bluuebunny/crossref_metadata_2025 huggingface dataset:
A random matrix approach to long range acoustic propagation in the ocean.
Authors: Hegewisch Katherine C. , Tomsovic Steven
Published: July 2011

Low frequency sound propagates in the ocean within a wave guide, formed by the confining effects of temperature, salinity, and pressure on the sound speed. Within the wave guide, sound scatters due to range dependent sound speed oscillations from internal waves. These weak perturbations in the sound speed serve to randomize the acoustic signal so that the structure formed by the time series of arrivals at the receivers (i.e., the timefront) contains only minimal average information about the propagation through the action of a generalized central limit theorem. This study characterizes this information by the parameters of a statistical ensemble model for the propagation. The propagation is described by the evolution of a unitary propagation matrix, whose elements are the complex probability amplitudes for modal transitions during the propagation. The ensemble model is constructed from a product of unitary random matrices utilizing complex Gaussian random variables with minimal information about the propagation to 50 km stored in a matrix of variances and a vector of mean phases. A comparison of the properties of the average intensity timefront resulting from this ensemble model is made with those from the simulated propagations for several ranges. [This work was supported by ONR and NSF.]
A method for numerical representation of arbitrary boundaries in acoustic wavefront propagation.
Authors: Martinelli Sheri
Published: July 2011

An enhancement to the application of a wavefront propagation algorithm for underwater acoustics based on the level set method is presented. The presence of discontinuities in the phase space at reflecting boundaries requires the use of specialized differencing techniques to prevent oscillations in the computed solutions of the acoustic phase. A weighted essentially non-oscillatory method is applied for this purpose, necessitating the use of uniformly spaced grids over the computational domain. In order to represent arbitrary boundaries in this implementation, one has to either modify the grid to include the boundary (reduces the convergence rate) or develop an appropriate boundary condition to apply within the region of interest. Earlier versions of this work approximated the actual boundary location by the location of the nearest grid point. This resulted in a stair-step effect in the solutions, which resolves with finer grid resolution. However, the phase space is high-dimensional; a highly resolved grid can be impractical. In this work, a new method is proposed and validated which applies a model based on ray interactions with the boundary to improve results on sparser grids. [Work supported by ONR 333 and by the Science, Mathematics, & Research for Transformation (SMART) Program.]
A dedispersion transform: Applications development.
Authors: Wang Ning , Yao Yuling , Gao Dazhi , Wang Haozhong
Published: July 2011

Shallow water sound propagation is of typically (mode) dispersive, in particular, significant for low frequency and long-range propagation. Recently, a novel transform we called to dedispersion transform (DDT) was introduced recently by authors [Ning Wang, 9th Western Pacific Acoustic Conference Beijing (2009)]. It is a bi-parameter Fourier-like unitary transform, which can remove multimode dispersion of acoustic signals in shallow water waveguide, the only parameter required known a prior is an approximate beta-value. Some preliminary results on real-data processing has shown that the DDT works very well. In the present presentation, we would like to present some applications and relevant developments on the DDT. (1) A review of dedispersion transform: motivations, some formula and two real-data applications (source depth estimation and optimization of beam-forming processing for transient signals). (2) An improved Wigner–Vills distribution suitable for dispersive multimode signals. It may be useful for dealing with various signal correlations in the time-frequency domain. (3) A theoretical exploration on the possibility for applications of DDT to mode-coupling and reverberation problems. (4) The final topic is a method using single mode dispersion to make low-frequency source ranging without referring any prior environmental information of sea bottom, real-data processing is also shown.
Convergence of polynomial chaos expansion based estimates of acoustic field and array beam response probability density functions.
Authors: Hayward Thomas J. , Oba Roger M.
Published: July 2011

The polynomial chaos expansion (PCE) method has been applied recently to the computation of acoustic field uncertainties arising from uncertainties of the acoustic propagation environment [Finette, J. Acoust. Soc. Am. 120(5)]. The present work investigates, through computational studies, the properties of acoustic field probability density functions (PDFs) and the rate and manner of convergence of PCE based approximations to those PDFs. The studies assume a stratified ocean waveguide, with uncertainties of sound speed and attenuation represented by joint PDFs. Numerically accurate computations of the field and beam response PDFs are first computed from the parameter PDFs using the normal-mode expansion and the change in variables’ theorem of probability theory. The resulting field and beam power PDFs exhibit irregular functional behavior and singularities associated with features of the mapping from the parameter space to the field or beam power space. The singularities have implications for the choice of suitable metrics for assessing the approximation of the field PDFs by PDFs derived from truncated polynomial chaos expansions. Function-space metrics based on existing theory of convergence of orthogonal polynomial expansions are investigated. Computational examples illustrate some qualitative aspects of the PDF approximations. [Work supported by the Office of Naval Research.]
Experimental determination of the three-dimensional primary field of a seismic airgun array.
Authors: Tashmukhambetov Arslan M. , Ioup George E. , Ioup Juliette W. , Sidorovskaia Natalia A. , Newcomb Joal J. , Stephens James M. , Rayborn Grayson H. , Summerfield Phil
Published: July 2011

The Littoral Acoustic Demonstration Center (LADC) recorded acoustic and related data on three moored arrays and ship-deployed hydrophones, which together spanned the full water column to measure the 3-D acoustic field of a seismic airgun array, in September 2007. The seismic source vessel shot specified lines to give detailed solid angle and range information concerning the field of the primary arrival. The data were collected in the western Gulf of Mexico between the East Break and Alamos Canyon regions. Peak pressures, sound exposure levels, total shot energy spectra, one-third octave band analyzes, and source directivity studies are used to characterize the field. Three-dimensional maps of these quantities are generated to show dependence on emission and azimuthal angles and range. Longer lines were shot for propagation analyzes. Source signatures from NUCLEUS and GUNDALF are used in propagation modeling. [Research supported by the Joint Industry Programme through the International Association of Oil and Gas Producers.]
Soundscape walking tour.
Authors: Paoletti Dennis A.
Published: July 2011

As part of the American Institute of Architects, San Francisco Chapter’s Architecture Festival, Dennis Paoletti led a walking tour through downtown, experiencing the City’s sights and sounds. Participants learned about environmental noise parameters and the importance of criteria for indoor and exterior spaces. They learned how sound is evaluated in the acoustical community. A brief introduction to the basics of acoustics was presented at the SMW office before the group toured downtown. Real life environmental noise conditions were experienced including where and how to achieve a level of calm and quiet within the hectic din of the City’s soundscape environment. Stories about architectural acoustics were illustrated from the many local buildings that Dennis had consulted on. Additionally, the group occasionally stepped into a building where Dennis illustrated some practical examples of the acoustical parameters and criteria previously discussed. Paoletti was interviewed on public radio and asked to repeat the Soundscape Walking Tour for the City Guides, a group of volunteers who lead tours throughout San Francisco. One of the representative comments received: “Thank you for leading the Soundscape Walking Tour; all of us “heard” a version of the City we had never encountered before.”
A case history of office building plumbing noise, its causes and reduction.
Authors: Robinson James E.
Published: July 2011

Short cuts in commercial construction often lead to acoustical problems after occupancy. In this example, a restroom was located immediately adjacent to the private office of a top executive in a hospital office building. Plumbing noise and vibration were being transmitted through the common partition’s structure and through airborne paths. Short comings in the partition design and construction are discussed and several noise paths are identified. Recommended solutions are outlined and after implementation the client was pleased with the result.
A subjective evaluation of the American Society of Heating, Refrigerating and Air-Conditioning Engineers plumbing noise guidelines.
Authors: Yantis Michael R.
Published: July 2011

An evaluation of the ASHRAE plumbing noise guidelines was made by measuring plumbing noise and asking a small, trained jury to evaluate the noise subjectively. Measurements were made of supply and waste noise in a residential building where the plumbing system was isolated from direct contact with the structure and another residential building where no isolation was present. Background noise levels were also documented. In addition to listening to and evaluating the plumbing noise in the sample buildings, the plumbing noise was recorded during the measurements and played back to jury members in various room types and in the midst of various background noise levels. In addition to evaluating the acceptability of the noise versus the A-weighted noise level, the frequency characteristics of isolated and non-isolated plumbing noise were evaluated in an attempt to determine if A-weighted criteria are sufficient to identify acceptable plumbing noise levels.
Plumbing noise control strategies in wood structures.
Authors: LoVerde John , Dong Wayland
Published: July 2011

There are a number of strategies that have been developed to isolate plumbing piping from structures. Generally effective methods of plumbing noise control include the installation of cast iron waste/vent/storm drain piping, and installing pre-manufactured or custom isolating clamps and brackets on all piping connection points [LoVerde and Dong, J. Acoust. Soc. Am. 118, 1856 (2005)]. The level of isolation provided by these methods is relatively well understood and the methods are selected based on the level of plumbing noise reduction desired. However, there are many projects where the capability of the tradesman, constructability, and/or budget allow for little or no vibration isolation. For these projects, the authors have developed alternative strategies including space planning, plumbing routing, materials choices, and isolation at limited locations, which have been successful in controlling plumbing noise. Examples are given of successful acoustical designs with these limitations.
The role of acoustics in defining killer whale populations and societies in the Northeastern Pacific Ocean.
Authors: Ford John K. B. , Yurk Harald , Deecke Volker B.
Published: July 2011

Stable, culturally inherited repertoires of discrete pulsed calls are characteristic of the acoustic behavior of killer whales. Call repertoires may have important roles in the evolution of social segregation and reproductive isolation of sympatric killer whale populations. Here we present the results of analyzes of recordings collected from killer whale populations in coastal waters of the Northeastern Pacific from the Aleutian Islands to the Gulf of California over the past 30 years. At least three acoustically, genetically, and ecologically distinct lineages of killer whales, known as residents, transients, and offshores, inhabit these waters. Call repertoires within these lineages can further distinguish populations, communities, or smaller social groups, depending on social structure and patterns of dispersal. Salmon-feeding residents live permanently in their natal matrilines and have group-specific dialects that encode maternal genealogy. Mammal-feeding transient groups have less stable societies and tend not to have group-specific dialects, though there are regional call differences among subpopulations. Offshore killer whales, which range widely along the continental shelf and may specialize on sharks, have distinct call repertoires that appear to vary among groups. Killer whale calls can provide important insights into the structure of populations at a scale that cannot be resolved through genetic studies.
Investigating acoustics, behavior and vessel noise exposure in endangered killer whales (Orcinus orca) using digital acoustic recording tags.
Authors: Holt Marla M. , Hanson M. Bradley , Emmons Candice K. , Baird Robin W. , Hogan Jeff , Foster Jeff , Giles Deborah , Balcomb Kenneth C.
Published: July 2011

Southern resident killer whales (SRKWs) are a fish-eating, endangered population that frequents the inland waters of Washington and British Columbia. Several risk factors have been identified that could hinder population recovery, including prey quantity and/or quality and disturbance by vessel presence and/or noise. There is a well-developed whale watching industry in the area, with an average of about 20 vessels viewing SRKWs during summer daylight hours. In some studies, killer whales decreased foraging behavior with vessel presence but details about noise exposure and prey capture events were lacking. Other research has characterized how vessel traffic increased background noise levels in SRKW habitat but data on how such exposure varies in a diving killer whale were also lacking. Our current research involves using suction cup attached digital acoustic recording tags (DTAGs) equipped with hydrophones and dive sensors on SRKWs to better characterize their use of sound, particularly during foraging, and to quantify vessel noise received at the whale. Data on vessel type and behavior and whale behavior, as well as prey samples, are also collected concurrently. This paper will describe the experimental approach taken and some preliminary results assessing risk factors potentially affecting the recovery of SRKWs.
Detecting killer whale whistles and squeals.
Authors: Mellinger David K.
Published: July 2011

An algorithm has been devised for detection of tonal sounds, including whistles of odontocetes and moans and other sounds of baleen whales [Mellinger et al., J. Acoust. Soc. Am. (in press)]. Here we test for detection of whistles, squeals, burst pulses, and other tonal and tonal-like sounds of killer whales (Orcinus orca). The method is controlled using a large number of parameters, and these parameters must be chosen to as to detect killer whale sounds and not sounds of other cetaceans. The cosmopolitan range of killer whales means that they are sympatric with nearly every other species of cetacean, and thus detection must handle these other species. Here detectors are configured to detect orca tonal sounds and to avoid detecting sounds of sympatric cetaceans, such as pilot whales (Globicephala spp.), that produce whistles and other tonal vocalizations that overlap the frequency range of killer whales.
Masking of southern resident killer whale signals by commercial ship noise.
Authors: Veirs Scott R. , Veirs Val R.
Published: July 2011

The endangered southern resident killer whales (SRKWs) emit sound to communicate with each other and to hunt fish. Communication or fishing are possible only within a distance (R) at which a signal can be detected. We determine detection distance by comparing the power spectra of the ambient noise and the received signal, with attention to the auditory response curve of the receiver. In Haro Strait, the center of the SRKW critical habitat, about 21 commercial ships per day, increases the ambient noise level by about 20 dB. To assess how ship noise may affect the SRKW communication and hunting, we define the fractional reduction in the zone of audibility at any location and time as the ratio of the area where signal detection is expected to occur in the increased noise regime to the maximum detection area expected under ideal conditions R2/Rmax2. We map the decreased zones of audibility in Haro Strait during average and extreme ship noise by combining field measurements of spreading rates with source power spectra (1–100 kHz) of common SRKW signals and typical ships.
Shipping noise and vocal compensation by Southern Resident killer whales: Haro Strait as a study case.
Authors: Wood Jason D. , Foreman Peggy , Veirs Val , Veirs Scott
Published: July 2011

Southern resident killer whales (SRKWs) use acoustic signals to navigate, forage, and facilitate social dynamics. Researchers have published evidence that suggests SRKW compensate for increased background noise by increasing the source level and duration of their signals. Unpublished reports have also suggested that SRKW may compensate for background noise by repeating their signals and by preferentially using certain signal types. Most of this work has focused on noise from whale watching vessels or general background noise. Haro Strait is both the center of the summertime home range of the SRKW and an important shipping channel. From September 2009 to December 2010 almost 10 000 ships transited through Haro Strait with an average of 21 ships passing per day. Ship transits in Haro Strait can increase background noise by up to 20 dB and are detectable above background noise for up to 30 min. This may be impacting the ability of SRKW to detect and utilize their acoustic signals. A five hydrophone array and Automatic Identification System receiver located at the Lime Kiln Lighthouse were used to record passing ships and SRKW in Haro Strait. This project investigates signal compensation strategies in SRKW in correlation with increased noise from passing ships.
Orca hearing weighted decibels: Underwater sound measurements appropriate to studies of Orcinus (killer whales).
Authors: Bain David , Veirs Scott , Veirs Val
Published: July 2011

In community noise studies, sound levels are usually measured under the dB-A weighting scheme, which was introduced 50 years ago in an effort to match noise measurements to the response of human listeners. Here we propose an underwater noise decibel weighting scheme matched to the hearing sensitivity of killer whales (dB-O). This scheme is based on a convolution of the spectral energy of sound with the frequency-specific hearing detection thresholds of killer whales. The biological significance of noise sources may be more readily discerned if underwater sounds are quantified dB-O weighted. Further, use of this measure would emphasize the importance of broad-band measurement of noise rather than characterizing noise sources by the frequency with the peak power-spectral density and the source level of low frequency components. We compare the measures of representative noise sources, which have been recorded within the range of Southern Resident Killer Whales, including small boats, ships, airguns, and midfrequency sonar, using both flat and db-O weighted levels. While dB-O provides a more relevant characterization of noise than flat measurements (e.g., for predicting noise-induced stress), more detailed measurements will be required to address masking of biological signals, whose frequency structure varies with type of phonation and direction.
Are click rates in killer whales an indicator of group behavior and foraging hotspots?
Authors: Beneze Erica L. , Wood Jason , Veirs Scott , Veirs Val
Published: July 2011

Killer whales use sound to communicate, find food, and navigate through the ocean. Southern Resident killer whales are specialized hunters and predominantly target Chinook salmon. It is presumed that these whales use echolocation clicks to distinguish between different species of salmon and to navigate. If this is the case, then click rates should vary by group behavior as the need for locating prey and navigating change. It has also been suggested that certain areas are utilized heavily by this population for foraging (hotspots) and some of these areas have been included in NOAAs proposed “no-go” zone. If click rates during foraging are distinct, then hotspots should be identifiable by click rates. This study tested if click rates varied by behavior state and geographic area. Group behavior was categorized into five states: foraging, traveling, milling, resting, and socializing. Click rate varied significantly by behavior state and by area. Socializing had the highest click rate followed by foraging, traveling, milling, and then resting. The Southern Residents had higher click rates in foraging hotspots.
Killer whale vocal behavior during joining events.
Authors: Grebner Dawn M. , Bradley David L.
Published: July 2011

Killer whale discrete pulsed calls (DPCs) have been hypothesized to maintain group cohesion, but the specific usage of these calls in relation to animal movements (trajectory, orientation, joinings, etc.) is not well understood. We examine here the use of DPCs by individuals and small groups involved in joining events. DPC rates were examined before and after joining events, while vocal behavior during call initiations and one- and two-way vocal exchanges were also explored. Acoustic data were obtained using a triangular hydrophone array in Johnstone Strait in the summers of 2006 and 2007, while killer whale behaviors and locations were observed from a cliff using a video camera and theodolite, respectively. The relative arrival times of the killer whale sounds at each array hydrophone was used to determine the location of the vocalizing whale. Sounds were then associated in time and space with the corresponding killer whale’s position and behavior. Both DPC rates and the number of two-way vocal exchanges were found to be greater prior to joinings. These results indicate that DPCs play an important role in the vocal exchanges between killer whales prior to joinings.
Acoustic monitoring of killer whale populations off the west coast of Vancouver Island.
Authors: Riera Amalis , Ford John K. , Hildebrand John A. , Chapman N. Ross
Published: July 2011

Killer whales inhabiting the waters of British Columbia and Washington are at risk. The occurrence of these animals has been extensively monitored in protected inshore waters off the east coast of Vancouver Island and Puget Sound, but there has been very little visual effort off Southwestern Vancouver Island and Washington. The objective of this study is to use acoustic techniques to determine the seasonal use of that area by different lineages of killer whales. Other questions include whether the current critical habitat needs to be expanded, or if there is any habitat sharing between different populations. Long-term acoustic data were obtained from passive acoustic devices including high frequency acoustic recording packages at three different sites. The recordings were analyzed using long term spectral averages, a tool that allows efficient analysis of large data sets in shorter periods of time. California-type transient calls were heard throughout the year, Southern Residents were detected from February through June, and Northern Residents were found from July through September. These results show a considerable overlap in habitat range between Southern and Northern Residents, as the latter use the southern parts of their range more frequently than previously thought.
Monitoring southern resident killer whale behavior on the outer coast of Washington using passive acoustics.
Authors: Emmons Candice K. , Hanson M. Bradley , Holt Marla M. , Noren Dawn P. , Lammers Marc O.
Published: July 2011

Killer whales produce population-specific pulsed calls, and remote acoustic monitoring has been utilized to better assess the seasonal distribution and movements of southern resident killer whales (SRKWs) in the coastal waters of Washington State due to the many factors that limit visual sightings. In 2008 and 2009, Ecological Acoustic Recorders (EARs) were deployed at four locations spanning the Washington coast. The EARs were duty cycled to record for 30 s at 5- and 7-min intervals providing additional information about length of detections and acoustic behavior. SRKW were detected at all four locations. 26 of the 48 SRKW detections had sufficient data for analysis of acoustic behavior, and detections ranged in duration from a few minutes to one 24-h period. For each recording, we classified the presence, absence, and rates of various killer whale sounds to determine how they differed spatially and temporally. These preliminary data will be compared to multiple studies whose findings have demonstrated how the acoustic behavior of piscivorous killer whales differs among activity states: resting, socializing, foraging and traveling. These differences can provide information necessary to help identify important foraging areas and times on the outer coast in the absence of visual sightings.
Acoustic presence of killer whales in Resurrection Bay, Alaska during May–June 2010.
Authors: Love Sandra , Ŝirović Ana
Published: July 2011

Killer whales produce three different types of calls: whistles, pulsed calls, and clicks. Pulsed calls have been studied in detail to determine their relation to social organization and behavior as well as pod or individual identification. The functions of whistles is not well known, but are thought to be used for close-range communication. Clicks are mainly used for echolocating. The vocal repertoire of killer whales recorded in Resurrection Bay, AK during May and June 2010 was investigated to determine their call characteristics and diel calling patterns. Data were recorded using an Ecological Acoustic Recorder, which sampled at 20 kHz on a 75% duty cycle. The characteristics of 12 loud and clear calls were compared to calls of known resident and transient pods [Yurk et al. (2002); Saulitis et al. (2005), respectively] to determine which pods were present in Resurrection Bay during this time. The most commonly identified calls were pulsed calls. Four calls could have belonged to resident pods (AD, AJ, or AK) and one could have belonged to the AT1 transient pod. Calling occurred more often during the day, but there was no real night time during the survey. Daytime calling may have been used for socializing.
Vocalizations and site fidelity of transient killer whales of the Pribilof Islands, Alaska.
Authors: Newman Kelly A. , Springer Alan M.
Published: July 2011

Acoustic recorders can be superior to visual techniques for detecting marine mammals. Monitoring the presence of predators that exploit depleted prey populations, such as killer whales and northern fur seals at the Pribilof Islands in the Bering Sea, At, facilitates a better understanding of the role predators play in prey population dynamics and ecosystem function. Killer whales frequent the Pribilofs and prey upon fur seals when they are abundant during spring-fall, but their broader geographic range, stock structure, and fidelity to this predation hot spot are unknown. Identifying killer whale call types can address these questions because killer whale groups share calls. This study documented nine killer whale call types at the Pribilofs during the summers of 2006–2008. Calls were characterized by spectral and temporal properties, component structure and contour shape. The two most common calls were detected at one island more than another 64 km away, which suggests site preference. Calls during feeding observations are described as well as the efficacy of using bottom-mounted recorders to study ecological interactions. Pribilof calls are structurally distinct from other published records of Alaskan killer whale calls, and with further study will foster a deeper understanding of predator impacts in biologically sensitive areas.
Methods of quantifying muscle properties in cervical pain via sonoelastography and tactile imaging.
Authors: Ballyns Jeffrey J. , Egorov Vladimir , Sarvazyan Armen , Hammond Jennifer , Shah Jay P. , Gerber Lynn , Sikdar Siddhartha
Published: July 2011

Myofascial trigger points (MTrPs) are a very common, yet poorly understood and overlooked, cause of nonarticular musculoskeletal pain. MTrPs are localized, stiff, hyperirritable tender nodules, palpated in taut bands of skeletal muscle. We are investigating sonoelastography and tactile imaging as complementary objective methods to measure the physical and mechanical properties of MTrPs. Sonoelastography was performed with an external 92-Hz vibration in the upper trapezius muscles in patients with acute neck pain (n=45). The area of reduced vibration amplitude was measured as an estimate of the size of the stiff MTrPs. A subset of patients (n=3) was studied via tactile imaging, using an array of pressure sensors mimicking a physical examination. Young’s modulus of MTrPs was estimated using a previously developed technique for breast lesion characterization. Using sonoelastography, active sites (spontaneously painful with palpable MTrPs) had larger MTrPs (0.57±0.20 cm2) compared to latent (MTrPs painful on palpation) sites (0.36±0.16 cm2), or palpably normal (0.17±0.22 cm2) sites [P<0.01, one-way analysis of variance (ANOVA)]. Using tactile imaging, preliminary trends show that active sites are likely to be stiffer (61±25 kPa) than latent sites (38±18 kPa). These results demonstrate that MTrPs may be objectively imaged and quantitatively characterized. Further studies are needed to confirm these preliminary results.
Detection of hemorrhage regions in the brain using ultrasound vibrometry.
Authors: Cameron Peter , Rogers Peter , Gray Michael , Martin James
Published: July 2011

Detection of hemorrhage regions in the brain using an ultrasound technique was investigated. Ultrasound techniques are desirable to complement magnetic resonance imaging and computed tomography x-ray techniques for several reasons. Ultrasound does not subject the body to harmful radiation, the equipment is more portable and relatively inexpensive, and ultrasound does not have restrictions on use around metal objects. The technique could thus have application to monitoring patients with a high probability of brain hemorrhage. Efforts have been focused on developing a finite element model and corresponding laboratory experiment. The approach was to apply a low-frequency translational vibration which generated shear waves in the tissue material that could be interrogated using a ranging ultrasonic vibrometer. The experiment consisted of a synthetic tissue phantom encapsulated in a solid shell. The material properties in a hematoma vary with time as coagulation occurs, beginning as a liquid and transitioning to a soft elastic solid. The relatively short wavelength in an inclusion containing coagulating blood compared to that in tissue provided contrast to the inclusion region. The effect was enhanced by the fact that wavelengths at practical excitation frequencies were comparable to typical inclusion dimensions causing high amplitudes due to resonance.
Time-reversal techniques in ultrasound-assisted deep vein thrombosis treatment: Technology development and in vitro evaluation.
Authors: Lewis George K. , Olbricht William L. , Sarvazyan Armen
Published: July 2011

We describe a thrombolysis method that combines time-reversal acoustic (TRA) focusing with an AngioJet thrombectomy catheter to improve the dissolution of thrombus in the treatment of deep venous thrombosis (DVT). Commercially available ultrasound-assisted DVT systems have been shown to accelerate thrombolysis by up to 40% and reduce the amount of thrombolytic drug required for treatment by 50%–70%. Current ultrasound-assisted DVT treatments utilize a specially designed intravascular catheter with therapeutic ultrasound transducer on the tip and side. Additionally, MRI guided high intensity focused ultrasound systems have shown to rapidly lyse thrombus. We describe a novel TRA focusing system that is used to infuse fluids into the thrombus while simultaneously exposing the clot to safe levels of 1-MHz ultrasound energy. The system includes a combined infusion catheter-hydrophone, a ten-channel ultralow-output impedance amplifier, a broad-band ultrasound resonator, and MATLAB-based, TRA control and user-interface. TRA allows easy focusing of ultrasound therapy to the catheter tip from an external source, without complex phase-correction and array design. The system has been tested in vitro in a DVT phantom model, and results show that it provides 1-mm spatial resolution focusing. We present results in using TRA focusing to lyse bovine blood clots in the physiological size DVT phantom.
Three-dimensional detection of metastases in freshly excised human lymph nodes using quantitative ultrasound backscatter and envelope parameters.
Authors: Mamou Jonathan , Coron Alain , Saegusa-Beecroft Emi , Hata Masaki , Oelze Michael L. , Yanagihara Eugene , Yamaguchi Tadashi , Laugier Pascal , Machi Junji , Feleppa Ernest J.
Published: July 2011

High-frequency quantitative ultrasound (QUS) may offer a reliable means of identifying tumor foci in dissected lymph nodes. Detection of metastases is essential for staging and treatment planning. Conventional histopathology methods do not allow nodes to be examined over their entire volume. Therefore, our objective is to develop QUS methods to improve detection of clinically significant lymph-node metastases. A single-element 26-MHz ultrasound transducer was used to scan and digitally acquire rf echo-signal data in three-dimensional (3D) from more than 200 lymph nodes. Thirteen QUS estimates based on backscatter spectra and envelope statistics were computed in 3D. Serial-sectioning histology was performed at 50-μm intervals to depict cancer foci in 3D. Classification based on QUS estimates was performed using linear-discriminant analyzes; areas under ROC curves (AUCs) were computed. The most-significant QUS estimates for metastases detection were identified. Comparison of the 3D QUS results and 3D histology showed promising classification results. The AUC for the linear combination of four QUS estimates was 0.91 for a dataset of 73 breast-cancer nodes. Similarly, using only two QUS estimates, an AUC of 0.97 was obtained for a dataset of 143 colorectal-cancer nodes. These results suggest that QUS may be effective in distinguishing metastatic nodes from normal nodes.
A coded excitation technique for the functional imaging of coronary atherosclerosis using ultrasound contrast agents.
Authors: Shekhar Himanshu , Doyley M.M.
Published: July 2011

Acute coronary syndromes may occur when life-threatening atherosclerotic plaques rupture in the advanced stages of cardiovascular disease. There is increasing evidence that plaque neovascularization accelerates the progression and disruption of atherosclerotic plaque. Plaque neovessels may be detected by subharmonic intravascular ultrasound (IVUS) imaging with ultrasound contrast agents (UCAs). The assessment of plaque neovascularity and perfusion at high spatial and contrast resolution may help identify those most at risk of acute coronary syndromes. While theoretical considerations dictate the use of high peak pressures and long excitation pulses for obtaining high contrast subharmonic IVUS images, microbubble disruption and the risk of hemorrhage limit the peak pressures practicable. Moreover, the use of long pulses degrades the axial resolution of achievable. In this paper, we report a novel excitation strategy using preemphasized chirps for microbubble insonation, which significantly enhances subharmonic signal from UCA. Therefore, low peak pressures can be employed to obtain high contrast resolution and the axial resolution can be restored by pulse compression. This technique was validated by numerical simulations and flow studies at high transmit frequencies (20 MHz). High spatial and contrast resolution achievable by this technique may significantly enhance the clinical potential for functional imaging of coronary atherosclerosis.
Complex wavelet analysis of high frequency ultrasound backscatter from low echogenic biospecimen.
Authors: Srinivas Sushma , Fleischman Aaron
Published: July 2011

Conventional microscopic methods of imaging biological specimen are subjected to various limitations. These include a tradeoff between high spatial resolution and field-of-view, limited depth-of-field, and the need to fix and stain the samples among many other limitations. Although ultrasound biomicroscopy allows the visualization of tissues at the microscopic level, improvement in the device resolution alone may not suffice to image a thin layer of biospecimen like a layer of cells due to their low echogenicity. A new method of image generation of the biospecimen using high frequency ultrasound without some of the aforementioned limitations is reported. Madin-Darby Canine Kidney epithelial cells in culture were imaged using a 40 MHz focused polyvinylidene fluoride polymer transducer. Modulation of the backscattered signal from this low echogenic biological specimen was detected. The backscattered signal better represented as a nonstationary signal when analyzed using complex wavelet analysis resulted in the detection of inflection points in the signal and the change in waveform due to propagation through the biological interface. Results demonstrate that the proposed technique better delineates a thin layer of low echogenic biospecimen layer than conventional or discrete wavelet methods. [Work supported by Cleveland State University Research Council’s Doctoral Dissertation Research Expense Award Program and American Heart Association predoctoral fellowship].
A dual pulse technique for improving the point spread function of superharmonic imaging systems.
Authors: Verweij Martin D. , Demi Libertario , van Neer Paul L. M. J. , Danilouchkine Mikhail G. , de Jong Nico , van Dongen Koen W. A.
Published: July 2011

Nonlinear propagation causes the generation of higher harmonics of the emitted fundamental spectrum. Nowadays, medical echography employs reflections of the second harmonic, because this yields improved axial and lateral resolutions, and less reflections from nearby artifacts and grating lobes, as compared to fundamental imaging. To further exploit the benefits of higher harmonic imaging while keeping sufficient signal strength for detection, superharmonic imaging combines reflections of the third, fourth, and fifth harmonics. A drawback of adding harmonic reflections is the possible occurrence of ripples in the point spread function (PSF). Recently, a dual pulse technique was proposed for avoiding these ripples. This technique uses the emission of two consecutive pulses with a slightly different frequency, and performs imaging after summation of both superharmonic reflections. In this presentation, it is theoretically explained why this approach yields a better PSF than single pulse superharmonic imaging. For a superharmonic imaging system with an interleaved phased array, numerical results obtained with the iterative nonlinear contrast source method are shown. Moreover, these are validated against experimental results. The results confirm that the proposed technique significantly reduces ripple artifacts and gives a more compact PSF than the third harmonic alone. [Work supported by the STW and the NCF.]
Two-dimensional simulations of ultrasound propagation in random anisotropic media: Application to trabecular bone assessment.
Authors: Muller Marie , Dobigny Blandine , Bossy Emmanuel , Derode Arnaud
Published: July 2011

A better understanding of the mechanisms of ultrasound propagation in trabecular bone could considerably help improving the quantitative ultrasonic techniques commonly used to assess bone quality. Some phenomena experimentally observed in trabecular bone remain poorly understood, such as the possible propagation of two compressional waves with different velocities. In this study, elastic wave propagation has been simulated using a finite-difference time-domain method in two-dimensions. Trabecular bone was modeled by a binary random medium with fully controlled elasticity and anisotropy. To do so, elliptic-shaped patterns were randomly distributed on two-dimensional (2-D) maps with an orientation ensuring global anisotropy. The coherent wave was obtained by averaging over a large number of random maps. Several conditions for the observation of the two waves have been identified: (i) The propagation has to occur in a direction parallel to the main orientation of the medium. (ii) some of the elliptic pattern elements had to be connected, which suggests the importance of a percolation threshold. (iii) It is necessary to take into account shear waves in the solid phase. This suggests that bone microarchitecture parameters (anisotropy and connectivity) could be retrieved from ultrasonic measurements, improving the evaluation of fracture risk.
Numerical modeling of photoacoustic imaging of brain tumors.
Authors: Firouzi Kamyar , Saffari Nader
Published: July 2011

Photoacoustic imaging has shown great promise for medical imaging, where optical energy absorption by blood haemoglobin is used as the contrast mechanism. A numerical method has been developed for the in silico assessment of the photoacoustic image reconstruction of the brain. Image segmentation techniques were used to prepare a digital phantom from MR images. Then, light transport through brain tissue was modeled using the finite element approach. The resulting acoustic pressure was then estimated by pulsed photoacoustics considerations. The forward acoustic wave propagation was modeled by linearized coupled first order wave equations and solved by the acoustic k-space method. Since skull bone is an elastic solid and strongly attenuates ultrasound (due to scattering and absorption), a k-space method was developed for elastic media. To model scattering effects, a new approach was introduced based on propagation in random media. In addition, absorption effects were incorporated using a power law. Finally, the acoustic pressure was reconstructed using the k-space time reversal technique. The simulations were run in three dimensions to produce the photoacoustic tomogram of a brain tumor. The results show that relying on optical energy absorption by blood hemoglobin as the contrast mechanism, as is the current practice, leads to poor image quality.
A first-order k-space model for elastic wave propagation in heterogeneous media.
Authors: Firouzi Kamyar , Cox Benjamin , Treeby Bradley , Saffari Nader
Published: July 2011

A pseudospectral model of linear elastic wave propagation is described based on the first order elastodynamic equations. A k-space adjustment to the spectral gradient calculations is derived from the dyadic Green’s function solution to the second-order elastic wave equation and used to ensure the solution is exact for homogeneous wave propagation for time-steps of arbitrarily large size. This adjustment also allows larger time-steps without loss of accuracy in weakly heterogeneous media. Along with an appropriate smoothing function, the model is applied for media with high-contrast inhomogeneities. An absorbing boundary condition has been developed to effectively impose a radiation condition on the wavefield. The staggered grid, which is essential for accurate simulations, is described in detail, along with other practical details of the implementation. The model compares favorably to exact solutions for canonical examples and to the conventional pseudospectral and finite difference time-domain codes. The numerical results show the accuracy of the method. It is also very efficient compared to alternative numerical techniques due to the use of the FFT to calculate the gradients in k space leading to reduced number of point per-wavelength and larger time-steps are made possible by the k-space adjustment.
Disorder in subordinate oscillators arrays used to shape the response of dynamic systems.
Authors: Glean Aldo A. J. , Vignola Joseph F. , Judge John A. , Woods Teresa J. , O’Malley Patrick F.
Published: July 2011

Earlier work has shown [J. Acoust. Soc. Am. 126, 1 (2009)] that the time and frequency responses of a lightly damped oscillating structure can be tailored by attaching an array of much smaller subordinate oscillators. Exact analytic governing equations of motion are used to describe the behavior of the coupled system that is composed of the primary system and the subordinate array. Further, it is shown that this tailoring can be achieved using a relatively small number (<100) of attached oscillators whose total mass is small (∼<1%) relative to the primary structure. This presentation will show how disorder in the property distributions within the array of attachments affects the tailored responses. Then with this general understanding, applications including time domain step response manipulation, bandpass filtering, and multianalyte detection based on dynamic response of microcantilevers are discussed. These examples represent case studies where sensitivity to disorder is either an asset or an encumbrance.
Using sound speed to determine volume fractions in a two-phase flow.
Authors: Chaudhuri Anirban , Osterhoudt Curtis F. , Sinha Dipen N.
Published: July 2011

This paper presents a method of determining the volume fractions of two immiscible fluids in a two-phase flow by measuring the speed of sound through the composite fluid and the instantaneous temperature. Two separate algorithms are developed, based on earlier work by Urick [J. Appl. Phys. (1947)] and & Toksoz [Geophys (1974)]. The main difference between these two models is the representation of the composite density as a function of the individual densities; the former uses a linear rule-of-mixtures approach, while the latter uses a non-linear formulation. Both methods lead to a quadratic equation, the root of which yields the volume fraction (φ), subject to the condition 0⩽φ⩽1. We present results of a study with mixtures of crude oil and processed water, and a comparison of our results with a Coriolis meter. The fluid densities and sound speeds are calibrated at various temperatures for each fluid component, and the coefficients are used in the final algorithm. Analytical and numerical studies of sensitivity of the calculated volume fraction to temperature changes are also presented. [This work was supported by Chevron USA.]
A multimicrophone tube for measurement of material acoustic absorption.
Authors: Oppenheimer C. H.
Published: July 2011

A multimicrophone approach for measurement of the acoustic absorption of small material samples is presented. Like the two-microphone method of ASTM E1050, the multimicrophone tube involves a material sample at one end of a tube and a loudspeaker at the other end. Unlike the two-microphone method, the multimicrophone tube uses an arbitrary number, greater than two, of microphones and a distinct algorithm to relate microphone pressures to material acoustic properties. A multimicrophone tube with four microphones was fabricated. Using this tube, material acoustic absorption was determined by the two-microphone approach and by the multimicrophone approach. The multimicrophone approach was observed to extend the bandwidth of accurate determination of material acoustic absorption. Accuracy improvements occurred not only at low frequencies, where tube axis phase changes are small, but also at high frequencies beyond the frequency at which a half wavelength spans the microphone pair of the two microphone method of ASTM E1050.