Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “ACOUSTICS”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 991 records · Page 55Linked to original sources
PubMed2000

Laser-induced acoustic emissions in experimental dental composites.

A laser thermoacoustic technique was innovated to evaluate laser-induced acoustic emissions (AEs) in experimental dental composites aged with 75% ethanol solution. Experimental composite systems of 75/25 BisGMA/TEGDMA resin filled with 0, 12.6, 30.0, and 56.5 vol% of 8-microm silanized and unsilanized BaSiO6 were analyzed. The sample size was 4.65 mm (diameter) x 0.5 mm (thick). Aging effects of immersing in 75% ethanol for up to 14 h on AEs were then evaluated. A continuous-wave CO2 laser was used to heat the samples. Acoustic emissions were collected as a function of filler fraction, laser power, silanization, and immersion time. Onset of burst-pattern acoustic signals characteristic of fracturing occurred at different laser powers for different tested groups. Acoustic emissions generally increased with laser power, in which lower laser powers produced low-amplitude (45-50 dB) signals; the amplitude distribution (50-85 dB) became more extensive as laser powers increased. After immersion, the lower laser powers could produce the same phenomenon. The higher the filler fraction, the fewer AEs generated. A large percentage AE reduction due to silanization was noted as a function of filler fraction. Unsilanized specimens showed more thermal damages than did silanized ones.

Acoustics↗
PubMed2004

Investigation of fatigue crack growth in acrylic bone cement using the acoustic emission technique.

Failure of the bone cement mantle has been implicated in the loosening process of cemented hip stems. Current methods of investigating degradation of the cement mantle in vitro often require sectioning of the sample to confirm failure paths. The present research investigates acoustic emission as a passive experimental method for the assessment of bone cement failure. Damage in bone cement was monitored during four point bending fatigue tests through an analysis of the peak amplitude, duration, rise time (RT) and energy of the events emitted from the damage sections. A difference in AE trends was observed during failure for specimens aged and tested in (i) air and (ii) Ringer's solution at 37 degrees C. It was noted that the acoustic behaviour varied according to applied load level; events of higher duration and RT were emitted during fatigue at lower stresses. A good correlation was observed between crack location and source of acoustic emission, and the nature of the acoustic parameters that were most suited to bone cement failure characterisation was identified. The methodology employed in this study could potentially be used as a pre-clinical assessment tool for the integrity of cemented load bearing implants.

Acoustics↗
PubMed2002

Tactile, acoustic and vestibular systems sum to elicit the startle reflex.

The startle reflex is elicited by intense tactile, acoustic or vestibular stimuli. Fast mechanoreceptors in each modality can respond to skin or head displacement. In each modality, stimulation of cranial nerves or primary sensory nuclei evokes startle-like responses. The most sensitive sites in rats are found in the ventral spinal trigeminal pathway, corresponding to inputs from the dorsal face. Cross-modal summation is stronger than intramodal temporal summation, suggesting that the convergence of acoustic, vestibular and tactile information is important for eliciting startle. This summation declines sharply if the cross-modal stimuli are not synchronous. Head impact stimuli activate trigeminal, acoustic and vestibular systems together, suggesting that the startle response protects the body from impact stimuli. In each primary sensory nucleus, large, second-order neurons project to pontine reticular formation giant neurons critical for the acoustic startle reflex. In vestibular nucleus sites, startle-like responses appear to be mediated mainly via the vestibulospinal tract, not the reticulospinal tract. Summation between vestibulospinal and reticulospinal pathways mediating startle is proposed to occur in the ventral spinal cord.

Acoustic Stimulation↗
PubMed2002

Rapid auditory processing and MGN morphology in microgyric rats reared in varied acoustic environments.

Adult male rats with induced microgyric lesions exhibit significant deficits in rapid auditory processing, as well as morphological alterations in the medial geniculate nucleus (MGN) of the thalamus. These findings are considered striking in light of similar anatomical and auditory processing anomalies in language disabled humans. Given evidence from clinical and animal studies that acoustic experience may alter sensory processing at behavioral and neurophysiological levels, the current study examined effects of developmental exposure to auditory stimulation on behavioral and anatomical indices in microgyric and sham rats. Stimulation (E7-P 70) included: (1). chronic white noise (80 dB) with standard housing; (2). 3 h/day of 78 dB filtered light classical music with social housing; or (3). standard acoustic environment (control) with standard housing. Microgyric effects on auditory processing and thalamic morphology were evident regardless of environmental condition. In sum, the effects of microgyria on brain and behavior appear to be robust, and largely orthogonal to any main effect of acoustic stimulation on auditory processing. These findings suggest that a more active form of acoustic stimulation (e.g., training) may be required to ameliorate the deleterious behavioral and anatomical consequences of focal microgyric lesions.

Acoustic Stimulation↗
PubMed2001

Acoustic analysis of voice in children with noduli vocales.

The acoustic tests of voice were carried out on 46 children with noduli vocales before the treatment and after its completion. Acoustic parameters of voice were compared with the control group of children without voice pathology. The results of the investigation were analysed acoustically. It has been proved that jitter, shimmer, Fo tremor and HNR values significantly differentiate the children with noduli vocales from the children without pathological changes in the larynx. These parameters during treatment tend to approach normal values. Therefore, the acoustic analysis of voice may be used in treatment monitoring.

Adolescent↗
PubMed1999

Detection of the nasal cycle with acoustic rhinometry: techniques and applications.

Acoustic rhinometry is an appropriate method for detecting and recording the nasal cycle in normal subjects in terms of the cross-sectional areas and volume of the nasal cavity. In this study, we tried to detect and to define the nasal cycle in normal subjects so that we might develop a reliable and reproducible technique to be used in conjunction with studies on the physiology and pathology of nasal disease. We used normal volunteer adult subjects and performed bilateral acoustic rhinometry measurements every 15 minutes over 4 hours, along with the use of a visual analog scale for assessment of the subjective feeling of congestion (or patency) just before each acoustic rhinometry measurement. Volume and cross-sectional area changes were observed along with subjective patency-score changes in each subject. The subjective feeling of patency was not related to the volume and cross-sectional area changes measured simultaneously. The technique of recording the nasal cycle with acoustic rhinometry in nasal research is presented.

Acoustics↗
PubMed1996

Fast spin echo magnetic resonance imaging: clinical application in screening for acoustic neuroma.

The advent of magnetic resonance imaging has greatly improved our ability to diagnose acoustic tumors, but it is a relatively expensive imaging modality. In the present climate of medical cost restraints, methods that reduce costs but maintain quality are extremely desirable. We report a new magnetic resonance imaging technique that uses fast spin echo without gadolinium. It provides ultrahigh-resolution images of the internal auditory canal and cerebellopontine angle. The sensitivity of this technique for the detection of acoustic tumors is equivalent to conventional gadolinium-enhanced magnetic resonance imaging, but the global cost is comparable with that of brain stem audiometry. In our practice fast spin echo magnetic resonance imaging has replaced brain stem audiometry as a screening modality to evaluate most acoustic tumor suspects. Also, the intricate detail of the internal auditory canal anatomy provided by this technique is useful in planning surgical removal of acoustic tumors.

Adult↗
PubMed1997

Are acoustic neuromas encapsulated tumors?

In articles and chapters on the subject of acoustic neuroma, it is almost invariably stated that they are well-encapsulated tumors. During surgical procedures, blunt mechanical dissection defines a natural subsurface cleavage plane that leaves intact a several millimeter thick rind of tumor surface. Occasionally, as a concession to neural integrity, less than complete resection is elected, leaving behind this "capsular" remnant. To clarify the nature of the surface of acoustic neuromas and to test whether this long held description is indeed correct, a microscopic analysis of 10 surgical specimens was performed. A wedge was harvested from the free surface of the tumor in the mid cerebellopontine angle that included a large, undisturbed section of the tumor surface. Histologic analysis showed that for most of the tumor surface only an extremely thin (3 to 5 microm) layer of connective tissue envelops the tumor. Neoplastic Schwann cells, which extend essentially to the margin of the tumor, were found to be somewhat flattened and compressed in the vicinity of the surface. Although acoustic neuromas are surrounded by a continuous layer of connective tissue, it is so exceptionally thin (on average less than the diameter of a red blood cell) that its edge cannot be visualized intraoperatively by a surgeon. Because the pathologic definition of a capsule is a thick, enveloping layer of connective tissue that is both micro- and macroscopically evident, it must be concluded that acoustic neuromas are nonencapsulated, at least in the conventional sense of the term. The surface peel observed intraoperatively is surgically produced during tumor debulking by cleaving of the looser central component from the more compressed portion of neoplastic cells that lies immediately beneath the free margin of the lesion.

Connective Tissue↗
PubMed2003

Lead stimulus modality change and the attentional modulation of the acoustic and electrical blink reflex.

Two experiments investigated the effects of the sensory modality of the lead and of the blink-eliciting stimulus during lead stimulus modality change on blink modulation at lead intervals of 2500 and 3500 ms. Participants were presented with acoustic, visual, or tactile change stimuli after habituation training with lead stimuli from the same or a different sensory modality. In Experiment 1, latency and magnitude of the acoustic blink were facilitated during a change to acoustic or visual lead stimuli, but not during a change to tactile lead stimuli. After habituation to acoustic lead stimuli, blink magnitude was smaller during tactile change stimuli than during habituation stimuli. The latter finding was replicated in Experiment 2 in which blink was elicited by electrical stimulation of the trigeminal nerve. The consistency of the findings across different combinations of lead stimulus and blink-eliciting stimulus modalities does not support a modality-specific account of attentional blink modulation. Rather, blink modulation during generalized orienting reflects modality non-specific processes, although modulation may not always be found during tactile lead stimuli.

Acoustics↗
PubMed2001

Experimental imaging of the acoustic nonlinearity parameter B/A for biological tissues via a parametric array.

The acoustic nonlinearity parameter B/A is an important parameter in nonlinear acoustics and has been suggested to be a novel parameter for ultrasound tissue characterization. In this paper, the principle and experimental results for B/A imaging by using a parametric array are presented. As two primary waves with different frequencies are radiated simultaneously from a circular piston source, a secondary wave at the difference frequency is generated due to the nonlinear interaction of the two primary waves. The axial sound pressure amplitude curve for the generated difference frequency wave in the near field is measured and agrees well with the theoretical calculation. Unlike the second harmonic wave, the difference frequency component of the parametric array grows almost linearly with distance from the piston source and goes through fewer oscillations in the near field. It therefore provides a better source for acoustic nonlinearity parameter tomography. On the basis of the finite amplitude insert substitution method and the conventional CT technology, an experimental imaging system for acoustic nonlinearity parameter B/A via a parametric array is set up. B/A images for several biological specimens, including normal and pathological tissues, are obtained.

Acoustics↗
PubMed2002

New data on histology and physico-mechanical properties of human tooth tissue obtained with acoustic microscopy.

Quantitative evaluation of human tooth structural elements, revealed in acoustic images, has been carried out. It has been shown that tissue elements with different acoustic impedances differed in acoustic images by intensity of grey color, and also feature with different longitudinal sound velocities (C(L)). In the layer of mantle dentin, C(L) is 7% to 8% lower than in bulk dentin, and in the layer of dentin around the pulp chamber, C(L) is 15% lower. In carious enamel and dentin, C(L) decreases up to 7% to 17%. In pathologic teeth, dentin areas with higher density can be revealed; they feature higher C(L); in transparent dentin C(L) can be 15% to 20% higher than in bulk dentin. Results of the present study show that acoustic images reflect internal biomechanical properties of tooth tissue microstructure that can be evaluated quantitatively by means of longitudinal sound velocity determination.

Acoustics↗
PubMed1998

Acoustic performance and clinical use of a fibreoptic hydrophone.

Initial clinical experience with the use of an optical fibre hydrophone for in vivo ultrasound dosimetry is reported. The hydrophone, originally described by Beard and Mills (1997), operates as an extrinsic, low-finesse Fabry-Perot optical sensor where acoustically-induced thickness changes in a polymer film modulate the phase difference between light beams reflected from the two surfaces of the film. The pressure waveforms from the sensor are compared with those from a calibrated piezoelectric polymer membrane hydrophone. The sensor is found to have a frequency resonance at around 12 MHz, corresponding to the thickness mode of the 50-micron polymer film. The directional responses at 0.16 MHz, 1.0 MHz and 5.0 MHz are found to be similar to those predicted for a plane piston receiver with the same diameter as that of the polymer film (400 microns). The performance of the sensor as a broad-band hydrophone is degraded by the relatively low acoustical impedance of the adhesive used in the fibre-film bond. The hydrophone was used in the clinic for measurement of acoustic pressures within the ureter of 4 patients undergoing clinical extracorporeal shock-wave lithotripsy on a Dornier HM3 lithotripter. Pressures in the range 0.5 to 5.0 MPa were recorded in the ureter at positions over 10 cm from the renal pelvis. Problems related to the clinical use of the sensor, including instability in the sensitivity of the sensor following handling and its mechanical strength in high-amplitude acoustic fields, are discussed.

Acoustics↗
PubMed1997

Acoustic and electric forward-masking of the auditory nerve compound action potential: evidence for linearity of electro-mechanical transduction.

We investigated electro-mechanical transduction within the cochlea by comparing masking of the auditory nerve compound action potential (CAP) by acoustical and electrical maskers. Forward-masking of the CAP reflects the response to the masker of the cochlear location tuned to the probe. Electrical stimulation was delivered through bipolar stimulating electrodes within the basal turn of the scala tympani. The growth of masking of high-frequency probes which excite cochlear locations close to the stimulating electrodes was similar for both acoustic and electrical maskers, suggesting a linear transduction of electrical energy to mechanical energy. Exposure to intense acoustic stimulation caused an equal loss of sensitivity to acoustic and electrical maskers. Masking of lower-frequency probes by electrical maskers increased rapidly with masker current, suggesting the direct electrical stimulation of neural elements. This masking was reduced by the administration of strychnine suggesting a contribution by the efferents towards masking of these low-frequency probes.

Acoustic Stimulation↗
PubMed2000

Translabyrinthine removal of large acoustic neuromas in young adults.

OBJECTIVE: the authors reviewed the clinical manifestations and the surgical outcomes in a series of young patients who underwent removal of large acoustic neuromas via the translabyrinthine approach. METHODS: 40 young adults who underwent a translabyrinthine removal of acoustic neuromas 3 cm or greater in size were analyzed. The patient's age ranged from 17 to 30 years. The mean size of tumor was 4.25 cm. RESULTS: the primary symptoms are similar to those in adult but usually less intense. The average interval time between the primary symptom and the diagnosis was 17 months. A high percentage of preoperative normal hearing (35%) and good facial function (100%) were noted. Translabyrinthine approach was used in all cases. Total removal was realised in 39 patients (97.5%). The facial nerve was anatomically preserved in 37 patients (92.5%). Twenty-six patients (65%) had a good facial function (House-Brackmann grade I or II) immediately or at 1 month after surgery, 11 patients (28%) achieved grade III or IV. Three patients underwent an immediate nerve repair after tumor removal. All of them recovered to grade III or IV 1 year after surgery. Postoperative complications were minimal. CONCLUSIONS: young adults may have a rapid growth rate but usually have minimal symptoms even with a large acoustic neuroma. The translabyrinthine approach has been used successfully in removal of large acoustic tumors of young patients, with the good result of facial nerve preservation and long-term tumor control.

Adolescent↗
PubMed2001

Hearing loss and growth rate of acoustic neuromas in follow-up observation policy.

OBJECTIVE: It is important to know the growth rate of acoustic neuroma in setting up its observation policy. One aimed to evaluate the significance of growth rate and hearing loss speed from a retrospective study of 31 patients. METHODS: Thirty-one patients with acoustic neuroma (mean age, 57.1 years; range, 9-81 years) who had undergone MRI and audiometry were retrospectively examined. Changes in tumor size and hearing level during follow-up periods were analyzed. RESULTS: The mean annual growth rate was 2.4 mm/year (maximum, 17 mm/year), and the average annual hearing loss speed was 2.3 dB/year (-15.0 - 19.2 dB/year) in the follow-up, and a correlation was recognized between them. Whereas significant difference was noted in annual growth rate and hearing loss speed between the sexes, no correlation was recognized between the annual growth rate or hearing loss speed and the age, tumor size and pure tone average (PTA) at the initial diagnosis. CONCLUSION: Attention must be paid to the acoustic neuroma cases where tumor growth rate is markedly high and those where hearing level rapidly declines during follow-ups. It is difficult, however, to estimate tumor diameter in relation with the changes in hearing level because the natural course of an acoustic neuroma varies in each individual.

Adolescent↗
PubMed1996

The inferior collicular potential in acoustic and electrical stimulation of the cochlea: an experimental study of guinea pig.

We made experiments of the inferior collicular potentials in acoustic and electrical stimulation for the purpose of studying fundamental issues for cochlear implantation. Guinea pigs with normal Preyer's reflex were used for this study. The results were as follows: (1) in acoustic stimulation relatively wide and large waveforms were gained but in electrical stimulation sharp and narrow ones were gained, (2) in acoustic stimulation the input-output curve of latency and amplitude was biphasic but in electrical stimulation it was monophasic. For this reason, in acoustic stimulation by click, when the intensity is low (under 80 dB SPL) stimulus site would be comparatively low frequency fibers. When the intensity is high (over 80 dB SPL) the stimulus site would shift to high frequency fibers. Therefore, many more neighboring fibers start responding. This results in biphasic input-output curves of latecy and amplitude. By electrical stimulation, however, it would be possible to stimulate only a restricted area among the bipolar electrode. Therefore, as the intensity increases, the response amplitude increases and becomes saturated at a constant level. This results in monophasic input-output curves of latency and amplitude.

Acoustic Stimulation↗
PubMed1999

The protective effect of the sympathetic nervous system against acoustic trauma.

OBJECTIVE: the cochlea is innervated by the sympathetic nerve fibers. However, the functions of those fibers in the cochlea are still controversial. The present study was designed to determine whether the sympathetic nervous system (SNS) exerts a protective or enhancing effect on acoustic trauma. METHODS: acoustic overstimulation (either of 110, 115, or 130 dB SPL for 10 min) was performed in guinea pigs during electrical stimulation of the ipsilateral cervical SNS, after its surgical elimination or in the non-treated condition. The threshold shift of the compound action potential (CAP) from the pre-exposure value was measured at 1 h and at 1 week after acoustic overstimulation. Two-way analyses of variance (ANOVAs) were completed for the SNS conditions and the frequencies. RESULTS: although no significant difference was found at 1 h after overstimulation among these three groups, the CAP threshold shift at 1 week (110 and 115 dB SPL) was significantly smaller in the SNS stimulation group than in the other two groups. CONCLUSION: a protective effect was observed in the SNS stimulation group 1 week after the exposure to acoustic overstimulation of moderate intensity (from 110 to 115 dB SPL for 10 min).

Acoustic Stimulation↗
PubMed1997

The use of active noise control (ANC) to reduce acoustic noise generated during MRI scanning: some initial results.

MRI scanning generates high levels of acoustic noise that cannot only pose a safety hazard, but also impair communication between staff and patient. In this article we present active noise control (ANC) techniques that introduce antiphase noise to destructively interfere with the MRI noise and with the aim of producing a zone of quiet around the patient's ears. Using noise recorded from a 1.0 Tesla midfield MR scanner the acoustic noise generated by three standard MR imaging sequences was replayed to a real time two channel ANC system. The results obtained show a useful attenuation of low-frequency periodic acoustic noise components. Therefore, in combination with standard passive ear protection, this suggests that MR generated acoustic noise can be effectively attenuated at both low and high frequencies leading to improved patient comfort.

Acoustics↗