bluuebunny/crossref_metadata_2025 huggingface dataset:
Paired-Angle Multiplicative Compounding
Authors: Macione James , Yang Zhi , Fox Martin
Published: March 2013

Ultrasound compounding is a method of combining multiple images from different angles in order to create a single image with improved resolution and reduced angular-dependent artifactual detail. Compounding methods traditionally calculate each pixel in the compound image as a simple functional relationship between pixel elements in the component image set. In order to achieve an even better resolution and further reduce angular-dependent artifacts, this paper investigates a new type of compounding we call paired angle multiplicative compounding (PAMC), in which compound images are produced by a summation of multiplied pairs of component images acquired at different angles. A PAMC image of a breast phantom demonstrates improved delineation of microcalcifications in comparison to the mean operation. Images of the forearm are used to investigate larger angles of paired multiplication, the best improving contrast ratio (28%) and signal to noise ratio (24%) when compared to the mean method. The PAMC method is found to be similar to the MEM and median compounding operations, the largest difference being that it is better preserving contributions from normal incidence but at the expense of needing a larger angular range.
Noninvasive and Transient Blood-Brain Barrier Opening in the Hippocampus of Alzheimer's Double Transgenic Mice Using Focused Ultrasound
Authors: Choi James J. , Wang Shougang , Brown Truman R. , Small Scott A. , Duff Karen E. K. , Konofagou Elisa E.
Published: March 2013

The spatio-temporal nature of focused ultrasound-induced blood-brain barrier (BBB) opening as a brain drug delivery method was investigated in Alzheimer's disease model mice. The left hippocampus of transgenic (APP/PS1, n = 3) and nontransgenic ( n = 3) mice was sonicated (frequency: 1.525 MHz, peak-negative pressure: 600 kPa, pulse length: 20 ms, duty cycle: 20%, duration: 1 min) in vivo, through their intact skin and skull, after intravenous injection of microbubbles (SonoVue®5; 25 μl). Sequential, high-field MR images (9.4 Tesla) were acquired before and after injection of gadolinium (Omniscan™ 0.75 ml, molecular weight: 573.7 Da) on two separate days for each mouse. Gadolinium deposits through the ultrasound-induced BBB opening in the left hippocampus revealed significant contrast-enhancement in the MRI. On the following day, MRI revealed significant BBB closure within the same region. However, the BBB opening extent and BBB closing timeline varied in different regions within the same sonicated location. This indicates that opening and closing were dependent on the brain region targeted. No significant difference in BBB opening or closing behaviors was observed between the APP/PS1 and the nontransgenic mice. In conclusion, a BBB-impermeable molecule was noninvasively, transiently and reproducibly delivered to the hippocampus of Alzheimer's APP/PS1 mice.
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.
Tracking in High-Frame-Rate Imaging
Authors: Wu Shih-Ying , Wang Shun-Li , Li Pai-Chi
Published: March 2013

Speckle tracking has been used for motion estimation in ultrasound imaging. Unlike conventional Doppler techniques, which are angle-dependent, speckle tracking can be utilized to estimate velocity vectors. However, the accuracy of speckle-tracking methods is limited by speckle decorrelation, which is related to the displacement between two consecutive images, and, hence, combining high-frame-rate imaging and speckle tracking could potentially increase the accuracy of motion estimation. However, the lack of transmit focusing may also affect the tracking results and the high computational requirement may be problematic. This study therefore assessed the performance of high-frame-rate speckle tracking and compared it with conventional focusing. The effects of the signal-to-noise ratio (SNR), bulk motion, and velocity gradients were investigated in both experiments and simulations. The results show that high-frame-rate speckle tracking can achieve high accuracy if the SNR is sufficiently high. In addition, its computational complexity is acceptable because smaller search windows can be used due to the displacements between frames generally being smaller during high-frame-rate imaging. Speckle decor-relation resulting from velocity gradients within a sample volume is also not as significant during high-frame-rate imaging.
Interlaboratory Comparison of Backscatter Coefficient Estimates for Tissue-Mimicking Phantoms
Authors: Anderson Janelle J. , Herd Maria-Teresa , King Michael R. , Haak Alexander , Hafez Zachary T. , Song Jun , Oelze Michael L. , Madsen Ernest L. , Zagzebski James A. , O'Brien William D. , Hall Timothy J.
Published: March 2013

Utrasonic backscatter is useful for characterizing tissues and several groups have reported methods for estimating backscattering properties. Previous interlaboratory comparisons have been made to test the ability to accurately estimate the backscatter coefficient (BSC) by different laboratories around the world. Results of these comparisons showed variability in BSC estimates but were acquired only for a relatively narrow frequency range, and, most importantly, lacked reference to any independent predictions from scattering theory. The goal of this study was to compare Faran-scattering-theory predictions with cooperatively-measured backscatter coefficients for low-attenuating and tissue-like attenuating phantoms containing glass sphere scatterers of different sizes for which BSCs can independently be predicted. Ultrasonic backscatter measurements were made for frequencies from 1 to 12 MHz. Backscatter coefficients were estimated using two different planar-reflector techniques at two laboratories for two groups of phantoms. Excellent agreement was observed between BSC estimates from both laboratories. In addition, good agreement with the predictions of Faran's theory was obtained, with average fractional (bias) errors ranging from 8–14%. This interlaboratory comparison demonstrates the ability to accurately estimate parameters derived from the BSC, including an effective scatterer size and the acoustic concentration, both of which may prove useful for diagnostic applications of ultrasound tissue characterization.
Dispersion and Shear Modulus Measurements of Porcine Liver
Authors: Orescanin Marko , Qayyum Muqeem A. , Toohey Kathleen S. , Insana Michael F.
Published: March 2013

A narrow-band ultrasonic shear-wave imaging technique for estimating phase speed was applied to fresh and thermally damaged porcine liver in vitro. Two constitutive models were applied to the measurements to represent rheological behavior of the tissue and estimate the complex shear modulus at frequencies between 50 and 300 Hz. Our results were compared to similar values from the literature to assess how well models represent liver measurements over a range of shear-wave frequencies, experimental conditions and mammalian species. We found remarkable consistency in some parameters but not in others, suggesting that the Kelvin-Voigt model commonly applied in elasticity-imaging situations is representative of tissue dispersion but the description it offers is incomplete. Data are consistent with the theory that viscoelastic contrast is more likely due to changes in protein and other biomolecular-scale structures than from tissue anatomy larger than a cell. Dispersion measurements at frequencies between 0.5–1000 kHz are needed to more completely evaluate models for the viscoelastic behavior liver.
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.
Software Beamforming: Comparison between a Phased Array and Synthetic Transmit Aperture
Authors: Li Yen-Feng , Li Pai-Chi
Published: March 2013

The data-transfer and computation requirements are compared between software-based beamforming using a phased array (PA) and a synthetic transmit aperture (STA). The advantages of a software-based architecture are reduced system complexity and lower hardware cost. Although this architecture can be implemented using commercial CPUs or GPUs, the high computation and data-transfer requirements limit its real-time beamforming performance. In particular, transferring the raw rf data from the front-end subsystem to the software back-end remains challenging with current state-of-the-art electronics technologies, which offset the cost advantage of the software back end. This study investigated the tradeoff between the data-transfer and computation requirements. Two beamforming methods based on a PA and STA, respectively, were used: the former requires a higher data transfer rate and the latter requires more memory operations. The beamformers were implemented in an NVIDIA GeForce GTX 260 GPU and an Intel core i7 920 CPU. The frame rate of PA beamforming was 42 fps with a 128-element array transducer, with 2048 samples per firing and 189 beams per image (with a 95 MB/frame data-transfer requirement). The frame rate of STA beamforming was 40 fps with 16 firings per image (with an 8 MB/frame data-transfer requirement). Both approaches achieved real-time beamforming performance but each had its own bottleneck. On the one hand, the required data-transfer speed was considerably reduced in STA beamforming, whereas this required more memory operations, which limited the overall computation time. The advantages of the GPU approach over the CPU approach were clearly demonstrated.
Effect of Graphite Concentration on Shear-Wave Speed in Gelatin-Based Tissue-Mimicking Phantoms
Authors: Anderson Pamela G. , Rouze Ned C. , Palmeri Mark L.
Published: March 2013

Elasticity-based imaging modalities are becoming popular diagnostic tools in clinical practice. Gelatin-based, tissue mimicking phantoms that contain graphite as the acoustic scattering material are commonly used in testing and validating elasticity-imaging methods to quantify tissue stiffness. The gelatin bloom strength and concentration are used to control phantom stiffness. While it is known that graphite concentration can be modulated to control acoustic attenuation, the impact of graphite concentration on phantom elasticity has not been characterized in these gelatin phantoms. This work investigates the impact of graphite concentration on phantom shear stiffness as characterized by shear-wave speed measurements using impulsive acoustic-radiation-force excitations. Phantom shear-wave speed increased by 0.83 (m/s)/(dB/(cm MHz)) when increasing the attenuation coefficient slope of the phantom material through increasing graphite concentration. Therefore, gelatin-phantom stiffness can be affected by the conventional ways that attenuation is modulated through graphite concentration in these phantoms.
Subharmonic Contrast Microbubble Signals for Noninvasive Pressure Estimation under Static and Dynamic Flow Conditions
Authors: Halldorsdottir Valgerdur G. , Dave Jaydev K. , Leodore Lauren M. , Eisenbrey John R. , Park Suhyun , Hall Anne L. , Thomenius Kai , Forsberg Flemming
Published: March 2013

Our group has proposed the concept of subharmonic aided pressure estimation (SHAPE) utilizing microbubble-based ultrasound contrast agent signals for the noninvasive estimation of hydrostatic blood pressures. An experimental system for in vitro SHAPE was constructed based on two single-element transducers assembled confocally at a 60° angle to each other. Changes in the first, second and subharmonic amplitudes of five different ultrasound contrast agents were measured in vitro at static hydrostatic pressures from 0–186 mmHg, acoustic pressures from 0.35–0.60 MPa peak-to-peak and frequencies of 2.5–6.6 MHz. The most sensitive agent and optimal parameters for SHAPE were determined using linear regression analysis and implemented on a Logiq 9 scanner (GE Healthcare, Milwaukee, WI). This implementation of SHAPE was then tested under dynamic-flow conditions and compared to pressure-catheter measurements. Over the pressure range studied, the first and second harmonic amplitudes reduced approximately 2 dB for all contrast agents. Over the same pressure range, the subharmonic amplitudes decreased by 9–14 dB and excellent linear regressions were achieved with the hydrostatic pressure variations ( r2 = 0.98, p < 0.001). Optimal sensitivity was achieved at a transmit frequency of 2.5 MHz and acoustic pressure of 0.35 MPa using Sonazoid (GE Healthcare, Oslo, Norway). A Logiq 9 scanner was modified to implement SHAPE on a convex transducer with a frequency range from 1.5–4.5 MHz and acoustic pressures from 0–3.34 MPa. Results matched the pressure catheter ( r2 = 0.87). In conclusion, subharmonic contrast signals are a good indicator of hydrostatic pressure. Out of the five ultrasound contrast agents tested, Sonazoid was the most sensitive for subharmonic pressure estimation. Real-time SHAPE has been implemented on a commercial scanner and offers the possibility of allowing pressures in the heart and elsewhere to be obtained noninvasively.
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.
7.5 MHz Dual-Layer Transducer Array for 3-D Rectilinear Imaging
Authors: Chen Yuling , Nguyen Man , Yen Jesse T.
Published: March 2013

The difficulties associated with fabrication and interconnection have limited the development of 2-D ultrasound transducer arrays with a large number of elements (>5000). In previous work, we described a 5 MHz center frequency PZT-P[VDF-TrFE] dual-layer transducer that used two perpendicular 1-D arrays for 3-D rectilinear imaging. This design substantially reduces the channel count as well as fabrication complexity, which makes 3-D imaging more realizable. Higher frequencies (>5 MHz) are more commonly used in clinical applications or imaging targets near transducers, such as the breast, carotid and musculoskeletal tissue. In this paper, we present a7.5 MHz dual-layer transducer array for 3-D rectilinear imaging. A modified acoustic stack model was designed and fabricated. PZT elements were sub-diced to eliminate lateral coupling. This sub-dicing process made the PZT into a 2–2 composite material, which could help improve transducer sensitivity and bandwidth. Full synthetic-aperture 3-D data sets were acquired by interfacing the transducer with a Verasonics data-acquisition system (VDAS). Offline 3-D beamforming was then performed to obtain volumes of a multiwire phantom and a cyst phantom. The generalized coherence factor (GCF) was applied to improve the contrast of cyst images. The measured −6 dB fractional bandwidth of the transducer was 71% with a center frequency of 7.5 MHz. The measured lateral beamwidths were 0.521 mm and 0.482 mm in azimuth and elevation, respectively, compared with a simulated beamwidth of 0.43 mm.
Texture Feature Analysis for Breast Ultrasound Image Enhancement
Authors: Liao Yin-Yin , Wu Jui-Chen , Li Chia-Hui , Yeh Chih-Kuang
Published: March 2013

Texture analysis of breast ultrasound B-scans has been widely applied to the segmentation and classification of breast tumors. We present a parametric imaging method based on the texture features to preserve tumor edges and retain the texture information simultaneously. Four texture-feature parameters – homogeneity, contrast, energy and variance - were evaluated using the gray-level co-occurrence matrix. The local texture-feature parameter was assigned as the new pixel located at the center of the sliding window at each position. This process yielded the texture-feature parametric image as the map of texture-feature values. The signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were estimated to show the quality improvement of the images. The contours outlined from 11 experienced physicians and the gradient vector flow (GVF) snake algorithm segmentations were adopted to verify the edge enhancement of texture-feature parametric images. In addition, the Fisher's linear discriminant analysis (FLDA) and receiver-operating-characteristic (ROC) curve were used to test the performance of breast tumor classifications between texture-feature parametric images and B-scan images. The results show that the variance images have higher CNR and SNR estimates than those in the B-scan images. There was a high agreement between the physician's manual contours and the GVF snake automatic segmentations in the variance images, and the mean area overlap was over 93%. The area under the ROC curve from the B-scan images had 0.81 and 95% confidence interval of 0.72–0.88, and the texture-feature parametric images had 0.90 and 95% confidence interval of 0.84–0.96. These findings indicate that the texture-feature parametric imaging method can be not only useful for determining the location of the lesion boundary but also as a tool to improve the accuracy of breast tumor classifications.
Three-Dimensional, Extended Field-of-View Ultrasound Method for Estimating Large Strain Mechanical Properties of the Cervix during Pregnancy
Authors: House Michael , Feltovich Helen , Hall Timothy J. , Stack Trevor , Patel Atur , Socrate Simona
Published: March 2013

Cervical shortening and cervical insufficiency contribute to a significant number of preterm births. However, the deformation mechanisms that control how the cervix changes its shape from long and closed to short and dilated are not clear. Investigation of the biomechanical problem is limited by (1) lack of thorough characterization of the three-dimensional anatomical changes associated with cervical deformation and (2) difficulty measuring cervical tissue properties in vivo. The objective of the present study was to explore the feasibility of using three-dimensional ultrasound and fundal pressure to obtain anatomically-accurate numerical models of large-strain cervical deformation during pregnancy and enable noninvasive assessment of cervical-tissue compliance. Healthy subjects ( n = 6) and one subject with acute cervical insufficiency in the midtrimester were studied. Extended field-of-view ultrasound images were obtained of the entire uterus and cervix. These images aided construction of anatomically accurate numerical models. Cervical loading was achieved with fundal pressure, which was quantified with a vaginal pressure catheter. In one subject, the anatomical response to fundal pressure was matched by a model-based simulation of the deformation response, thereby deriving the corresponding cervical mechanical properties and showing the feasibility of noninvasive assessment of compliance. The results of this pilot study demonstrate the feasibility of a biomechanical modeling framework for estimating cervical mechanical properties in vivo. An improved understanding of cervical biomechanical function will clarify the pathophysiology of cervical shortening.
Effect of Prior Probability Quality on Biased Time-Delay Estimation
Authors: Byram Brett C. , Trahey Gregg E. , Palmeri Mark L.
Published: March 2013

When properly constructed, biased estimators are known to produce lower mean-square errors than unbiased estimators. A biased estimator for the problem of ultrasound time-delay estimation was recently proposed. The proposed estimator incorporates knowledge of adjacent displacement estimates into the final estimate of a displacement. This is accomplished by using adjacent estimates to create a prior probability on the current estimate. Theory and simulations are used to investigate how the prior probability impacts the final estimate. The results show that with estimation quality on the order of the Cramer-Rao lower bound at adjacent locations, the local estimate in question should generally exceed the Cramer-Rao lower-bound limitations on performance of an unbiased estimator. The results as a whole provide additional confidence for the proposed estimator.
A 5-MHz Cylindrical Dual-Layer Transducer Array for 3-D Transrectal Ultrasound Imaging
Authors: Chen Yuling , Nguyen Man , Yen Jesse T.
Published: March 2013

Two-dimensional transrectal ultrasound (TRUS) is being used in guiding prostate biopsies and treatments. In many cases, the TRUS probes are moved manually or mechanically to acquire volumetric information, making the imaging slow, user dependent, and unreliable. A real-time three-dimensional (3-D) TRUS system could improve reliability and volume rates of imaging during these procedures. In this article, the authors present a 5-MHz cylindrical dual-layer transducer array capable of real-time 3-D transrectal ultrasound without any mechanically moving parts. Compared with fully sampled 2-D arrays, this design substantially reduces the channel count and fabrication complexity. This dual-layer transducer uses PZT elements for transmit and P[VDF-TrFE] copolymer elements for receive, respectively. The mechanical flexibility of both diced PZT and copolymer makes it practical for transrectal applications. Full synthetic aperture 3-D data sets were acquired by interfacing the transducer with a Verasonics Data Acquisition System. Offline 3-D beamforming was then performed to obtain volumes of two wire phantoms and a cyst phantom. Generalized coherence factor was applied to improve the contrast of images. The measured −6-dB fractional bandwidth of the transducer was 62% with a center frequency of 5.66 MHz. The measured lateral beamwidths were 1.28 mm and 0.91 mm in transverse and longitudinal directions, respectively, compared with a simulated beamwidth of 0.92 mm and 0.74 mm.
Rapid Transient Pressure Field Computations in the Nearfield of Circular Transducers Using Frequency-Domain Time-Space Decomposition
Authors: Alles E. J. , Zhu Y. , van Dongen K. W. A. , McGough R. J.
Published: March 2013

The fast nearfield method, when combined with time-space decomposition, is a rapid and accurate approach for calculating transient nearfield pressures generated by ultrasound transducers. However, the standard time-space decomposition approach is only applicable to certain analytical representations of the temporal transducer surface velocity that, when applied to the fast nearfield method, are expressed as a finite sum of products of separate temporal and spatial terms. To extend time-space decomposition such that accelerated transient field simulations are enabled in the nearfield for an arbitrary transducer surface velocity, a new transient simulation method, frequency-domain time-space decomposition (FDTSD), is derived. With this method, the temporal transducer surface velocity is transformed into the frequency domain, and then each complex-valued term is processed separately. Further improvements are achieved by spectral clipping, which reduces the number of terms and the computation time. Trade-offs between speed and accuracy are established for FDTSD calculations, and pressure fields obtained with the FDTSD method for a circular transducer are compared with those obtained with Field II and the impulse response method. The FDTSD approach, when combined with the fast nearfield method and spectral clipping, consistently achieves smaller errors in less time and requires less memory than Field II or the impulse response method.
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.
Ultrasonic Attenuation Tomography of Soft Tissues
Authors: Dines K. A. , Kak A. C.
Published: March 2013

In this paper we show that one can measure integrated attenuation for a soft-tissue structure simply by measuring the center frequencies of the incident and transmitted pulses. Except for a multiplicative constant, the integrated attenuation is equal to the difference of these two frequencies. Also, this method is independent of transmittances at tissue-tissue and tissue-couplant interfaces. Since the attenuation information is derived from frequency shifts rather than the signal amplitudes, this new method is somewhat insensitive to a partial loss of signal caused by beam refraction. This technique is based on the power spectra of transmitted ultrasonic pulses approximating Gaussian functions. The validity of this approach has been checked by computer simulation. Tomographic reconstructions of the experimental data using the various attenuation measurement techniques are presented.
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.
Application of Kalman Filtering Techniques to Diagnostic Ultrasound
Authors: Kuc Roman B.
Published: March 2013

Kalman filtering techniques are applied to ultrasound signals to improve resolution capability and to extract tissue characterization information. A state-space representation of the propagating acoustic pulse, required for tractability by Kalman filtering, is described. A recently developed reflection coefficient estimator is applied to simulated and observed data using 2nd, 4th, and 6th order system model approximations. A state-space representation of a second order system is derived.
Ultrasonic Reflectivity Tomography: Reconstruction with Circular Transducer Arrays
Authors: Norton Stephen J. , Linzer Melvin
Published: March 2013

An analysis is presented of backprojection methods for reconstructing cross-sectional images of ultrasonic reflectivity from scattering measurements. A circular array of transducer elements is considered, using three basic modes of data acquisition and image reconstruction: (1) the same element serves as transmitter and receiver and data is backprojected along circular paths centered at the element (2) distinct transmitter and receiver with fixed separation and backprojection along elliptical paths with the elements at the foci and (3) distinct transmitter and receiver with varying separations and backprojection along corresponding elliptical paths. The point spread function (PSF) for each of these cases is derived and is shown to depend on the shape of the acoustic pulse used. PSF's are evaluated for three different pulses — a narrowband, wideband, and an analytically-derived optimum pulse which yields the best sidelobe response and a mainlobe width equal to 0.3ΛC, where ΛC is the wavelength corresponding to the cutoff frequency of the pulse. When backprojection is performed along elliptical paths, the mainlobe width is shown to be broadened by a factor proportional to the cosine of half the angle subtending the transmit and receive elements at the center of the array. The close analogy between the techniques used here to reconstruct reflectivity and the convolution/backprojection method used in computerized x-ray tomography is discussed in detail. Salient properties predicted by the analytically-derived PSF's are confirmed in computer simulations. The characteristics of the PSF's are also examined as a function of the number of array elements, the location of a reflecting point in the object and the shape of the ultrasonic pulse.
Ultrasonic Reflectivity Imaging in Three Dimensions: Reconstruction with Spherical Transducer Arrays
Authors: Norton Stephen J. , Linzer Melvin
Published: March 2013

Three-dimensional backprojection for reconstructing acoustic reflectivity within a volume is examined. The reflectivity data are acquired by means of a spherical array of point sources-receivers which encloses the object under study. Reconstruction of the image is obtained by back-projecting the recorded pulse-echo data over spherical surfaces in image space. An analytical expression for the point spread function (PSF) generated by the backprojection process has been derived. This expression was evaluated for several different choices of the acoustic pulse: a narrowband pulse, wideband pulse, and two analytically-derived optimum pulses which provide the best sidelobe response and a mainlobe width equal to approximately 0.4Λc, where Λc is the wavelength corresponding to the upper cutoff frequency of the pulse. Excellent agreement was obtained between the theoretical PSF's for the different pulses and those obtained by computer simulation. A number of potential advantages of direct three-dimensional reconstruction relative to two-dimensional tomographic techniques are discussed, including (1) high resolution in three dimensions (2) the possibility of incorporating refraction effects in the reconstruction process (3) reduced sensitivity to limited viewing anglesand (4) improved signal-to-noise ratio (thus minimizing requirements for data redundancy).
Efficient Convolution Kernels for Computerized Tomography
Authors: Kenue Surender K. , Greenleaf James F.
Published: March 2013

Three concepts are presented: 1) Extended kernels: The Ramachandran-Lakshminarayanan convolution kernel has one zero between each non-zero value in the spatial domain. By extending the kernel in Fourier space, it is shown that each extension leads to two additional zeros in the spatial domain of the convolution kernel, thus decreasing the required number of multiplications necessary for convolution. Any known kernel can be extended and in the limit of extension a simple backprojection reconstruction is obtained. 2) Binary kernels: A technique for generating binary approximations to any convolution kernel is described. Excluding the central element, all other elements of the kernel are approximated by an even power of two thus, multiplications are replaced by shift operations in the convolution procedure. 3) Recursive convolution: It is shown how additions can be saved by using a recursive formulation which generates new elements in the convolution procedure utilizing only a few summation steps. Results from both extended kernels and their binary approximations are described for simulated phantoms and ultrasound data obtained from breast scans of patients.
Ultrasonic Imaging System Using Spatial and Temporal M-Sequences
Authors: Sato Takuso , Wadaka Shusou
Published: March 2013

A new ultrasonic imaging system combining temporal modulation of the ultrasonic signal by an M-sequence with spatial modulation of the wave field by a rotating M-sequence phase disk has been developed. This system uses neither beam forming nor transducer scanning, and has high resolution both in range and azimuth. The correlation function of the temporal M-sequence determines the range resolution, while the azimuth resolution is determined by the configuration of the rotating M-sequence phase disk. The use of the M-sequence modulations also results in images with high signal-to-noise ratio.
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.
Visualization of Multimode Radiation Patterns of Acoustic Transducers by Acousto-Optic Diffraction
Authors: Hanafy Amin
Published: March 2013

Information concerning the spatial response of a wideband acoustic transducer when excited by a wideband signal is essential, specifically when the transducer exhibits extraneous modes within the bandwidth of both the transducer and the excitation signal. A method is presented by which the radiation patterns of these modes can be visualized discretely under short pulse excitation.
Acoustic Speckle: Theory and Experimental Analysis
Authors: Abbott John G. , Thurstone F. L.
Published: March 2013

A theoretical and experimental study of speckle, as applied to ultrasonic imaging, is presented. The concept of laser speckle is briefly reviewed and is used as a starting point to explain the origin of acoustic speckle. The primary differences between these two phenomena are discussed and are confirmed by experiment. An experimental study of speckle reduction by summation of multiple images is also presented. Several techniques for generating independent speckle patterns for use in image summation schemes are proposed. A phased array, dynamically focused sector imaging system was used in all of the experimental studies reported.
Broadband Random Phase Diffuser for Ultrasonic Imaging
Authors: Alphonse Gerard A. , Vilkomerso David
Published: March 2013

In reflective imaging, waves must be scattered by the object over a broad solid angle so that some of the reflected waves impinge upon the collecting aperture. Surfaces such as biological specimens under study in acoustic imaging are considered smooth at the wavelengths used (e.g., 1 mm) and therefore act as specular reflectors. In order to obtain reflection over a broad spatial range, large aperture, sector or compound scanning are used. In certain types of systems, diffuse insonification is sometimes used by imaging a raster of random phase points onto the surface. However interference between the waves from these point sources produces random fringes or “speckle-like” patterns overlaying the image. In optics these fringes have been reduced by rotating the diffuser. A similar approach has been taken here. This paper describes a simple random phase plate having two levels, 0° and 180 phase that can, by rotation, change the relative phases of the diffuse insonification points so as to reduce the speckle-like effect in the image. The temporal bandwidth of the random phase plate is narrow because of standing waves in it. To reduce standing waves the diffuser is intimately coupled to a wedged transducer. This combination is used to obtain diffuse insonification with broad spatial and temporal bandwidth.
A New Automated, High Resolution Ultrasound Breast Scanner
Authors: Dick Donald E. , Elliott Raymond D. , Metz Robert L. , Rojohn D. Scott
Published: March 2013

Ultrasound breast scanning has proved valuable in research settings but has not received widespread clinical usage due to the lack of suitable, commercially-available instruments. A new scanner designed for ultrasound breast screening has been developed with innovations in four areas: resolution, patient positioning, automation, and image storage and display. These innovations are described and representative scans are shown.
Dynamic Intraesophageal Imaging of the Heart with Ultrasound
Authors: Fearnot N. E. , Babbs C. F. , Bourland J. D. , Geddes L. A.
Published: March 2013

Real-time images of the heart from within the esophagus are produced by a new intraesophageal ultrasonic sector scanner. Sixty images per second are displayed on a gray scale CRT in real-time and recorded on standard videotape for review. By interactive positioning of the esophageal probe, heart ventricles, atria, and valves can be visualized and their dynamics can be studied. The esophageal probe comprises four 5 MHz PZT-5 piezoelements of 6.35 mm diameter mounted on a shaft that rotates at 900 rpm. The piezoelements are pulsed at a 5 kHz rate and the echoes are processed electronically.
Spatial Response of Arbitrarily Electroded Piezoelectric Plates by Plane-Wave Decomposition
Authors: Noorbehesht Behzad , Flesher Gail , Wade Glen
Published: March 2013

The spatial response of resonant piezoelectric plates used in various acoustic imaging systems is of significant practical interest and is closely related to the resolving ability of these systems. In a certain class of applications, in order to achieve the desired transducing action, the faces of the plate are only partially electroded. There, it is advantageous to be able to predict and control the spatial distribution of the acoustic output from the knowledge of the spatial distribution of the electrodes. A new technique is presented for determining the spatial distribution of the acoustic output of an arbitrarily electroded piezoelectric plate. This technique regards the transducer as a linear spatial system, with the electrode pattern considered as the input and the resulting acoustic particle displacement pattern immediately in front of the transducer in the propagation medium as the output. Once the spatial transfer function or the spatial impulse response of the system is known, the output for any electrode configuration can be found using Fourier techniques. Experimental measurements of the output of several piezoelectric plates due to different electrode patterns compare closely with calculations based on the above theory.
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.
Numerical Ray Tracing in Media Involving Continuous and Discrete Refractive Boundaries
Authors: Smith A.M. , Goldberg M. , Liu E.S.K.
Published: March 2013

Attempts to improve the performance of ultrasonic medical imaging techniques have led to an interest in digital methods for tracing rays through inhomogeneous media. Biological tissues involve both continuously varying and discrete refractive index boundaries. A ray tracing technique applicable for both cases is described. The performance of a simulation program is illustrated and discussed for a variety of boundary conditions.
Dead Zone Elimination in Acoustic Arrays
Authors: Hanafy Amin
Published: March 2013

Acoustic imaging systems utilizing multi-element acoustic transducers in the transmit receive mode suffer from an artifact named dead zone area due to the loss of the acquired information in that area. The artifact shows up on the displayed image as a very bright region due to the receivers saturation next to the transducer face and extending further out in the field as a fixed pattern noise. An investigation of the cause of this artifact, and a method for its elimination is presented in this paper.
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.
Textural Variations in B-Mode Ultrasonography: A Stochastic Model
Authors: Flax Stephen W. , Glover Gary H. , Pelc Norbert J.
Published: March 2013

Analysis of textural patterns in gray-scale ultrasonography is frequently the basis for clinical diagnosis. It has been found, however, that texture is shaped not only by tissue microstructure but by characteristics of the imaging system as well. This paper describes computer and analytic models which give insight into the role of the imager in texture formation. It is shown that spatial resolution and texture granularity are not simply related, and that axial and lateral texture are determined by unrelated phenomena. Experimental results are given which confirm the modeling.
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.
Texture Analysis of Ultrasonic Signals - A Comparison of the Use of Radiofrequency and Demodulated A-Scan Data
Authors: Lerski R. A. , Morley P. , Mills P. R. , Watkinson G.
Published: March 2013

Previous work by our group has shown that the application of texture analysis to digitally recorded radiofrequency ultrasonic signals can provide useful diagnostic information in diffuse liver disease. It has now been investigated whether similar information can be obtained with demodulated signal data and established that reduced diagnostic accuracy due to an increased false negative rate results. From this study it would seem unlikely that ultrasonic image data stored in a digital scan converter could provide results as good as those obtainable from the analysis of radiofrequency signals.