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BRL Abstracts Database |
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Your search for ultrasound produced 3296 results. Page 200 out of 330
| Title |
Possible explanation for the unexpected.absence of gross biological damage to.membranes of cells insonated in suspension.and in surface culture in chambers exposed to.standing and progressive wave fields. |
| Author |
Watmough DJ, Quan KM, Shiran MB. |
| Journal |
Ultrasonics |
| Volume |
|
| Year |
1990 |
| Abstract |
Quoted values of cavitation thresholds reported in the literature vary over several.orders of magnitude. This paper describes an investigation of the threshold in a.chamber with acoustically transparent windows, situated around the last axial.maximum of a 0.75 MHz standing wave field. The chamber, the transducer and.the reflector are submerged in a tank containing distilled water which also fills.the chamber. The formation of bubbles outside the chamber, both above and.below it, occurred at lower intensities than those needed to generate bubbles in.the chamber. This unexpected finding led to a theoretical study of streaming.patterns in progressive and standing wave fields. These showed that there is a.region around the last axial maximum in which there is no gradient of energy.density. Therefore if this region is enclosed by an acoustically transparent.chamber, no significant bulk streaming occurs within it. We speculate on how.this lack of streaming raises the cavitation threshold. The cavitation phenomenon.is also examined by Doppler ultrasound of frequency 8 MHz. This confirms the.occurrence of increased intensity thresholds within the chamber. It also shows.that the time between filling the chamber and the start of sonication strongly.influences the magnitude of the cavitation threshold. We expect that the effects.described here may have consequences for sonication of cells in suspension.culture when the samples are held in chambers situated around the last axial.maximum of an ultrasound beam from a plane transducer. .. |
| Title |
Possible hazards of diagnostic ultrasound. |
| Author |
Taylor KJW, Dyson M. |
| Journal |
Ultrasound |
| Volume |
|
| Year |
1972 |
| Abstract |
The ideal agent for therapy and investigative techniques in medicine is one that is rapidly effective, completely non-toxic, and may be administered without discomfort to the patient. At the very least, the benefits accruing from the use of an agent, in the majority of patients, must exceed the disadvantages. Most agents fall between these extremes but the effective dose should be small compared to the toxic one. On such criteria diagnostic ultrasound, as currently used, rates high, for information is rapidly obtained, no deleterious effects have been reported with the dose regime at present used for diagnosis, and its application involves no discomfort nor indignity to the patient. Larger doses have been shown to produce damage in the tissues of experimental animals and this paper attempts to review the evidence for the safety of current techniques, the dosage required for harmful effects and, by comparing these, to estimate the ratio of effective to toxic dose. It is thus necessary to determine time and intensity thresholds for biological changes.
Obstetrics forms one of the largest applications of the technique. For the past two decades, there has been a growing realization that many unrelated environmental influences may result in fetal abnormalities. The search for teratogenic agents is complicated by the geographical variation in incidence of fetal abnormalities and differences in the type of abnormalities produced by the same agent in different races or species. As a result the medical profession has, quite properly, become most sensitive and conservative about any therapy or investigative techniques in the early stages of gestation. More recently, there has appeared evidence that environmental influence s in late pregnancy may affect postnatal development. Finally, when embryonic ovaries are involved there is always the possibility that mutations may occur that will not be apparent for at least another generation. Thus, conclusive evidence on the safety of any new technique cannot be completely established within a single generation. One can only use experimental models and clinical observation after insonation to indicate that the method appears to be safe.
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| Title |
Possible misdiagnosis of sound attenuating breast masses as detected by ultrasound visualization techniques and solutions to this problem. |
| Author |
Kelly-Fry E, Harper P, Gardner GW. |
| Journal |
Pro 23rd Annual Meeting Am Inst Ulrasound Med |
| Volume |
|
| Year |
1978 |
| Abstract |
No abstract available. |
| Title |
Post-beamforming second-order volterra filter for pulse--echo ultrasonic imaging. |
| Author |
Phukpattaranont P Ebbini ES. |
| Journal |
IEEE Trans UFFC |
| Volume |
|
| Year |
2003 |
| Abstract |
We present a new algorithm for deriving a second-order Volterra filter (SVF) capable of separating linear and quadratic components from echo signals. Images based on the quadratic components are shown to provide contrast enhancement between tissue and ultrasound contrast agents (UCAs) without loss in spatial resolution. It is also shown that the quadratic images preserve the low scattering regions due to their high dynamic range when compared with standard B-mode or harmonic images. A robust algorithm for deriving the filter has been developed and tested on real-time imaging data from contrast and tissue-mimicking media. Illustrative examples from image targets containing contrast agent and tissue-mimicking media are presented and discussed. Quantitative assessment of the contrast enhancement is performed on both the RF data and the envelope-detected log-compressed image data. It is shown that the quadratic images offer levels of enhancement comparable or exceeding those from harmonic filters while maintaining the visibility of low scattering regions of the image. |
| Title |
Postnatal sequelae of ultrasound exposure at fifteen days of gestation in the rat (work in progress). |
| Author |
Sikov MR, Hildebrand BP, Stearns JD. (White D, Brown RE eds.) |
| Journal |
Ultrasound Med |
| Volume |
|
| Year |
1977 |
| Abstract |
Introduction: There have been a number of studies on the effects of ultrasound on prenatal development. Although many of the earlier studies did not report embryotoxicity, the more sophisticated approaches and higher intensities used more recently have demonstrated deleterious effects (1). Most of these studies used prenatal assessment and it had been in the last few days that postnatal growth and survival were considered (2,3).
Experiments in our laboratory are examining a wider variety of the possible postnatal effects of exposure of the rat fetus to ultrasound at 25 days of gestation. We are presently completing a series at 0.93 MHz continuous wave (c.w.) which is described here. Studies with 2.5 MHz pulsed and c.w. ultrasound, which employ a similar approach, are also in progress.
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| Title |
Postnatal sequelae of ultrasound exposure of gestation in the rat (work in progress). |
| Author |
Sikov MR,Hildebrand BP, Stearns JD. |
| Journal |
Ultrason Med |
| Volume |
|
| Year |
1977 |
| Abstract |
There have been a number of studies on the effects of ultrasound of prenatal development. Although many of the earlier studies did not report embryotoxicity, the more sophisticated approaches and higher intensities used more recently have demonstrated deleterious effects (1). Most of these studies used prenatal assessment and it has only been in the last few years that postnatal growth and survival were considered (2,3)..Experiments in our laboratory are examining a wider variety of the possible postnatal effects of exposure of the rat fetus to ultrasound at 15 days of gestation. WE are presently completing a series at 0.93 MHz continuous wave (c.w.) which is described here. Studies with 2.5 MHz pulsed and c.w. ultrasound, which employ a similar approach, are also in progress.. |
| Title |
Potassium concentration changes in thymocytes in vitro associated with sub-lethal exposure to ultrasound. |
| Author |
Tucker S, Chapman IV. |
| Journal |
Meet Bioacoust |
| Volume |
|
| Year |
1976 |
| Abstract |
The changes in the potassium content of rat thymocytes exposed to ultrasound in vitro will be discussed. Sublethal exposure was taken to be the levels of ultrasound at which neither cell lysis nor increased membrane permeability to Erythrosin B, occurred.
The results obtained will be compared with results from a previous study, and reasons for the difference discussed.
The three main biophysical modes of action ultrasound will be examined in an effort to elucidate the damage mechanism operating. To do this, results from three series of experiments will be presented.
Heating effects were measured using a thermocouple, and the effect of similar temperature rises on the thymocytes examined. To reduce the occurrence of cavitation, the Krebs-Ringer solution used was made up with distilled water that had been previously vacuum evaporated. Preliminary results from studies using potassium-42 will be discussed with a view to locating the site of damage to the cell. |
| Title |
Potential hazards of the dental ultrasonic descaler. |
| Author |
Walmsley AD. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1988 |
| Abstract |
The use of a dental ultrasonic descaler may be associated with biological hazards to structures within the oral cavity. Thermal hazards may result from either frictional contact between the oscillating probe and tooth or from absorption of acoustic energy within the tooth. Transmission of ultrasound along the tooth may result in thrombogenic damage to nearby blood vessels. The vibrating probe tip may produce scratching of the tooth surface, and incorporation of oral bacteria within the aerosol generated by the instrument which may result in transmission of infected material. Damage to the ear may arise from the coupling of ultrasound to the bones of the skull via the tooth. Furthermore the electro-magnetic field produced by these devices may interfere with cardiac pacemakers. It is the patient receiving treatment who is mainly exposed to these potential hazards. However, the clinician and his supporting staff may also be at risk.
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| Title |
Potential of automatic control of frequency, image contrast and received bandwidth for image characterization of solid breast masses. |
| Author |
Kelly-Fry E, Morris ST, Holden RW, Jackson VP, Sanghvi NT. |
| Journal |
J Ultrasound Med |
| Volume |
|
| Year |
1988 |
| Abstract |
A new approach has been used for ultrasound detection of small benign and malignant breast masses, namely, control of scattering in such a manner that a small mass can be easily recognized because of the effect of the scattering on the contrast between the mass and the surrounding normal tissue. Maintenance of good resolution as scattering is varied is an essential aspect of this approach. Image contrast is dependent on a number of instrumentation parameters but, in a fundamental sense, it is related to differences in the amount of scattering between a solid breast mass and the surrounding normal tissue. A unique technique for varying center frequency without switching transducers was developed, namely, the use of a wide bandwidth, co-polymer PVDF transducer, in combination with certain instrumentation conditions which allow the center frequency output of a single ultrasound transducer to vary over a relatively wide frequency range. Using this technique, an automatic B-mode ultrasound imaging breast instrument which allows emission of 3.5, 4.5, 6.5 and 11MHz ultrasound frequencies from the same co-polymer transducer was used to examine patients with solid breast masses. Both a wide band-pass receiver (which allows variation of the band-pass from wide to narrow) was used with this automated system. Using the standard receiver system, it was found that there are advantages to having a range of transducer frequencies immediately available for breast examination. These include: (1) improved detection of masses located in highly attenuating regions of breast (by decreasing frequency); (2) availability of diagnostically relevant information at some one frequency which may not be apparent at other frequencies. Using the multiple frequency system and the standard receiver, it was found that the most appropriate examinatio frequencies for detection and diagnosis of fibroadenomas are higher frequencies (8 to 11MHz). This is particularly true in the case of fibroadenomas in fatty breasts. By using higher frequencies (10MHz and above) along with band-pass filtering of the tunable receiver, it was possible to produce a significant difference in scattering between a mass and the surrounding normal tissue, while maintaining or improving resolution. Images obtained under these circumstances show intense backscattering from normal breast tissues and significantly less scattering from breast masses, whether benign or malignant. This technique may have significant potential for detection of small breast masses since it allows such masses to be sharply outlined in high contrast to their surroundings. Preliminary data also indicates that htis technique may provide image characterization of benign and malignant breast masses. |
| Title |
Potentiation of chemotherapy by low-level ultrasound. |
| Author |
Harrison GH, Balcer-Kubiczek EK, Eddy HA. |
| Journal |
Int J Radiat Biol |
| Volume |
|
| Year |
1991 |
| Abstract |
No abstract available. |
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