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PubMed2002

Nondestructive imaging of shallow buried objects using acoustic computed tomography.

The nondestructive three-dimensional acoustic tomography concept of the present investigation combines computerized tomography image reconstruction algorithms using acoustic diffracting waves together with depth information to produce a three-dimensional (3D) image of an underground section. The approach illuminates the underground area of interest with acoustic plane waves of frequencies 200-3000 Hz. For each transmitted pulse, the reflected-refracted signals are received by a line array of acoustic sensors located at a diametrically opposite point from the acoustic source line array. For a stratified underground medium and for a given depth, which is represented by a time delay in the received signal, a horizontal tomographic 2D image is reconstructed from the received projections. Integration of the depth dependent sequence of cross-sectional reconstructed images provides a complete three-dimensional overview of the inspected terrain. The method has been tested with an experimental system that consists of a line array of four-acoustic sources, providing plane waves, and a receiving line array of 32-acoustic sensors. The results indicate both the potential and the challenges facing the new methodology. Suggestions are made for improved performance, including an adaptive noise cancellation scheme and a numerical interpolation technique.

Acoustics↗
PubMed2002

Combined Helmholtz equation-least squares method for reconstructing acoustic radiation from arbitrarily shaped objects.

A combined Helmholtz equation-least squares (CHELS) method is developed for reconstructing acoustic radiation from an arbitrary object. This method combines the advantages of both the HELS method and the Helmholtz integral theory based near-field acoustic holography (NAH). As such it allows for reconstruction of the acoustic field radiated from an arbitrary object with relatively few measurements, thus significantly enhancing the reconstruction efficiency. The first step in the CHELS method is to establish the HELS formulations based on a finite number of acoustic pressure measurements taken on or beyond a hypothetical spherical surface that encloses the object under consideration. Next enough field acoustic pressures are generated using the HELS formulations and taken as the input to the Helmholtz integral formulations implemented through the boundary element method (BEM). The acoustic pressure and normal component of the velocity at the discretized nodes on the surface are then determined by solving two matrix equations using singular value decomposition (SVD) and regularization techniques. Also presented are in-depth analyses of the advantages and limitations of the CHELS method. Examples of reconstructing acoustic radiation from separable and nonseparable surfaces are demonstrated.

Acoustics↗
PubMed1990

Bacterial luminescence: a new tool for investigating the effects of acoustic energy and cavitation.

An assay utilizing luminescent bacteria, Photobacterium phosphoreum, was adapted to assess the antibacterial effects of acoustic energy. Acoustic pressures up to 67 kPa in the 100- to 800-Hz frequency range were applied to bacteria freely suspended in a liquid medium. Bacterial luminescence decreased after sonication, thus showing sensitivity to the effects of acoustic energy. This decreased luminescence was linearly related to exposure duration, appeared independent of acoustic frequency in this range, and was significantly heightened by the presence of cavitation. High-frequency components of the acoustic emission were recorded from the sonicated fluid, and it was found that the decrease in luminescence due to sonication was directly related to the logarithm of the acoustic emission. Viability studies on exposed bacteria indicated a diminution of luminescence without bacterial death. The potential use of luminescent bacteria in assessing the biological effects of acoustic energy-generating systems is discussed.

Acoustics↗
PubMed1991

Acoustic myography as an indicator of force during sustained contractions of a small hand muscle.

To test the hypothesis that muscle sound amplitudes would remain constant during sustained submaximal isometric contractions, we recorded acoustic myograms from the abductor digiti minimi muscle in 12 subjects at 15, 25, 50, and 75% of a maximum voluntary contraction (MVC). Muscle sounds were detected with an omni-directional electret microphone encased in closed-cell foam and attached to the skin over the muscle. Acoustic amplitudes from the middle and end of the sustained contractions were compared with the amplitudes from the beginning of contractions to determine whether acoustic amplitudes varied in magnitude as force remained constant. Physiological tremor was eliminated from the acoustic signal by use of a Fourier truncation at 14 Hz. The amplitudes of the acoustic signal at a contraction intensity of 75% MVC remained constant, reflecting force production over time. At 50% MVC, the root-mean-square amplitude decreased from the beginning to the end of the contraction (P less than 0.05). Acoustic amplitudes increased over time at 15 and 25% MVC and were significantly higher at the end of the contractions than at the beginning (P less than 0.05). Alterations in the acoustic amplitude, which reflect changes in the lateral vibrations of the muscle, may be indicative of the different recruitment strategies used to maintain force during sustained isometric contractions.

Acoustics↗
PubMed1997

Acoustic measurement of change in voice quality with treatment for chronic posterior laryngitis.

Sixteen patients who had symptoms and signs of chronic posterior laryngitis were evaluated before, during, and after treatment with omeprazole and nocturnal antireflux precautions. Data were analyzed for patients who complained of some hoarseness, who had no smoking history, and who completed all of the voice recording protocol. The patients' voices were recorded before, during, and following treatment with omeprazole and nocturnal antireflux precautions. Voice quality was analyzed by perceptual analysis, and acoustic signal data were measured for jitter, shimmer, and signal-to-noise ratio. Measures of jitter, shimmer, and signal-to-noise ratio changed significantly with treatment of posterior laryngitis (p < .01 for change in each of the measures). Acoustic measures showed some trend of deterioration with cessation of treatment, although the overall improvement in acoustic measures of voice quality was still statistically significant after treatment with omeprazole was discontinued. Although perceived abnormality of voice increased and decreased with the magnitude of measured perturbation of the acoustic signal for some patients, the perceptual assessments were not highly correlated with acoustic measures for individual patients, and the perceptual analysis group data did not show a significant change with time during treatment, in contrast to the significance of change in acoustic measures. The data demonstrate that acoustic measures of jitter, shimmer, and signal-to-noise ratio improve significantly with antisecretory and antireflux treatment of chronic posterior laryngitis, and that for individual patients, these are changes that are detected by trained listeners, but not at statistically high levels of confidence.

Adult↗
PubMedDate not supplied

Units of intonation in discourse: a comparison of acoustic and auditory analyses.

Measurements were made of the correspondence between acoustic (declination) units and auditory (intonation) units in American English conversation in an attempt to relate these two levels of description. The results showed that 99% of the acoustic unit boundaries coincided with auditory unit boundaries, indicating that the acoustic cues of F0 reset, pause, and speaker change used in defining the acoustic units were perceived, verifying the validity of both types of analyses. However, the units differed in scope, with many more auditory units occurring than acoustic units. This result suggests that the common practice of assuming the 'intonational phrase' to be the primary domain of prosodic phenomena such as declination does not adequately account for our data of larger periods of speech. Both acoustic and auditory analysis are needed for a satisfactory description of intonation. The establishment of a methodological connecting link between the acoustic and auditory dimensions suggests that further comparisons of such different data types may yield guidelines for regularizing the relationship between the two levels.

Adult↗
PubMed1992

Acoustic stimulation as a diagnostic test: comparison with oxytocin challenge test.

The usefulness of an acoustic stimulation test as a marker of fetal well-being was evaluated in a randomized controlled study of 121 pregnant women exhibiting a non-reactive fetal non-stress test at term. The women were randomly divided into two groups; those in the first group (n = 62) underwent an acoustic stimulation test immediately prior to an oxytocin challenge test, while those in the second (n = 59) underwent an oxytocin challenge test only. Fetal response to the acoustic stimulation was non-reactive in 22.5% of the women tested in the first group. The incidence of abnormal oxytocin challenge test among the women who were previously subjected to an acoustic stimulation was somewhat lower than among those who did not (14.5% vs. 23.7%), but the difference was not significant. In the prediction of an abnormal oxytocin challenge test, a non-reactive acoustic stimulation test had a sensitivity of 100%, a positive predictive value of 64% and a specificity of 91%. As a single test for the prediction of fetal distress in labor (n = 62), the acoustic stimulation test had a specificity and a positive predictive value similar to those of the oxytocin challenge test (n = 121), and its sensitivity was even higher (88% vs. 71%). We conclude that the acoustic stimulation test is at least as reliable as the oxytocin challenge test in the evaluation of fetal well-being in women exhibiting a non-reactive non-stress test at term.

Acoustic Stimulation↗
PubMed2003

Acoustic estimation of infestations and population densities of white grubs (Coleoptera: Scarabaeidae) in turfgrass.

Incidental sounds produced by Phyllophaga crinita (Burmeister) and Cyclocephala lurida (Bland) (Coleoptera: Scarabaeidae) white grubs were monitored with single- and multiple-sensor acoustic detection systems in turf fields and golf course fairways in Texas. The maximum detection range of an individual acoustic sensor was measured in a greenhouse as approximately the area enclosed in a 26.5-cm-diameter perimeter (552 cm2). A single-sensor acoustic system was used to rate the likelihood of white grub infestation at monitored sites, and a four-sensor array was used to count the numbers of white grubs at sites where infestations were identified. White grub population densities were acoustically estimated by dividing the estimated numbers of white grubs by the area of the detection range. For comparisons with acoustic monitoring methods, infestations were assessed also by examining 10-cm-diameter soil cores collected with a standard golf cup-cutter. Both acoustic and cup-cutter assessments of infestation and estimates of white grub population densities were verified by excavation and sifting of the soil around the sensors after each site was monitored. The single-sensor acoustic method was more successful in assessing infestations at a recording site than was the cup-cutter method, possibly because the detection range was larger than the area of the soil core. White grubs were recovered from >90% of monitored sites rated at medium or high likelihood of infestation. Infestations were successfully identified at 23 of the 24 sites where white grubs were recovered at densities >50/m2, the threshold for economic damage. The four-sensor array yielded the most accurate estimates of the numbers of white grubs in the detection range, enabling reliable, nondestructive estimation of white grub population densities. However, tests with the array took longer and were more difficult to perform than tests with the single sensor.

Acoustics↗
PubMedDate not supplied

[Effect of noise on changes in the acoustic reflex].

Acoustic, stapedial reflex represents a response of the m. stapedius to a sonic excitation of supra speech intensity. It is the constitutive part of impendancmetric investigations, it is performed on the same apparatus after tympanometry, and it is the inseparable part in representation of impendancmetric findings. Until now, the most frequently monitored parameters of acoustic reflex of clinical importance are: threshold, amplitude, output and input angle of the reflex curve. The aim of this work was to performed detailed analysis of mentioned parameters in workers exposed to extensive action of industrial noise of known physical characteristics (of different durations) and to establish which changes occurred in these workers, to what extent and under which conditions. Investigations included 173 industrial workers (346 ears), which work in working unit "Forge", where during the working process noise is produced which is above permissible limits and of the unfavorable frequency content. Workers were divided into two groups. The first group consisted of workers who were spending the whole working time in the workroom with noise above permissible limits, the second group consisted of workers who were spending 3 hours of the working time in that workroom, while the control group consisted of workers who were spending the whole working time in that workroom but they did not have any hearing impairment. Workers of the first and the second group had the hearing impairment, which occurred exclusively as a consequence of chronical acoustic trauma. For all the workers the anamnesis was taken, as well as ORL status and audiometric and impendancmetric investigations were performed, namely the tympanometry and acoustic reflex. Results have shown that the acoustic reflex threshold at 500 Hz and at 1000 Hz for the first group (95.10 dB) was increased with respect to the reflex threshold of the second and the control group (84 dB). At higher frequencies of 2000 Hz and 4000 Hz an increase of the reflex threshold was found for the first and the second group (96 dB) with respect to the control group (87 dB). The amplitude of acoustic reflex was increased, at frequencies 500 Hz and 1000 Hz (3.38), with respect to the second group (2.78) and the control group (2.36), and at higher frequencies, this increase is more prominent. The input angle of the reflex curve was, for the first and the second group, within limits 41 degrees to 50 degrees, and for the control group was from 31 degrees to 50 degrees. The output angle was, at majority of ears of the first and the second group, from 26 degrees to 35 degrees, and for the control group it was from 16 degrees to 35 degrees. Acoustic reflex, as the noninvasive method, short term one, objective and simple for application, does not require collaboration of workers, what provides for objectivity of obtained results and what caused that wrongful estimations, impressions and subjective reactions of workers were avoided.

Hearing Loss, Noise-Induced↗
PubMed2003

Startle response to short acoustic stimuli in rats.

The acoustic startle (ASR) is a transient motor response to an unexpected, intensive stimulus. The response is determined by stimulus parameters such as its intensity, rise time and duration. The dependence of the ASR on the stimulus duration is more complex than could be assumed from physical properties of acoustic pulse. This effect attracted the attention of few researchers. Some authors reported noticeable changes in the ASR amplitude only for very short (less than 4-6 ms) acoustic pulses. The systematic studies on the effect, however, have not been performed so far. The purpose of this study was to determine to what extent the ASR parameters are affected by the durations of the short stimulus. The amplitude of the acoustic startle reflex was assessed for a fixed tonal frequency (6.9 kHz), and for a variety of stimulus durations ranging between 2 and 10 ms. ASRs were studied in 11 adult, hooded rats exposed to a sequence of tone pulses (110 dB SPL) of different durations, presented in random order, with or without 70 dB white noise as a background. Statistical analysis revealed significant differences between ASR amplitudes for different durations. The startle amplitude increased with acoustic pulse duration and distinguishable differences were seen for stimulus duration between 2 and 8 ms. Further increase of pulse duration had no effect on ASR amplitude. The same pattern of changes was observed when the acoustic stimulus was presented with the white noise. In the tested range of stimulus duration no significant differences in the ASR latency were found. The observed differences may be attributed to changes of stimulus acoustic energy and to physiological characteristic of auditory system in the rat.

Acoustic Stimulation↗
PubMed1997

[Recurrent acoustic neuroma: report of 11 cases].

To improve the therapeutic effect of acoustic neuroma, 158 patients with acoustic neuroma treated in our hospital were retrospectively reviewed. Among them, 11 recurrent acoustic neuroma were found. The clinical analysis demonstrated that the recurrence of acoustic neuroma had close relationship with the size of the tumor, operative approach and extent of excision. All recurrent acoustic neuroma was large-sized when first operated. The more the tumor was excised, the lower the recurrent rate was. The recurrent rates were 19.4% for partial resection, 13.2% for near-total resection, 0% for total resection respectively. Retrolabyrinthine approach was more likely to recur than other approaches. The key to decrease recurrent rate was to excise as much tumor as possible. According to growth rate and double time of acoustic neuroma measured in this study, regular follow-up with CT or MRI at interval of 6 months was emphasized. X-knife was effective for early-diagnosed recurrent acoustic neuroma.

Adult↗
PubMed2000

[Neurootologic study of acoustic neuroma].

OBJECTIVE: To summarize the outcome of neurootologic examination of acoustic neuroma and study of diagnostic significance of neurootologic examination on acoustic neuroma. METHOD: 13 patients were examined with pure tune test, acoustic immittance, electronystagmography, acoustic brainstem evoked response, electrocochleogram, otoacoustic emissions and facial electroneurography. RESULT: All patients had subjective hearing loss. One patient had normal pure tone audiogram, other 4 patients had normal pure tone test at the frequency < 2000 Hz. The outcome of acoustic immittance is various. 5 patients were normal in caloric test, but all were abnormal in visual-vestibular optokinetic response. ABR are positive in 90.9% of cases, but 2 patients had no response. 7 patients were abnormal in facial electroneurography, 3 (of 3) eletrocochleogram and 2 (of 2) otoacoustic emissions revealed retrocochlear pathology. CONCLUSION: Neurootologic examination played important role in filtering diagnosis of acoustic neuroma, results should be considered synthetically, acoustic neuroma should not be ruled out if any one test was negative.

Adult↗
PubMed1992

Hearing preservation in acoustic neurinoma surgery.

The chances of hearing conservation in patients with acoustic neurinoma increases by early diagnosis of small tumors. An early diagnosis of an acoustic neurinoma is achieved through the application of a minimal diagnostic test battery to evaluate unilateral otological complaints such as tinnitus, sensorineural hearing loss and balance disturbances. This minimal evaluation comprises puretone audiometry and ABR. Patients showing abnormal findings should be pursued with imaging evaluation such as MRI with gadolinium contrast. The choice of surgical approach for removal of an acoustic neurinoma (transtemporal, translabyrinthine or suboccipital) will depend on the size of the tumor and the patients' hearing. The possibilities should be discussed with the patients. Postponing the surgical intervention due to the possibility of facial paralysis or loss of hearing is difficult to rationalise. During the last 15 years, the development in diagnostic and surgical techniques has made it possible to conserve hearing during surgery at least in some patients suffering from acoustic neurinoma. Early diagnosis of small tumors increases the chances to conserve hearing. Therefore, all nonspecific early otologic symptoms should be thoroughly evaluated to exclude the presence of an acoustic neurinoma. Acoustic neurinomas usually arise within the internal auditory meatus and grow further into the posterior cranial fossa. The first symptoms usually are hearing loss, tinnitus and balance disturbance. These symptoms can occur in combination or individually. Accordingly, all cases presenting with one or all of these symptoms in the absence of an obvious etiology, such as posttraumatic hearing loss, require the exclusion of an acoustic neurinoma.(ABSTRACT TRUNCATED AT 250 WORDS)

Audiometry, Pure-Tone↗
PubMedDate not supplied

[Smooth pursuit eye movements evoked by head-phone acoustic stimulation].

Smooth pursuit eye movement evoked by binaural acoustic stimulation is examined in the present work. The effect of lateralization was achieved by modulating the interaural difference in intensity, within the headphone, following a pendular pattern. The test was performed on 10 healthy subjects; oscillation frequencies of the acoustic target being 0.15, 0.5 and 0.83 Hz, stimulus intensity 65 and 92 dB SPL. The acoustic signal consisted of white noise. Each trial was performed with eyes closed and then with eyes open. The results demonstrate that sinusoidal eye movement can only be obtained in a few subjects when the acoustic target has the lowest velocity and especially at the higher intensity. In all other cases eye movement was characterized by multiple saccades. The variability in eye movement amplitude is reduced and the value of this parameter decreases significantly under open-eye conditions. The data obtained are in agreement with other reports obtained with free field acoustic stimulation and demonstrate that smooth pursuit eye movement is principally an ocular reflex. In conclusion, acoustic smooth pursuit eye movement appears normally to be characterized by multiple saccades whose pattern can be modulated by intensity and oscillation frequency of the acoustic target as well as by the presence of visual inputs and attentional factors.

Acoustic Stimulation↗
PubMed1995

[Ultrasonic tissue characterization of diseased myocardium by scanning acoustic microscopy].

Ultrasonic tissue characterization of the myocardium has become very important because the requirement for evaluating local cardiac function has increased. In the present study, the acoustic properties of the tissue elements in myocardial infarction were measured by a specially developed scanning acoustic microscope (SAM) system, and the echo intensity of the infarcted myocardium was assessed. Ten samples of infarcted myocardium obtained at autopsy were formalin-fixed, paraffin-embedded and cut into 10 microns thick slices. The SAM system was operated in the frequency range of 100 to 200 MHz. The values of the attenuation constant and sound speed were measured in five tissue elements, normal myocardium, degenerated myocardium, fibrosis, granulation, and hemorrhage by comparing the optical microscopic image and acoustic images. The density of each tissue element was measured by the CuSO4 method, and the specific acoustic impedance was calculated by multiplying the sound speed and the density of each tissue element. The specific acoustic impedance was 1.75 x 10(6) Ns/m3 in normal myocardium, 1.69 x 10(6) Ns/m3 in degenerated myocardium, and 1.85 x 10(6) Ns/m3 in fibrosis. The intensity of the reflected ultrasound at the interface between two different tissue elements was calculated by the difference of specific acoustic impedance. Using the sensitivity changing method in clinical echocardiography, the intensity of myocardial scar was -15 dB compared to the pericardial echo. The corrected ideal ultrasonic reflection between degenerated myocardium and fibrosis was calculated as -15.4 dB. The results suggest that measurement of acoustic properties is very important to provide basic data for ultrasonic characterization of myocardium tissue.

Acoustics↗
PubMed1995

Efficacy of auditory brainstem response as a screening test for small acoustic neuromas.

Auditory brainstem response (ABR) has been advocated as a high sensitivity screening test for acoustic neuroma. With the advent of magnetic resonance imaging (MRI), smaller size acoustic neuromas are now detectable. A prospective trial was performed to determine the sensitivity of ABR in diagnosing small acoustic neuromas. One hundred five randomly selected patients with surgically proved acoustic neuromas underwent preoperative ABR tests within 2 months of their surgery. Patients with a histologic diagnosis other than acoustic neuroma were excluded from this study. A test was considered abnormal when the interaural wave I-V latency difference was greater than 0.2 ms, the absolute wave V latency was abnormally prolonged, or there was abnormal or absent waveform morphology. Of the 105 patients tested 92 (87.6%) had abnormal ABR test, and 13 (12.4%) had completely normal waveforms and wave latencies. Eighteen patients had tumors over 2 cm in total diameter. Of these, 12 were 2.5 cm or larger and 6 were between 2.1 and 2.4 cm. All of these 18 patients had abnormal ABR tests. Of the 29 patients with tumors 1.6-2.0 cm in size, 25 (86%) had abnormal ABRs. In the 1.0-1.5 cm diameter range there were 45 patients who underwent a preoperative ABR. Of these, 40 (89%) had abnormal ABRs. Of 13 patients with tumors 9 mm or smaller, only 9 (69%) had abnormal ABR test (p < .05). Thus, it appears that ABR sensitivity decreases with tumor size and is particularly inadequate for tumors of less than 1 cm in diameter. The authors conclude that ABR is not a good screening test for smaller acoustic neuromas and recommend MRI for patients with suspected acoustic neuroma.

Contrast Media↗
PubMed1996

Low-cost high-resolution fast spin-echo MR of acoustic schwannoma: an alternative to enhanced conventional spin-echo MR?

PURPOSE: To determine whether unenhanced high-resolution T2-weighted fast spin-echo MR imaging provides an acceptable and less expensive alternative to contrast-enhanced conventional T1-weighted spin-echo MR techniques in the diagnosis of acoustic schwannoma. METHODS: We reviewed in a blinded fashion the records of 25 patients with pathologically documented acoustic schwannoma and of 25 control subjects, all of whom had undergone both enhanced conventional spin-echo MR imaging and unenhanced fast spin-echo MR imaging of the cerebellopontine angle/internal auditory canal region. The patients were imaged with the use of a quadrature head receiver coil for the conventional spin-echo sequences and dual 3-inch phased-array receiver coils for the fast spin-echo sequences. RESULTS: The size of the acoustic schwannomas ranged from 2 to 40 mm in maximum dimension. The mean maximum diameter was 12 mm, and 12 neoplasms were less than 10 mm in diameter. Acoustic schwannoma was correctly diagnosed on 98% of the fast spin-echo images and on 100% of the enhanced conventional spin-echo images. Statistical analysis of the data using the kappa coefficient demonstrated agreement beyond chance between these two imaging techniques for the diagnosis of acoustic schwannoma. CONCLUSIONS: There is no statistically significant difference in the sensitivity and specificity of unenhanced high-resolution fast spin-echo imaging and enhance T1-weighted conventional spin-echo imaging in the detection of acoustic schwannoma. We believe that the unenhanced high-resolution fast spin-echo technique provides a cost-effective method for the diagnosis of acoustic schwannoma.

Adult↗
PubMed1996

Acoustic cues to grammatical structure in infant-directed speech: cross-linguistic evidence.

Several theorists have suggested that infants use prosodic cues such as pauses, final lengthening, and pitch changes to identify linguistic units in speech. One potential difficulty with this proposal, however, is that the acoustic shape of an utterance is affected by many factors other than its syntax, including its phonetic, lexical, and discourse structure. This has raised questions about how the infant could use timing and pitch as cues to any aspect of linguistic structure without simultaneously factoring out other effects. Acoustic analyses of connected samples of spontaneous speech addressed to 13.5-14-month-old infants by American English- and by Japanese-speaking mothers revealed that both utterance- and phrase-level acoustic regularities were large enough to be detected in spontaneous speech without correcting for other influences on the same acoustic features. (1) Utterance-final vowels were lengthened and underwent exaggerated pitch changes in both languages, and (2) local acoustic changes in duration (English) or pitch (Japanese) were reliably associated with some phrase boundaries within utterances. These findings suggest that a naive listener could estimate a rough prosodic template for each language based on robust acoustic patterns in observed sentences. We discuss ways in which the learner could combine acoustic and distributional analyses across utterances to acquire language-specific variations in prosodic bracketing cues and to obtain indirect perceptual evidence for the internal structure of utterances.

Child Development↗