bluuebunny/crossref_metadata_2025_split huggingface dataset:
Weakly Inhomogeneous Media Tomography
Authors: Ferrière Robert , Mensah Serge , Lefebvre Jean-Pierre 
Published: March 2013

Our objective is to develop an ultrasonic scanner for breast imaging. High resolution is obtained by using wide-band spherical waves transmitted and measured in the near field zone (i.e., close to the skin) all around the organ. The tomographic approach that we adopt allows us to use low central frequency waves (3–7 MHz) that are suitable for good penetration while maintaining high resolution and contrast. The procedure is thus suitable for early detection of tumors and increases the chances of total recovery. The novelty of the present reconstruction procedure is that it associates the signals acquired in transmission to the data measured in reflection over a large aperture. This enables us to correct the phase aberration induced by weak inhomogeneities whose sizes might be several wavelengths. Numerical tests based on Finite Difference Time Domain (FDTD) simulations demonstrate the greater fidelity of the reconstruction.
Soft tissue Absorption Tomography with Correction for Scattering Aberrations
Authors: Franceschini Emilie , Pauzin Marie-Christine , Mensah Serge , Groby Jean-Philippe 
Published: March 2013

Among the many factors involved in ultrasound attenuation phenomena, scattering effects play a major role, even in the unexpected case of soft tissues. It is proposed in this study to quantitatively evaluate the scattering affecting the measurements before reconstructing the absorption parameter alone. The reconstruction procedure involves three steps: (1) Estimating the sound speed map using a transmission tomography algorithm. This estimation procedure provides a numerical phantom of the organ probed, cleared of all dissipative components. This absorption free phantom mimics the (viscoacoustic) tissues imaged except for the density and absorption characteristics: the density a priori equals 1000 kg/m3 and the absorption is not taken into account. The impedance fluctuations in the object are therefore approximated on the basis of the sound speed contrast. (2) Synthesing the field scattered by the absorption free phantom; the attenuation observed here results solely from the scattering phenomenon. The synthesis is carried out using a finite-element time domain code simulating the ultrasonic propagation through the phantom. It provides the scattering distortion reference introduced into the log spectral absorption estimator. (3) Reducing the scattering distortions affecting the integrated absorption measured along the ray paths using a log spectral procedure. The corrected integrated absorption is then processed using a tomographic reconstruction procedure that provides an estimate of the absorption distribution. Simple numerical simulations show the improvement obtained in the absorption estimates with this approach.
75 MHz Ultrasound Biomicroscopy of Anterior Segment of Eye
Authors: Silverman Ronald H. , Cannata Jonathan , Shung K. Kirk , Gal Omer , Patel Monica , Lloyd Harriet O. , Feleppa Ernest J. , Coleman D. Jackson 
Published: March 2013

Very high frequency ultrasound (35–50 MHz) has had a significant impact upon clinical imaging of the anterior segment of the eye, offering an axial resolution as small as 30 μm. Higher frequencies, while potentially offering even finer resolution, are more affected by absorption in ocular tissues and even in the fluid coupling medium. Our aim was to develop and apply improved transducer technology utilizing frequencies beyond those routinely used for ultrasound biomicroscopy of the eye. A 75-MHz lithium niobate transducer with 2 mm aperture and 6 mm focal length was fabricated. We scanned the ciliary body and cornea of a human eye six years post-LASIK. Spectral parameter images were produced from the midband fit to local calibrated power spectra. Images were compared with those produced using a 35 MHz lithium niobate transducer of similar fractional bandwidth and focal ratio. The 75-MHz transducer was found to have a fractional bandwidth (-6 dB) of 61%. Images of the post-LASIK cornea showed higher stromal backscatter at 75 MHz than at 35 MHz. The improved lateral resolution resulted in better visualization of discontinuities in Bowman's layer, indicative of microfolds or breaks occurring at the time of surgery. The LASIK surface was evident as a discontinuity in stromal backscatter between the stromal component of the flap and the residual stroma. The iris and ciliary body were visualized despite attenuation by the overlying sclera. Very high frequency ultrasound imaging of the anterior segment of the eye has been restricted to the 35–50 MHz band for over a decade. We showed that higher frequencies can be used in vivo to image the cornea and anterior segment. This improvement in resolution and high sensitivity to backscatter from the corneal stroma will provide benefits in clinical diagnostic imaging of the anterior segment.
3-D Spatial Compounding Using a Row-Column Array
Authors: Awad Samer I. , Yen Jesse T. 
Published: March 2013

2-D spatial compounding has long been investigated to reduce speckle in ultrasound images. To further reduce speckle, several 3-D spatial compounding studies using 1-D and 1.5 D arrays with mechanical translation and position tracking have been reported. However, the fixed elevational focus and mechanical translation can degrade image quality in elevation. Using 2-D arrays, a better elevational resolution can be achieved with electronic focusing. Furthermore, 2-D arrays can generate greater number of independent images than 1-D arrays and the need for mechanical scanning is eliminated. In this paper, we present our 3-D spatial compounding images of two gel-based contrast phantoms and one resolution phantom. These images were acquired using a prototype 4 cm × 4 cm ultrasonic row-column prototype 2-D array operating at 5 MHz. Compounding nine decorrelated volumes showed a speckle signal-to-noise ratio (SNR) improvement of 2.68. The average improvement of the lesion contrast-to-noise ratio (CNR) was 2.45. However, using a smaller aperture to generate these volumes worsened the lateral resolution as predicted by theory.
Comparison of Physiological Motion Filters for In Vivo Cardiac ARFI
Authors: Giannantonio Doug M. , Dumont Douglas M. , Trahey Gregg E. , Byram Brett C. 
Published: March 2013

Acoustic radiation force impulse (ARFI) imaging is being utilized to investigate mechanical properties of cardiac tissue. The underlying physiological motion, however, presents a major challenge. This paper aims to investigate the effectiveness of various physiological motion filters using in vivo canine data with a simulated ARFI push pulse. Ideally, the motion filter will exactly model the physiological motion and, when subtracted from the total displacement, leave only the simulated ARFI displacement profile. We investigated three temporal quadratic motion filters: (1) interpolation, (2) extrapolation and (3) a weighted technique. Additionally, the various motion filters were compared when using 1-D versus 2-D autocorrelation methods to estimate motion. It was found that 2D-autocorrelation always produced better physiological motion estimates regardless of the type of filter used. The extrapolation filter gives the most accurate estimate of the physiological motion at times immediately after the ARFI push (0.1 ms) while a close-time interpolation filter using displacement estimates at times before full tissue recovery gives the most accurate estimates at latertimes after the ARFI push (0.7 ms). While improvements to the motion filter during atrial systole and the onset of ventricular systole are needed, the weighted, close-time interpolation and extrapolation motion filters all offer promising results for estimating cardiac physiological motion more accurately, while allowing faster ARFI frame rates than previous motion filters. This study demonstrates the ability to eliminate physiological motion in a clinically-feasible manner, opening the door for more extensive clinical experimentation.
Noninvasive Assessment of Wall-Shear Rate and Vascular Elasticity Using Combined ARFI/SWEI/Spectral Doppler Imaging System
Authors: Dumont Douglas M. , Doherty Joshua R. , Trahey Gregg E. 
Published: March 2013

The progression of atherosclerotic disease is a complex process believed to be a function of the localized mechanical properties and hemodynamic loading associated with the arterial wall. It is hypothesized that measurements of cardiovascular stiffness and wall-shear rate (WSR) may provide important information regarding vascular remodeling, endothelial function and the growth of soft lipid-filled plaques that could help a clinician better predict the occurrence of clinical events such as stroke. Two novel ARFI based imaging techniques, combined on-axis/off-axis ARFI/Spectral Doppler Imaging (SAD-SWEI) and Gated 2D ARFI/Spectral Doppler Imaging (SAD-Gated), were developed to form co-registered depictions of B-mode echogenicity, ARFI displacements, ARF-excited transverse wave velocity estimates and estimates of wall-shear rate throughout the cardiac cycle. Implemented on a commercial ultrasound scanner, the developed techniques were evaluated in tissue-mimicking and steady-state flow phantoms and compared with conventional techniques, other published study results and theoretical values. Initial in vivo feasibility of the method is demonstrated with results obtained from scanning the carotid arteries of five healthy volunteers. Cyclic variations over the cardiac cycle were observed in on-axis displacements, off-axis transverse-wave velocities and wall-shear rates.
Blood Flow Measurement Using the Attenuation-Compensated Volume Flowmeter
Authors: Hottinger Charles F. , Meindl James D. 
Published: March 2013

Measurement of blood volume flow using Doppler ultrasound has traditionally required determination of the Doppler angle, vessel size, and shape of the velocity profile. In transcutaneous measurements of blood flow, this problem has been a serious drawback in clinical usage. Volume flow is formally defined as the area integral of fluid flux normal to an arbitrary sample plane. Based on this definition, a pulsed Doppler volume flowmeter has been developed which measures flow normal to a thin uniformly illuminated sample volume. Calibration of the flowmeter is described, and implications for clinical use are discussed.
The Wedged Transducer — A Transducer Design for Broad Band Characteristics
Authors: Alphonse Gerard A. 
Published: March 2013

This paper presents a method of increasing the bandwidth of transducers feeding low acoustic impedance loads such as fluids and of electrically matching them over the full bandwidth. It consists of interposing between the transducer and the actual load, a wedge made out of a material having the desired acoustic impedance. The wedge angle is chosen such that no reflected wave from the wedge-load interface can return to the transducer. In this manner, the effective load seen by the transducer is that of the wedge itself, regardless of the actual load. The appropriate electrical matching is achieved by means of a hybrid band pass filter containing both electrical and mechanical components, with the transducer as an integral part. Experimental results on a 4-inch diameter PZT-4 transducer, coupled to water through a brass wedge, demonstrate a bandwidth of 75 percent and an insertion loss of 8.5 dB, well in accordance with theory. Without the wedge, the bandwidth would be only 3.2 percent.
Ultrasonic Instrumentation for Hematology
Authors: Shung K. K. , Reid J. M. 
Published: March 2013

In this paper recent progress on our effort to utilize ultrasound for diagnosing blood disorders is reported. Since the processes of erythrocyte aggregation and hemolysis will alter the acoustic scattering property of the blood, which is a function of the volume concentration as well as the dimension of the cells, ultrasonic backscattering characteristics from erythrocytes were used to study the problem of red cell aggregation and osmotic fragility. Changes in ultrasonic attenuation of the erythrocytes in Sickle Cell disease were used to characterize the tendency of red cells to sickle or deform under hostile physiological environment. Close relationships between ultrasonic absorption, cell morphology, pH, and oxygen tension of the blood have been observed.
Power-Spectrum Centroid Detection for Doppler Systems Applications
Authors: Gerzberg Levy , Meindl James D. 
Published: March 2013

The theoretical basis for the development of a power-spectrum centroid detector is presented, and known and new applications to centroid detection are described. Based on these applications, the requirements are formulated for a versatile centroid detector which can be employed in various types of ultrasonic doppler systems. An analysis method for centroid estimation is developed and applied to the correlation- and √f-type detectors. Closed-form expressions for estimation errors are derived and used for detector evaluation with and without additive noise at the input. A noise-reduction technique is introduced that enables accurate centroid detection despite the presence of strong input noise. Based on the results of this analysis, theoretical comparisons of the detectors, and system requirements, the √f detector is selected for implementation and use.
Computer Reconstruction Techniques in Compound Scan Pulse-Echo Imaging
Authors: Robinson D.E. , Knight P.C. 
Published: March 2013

Reconstruction techniques currently used for forming pulse-echo compound scan images are reviewed. A computer based system for acquiring and storing the pulse-echo data in video line-mode form, (i.e. the detected echo waveform and deflection co-ordinates for each transmitted pulse) is described in both its hardware and software aspects. The performance of peak detected, minimum detected, integrated and averaged reconstruction on point targets is illustrated and discussed. The properties of the various techniques in reconstructing clinical data obtained from the pregnant uterus, abdomen and breast are outlined and future clinical applications suggested.
Construction and Performance of an Experimental Phased Array Acoustic Imaging Transducer
Authors: Dias J. Fleming 
Published: March 2013

A technique for electrically connecting to the PZT elements in a phased array transducer of a cardiac imaging probe is described. The transducer is a stack consisting of a PZT substrate with metallized faces and is bonded to an acoustic absorber across a thin alumina substrate of proper acoustic impedance. The PZT substrate is sawed into an array of elements and a metal foil with an integrally moulded acoustic lens is bonded to the tops of the elements to form the common ground connection. The transducer stack is enclosed in an alumina box and the electrical connection to the PZT elements is made by silk-screened metallic conductors on the sides of the box. The stack transducer module is enclosed in a two part linen bakelite case which is sealed by injecting silicone rubber. A technique that was used to prepare the surface of the acoustic absorber, which resulted in wide bandwidth transducers, is described. Finally, we show the pulse-echo response of the completed transducer imaging a point target in water.
An Experimental Investigation of the Cross-Coupling between Elements of an Acoustic Imaging Array Transducer
Authors: Dias J. Fleming 
Published: March 2013

In a phased array acoustic imaging transducer, the cross coupling between elements of the array can lead to a loss in range resolution, cause an increase in rolloff with angle of the sector scan, and increase the ringdown time. In this paper, we present results of an experimental investigation of an acoustic mode that couples the elements through the propagation of surface waves on the surface of the acoustic absorber. These results indicate that the strength of the mode is enhanced by the coherent reflections from adjacent neighbor elements which act as efficient reflectors of the surface waves. We also demonstrate a technique whereby reflections can be made to interact destructively to reduce the strength of that coupling mode. A further reduction can be obtained by stiffening the structure by bonding to the tops of the elements a thick brass foil and by using it as a common ground connection.
Behavior of Arterial Grafts at the Hip and Knee Joints
Authors: Clifford P. C. , Skidmore R. , Woodcock J. P. , Baird R. N. 
Published: March 2013

Real time ultrasonic scanning with a Duplex scanner (A.T.L.) was used to study Dacron arterial grafts crossing the hip and knee joints in 27 patients (25 males, 2 females), mean age 61 years. Ultrasonic imaging of the grafts was rapid and demonstrated kinking during knee flexion in 83 percent of grafts anastomosed to the distal popliteal artery. Only 7 percent of grafts crossing the inguinal ligament kinked during 60° of hip flexion. Graft kinking during knee flexion may be a factor in acute thrombosis associated with long periods of immobility, such as during air travel.
High Frequency Ultrasonic Imaging of Skin: Experimental Results
Authors: Dines K. A. , Sheets P. W. , Brink J. A. , Hanke C. W. , Condra K. A. , Clendenon J. L. , Goss S. A. , Smith D. J. , Franklin T. D. 
Published: March 2013

Experimental results are presented demonstrating the application of pulse echo ultrasound to imaging the skin. A laboratory prototype B-mode mechanical scanner was employed to obtain images of human skin, both in vitro and in vivo, using broadband pulsed ultrasound at 25 MHz. Images were formed by processing digitized A-mode waveforms and displaying the resulting two-dimensional cross sections using a digital imaging system. Images obtained by rectifying the A-modes are compared to those derived using a software-based cross-correlation technique. Scans of test targets demonstrate that an axial resolution of 100 m can be achieved at 25 MHz when the digital correlation method is employed. Lateral resolution is limited by the 0.25 mm half-power focal beamwidth of the transducer. Seventeen in vitro ultrasonic scans of human skin were compared to frozen section histology. Average skin depth was well correlated between the two techniques (= 0.99, p < 0.001). Application of cross-correlated processing to 25 MHz in vivo images produced good delineation of epidermis, papillary, and reticular dermis. Conversion to a 50 MHz transducer did not delineate skin layers as well as the 25 MHz transducer due to inherent difficulties with transducer reverberations.
Response to Comment on Vaknine, R. and Lorenz, W.J. Lateral Filtering of Medical Ultrasonic B-Scans before Image Generation,

Ultrasonic Imaging 6

, 152–158 (1984)
Authors: Vaknine R. 
Published: March 2013

The technique presented in our paper was not intended to process the random fluctuations in received echo amplitudes nor the effect of the demodulation process on B-scan image resolution. It is a method which deconvolves the B-scan image data only in the lateral direction, before image generation, with the assumptions that led to Eq. (1) in our paper. The axial resolution is assumed to be good compared to the poor lateral resolution and the point spread function considered has a form of the normal distribution function [1]. As Dr. Dickinson mentions in his comment, the speckle process can be modeled as a linear convolution similar to that of conventional image formation and the low contrast resolution is not improved if the deconvolution in the lateral direction is performed before or after demodulation. I agree that the low contrast resolution in B-scan images can be improved if a deconvolution in the axial direction is followed by lateral deconvolution. It would be inappropriate to perform an axial deconvolution without taking into consideration the deconvolution in the lateral direction to improve the poor lateral resolution. Our lateral filtering method has been applied to B-scan image data which were not previously processed by axial deconvolution. It can certainly be applied after axial deconvolution and elimination of the demodulation process.
Analysis of a System for Ultrasonic Imaging of Attenuation and Texture in Soft Tissue
Authors: Salomonsson Göran , Löfström Benny 
Published: March 2013

Attenuation in tissue decreases both the amplitude and the bandwidth of a reflected ultrasonic signal. Only the amplitude is restored in conventional ultrasonic equipment by amplifying the signal in a time-gain-compensator. This paper describes a method for restoring both the amplitude and bandwidth of the signal and an implemention of this method is proposed. This consists of two main parts: a device for estimating the attenuation and a time-variable circuit. The time-variable circuit is controlled by the estimated attenuation such that its transfer function approximates the inverse of the transfer function of the attenuation within the transducer passband. Its output is then almost independent of the attenuation and contains information on the texture of the tissue. Both the texture and attenuation estimates are displayed graphically. The quality of the image of the texture can be improved by choosing a wideband transducer, since it is almost exclusively dependent of transducer bandwidth. The performance of the method is studied using both simulated signals and signals measured in vitro.
An Improved Ultrasound Simulation Model: Use in Evaluating Log versus Linear Processing for Lesion Detection
Authors: Goodsitt Mitchell M. , Bleier Alan R. , Barber Frank E. 
Published: March 2013

This paper reports the development of an improved three-dimensional computer simulation model for evaluation of ultrasonic imaging systems. This model was used to successfully evaluate a signal processing method for improving lesion detection in ultrasound imaging. Linear processing of the rf signal amplitudes from a limited region of tissue was compared with the logarithmic compression employed by most commercial scanners. Two lesions were simulated by spherical distributions of scatterers having backscatter coefficients greater than the scatterers in the surrounding medium. Linear processing improved the differential contrast by a factor of about two. The simulation is based on the three-dimensional distribution of acoustic frequency spectra in a transducer beam and integration of scattered pulses from a corresponding three-dimensional array of scatterers. The simulation reported in previous papers depended upon physical measurement of the impulse response of a transducer. An original contribution described briefly herein, and in more detail in a companion article, is the addition of a model of the transducer's pulse waveform generation. Another new addition is the definition of a specific lesion detection task for objective assessment of a change in image quality following perturbation of some system parameter.
Computerized Ultrasound B-Scan Texture Analysis of Experimental Fatty Liver Disease: Influence of Total Lipid Content and Fat Deposit Distribution
Authors: Layer G. , Zuna I. , Lorenz A. , Zerban H. , Haberkorn U. , Bannasch P. , van Kaick G. , Räth U. 
Published: March 2013

Statistical pattern recognition procedures allow a quantitative description of ultrasound-B-scan image texture. According to well-established animal models, different types of fatty liver disease were induced in female Wistar rats. For the correlation of the computerized ultrasound image with its underlying histology a variable tissue model based on histomorphological data, texture analysis of the histological image and biochemical measurements of total lipid, water and hydroxyprolin content was created. Whereas a regional arrangement of large fat deposits leads to a significant increase in the “mean grey level” (measure of image brightness) of the ultrasound-B-scan image, there is no difference in image brightness between normal liver tissue and liver steatosis for the tissue model with diffuse homogeneous fatty infiltration. It is demonstrated by multiple linear regression analysis that the “mean grey level” of the ultrasound-B-scan image depends not only on total lipid content but even more on the histomorphological fat deposit distribution.