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Results for “ULTRASONICS”

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At least 667 records · Page 37Linked to original sources

PubMed1989

Effect of ultrasonic instrumentation on Bacteroides intermedius.

Two physical mechanisms of ultrasound, cavitation and acoustic streaming, were investigated in an ultrasonic endodontic unit. In addition, the potential of ultrasonic instrumentation for disruption of Bacteroides intermedius was examined at various time intervals. The ultrasonic file could not generate cavitation within the recommended power settings indicated for endodontic purposes. However, there was evidence of acoustic streaming. The latter phenomenon resulted in destruction of 21.6%, 30.4% and 92.9% of test bacteria after 1, 5 and 15 min sonication respectively. It appears that ultrasonic instrumentation of root canals has little bactericidal effect.

Bacteroides Infections↗

PubMed2001

Photodisruptive laser nucleation of ultrasonic cavitation for biomedical applications.

Pulses of high intensity laser light, when focused into transparent materials, may produce localized electron-ion plasmas through optical breakdown. By simultaneously incorporating the resulting volume of vaporized material within the focal volume of a high intensity ultrasound source, the photodisruption (1.05 microm wavelength) void served as a nucleation site for ultrasonic cavitation. Dilute suspensions of canine erythrocytes in phosphate buffered saline were exposed in a flow-through exposure chamber and the percentage of lysed cells was used as a measure of the biologically effective cavitation activity produced in the chamber. Brief (about 30 micros) acoustic emissions were detected from the photodisruption alone (indicating laser nucleation of bubbles), but the cell lysis produced was undetectable against the background. However, combined exposure greatly increased both the duration of the acoustic emissions (up to 1.5 ms) and the amount of cell lysis above an ultrasonic pressure amplitude threshold of about 4.3 MPa at 2.5 MHz. The amount of cell lysis (sometimes approaching 100%) increased with increasing ultrasonic intensity, laser pulse energy and laser PRF. Addition of 5% serum albumin enhanced the effect, apparently by stabilizing bubbles and nuclei. Photodisruptive laser nucleation of ultrasonic cavitation can provide controlled and synergistic enhancement of bioeffects.

Animals↗

PubMed1997

Temperature monitoring of ultrasonically heated muscle with RARE chemical shift imaging.

The ability to monitor tissue temperature in ultrasonically heated rabbit muscle is demonstrated using a chemical shift imaging approach based on the rapid acquisition with relaxation enhancement (RARE) fast imaging method [Hennig et al., Magn. Reson. Med. 3, 823-833 (1986)] applied in a line scan format. A three echo sequence with a 16 Hz spectral resolution with 64 ms echo readouts and 78 ms echo spacings is shown capable of measuring relevantly small water frequency shifts in phantoms. Applied to the in vivo model of ultrasonically heated rabbit muscle, water resonance frequencies at the ultrasonic focal point were found to be linearly related to temperature with a slope of -0.007 +/- 0.001 ppm/degree C (N = 6 studies). Measurements of the frequency shift in unheated tissue located away from the ultrasonically heated tissue varied by approximately 0.011 ppm over the course of the experiments, leading to an estimated temperature accuracy of +/- 1.6 degrees C in vivo.

Animals↗

PubMed2004

Old world frog and bird vocalizations contain prominent ultrasonic harmonics.

Several groups of mammals such as bats, dolphins and whales are known to produce ultrasonic signals which are used for navigation and hunting by means of echolocation, as well as for communication. In contrast, frogs and birds produce sounds during night- and day-time hours that are audible to humans; their sounds are so pervasive that together with those of insects, they are considered the primary sounds of nature. Here we show that an Old World frog (Amolops tormotus) and an oscine songbird (Abroscopus albogularis) living near noisy streams reliably produce acoustic signals that contain prominent ultrasonic harmonics. Our findings provide the first evidence that anurans and passerines are capable of generating tonal ultrasonic call components and should stimulate the quest for additional ultrasonic species.

Animal Communication↗

PubMed1978

Frequency dependence of ultrasonic absorption in mammalian testis.

The earlier report that the frequency dependence of ultrasonic absorption of mammalian testis memicked a single relaxation process is explained as an effect of ultrasonic beam width upon the transient thermoelectric technique. More detailed measurements show that the frequency dependence of the ultrasonic absorption in testis is much the same as the attenuation in other soft tissues, viz., a proportional to f1.1. The earlier finding that testis exhibits an ultrasonic absorption coefficient significantly lower than reported for other tissues is confirmed.

Animals↗

PubMed1984

Effect of flow disturbance on ultrasonic backscatter from blood.

Due to the better resolution and performance provided by the new generation of real-time high resolution ultrasonic scanners, blood now becomes a tissue which can also be visualized ultrasonically. There is strong experimental evidence indicating that the echogenicity of blood is increased as a result of erythrocyte aggregation. In this paper, we will show that flow disturbance may also play a significant role in influencing blood ultrasonic backscatter or echogenicity. Our results indicate that the introduction of turbulent flow can cause ultrasonic backscatter from erythrocyte suspensions to increase appreciably for hematocrits greater than 10%. We will also show that this increase may be correlated to the turbulent intensity. Moreover, the scattering peak is observed to shift to lower hematocrits when turbulence is eliminated. Experimental results obtained for uniform flow are in excellent agreement with theoretical models for small spherical scatterers which predict a scattering maximum at a hematocrit of 13%.

Animals↗

PubMed1985

Effects of heat conduction and sample size on ultrasonic absorption measurements.

The absorption coefficient of a material can be determined by measuring the heating which occurs as a result of ultrasonic irradiation. When narrow focused beams are used to heat a sample, or when the available volume of a material is restricted to small dimensions, then the effect of heat conduction to surrounding unheated regions becomes significant, complicating the relation between measured temperatures and acoustic parameters. In this paper new analytical expressions, which account for radial and axial heat flow in a medium, are derived for the case of Gaussian-shaped ultrasonic beam patterns in thin or semi-infinite absorbing materials. Solutions are given for temperature histories resulting from an ultrasonic impulse (pulse decay method) or a step input (rate of heating method). The use of these equations in absorption measurements is discussed, and experimental results are given. These expressions provide flexibility in choice of laboratory ultrasonic parameters, and the results are especially useful for many biomedical measurements where the volume of tissue available is restricted.

Hyperthermia, Induced↗

PubMed1988

Use of focused ultrasonic receivers for remote measurements in biological tissues.

The feasibility of using a focusing ultrasonic transducer as a sound pressure receiver is discussed. It is shown theoretically that, at certain angular apertures of the receiver, its output signal is proportional to the sound pressure in the field point coincident with the receiver center of curvature. The receivers of this type have been demonstrated suitable for remote measurements of field spatial distribution of plane and focused ultrasonic radiators. Data are presented on the experimental testing of focused receivers in measuring acoustic fields in water, air, and certain samples of biological tissues. The instruments are sufficiently universal and allow the measurement not only of acoustic fields, but also of temperature increments in locally heated media, as well as permit one to follow the initiation and development of ultrasonic cavitation and study nonlinear effects. The remote sensing ability and high sensitivity of focused ultrasonic receivers allow their practical use in biomedical acoustics for noninvasive measurements.

Animals↗

PubMed1997

Simulation of ultrasonic pulse propagation through the abdominal wall.

Ultrasonic pulse propagation through the abdominal wall has been simulated using a model for two-dimensional propagation through anatomically realistic tissue cross sections. The time-domain equations for wave propagation in a medium of variable sound speed and density were discretized to obtain a set of coupled finite-difference equations. These difference equations were solved numerically using a two-step MacCormack scheme that is fourth-order accurate in space and second-order accurate in time. The inhomogeneous tissue of the abdominal wall was represented by two-dimensional matrices of sound speed and density values. These values were determined by processing scanned images of abdominal wall cross sections stained to identify connective tissue, muscle, and fat, each of which was assumed to have a constant sound speed and density. The computational configuration was chosen to simulate that of wavefront distortion measurements performed on the same specimens. Qualitative agreement was found between those measurements and the results of the present computations, indicating that the computational model correctly depicts the salient characteristics of ultrasonic wavefront distortion in vivo. However, quantitative agreement was limited by the two-dimensionality of the computation and the absence of detailed tissue microstructure. Calculations performed using an asymptotic straight-ray approximation showed good agreement with time-shift aberrations predicted by the full-wave method, but did not explain the amplitude fluctuations and waveform distortion found in the experiments and the full-wave calculations. Visualization of computed wave propagation within tissue cross sections suggests that amplitude fluctuations and waveform distortion observed in ultrasonic propagation through the abdominal wall are associated with scattering from internal inhomogeneities such as septa within the subcutaneous fat. These observations, as well as statistical analysis of computed and observed amplitude fluctuations, suggest that weak fluctuation models do not fully describe ultrasonic wavefront distortion caused by the abdominal wall.

Abdomen↗

PubMed1999

Full-field mapping of ultrasonic field by light-source-synchronized projection.

A simple method for imaging ultrasonic fields in clear media is introduced. A modulated laser source is used to project the ultrasonic field onto a CCD camera. By use of the source-synchronized lock-in detection scheme, 2D images of the amplitude and phase distributions can be determined simultaneously. This technique is experimentally demonstrated with a 1-MHz and a 3.5-MHz ultrasonic transducer operated in continuous-wave mode. This method is very straightforward to implement and can be combined with the traditional tomographic reconstruction technique to obtain the 3D distribution of an ultrasonic field.

Humans↗

PubMed1976

Effect of ultrasonic waves on the heat resistance of Bacillus spores.

The effect of ultrasonic treatment on the heat resistance of Bacillus spores differs widely both with the species and the strain tested. Ultrasonic waves do not affect the heat resistance of some strains, whereas they greatly reduce that of other strains of the same species. The heat-sensitizing effect of ultrasonic waves is more pronounced when short heating periods are used. Ultrasonic treatment does not seem to affect the "Z value".

Bacillus cereus↗

PubMedDate not supplied

[Flavonoids as effective protectors of urease from ultrasonic inactivation in solutions].

Inactivation of soybean urease in aqueous solution at pH 5.4, 36 degrees C, and high-frequency sonication (2.64 MHz, 1.0 W/cm2) is substantially reduced in the presence of seven structurally different flavonoids. A comparative kinetic study of the effect of these flavonoids on the effective first-order rate constants that characterize the total (thermal and ultrasonic) inactivation k(i), thermal inactivation k(i)*, and ultrasonic inactivation k(i)(US) of 25 nM enzyme solution was carried out. The dependences of the three inactivation rate constants of the urease on the concentrations of flavonoids within the range from 10(-11) to 10(-4) M were obtained. The following order of the efficiency of the flavonoids used in respect of the urease protection from ultrasonic inactivation was found: astragalin > silybin > naringin > hesperidin > quercetin > kaempferol > morin. The results confirm a significant role in the inactivation of the urease of HO* and HO2*, free radicals, which are formed in the ultrasonic cavitation field.

Flavanones↗

PubMed2004

Neuronal encoding of ultrasonic sound by a fish.

Many species of odontocete cetaceans (toothed whales) use high-frequency clicks (60-170 kHz) to identify objects in their environment, including potential prey. Behavioral studies have shown that American shad, Alosa sapidissima, can detect ultrasonic signals similar to those of odontocetes that are potentially their predators. American shad also show strong escape behavior in response to ultrasonic pulses between 70 and 110 kHz and can determine the location of the sound source at least in the horizontal plane. The present study examines physiological aspects of ultrasound detection by American shad and provides the first insights into the neural encoding of ultrasound signals in any nonmammalian vertebrate. The recordings were obtained by penetration through the cerebellar surface. All but two units responded exclusively to ultrasound. Ultrasound-sensitive units did not phase-couple to any stimulus frequency. Some units resembled the response of constant latency neurons found in the ventral nucleus of the lateral lemniscus of bats. We suggest that ultrasonic and sonic signals are processed along different pathways in Alosa. The ultrasonic pathway in Alosa appears to be a feature detector that is likely to be adapted (e.g., frequency, intensity) to odontocete echolocation signals.

Acoustic Stimulation↗

PubMed1995

Relation of ultrasonic backscatter and acoustic propagation properties to myofibrillar length and myocardial thickness.

BACKGROUND: Ultrasonic backscatter demonstrates a cardiac cycle-dependent modulation. The exact mechanism of the modulation is under debate. The objective of the present study was to test the hypothesis that a change in size and configuration of myofilaments from systole to diastole alters acoustic propagation properties and backscatter. METHODS AND RESULTS: In vivo measurements were made of integrated backscatter at 5 MHz (IBR5), followed by in vitro measurements of ultrasonic attenuation, speed, and heterogeneity index using a scanning laser acoustic microscope at 100 MHz. Studies were performed in canine hearts (16) arrested in systole (8) with calcium chloride or arrested in diastole (8) with potassium chloride. Sarcomere length was measured with a calibrated eyepiece on a Ziess microscope. Wall thickness was measured with calipers. The attenuation coefficient of 220 +/- 34 dB/cm during systole was significantly higher than the coefficient of 189 +/- 24 dB/cm during diastole (P < .01); the IBR5 of -44.7 +/- 1.2 dB during systole was significantly greater than the IBR5 of -47.0 +/- 1.0 dB during diastole (P < .01); the ultrasonic speed of 1591 +/- 11 m/s during systole was higher than the speed of 1575 +/- 4.2 m/s during diastole (P < .01); and the heterogeneity index of 7.4 +/- 1.8 m/s during systole was significantly lower than the index of 9.0 +/- 2.0 m/s during diastole (P < .02). The sarcomere length of 1.804 +/- 0.142 microns during diastole was significantly higher than the length of 1.075 +/- 0.177 micron during systole (P < .01). Wall thickness was significantly greater during systole than during diastole (20 +/- 3 versus 9 +/- 3 mm, P < .01). CONCLUSIONS: Ultrasonic backscatter and propagation properties are directly related to sarcomere length and myocardial thickness and may be responsible for cardiac cycle-dependent variation in backscatter.

Animals↗

PubMed1997

Ultrasonic nebulization for efficient delivery of surfactant in a model of acute lung injury. Impact on gas exchange.

We investigated the effect of ultrasonic nebulization versus instillation of exogenous surfactant on gas exchange abnormalities provoked by detergent inhalation in perfused rabbit lungs. Ventilation-perfusion (VA/Q) distribution was assessed by the multiple inert gas elimination technique. For nebulization of natural bovine surfactant (Alveofact), an ultrasonic device was placed in line with the inspiratory gas flow tubing, manufacturing particles with a mass median aerodynamic diameter of approximately 4.5 microM and high aerosol concentration. In vitro studies demonstrated biochemical and biophysical integrity of postnebulization surfactant. Lung aerosol deposition was monitored by a laser-photometric technique. In lungs with sham inhalation of saline, tracheal instillation of surfactant (approximately 11 mg/kg body weight, infused over 50 min) provoked substantial VA/Q mismatch and limited shunt flow, whereas lung surfactant deposition by ultrasonic nebulization (approximately 7 to 9 mg/kg body weight; nebulization time, 50 min) did not interfere with physiologic gas exchange. Tween 20 inhalation provoked severe VA/Q mismatch with predominant shunt-flow (approximately 21%). This was not reversed by "rescue" application of instilled surfactant, but largely reversed by nebulized surfactant (shunt reduced to 5.5%; p < 0.01). Analysis of postaerosol lavage fluid demonstrated partial reconstitution of surface activity by nebulized surfactant. We conclude that ultrasonic nebulization may be employed for efficient delivery of functionally intact natural surfactant to the distal bronchoalveolar space. This approach effects rapid improvement of gas exchange in a model of acute homogeneous lung injury.

Aerosols↗

PubMed1993

Delivery of ultrasonic nebulized aerosols to a lung model during mechanical ventilation.

Ultrasonic nebulizers may be particularly suitable for the administration of therapeutic aerosols to patients undergoing mechanical ventilation, but the amount of aerosol that reaches the patients' respiratory tract during ultrasonic nebulization has not been adequately studied. The delivery through an endotracheal tube of nebulized aerosols labeled with 99mTechnetium human serum albumin was therefore measured for five commercially available ultrasonic nebulizers using an in vitro model representing mechanical ventilation of an adult patient. Delivery of aerosol through the endotracheal tube ranged from 3.1 +/- 0.3% for Samsonic to 10.1 +/- 2.0% for Portasonic using 3 ml nebulizer solution. Increasing the volume of nebulizer solution to 18 ml (not possible for the Portasonic) increased delivery to 11.5 +/- 2.0 for the DP 100, 8.7 +/- 3.1 for Ultraneb, and 15.9 +/- 1.8% for Samsonic. Addition of a 600 ml aerosol storage chamber to the ventilator circuit increased delivery for the Samsonic (18 ml solution) to 22.3 +/- 5.0%. Aerosol delivery was also increased by reducing the respiratory rate and minute volume and by increasing the inspiratory time settings on the ventilator. These results confirm the potential value of ultrasonic nebulizers during mechanical ventilation and indicate that clinical trials in ventilated patients are warranted.

Adult↗

PubMed1991

In vivo measurements of ultrasonic beam distortion in the breast.

The phase aberrations encountered by ultrasonic pulses propagating through breast tissue in twenty-two female volunteers were measured. The experiments were designed to assess the impact of these aberrations on clinical ultrasonic image quality for a variety of transducer and imaging geometries. The phase aberration profiles of a given patient were correlated with the amount of parenchymal tissue determined from that patient's mammogram. These data are useful in assessing the image quality achievable with conventional ultrasonic imaging systems, and the potential application of adaptive ultrasonic imaging systems. The results indicate that phase aberrations significantly degrade breast image quality for typical transducer frequencies and sizes.

Breast Neoplasms↗

PubMed1986

Intraoperative auditory brain stem response monitoring during ultrasonic aspiration of posterior fossa tumors.

The use of an ultrasonic aspirator may decrease the morbidity associated with the surgical removal of intracranial tumors by reducing the duration of surgery. In this study we monitored the auditory brain stem response (ABR) during ultrasonic surgical aspiration of 20 posterior fossa tumors. Twelve subjects had a transient decrement in the ABR during use of the ultrasonic aspirator; one had a temporary sensorineural hearing loss contralateral to the side of the surgery. Monitoring of the ABR during use of the ultrasonic aspirator in the posterior fossa helped minimize the risk of injury to normal structures. Changes in latency, amplitude, and interpeak interval of the ABR waves alert the surgeon to the need to adjust the aspirator settings or the conditions in the operative field before continuing to use the tool.

Adult↗