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E C Everbach

Publications and source records attributed to E C Everbach.

17 recordsLinked to original sources
PubMed2001

A comparison of the hemolytic potential of Optison and Albunex in whole human blood in vitro: acoustic pressure, ultrasound frequency, donor and passive cavitation detection considerations.

This project tested the hypothesis that a "second-generation" ultrasound (US) contrast agent (Optison), offering extended echogenicity over that of its "first-generation" predecessor (Albunex), would have the greater potential for sonolysis of human erythrocytes in vitro. Whole human blood, obtained from apparently healthy donors, was anticoagulated and subsequently exposed in vitro to US in the presence of one of each or neither of the two US contrast agents. The US exposures were for 30 s and involved frequency (1.0, 2.2 and 3.4 MHz) and amplitude (approximately 2.8 to 0.38 MPa P(-)) regimens; pulse duration (200 micros) and interpulse interval (20 ms) were held constant. The data supported the hypothesis, with an overall ratio of approximately 2.5 for relative extent of background-corrected US-induced hemolysis of the Optison/Albunex regimens. Passive cavitation detection analyses corroborated the results obtained with hemolysis.

Adult↗
PubMed2001

Effectiveness of transcranial and transthoracic ultrasound and microbubbles in dissolving intravascular thrombi.

OBJECTIVE: To examine the effectiveness of 1 -MHz and 40-kHz ultrasound with and without microbubbles in fragmenting thrombi in attenuated conditions. METHODS: First, an vitro transcranial model was used to examine the ability of these frequencies to fragment thrombi in the presence or absence of perfluorocarbon-exposed sonicated dextrose albumin microbubbles. Second, an in vivo transthoracic model was used to test the effectiveness of these same frequencies with intravenous perfluorocarbon-exposed sonicated dextrose albumin in fragmenting left circumflex coronary thrombotic occlusions. RESULTS: In the in vitro model, both transcranial 1-MHz and 40-kHz ultrasonic frequencies were effective at fragmenting thrombi only in the presence of microbubbles. In the in vivo model, 1-MHz ultrasound with intravenous perfluorocarbon-exposed sonicated dextrose albumin angiographically recanalized only 4 of 14 occlusions but was consistently effective at improving myocardial blood flow to the risk area even in the absence of angiographic recanalization. Both 40-kHz and 1-MHz ultrasound with perfluorocarbon-exposed sonicated dextrose albumin improved regional wall-thickening and electrocardiographic abnormalities (P < .05 compared with control or ultrasound alone). CONCLUSIONS: Transcranial and transthoracic ultrasound in the presence of intravenous microbubbles can improve flow to ischemic regions and should be considered as a supplement to current pharmacologic therapy.

Adult↗
PubMed2000

Cavitational mechanisms in ultrasound-accelerated thrombolysis at 1 MHz.

Inertial cavitation is hypothesized to be a mechanism by which ultrasound (US) accelerates the dissolution of human blood clots when the clot is exposed to a thrombolytic agent such as tissue plasminogen activator (t-PA). To test this hypothesis, radiolabeled fibrin clots were exposed or sham-exposed in vitro to 1 MHz c.w. US in a rotating sample holder immersed in a water-filled tank at 37 degrees C. Percent clot dissolution after 60 min of US exposure was assessed by removing the samples, centrifuging, and measuring the radioactivity of the supernatant fluid relative to the pelletized material. To suppress acoustic cavitation, the exposure tank was contained within a hyperbaric chamber capable of pneumatic pressurization to 10 atmospheres (gauge). Various combinations of static pressure (0, 2, 5, and 7.5 atm gauge), US (0 or 4 W/cm(2) SATA), and t-PA (0 or 10 microg/mL) were employed, showing statistically significant reductions in thrombolytic activity as static pressure increased. To gain further insight, an active cavitation detection scheme was employed in which 1-micros duration tonebursts of 20-MHz US (< 1 kPa peak negative pressure, 1 Hz PRF) were used to interrogate clots subjected to US and static pressure. Results of this cavitation detection scheme showed that scattering from within the clot and broadband acoustic emissions that were both present during insonification were significantly reduced with application of static pressure. However, only about half of the acceleration of thrombolysis due to US could be removed by static pressure, suggesting the possibility of other mechanisms in addition to inertial cavitation.

Humans↗
PubMed1998

Effect of acoustic cavitation on platelets in the presence of an echo-contrast agent.

A suspension of human platelets in autologous plasma or buffer solution with and without a microbubble echo-contrast agent was exposed in vitro to 730 W/cm2 (ISPPA) ultrasound pulses of duration 40-160 microseconds at 1 MHz and 20-Hz pulse repetition frequency. Inertial cavitation occurring within the samples was monitored during the exposures and a measure of average cavitational activity was calculated for each 5-min exposure. This quantity, with the other acoustic parameters, accounted for up to 75% of the variation in the destruction of platelets as measured by Coulter counter and 83.5% of the release of bound radiolabel using a multiple-interaction statistical model. When the echo-contrast agent was absent, negligible cavitation occurred and the amount of platelet destruction was statistically indistinguishable from sham (no-ultrasound) exposures. Therefore, microbubble echo-contrast agents may interact with ultrasound to cause platelet lysis through the mechanism of inertial cavitation.

Acoustics↗
PubMed1998

Bacterial stress responses to 1-megahertz pulsed ultrasound in the presence of microbubbles.

Members of a panel of stress-responsive biosensors have been used to study the effect of megahertz frequency ultrasound on Escherichia coli. Insonification causes acoustic cavitation, the collapse of oscillating microbubbles in solution, which can damage bacterial cells. A focused 1-MHz ultrasound transducer, capable of generating a spatial peak pulse average intensity of 500 W/cm2, was used to treat liquid bacterial cultures. Stress-responsive promoters fused to luxCDABE allowed the continuous measurement of light produced as a result of protein damage, DNA damage, oxidative stress, and membrane perturbation. A promoter responsive to ammonia limitation was not transcriptionally activated under test conditions. In contrast to bacteria in exponentially growing cultures, those in stationary-phase cultures were more resistant to the effects of ultrasound treatment. Quantification of the degree of acoustic cavitation due to symmetric bubble collapse was measured by a 20-MHz passive transducer, the output of which appears to be only partially correlated with cellular damage and survival. The methods and results summarized here provide the basis for further investigation into applications, including the purification of water samples.

Ammonia↗
PubMed1997

Correlation of ultrasound-induced hemolysis with cavitation detector output in vitro.

A 20-MHz passive acoustic detector was used to quantify the amount of transient acoustic cavitation occurring in a sample exposed to intense pulsed ultrasound. A dilute suspension of human erythrocytes with and without a microbubble echo-contrast agent was exposed in vitro to 500 W/cm2 (SPPA) ultrasound of center frequency 1 MHz and tone burst duration 20, 100, 200, 500 and 1000 microseconds at a pulse repetition frequency of 20 Hz. Inertial cavitation occurring within the sample, as measured by the temporal average of the detector output, correlated well with hemolysis, suggesting that violent bubble collapse is responsible for cell damage. The result also raises the prospect of cavitation monitoring as a possible predictor of adverse bioeffects when echo-contrast agents are used clinically.

Albumins↗
PubMed1996

Measurement of pressure and assessment of cavitation for a 22.5-kHz intra-arterial angioplasty device.

This study was performed to understand better the mechanisms of action of an (22.5 kHz) ultrasonic wire catheter device used to remove atheromatous plaque in diseased blood vessels (ultrasonic angioplasty). During a clinical procedure, the wire acts as an acoustic waveguide to transfer acoustic energy from a generator outside the body to the ball tip of the wire, which is inserted in the blood vessel. The acoustic field radiated by the vibrating ball tip (1.5- to 3.0-mm diameter), was mapped in a relatively large (600 L) water tank and compared to the field from a well-characterized simple source. A dipolelike radiation pattern due to the translating ball tip was observed. At low power settings, standing wave effects in a smaller cylindrical volume (200-mm diameter, 350-mm height), which was used to simulate anthropometric dimensions, increase relative to the larger tank measurements. The standing wave ratio is dependent upon the pc characteristics of the medium and the dimensions of the volume, rather than on the absorption at this frequency. At high power-settings of the device, cavitation at the tip of the wire was measured using a 20-MHz passive cavitation detection scheme.

Acoustics↗
PubMed1995

An interferometric technique for B/A measurement.

An isentropic phase method is described for measuring in vitro the acoustic nonlinearity parameter B/A of several aqueous buffers, protein solutions, lipid oils, and emulsions. The technique relies upon the use of an acoustic interferometer to measure the small changes in sound speed that accompany a rapid hydrostatic pressure change of between one and two atmospheres. Average accuracies of 0.85% are attainable with this method.

Acoustics↗
PubMed1993

Transient acoustic cavitation in gallstone fragmentation: a study of gallstones fragmented in vivo.

The mechanism of gallstone fragmentation by shock waves in vivo is uncertain. We used scanning electron microscopy to study 9 partially fragmented stones obtained from 6 patients who underwent lithotripsy and subsequently had surgery because of incomplete fragmentation. Surface characteristics of the stone were studied using scanning electron microscopy and compared to gallstones fragmented in degassed water in vitro and to control stones obtained from patients with uncomplicated cholelithiasis. Characteristic damage caused by transient acoustic cavitation was visible in all stones fragmented in vivo and in vitro as pits 10-100 microns diameter. In these pits, cholesterol crystals were fractured, and the symmetry of crystal boundaries was damaged. In areas of more severe damage, individual pits coalesced to form craters on the stone surface. High magnification of the pit walls revealed cracks, which in some instances radiated out onto the unpitted surface of the stone. We conclude that transient acoustic cavitation plays a role in gallstone fragmentation in vivo through the mechanism of surface pitting and the formation of cracks that radiate outward from the surface pits. Measures to enhance cavitation may improve the results of gallstone lithotripsy.

Adult↗
PubMed1993

Internal stress wave measurements in solids subjected to lithotripter pulses.

Semiconductor strain gauges were used to measure the internal strain along the axes of spherical and disk plaster specimens when subjected to lithotripter shock pulses. The pulses were produced by one of two lithotripters. The first source generates spherically diverging shock waves of peak pressure approximately 1 MPa at the surface of the specimen. For this source, the incident and first reflected pressure (P) waves in both sphere and disk specimens were identified. In addition, waves reflected by the disk circumference were found to contribute significantly to the strain fields along the disk axis. Experimental results compared favorably to a ray theory analysis of a spherically diverging shock wave striking either concretion. For the sphere, pressure contours for the incident P wave and caustic lines were determined theoretically for an incident spherical shock wave. These caustic lines indicate the location of the highest stresses within the sphere and therefore the areas where damage may occur. Results were also presented for a second source that uses an ellipsoidal reflector to generate a 30-MPa focused shock wave, more closely approximating the wave fields of a clinical extracorporeal lithotripter.

Acoustics↗
PubMed1992

Gallstone movement during lithotripsy: mechanisms and effects on fragmentation.

We sought to examine the mechanisms of gallstone movement and its effect on gallstone fragmentation in vitro. Two experiments were performed in four specially constructed phantoms that allowed decreasing degrees of movement during the application of shock waves. Shock waves caused displacement of the stone from the focus, but the stone and its fragments were returned to the focus by streaming movements in the coupling liquid when the volume of surrounding fluid was small. Streaming movements were ineffective in large volumes. Restraining movements of the gallstone did not improve the results of fragmentation. We conclude that radiation force and the streaming motion of the surrounding liquid account for movements of the stone and fragments during lithotripsy. Lithotripsy is more effective when smaller volumes are used because streaming brings fragments back to the focus of the lithotripter. Total immobilization of the stone in the focus of the lithotripter, however, offers no benefit, probably because it inhibits rotational movement of the stone.

Cholelithiasis↗
PubMed1991

Gas in gallstones: quantitative determinations and possible effects on fragmentation by shock waves.

The presence of gas in a gallstone can profoundly affect the ability of shock waves to fragment the stone by various mechanisms. In the present study, the aim was to determine the gas content of gallstones and determine if increasing the gas content of the stone affected the outcome of lithotripsy. Thirty human gallstones, transferred directly from gallbladder bile into sterile saline, were studied. The initial gas content of all stones was determined by differential weighing under saline before and after degassing. Eighteen gallstones were pairs; each pair was from a single patient and of similar size and composition. One gallstone of each of the pairs was exposed to air and the other was kept under saline. Then each of the paired gallstones was subjected to 1000 pulses at power level 3 (highest) in a Diasonics Therasonic lithotripter (Diasonics, Milpitas, CA). The volume of gas present at the beginning of the experiment in all groups of stones was 2.4 +/- 2.1 mm3, and 27% of all gallstones tested contained measurable amounts of gas initially. There was no significant difference in the volume of gas present in the paired stones at the beginning of the experiment (group A, 1 +/- 0.4 mm3; group B, 2 +/- 1 mm3). After group A stones were exposed to air, the gas content was significantly higher (36 +/- 18 mm3) than in the paired group B stones stored under saline (3 +/- 2 mm3; P less than 0.05). Stones exposed to air fragmented more easily than stones stored under saline. The mean number of pulses required to cause initial fragmentation was significantly lower in the group of stones exposed to air (22 +/- 7) compared with those stored under saline (610 +/- 139; P less than 0.05). The fragments were smaller and more numerous in the group of stones exposed to air than in those stored under saline. It is concluded that gas is present in some gallstones and that the efficacy of lithotripsy increases with increasing stone gas content. Our data suggest that alterations in the physical characteristics of gallstones can have profound effects on the outcome of lithotripsy.

Analysis of Variance↗
PubMed1991

Applications of mixture laws for predicting the compositions of tissue phantoms.

This paper generalizes the mixture law methodology for ultrasonic tissue characterization by combining mixture laws used by Apfel and Seghal et al. in producing nine different combinations. After applying these combinations of mixture laws to 10 tissue phantoms, it is shown that three of the combinations consistently give better predictions of the composition of the phantoms than others. The results verify directly that the phase shift parameter law is probably not a good choice in predicting tissue composition. The potential uses of the mixture methodology are discussed.

Models, Structural↗
PubMed1991

The appreciation of colour in endoscopy.

The perception of colour at endoscopy has been taken for granted since the discovery of the fibreoptic bundle and the advent of fibreoptic endoscopy. Fibreoptic and lens assemblies can distort the impression of colour by selectively absorbing some wavelengths of light. In the case of electronic endoscopes, the principal sensor is the charge-coupled device (CCD), a small microelectronic device that converts an image into a sequence of electronic signals which, after appropriate processing, are transformed into an image on the monitor screen. The image is therefore visualized as a mosaic of small images, one from each sensing element. Colour is synthesized by using sequential illumination using filters or by filters placed over the CCD. Fibre-endoscopes may alter colour by selectively transmitting certain portions of the visible spectrum, while electronic endoscopes are susceptible to errors due to poor calibration of the instrument and manipulation of the colour controls by endoscopists. Colour information provides the endoscopist with clues to the nature of the lesion and also a site for biopsy. In experimental situations, colour information has been used to determine blood flow and classify lesions. Much work needs to be done to define normal and abnormal colour in the gastrointestinal tract and to develop a standard terminology for colour nomenclature in endoscopy.

Color Perception↗
PubMedDate not supplied

Endoscopic measurement of lesion size: improved accuracy with image processing.

Endoscopic measurement of lesions is of great importance in the design and performance of clinical trials, as, for example, in studies of ulcer disease. Endoscopes are constructed with wide-angle lenses that significantly distort the image by creating a relative compression of points in its periphery. We have recently developed a computer program to correct the distortion of the wide-angle lens. We sought to determine the accuracy of the currently used open-biopsy forceps measurement technique and compare it to that of an image-processing technique designed to correct image distortion. The overall error of the open-biopsy forceps technique using an in vitro ulcer model was under-estimation of lesion size by 41.8% +/- 23.3%. When image processing was used to correct distortion, error was significantly decreased to 1.8% +/- 2.2% (p < 0.05). In vivo measurements were made using an inserted object of known size (coated chewing gum). The mean error of the forceps technique in vivo was 26.5% +/- 5.7% (under-estimation of size), which improved significantly to an error of 2.8% +/- 3.2% (p < 0.05) with the image-processing technique. We conclude that image processing significantly enhances the accuracy of measurement at endoscopy.

Biopsy↗