time Scan Conversion Algorithm on Commercially Available Microprocessors
Authors: Basoglu Chris , Kim Yongmin , Chalana Vikram
Published: March 2013

We have developed a new ultrasound scan conversion algorithm that can be executed very efficiently on modern microprocessors. Our algorithm is designed to handle the address calculations and input and output (I/O) data loading concurrently with the interpolation. The processing unit's computing power can be dedicated to performing pixel interpolations while the other operations are handled by an independent direct memory access (DMA) controller. By making intelligent use of the I/O transfer capabilities of the DMA controller, the algorithm avoids spending the processing unit's valuable computing cycles in address calculations and nonactive pixel blanking. Furthermore, the new approach speeds up the computation by utilizing the ability of superscalar and very long instruction word (VLIW) processors to perform multiple operations in parallel. Our scan conversion algorithm was implemented on a multimedia and imaging system based on the Texas Instruments TMS320C80 Multimedia Video Processor (MVP). Computing cycles are spent only on predeterminable nonzero output pixels. For example, an execution time of 11.4 ms was achieved when there are 101,829 nonzero output pixels. This algorithm demonstrates a substantial improvement over previous scan conversion algorithms, and its optimized implementation enables modern commercially available programmable processors to support scan conversion at video rates.
Reduction of the Clutter Component in Doppler Ultrasound Signals Based on Singular Value Decomposition: A Simulation Study
Authors: Ledoux Léon A.F. , Brands Peter J. , Hoeks Arnold P.G.
Published: March 2013

In pulsed Doppler ultrasound systems, the ultrasound radiofrequency (RF) signals received can be employed to estimate noninvasively the time-dependent blood flow velocity distribution within an artery. The RF signals are composed of signals originating from clutter (e.g., vessel walls) and scatterers (e.g., red blood cells). The clutter, which is induced by stationary or slowly-moving structure interfaces, must be suppressed to get reliable estimates of the mean blood flow velocities. In conventional pulsed Doppler systems, this is achieved with a static temporal high-pass filter. The static cut-off frequency and the roll-off of these filters cause the clutter not always to be optimally suppressed. This paper introduces a clutter removal filter that is based on Singular Value Decomposition (SVD). Unlike conventional high-pass filters, which take into account only the information of the temporal direction, the SVD filter makes use of the information of the temporal and spatial directions. The advantage of this approach is that it does not matter where the clutter is located in the RF signal. The performance of the SVD filter is examined with computer-generated Doppler RF signals. The results are compared with those of a standard linear regression (SLR) filter. The performance of the SVD filter is good, especially if a large temporal window (i.e., approximately 100 RF signals) is applied, which improves the performance for low blood flow velocities. A major disadvantage of the SVD filter is its computational complexity, which increases considerably for larger temporal windows.
Detection of Cardiac Boundaries in Echocardiographic Images Using a Customized Order Statistics Filter
Authors: Belohlavek Marek , Greenleaf James F.
Published: March 2013

Order statistics filters are nonlinear filters that suppress impulsive and Gaussian noise while preserving edges. These features are particularly useful for cardiac boundary detection in ultrasound images. Based on these facts, we have analyzed performance of a combined ranked order statistics filter. The filter subtracts ranks of ordered highest and lowest intensity values of pixels encompassed in a filter window. The rank extent and window size selection allow adjustment of filter properties for a particular application. Increasing the rank fosters the low-pass characteristics of the filter. Increasing the window size supports noise removal but reduces anatomic selectivity. The filter highlights cardiac boundaries in clinical echocardiograms with intensity proportional to the local probability of a presence of the boundary.
A Least-Squares Strain Estimator for Elastography
Authors: Kallel Faouzi , Ophir Jonathan
Published: March 2013

A least-squares strain estimator (LSQSE) for elastography is proposed. It is shown that with such an estimator, the signal-to-noise ratio in an elastogram ( SNRe) is significantly improved. This improvement is illustrated theoretically using a modified strain filter and experimentally using a homogeneous gel phantom. It is demonstrated that the LSQSE results in an increase of the elastographic sensitivity (smallest strain that could be detected), thereby increasing the strain dynamic range. Using simulated data, it is shown that a tradeoff exists between the improvement in SNRe and the reduction of strain contrast and spatial resolution.