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PubMed1991

Acoustic neuroma: postoperative deficits and the role of the neuroscience nurse.

Although the technical aspects of nursing care and management of acoustic neuroma patients have been discussed in literature, both the apparent and subtle neurological and psychological residuals of acoustic tumor have been largely overlooked. Long-term sequelae, unless acute, usually are not attended by the neuroscience nurse. However, nursing instruction and enhanced care while hospitalized can prepare the patient for self-care and improve final recovery. Responses of 541 members of the Acoustic Neuroma Association to a multipart questionnaire on aspects of the acoustic neuroma experience reveal the nurse plays an important role in preparing the patient for maximum recovery after hospital discharge.

Humans↗
PubMed2000

Acoustic preference functions and song variability in the Hawaiian cricket Laupala cerasina.

Female preference functions for different sexual traits can differ significantly, from 'unimodal' to 'open ended'. Through the study of acoustic communication in anurans, several studies have reported an association between static (stereotyped) traits versus dynamic (variable) traits and preference function shape (unimodal versus open ended, respectively). Observing a similar pattern in a phylogenetically independent group would suggest that deterministic forces have caused a relationship between signal variability and preference function shape in acoustic signalling systems. We examined this phenomenon in crickets, another animal characterized by intersexual acoustic communication. We measured the within-male variability for three acoustic features of the male calling song in Laupala cerasina and the corresponding shape of the female preference function for each of these features. We offer support for the generalization that open-ended preference functions correspond to relatively dynamic courtship traits and unimodal preference functions correspond to relatively static courtship traits. We discuss the evolutionary significance of these findings in the context of the natural history of the Laupala species radiation.

Acoustic Stimulation↗
PubMed1994

A theoretical model for magneto-acoustic imaging of bioelectric currents.

A theoretical model of magneto-acoustic current imaging is derived, based on fundamental equations of continuum mechanics and electromagnetism. In electrically active tissue, the interaction between an applied magnetic field, B, and action currents, J, creates a pressure distribution. In the near field limit, this pressure obeys Poisson's equation, with a source term (delta x J).B. The displacement and pressure fields are calculated for a dipole (q), oriented either parallel or perpendicular to the applied magnetic field (B), at the center of an elastic, conducting sphere (radius a, shear modulus G). Surface displacements are on the order of qB/(4 pi Ga), which is about 1 nm for typical biological parameters. If the applied magnetic field is changing with time, eddy currents induced in the tissue may be larger than the action currents themselves. The frequency of the pressure and displacement arising from these eddy currents, however, is twice the frequency of the applied magnetic field, so it may be possible to eliminate this artifact by filtering or lock-in techniques. Magneto-acoustic and biomagnetic measurements both image delta x J in a similar way, although magneto-acoustic current imaging has the disadvantage that acoustic properties vary among tissues to a greater degree than do magnetic properties.

Acoustics↗
PubMed1999

Acoustic noise analysis in echo planar imaging: multicenter trial and comparison with other pulse sequences.

The purpose of this study was to evaluate acoustic noise in echo planar imaging (EPI) at various magnetic resonance imaging (MRI) centers and to compare EPI acoustic noise with that in other fast pulse sequences. We measured A-weighted root-mean-square sound pressure levels and peak impulse sound pressure levels for EPI, under the same conditions, in eleven clinical super-conducting MRI systems. We also compared sound pressure levels for the EPI and six different pulse sequences and analyzed the acoustic noise spectra. Sound pressure levels during the use of the EPI differed greatly among institutions. Moreover, sound pressure levels of the EPI were not significantly different from those of other fast pulse sequences and were within permissible noise exposure levels. In comparison to other fast sequences, the EPI had significantly greater acoustic noise in the high-octave band frequency.

Acoustics↗
PubMed2002

Design of ultrasonic array elements for acoustic power considerations.

In sound-transmitting applications such as therapeutic ultrasound, the acoustic power at a particular operating frequency is a critical figure of merit for transducer/array design. A design methodology for enhancing the acoustic power radiated from fluid-loaded piezoelectric array elements at a fixed frequency is developed in this paper. A gradient-based optimization algorithm is integrated within the finite element framework to guide the determination of the two design variables, the piezoelectric element thickness and the matching layer thickness, to optimize the acoustic power output. A method for avoiding explicit remeshing in the optimization iteration is presented. Optimized designs are determined numerically, and the effectiveness of the design method is confirmed by experimental measurements. The validated numerical analysis also shows that conventional design strategies using one-dimensional transducer analysis and rule-of-thumb matching layer or protection layer sizing rules may not give the best design for array elements in acoustic power applications.

Acoustics↗
PubMed2004

Determination of the acoustic pressure at and the reflection coefficient of a target through measurements of the absorbed power and the emitter voltage.

A harmonic acoustic wave, fed back by a reflecting target, modifies the electric impedance of the emitter. This effect is studied using a tightly focused beam and various flat targets with known reflection coefficients, which are placed at pressure maxima or minima of the standing wave in the focal zone. It is possible to establish relationships that allow one to determine, for flat targets with unknown acoustic properties, the acoustic impedance and reflection coefficient of the target as well as the acoustic pressure present at the target, only from measurements of the absorbed power and the emitter voltage.

Acoustics↗
PubMed2005

Optical observations of acoustical radiation force effects on individual air bubbles.

Previous studies dealing with contrast agent microbubbles have demonstrated that ultrasound (US) can significantly influence the movement of microbubbles. In this paper, we investigated the influence of the acoustic radiation force on individual air bubbles using high-speed photography. We emphasize the effects of the US parameters (pulse length, acoustic pressure) on different bubble patterns and their consequences on the translational motion of the bubbles. A stream of uniform air bubbles with diameter ranging from 35 microm to 79 microm was generated and insonified with a single US pulse emitted at a frequency of 130 kHz. The bubble sizes have been chosen to be above, below, and at resonance. The peak acoustic pressures used in these experiments ranged from 40 kPa to 120 kPa. The axial displacements of the bubbles produced by the action of the US pulse were optically recorded using a high-speed camera at 1 kHz frame rate. The experimental results were compared to a simplified force balance theoretical model, including the action of the primary radiation force and the fluid drag force. Although the model is quite simple and does not take into account phenomena like bubble shape oscillations and added mass, the experimental findings agree with the predictions. The measured axial displacement increases quasilinearly with the burst length and the transmitted acoustic pressure. The axial displacement varies with the size and the density of the air bubbles, reaching a maximum at the resonance size of 48 microm. The predicted displacement values differ by 15% from the measured data, except for resonant bubbles for which the displacement was overestimated by about 40%. This study demonstrates that even a single US pulse produces radiation forces that are strong enough to affect the bubble position.

Acoustics↗
PubMed2005

Bubble-based acoustic radiation force elasticity imaging.

Acoustic radiation force is applied to bubbles generated by laser-induced optical breakdown (LIOB) to study viscoelastic properties of the surrounding medium. In this investigation, femtosecond laser pulses are focused in the volume of gelatin phantoms of different concentrations to form bubbles. A two-element confocal ultrasonic transducer generates acoustic radiation force on individual bubbles while monitoring their displacement within a viscoelastic medium. Tone burst pushes of varying duration have been applied by the outer element at 1.5 MHz. The inner element receives pulse-echo recordings at 7.44 MHz before, during, and after the excitation bursts, and crosscorrelation processing is performed offline to monitor bubble position. Maximum bubble displacements are inversely related to the Young's moduli for different gel phantoms, with a maximum bubble displacement of over 200 microm in a gel phantom with a Young's modulus of 1.7 kPa. Bubble displacements scale with the applied acoustic radiation force and displacements can be normalized to correct for differences in bubble size. Exponential time constants for bubble displacement curves are independent of bubble radius and follow a decreasing trend with the Young's modulus of the surrounding medium. These results demonstrate the potential for bubble-based acoustic radiation force methods to measure tissue viscoelastic properties.

Computer Simulation↗
PubMed2006

Ultrasonic tracking of acoustic radiation force-induced displacements in homogeneous media.

The use of ultrasonic methods to track the tissue deformation generated by acoustic radiation force is subject to jitter and displacement underestimation errors, with displacement underestimation being primarily caused by lateral and elevation shearing within the point spread function (PSF) of the ultrasonic beam. Models have been developed using finite element methods and Field II, a linear acoustic field simulation package, to study the impact of focal configuration, tracking frequency, and material properties on the accuracy of ultrasonically tracking the tissue deformation generated by acoustic radiation force excitations. These models demonstrate that lateral and elevation shearing underneath the PSF of the tracking beam leads to displacement underestimation in the focal zone. Displacement underestimation can be reduced by using tracking beams that are narrower than the spatial extent of the displacement fields. Displacement underestimation and jitter decrease with time after excitation as shear wave propagation away from the region of excitation reduces shearing in the lateral and elevation dimensions. The use of higher tracking frequencies in broadband transducers, along with 2D focusing in the elevation dimension, will reduce jitter and improve displacement tracking accuracy. Relative displacement underestimation remains constant as a function of applied force, whereas jitter increases with applied force. Underdeveloped speckle (SNR < 1.91) leads to greater levels of jitter and peak displacement underestimation. Axial shearing is minimal over the tracking kernel lengths used in acoustic radiation force impulse imaging and thus does not impact displacement tracking.

Acoustics↗
PubMed1993

Validation of acoustic rhinometry by using the Cavalieri principle to estimate nasal cavity volume in cadavers.

The ability of acoustic rhinometry to provide valid estimates of nasal cavity volume has been tested using cadaveric heads. Values obtained for the cavities in five intact heads were compared with unbiased estimates of the volumes of the same specimens. An unbiased estimate is one which does not depart in a systematic manner from the true value. Here, unbiased estimates were made by applying the Cavalieri principle to uniform random samples of 4-7 macroscopic slices per specimen. Using acoustic rhinometry, the mean volume (left and right sides combined) amounted to 31.3 ml with a co-efficient of variation of 77%. On the same specimens, the Cavalieri estimate of mean volume (both cavities plus the adjacent nasopharynx) was 31.1 ml (66%). There was a significant and positive correlation between the two data sets (correlation co-efficient 0.97). Repeated acoustic measurements on the same cavities gave a measuring error of about 4%. We conclude that acoustic rhinometry can provide valid and efficient estimates of the volume of the nasal cavity plus nasopharynx.

Acoustics↗
PubMed2005

Assessment of Cottle's areas through the application of a mathematical model deriving from acoustic rhinometry and rhinomanometric data.

OBJECTIVES: Each nasal area, as defined by Cottle, has a different influence on the nasal airflow. The longitudinal distribution of resistances in nasal cavities was calculated by the anterior rhinomanometry and acoustic rhinometry data. DESIGN: Dynamic study of Cottle's areas in normal subjects was carried out by rhinomanometry and acoustic rhinometry. SETTING: Study by the Department of Otolaryngology of the University of Rome-La Sapienza. PARTICIPANTS: Twenty-seven Caucasian adults in local and general healthy conditions took part and completed this study, with a total of 54 nasal cavities included because of negativity at ENT-examination and clinical history, with normal respiratory parameters at the rhinomanometry and acoustic rhinometry. MAIN OUTCOME MEASURES: We determined nasal and acoustic resistances, nasal volumes and cross-sectional surface areas, as defined by Cottle, using nasal endoscopy. The longitudinal distribution of nasal resistances was obtained by integrating experimental surface areas using a novel mathematical model. The estimation of the longitudinal nasal resistance variations as a result of a theoretical reduction of the surface areas. RESULTS: The reduction of the 2-3-1 areas (in this order of importance) showed the greatest influence on the nasal resistances with coefficients of determinations greater than 0.98, this being quite different from that of the areas 4 and 5 for quite smaller area reduction percentages. CONCLUSIONS: The areas 2-3-1 control the overall nasal resistance so the surgical procedures on these areas greatly influence the dynamics of nasal airflow. The mathematical model developed here gives useful information to nasal functional surgery and may be applied to other schemes of nasal cavity.

Acoustics↗
PubMed1992

Reduction in adherence of Actinomyces viscosus after exposure to low-frequency acoustic energy.

The ability of low-frequency (200 Hz) acoustic energy to reduce the adherence of Actinomyces viscosus T14V to saliva-treated hydroxyapatite (SHA) disks was studied. An acoustic pressure range between 0 and 65 kPa and exposure durations between 0 and 8 min were used to study the levels necessary to significantly alter adherence. The effects of acoustic exposure on both bacteria in liquid and bacteria already adhering to SHA disks were studied. A modified enzyme-linked immunosorbent assay was used to assess bacterial adherence. For bacterial suspensions exposed prior to addition to SHA disks, it was found that reductions in adherence were greater for lower bacterial concentrations. Exposure of bacteria already adhering to SHA disks resulted in a decrease in adherence that was independent of the bacterial concentration and linearly related to the logarithm of the exposure duration. In addition to affecting adherence, acoustic energy also dispersed bacterial aggregates. Our results support the concept that low-frequency sonic energy applied orally may be of therapeutic value in reducing adherence and colonization of teeth by plaque bacteria.

Acoustic Stimulation↗
PubMed1992

A four-year follow-up of hearing and development in children exposed in utero to vibro-acoustic stimulation.

OBJECTIVE: To obtain information of hearing and neuro-development in children exposed to vibro-acoustic stimulation in utero. DESIGN: Information collected from Swedish child care programmes. SETTING: Department of Obstetrics and Gynaecology, Karolinska Institutet, Danderyd University Hospital, Sweden. SUBJECTS: Children of 460 mothers exposed to vibro-acoustic stimulation for the assessment of fetal well-being during high- and low-risk pregnancies during 1985-1987. MAIN OUTCOME MEASURES: Auditory test (20-25 dB at eight frequencies between 500 and 8000 Hz) and general neurological examination at four years of age. RESULTS: No hearing damage or neuro-developmental abnormalities that could be connected to the vibro-acoustic stimulation were found. CONCLUSIONS: Vibro-acoustic stimulation, as applied in clinical practice, did not endanger either neurological development or hearing in children exposed in utero.

Acoustic Stimulation↗
PubMedDate not supplied

Acoustic cardiographic parameters and their relationship to invasive hemodynamic measurements in patients with left ventricular systolic dysfunction.

Data obtained at cardiac catheterization were used to evaluate the utility of acoustic cardiographic data in assessing the hemodynamic abnormalities associated with left ventricular systolic dysfunction (LVSD). Thirty-seven patients (mean age, 62.6 years) underwent catheterization, and hemodynamic data were recorded. Acoustic cardiographic recordings were obtained using a system that records and algorithmically interprets diastolic heart sounds and parameters analogous to traditional systolic time intervals. Seventeen patients had LVSD (defined as ejection fraction <50%). The 17 patients with LVSD composed the cohort for analysis. There were strong associations between acoustic cardiographic parameters and left ventricular end-diastolic pressure, ejection fraction, and maximum contractility. Heart rate tended to influence the strength of these correlations. The authors conclude that acoustic cardiographic data can be used in the evaluation of patients with known or suspected LVSD, and specifically in the selection of patients for cardiac resynchronization therapy and the optimization of the settings of implanted resynchronization devices.

Acoustics↗
PubMed2005

Comparison of acoustic densitometry and dobutamine echocardiography for an assessment of myocardial viability.

AIM: The aim of this study has been to compare acoustic densitometry and dobutamine echocardiography for an assessment of myocardial viability. METHODS AND RESULTS: Thirty-four patients with coronary artery disease and dysfunctional myocardial segments, who were referred for myocardial revascularization, underwent a viability assessment using low-dose dobutamine echocardiography and acoustic densitometry. Results of the two techniques were compared to follow-up resting echocardiography. This follow-up examination was performed at a mean of 3 months after successful revascularization in order to assess the recovery of function in revascularized, initially dysfunctional segments. Echocardiography was performed in standard views using 16-segment model of the left ventricle. Viable myocardium was identified by the augmentation of systolic thickening of an abnormal segment by at least one grade during dobutamine infusion and by the value of the maximal amplitude of cyclic variation of integrated backscatter. Acoustic densitometry had the sensitivity and specificity to predict functional recovery 90% and 77%, respectively. Dobutamine echocardiography had the sensitivity and specificity to predict contractile reserve 83% and 81%, respectively. The results were statistically comparable. Concordance between these methods was 80%. CONCLUSION: Acoustic densitometry and dobutamine echocardiography did not statistically differ in the prediction of functional recovery dysfunctional myocardial segments after revascularization.

Acoustics↗
PubMedDate not supplied

Diffraction-free acoustic detection for optoacoustic depth profiling of tissue using an optically transparent polyvinylidene fluoride pressure transducer operated in backward and forward mode.

An optoacoustic detection method suitable for depth profiling of optical absorption of layered or continuously varying tissue structures is presented. Detection of thermoelastically induced pressure transients allows reconstruction of optical properties of the sample to a depth of several millimeters with a spatial resolution of 24 mum. Acoustic detection is performed using a specially designed piezoelectric transducer, which is transparent for optical radiation. Thus, ultrasonic signals can be recorded at the same position the tissue is illuminated. Because the optoacoustical sound source is placed in the pulsed-acoustic near field of the pressure sensor, signal distortions commonly associated with acoustical diffraction are eliminated. Therefore, the acoustic signals mimic exactly the depth profile of the absorbed energy. This is illustrated by imaging the absorption profile of a two-layered sample with different absorption coefficients, and of a dye distribution while diffusing into a gelatin phantom.

Absorption↗
PubMed2000

A noninvasive method for estimating acoustic admittance at the tympanic membrane.

The acoustic admittance at the tympanic membrane (TM), Y(TM), describes the linear acoustic properties of the ear. Here, a noninvasive measurement procedure is developed for estimating Y(TM) in intact ears. The method consists of (1) measuring the admittance in the ear canal Y(EC) with a commercially available earphone-and-microphone system, and (2) estimating Y(TM) via a uniform-tube approximation of the space between the measurement point and the TM. The dimensions of this space are estimated from Y(EC) via an area-estimation algorithm [Keefe et al., J. Acoust. Soc. Am. 91, 470 (1992)] and measurements made with controlled static pressures in the canal. Measurements in artificial loads are used to test the accuracy of the measurement system and to determine sources of error. For accurate admittance measurements: (1) extension of the microphone tube medially beyond the earphone's port is necessary for frequencies above 2 kHz; (2) the acoustic system must be calibrated in known loads with diameters within 15% of the canal diameter, because the source's output characteristics vary with load diameter. The method is applied to intact ears of anesthetized domestic cats; for frequencies below 5 kHz, the estimated Y(TM) in four ears have features that are similar to those of previous measurements made at the cat TM. Sources of error include nonuniform waves generated at the earphone's narrow port, inaccuracy in estimation of canal dimensions, irregular geometry of the canal, and earphone-microphone cross talk.

Acoustics↗
PubMed2001

Simulations of the thermo-acoustic lens effect during focused ultrasound surgery.

Laboratory measurements of soft tissue properties show a dependence of background propagation properties on temperature. For typical focused ultrasound surgery (FUS) applications, only the slow variations in tissue background parameters need to be accounted for when computing the outcome of a FUS sonication. The cumulative effect of slowly varying sound speed has been referred to in the literature as a thermal lens, or a thermo-acoustic lens because of its beam-distorting properties. An algorithm to solve the coupled acoustic-thermal problem is described, and numerical results are presented to illustrate the effects of dynamic sound-speed profiles in layered tissues undergoing FUS. The results of simulations in liver with and without a fat layer indicate that the thermal-acoustic interaction results in more complex dynamics in FUS than a simple model will predict. Both the size and the position of the lesions predicted from the simulations are affected by the thermo-acoustic lens effect. However, the overall effect from short sonications at high power from sharply focused single element sources (F-no. from 0.8 to 1.3) around 1 MHz similar to those used in clinical setups is found to be small.

Acoustics↗