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BRL Abstracts Database |
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Your search for ultrasound produced 3296 results. Page 324 out of 330
| Title |
Uncertainties in estimates of lesion detectability in diagnostic ultrasound. |
| Author |
Wear KA, Gagne RM, Wagner RF. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
1999 |
| Abstract |
Statistical properties of estimates of focal lesion detectability for medical ultrasonic imaging systems are investigated. Analytic forms for bias and variance of estimates of detectability of a lesion consisting of fully developed speckle embedded within a speckle background are derived. Bias and variance of estimates of detectability are investigated using a computer simulation and experiments on tissue-mimicking phantoms. This work offers a systematic methodology for interpreting measurements on phantoms in order to assess lesion detectability. In addition, it provides useful results which may be used to improve design of phantoms and experiments for imaging-system performance assessment. |
| Title |
Unchanged growth patterns of acanthamoeba exposed to intermediate intensity ultrasound. |
| Author |
Brown RC, Coakley WT. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1975 |
| Abstract |
Gelled suspensions of the amoeba Acanthamoeba castellanii have been exposed to 1 MHz ultrasound at 10?C at continuous and pulsed intensity/time regimes which would result in lesions in tissue. Samples from logarithmically growing and from synchronous cultures have been treated in free field and standing wave conditions. No difference in the growth of treated and control samples was observed. The implication of the results for understanding any non-thermal, non-cavitational interaction between cells and ultrasound is discussed. |
| Title |
Understanding the limitations of ultrasonic backscatter measurements from microbubble populations. |
| Author |
Sboros V, Ramnarine KV, Moran CM, Pye SD, McDicken WN. |
| Journal |
Phys Med Biol |
| Volume |
|
| Year |
2002 |
| Abstract |
Despite over ten years of in vitro investigations of ultrasound contrast agents, the level of understanding of their behaviour in ultrasound fields is limited. Several problems associated with these investigations, particular to the nature of contrast agents, are discussed. Using a commercial scanner the RF normalized backscatter of two different contrast agents (Definity and Quantison TM) was measured at different suspension concentrations and acoustic pressures. Both contrast agents scattered ultrasound nonlinearly and the backscatter showed a dependence on acoustic pressure. In order to access the average behaviour of the agents across the range of acoustic pressures and microbubble concentrations the experimental data were fitted to a theoretically acceptable model using nonlinear regression analysis. The analysis showed that both the backscatter and the attenuation of the Quantison TM suspensions displayed a higher order of dependence on acoustic pressure than the Definity suspensions. It was also discovered that Quantison TM microbubbles did not demonstrate uniform behaviour across the acoustic pressure range. At lower acoustic pressures the behavior could not follow a model similar to that which predicted the behaviour at higher acoustic pressures, wich was mainly due to the fact that free bubbles were released in a fashion dependent on acoustic pressure. The fact that two different populations of scatterers exist in the same suspensions makes the assessment of the behaviour of the particular agent impossible with the high concentrations that are commonly used. Very low concentration suspensions whereby single scattering events cnan be monitored should be more useful. In conclusion, the approach of using high microbubble concentrations in order to investigate the properties of ultrasonic contrast agents is limited in that the results of such studies cannot be used to understand the behavior of single microbubbles. |
| Title |
Unfocused multielement and tapered phased array ultrasound transducers for hyperthermia treatment. |
| Author |
Benkeser PJ. |
| Journal |
Thesis(PhD): Univ of Illinois |
| Volume |
|
| Year |
1985 |
| Abstract |
Currently used ultrasound clinical hyperthermia systems lack adequate control of the energy deposition used to heat tumors. This thesis discusses the development and testing of two different ultrasound hyperthermia transducers which allow improved control of the energy deposition. |
| Title |
Unfocused ultrasound for localized tissue destruction in rabbit kidneys. |
| Author |
Fridd CW, Linke CA, Barbaric Z, Elbadawi A, Carstensen EL. |
| Journal |
Invest Urol |
| Volume |
|
| Year |
1977 |
| Abstract |
The rabbit kidney was subjected to exposure from an unfocused ultrasound source in an effort to create a relatively large volume of ultrasound-damaged tissue in the rabbit kidney. The results of this exposure were followed for 1 year. An insignificant change in blood pressure was noted up to 1 month after exposure to ultrasound and no persistent hypertension was noted thereafter. Marked gross, histologic, and vascular changes were found in the area of exposure culminating in marked absorption of renal substance (in excess of 25 per cent of total kidney weight). Calcific stones formed in the pelvis of the kidney in virtually all animals observed from 6 months to 1 year after ultrasound exposure. These stones appeared to be related to the calcification within the transitional epithelium of tubules at the junction of normal and ultrasound-damaged tissue. The marked ability of the absorptive processes to ablate large volumes of physically damaged tissue is demonstrated. |
| Title |
Unified approach to the detection and classification of speckle texture in diagnostic ultrasound. |
| Author |
Wagner RF, Insana MF, Brown DG. |
| Journal |
Opt Eng |
| Volume |
|
| Year |
1986 |
| Abstract |
Second-order statistics have been derived for the speckle in diagnostic ultrasound that arises from diffuse (incoherent) scattering in the presence of distributed and organized specular (coherent) scattering. They serve as the basis for a three-dimensional feature space in which tissue textures can be classified. The covariance matrix of the measurements in this space is a generalization of the speckle spot number or sampling concept that arises in the study of signal or lesion detectability. |
| Title |
Unusual lipids. II. Head oil of the north atlantic pilot whale, Globicephala melaena melaena. |
| Author |
Blomberg J. |
| Journal |
Lipids |
| Volume |
|
| Year |
1974 |
| Abstract |
Pilot whale head oil (blackfish head oil, raw) was analyzed by means of IR spectroscopy, NMR, thin layer chromatography, and gas liquid chromatography-mass spectroscopy. The oil consisted of hydrocarbons (mainly pristane) (3%); waxes and cholesterol esters (9%); triglycerides (87%) (i.e., non-11%, mono-19%, and di-57% isovalero trigylcerides) and cholesterol and diglycerides (1%). By mass spectrometry, the diisovalero triglycerides where shown to be mainly symmetrical. Fatty acids were iso-branched or normal (only traces of ante-iso acids were found), saturated, or monounsaturated. Isovaleric acid predominated (54 mole % fatty acids), the rest having 10-18 carbon atoms. A 5-carbon fatty acid was the only acid found in the waxes. The alcohol composition qualitatively resembled that of the fatty acids, but major quantitative differences were present. This rules out direct interconversion of all fatty acids and alcohols. The possible role of these lipids in ultrasound transmission is discussed. |
| Title |
Update on safety of diagnostic.ultrasonography. |
| Author |
Miller DL. |
| Journal |
J Clin Ultrasound |
| Volume |
|
| Year |
1991 |
| Abstract |
Safety considerations for diagnostic ultrasonography have.gradually changed as new instruments, not only more powerful in performance but also in ultrasonic exposure, have come into use. Nonthermal cavitational bioeffects of ultrasound have a problematic role in risk assessment for clinical applications, but should serve as cautionary reminders that there potentially could.be low-level risks. Recent analyses have indicated possible areas.of concern related to the thermal mechanism of bioeffects, particularly if trends for higher intensities continue into the future. The most critical area of concern is in fetal examinations, for which developing bone is unavoidably heated by relatively powerful pulsed-Doppler beams. Fortunately, because of the threshold nature of thermal damage, development of flexible, use-driven upper limits on output should completely resolve this impending safety problem. The ultrasonics community is now responding to these evolving safety issues with improved.instrument characterization standards, new bioeffects research, and initiatives in continuing education for sonographers. |
| Title |
Use of amplitude-modulated focused ultrasound for diagnosis of hearing disorders. |
| Author |
Tsirulnikov EM, Vartanyan IA, Gersuni GV, Rosenblyum AS, Pudov VI,Gavrilov LR. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1988 |
| Abstract |
Focused ultrasound with a frequency of 2.5 MHz and amplitude-modulated in the range of.audiometric frequencies (125-8000 Hz) was employed to examine 50 normal hearing persons.and in complex diagnostics of over 500 patients suffering from sensorineural deafness,.otosclerosis, chronic otitis media, and acoustic neurinoma. Typical diagnostic signs of these.diseases were revealed. Modulated ultrasound is shown to offer an improved diagnosis of.hearing diseases. The results confirm the previous observation that amplitude-modulated.ultrasound may excite not only the acoustic receptors but also the acoustic nerve fibres. Possible.mechanisms of the stimulating effect of focused modulated ultrasound are discussed. |
| Title |
Use of anthropomorphic compressed breast phantoms for comparing ultrasound beast imagers |
| Author |
Kelly-Fry E, Madsen EL, Frank GR. |
| Journal |
Arch Acoust |
| Volume |
|
| Year |
1991 |
| Abstract |
Two anthropomorphic breast phantoms were used to compare state-of the art ultrasound imagers. The phantoms mimic refractive effects at fat to nonfat boundaries, and include simulated and pathological structures like fibroadenomas, cysts, calcifications and malignant tumors. Images of those structures obtained by means of various ultrasound systems are compared and discussed. In conclusion, the authors recommend use anthropomorphic breast phantoms which simulate the acoustic characteristics of normal and pathological preast tissues to test ultrasound mammography systems prior to their routine use on patients. |
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