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PubMed2000

MRI screening for acoustic neuroma: a comparison of fast spin echo and contrast enhanced imaging in 1233 patients.

Gadolinium enhanced MRI is the gold standard investigation for the detection of acoustic neuroma. Non-contrast MRI sequences have been suggested as an alternative for screening examinations. In order to determine the utility of fast spin echo imaging, both gadolinium enhanced T1 weighted images and fast spin echo T2 weighted images were acquired in 1233 consecutive patients referred for exclusion of acoustic neuroma. Two radiologists independently recorded their findings. Fast spin echo T2 weighted images were evaluated with respect to the visibility of nerves within the internal auditory canals and allocated a confidence score for the presence or absence of acoustic neuroma. 33 acoustic neuromas were identified. Only 56% were confidently identified on fast spin echo T2 weighted images alone; gadolinium enhanced T1 weighted images were required to confirm the diagnosis in 44% of the cases, including 9 of the 10 intracanalicular tumours. However, when identification of two normal intracanalicular nerves is employed as the criterion of normality, the single fast spin echo T2 weighted sequence excluded acoustic neuroma in 59% of this screened population. It is concluded that an imaging strategy intended to identify small intracanalicular acoustic neuromas cannot rely on fast spin echo T2 weighted imaging alone. Gadolinium enhanced T1 weighted imaging could be restricted to patients where fast spin echo images do not exclude acoustic neuroma but this strategy requires continuous supervision by an experienced radiologist. In most practices the screening examination should continue to include a gadolinium enhanced sequence in order to optimize the detection of small acoustic neuromas.

Adolescent↗

PubMed2004

Acoustic evolution in crickets: need for phylogenetic study and a reappraisal of signal effectiveness.

Cricket stridulums and calls are highly stereotyped, except those with greatly modified tegmina and/or venation, or "unusual" frequency, duration and/or intensity. This acoustic diversity remained unsuspected until recently, and current models of acoustic evolution in crickets erroneously consider this clade homogeneous for acoustic features. The few phylogenetic studies analyzing acoustic evolution in crickets demonstrated that acoustic behavior could be particularly labile in some clades. The ensuing pattern for cricket evolution is consequently extremely complex. We argue that: (1) phylogeny should always be considered when analyzing acoustic evolution, whatever characters are considered (signals, stridulums or behaviors). Consequently, future studies should be devoted to entire clades, and not consider isolated taxa; character and character state definitions should allow significant reconstructions of character evolutionary transformations; and homologies should be carefully defined for all characters, including behavior. (2) The factors responsible for song effectiveness should be reconsidered and hypotheses on their potential influence on signal evolution tested jointly by phylogenies (for example, to assess correlated transformations of acoustic and ecological features), and population studies (for example, to correlate call range and population structure, or test the predation risk associated with a signal structure). Better understanding these points should help clarifying acoustic evolution in crickets.

Acoustics↗

PubMed1989

[Magnetic resonance imaging in 38 cases of acoustic tumors].

The value of magnetic resonance imaging (MRI) in the diagnosis of acoustic tumors was retrospectively assessed in 38 cases. A 0.15 Tesla permanent magnet and a 1.5 Tesla superconducting magnet were employed in 24 and 14 cases, respectively. Gadolinium diethylene triamine pentaacetic acid (Gd-DTPA), a paramagnetic contrast agent, was used in 10 cases. Acoustic tumors were identified in all cases. Small, medium, and large tumors were depicted with equal clarity by MRI and computed tomography (CT). However, tumor contour and extension, accompanying cysts, and brainstem displacement were more clearly visualized on MRI. The use of Gd-DTPA improved the quality of the MR images by markedly enhancing the acoustic tumors in all cases. In particular, detection of small acoustic tumors and intra- or paratumoral cysts was facilitated by the use of Gd-DTPA. The possibility of a correlation between acoustic tumor histology and MRI features was studied by calculation of the contrast to noise (C/N) ratio in 10 cases of acoustic tumor and 7 cases of meningioma. No definite correlation was demonstrated, but there appeared to be some difference in the C/N ratio between acoustic tumors and meningiomas. In three volunteers, MRI demonstrated intracanalicular nerves, separately. Because of its higher resolution, MRI can be expected to replace CT and air CT in the diagnosis of acoustic tumors.

Adult↗

PubMed1999

Non-contrast high resolution fast spin echo magnetic resonance imaging of acoustic schwannoma.

AIM OF STUDY: The current gold-standard of examination for the exclusion of acoustic schwannomas is contrast-enhanced magnetic resonance (MR) imaging. Many patients however, still cannot afford to pay for the cost of this examination. As a result, many clinicians still resort to contrast-enhanced computed tomography (CT) scan; an examination which could miss small intracanalicular acoustic schwannomas. The aim of this study was to report on our experience on the usage of the more affordable high-resolution fast spin-echo (FSE) MR imaging for the diagnosis of acoustic schwannoma. METHODOLOGY: A study involving 123 patients with symptoms of sensorineural hearing loss, vertigo and tinnitus was carried out between August 1996 and March 1997. All cases were scanned with a 1.5 T MR unit using a quadrate head coil. The section thickness was 1.5 mm, with TR/TE of 4000/96. Any mass arising from the vestibulocochlear nerve was considered to be an acoustic schwannoma, and most of these positive cases underwent further contrast-enhanced MR imaging to confirm the diagnosis. RESULTS: A total of 7 acoustic schwannomas were detected on high resolution FSE MR imaging and for 5 of these cases, the diagnosis was confirmed with contrast-enhanced MR imaging. Three of the 7 positive patients had contrast-enhanced CT scan done just prior to the MR study and the tumours were not detected on CT scan. The smallest acoustic schwannoma detected on high-resolution FSE MR imaging had a dimension of 0.5 x 0.4 x 0.5 cm. CONCLUSION: High resolution FSE MR imaging is more sensitive than contrast-enhanced CT scan in the diagnosis of acoustic schwannoma. Although the sensitivity is less than that of contrast-enhanced MR imaging, high resolution FSE MR is more affordable and therefore can play a role in the screening for acoustic schwannomas in selected groups of patients.

Adolescent↗

PubMedDate not supplied

CT in diagnosis of acoustic neuromas.

A detailed analysis of the CT findings in 75 cases of acoustic neuroma is presented. The method of examination included plain and enhanced CT, metrizamide CT cisternography (M-CTC), and gas CT cisternography (gas-CTC). The common CT appearances of acoustic neuromas were as follows: 93.6% appeared as isodense or hypodense on precontrast scan; homogeneous enhancement was observed in 53.8% on postcontrast scan; the tumor center, mostly located at the level of the internal acoustic canal, was spherical in shape with an acute angle between the lateral tumor border and petrous bone; and there was widening of the internal acoustic canal or destruction of petrous bone. However, the presence of an acoustic neuroma could not be excluded if widening of the internal acoustic canal was absent. It was not certain whether contrast filling of the internal acoustic canal occurred at M-CTC in the four cases so examined. One case of intracanalicular neuroma was diagnosed by gas-CTC, which is the most sensitive and reliable technique for detecting and excluding small tumors. The significance of various CT appearances, early diagnosis, and differential diagnosis of acoustic neuroma from other cerebellopontine-angle tumors, particularly meningioma, are discussed.

Adolescent↗

PubMed1983

[Brief acoustic stimuli for the recording of brain stem potentials by computer controlled system analysis].

Brief acoustic stimuli are used in the objective assessment of the auditory threshold and in topodiagnosis of pathological processes in the auditory path via registration of brain stem potentials. The type of stimulus, duration, frequency and phase are decisive for the evocation of the brain stem potentials. However, it is still a somewhat unsolved problem as to how to obtain an optimally reproducible kind of stimulation. The pattern of progression of acoustic stimuli is of crucial importance for the recording of early acoustic evoked potentials (EAEP). Using an artificial auditory canal, a measurement device was constructed for recording acoustic stimulus sequences in the auditory meatus. With the help of electronic monitoring it became possible to produce digitally controlled stimulation resulting in utilizing forms of electrical stimuli which cannot be produced in the audiometer, for obtaining suitable electric stimuli. Whereas the curves of the acoustic pressures largely deviate from those of the electrical stimuli, as shown by measurements in the artificial auditory canal (the deviations depending on the headphones used in each case), the transmission properties of the electro-acoustic transducers are processed mathematically on the basis of Fourier's transformation, and such processing makes it possible to electrically produce any desired sequences of acoustic stimuli, taking the transmission properties of the headphones into account. In this manner, synchronous discharging of the sensory cells by brief acoustic stimuli, which is required for EAEP recording, can be optimized.

Acoustic Stimulation↗

PubMed2003

Acoustic streaming: a new technique for assessing adnexal cysts.

OBJECTIVES: To determine whether acoustic streaming has clinical value in the differentiation between various ovarian and adnexal cysts. METHODS: We assessed 29 adnexal cysts, for which pathological diagnosis was available, for the presence of acoustic streaming during B-mode and color sonographic evaluation. RESULTS: Acoustic streaming was detected in 15 (52%) of the cysts. The most common cyst, endometrioma (n = 7), did not exhibit acoustic streaming in any case, while of the remaining 22 cysts, 15 exhibited acoustic streaming (P = 0.0017). Dermoid cysts exhibited acoustic streaming in two of six (33%) cases. In addition acoustic streaming was noted in two of two (100%) hemorrhagic cysts, eight of ten (80%) cystadenomas, two of three (67%) malignant cysts and in the one abscess. CONCLUSIONS: Acoustic streaming is the first sonographic feature that may be able to completely exclude endometrioma as a possible diagnosis for an adnexal cyst.

Adnexa Uteri↗

PubMed2006

The effects of tempol, 3-aminobenzamide and nitric oxide synthase inhibitors on acoustic injury of the mouse cochlea.

Oxygen free radicals have been implicated in the pathogenesis of acoustic injury of the cochlea. The purpose of this study was to evaluate the effects of tempol (a superoxide anion scavenger), 3-aminobenzamide (a poly (ADP-ribose) synthetase (PARS) inhibitor), N-nitro-l-arginine (a non-selective nitric oxide synthase (NOS) inhibitor), 7-nitroindazole (a selective neuronal NOS inhibitor) and aminoguanidine (a selective inducible NOS inhibitor) on acoustic injury. Mice were exposed to a 4 kHz pure tone of 110-128 dB SPL for 4h. Tempol, 3-aminobenzamide or N-nitro-l-arginine was intraperitoneally administered immediately before the onset of acoustic overexposure, while 7-nitroindazole or aminoguanidine was intraperitoneally administered every 12h starting immediately before the onset of acoustic overexposure. The threshold shift of the auditory brainstem response (ABR) and hair cell loss were then evaluated one and two weeks after acoustic overexposure. Tempol and 3-aminobenzamide significantly protected the cochlea against acoustic injury, whereas the NOS inhibitors did not exert any protective effect. These findings suggest that reactive oxygen species and PARS are involved in acoustic injury of the cochlea. However, further study is necessary to elucidate the roles of nitric oxide and nitric oxide synthase in acoustic injury.

Analysis of Variance↗

PubMed2006

Generation and detection of acoustic solitons in crystalline slabs by laser ultrasonics.

Acoustic solitons have been recently observed in different systems (Si, Sapphire, MgO, alpha-quartz). Such acoustic waves could lead to sub-picosecond acoustic pulses. In this paper, we report on the formation of acoustic solitons in a GaAs crystalline slab. A short picosecond acoustic pulse is generated by absorption of a femtosecond laser pulse in an aluminum thin film deposited on one side of the slab. This strain pulse travels through the sample up to the opposite side where it is detected by a time delayed laser pulse reflected by an aluminum transducer. We use interferometric detection to measure independently the real and imaginary parts of the relative change in optical reflectivity induced by the acoustic pulse. We find that, at low temperature and with a laser pump pulse energy of 10 nJ, an acoustic soliton clearly separates from the acoustic pulse in GaAs slab. The soliton shape is compared with numerical simulations for different excitation conditions. From the very unique properties of solitons, we infer a soliton pulse duration of about 2.3 ps which corresponds to a spatial extent of only 12 nm.

Journal Article↗

PubMed2006

FEM calculation of an acoustic field in a sonochemical reactor.

The spatial distribution of the acoustic amplitude in a sonochemical reactor has been numerically calculated using the finite element method (FEM). In the FEM program, the acoustic field in a sonochemical reactor is coupled with the vibration of the reactor's wall. The present calculations have revealed that the thin (thick) glass or stainless steel wall is nearly a free (rigid) boundary and that the glass wall is freer than the stainless steel wall. The influence of the attenuation coefficient of ultrasound on the acoustic field has also been studied in order to see the effect of bubbles on the acoustic field. As the attenuation coefficient increases, the vibration amplitude of the reactor's wall becomes smaller and the acoustic emission from the vibrating wall becomes weaker. The qualitative feature of the spatial pattern of sonochemiluminescence from an aqueous luminol solution has been reproduced by the calculation when the attenuation coefficient is in the range of 0.5-5m(-1). When the attenuation coefficient is less than about 0.05 m(-1), the standing wave pattern of an acoustic field in the liquid is very complex due to the acoustic emission from the vibrating wall. The present calculations have also revealed that some stripes of pressure antinodes have also been disconnected when the radius of the transducer is much smaller than the side length of the vibrating plate. The dependence of the acoustic field on the liquid height is also discussed.

Journal Article↗

PubMed1981

Acoustic microscopy of living cells.

This paper reports preliminary results of the observation by acoustic microscopy of living cells in vitro. The scanning acoustic microscope uses high-frequency sound waves to produce images with submicrometer resolution. The contrast observed in acoustic micrographs of living cells depends on the acoustic properties (i.e., density, stiffness, and attenuation) and on the topographic contour of the cell. Variation in distance separating the acoustic lens and the viewed cell also has a profound effect on the image. When the substratum is located at the focal plane, thick regions of the cell show a darkening that can be related to cellular acoustic attenuation (a function of cytoplasmic viscosity). When the top of the cell is placed near the focal plane, concentric bright and dark rings appear in the image. The location of the rings can be related to cell topography, and the ring contrast can be correlated to the stiffness and density of the cell. In addition, the character of the images of single cells varies dramatically when the substratum upon which they are grown is changed to a different material. By careful selection of the substratum, the information content of the acoustic images can be increased. Our analysis of acoustic images of actively motile cells indicates that leading lamella are less dense or stiff than the quiescent trailing processes of the cells.

Animals↗

PubMed2006

Therapeutic time window of methylprednisolone in acoustic injury.

HYPOTHESIS: This study aims to investigate the therapeutic time window of methylprednisolone in acoustic injury. BACKGROUND: Although glucocorticoids have been widely used in the treatment of acoustic injury, the therapeutic time window of glucocorticoids in acoustic injury has never been examined. METHODS: Mice were exposed to 4-kHz pure tone of 128-dB sound pressure level for 4 hours. Auditory brainstem response was examined before, immediately after, and 2 weeks after acoustic overexposure. RESULTS: Methylprednisolone significantly improved the auditory brainstem response threshold shifts 2 weeks after acoustic overexposure when it was administered before or immediately after acoustic overexposure, but not when administered 3 hours after acoustic overexposure. CONCLUSION: The present findings suggest that methylprednisolone possesses protective effects against acoustic injury of the cochlea with a short therapeutic time window.

Analysis of Variance↗

PubMed2006

Otoacoustic emissions and persistent tinnitus after acute acoustic trauma.

OBJECTIVES: To follow up the auditory status of military personnel after an acute acoustic trauma and to identify the possible predictive value of hearing thresholds and otoacoustic emissions during the first 24 hours after the acoustic trauma. STUDY DESIGN: A group of 24 young military subjects, aged 22 +/- 2.3 years, without any otologic problem before the acoustic trauma, were examined at three time intervals after an accidental acoustic trauma caused by the discharge of a firearm: 24 hours, 72 hours, and 15 days. METHODS: Each subject was submitted to medical examination and to a questionnaire detailing the circumstances of the acoustic trauma. Pure tone audiometry was performed from 1 to 8 kHz per half octave. Transiently evoked otoacoustic emissions were recorded in the nonlinear mode at 80 dB pSPL, and distortion product otoacoustic emissions were recorded from 1 to 6 kHz, using a distortion product-gram type procedure, at 65/55 dB SPL, with f2/f1 = 1.22. Two groups of subjects were defined: group 1 (n = 8) represented subjects with short-lasting tinnitus (<72 h) and group 2 (n = 16) subjects with long-lasting tinnitus (>72 h). RESULTS: Hearing thresholds did not differ significantly between these two groups 24 hours after the acoustic trauma. However, otoacoustic emissions showed significantly lower amplitudes 24 hours after the acoustic trauma in subjects showing a longer lasting tinnitus. CONCLUSION: Otoacoustic emissions appear to be a better predictor of the persistence of tinnitus than hearing thresholds alone 24 hours after an acute acoustic trauma.

Acute Disease↗

PubMed2001

Noise transmission from a curved panel into a cylindrical enclosure: analysis of structural acoustic coupling.

Much of the research on sound transmission through the aircraft fuselage into the interior of aircraft has considered coupling of the entire cylinder to the acoustic modes of the enclosure. Yet, much of the work on structural acoustic control of sound radiation has focused on reducing sound radiation from individual panels into an acoustic space. Research by the authors seeks to bridge this gap by considering the transmission of sound from individual panels on the fuselage to the interior of the aircraft. As part of this research, an analytical model of a curved panel, with attached piezoelectric actuators, subjected to a static pressure load was previously developed. In the present work, the analytical model is extended to consider the coupling of a curved panel to the interior acoustics of a rigid-walled cylinder. Insight gained from an accurate analytical model of the dynamics of the noise transmission from the curved panels of the fuselage into the cylindrical enclosure of an aircraft is essential to the development of feedback control systems for the control of stochastic inputs, such as turbulent boundary layer excitation. The criteria for maximal structural acoustic coupling between the modes of the curved panel and the modes of the cylindrical enclosure are studied. For panels with aspect ratios typical of those found in aircraft, results indicate that predominately axial structural modes couple most efficiently to the acoustic modes of the enclosure. The effects of the position of the curved panel on the cylinder are also studied. Structural acoustic coupling is found to not be significantly affected by varying panel position. The impact of the findings of this study on structural acoustic control design is discussed.

Journal Article↗

PubMed2004

Development of an accelerometer-based underwater acoustic intensity sensor.

An underwater acoustic intensity sensor is described. This sensor derives acoustic intensity from simultaneous, co-located measurement of the acoustic pressure and one component of the acoustic particle acceleration vector. The sensor consists of a pressure transducer in the form of a hollow piezoceramic cylinder and a pair of miniature accelerometers mounted inside the cylinder. Since this sensor derives acoustic intensity from measurement of acoustic pressure and acoustic particle acceleration, it is called a p-a intensity probe. The sensor is ballasted to be nearly neutrally buoyant. It is desirable for the accelerometers to measure only the rigid body motion of the assembled probe and for the effective centers of the pressure sensor and accelerometer to be coincident. This is achieved by symmetric disposition of a pair of accelerometers inside the ceramic cylinder. The response of the intensity probe is determined by comparison with a reference hydrophone in a predominantly reactive acoustic field.

Journal Article↗

PubMed2000

Acoustic normal mode fluctuation statistics in the 1995 SWARM internal wave scattering experiment

In order to understand the fluctuations imposed upon low frequency (50 to 500 Hz) acoustic signals due to coastal internal waves, a large multilaboratory, multidisciplinary experiment was performed in the Mid-Atlantic Bight in the summer of 1995. This experiment featured the most complete set of environmental measurements (especially physical oceanography and geology) made to date in support of a coastal acoustics study. This support enabled the correlation of acoustic fluctuations to clearly observed ocean processes, especially those associated with the internal wave field. More specifically, a 16 element WHOI vertical line array (WVLA) was moored in 70 m of water off the New Jersey coast. Tomography sources of 224 Hz and 400 Hz were moored 32 km directly shoreward of this array, such that an acoustic path was constructed that was anti-parallel to the primary, onshore propagation direction for shelf generated internal wave solitons. These nonlinear internal waves, produced in packets as the tide shifts from ebb to flood, produce strong semidiurnal effects on the acoustic signals at our measurement location. Specifically, the internal waves in the acoustic waveguide cause significant coupling of energy between the propagating acoustic modes, resulting in broadband fluctuations in modal intensity, travel-time, and temporal coherence. The strong correlations between the environmental parameters and the internal wave field include an interesting sensitivity of the spread of an acoustic pulse to solitons near the receiver.

Journal Article↗

PubMed2000

Experimental validations of the HELS method for reconstructing acoustic radiation from a complex vibrating structure

This paper presents experimental validations of the Helmholtz Equation Least Squares (HELS) method [Wang and Wu, J. Acoust. Soc. Am. 102, 2020-2032 (1997); Wu and Wang, U.S. Patent Number 5712805 (1998); Wu, J. Acoust. Soc. Am. 107, 2511-2522 (2000)] on reconstruction of the radiated acoustic pressures from a complex vibrating structure. The structure under consideration has geometry and dimensions similar to those of a real passenger vehicle front end. To simulate noise radiation from a vehicle, a high fidelity loudspeaker installed inside the structure at the location of the engine is employed to generate both random and harmonic acoustic excitations. The radiated acoustic pressures are measured over a finite planar surface above the structure by a microphone. The measured data are taken as input to the HELS formulation to reconstruct the acoustic pressures on the top surface of the structure as well as in the field. The reconstructed acoustic pressures are then compared with measured ones at the same locations. Also shown are comparisons of the reconstructed and measured acoustic pressure spectra at various locations on the surface. Results show that satisfactory reconstruction can be obtained on the top surface of the structure subject to both random and harmonic excitations. Moreover, the more measurements and the closer their distances to the source surface, the more accurate the reconstruction. The efficiency of the HELS method may decrease with increasing of the excitation frequency. This high frequency difficulty is inherent in all expansion theories.

Journal Article↗

PubMed1984

Acoustic microscopy--principles and applications in the studies of biomaterial microstructure.

The acoustic microscopy is based on totally different physical concepts than both the optical and electron microscopes. Therefore, the information obtained with an acoustic microscope is significantly different from those obtainable by the other two. By employing elastic waves, detailed microscopic information regarding biomaterial properties like density, elasticity, viscosity and viscoelasticity are obtained with an acoustic microscope. Live tissue can be examined without fixing or chemical staining. The Scanning Laser Acoustic Microscope (SLAM) and the Scanning Acoustic Microscope (SAM) are the only acoustic microscopes commercially available today. The SAM operates at as high as 4.2 GHz frequency providing at least five times better resolution than the optical limit. The SLAM, however, operates generally at 100 or 500 MHz and can therefore examine thicker samples than the SAM, but at lower resolutions. For optically translucent samples, the SLAM can also provide an optical image simultaneously with the acoustical one. A laser beam is employed in the scanning mechanism in the SLAM, compared to mechanically translating the sample in the SAM. Consequently, the scanning rate is much faster in the SLAM at about 30 frames per second, compared to several seconds per frame for the SAM. Both qualitative as well as quantitative information is obtainable about the material under examination. As a qualitative tool, the information is used to classify and sort materials and detect and localize flaws and defects in optically opaque samples. A microscopic map of the specimen's mechanical properties can be produced using information from the acoustic image. This information may then lead to better understanding of biomaterial microstructure and also can be a valuable aid in characterization of certain subtle morphological differences.

Animals↗