bluuebunny/crossref_metadata_2025 huggingface dataset:
Amplitude variations in coarticulated vowels
Authors: Jacewicz Ewa , Fox Robert Allen
Published: May 2008

This paper seeks to characterize the nature, size, and range of acoustic amplitude variation in naturally produced coarticulated vowels in order to determine its potential contribution and relevance to vowel perception. The study is a partial replication and extension of the pioneering work by House and Fairbanks [J. Acoust. Soc. Am. 22, 105–113 (1953)], who reported large variation in vowel amplitude as a function of consonantal context. Eight American English vowels spoken by men and women were recorded in ten symmetrical CVC consonantal contexts. Acoustic amplitude measures included overall rms amplitude, amplitude of the rms peak along with its relative location in the CVC-word, and the amplitudes of individual formants F1–F4 along with their frequencies. House and Fairbanks’ amplitude results were not replicated: Neither the overall rms nor the rms peak varied appreciably as a function of consonantal context. However, consonantal context was shown to affect significantly and systematically the amplitudes of individual formants at the vowel nucleus. These effects persisted in the auditory representation of the vowel signal. Auditory spectra showed that the pattern of spectral amplitude variation as a function of contextual effects may still be encoded and represented at early stages of processing by the peripheral auditory system.
Optimization of transmitting beam patterns of a conformal transducer array
Authors: He Zhengyao , Ma Yuanliang
Published: May 2008

A method is presented to calculate the driving-voltage weighting vector of a conformal array of underwater acoustic transmitting transducers to obtain a low-sidelobe beam pattern based on the measured receiving array manifold. The relationship among three quantities is given, which are, respectively, the radiated acoustic field, the measured receiving array manifold matrix and the driving-voltage weighting vector of the transducer array. Then, the driving-voltage weighting vector of the array is calculated using the optimization method to obtain a low-sidelobe transmitting beam pattern. At the frequency of 12.5kHz, the receiving array manifold matrix of a 27-element conformal array is measured in an anechoic water tank. The driving-voltage weighting vector of the array is calculated using the proposed method. In addition, the computer simulation and experiments are carried out. The results agree well and show that the proposed method can obtain a low-sidelobe transmitting beam pattern and at the same time provide the largest amplitude of pressure in the axial direction when the maximum amplitude of the driving voltages of the array elements keeps unchanged.
The frequency response of rat vibrissae to sound
Authors: Shatz Lisa F. , Christensen Craig W.
Published: May 2008

The motion of isolated rat vibrissae due to low frequency sound has been modeled and measured with good agreement (within a factor of 2) between the data and the model’s predictions. As had been done in previous studies on the response of rat vibrissae to tactile stimulation [Hartmann, M. J., Johnson, N. J., Towal, R. B., and Assad, C., J. Neurosci 23, 6510–6519 (2003) and Neimark, M. A., Andermann, A. L., Hopfield, J. J., and Moore, C. I., J. Neurosci 23, 6449–6509 (2003)] the vibrissae were modeled as thin conical beams. The force of the vibrating air on a vibrissa was modeled using the exact solution for a vibrating infinite cylinder in linear fluid. A finite element method was used to model the motion of a single vibrissa fixed at its base, using the aforementioned fluid force. Values for Young’s modulus and vibrissa mass density were taken from a previous study [Neimark et al. (above)]. The model had no freely fitted parameters. Motion of isolated vibrissae was measured using a video camera with microscope. The sound stimulation was created using a stereo speaker connected to a signal generator. The tuning was found to be sharp, with quality factors that varied between 3 and 7, much sharper than the motion of cricket cercal hairs or in vitro inner ear hair bundles.
How sound from human activities affects marine mammals
Authors: Tyack Peter
Published: May 2008

Effects of sound on marine mammals have traditionally been defined either as injury or disruption of behavior. The earliest concern about behavioral disruption was that elevated noise could reduce the range of communication by masking faint signals. Few studies have documented this effect, but recent work emphasizes mechanisms animals use to compensate for elevated noise. Many studies have documented changes in behavior as a function of exposure, but it has proven difficult to relate these to effects on the welfare of individual animals or on the status of populations. Promising approaches to interpreting effects include avoidance of habitat, energetics of foraging, and applying models of anti-predator behavior to human disturbance. During the 1990s acoustic criteria for injury were designated based upon temporary hearing loss. Accumulating evidence of atypical mass strandings of beaked whales coincident with naval sonar exercises suggest that injury or death may result from behavioral responses of some species at lower exposure levels in some settings. A tagged beaked whale showed similar but weaker responses to experimental playback of a mid-frequency sonar sound compared to calls of killer whales, suggesting that anti-predator response may harm animals after exposure to levels of sound very unlikely to cause injury directly.
Possibilities for acoustic improvement of the far field in open-plan offices
Authors: Humer Catrin , Muellner Herbert
Published: May 2008

An increase in open-plan offices has occurred recently. This makes it necessary to examine and, if necessary, to improve the acoustic conditions in the planning phase. With acoustic simulations it is possible to verify the acoustic quality of offices without much increase in money and time. In order to get the needed absorption area of the room to reduce the reverberation time and the sound level, open-plan offices are usually partitioned with screens. To improve the acoustics in the close range, special conditions, which mainly concern the height, have to be met. Also the absorption and the height of the ceiling have a strong influence on the acoustic quality of the neighbouring workstations. In the far field additional planning bases apply - particularly to raise the horizontal absorption and to get the optimal screening effect. This report highlights the possibilities of the acoustic improvements in the far field in open-plan offices and shows examples of simulated and improved options.
A comparison between shoebox and non-shoebox halls based on objective measurements in actual halls
Authors: Hidaka Takayuki , Beranek Leo L. , Nishihara Noriko
Published: May 2008

In recent papers, the sound absorption by chairs and audiences were determined for shoebox (SB) and non-shoebox (NSB) types of concert halls (Beranek, JASA 120, 1399 (2006); Hidaka, Proc. ICA2007). The purpose of this paper is to examine objective differences in the sound fields in these two hall types. This investigation follows reports of music goers that the average subjective sound quality in NSB and SB halls differs appreciably and that there are greater subjective differences in sound quality from one seating location to another in NSB halls. Special attention is given to the temporal and amplitude structure in the early part (before 80 msec) of the impulse responses measured at various seat positions in six well-known halls (three SB and three NSB). To the extent the data permit, the usual objective parameters are also analyzed, both averaged and at various seat locations, in a total of 12 halls: reverberation time, early decay time, C80 (3-band), interaural cross-correlation coefficient (3-band middle frequency early before 80 ms), initial-time-delay-gap, bass ratio, and strength factors at low- and mid-frequencies. The differences found are discussed with reference to the subjective reports.
Describing measurement uncertainties in room acoustics with the concept of GUM
Authors: Witew Ingo , Vitale Renzo
Published: May 2008

Considering the uncertainties in room acoustical measurements is a crucial step towards quality evaluation, comparability between different measurements methods and instrumentation. In the preceding discussion it was shown that the concepts specified in the "Guide to the expression of Uncertainty in Measurements" (GUM) can well be applied for room acoustical measurement tasks. In this initiatory step a detailed analytical formulation of a model function was avoided for reasons of simplicity and practicability. The waiving of complex modeling, however, requires comprehensive series of measurements to assess the measurement uncertainties. In this paper it is discussed how modeling can reduce such requirements. A special focus is placed on the influence of the directional radiation properties of sound sources.
Dexterity and Spirit: The Peter Kiewit Concert Hall at the Holland Performing Arts Center
Authors: Schuette Dawn
Published: May 2008

Bathed in natural light, the Peter Kiewit Concert Hall is the focal point of the architecturally innovative Holland Performing Arts Center. The space features cast plaster panels for acoustic diffusion, a tunable canopy over stage for acoustic support, and natural felt banners for reverberation and reflection control. The space transforms easily from an orchestral concert setting to an environment friendly to amplified sound, allowing orchestral music one night to seem as naturally suited to the room as amplified music the following evening. The world-class concert hall acoustics provided by this venue meld seamlessly with the amplified use as well resulting in a unique venue for the music community. This hall is an excellent starting point for a continued discussion about how to successfully incorporate variability in high quality acoustic venues. [Work completed while author was employed as a Principal Consultant at Kirkegaard Associates.]
Acoustical characterization of orchestra platforms
Authors: Giovannini Maria , Astolfi Arianna , Barbato Giulio
Published: May 2008

In concert halls and other performance spaces it is important that acoustic conditions allow the musicians to hear each other and that there is a sufficient response from the room. Acoustical characterization of spaces for musicians, such as orchestra platforms, orchestra pits, and rehearsal rooms requires the measurements of the Early and Late Support, and other acoustical parameters described in the ISO/DC 3382-1 and in Literature. This work shows results from measurements carried out on five orchestra platforms, different in shape, size and materials of the boundary surfaces. Up to eight source positions were chosen in order to represent the main instrumental sections of the orchestra playing on the platform. Measurements were carried out without musicians, in conditions of empty stage and stage equipped as in concert configuration with stands, chairs, and risers. Some metrological problems connected with the reproducibility of results are considered as the directivity of the source and the small movements of the source and the microphone. The correlations between objective data show that the measured parameters are not always independent, but some groups of correlated measures, not completely separated, are found. The comparison of results allows to draw some connections with the main stage architectural features.
The effects of fluctuating interaural cues on the segregation of speech in rooms: Revisited
Authors: Brungart Douglas S. , Iyer Nandini
Published: May 2008

Spatial separation is known to improve the segregation of talkers in anechoic environments, but spatial auditory cues can be severely degraded in reverberant rooms. One might expect the random disruptions in the interaural time and level differences (ILDs and ITDs) that occur in reverberant environments to eliminate many of the intelligibility benefits that normally occur for spatially separated speech. However, the precedence effect often leads to a robust perception of spatial location even in extremely echoic environments. This can result in an apparent separation between talkers that may facilitate selective attention to the location of the target speech even in a highly reverberant room. Also, random fluctuations in ITD and ILD may lead to differences in the apparent source widths of the target and masking sounds, which might serve as a segregation cue. In this talk, we examine the effects fluctuating interaural difference cues have on the segregation of target speech from competing speech or noise. These results, originally scheduled for presentation at the 152nd meeting, suggest that differences in apparent source width can be used to segregate competing speech signals even when the target and masking signals appear to originate from the same direction relative to the listener.
A reverberation-robust automatic speech recognition system based on temporal masking
Authors: Brown Guy J. , Palomäki Kalle J.
Published: May 2008

Previously, we have proposed a reverberation-robust system for automatic speech recognition (ASR) based on a temporal masking principle. In the first pathway of this system, speech is analysed by a bank of auditory filters, in order to provide acoustic features for the recogniser. In the second pathway, a bandpass modulation filter (1.5 Hz - 8.2 Hz) detects regions of the envelope in each filter channel that contain strong speech energy. Regions of the modulation filter output that exceed a threshold are labelled as reliable evidence for the speech in a time-frequency mask; regions that fall below the threshold are dominated by reverberation and labelled as unreliable. The acoustic features and time-frequency mask are then decoded by a “missing data” ASR system. Here we describe modifications of this system that bring it into closer agreement with purported mechanisms of human perceptual compensation for reverberation, as determined by psychophysical studies [Watkins & Makin, JASA 121, 257-266]. Specifically, we use a metric for identifying regions of reliable speech that gives greater emphasis to reverberation “tails,” and is computed independently for each frequency band. The performance of the system is evaluated on a corpus of spoken digits convolved with recorded room impulse responses.
Enhancing bass absorbers using activated carbon
Authors: Bechwati Fouad , Cox Trevor J. , Umnova Olga , Avis Mark R.
Published: May 2008

Bass absorbers, either Helmholtz or membrane devices, are commonly used in small rooms to reduce the effects of standing wave modes. Previously, it has been shown that activated carbon can be used to change the compliance of loudspeaker enclosures. It has also been shown that activated carbon displays excess absorption at low frequencies. It has been suggested that the change in compliance and absorption is due to adsorption and desorption of air molecules on the surface of the carbon, caused by the compressions and rarefactions of sound waves. This paper investigates the extent of these effects to and their significance for resonant absorbers. The results show that activated carbon can lower the resonant frequency of a Helmholtz absorber, and also increases the quality factor of the resonance. The paper will discuss what the results mean in terms of the physical interaction between activated carbon and sound, as well as the practical application of the material to bass absorbers.
Control of low-frequency sound to improve spatial uniformity in music production spaces
Authors: Eligator Ronald
Published: May 2008

Commercial music post-production spaces are often less than 300 ft2 (28 m2) and 2700 ft3 (76.5 m3), and it is not uncommon for them to be one-third to one-half this area. Even with careful room design, creating spatially-uniform sound fields, especially at low-frequencies, can be thwarted by the physical restraints imposed by the room's dimensions, boundary conditions and restraints imposed by other functional requirements and budget. This paper presents successful, and not so successful, approaches to managing these challenges through speaker selection, placement and mounting, as well as room shaping and finishes and furniture design. Results of design analysis, room acoustic testing, and listening tests are compared.
Effects of sound on the behavior of toothed whales
Authors: Tyack Peter , Boyd Ian , Claridge Diane , Clark Christopher W. , Moretti David , Southall Brandon
Published: May 2008

We report initial results from a study on behavioral responses of beaked and other whales to sonar and other sounds. This research is designed to provide new science-based approaches for mitigating the risk of sonar to beaked and other whales. The study was conducted at the Atlantic Undersea Test and Evaluation Center (AUTEC) range near Andros Island in the Bahamas, where Blainville's beaked whales (Mesoplodon densirostris) can regularly be detected using passive acoustic monitoring of their echolocation clicks. Tags recorded sound at the whale and behavior of the whale. Data were collected from 10 tag deployments, 6 on Blainville's beaked whales and 4 on pilot whales. 109 hours of data were collected from tags, 74 hours from beaked whales and 34 hours from pilot whales. Playbacks of mid-frequency sonar and killer whale calls were performed on 3 of the tagged whales, 1 beaked whale and 2 pilot whales. The tagged beaked whale responded to both sonar and killer whale sounds by premature cessation of clicking during foraging dives (RL = ∼117 dB re 1 μPa for the killer whale sound, ∼145 dB for the sonar), and an unusually slow and long ascent.
Anthropogenic sounds - Potential effects on fish
Authors: Popper Arthur , Lo/kkeborg Svein , McCauley Robert
Published: May 2008

There is concern that human-generated sounds may have deleterious effects on fish. This paper will review some of what is currently known about these effects, and consider the questions that have to be answered before developing models to enable "prediction" of sound effects on particular fish species. A major restriction is that there are few peer-reviewed data on effects of anthropogenic sources on fish. Extrapolation from these results is further confounded since experiments differ in many ways, each of which may alter the resultant impact on fish. For example, studies vary in sounds types tested (e.g., pile driving vs. ship noise), signal parameters (intensity, number of repetitions), species used, fish age, etc. Moreover, a singularly important issue is that while many of the issues and impact mechanisms are potentially amenable to experimental lab study, the ultimate questions regarding the effects of sound on fish behavior need to field based and require long-term observations where behaviour of wild fish is not constrained. Only by observing fish in the wild will we ultimately understand if, and how, anthropogenic sounds impact fish both during exposure and, more importantly, for extended periods after the termination of the sound.
Proposed Marine Mammal Noise Exposure Criteria: Current Data Base, Limitations, and Research Needs
Authors: Ketten Darlene R. , Bowles Ann E. , Ellison William T. , Finneran James J. , Gentry Roger L. , Greene Charles R. , Kastak David , Miller James H. , Nachtigall Paul E. , Richardson W J. , Southall Brandon , Thomas Jeanette A. , Tyack Peter
Published: May 2008

This paper presents the findings of an inter-disciplinary expert panel based on comprehensive review of hearing and noise effects data for marine and land mammals. The principal motivation for the review was to assist formulation of data-based noise exposure criteria in light of rapidly evolving research advances in marine mammal hearing and underwater noise effects. Levels estimated to induce permanent hearing loss were determined for single exposure events for cetaceans (in water) and pinnipeds (in air and water) for each of 15 sound type/animal group combinations. These recommendations represent a current best estimate only and are modular, with modifiable key variables; e.g., source and exposure, to facilitate revision as data improve. In some cases, relatively explicit injury limits are proposed, e.g., 186 dB re: 1μPa2-s (frequency-weighted sound exposure level) and 218 dB re: 1μPapeak (unweighted peak sound pressure level) for pinnipeds in water exposed to multiple sound pulses. In others, particularly for behavioural effects of multiple-pulse and non-pulse exposures, response severity and significance are quantitatively scored, but the data do not allow identification of specific broadly-applicable disturbance thresholds. These findings are a current best effort and include a discussion of limitations and recommended research needed to address data gaps.
Long-term variations of ice breaking noise in Antarctica
Authors: Gavrilov Alexander , Li Binghui
Published: May 2008

Numerous low frequency transient signals arriving from Antarctica have been detected in five-year sea noise recordings in 2002-2006 at the hydroacoustic listening station deployed off Cape Leeuwin in Western Australia as part of the International Monitoring System of the Comprehensive Nuclear-Test-Ban Treaty. The majority of these signals consist of a single arrival of mode 1 which dominates the higher modes and undergoes strong frequency dispersion due to long-range propagation in the polar ocean environment. These signals are believed to be emitted primarily by ice rifting and breaking events on the Antarctic shelf. Several regions along the Antarctic coast associated with certain glaciers and ice tongues were found to persistently be much more active in generating ice noise than other parts of the Antarctic shelf. An analysis of long-term changes in the frequency of occurrence of ice events showed noticeable seasonal cycles, but did not reveal any significant interannual variations against the background of short-term fluctuations. Some of the ice events detected at the Cape Leeuwin station were also identified in sea noise recordings made on autonomous acoustic loggers deployed on the Antarctic shelf, which allowed us to investigate characteristics of the acoustic signals from ice events near their origins.
Three-dimensional structure of thin zooplankton layers is impacted by foraging fish
Authors: Benoit-Bird Kelly
Published: May 2008

The role of predation by fish in the formation and persistence of zooplankton thin layers was assessed from three-dimensional observations using a multibeam sonar attached to a mechanical rotator. Zooplankton in Monterey Bay, CA, USA were found in intense layers with vertical scales of 0.5-2.5 m at night. These features comprised more than 90% of the zooplankton biomass and had volume scattering strengths of up to -35 dB. These thin zooplankton layers showed complex structure with significant though gradual undulations in their depth, thickness, and intensity. Fish spent significantly more time within zooplankton layers than was expected by chance, suggesting concentrated foraging activity. Sonar tracks of individual fish showed them diving through zooplankton layers. These dives were correlated with a decrease in the intensity of zooplankton scattering at the scale of tens of centimeters, resulting in the appearance of holes in the layer. Continued observation of layers revealed that these voids slowly filled in with zooplankton after the fish's departure. At the level of foraging observed, fish can have a significant effect on the distribution of zooplankton layers, however, the layers are resilient to apparent foraging by fish with reformation of the distinct layer often occurring post-predation.
Using a toroid transducer for thermal ablation by high-intensity-focused ultrasound increases the coagulated volume
Authors: Melodelima David , N'Djin William , Parmentier Hubert , Rivoire Michel , Chapelon Jean Yves
Published: May 2008

Here, we report that a new design of High Intensity Focused Ultrasound transducer can significantly enlarge the coagulated volume over short periods of time, and that treatment in the liver can be guided in real-time using an integrated ultrasound imaging probe. Eight ultrasound emitters, divided into 256 elements, were created by sectioning a single toroid piezocomposite transducer. The focal zone was conical in shape and located 70 mm from the transducer; enabling the treatment of deep-seated tumors. A single thermal lesion was created when the eight emitters performed alternative and consecutive 5 s ultrasound exposures. This paper presents in vivo evidence that the coagulated volume obtained from a 40 s total exposure in the liver was 7.0±2.5 cm3 (min 1.5 - max 20.0 cm3). All lesions were visible with high contrast on sonograms. The correlation between the diameter of lesions observed on sonograms and during gross examination was 92%. This method also allowed the user to easily enlarge the coagulated volume by juxtaposing single lesions. This approach may have a role in treating unresectable colorectal liver metastases and may also be used in conjunction with resection to extend its limits.
Histotripsy and the developing role of microbubbles in ultrasound therapy
Authors: Fowlkes Jeffrey B.
Published: May 2008

Microbubbles in therapeutic ultrasound has seen increasing interest in recent years. Once thought to be problematic, bubble production and interactions with ultrasound fields are yielding promising new methods and this presentation will review two areas of collaborative research at the University of Michigan investigating therapeutic applications utilizing microbubbles. Histotripsy uses short pulses of high intensity ultrasound produce cavitation in vivo and subdivide tissue at a subcellular level. The highly localized bubble activity homogenizes tissue to the point of reducing acoustic backscatter enabling lesion detection. Lesion margins are remarkably fine, even yielding fractional disruption of cells. The homogenized material is readily absorbed thus debulking tissue with little residual scar. At the other end of the acoustic intensity scale, microbubbles can be produced by triggering vaporization of superheated liquid droplets, termed acoustic droplet vaporization (ADV). ADV requires diagnostic levels of ultrasound to yield localized microbubbles production. The method is being investigated for direct occlusion therapy and perfusion control to augment other therapeutic methods including drug delivery among other potential applications. These methods highlight the growing field of microbubble-based therapies, which will expand with our increasing understanding of microbubbles and their interactions with surrounding environments. Supported in part by NIH EB00281, HL077629 and EB006476.
Local heating by a bubble excited by high intensity focused ultrasound
Authors: Kreider Wayne , Canney Michael S. , Bailey Michael R. , Khokhlova Vera A. , Crum Lawrence A.
Published: May 2008

A current topic of interest for high intensity focused ultrasound (HIFU) treatments involves the relative roles of bubbles and nonlinear acoustic propagation as heating mechanisms. At high amplitudes, nonlinear propagation leads to the generation of boiling bubbles within milliseconds; at lower amplitudes, cavitation bubbles can enhance heating through viscous dissipation, acoustic radiation, and heat conduction. In this context, understanding the physics attendant to HIFU bubbles requires consideration of gas-vapor bubble dynamics, including thermal effects in the nearby liquid. To this end, recent experimental observations with high-speed photography suggest that bubbles undergo a brief period of growth after application of HIFU has stopped. To explain this observation, a model is implemented that couples the thermodynamic state of a strongly driven bubble with thermal conditions in the surrounding liquid. From model simulations, liquid heating in the vicinity of a HIFU bubble is estimated. Calculations suggest that thermal conduction and viscous dissipation can lead to the evolution of a nontrivial thermal boundary layer. Development of a boundary layer that reaches superheated temperatures would explain the aforementioned experimental observation. As such, cavitation bubbles and boiling bubbles share important characteristics during HIFU. [Work supported by NIH DK43881 and NSBRI SMS00402.]
In vitro evaluation of an oscillating 5-element dual-mode transducer
Authors: Owen Neil , Bouchoux Guillaume , Birer Alain , Berriet Rémi , Chapelon Jean Yves , Fleury Gérard , Lafon Cyril
Published: May 2008

Miniature dual-mode transducers can be used for minimally invasive treatment of deep-seated tumors. While in contact with the tissue, the transducer guides and monitors localized necrosis. Here, an oscillating 5-element piezo-composite transducer was characterized, and then evaluated in vitro using porcine liver. Each element was 3.0 x 3.8 mm2 with a geometric cylindrical focus of 14 mm. The transmit frequency was determined by the maximal electro-acoustic efficiency, 65%, which was found at 5.6 MHz. The transmit-receive impulse response was 400 ns long at -6 dB, and the -6 dB fractional bandwidth, centered at 5.6 MHz, was 30%. Axial and lateral resolution measured with a 0.1 mm diameter wire was 0.5 mm and 2.0 mm, respectively. For therapy, all elements radiated simultaneously, and for imaging, independently. Treatment was performed at increments of 20° to form a composite volume of necrosis. At each angle, ultrasound was applied for 60 s at a transducer surface intensity of 15 W/cm2. Pulse-echo data were recorded while the transducer oscillated over a 180° sector to form images before and after treatment at each angle. Gross examination of lesion size agreed well with echogenic region size in the images. [Supported by ANR and Inserm Post-doctoral Fellowship.]
Techniques and modalities for high resolution imaging and assessment of skin with high-frequency ultrasound (20 to 100 MHz)
Authors: Vogt Michael , Ermert Helmut
Published: May 2008

High-frequency ultrasound (HFUS) in the 20 MHz range is routinely used in dermatological diagnosis for morphological skin imaging in order to support the identification of suspicious skin lesions and to evaluate the success of therapies. In this presentation, technical developments for the utilization of higher ultrasound frequencies in the range up to 100 MHz are presented, which allow for high-resolution imaging and assessment of skin structures with an axial resolution down to 10 μm. Furthermore, a new HFUS system for the assessment of elastic skin properties and quantitative strain imaging with 20 MHz ultrasound is presented as a new imaging modality. Also, a reflection-tomography skin imaging concept was implemented with a 20 MHz ultrasound limited-angle spatial compound system, which allows for multi-directional analysis of backscattered and reflected ultrasound waves from different insonation angles. The proposed techniques and modalities have been evaluated by measurements on phantoms and in vivo. Results show that high-resolution qualitative and quantitative skin assessment methods have been successfully implemented. HFUS based strain imaging enables the non-invasive assessment of skin and lesion properties, and HFUS limited-angle spatial compounding allows for improved skin analysis compared to the conventional linear-scan imaging approach.
Modeling scattering from cells and biological structures
Authors: Kolios Michael C. , Czarnota Gregory J.
Published: May 2008

The goal of ultrasonic tissue characterization is to extract information over and above the information conventionally displayed on imaging instruments which is typically the backscatter strength (B-mode image). The driving hypothesis of our work is that as the ultrasound wavelength approaches the size of a cell, the backscatter characteristics become more sensitive to the cells' physical attributes (size, structure, and composition) and changes in the cell structure due to therapeutic intervention. A better understanding of the interaction of acoustic waves with cells is required to interpret the backscatter data. An overview of our efforts to model scattering from individual cells, cell ensembles, and in-vivo cancer will be presented. Theoretical results will be presented comparing scattering from individual cells with experimental data from a variety of cells in suspension, cell ensembles with pellets (compact aggregates of cells) and in-vivo tumors. It will be shown that for the tumors we have studied there is a very good correlation of scattering characteristics between cell pellets and in-vivo tumors, indicating that in the tumors studied cell structure was the factor that dominated the scattering response. The goal of this work is to use quantitative ultrasound methods for diagnosis and monitoring the response to therapy.
Estimation of heterogeneity of scatterer densities for diagnosis of liver fibrosis
Authors: Yamaguchi Tadashi , Hachiya Hiroyuki
Published: May 2008

In the quantitative diagnosis using ultrasound, existence of the high or low echo which was indistinguishable from speckle serves as an index of diagnosis. In this study, we tried to clarify the relation between the scattering condition in the tissue and the probability density function of echo amplitude. Parameters to estimate the scattering condition were derived by Q-Q probability plot at computer simulation models and the clinical data of liver fibrosis. In the simulation model of heterogeneous medium, the result of Q-Q plot became a curve and the curvature was dependent on the difference of the scatterer density of two intermingled media. In the clinical data of liver fibrosis, curvature was large when many fibers were contained. On the other hand, curvature was small when cysts or minute blood vessels were intermingled in the speckle and the whole distribution function was able to be approximated by k-distribution. Moreover, the crooked point of the Q-Q plot was changed depending on the scatterer density of a mixture part. These results show that the mixture rate and scatterer distributions of two different distribution functions can be recognized parametrically in the liver in which minute diseased tissue was intermingled.
Improvements in liver diseases evaluation using transient elastography for obese patients
Authors: Sasso Magali , Miette Veronique , Sandrin Laurent
Published: May 2008

Transient elastography (Fibroscan®, Echosens, Paris, France) is a non invasive and rapid technique used to assess liver fibrosis by measuring liver stiffness. Clinical interest of liver stiffness measurement using Fibroscan® has been demonstrated for chronic liver diseases in adult patients. Clinically, the liver stiffness evaluation can be tricky in obese patients due to their large subcutaneous fat thickness. Obesity is a growing public health concern which requires dedicated liver evaluation procedures due to the patients' morphology and/or the specific diseases associated with obesity. Our study aims to show how Fibroscan® can adapt for liver diseases evaluation in obese patients. Clinical adaptations dedicated to over-weighted patients are shown: ultrasound guidance procedure, development of a dedicated probe for patients with a large subcutaneous fat thickness, development of new algorithms based on attenuation of both ultrasonic and shear waves. Performance is assessed and clinical interest of each adaptation is discussed in over-weighted, obese and morbid obese patients (body mass index greater than 25). These new procedures dedicated to obese patients improve liver diseases assessment using Fibroscan®.
High-frequency quantitative ultrasound imaging methods for human lymph nodes characterization ex vivo
Authors: Mamou Jonathan , Coron Alain , Hata Masaki , Machi Junji , Yanagihara Eugene , Laugier Pascal , Feleppa Ernest J.
Published: May 2008

High-frequency (>15 MHz, i.e., wavelength <100 μm) ultrasound has the potential to characterize biological tissues quantitatively at the microscopic level. In this study, quantitative ultrasound (QUS) methods were developed to evaluate freshly excised human lymph nodes from patients with possible metastatic cancer. The objectives were to improve detection of small but clinically significant lymph-node metastases that often are missed during routine histological evaluation. Three-dimensional (3D) ultrasound data acquisition was conducted on freshly excised nodes using a spherically-focused transducer with a center frequency of 21 MHz. Average scatterer sizes and acoustic concentrations were estimated using QUS methods with a Gaussian scattering model over a bandwidth extending from 11 to 27 MHz. Strategies were developed to recover lymph-node orientation and size after histological sectioning to allow for spatially matching QUS estimates to histology. The signal- and image-processing aspects of QUS estimation are presented and the preliminary results are shown that demonstrate our ability to acquire 3D ultrasound and histological data, to co-register them spatially, and to obtain scatterer-size and acoustic-concentration estimates for specific tissue types (cancer versus non-cancer) within the nodes. In future studies, these QUS estimates will be used to identify histologically difficult-to-detect micrometastases in lymph-nodes. [Supported by NIH R01CA100183.]
Extraction of the multiple scattering contribution in weakly scattering media: Application to human soft tissues
Authors: Aubry Alexandre , Derode Arnaud , Tanter Mickael
Published: May 2008

Waves scattered by a weakly scattering random medium contain a predominant single scattering contribution as well as a multiple scattering contribution which is usually neglected. But its investigation can be fruitful for characterization purposes because it provides measurements of statistical parameters such as the scattering mean free path. Our aim is to extract the multiple scattering contribution in a weakly scattering random medium. The experimental set up consists in an array of programmable transducers placed in front of the sample. The impulse responses between each couple of transducers are measured and form the interelement matrix. Our technique allows the extraction of multiple scattering signals by taking advantage of their randomness, contrary to single scattering contributions which are shown to exhibit a deterministic coherence along the antidiagonals of the array response matrix, whatever the distribution of scatterers. To illustrate the interest of this technique, we applied it to a synthetic medium (Agar gel) and to breast tissues. Surprisingly, the multiple scattering contribution is far from negligible in the breast around 4.3 MHz. The temporal evolution of its intensity can provide a new tool to complete information provided by standard echography; it also constitutes an experimental test of the Born approximation.
Noninvasive vascular ultrasound elastography of carotid arteries for stroke prevention
Authors: Cloutier Guy , Maurice Roch , Mercure Elizabeth , Giroux Marie-France , Soulez Gilles
Published: May 2008

Carotid plaque rupture leading to stroke involves alteration of arterial wall mechanical properties. This paper addresses reproducibility and potential clinical impact of non-invasive vascular elastography. Fifteen symptomatic and 15 asymptomatic patients with greater than 50% stenoses of their internal carotids, and 15 control subjects were scanned independently by two radiologists. Radio-frequency cine-loops were acquired on left and right common and proximal internal carotids. For control subjects, homogeneous strains with successive compression and dilatation of the vascular wall from systole to diastole and few shear patterns were observed. The axial strain did not differ between recording sites, sides and radiologists (ANOVA, p > 0.19). For patients, heterogeneous axial strain patterns with both compression and dilatation of tissues within plaques were noted along with shear concentrations at interfaces of tissue structures. Despite similar blood pressures, larger mean instantaneous axial strains were measured in symptomatic (1.5 ± 0.6%) versus asymptomatic (1.2 ± 0.5%) patients in systole for common carotids (t-test, p < 0.02). To conclude, reproducible results were obtained for control subjects and in patients, larger axial strains in common carotids may be associated with plaque rupture. This new imaging method may become a unique approach to characterize vulnerable plaques for stroke prevention.
A reflex transmission method for ultrasound thermometry
Authors: Farny Caleb H. , Clement Gregory
Published: May 2008

It is of great interest to develop ultrasound-based thermal imaging for monitoring thermal ablation procedures and as a tissue characterization technique. A phase contrast analysis for temperature mapping has been investigated, based on the temperature dependence of sound speed of water and tissue. The method employs reflex transmission imaging principles, planar projection and tomographic reconstruction techniques, for interrogating a region featuring a temperature contrast. Through-transmission and pulse-echo configurations were both used to image phase contrasts caused from a change in sound speed, in experimental measurements and numerical simulations. Tissue phantoms were used as a medium in which to create a steady-state sound speed contrast, and a raster scan was performed to acquire the sound field with a hydrophone. Two scans were acquired, a reference sound field and a scan featuring a phase contrast which corresponded to a 7 - 10°C peak temperature rise. The through-transmission configuration employed a 0.2-mm diameter needle hydrophone, while the pulse-echo measurement employed a custom-built thin-wire hydrophone to acquire the sound field between the interrogation transducer and tissue phantom. The method successfully located the location and amplitude of the phase contrast, and future steps necessary for tracking dynamic temperature changes will be discussed.
A method of HIFU field characterization in water and deration to tissue
Authors: Khokhlova Vera A. , Canney Michael S. , Bailey Michael R. , Bessonova Olga V. , Sapozhnikov Oleg A. , Crum Lawrence A.
Published: May 2008

Acoustic characterization of nonlinear HIFU fields is important for both the accurate prediction of ultrasound induced bioeffects and the development of regulatory standards for clinical HIFU devices. In this work a new characterization method is proposed and tested in water, tissue phantoms, and ex-vivo tissues. The method is based on the combined use of measurements and modeling. Experiments were performed with a 2 MHz transducer of 4.2 cm aperture and 4.5 cm focal length. Low amplitude measurements in water were used to establish boundary conditions for modeling based on the KZK-type equation. High amplitude focal waveforms then were simulated and measured with a fiber optic probe hydrophone in water, within tissue phantom, or adjacent to excised tissue. It was shown that at high amplitudes, the simulations of shock waveforms were more accurate than the measurements. The focal waveforms obtained in water were found to be in a good agreement with those produced in tissue with higher source pressure scaled to compensate for the linear attenuation on the way to focus. This result establishes a method to derate the focal HIFU pressures determined in water to tissue. [Work supported by NIH DK43881, NSBRI SMS00402 and RFBR.]
Uncertainty of power and intensity measurement in focused fields
Authors: Shaw Adam , Gelat Pierre
Published: May 2008

Currently, the methodology employed to measure acoustic intensity and acoustic power relies on the plane wave assumption, resulting in a simple relation between acoustic power and the normal component of the radiation force vector, and acoustic intensity and pressure magnitude. For a range of ultrasonic transducers, and for positions in the field beyond the last axial maximum, this assumption is a valid one. Nevertheless, there is a range of situations where the plane wave assumption may introduce significant uncertainty in the measurement, such as in near field measurements and in fields resulting from highly focused devices. This investigation looks at the acoustic fields generated by axisymmetric rigidly vibrating curved pistons over a range of diameters and radii of curvature at megahertz frequencies. Finite element and boundary element methods are used to evaluate the acoustic pressure field and the components of the particle velocity vector at specified field positions. The time-averaged acoustic intensity vector, the acoustic power, as well as the normal component of the radiation force vector on a perfectly absorbing target may then be derived. Experimental results are will also be presented comparing theory with radiation force measurements and with the new and more accurate buoyancy change method.
Standardisation and metrology for High Intensity focused ultrasound: a clinical perspective
Authors: Ter Haar Gail
Published: May 2008

The clinical application of HIFU is a young and rapidly expanding field, and it is essential that validated methods for measurement and testing are made available as soon as possible. These issues have not been addressed to date in any systematic fashion. There is, therefore, an urgent need to produce standard registration, testing equipment and methodology to allow users to characterize clinical HIFU systems for checking safety and reproducibility of a machine's output, comparing different devices or commissioning new systems. HIFU is delivered to the target volume via a number of routes. Extra-corporeal and trans-rectal probes are the most commonly used, although preliminary testing of intra-cavitary, catheter based devices is also underway19. These different devices present a wide range of different transducer geometries, f-numbers (∼0.8-1.8), operating frequencies (∼0.8 - 5 MHz), and focal peak intensities (∼7.5 102 - 3 104 W cm−2). Clinical HIFU systems are currently assessed on an ad hoc basis by individual clinical departments and manufacturers, using methods, many of which are unpublished. The main requirements from a clinical perspective are for the quantification of parameters which relate directly to individual HIFU treatments, allow reproducible treatments between different patients, and allow clinical trial data to be compared.
SLITA: A new slim towed array for AUV applications
Authors: Maguer Alain , Dymond Rodney , Mazzi Marco , Biagini Stefano , Fioravanti Stefano , Guerrini Piero
Published: May 2008

The typical 70 mm diameter towed array was developed for blue-water detection at long range and low frequencies in the 1960s. Since then, there has been a need for towed arrays that are lighter and less expensive, especially since the maturing field of autonomous vehicles has expanded the potential of such arrays. The marriage of AUVs and lightweight towed arrays is a natural progression in the development of littoral autonomous sensing networks for applications such Anti-Submarine Warfare, marine mammals, or ambient noise measurements. In August 2007, NURC began to design and build a new thin diameter (31 mm) high-frequency (up to 20 kHz) nested towed array for ASW purposes. An engineering at-sea trial of the array towed by OEX AUV was performed beginning of November 2007. The flow noise level of the array while towed and the potential influence of the AUV self-noise on the acoustic array were also measured. This paper will first describe the array design, its acquisition system and its integration on the OEX AUV. Then, the results obtained from the data analysis are presented. It is shown that the SLITA array has performance that will make it easily fit requirements of the applications previously mentioned.