bluuebunny/crossref_metadata_2025 huggingface dataset:
Minimum Requirement of Artificial Noise Level for Using Noise-Assisted Correlation Algorithm to Suppress Artifacts in Ultrasonic Nakagami Images
Authors: Tsui Po-Hsiang
Published: March 2013

The Nakagami image is a complementary imaging mode for pulse-echo ultrasound B-scan to characterize tissues. White noise in anechoic areas induces artifacts in the Nakagami image. Recently, we proposed a noise-assisted correlation algorithm (NCA) for suppressing the Nakagami artifact. In the NCA, artificial white noise is intentionally added twice to backscattered signals to produce two noisy data, which are used to establish a correlation profile for rejecting noise. This study explored the effects of artificial noise level on the NCA to suppress the artifact of the Nakagami image. Simulations were conducted to produce B-mode images of anechoic regions under signal-to-noise ratios (SNRs) of 20, 10 and 5 dB. Various artificial noise levels ranging from 0.1- to 1-fold of the intrinsic noise amplitude were used in the NCA for constructing the Nakagami images. Phantom experiments were conducted to validate the performance of using the optimal artificial noise level suggested by the simulation results to suppress the Nakagami artifacts by the NCA. The simulation results indicated that the artifacts of the Nakagami image in the anechoic regions can be gradually suppressed by increasing the artificial noise level used in the NCA to improve the image contrast-to-noise ratio (CNR). The CNR of the Nakagami image reached 20 dB when the artificial noise level was 0.7-fold of the intrinsic noise amplitude. This criterion was demonstrated by the phantom results to provide the NCA with an excellent ability to obtain artifact-free Nakagami images.
High-Frequency Annular Array Fabrication Using a Flex Circuit Matching Layer
Authors: Lay Holly S. , Simpson Eric A. , Griffin Greg , Lockwood Geoffrey R.
Published: March 2013

Fabricating arrays for high-frequency image applications such as ophthalmic imaging, intravascular imaging, and small animal imaging is challenging. For example, an array for intravascular imaging must be small enough to fit within the lumen of a catheter and inexpensive enough to be discarded after a single use. This article presents a new method for fabricating high-frequency annular arrays that is simple and inexpensive. The annular array elements are defined by the electrode pattern on a back surface of a polyimide quarter-wavelength matching layer that is glued to the front face of a ceramic transducer substrate (PZT5H). Electrical losses associated with bonding the matching layer to the transducer substrate are reduced by fabricating a second set of electrodes on the transducer substrate and then bonding the substrates using an anisotropic conductive epoxy. The feasibility of this technique was established by fabricating a seven-element, 20-MHz, 5-mm diameter annular array. The prototype array produced a pulse with a −6-dB factional bandwidth of 50%, an insertion loss of 22 dB, and secondary lobes in the radiation pattern at f/2 that decreased to −65 dB with respect to the main lobe with a peak amplitude of −53 dB.
Acoustic Radiation Force Impulse Imaging of Mechanical Stiffness Propagation in Myocardial Tissue
Authors: Hsu Stephen J. , Byram Brett C. , Bouchard Richard R. , Dumont Douglas M. , Wolf Patrick D. , Trahey Gregg E.
Published: March 2013

Acoustic radiation force impulse (ARFI) imaging has been shown to be capable of imaging local myocardial stiffness changes throughout the cardiac cycle. Expanding on these results, the authors present experiments using cardiac ARFI imaging to visualize and quantify the propagation of mechanical stiffness during ventricular systole. In vivo ARFI images of the left ventricular free wall of two exposed canine hearts were acquired. Images were formed while the heart was externally paced by one of two electrodes positioned on the epicardial surface and either side of the imaging plane. Two-line M-mode ARFI images were acquired at a sampling frequency of 120 Hz while the heart was paced from an external stimulating electrode. Two-dimensional ARFI images were also acquired, and an average propagation velocity across the lateral field of view was calculated. Directions and speeds of myocardial stiffness propagation were measured and compared with the propagations derived from the local electrocardiogram (ECG), strain, and tissue velocity measurements estimated during systole. In all ARFI images, the direction of myocardial stiffness propagation was seen to be away from the stimulating electrode and occurred with similar velocity magnitudes in either direction. When compared with the local epicardial ECG, the mechanical stiffness waves were observed to travel in the same direction as the propagating electrical wave and with similar propagation velocities. In a comparison between ARFI, strain, and tissue velocity imaging, the three methods also yielded similar propagation velocities.
Comparison of Ultrasound Attenuation and Backscatter Estimates in Layered Tissue-Mimicking Phantoms among Three Clinical Scanners
Authors: Nam Kibo , Rosado-Mendez Ivan M. , Wirtzfeld Lauren A. , Ghoshal Goutam , Pawlicki Alexander D. , Madsen Ernest L. , Lavarello Roberto J. , Oelze Michael L. , Zagzebski James A. , O’Brien William D. , Hall Timothy J.
Published: March 2013

Backscatter and attenuation coefficient estimates are needed in many quantitative ultrasound strategies. In clinical applications, these parameters may not be easily obtained because of variations in scattering by tissues overlying a region of interest (ROI). The goal of this study is to assess the accuracy of backscatter and attenuation estimates for regions distal to nonuniform layers of tissue-mimicking materials. In addition, this work compares results of these estimates for “layered” phantoms scanned using different clinical ultrasound machines. Two tissue-mimicking phantoms were constructed, each exhibiting depth-dependent variations in attenuation or backscatter. The phantoms were scanned with three ultrasound imaging systems, acquiring radio frequency echo data for offline analysis. The attenuation coefficient and the backscatter coefficient (BSC) for sections of the phantoms were estimated using the reference phantom method. Properties of each layer were also measured with laboratory techniques on test samples manufactured during the construction of the phantom. Estimates of the attenuation coefficient versus frequency slope, α0, using backscatter data from the different systems agreed to within 0.24 dB/cm-MHz. Bias in the α0 estimates varied with the location of the ROI. BSC estimates for phantom sections whose locations ranged from 0 to 7 cm from the transducer agreed among the different systems and with theoretical predictions, with a mean bias error of 1.01 dB over the used bandwidths. This study demonstrates that attenuation and BSCs can be accurately estimated in layered inhomogeneous media using pulse-echo data from clinical imaging systems.
In Vivo Classification of Breast Masses Using Features Derived From Axial-Strain and Axial-Shear Images
Authors: Xu Haiyan , Varghese Tomy , Jiang Jingfeng , Zagzebski James A.
Published: March 2013

Breast cancer is currently the second leading cause of cancer deaths in women. Early detection and accurate classification of suspicious masses as benign or malignant is important for arriving at an appropriate treatment plan. In this article, we present classification results for features extracted from ultrasound-based, axial-strain and axial-shear images of breast masses. The breast-mass stiffness contrast, size ratio, and a normalized axial-shear strain area feature are evaluated for the classification of in vivo breast masses using a leave-one-out classifier. Radiofrequency echo data from 123 patients were acquired using Siemens Antares or Elegra clinical ultrasound systems during freehand palpation. Data from four different institutions were analyzed. Axial displacements and strains were estimated using a multilevel, pyramid-based two-dimensional cross-correlation algorithm, with final processing block dimensions of 0.385 mm × 0.507 mm (three A-lines). Since mass boundaries on B-mode images for 21 patients could not be delineated (isoechoic), the combined feature analysis was only performed for 102 patients. Results from receiver operating characteristic (ROC) demonstrate that the area under the curve was 0.90, 0.84, and 0.52 for the normalized axial-shear strain, size ratio, and stiffness contrast, respectively. When these three features were combined using a leave-one-out classifier and support vector machine approach, the overall area under the curve improved to 0.93.
Expanding-Aperture Annular Array
Authors: Dietz D. R. , Parks S. I. , Linzer M.
Published: March 2013

A dynamically-focused annular array system for contact B-scanning has been developed. The design is based on a constant F-number approach, whereby, at short focal lengths, the aperture is increased in proportion to the focal length. This approach allows the use of larger area array elements, thus increasing the sensitivity of the system. Other major advantages include a substantial reduction in the time delays and refocusing rates required for the lens synthesis with a corresponding reduction in the electronic complexity of the system. The initial design employs an array operating at 2.25 MHz, with four annuli active at the near focal length of 1.5 cm. As the focal length increases, the array expands to a maximum of twelve rings, with 4.0 cm outer diameter, for focal lengths greater than 12 cm. A single, tapped delay line with 1 μs total duration provides the time delays for focusing on receive. A variable point or line focus is provided on transmit. Experimental measurements of the focusing properties of the system include beam profiles showing mainlobe width and sidelobe levels and B-scans of a standard test object.
Improvement of Range Resolution by Spectral Extrapolation
Authors: Papoulis A. , Chamzas C.
Published: March 2013

Under various simplifying assumptions, the reflected signal y(t) in the interrogation of a substance by an ultrasonic wave is a convolution of the transmitted signal x(t) with a function h(t) that is related to the reflection coefficient of the medium in the direction of propagation. The function h(t) can, in principle, be determined by deconvolution. However, since the band B of the spectrum X(ω) of x(t) is finite, the frequency components of h(t) outside B cannot be found reliably. In this paper, a method is presented for extrapolating X(ω) beyond B. The resulting increase in resolution is limited only by the level of noise. The method is particularly effective if h(t) is a sum of impulses.
Tissue as a Voigt Body for Propagation of Ultrasound
Authors: Ahuja Avtar S.
Published: March 2013

Biologic tissue has been modelled as a viscoelastic Voigt body for the propagation of ultrasound. The tissues considered are man and cow livers, dog myocardial tissue, and cow tongue. Published ultrasonic attenuation data have been correlated, on the basis of a single relaxation frequency, in the frequency range of 0.8–10 MHz. From this correlation, approximate values of elastic moduli have been estimated. The value of the shear modulus appears to be negligible compared to that of the bulk modulus. The value of the relaxation bulk modulus depends upon the type of tissue and its orientation to the sonic beam. The velocity dispersion in tissue has been estimated from the values of bulk moduli.
Ultrasonic Doppler Velocimeter Using Cross-Bispectral Analysis
Authors: Sato Takuso , Sasaki Osami
Published: March 2013

The cross-bispectral characteristics of three simultaneously-detected signals are used to realize a new ultrasonic Doppler vector velocimeter. This system has a special feature in that it is not affected by additive Gaussian noise. The principle, construction and some experimental results are shown.
Multiplexed Receiver for 2 MHz Transit Time Measurements for Implantation
Authors: Poore E. R.
Published: March 2013

Changes in the trunk dimensions of fetal sheep in utero have been monitored using ultrasonic transit-time measurements. The circuitry and operation of a multi-channel receiver and its associated driving circuitry, which enables up to eight distances to be measured in rapid sequence, are described in detail.
Reconstructions from Scattering Data: Analysis and Improvements of the Inverse Born Approximation
Authors: Vezzetti D. J. , Aks S. Ø.
Published: March 2013

The inverse Born approximation is used to reconstruct refractive index profiles from simulated scattering data. Conditions for the validity of the procedure are examined and graphical results for a range of scattering parameters are presented. An iterative procedure which extends the range of applicability of the inverse Born approximation is developed. Improved reconstructions are presented.
Reflection Coefficients at Collagen Interfaces in Soft Tissues
Authors: Ahuja Avtar S.
Published: March 2013

For the purpose of ultrasonic imaging, soft tissue has been modeled as a viscoelastic (Voigt) composite material consisting of collagen fibers (as the inhomogeneity) embedded in a continuum tissue (as the matrix). It is known that infarction enhances the collagen content in myocardial tissues. The published in vitro attenuation data in normal and infarcted myocardial tissues have been correlated with the Voigt body model. From the correlation parameters and mixture laws for the elastic moduli of tissue components, the bulk modulus of collagen has been estimated to be about 50–55% higher than that of the normal tissue. From a knowledge of the bulk moduli and mass densities of collagen and tissue matrix, amplitude reflection coefficients at collagen interfaces have been computed. The amplitude reflection coefficient at the saline-collagen or at the collagen-myocardium interface is about 6 times that at the saline-myocardium interface.
Further Development and Clinical Evaluation of the Expanding Aperture Annular Array System
Authors: Parks S. I. , Linzer M. , Shawker T. H.
Published: March 2013

This paper describes a more sensitive version of the expanding aperture annular array system reported recently. A preliminary clinical evaluation is presented.
Ultrasonic B-Scan Imaging: Theory of Image Formation and a Technique for Restoration
Authors: Fatemi Mostafa , Kak A. C.
Published: March 2013

This paper presents a theory for ultrasonic B-scan image formation. Our theory is based on the assumption that imaging is done using broadband signals and that all the information in the returned echos is utilized for image formation, as opposed to only the “video” detected envelopes. We also assume that the image is formed from the backscattered returns caused by inhomogeneities within soft tissue structures. In other words, we do not take into account the contributions from the specularly reflecting surfaces that represent large impedance discontinuities. (Surfaces that only represent small impedance changes and are “visible” to the transducer are accounted for by our theory.) Our main reason for this omission is the fact that although the contributions of the surfaces with large impedance changes are important to the delineation of features in some 3-scan images, it is the presentation of the backscattered echos from small inhomogeneities within the tissues that is more severely distorted by the radiation and the electromechanical properties of the transducer. Also, it is currently believed that the backscattered echoes from the small inhomogeneities within the tissues carry important pathological information. Our theory is also limited to the case of Linearly scanned transducers with unfocused apertures.

A major result of our theory is an analytical expression for the point spread function of the image degradation. As expected, this function is position variant. To simplify the computations required for image restoration, we have presented approximations that reduce the point spread function to the position-invariant form. We have shown experimentally that the resulting restoration filters retain their effectiveness over several centimeters of the object thickness. This has led us to conclude that the B-scan images of thick objects may be restored by using piecewise position-invariant techniques.
Amplitude Analysis of Pancreatic B-Scans: A Clinical Evaluation of Cystic Fibrosis
Authors: Shawker Thomas A. , Parks Stephen I. , Linzer Melvin , Jones Bonnie , Lester L. A. , Van Hubbard S.
Published: March 2013

Ultrasonic B-scan images of the pancreatic parenchyma in normal and cystic fibrosis patients were numerically analyzed. Images of both the maximum and minimum echoes from the tissue were generated by a recently-developed digital ultrasound system. Complete segregation of the two groups was achieved by averaging the echo amplitude over a selected region in the image. The dependence of the numerical values on the B-scan imaging mode, transducer properties, dynamic range compression curve, and operator scanning technique is discussed in depth.
Ultrasonic Backscatter from Contrast Producing Collagen Microspheres
Authors: Ophir J. , Gobuty A. , McWhirt R. E. , Maklad N. F.
Published: March 2013

Measurements of ultrasonic backscatter from solid collagen microspheres in suspension and from a standard erythrocyte suspension were performed. When normalized to a standard particle size and concentration, the back-scatter from the collagen was 29.6 dB above that of the erythrocytes. An in vivo canine experiment using commercial diagnostic equipment demonstrated enhanced backscatter from the liver after intravenous injection of the microspheres. Calculations show that the in vivo enhancement cannot be explained from the earlier studies. Possible mechanisms responsible for this effect are proposed.
Ultrasonic Scattering Theory. I: Scattering by Single Objects
Authors: Aks S. Ø. , Vezzetti D. J.
Published: March 2013

This is the first 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. This first paper deals with scattering by single objects and the second, which will appear in a future issue, with scattering by collection of objects.
Ultrasound Mammographic-Histopathologic Correlation
Authors: Fields Scott I.
Published: March 2013

A simple technique for the production of ultrasound mammograms employing unmodified commercially available B-scanners has been developed. Specific image criteria of breast lesions were correlated with the histopathologic appearances of the tissue. Special connective tissue stains were employed. The thickness and echogenicity of the breast tumor border correlated with the level of surrounding collagenosis and tumor invasion. The acoustic attenuation of breast tumors was qualitatively proportional to the amount of collagen within the tumor. The accuracies of specific image criteria for the diagnosis of carcinoma were determined. Water-lipid interfaces appear to be important in the production of echoes from within breast tissue and at the tumor margin.
Diffraction Tomography I: The Wave-Equation
Authors: Mueller R. K.
Published: March 2013

A general wave equation for sound propagation in a viscoelastic medium is obtained. From this general equation an approximate inhomogeneous wave equation is derived by perturbation methods. Born's and Rytov's approximations are considered. The equation is finally brought into a form which provides transformation properties under rotation of the test object required for diffraction tomography.
The Power-Spectrum Centroid Detector: System Considerations, Implementation, and Performance
Authors: Gerzberg Levy , Meindl James D.
Published: March 2013

Operation of the √f centroid detector with various doppler systems is discussed, and its design, implementation, and performance are described. It is determined that the detector can be employed in directional detection schemes to measure spectral moments and centroids with correct polarity and with no degradation in accuracy. Narrow- and wideband deterministic signal detection of both stationary and FM information is investigated, and it is found that the centroid detector can also serve as an FM demodulator with high AM rejection.

A versatile √f detector was realized in discrete form and evaluated with deterministic and random signals, and its measured variance agreed closely with the theoretical values. The validity and application of the noise-reduction method was verified on deterministic and random doppler signals. Applications of the detector and the noise-reduction method to blood-flow and velocity measurements are demonstrated.
Real Time Acoustic Imaging by Holographic Interferometry
Authors: Hanafy Amin , Zambuto Mauro
Published: March 2013

A two-step real time acoustic imaging system is presented. The system incorporates a novel acoustic image coupler which transfers an acoustical interference pattern from a water-bounded to an air-bounded surface with vibration amplitude amplification. An original technique termed step-biased real time holographic interferometry is used to convert the amplified mechanical vibration pattern, which carries all information about the insonified object, into a visual image with improved sensitivity.
Near-Field Uniform Beams for Pulsed Doppler Ultrasound
Authors: Fu Chong-Cheng , Noujaim Sharbel E. , Jaffe Robert S. , Gerzberg Levy , Melen Roger D.
Published: March 2013

A mathematical model for the beam pattern of a pulsed ultrasonic transducer is introduced. Beam-pattern analysis and simulation of a circular transducer based on this model agree well with the experimental results. It is demonstrated that, in its near field, the pulsed transducer is capable of generating a good approximation to a uniform ultrasonic field which cannot be achieved with a cw transducer. Preliminary error analysis indicates that the near-field beam pattern of the pulsed transducer is suitable for quantitative blood-flow measurement, and design criteria are developed for this application. A prototype has been fabricated and tested in in-vitro experiments, and the results verify the feasibility of the quantitative blood flowmeter principle and the pulsed-transducer near-field approach to the formation of uniform beams.
Pulsed Doppler and Real-Time “Duplex” Imaging of Dacron Arterial Grafts
Authors: Clifford P. C. , Skidmore R. , Bird D. R. , Lusby R. J. , Baird R. N. , Woodcock J. P. , Wells P. N. T.
Published: March 2013

Ultrasonic imaging was performed in 50 10 mm woven dacron arterial grafts. Patients were scanned either using a “duplex” echo-Doppler scanner or a multichannel pulsed Doppler scanner, or by both methods. The “duplex scanner” had the advantage of maneuverability of the scanning head, but accurate waveform sampling was better with the pulsed Doppler scanner. The development of fibrous pseudointima was detected in long dacron grafts by inference from pulse-echo and pulsed-Doppler imaging, but was not visualized by real-time B-mode scanning alone. The pseudointima developed in the distal ends of 75 percent of the iliopopliteal grafts, and was related to time since implantation. The average thickness of pseudointima was 0.8 mm, and the maximum stenosis seen was 34 percent.
Ultrasonic Attenuation in Soft Tissues: Reasons for Large Magnitude and Linear Frequency Dependence
Authors: Ahuja Avtar S.
Published: March 2013

By modeling soft tissue as a viscoelastic Voigt body, arguments are adduced to explain the large magnitude and linear frequency dependence of ultrasonic attenuation in soft tissues. A comment is also made on the similar values of ultrasonic velocity in soft tissues and water.
The Conical Scanner: A Two Transducer Ultrasound Scatter Imaging Technique
Authors: Foster F. S. , Patterson M. S. , Arditi M. , Hunt J. W.
Published: March 2013

A new two transducer ultrasound scatter imaging system has been developed. In operation, a large conical transducer generates an ultrasound beam that converges to a sharp line focus in the tissue being imaged. The second transducer is aimed along the axis of the cone and detects scattered ultrasound as a function of time, converting this information into a high resolution image. Excellent focusing properties are maintained over a large depth of field with no increase in the complexity of standard B-scanner electronics. As well, no increase in time is required to generate the image.

The performance of a 45° conical scanner is examined theoretically and experimentally. The FWHM of the lateral point response of the scanner remains 0.25 mm over a 5 cm depth of field. Images of phantoms and in vitro breast tissue demonstrate a great improvement in image quality compared with conventional pulse-echo imaging.
Digital Ultrasound Imaging Techniques Using Vector Sampling and Raster Line Reconstruction
Authors: Gehlbach Steve M. , Alvarez Robert E.
Published: March 2013

The use of digital techniques in acoustic imaging is receiving a great deal of attention due to the power and flexibility of digital signal processing as well as its steadily decreasing cost. In this paper we describe the theory and preliminary experimental results for a digital synthetic aperture imaging system which uses one or more transmit/receive cycles to gather data for reconstructing an entire image. The system uses quadrature frequency conversion prior to digitization to reduce the data rate and storage requirements. Using this approach, an imaging instrument design is presented that has the capability of reconstructing images in real time in TV format without conventional scan conversion. Freeze frame is also possible although no image memory is required.
Limitations of Tissue Differentiation by Spectral Measures of Backscattered Ultrasound
Authors: Reinhard D.K. , Gift D.A. , Harris G.I. , DeSostoa C.J.
Published: March 2013

A set of spectral measures and two decision algorithms have been investigated with respect to classification accuracy and robustness to measurement variables. Liver and spleen in normal subjects were selected as test tissues. Tissue classification was based on eight conventional measures derived from the digital Fourier transform of the signal. Decision algorithms based on both Euclidean and Mahalanobis distances were investigated. Classification accuracy of 80 percent was achieved with the latter. Classification accuracy is limited by inter and intra-subject variance as well as by the interdependence of the measures. Nearly all the data lie in a two dimensional plane within the eight dimensional feature space. Further improvement in classification accuracy requires identification of a discriminant measure which is more orthogonal to that data plane.
Vibration Analysis of Single Element Transducer in Acoustic Arrays
Authors: Hanafy Amin
Published: March 2013

This paper offers a method for the vibration analysis of single element transducer in acoustic arrays as a damped multi-degree of freedom mechanical system with forced excitation at the fundamental thickness mode. The link between the frequency response and the element structural modal shape is analyzed and a method for controlling these modes such that they introduce no artifacts in the performance of the final array and imaging system is discussed.
The Effects of Frequency and Angle on Ultrasonic Backscattering from the Upper Airway
Authors: Augustine Larry , Martin Roy W.
Published: March 2013

In vitro experiments on dog tracheas were performed at 5, 8, 11.7, 18, and 26 MHz to evaluate the backscattering as functions of frequency and transducer orientation angles with respect to the tissue to air surface. Additionally, more idealized flat and convex curved specular reflecting surfaces were also studied. The importance of transducer aperture size, frequency, and target distance in determining the maximum angle over which backscattering can be received from a flat specular surface is highlighted. Convex curvature causes a further increase in this maximum angle. The findings from the tissue studies were: 1) backscattering from the trachea became more diffuse in nature as frequency Increased, 2) backscattering from the anterior section of the trachea was detectable over larger angles than that from the posterior, and 3) at frequencies of 11.7 MHz and above, diffuse scattering was a major consideration in scattering from the anterior surface of the tracheas tested.
Vortex Characterization and Identification by Ultrasound Doppler
Authors: D'Luna L. J. , Newhouse V. L.
Published: March 2013

The detection of vortices is of potential interest in physiology (e.g. the detection of weak stenoses), and in fluid mechanics. In this paper a non-invasive method of detecting vortices in channel flows using pulsed RF Doppler ultrasound is described. A novel approach involving hybrid operation is taken in implementing a directional Doppler system. A scattering model of a vortex crossing an ultrasound beam is presented and theoretical simulations of the Doppler signals show good agreement with experiment. Experimental results showing the detection of both periodic and isolated vortices in channel flows are given. The Autoregressive or Maximum Entropy Method of spectral estimation is used to obtain the spectral estimates of the Doppler signals over short time intervals. It is shown that these spectral estimates can be used to estimate the velocity profiles of the detected vortices.
In Vivo Enhancement of Ultrasonic Image Luminance by Aqueous Solutions with High Speed of Sound
Authors: Tyler T. D. , Ophir J. , Maklad N. F. , Gobuty A.
Published: March 2013

Certain amino acids and chelating agents known to increase the velocity of sound in solution were assayed for median lethal dose (LD50). An estimation of each agent's ability to enhance ultrasonic image luminance in vivo was based on its ability to increase sound velocity in solution and on its LD50. The ability of the compound to increase sonogram screen luminance was tested by the infusion of each agent into a mouse being scanned, and concurrent screen luminance measurement with a photometer. The compounds were then ranked in order of their effect on the onset time for a statistically significant increase of image luminance over corresponding saline control values. The most rapid onset of increased luminance was found with the infusion of the amino acid 1-lysine hydrochloride, and the chelating agent calcium disodium edetate. The estimated rankings for these and most other compounds tested compared favorably with the observed results.
An Annular Array System for High Resolution Breast Echography
Authors: Arditi M. , Taylor W.B. , Foster F.S. , Hunt J.W.
Published: March 2013

Ultrasound B-mode imaging with electronically focused annular arrays has been associated in the past with fairly complex and expensive electronic circuits. When image quality rather than scanning speed is the prime concern, the concept of switched zone focusing offers an attractive alternative to true dynamic focusing previously reported. Strongly focused apertures used in both transmit and receive modes allow improved lateral resolution, lower side lobe levels, higher sensitivity, as well as simplified electronics.

This approach was investigated for the particular case of breast imaging. We outline some general design considerations for water path imaging with annular arrays, and describe the system adopted in the development of a high resolution breast scanner using a sealed, water filled head. Experimental results are compared to theoretical predictions, and grey scale images are presented to illustrate the performance of the instrument.
Ultrasonic Measurement of Small Displacements and Deformations of Tissue
Authors: Wilson L.S. , Robinson D.E.
Published: March 2013

A signal processing technique is described for analyzing radio frequency M-mode signals to obtain significantly better depth resolution than previously available. Displacement and deformation waveforms may be measured for displacements less than 0.1 mm and deformations of less than 1 percent. Waveforms of liver dynamics caused by aortic pulsation and vessel diameter variations are presented, and possible tissue characterization applications discussed.
Analysis of B-Scan Speckle Reduction by Resolution Limited Filtering
Authors: Parker Dennis L. , Pryor T. Allan
Published: March 2013

Much of the signal energy due to speckle in ultrasound images is shown to be of higher spatial frequency than the intrinsic pulse shape limited resolution in B-scan ultrasound images. A significant increase in signal to noise ratio can therefore be obtained by resolution limited spatial filtering which selectively removes energy of higher spatial frequency than the pulse envelope resolution limit. The concept is illustrated by resolution limited filtering ECG gated B-scan echocardiographic images. Signal to noise improvement is illustrated by comparing time-motion displays generated from both processed and unprocessed images.
In Vitro Evaluation of an Ultrasonic Three-Dimensional Imaging and Volume System
Authors: Brinkley James F. , Muramatsu Saundra K. , McCallum W. Desmond , Popp Richard L.
Published: March 2013

A method is described for developing three dimensional organ reconstructions and volumes from a series of arbitrarily oriented real time ultrasonic scans. In vitro evaluations of this method assessed the accuracy of three dimensional point determination and the accuracy of volume determination. The overall repeatability error of three dimensional point determination was found to be 0.6 cm in the horizontal direction and 0.3 cm in the vertical direction; most of this error was caused by the ultrasound resolution and errors in the 3D position locator. The accuracy of volume determination was assessed on balloons, kidneys and left ventricular molds. Thirty volume trials on 10 balloons gave 27 out of 30 calculations within 1.8 percent of true volume. Eighteen trials on 6 kidneys gave 17 out of 18 calculations within 5.1 percent of true volume. Fifteen trials on 5 human left ventricular molds gave 13 out of 15 calculations within −5.9 percent of the true volume. It is concluded that this technique provides the potential for accurate non-invasive volumes, for organs such as the heart, kidney or fetus.
Correcting for Ray Refraction in Velocity and Attenuation Tomography: A Perturbation Approach
Authors: Norton Stephen J. , Linzer Melvin
Published: March 2013

In velocity and attenuation tomography, ray refraction leads to errors in time-of-arrival, as well as to errors in attenuation due to phase cancellation and lateral beam displacement. Some authors have proposed iterative techniques based on numerical ray tracing to correct for these effects. In this paper, we consider an alternative approach using a perturbation analysis of refraction. This approach requires neither iteration nor numerical integration of the ray equation. Assuming that the index of refraction deviates from its mean on the order of the small quantity ε, we derive expressions for the refracted ray path whose departure from a straight line is first order in ε. Using this result, we obtain a perturbation expansion of the path integral of the refractive index along the refracted ray and derive a time-delay correction of order ε2 arising from the deviation of the refracted ray from a straight line. The expression for the first-order path is also used to obtain explicit corrections for phase-cancellation and beam-displacement errors that affect attenuation measurements when transducers of finite extent are employed. In addition, because of refraction, large aperture transducers are susceptible to an arrival-time uncertainty in a time-of-flight measurement; a first-order expression for the maximum value of this uncertainty is derived. In both two and three dimensions, the perturbation approach is much simpler computationally than numerical ray tracing methods. Computer simulated reconstructions are presented which clearly show the improvement that can be achieved with the second-order time delay correction.
Multipath Artifact Corrections in Ultrasonic Transmission Tomography
Authors: Crawford C. R. , Kak A. C.
Published: March 2013

This paper deals with computed imaging techniques for ultrasonic transmission tomography. Cross-sectional images of the refractive index in soft biological tissues can be obtained by measuring the arrival-time of signals that propagate between two transducers. An alternative method to obtain images is to measure the attenuation in the path between the pair of transducers. In practice, images of the refractive index exhibit a better quality than images of the attenuation coefficient. In this report we have shown through computer simulation that some of the degradations in images of the attenuation coefficient are due to the existence of multiple rays that link the transmitting and the receiving transducers. This condition is known as multipath. We have demonstrated two methods to reduce the influence of multipath on reconstructions of the attenuation coefficient. The first method employs homomorphic signal processing to estimate the attenuation coefficient for one of the linking rays. The second method applies median filtering in the projection space to remove the artifacts caused by multipath. The correction techniques were tested on data obtained by scanning tissue equivalent phantoms. Results obtained indicate that the correction methods significantly improve the quality of images of the attenuation coefficient.
Spectral Shifts of Ultrasonic Propagation through Media with Nonlinear Dispersive Attenuation
Authors: Ophir Jonathan , Jaeger Paul
Published: March 2013

The relationship between center frequency downshift and transmitted bandwidth was investigated for a pulse with Gaussian amplitude spectrum propagating through a lossy medium with power law frequency dependence of attenuation. Tissue equivalent material was characterized by multiple narrowband attenuation measurements, via a substitution method. Power law curves were fitted to the data. The parameters of the curves were used to predict the behavior of the center frequency downshift vs. transmitted bandwidth obtained from a second experiment. The results confirm the mathematical model.
Interpolation Scan Conversion in Pulse-Echo Ultrasound
Authors: Robinson D.E. , Knight P.C.
Published: March 2013

Some disadvantages of current digital scan conversion techniques are reviewed. An improved system is described which uses linear interpolation between available sampled data points to provide an estimate of the echo reflectivity at each grid point in the image. This approach avoids the problems of “missed pixels” inherent in the current approach, and the need to provide some smoothing or blurring function to remove them. The interpolated scan conversion allows data line spacing to be increased, leading to a reduced scan time for static scans and increased frame-rate for real-time, while retaining all the resolution available from the ultrasound system.
A Geometric Approach to the Filtered Backpropagation Algorithm
Authors: Oristaglio M. L.
Published: March 2013

We show how the filtered backpropagation algorithm [1] for parallel-beam diffraction tomography can be implemented geometrically by weighted straight-line projections. The resulting algorithm is formally equivalent to the original approach using Fourier transforms [2], but reorganizes the calculations to separately backpropagate each plane-wave component of the filtered data. In principle, at least, the projection method also suggests the design of an ultrasound scanner that records the wavefield with line detectors.
Breast Tissue Classification Using Diagnostic Ultrasound and Pattern Recognition Techniques: I. Methods of Pattern Recognition
Authors: Finette Steven , Bleier Alan , Swindell William
Published: March 2013

This paper discusses the application of statistical pattern recognition techniques to problems in diagnostic ultrasound. Using our own system as an example, we describe the concepts and specific methods that we have applied to a problem involving the computer-aided classification of breast tissue in vivo. Topics include feature generation, feature selection and classification, as well as a method which estimates the probability of error on classifying future data. An accompanying paper applies these methods to the classification of backscattered RF signals from normal and diseased breast tissue.
Spectral Characterization and Attenuation Measurements in Ultrasound
Authors: Flax Stephen W. , Pelc Norbert J. , Glover Gary H. , Gutmann Frank D. , McLachlan Maurice
Published: March 2013

Various means of characterizing ultrasonic attenuation in tissue are reviewed. A simple method for estimating frequency-dependent attenuation via measurement of the zero crossing density of the signal is presented and validated. Both the effects of the frequency dependence of scatter and stochastic variability of the measurement are considered and discussed. Results of measurements made in phantoms, animals and humans are presented and compared to the theoretical model. The technique is shown to be technically feasible.
The Improvement and Quantitative Assessment of B-Mode Images Produced by an Annular Array/Cone Hybrid
Authors: Patterson M. S. , Foster F. S.
Published: March 2013

Hybrid ultrasound imaging systems, which combine spherical focusing on transmit with axicon focusing on receive, provide excellent resolution over a useful depth of field. This paper presents a new hybrid design with improved sensitivity, in which the axicon focusing is achieved by two conical mirrors and a PZT 5A disk cut into 8 sectors. We have investigated two methods of processing the signals from the 8 sectors. In the first, phase insensitive sector addition (PISA), the B-scan is formed from the sum of the 8 demodulated signals. In the second, multiplicative processing (MP), the 8 rf waveforms are multiplied and the resultant is demodulated to form the image. Both techniques result in smoothed speckle but degraded lateral resolution. As well, MP decreases the off-axis sensitivity of the system and artifacts characteristic of axicon focusing. Quantitative assessment of the effects of PISA and MP was performed using a new approach called contrast-to-speckle ratio (CSR). The CSR data, which is a measure of the image contrast of cylindrical voids in a random scattering medium relative to contrast fluctuations due to speckle, shows the superiority of PISA and MP. This conclusion is supported by images of in vitro human breast tissue.
Generation of Separate Density and Compressibility Images in Tissue
Authors: Norton Stephen J.
Published: March 2013

A method is suggested for reconstructing separate images of the variations in density and compressibility in the same tissue sample. The images can be obtained from near-field scattering measurements using only two long, rectangular transducer elements. As in diffraction tomography, 180° access around the region of interest is required. This approach differs from conventional diffraction tomography, however, in that no transducer arrays are required and broadband illumination is used. A flat transducer, assumed long relative to the extent of the object, is used as a source of broadband, plane-wave illumination, and as a receiver of the backscattered sound. A second transducer, oriented at a different angle with respect to the first, is used as a receiver only. The two transducers are rotated together 180° around the object, and the scattered sound is recorded at all angles during the rotation. This arrangement can be shown to sample the plane-wave spectrum of the object directly, and provides sufficient information to reconstruct independent images of the variations in both the density and compressibility of the scattering medium. Image resolution is limited by the bandwidth of the illuminating sound.
A Three Dimensional Model for Generating the Texture in B-Scan Ultrasound Images
Authors: Goodsitt Mitchell M. , Madsen Ernest L. , Zagzebski James A.
Published: March 2013

A three-dimensional model for production of gray scale texture in ultrasound B-mode images is described. The model computes time-dependent echo signals resulting from scattering of acoustic pulses by particles randomly distributed in an attenuating medium and transforms these signals into a gray scale image. Specific transducer and pulser-receiver characteristics are accounted for, as well as the three-dimensional nature of the problem, without loss of computational efficiency. The model generates texture that closely corresponds to that found experimentally in ultrasound images of tissue-mimicking phantoms. The dependence of the texture upon the depth of the region that was scanned and on the characteristics of the transducer-receiver system were clearly demonstrated. Good agreement between theory and experiment was found for the texture in phantoms containing simulated spherical low-scatter tumors.
Ultrasound Velocity in Fixed Human Liver: Empirical Anova and Regression Modelling on Histologically Assessed Abnormalities
Authors: Zimmermann K.P. , Smith J.C.
Published: March 2013

Anova and “dummy variables” least squares regression methods are used to investigate the dependence of ultrasound propagation velocity on the presence or absence of fat and on the rank ordered level of cirrhosis in fixed human liver. Cirrhosis is found to affect velocity in a nonlinear fashion, while fat depresses the velocities toward lower values. Quantifications of these effects and statistical analyses of their magnitudes are presented. The results represent a contribution toward the empirical understanding of the effects of tissue abnormalities on the velocity of ultrasound propagation in fixed human tissues.
Imaging the Nonlinear Ultrasonic Parameter of a Medium
Authors: Ichida Nobuyuki , Sato Takuso , Linzer Melvin
Published: March 2013

A technique for imaging the nonlinear ultrasonic parameter B/A has been developed. The nonlinear parameter describes the dependence of ultrasonic velocity on pressure and may well provide a new and powerful tool for characterizing both biological and nonbiological media.

Our approach is based on observing the interaction of two ultrasonic waves with different frequencies and power levels. A low frequency pump wave, with power level suitable for medical diagnosis (1 mW/cm2), is used to sinusoidally modulate the sound pressure over the region of interest. A much lower intensity high-frequency probe beam is propagated perpendicularly to the pump beam. The phase of the probe wave is modified in proportion to the integral of the product of the nonlinear parameter B/A and the pressure of the pump wave, which varies sinusoidally along the probe beam. This phase change provides a Fourier component of the distribution of the nonlinear parameter B/A for the spatial frequency corresponding to the inverse of the pump wavelength. By changing the frequency of the pump waves, the spatial frequency is changed and a set of spatial Fourier coefficients of the distribution of the nonlinear parameter B/A is obtained. An inverse operation then gives the one-dimensional image along the probe beam. If the probe beam is scanned mechanically, the entire cross-sectional image is obtained.

Several images of the nonlinear parameter of biological objects were generated with our system. To our knowledge, these represent the first images of the nonlinear parameter to be reported in the literature. The nonlinear parameter of water was also measured and agreed well with values obtained by other techniques.