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At least 973 records · Page 54Linked to original sources

PubMed1983

A waveguide pulse-echo system for ultrasonic absorption measurements in biological media.

The system described has been designed for measurements of ultrasonic absorption in suspensions of biological cells. A novel feature of the design is the provision of a wave-guide sample tube which prevents beam diffraction. This ensures that the ultrasonic energy is wholly constrained between a single transducer and a moveable air-backed reflector, and is lost only by absorption in the sample. The associated electronics comprises a simple ultrasonic generator with variable power output, carrier frequency and mark-space ratio, and a digital thermometer with a thermistor probe for measuring the sample temperature.

Absorption↗

PubMed1986

Depression of postejaculatory ultrasonic vocalization by (+)-bicuculline.

The male rat emits ultrasonic (22 kHz) vocalizations after ejaculation and behavioural and electrophysiological evidence suggests that this vocalization reflects an inhibitory state underlying and determining the postejaculatory refractory period (PEI). Present results show that injection into the preoptic-anterior hypothalamic area of (+)-bicuculline methiodide, a GABA antagonist, shortens the PEI and reduces ultrasonic vocalization. It is suggested that the suppression of ultrasonic vocalization following bicuculline treatment reflects a depression of an inhibitory state normally produced by ejaculation.

Animals↗

PubMed1994

Ultrasonic vocalization induced by intracerebral carbachol in rats: localization and a dose-response study.

It has been recently demonstrated that application of a cholinergic agonist, carbachol, into the anterior hypothalamic-preoptic area in the rat can induce 22 kHz ultrasonic vocalization. Functional mapping of the response in the forebrain and diencephalic regions of the rat brain, as well as the relationship between the dose of carbachol and the multi-parameter recording of vocalization are analyzed in the present study. Direct pressure injection of carbachol into the brain of adapted rats induced a 22 kHz ultrasonic vocalization from a limited region of the anterior hypothalamic-preoptic area and the vicinity of the septum. The response was antagonized by a local pretreatment with atropine and could not be induced by injections of saline vehicle or by handling. Measurements of summed duration of individual calls and response duration showed a typical dose-response relationship for 32-fold range of carbachol doses with ED50 = 0.73 micrograms (4.0 nmol). The increasing dosage of carbachol did not influence the frequency of emitted ultrasounds. On the other hand, the sound intensity increased and the bandwidth decreased with the increasing dosage of carbachol. The mean duration of single calls was also significantly decreased with the carbachol dosage. However, higher doses of carbachol decreased the number of short calls (100-150 ms) but increased the number of longer calls (300-400 ms). The duration of individual calls appeared to be a sensitive index of the response intensity. The results suggest that the cholinergic input into the mediobasal forebrain may play a physiological role in initiating and emitting the 22 kHz ultrasonic vocalization in rats, and that changes in call duration, intensity and bandwidth may be involved in conveying information for conspecifics.

Animals↗

PubMed1996

Contribution of the ascending cholinergic pathways in the production of ultrasonic vocalization in the rat.

It has been well documented that cholinergic stimulation of the mediobasal forebrain structures induces 20-30 kHz ultrasonic vocalization in adult rats. If the cholinergic system plays a triggering role for ultrasonic vocalization, the question arises as to where the source of the cholinergic fibres, which innervate the mediobasal forebrain and induce vocalization, is located. In the present study, the role of the ascending cholinergic projection from the ponto-mesencephalic cholinergic nuclei to the mediobasal hypothalamic-preoptic region in production of 22 kHz calls was investigated. Cholinergic neurons were stimulated by local injection of L-glutamate and eventual vocalization was recorded by a S200 bat detector and analyzed sonographically. Intracerebral injection of L-glutamate into the laterodorsal tegmental nucleus induced short latency, 20-30 kHz ultrasonic calls. Sound frequency (pitch) and single call duration of the L-glutamate-induced vocalization did not differ from those obtained by cholinergic stimulation of the mediobasal hypothalamic-preoptic region with carbachol. However, L-glutamate stimulation of the laterodorsal tegmental nucleus was ineffective or less effective in 70% of responses, when the terminal fields in the mediobasal hypothalamic-preoptic region were pretreated with scopolamine, a muscarinic antagonist. The results demonstrate that the ascending cholinergic projection from the laterodorsal tegmental nucleus plays a triggering role for 20-20 kHz vocalization in adult rats.

Animals↗

PubMed1978

Ultrasonic studies of lipid bilayer. Phase transition in synthetic phosphatidylcholine liposomes.

The ultrasonic velocity at 3 MHz and the density in the nonsonicated and sonicated liposomes of dipalmitoylphosphatidylcholine have been measured in the temperature range from 0 degrees C to 55 degrees C. The results indicate that nonsonicated multilamellar vesicles undergo a weak first order transition which is analogous to the nematic-isotropic transition of liquid crystals. A sharp change in the ultrasonic velocity associated with the first order transition disappears when the multilamellar vesicles are sonicated. The bulk modulus of the lipid bilayer calculated from the ultrasonic velocity and the density of sonicated liposomes has a value of 3.0 X 10(10) dyne/cm2 at 20 degrees C, reaches a minimum value of 2.1 X 10(10) dyne/cm2 at its transition temperature and increases slightly to 2.2 X 10(10) dyne/cm2 at 50 degrees C.

Chemical Phenomena↗

PubMed1981

Ultrasonic measurements of two-component lipid bilayer suspensions.

Two-component lipid bilayers of dipalmitoylphosphatidylcholine and dimyristoylphosphatidylcholine were studied by measuring ultrasonic velocity and absorption at 3 MHz. The phase diagram of the two-component lipid bilayers is discussed based upon the transition anomalies of the ultrasonic velocity as well as absorption, and it is suggested that this binary system has two critical points. The bulk modulus of lipid bilayers was determined from the ultrasonic velocity to be (2.2-3.0) x 10(10) dyne/cm2, whereas the bulk viscosity calculated from the absorption was 10-20 P except for the transition regions.

Dimyristoylphosphatidylcholine↗

PubMed1982

An annular focus ultrasonic lens for local hyperthermia treatment of small tumors.

A system for applying local hyperthermia employing ultrasonic transducers with annular focusing lenses gave better temperature uniformity in small fibrosarcomas than conventional unfocused transducers. The lenses were designed for ultrasonic frequencies of 3, 4, 5 and 9 MHz for tumors approximately 6 mm dia. Tests in degassed water indicated that the focusing lenses concentrated approx. 80% of the ultrasonic energy into an annular-shaped focus of 6 mm dia. located at a distance of 3 cm in front of the lens. These transducers were used to heat subcutaneous PARA-7 fibrosarcomas in hamsters. Steady-state temperature measurements indicated temperature gradients within tumors of 0.5-1.0 degree C when transducers employing annular-focused lenses were used, versus gradients of 2.0-2.3 degree C with 10 mm dia. unfocused transducers.

Animals↗

PubMedDate not supplied

Subharmonic emission as an indicator of ultrasonically-induced biological damage.

This paper describes work in which subharmonic emissions from ultrasonically irradiated biological samples are integrated over time, and the resultant signal (which is believed to be indicative of cavitation activity) is found to correlate well with the extent of cellular damage. Specifically, three studies have been carried out, in which the subharmonic energy emitted from suspension cultures of V79 cells is integrated during exposure to 1 MHz ultrasound. The effect of raised ambient pressure and sample rotation speed on the occurrence of cavitation, and of cavitation related cell death, have been investigated. Use of the subharmonic emission technique has also yielded additional evidence for the occurrence of an ultrasonically induced mechanism for damage that is neither thermal nor cavitational in origin, in experiments where cells are exposed to ultrasound whilst being held at an elevated temperature (43 degrees C). The potential of the use of subharmonic emission monitoring as a quantitative predictor of ultrasonically induced biological damage, both in vitro and in vivo, is discussed.

Animals↗

PubMedDate not supplied

The combined effect of ultrasonic exposure and protein restriction on maternal and fetal mice.

This investigation was undertaken to assess the combined effects of protein restriction and ultrasonic energy exposure during pregnancy on the maternal and fetal mouse. Pregnant female mice were fed diets containing either 18% casein (control diet) or 6% casein (restricted protein diet) during gestation. All animals were subjected to the ultrasonic exposure procedure (actual: 2.5 W/cm2 spatial peak; sham: 0 W/cm2; continuous wave for 20 sec at a frequency of 1 MHz) on day 8 of gestation. On day 18 of gestation, the animals were sacrificed. Products of conception were examined, and chemical analysis were performed on maternal liver, placenta and fetus. Our results suggest that there are possible influences of ultrasonic energy exposure to the mouse fetus and placenta, as indicated by the tendency toward decreases of fetal weight, placental weight, and DNA and RNA contents of both fetus and placenta, especially with restricted protein in the maternal diet during gestation. Protein restriction during pregnancy had an adverse influence on both the maternal organism and her products of conception. The nutritional needs for the fetus were not met at the expense of the maternal organism. Parameters of fetal cellular growth were reduced by gestational protein restriction indicating that there is competition for available nutrients between the fetus under time of stress. Results also show that the trends of fetal and placental growth are in the same general direction suggesting the possible usefulness of human placental tissue as a maker for fetal growth in subsequent population studies.

Animals↗

PubMedDate not supplied

Ultrasonically guided cholangiography and bile drainage.

Ultrasonically guided percutaneous transhepatic cholangiography (UG-PTC), bile drainage (UG-PTBD) and gallbladder drainage procedure (UG-PTGBD), developed by us, were performed in 47, 183 and 36 patients, respectively. In 47 patients UG-PTC was successfully performed 51 times without complications. By UG-PTBD 220 intubations were carried out successfully and four attempts failed (1.8%). The main complication was that the catheter slipped out from the bile duct. It was experienced 27 times (12.3%) in 23 patients (12.4%) from two to 47 days after intubation. UG-PTGBD was successfully performed 36 times. Bleeding from the catheter was experienced in four patients. However, other complications such as cholascos were not experienced. Due to the development of ultrasonic diagnosis and the UG-PTBD procedure, the indications for percutaneous transhepatic cholangiography (PTC) are now limited. For differentiation of jaundice, ultrasonic examination takes over from PTC. For preparation of PTBD, thin needle cholangiography is no longer necessary because UG-PTBD is a single-step procedure without the need for cholangiography. Therefore, the indication for PTC is limited to patients with partial dilatation of intrahepatic bile ducts without jaundice, for example when only the left hepatic duct is dilated due to hepatolithiasis.

Bile↗

PubMed1986

Ultrasonically induced intravascular streaming and thrombus formation adjacent to a micropipette.

Ultrasonically induced microstreaming around bubbles of gas have been shown to cause damage to biological materials in vitro at clinical exposure levels. The potential for ultrasonically induced cavitation and microstreaming in mammalian systems is of interest with respect to the safe application of clinical ultrasound. Ultrasonically induced intravascular microstreaming and formation of thrombi at 1 MHz is demonstrated adjacent the tip of a micropipette in contact with a mesenteric vessel of the mouse. These effects occur at or above therapeutic levels.

Animals↗

PubMed1987

A review of the ultrasonic bioeffects of microsonation, gas-body activation, and related cavitation-like phenomena.

Ultrasonic exposures localized to regions smaller than a wavelength minimize the thermal mechanism, but promote nonthermal mechanisms of ultrasonic bioeffects. Microsonation experiments with vibrating needles or wires exploit this situation for the study of nonthermal mechanisms such as acoustic microstreaming flow. Shear stress in microstreaming flow, which is in excess of critical values for biomembranes, leads to cell lysis. Plane wave exposure of small bodies of gas also yields localized exposure, with further amplification of nonthermal mechanisms by resonance activation of oscillation. Gas body activation in vitro causes gathering of suspended cells by radiation forces, aggregation, cellular effects and lysis by microstreaming. When suitable gas bodies are present, these effects may occur at levels below the threshold for ultrasonic cavitation. In vivo, gas body activation generates intracellular microstreaming in Elodea leaves and disrupts the cells for super-critical shear stress levels. Similar phenomena seem to account for cell death, growth and mitotic index reductions in other plant tissues, and developmental abnormalities and delayed death in fruit flies. Only fragmentary and equivocal evidence presently exists on the medically relevant question of whether such subthreshold cavitation-like activity and bioeffects occur in vertebrates.

Animals↗

PubMed1988

The effect of solvation on the ultrasonic absorption of bovine serum albumin solutions.

The role of solvation and structural equilibria in determining the ultrasonic absorption of aqueous solutions of bovine serum albumin has been investigated using chemical agents to denature the protein in solution. The agents used were methanol, ammonium sulphate, and guanidine hydrochloride. Two different techniques of measurement were used to cover the frequency range 200 kHz to 30 MHz. The results show that only guanidine hydrochloride produces a significant change in ultrasonic absorption even though the other agents were used at concentrations close to those which would produce protein precipitation. The conclusion is that in the above frequency range structural and solvation-related equilibria are unimportant and only perturbation of proton-transfer equilibria associated with the protein amino acid residues leads to the bulk of the ultrasonic absorption.

Absorption↗

PubMed1991

Measurements of ultrasonic fields with optical diffraction tomography.

This article describes a light diffraction technique that allows a measurement of ultrasonic pressure and phase in the cross-section of an ultrasonic beam. The light diffraction measurements are based on the Raman-Nath model of ultrasonic continuous-wave light diffraction. The diffracted light intensity can be expressed as an integration of sound pressure along the light path. This integration is analogous to the integration of the absorption coefficient in x-ray tomography. Tomography algorithms can be employed on the light measurement data to calculate the pressure and phase in a measuring plane perpendicular to the ultrasound propagation vector. The reconstruction of the measurement plane is done with an implementation of an algebraic reconstruction technique (ART). Satisfactory results are obtained with 10 projections. The measurement method is applicable up to Raman-Nath parameter values of 2.3. The experimental results are compared to miniature PVDF hydrophone measurements.

Algorithms↗

PubMed1993

Cell density dependence of the ultrasonic degassing of fixed erythrocyte suspensions.

Ultrasonic cell lysis in vitro shows a strong dependence on the cell density of the suspensions. The major determinant in this phenomenon appears to be the suspended particle density per se. Reported are the results of experiments designed to test the hypothesis that the majority of the cell density effect arises as a consequence of the cell density-dependent formation of cellular aggregates around oscillating bubbles in an ultrasound field (Nyborg and Miller 1982), which in turn diminishes the potential for the occurrence and sustenance of destructive cavitational events in the bulk suspension fluid. The hypothesis was tested indirectly using manometric methods to measure ultrasound-induced release of dissolved gas from saline solutions and fixed erythrocyte suspensions. Ultrasonic degassing of the fluids in excess of that attributable to thermal effects was observed, and was suppressed by the presence of fixed erythrocytes when the cell density was greater than 5 x 10(6) cells/mL. At higher cell densities, the inhibition of ultrasonic degassing by fixed cells increased monotonically with increasing cell density, attaining complete suppression at a cell density of 5 x 10(8) cells/mL. The data thus support the hypothesis.

Blood Cell Count↗

PubMed1994

A computer model for simulating ultrasonic scattering in biological tissues with high scatterer concentration.

Scattering of ultrasonic waves by biological tissues at different scatterer concentrations is investigated using one- and two-dimensional computer simulation models. The backscattered power as a function of scatterer concentrations is calculated using two types of incident waves, a Gaussian shaped pulse and a continuous wave (CW). The simulation results are in good agreement with the Percus-Yevick packing theory within the scatterer concentrations, from 0% to 100% in one-dimensional (1D) space, and 0% to 46% in two-dimensional (2D) space. In all cases, the simulation results from a pulsed incident wave show a much smaller standard deviation (SD) than those from an incident CW. The simulation can serve as a useful tool to verify scattering theories, simulate different experimental conditions, and to investigate the interaction between the scatterer properties and the scattering of ultrasonic waves. More importantly, the 2D simulation procedure serves as an initial step toward the final realization of a true three-dimensional (3D) simulation of ultrasonic scattering in biological tissues.

Blood↗

PubMed1994

Characterization of ultrasonic transducers using a fiberoptic sensor.

The PVDF (polyvinylidene fluoride) hydrophones, commonly used to measure the characteristics of ultrasonic transducers, suffer from a number of drawbacks. They disturb the field distribution to be measured and cause spatial averaging effects because of their finite aperture. In addition, they are very delicate and susceptible to damage. To overcome some of these problems, the authors previously proposed the use of an optical fiber-based probe to measure the ultrasonic fields. In this paper, this fiberoptic ultrasonic sensor is used to measure the characteristics of six transducers, focused as well as unfocused, covering a frequency range of 2.25 MHz to 20 MHz. Results obtained using the fiberoptic sensor are compared with those obtained using a calibrated PVDF needle hydrophone with an effective diameter of 0.5 mm. The temporal responses as well as the beam profiles of the transducers measured using the fiberoptic sensor show excellent agreement with the results obtained using the PVDF needle hydrophone.

Fiber Optic Technology↗

PubMed1993

Orthodontic bracket removal using conventional and ultrasonic debonding techniques, enamel loss, and time requirements.

The purpose of this study was to examine the effects of ultrasonic orthodontic bracket removal and cleanup and compare them with conventional debonding and cleaning of the enamel surfaces with burs and polishing disks. The amount of enamel loss and time for bracket removal and clean-up were also addressed. Thirty extracted human premolars were collected. The teeth were randomly placed in one of the three debonding groups: debonding with orthodontic pliers and enamel clean-up with finishing burs and polishing disks (group 1), debonding with orthodontic pliers and ultrasonic clean-up of the enamel surface (group 2), and ultrasonic debonding enamel clean-up (group 3). The teeth were stored for 48 hours in 100% humidity before bracket removal. All brackets were then removed. Polyvinyl siloxane impressions were made before and after bracket removal. Direct measurements of the teeth in micrometers were made at all steps. An additional 30 teeth were similarly prepared, and the brackets were debonded and cleaned-up as in the three groups previously described. The total time for bracket removal and enamel clean-up for each group was recorded in seconds.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Variance↗