bluuebunny/crossref_metadata_2025 huggingface dataset:
On the Feasibility of Imaging Peripheral Nerves Using Acoustic Radiation Force Impulse Imaging
Authors: Palmeri Mark L. , Dahl Jeremy J. , Macleod David B. , Grant Stuart A. , Nightingale Kathryn R.
Published: March 2013

Regional anesthesia is preferred over general anesthesia for many surgical procedures; however, challenges associated with poor image guidance limit its widespread acceptance as a viable alternative. In B-mode ultrasound images, the current standard for guidance, nerves can be difficult to visualize due to their similar acoustic impedance with surrounding tissues and needles must be aligned within the imaging plane at limited angles of approach that can impede successful peripheral nerve anesthesia. These challenges lead to inadequate regional anesthesia, necessitating intraoperative interventions, and can cause complications, including hemorrhage, intraneural injections and even nerve paralysis. ARFI imaging utilizes acoustic radiation force to generate images that portray relative tissue stiffness differences. Peripheral nerves are typically surrounded by many different tissue types (e.g., muscle, fat and fascia) that provide a mechanical basis for improved image contrast using ARFI imaging over conventional B-mode images. ARFI images of peripheral nerves and needles have been generated in cadaveric specimens and in humans in vivo. Contrast improvements of >600% have been achieved for distal sciatic nerve structures. The brachial plexus has been visualized with improved contrast over B-mode images in vivo during saline injection and ARFI images can delineate nerve bundle substructures to aid injection guidance. Physiologic motion during ARFI imaging of nerves near arterial structures has been successfully suppressed using ECG-triggered image acquisition and motion filters. This work demonstrates the feasibility of using ARFI imaging to improve the visualization of peripheral nerves during regional anesthesia procedures.
Novel Acoustic Radiation Force Impulse Imaging Methods for Visualization of Rapidly Moving Tissue
Authors: Hsu Stephen J. , Bouchard Richard R. , Dumont Douglas M. , Ong Cheng W. , Wolf Patrick D. , Trahey Gregg E.
Published: March 2013

Acoustic radiation force impulse (ARFI) imaging has been demonstrated to be capable of visualizing changes in local myocardial stiffness through a normal cardiac cycle. As a beating heart involves rapidly-moving tissue with cyclically-varying myocardial stiffness, it is desirable to form images with high frame rates and minimize susceptibility to motion artifacts.

Three novel ARFI imaging methods, pre-excitation displacement estimation, parallel-transmit excitation and parallel-transmit tracking, were implemented. Along with parallel-receive, ECG-gating and multiplexed imaging, these new techniques were used to form high-quality, high-resolution epicardial ARFI images. Three-line M-mode, extended ECG-gated three-line M-mode and ECG-gated two-dimensional ARFI imaging sequences were developed to address specific challenges related to cardiac imaging. In vivo epicardial ARFI images of an ovine heart were formed using these sequences and the quality and utility of the resultant ARFI-induced displacement curves were evaluated. The ARFI-induced displacement curves demonstrate the potential for ARFI imaging to provide new and unique information into myocardial stiffness with high temporal and spatial resolution.
Importance of Axial Compression Verification to Correct Interpretation of Axial-Shear Strain Elastograms in Breast Lesions
Authors: Thittai Arun K. , Galaz Belfor , Ophir Jonathan
Published: March 2013

We have recently shown that the appearance of Axial-Shear Strain Elastograms (ASSEs) for the case of loosely-bonded, elliptical inclusions (like fibroadenomas in the breast) is unique and therefore has the potential to distinguish benign fibroadenomas from malignant tumors in the breast. The ASSEs were obtained using quasi-static axial compressions, in a like manner as in normal axial-strain elastography. However, strict axial compression is achieved most often only by computer-controlled acquisitions and not by more practical freehand acquisitions. In a freehand acquisition, the frame sequence may contain several frames that do not experience strict axial compression but may also experience rotation or shear deformations. In this paper, we demonstrate the importance of accounting for the type of deformation applied to a target tissue for the correct interpretation of the resulting ASSEs. Using freehand acquired in vivo examples, we show that such a frame experiencing rotation or shear deformations results in ASSEs that may potentially be misinterpreted. This may be far more detrimental compared to the corresponding axial elastogram frames that may only suffer from inferior image quality in terms of contrast-to- noise ratio (CNR). Further, we show that we may be able to eliminate these frames from a sequence of freehand acquired in vivo breast lesion data by implementing a special filtering scheme, thus significantly improving the reliability of the remaining ASSE frames. This work further suggests that under freehand conditions, frames have to be checked for the presence of undesirable deformations.
Acoustic Radiation Force Impulse (ARFI) Imaging-Based Needle Visualization
Authors: Rotemberg Veronica , Palmeri Mark , Rosenzweig Stephen , Grant Stuart , Macleod David , Nightingale Kathryn
Published: March 2013

Ultrasound-guided needle placement is widely used in the clinical setting, particularly for central venous catheter placement, tissue biopsy and regional anesthesia. Difficulties with ultrasound guidance in these areas often result from steep needle insertion angles and spatial offsets between the imaging plane and the needle. Acoustic Radiation Force Impulse (ARFI) imaging leads to improved needle visualization because it uses a standard diagnostic scanner to perform radiation force based elasticity imaging, creating a displacement map that displays tissue stiffness variations. The needle visualization in ARFI images is independent of needle-insertion angle and also extends needle visibility out of plane. Although ARFI images portray needles well, they often do not contain the usual B-mode landmarks. Therefore, a three-step segmentation algorithm has been developed to identify a needle in an ARFI image and overlay the needle prediction on a coregistered B-mode image. The steps are: (1) contrast enhancement by median filtration and Laplacian operator filtration, (2) noise suppression through displacement estimate correlation coefficient thresholding and (3) smoothing by removal of outliers and best-fit line prediction. The algorithm was applied to data sets from horizontal 18, 21 and 25 gauge needles between 0–4 mm offset in elevation from the transducer imaging plane and to 18G needles on the transducer axis (in plane) between 10° and 35° from the horizontal. Needle tips were visualized within 2 mm of their actual position for both horizontal needle orientations up to 1.5 mm offset in elevation from the transducer imaging plane and on-axis angled needles between 10°–35° above the horizontal orientation. We conclude that segmented ARFI images overlaid on matched B-mode images hold promise for improved needle visibility in many clinical applications.
Synergistic Effects of Ultrasound-Activated Microbubbles and Doxorubicin on Short-Term Survival of Mouse Mammary Tumor Cells
Authors: Ghoshal Goutam , Swat Stanley , Oelze Michael L.
Published: March 2013

The primary focus of this paper is to quantify the therapeutic synergism when combining ultrasound, ultrasound contrast agents (UCAs) and doxorubicin for breast cancer treatment using an in vitro experimental configuration with mouse mammary tumor (4T1) cells. The 4T1 cells were grown in 96 well plates and allowed to grow to 90% confluency. A 1-MHz focused (f/3) single-element transducer was used to expose the microbubbles (MBs) (Definity) with ultrasound near the surface of the cells. After the ultrasound exposure, different doses of doxorubicin were added and incubated for 24 hours at 37 °C, 100% humidity and 5% CO2. The efficacies of the drug only and ultrasound-activated MBs combined with drug therapies to kill cells were then quantified by analyzing the cell viability after 24 hours of treatment using the MTT Cell Proliferation Assay. The combined therapy resulted in 60±5.9% of cell viability compared to 82±4.5% when only doxorubicin was used. The cell viability was 72±5.8% when only ultrasound-activated MBs were used with a similar acoustic pressure condition. No significant increase in cell death was observed for higher concentrations of doxorubicin whereas higher peak negative pressure of the ultrasound wave resulted in increased cell death.
Echocardiographic-Based Assessment of Myocardial Fiber Structure in Individual, Excised Hearts
Authors: Milne Michelle L. , Singh Gautam K. , Miller James G. , Holland Mark R.
Published: March 2013

The objective of this study was to assess the feasibility of using echocardiographic imaging as an approach for determining the myocardial fiber structure of intact, individual hearts. Seven formalin-fixed, ex vivo sheep hearts were imaged using a commercially available echocardiographic imaging system, and the intrinsic fiber structure for the reconstructed short-axis cross section was determined for a specific distance from the apex of each heart. Diffusion tensor magnetic resonance (DT-MR) images of each heart were acquired and fiber maps were created for comparison with the fiber structure obtained from the corresponding reconstructed echocardiographic images. These two methods of obtaining the fiber structure showed relatively good agreement, suggesting that measurements of fiber orientation for individual hearts can be derived from echocardiographic images. Further development of this method may provide a clinically useful approach for mapping the fiber orientation in individual patients over the heart cycle.
Improvements in the Analysis of Ultrasonic Scattering from Inhomogeneities in Tissue
Authors: Aks S. Ø. , Vezzetti D. J.
Published: March 2013

The elementary scattering theory of Rayleigh and Born is extended to account for effects of finite absorption and of sample geometry including boundary refraction. Examples of the procedure are given for several scatterer configurations and results compared with those of the Rayleigh-Born procedure. It is shown that for a realistic choice of tissue parameters these effects modify the Rayleigh-Born results by factors of the order of 10 percent or less provided observations are made over a suitably limited range of angles about the backward direction.
1 mm Catheter Tip Doppler Probe Using a Single Crystal and Bridge
Authors: Poore E. R.
Published: March 2013

The construction of an inexpensive 1 mm diameter 10 MHz single crystal catheter tip Doppler ultrasound probe for measuring blood velocities in fetal vessels is described. A simple bridge circuit which enables single crystal transducers to be used is also described.
Aqueous Solutions as Potential Ultrasonic Contrast Agents
Authors: Ophir J. , McWhirt R. E. , Maklad N. F.
Published: March 2013

Enhancement of ultrasonic backscatter and reflectivity from tissues has been demonstrated in the past using gas bubbles and thermal effects. This paper presents a new approach, whereby such enhancement can be achieved by the introduction of suitable aqueous solutions into tissue. Ideally, such solutions should exhibit low toxicity and ultrasonic properties markedly different from those of tissue. Twenty-two potential materials were identified and the speed of sound, density and acoustic impedance in their solutions were determined as a function of concentration. Some of these solutions were used in preliminary in vitro and in vivo canine experiments and echo enhancement was demonstrated.
Ultrasonic Scattering Theory II: Scattering from Composites
Authors: Vezzetti D. J. , Aks S. Ø.
Published: March 2013

This is the second of two papers which present the fundamental concepts and terminology of acoustical scattering theory in a manner suitable for use by those involved in ultrasonic tissue characterization. The first paper [1] dealt with scattering by single objects. The present paper discusses scattering by collections of objects, including statistical aspects of scattering and the theory of the index of refraction for ultrasonic waves.
The Detection of Blood Impurities Using Ultrasound Doppler
Authors: Newhouse V. L. , Hoover M. L. , Ash S. R.
Published: March 2013

The atraumatic detection of blood impurities such as charcoal particles has potential importance in the monitoring of extracorporeal blood flow for hemodialysis systems using carbon slurry in the dialisate and for blood detoxification using carbon columns. It is shown that existing clinical ultrasound Doppler systems can detect carbon particles whose diameter is comparable to that of an erythrocyte in concentrations as low as 1.5 times 10−6 g/ml in less than one second. It is shown that for particle detection in flow, Doppler systems are more sensitive than pulse echo systems of equivalent resolution by the ratio of the velocity of sound to that of the flow.
Transient Fields of Concave Annular Arrays
Authors: Arditi Marcel , Foster F. Stuart , Hunt John W.
Published: March 2013

A new analytic expression for the impulse response of concave radiators is used to compute the transient pressure distributions of phased annular arrays with spherical geometry. The process of phasing the array to achieve variable focusing is treated by summing the delayed impulse responses of the individual annuli. The example of pressure distributions of a five element annular array is treated in detail, and some recommendations are given for practical computer studies.
Effects of Anisotropy in the Ultrasonic Attenuation of Tissue on Computed Tomography
Authors: Brandenburger G. H. , Klepper J. R. , Miller J. B. , Synder D. L.
Published: March 2013

We examine the consequences of anisotropy in the ultrasonic attenuation on computed tomography. A phenomenological model for anisotropy in the ultrasonic attenuation of soft, inhomogeneous, tissue-like media is presented. Based upon the model, the effects of anisotropy on transmission tomography are investigated analytically and by computer simulation for simple geometries. Sources of apparent anisotropy in ultrasonic measurements made on intrinsically isotropic media are also discussed. Results of simulations are compared with tomograms of tissue studied in vitro. In particular, reconstruction of a simulated anisotropic heart showed good agreement with the reconstruction of an actual heart.
An Improved Medical Ultrasonic Imaging System for Scanning Peripheral Anatomy
Authors: Marich K. W. , Ramsey S. D. , Wilson D. A. , Holzemer J. F. , Burch D. J. , Taenzer J. C. , Green P. S.
Published: March 2013

An Improved Ultrasonic B-scan/Doppler system has been developed for the noninvasive assessment of atherosclerotic arterial disease. Very high-resolution cross-sectional images of anatomic structures are produced by the 10-MHz B-scan subsystem. Instantaneous profiles of blood flow velocity as a function of position are produced by a bidirectional 16-channel pulsed-Doppler subsystem, operating at 5 MHz. Flow profiles are superimposed on the B-scan image, allowing simultaneous evaluation of anatomic structure and blood flow dynamics. Images of the carotid artery, thyroid gland, testicle, and eye are presented to demonstrate the diagnostic potential for imaging peripheral anatomy.
Ultrasonic Backscattering from Non-Uniform Scatterers
Authors: Koch Ingeborg
Published: March 2013

For random arrays of cylindrical scatterers a model of ultrasonic backscattering is described which includes first order multiple scattering effects. Velocity and attenuation are not constant in the scattering array; different values as well as small fluctuations from one scatterer to another are considered. A theoretical description and analysis of effects on the echo from these non-uniform scatterers are presented and confirmed by computer simulations.
A Ternary Solution for Independent Acoustic Impedance and Speed of Sound Matching to Biological Tissues
Authors: Ophir Jonathan , Jaeger Paul
Published: March 2013

In applications requiring a liquid which is acoustically well matched to biological tissues, it is often difficult to find a material which is matched well in terms of both the acoustic impedance and speed of sound propagation in it; changing one parameter invariably affects the other. A three component liquid system is described, which allows independent adjustment of these two acoustic parameters over a wide range. This range encompasses the soft tissues of the body. Results of parameter measurements are presented in the form which allows simple determination of the mixture required to match any combination of acoustic impedance and speed of sound propagation over a given range.
A New Wire Phantom for Accurate Measurement of Acoustical Resolution
Authors: Trimmer William Stuart Newberry , Vilkomerson David
Published: March 2013

This article describes a phantom which is easier to use and gives more accurate results than a phantom made from several pairs of solid wires. This phantom employs two concepts: spatially modulated wires and diverging wires.

Spatially modulated wires, such as helically twisted wires, reflect the sound into a broad range of angles. This has two advantages. One, it is easier to align the transducer with the reflected beam. Two, the diffuse reflection is similar to the scattering from tissue, and the system gain need not be turned abnormally low.

Diverging wires improve the accuracy and convenience of the measurement. Rather than many pairs of parallel wires, a single pair of wires which diverge from an apex is used. By scanning across this pair until the wires are just resolved, the resolution can be easily calculated.
Propagation of Brdadband Ultrasound in Attenuating Media
Authors: Simonds R. M.
Published: March 2013

An expression describing the time dependent evolution of broadband ultrasound wave forms is derived for signals propagating in a homogeneous tissue equivalent medium w ith an attenuation coefficient which is linearly proportional to frequency and for a class of pulse modulations which are analytic in the complex frequency plane. Results of the analys is are compared with those obtained by using a simple Gaussian modulation. It is shown that the frequency down shift produced by the medium causes predictable modifications in ultrasound beam widths and theoretical estimates are compared with published experimental data.
Automatic Real-Time Endocardial Edge Detection in Two-Dimensional Echocardiography
Authors: Melton Hewlett E. , Collins Steve M. , Skorton David J.
Published: March 2013

Previous approaches to automatic border recognition in two-dimensional echocardiography have utilized off-line computer image analysis. In this paper, we describe a hardware technique for real-time endocardial edge detection during the echocardiographic examination. This technique is based on a new method of line-by-line compensation for ultrasound attenuation. The detected edges and composite edge images can be displayed alone or superimposed upon the usual echocardiographic display. To test the accuracy of our real-time technique, we obtained echocardiograms of excised hearts and compared real-time edges with edges manually traced by an experienced observer. Left ventricular cavity areas and endocardial perimeters derived from real-time edges correlated well with those derived from observer-defined edges.
Computer Simulations of Speckle in B-Scan Images
Authors: Foster D.R. , Arditi M. , Foster F.S. , Patterson M.S. , Hunt J.W.
Published: March 2013

The granularity or speckle in medical ultrasound images tends to mask the presence of small lesions. As well, artifactual filling in of anechoic regions such as cysts, reduces the diagnostic potential of the images. These effects depend not only on the acoustic properties of the tissue but also are strongly influenced by the imaging system, especially the transducer geometry.

To study the effect of the transducer on the final B-scan image, a computer model has been developed simulating the interaction of ultrasound with a simple scattering medium. This model, incorporating the position dependence of the point response of the transducer, is based on single scattering from a collection of points positioned randomly in a three-dimensional volume. Using this approach, B-scan images showing speckle have been generated for different transducer geometries. Inclusion of a 2.6 mm void mimicking a cyst within the three-dimensional scattering volume has allowed us to predict the cyst contrast in the image for the different transducer systems.

Experimental B-scan images of a scattering phantom were obtained using the different pulse echo systems. Quantitative assessment using first and second order statistics of the images shows good agreement between experiment and theory.
Inverse Scattering Solutions by a Sinc Basis, Multiple Source, Moment Method -- Part I: Theory
Authors: Johnson Steven A. , Tracy Michael L.
Published: March 2013

A new method for solving the inverse scattering problem for the scalar, inhomogeneous, exact, Helmholtz wave equation is presented. No perturbation approximations are used and the method is applicable even for many cases where weak to moderate attenuation and moderate to strong refraction of incident fields occur. The ill-posed nature of the inverse scattering problem for a single monochromatic source is known. However, the use of multiple sources, the collection of redundant (i.e., overdetermined) data, and the constraining of the fields and complex refractive index to be spatially band limited constitutes a new problem. The cases we have tested by computer simulation indicate that the new problem is well posed, has a unique solution, and is stable with noisy data. The method is an application of the well-known method of moments with sinc basis and delta testing functions to discretize the problem. The inverse scattering solution may be obtained by solving the resulting set of simultaneous, quadratic, multivariate equations. Several algorithms for solving these equations are given.
Inverse Scattering Solutions by a Sinc Basis, Multiple Source, Moment Method -- Part II: Numerical Evaluations
Authors: Tracy Michael L. , Johnson Steven A.
Published: March 2013

In part I, we presented a method for solving the inverse scattering problem using multiple sources and detectors. Allowance for multiple angles of incident radiation improves the ill-posed nature of the inverse problem by improving the quality and quantity of information gathered at detector points. This paper describes implementation and numerical evaluation of the method. An 11 by 11 image reconstructed from noisy scattered field data is shown to closely match the original scattering object, and the improvement possible by constraining the reconstruction to be spatially band limited is demonstrated. Furthermore, for a somewhat simpler “pseudo-inverse problem,” we give findings on the effects that detector radius, degree of overdetermination, noise, and object contrast have on reconstruction quality.
Tomographic Imaging of Ultrasonic Reflectivity with Correction for Acoustic Speed Variations
Authors: Kim Jin H. , Park Song B. , Johnson Steven A.
Published: March 2013

The effect of acoustic speed variations, i.e., inhomogeneous index of refraction, on ultrasonic reflection tomography is examined by computer simulation and experiment. The result shows that the resolving power of reflection tomography is lowered and structural distortions are caused by acoustic speed variations even in the case of small refractive index fluctuations, as in biological objects. A method based on transmission time-of-flight measurements is developed to correct this refraction effect, and its validity was experimentally verified for a test phantom and dog hearts.
A New Scan Conversion Algorithm for Ultrasound Compound Scanning
Authors: Lee Seung-Woo , Park Song-Bai
Published: March 2013

An improved scan conversion algorithm for ultrasound compound scanning is proposed. In this algorithm, the input data in the spatial domain is sampled by the concentric square raster sampling (CSRS) method, and the display pixel data are filled by one-dimensional linear interpolation. The reconstruction error of the proposed algorithm is much smaller than that of other algorithms, because only one-dimensional, rather than two-dimensional, interpolation is involved. This algorithm greatly simplifies implementation of a real-time digital scan converter (DSC) for spatial compounding of ultrasound images.
Myocardial Tissue Characterization Using Pattern Recognition Procedures on Backscattered Ultrasonic Signals
Authors: Dyer R.A.G. , Dyer S.A. , Bhagat P.K.
Published: March 2013

Pattern recognition techniques were applied to backscattered signals obtained in vitro from normal and abnormal canine and human heart samples. Orthogonal transforms, in conjunction with the variance criterion, comprised the feature extractors. The minimum-distance (MD) and nearest-neighbor (NN) rules were used as classifiers. When the MD rule was used, the magnitude of the DFT gave the best performance for both canine and human samples. When the NN rule was used, all the transforms performed comparably. The classification performances were improved for both species when the NN rule was used with feature extractors containing phase information.
Estimate of Attenuation Coefficient for Ultrasonic Tissue Characterization Using Time-Varying State-Space Model
Authors: Shih Li Y. , Barnes Casper W. , Ferrari Leonard A.
Published: March 2013

The images generated from ultrasound pulse-echo signals have long been used to aid clinical diagnosis. Recently, there has been a growing interest in quantitatively determining the acoustic parameters of the tissue as a means of classification and diagnosis. For example, the frequency-dependent attenuation is known to be correlated with different diseases in the liver. In this paper we introduce a new technique for estimating the attenuation coefficient. The effect of attenuation on an interrogating signal with a gaussian-shaped spectrum can be obtained by studying the Wigner distribution of reflected rf data based on a one-dimensional signal model. We show that under the condition that the attenuation varies linearly with frequency, the spectral mean of the reflected signal decreases linearly with time. The estimation algorithm models the pulse-echo signal as the output of a second-order time-varying state-space innovations model driven by white noise. The state coupling matrix A and the output coupling vector C vary with time in a known fashion; moreover, they are also functions of an unknown constant parameter θ. The attenuation coefficient, which is one of the elements of θ, can be estimated directly using a recursive system identification algorithm. The algorithm was verified using both computer-generated synthetic data and in-vivo liver data of known diagnosis. The results show correlation between the estimated parameter and the pathological State Of the tissue.
Adapting Parametric Acoustic Arrays for Tomographic Imaging
Authors: Cai Anni , Sun Jing Ao , Wade Glen
Published: March 2013

In this paper, we present a theoretical model of a parametric array for tomographic applications. The array in the model is assumed to extend right up to the receiver and its cross section is assumed not to be negligible. These two assumptions have not been previously made in applications concerned with tomography. We invoke conditions that permit the derivation of a simple relation for tomographic reconstruction of variations in the acoustic nonlinear parameter throughout the cross section of an object.
Modeling and Computer Simulation of Ultrasound Imaging Systems and Human Tissues
Authors: Lee Bum S. , Park Song B.
Published: March 2013

A simulator has been developed for an ultrasound linear scan B-mode imaging system. First, a numerical method of calculating field patterns or pulse echo patterns is presented for a full-aperture system with a given transducer geometry in nonattenuating and attenuating media, based on the measured temporal impulse response for a single transducer element immersed in water, and taking into account the variation of attenuation and acoustic velocity in human tissue. The simulator then models and simulates the receiver subsystems in detail using the received pulse echo. In particular, a dynamic inverse filter, to improve the axial resolution, and an unconventional TGC gain function, to reduce the SNR deterioration through logarithmic compression, are proposed. Finally, simulation and experimental results are presented and discussed.
Scattered Wave Inversion by Image Projections
Authors: Rouseff Daniel , Porter Robert P. , Ewart Terry E.
Published: March 2013

A three-dimensional diffraction tomography algorithm based on image projections is implemented. For each view, the measured scattered field is directly backpropagated onto a single plane in the image space. The backpropagated field evaluated on the plane is defined as the image projection because it closely approximates the straight line projection of the object. The object is then reconstructed by parallel slices using conventional straight ray tomographic techniques. This approach permits practical three-dimensional reconstruction using a limited number of views. The reconstructions made with image projections are of comparable quality to ideal diffraction-limited images. By backpropagating the field prior to filtering, curved or misaligned recording surfaces can be used. The limits on the image projection technique for multiple object systems are explored. A diffuse structure is reconstructed.
Phase-Derivative Imaging III: Theoretical Derivation of First and Second Order Statistics
Authors: Thijssen J.M. , Oosterveld B.J. , Romijn R.L.
Published: March 2013

The echo signal obtained from a homogenous and isotropically scattering medium can be described as a Poisson time series which is convolved with the transmission pulse of the transducer. The probability density function (pdf) of this signal approximates to a Gaussian pdf for a narrowband pulse waveform. Methods to derive the phase-derivative (PD) signal from the complex envelope and the preenvelope of the echo signal are described. The first order pdf of the PD asymptotically becomes a Gaussian pdf by smoothing. Since the rectified PD is employed to obtain 2-dimensional grey scale images, the first order pdf as well as the signal-to-noise ratio (SNR) of this signal are also derived. The rectified PD is further smoothed by a cosine time window prior to the imaging. The SNR and the autocorrelation function (in the axial direction) of this latter signal can be derived under the assumption of a Gaussian spectrum of the transmission pulse. These first and second order characteristics of the PD images are calculated for the conditions employed in simulations and experiments reported previously and are quantitatively compared to the values obtained from these.
Preliminary Results for Shear Wave Speed of Sound and Attenuation Coefficients from Excised Specimens of Human Breast Tissue
Authors: Burke Thomas M. , Blankenberg Tikoes A. , Sui Albert K. Q. , Blankenberg Francis G. , Jensen Hanne M.
Published: March 2013

A pilot study involving 53 specimens of excised human female breast tissue was performed to provide preliminary estimates of the acoustic shear wave speed of sound and linear attenuation coefficient associated with high risk for development of invasive breast cancer. The measured shear wave properties were studied as a function of: 1. whether the tissue was presented as a 2.0 to 4.0 gram mass biopsy sample or a 2.0 to 4.0 gram mass subsample taken from a larger mastectomy source; 2. the time post-excision prior to shear wave characterization; 3. the risk factor associated with the number and types of lesions found in the specimen; and 4. the percent by volume of fat or collagen present in the sample. The shear speed of sound was found to range between 20 and 900 m/s with a tendency for lower speeds as a function of time post excision. The results for shear attenuation coefficients ranged from 300 to 9000 cm-1 and did not show a marked time dependence. Average results from mastectomy specimens differed from those for biopsies, but the difference may have been due to variations in tissue composition and time post excision before shear wave Characterization.
In Vivo Measurements of Ultrasonic Beam Distortion in the Breast
Authors: Trahey G.E. , Freiburger P.D. , Nock L.F. , Sullivan D.C.
Published: March 2013

The phase aberrations encountered by ultrasonic pulses propagating through breast tissue in twenty-two female volunteers were measured. The experiments were designed to assess the impact of these aberrations on clinical ultrasonic image quality for a variety of transducer and imaging geometries. The phase aberration profiles of a given patient were correlated with the amount of parenchymal tissue determined from that patient's mammogram. These data are useful in assessing the image quality achievable with conventional ultrasonic imaging systems, and the potential application of adaptive ultrasonic imaging systems. The results indicate that phase aberrations significantly degrade breast image quality for typical transducer frequencies and sizes.
Elastography: A Quantitative Method for Imaging the Elasticity of Biological Tissues
Authors: Ophir J. , Céspedes I. , Ponnekanti H. , Yazdi Y. , Li X.
Published: March 2013

We describe a new method for quantitative imaging of strain and elastic modulus distributions in soft tissues. The method is based on external tissue compression, with subsequent computation of the strain profile along the transducer axis, which is derived from cross-correlation analysis of pre- and post-compression A-line pairs. The strain profile can then be converted to an elastic modulus profile by measuring the stresses applied by the compressing device and applying certain corrections for the nonuniform stress field. We report initial results of several phantom and excised animal tissue experiments which demonstrate the ability of this technique to quantitatively image strain and elastic modulus distributions with good resolution, sensitivity and with diminished speckle. We discuss several potential clinical uses of this technique.
An Efficient Algorithm to Remove Low Frequency Doppler Signals in Digital Doppler Systems
Authors: Hoeks A.P.G. , van de Vorst J.J.W. , Dabekaussen A. , Brands P.J. , Reneman R.S.
Published: March 2013

In color flow imaging, a high flow map rate in combination with a reasonable width of the map and good velocity resolution is essential to properly appreciate the time-dependent phenomena. The velocity resolution depends on the length of the signal segment considered in combination with the settling time of the high pass filter used to eliminate transients and low frequency artifacts. The latter can be reduced by appropriate processing. This paper presents an algorithm to suppress low frequency Doppler signals effectively and efficiently, while all the data points within the segment considered contribute equally to the average Doppler frequency computed. The algorithm is applied to computer generated Doppler signals to evaluate their time and frequency behavior. It is concluded that the proposed scheme functions adequately under various signal conditions.
An Iterative Algorithm for Scanning Tomographic Acoustic Microscopy
Authors: Meyyappan A. , Wade G.
Published: March 2013

Acoustic microscopy is capable of providing high-resolution images of small objects. When such a microscope operates in the transmission mode, it produces simply a shadowgraph of all the structures encountered by the acoustic wave passing through the object. The resultant images are difficult to comprehend because of diffraction and overlapping of complex structures. Scanning tomographic acoustic microscopy (STAM) overcomes these difficulties and produces unambiguous micrographs of objects of substantial thickness and complexity. STAM uses the back-and-forth propagation algorithm to reconstruct tomograms of various layers to be imaged. When these layers are physically close to one another, ambiguities appear in the reconstructed images. Using an iterative algorithm eliminates these ambiguities and resolves layers that are only two wavelengths apart.
Improved Resolution Backscatter Coefficient Imaging
Authors: Boote Evan J. , Hall Timothy J. , Madsen Ernest L. , Zagzebski James A.
Published: March 2013

This paper reports the extension of a method for imaging acoustic backscatter coefficients that allows for greater spatial resolution in the resulting images. This is done by using a broad-band excitation pulse and short-duration time gates in the analysis. The images produced had better spatial resolution than the previously reported technique [Ultrasonic Imaging 10, 121–138]. Furthermore, the pixel values were based upon quantitatively accurate backscatter coefficients at given spatial locations. The paper also discusses the additional computational requirements of greater spatial resolution and proposes a least-squares fit to a smoothly varying set of sparse data to generate the data points in between.
Synthetic Aperture Imaging Using a Lagrange Based Filtering Technique
Authors: Li Pai-Chi , O'Donnell M.
Published: March 2013

Synthetic aperture imaging using a catheter based, circular phased array providing high resolution, dynamic focusing has been explored. Due to the high input impedance and low signal-to-noise ratio (SNR) of a classic single element synthetic aperture system, multi-element synthetic aperture processing has been proposed with SNR improvement of about 8 dB for a 33 element aperture. Reconstruction in this case uses an optimal filtering approach based on minimizing the mean square error between filter output and desired beam pattern. This approach, however, does not directly control both mainlobe beamwidth and sidelobe levels. To overcome this problem, a Lagrange based filter design technique has been developed that not only satisfies the minimum energy criterion, but also constrains sidelobe levels under a certain threshold. The new technique provides better spatial and contrast resolution. Both the mathematical formulation and simulation results are presented.
Real-Time Ultrasonic Scan Conversion via Linear Interpolation of Oversampled Vectors
Authors: Richard William D. , Arthur R. Martin
Published: March 2013

Scan conversion is required in order to display conventional B-mode ultrasonic signals, which are acquired along radii at varying angles, on standard Cartesian-coordinate video monitors. For real-time implementations, either nearest-neighbor or bilinear interpolation is usually used in scan conversion. If the sampling rate along each radius is high enough, however, the gray-scale value of a given pixel can be interpolated accurately using the nearest samples on two adjacent vectors. The required interpolation then reduces to linear interpolation. Oversampling by a factor of 2 along with linear interpolation was superior to bilinear interpolation of vectors sampled to match pixel-to-pixel spacing in 6 representative B-mode images. A novel 8-bit linear interpolation algorithm was implemented as a CMOS VLSI circuit using a readily available, high-level synthesis tool. The circuit performed 30 million interpolations per second. Arithmetic results produced by the 8-bit interpolator on 7-bit samples were virtually identical to IEEE-format, single-precision, floating-point results.
Postprocessing of Velocity Distributions in Real-Time Ultrasonic Color Velocity Imaging
Authors: Collaris R.J. , Hoeks A.P.G.
Published: March 2013

A robust processing scheme is proposed that improves the presentation of 2-dimensional velocity distributions in real-time ultrasonic color velocity images. Essentially, the algorithm is a modification of a first order recursive filter, processing each velocity signal in the spatial distribution separately from the others. It restores the sudden holes and notches in the velocity profiles that occur wherever the observed blood velocity is incidentally close to zero. At the same time, unlike conventional persistence filters, it does not influence any of the true velocity information that is measured. The result is a consistent sequence of color velocity images with smooth transitions between the borders of the consecutive velocity profiles and with an improved definition of the regions containing blood.
Methods for Estimation of Subsample Time Delays of Digitized Echo Signals
Authors: Céspedes I. , Huang Y. , Ophir J. , Spratt S.
Published: March 2013

Time delay estimation (TDE) is commonly performed in practice by crosscorrelation of digitized echo signals. Since time delays are generally not integral multiples of the sampling period, the location of the largest sample of the crosscorrelation function (ccf) is an inexact estimator of the location of the peak. Therefore, one must interpolate between the samples of the ccf to improve the estimation precision. Using theory and simulations, we review and compare the performance of several methods for interpolation of the ccf. The maximum likelihood approach to interpolation is the application of a reconstruction filter to the discrete ccf. However, this method can only be approximated in practice and can be computationally intensive. For these reasons, a simple method is widely used that involves fitting a parabola (or other curve) to samples of the ccf in the neighborhood of its peak. We describe and compare two curve-fitting methods: parabolic and cosine interpolation. Curve-fitting interpolation can yield biased time-delay estimates, which may preclude the use of these methods in some applications. The artifactual effect of these bias errors on elasticity imaging by elastography is discussed. We demonstrate that reconstructive interpolation is unbiased. An iterative implementation of the reconstruction procedure is proposed that can reduce the Computation time significantly.
Measuring the Elastic Modulus of Small Tissue Samples
Authors: Erkamp R.Q. , Wiggins P. , Skovoroda A.R. , Emelianov S.Y. , O'Donnell M.
Published: March 2013

Independent measurements of the elastic modulus (Young's modulus) of tissue are a necessary step in turning elasticity imaging into a clinical tool. A system capable of measuring the elastic modulus of small tissue samples was developed. The system tolerates the constraints of biological tissue, such as limited sample size (≤1.5 cm3) and imperfections in sample geometry.

A known deformation is applied to the tissue sample while simultaneously measuring the resulting force. These measurements are then converted to an elastic modulus, where the conversion uses prior calibration of the system with plastisol samples of known Young's modulus. Accurate measurements have been obtained from 10 to 80 kPa, covering a wide range of tissue modulus values. In addition, the performance of the system was further investigated using finite element analysis. Finally, preliminary elasticity measurements on canine kidney samples are presented and discussed.
3D Ultrasound Tissue Motion Tracking Using Correlation Search
Authors: Morsy A.A. , Von Ramm O.T.
Published: March 2013

Several methods for ultrasound tissue motion tracking and blood velocity estimation have been proposed and clinically applied. While providing valuable information to the clinician that was not obtainable from B-mode anatomical imaging, these methods still suffer from various fundamental and practical limitations that compromise their performance in certain clinical situations. A significant limitation is the inability of most of these methods to estimate the complete 3D motion or velocity vectors. With the introduction of ultrasound volumetric imaging, the need for a method that is capable of obtaining the complete motion vector is even more pressing. In this paper, we investigate the implementation of a correlation search scheme to estimate the 3D motion vectors using successive volumetric ultrasound scans. We present tracking results for motion along different axes and discuss the advantages and limitations of performing the correlation search in 3D.
Application of Radiation Force in Noncontact Measurement of the Elastic Parameters
Authors: Fatemi Mostafa , Greenleaf James F.
Published: March 2013

Ultrasound-stimulated vibro-acoustic spectrography is a recently-developed method that employs the radiation force of two intersecting continuous ultrasound beams to remotely vibrate an object at an arbitrary low frequency. Object vibration produces a sound field (acoustic emission) in the medium, which is a function of object mechanical properties. By measuring the acoustic emission field, one can obtain information about the mechanical parameters of the object. In this paper, we use this method for remote (noncontact) measurement of the dynamic Young's modulus of a rod based on its fundamental resonance frequency. Experimental results on an aluminum rod agree with the published data.
Volumetric Hall Effect Tomography — A Feasibility Study
Authors: Wen Han
Published: March 2013

Hall effect imaging is an ultrasound-based method of mapping spatial variations in the dielectric constants of an acoustically-uniform sample. This paper presents three-dimensional Hall effect images of phantoms obtained by scanning a single transducer across a two-dimensional grid, effectively simulating two-dimensional phased-array signal reception. The experiments demonstrate the feasibility of volumetric Hall effect tomography and show the advantage of volumetric scans over planar scans. The images reflect several limitations of the current scanning method and point to directions for further hardware development. The inherent limitations of Hall effect imaging are also discussed in light of these results.
Gamed by the System
Authors: Hochbein Craig , Mitchell Amanda M. , Pollio Martin
Published: February 2013

The recent policy focus on the turnaround of persistently low-achieving schools has generated considerable debate about the reforms needed to dramatically and quickly increase school performance. The purpose of this article is not to focus on specific turnaround interventions, but rather on the identification of schools slated to receive these interventions. Results from the study of 1,059 public schools suggested that operational definitions that relied on No Child Left Behind Act of 2001 metrics overidentified high schools educating diverse populations.
Tumoral Calcinosis Form of Hydroxyapatite Deposition Disease in Related Red-Bellied Short-Necked Turtles, Emydura subglobosa
Authors: Burns R. E. , Bicknese E. J. , Westropp J. L. , Shiraki R. , Stalis I. H.
Published: March 2013

Ten of 12 red-bellied short-necked turtles from a single clutch presented at 9 months of age with multiple white to tan nodules on their feet. Histologically, the nodules were composed of large periarticular deposits of mineralized crystalline material that extended into the joint spaces of interphalangeal joints and was surrounded by granulomatous inflammation and fibrosis. Crystallographic analysis determined the material to be apatite (calcium phosphate hydroxide) consistent with the tumoral calcinosis form of hydroxyapatite deposition disease (HADD). HADD has previously been described in aquatic turtles and rarely lizards and must be differentiated from gout in reptiles. A cause for the tumoral calcinosis lesions in these turtles could not be determined; however, based on previous reports in this species, a species-specific predilection, in conjunction with unknown environmental factors, is suspected. The use of the terms HADD, pseudogout (calcium pyrophosphate crystal deposition disease), and calcinosis circumscripta has been inconsistent, creating confusion in the literature.