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BRL Abstracts Database |
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Your search for ultrasound produced 3296 results. Page 63 out of 330
| Title |
Changes of potentials and temperature gradients in membranes caused by ultrasound. |
| Author |
Lehmann JF, Biegler R. |
| Journal |
Arch Phys Med Rehabil |
| Volume |
|
| Year |
1954 |
| Abstract |
In this paper Lehmann recognizes that important biophysical events may occur at, or otherwise involve, the ubiquitous biological membrane and strongly urges that they studied. In this early work both mechanical and thermal events were identified as possible explanations for the observed potential changes across the membrane. The former is attributed to a stirring effect which depletes concentration gradients at the membrane surface. The latter affected electric charges on membrane proteins. |
| Title |
Changes produced in the central nervous system by ultrasound. |
| Author |
Wall PD, Fry WJ, Stephens R, Tucker D, Lettvin JY. |
| Journal |
Science |
| Volume |
|
| Year |
1951 |
| Abstract |
No abstract available. |
| Title |
Channel defect detection in food packages using integrated backscatter ultrasound imaging. |
| Author |
Raum K, Ozguler A, Morris SA, O'Brien WD Jr. |
| Journal |
IEEE Trans UFFC |
| Volume |
|
| Year |
1998 |
| Abstract |
Hermetically-sealed flexible food packages require very effective seal integrity testing to extend the shelf stability of thermally processed food. The initial goal of this study was to estimate the detection limits of laboratory-generated channels which simulate defects in food packages using pulse-echo ultrasonic imaging techniques. Packages with well characterized (via transmission optical microscopy) laboratory-generated channels that simulate defects with diameters between 9 and 325 ?m in the seal plane traversing the major axis of the heat seal were generated in heat-sealed microwavable retort-pouch plastic film (trilaminate). Pulse-echo techniques in the 13-17 MHz center frequency range were investigated. The samples were examined with a conventional B-mode imaging technique, which was found to be inadequate for subwavelength imaging of the types of typical channel defects found in shelf-stable food packages. Based on conventional B-mode image features, a new goal of this study was established to develop and evaluate an imaging technique which would exhibit subwavelength imaging capabilities. The new imaging technique called backscattered amplitude integral (BAI) is introduced here. It was observed that BAI-mode imaging has the ability for subwavelength detection of channel defects, e.g., detection of a 10?m diameter channel defect at a center frequency of 13.1 MHz (λ = 182 ?m). |
| Title |
Characteristics of absorption and energy transfer of microwaves and ultrasound in tissues. |
| Author |
Schwan HP. |
| Journal |
Med Phys |
| Volume |
|
| Year |
1960 |
| Abstract |
No abstract available. |
| Title |
Characteristics of intracellular motion induced by ultrasound. |
| Author |
Dyer HJ, Nyborg WL. |
| Journal |
Proc Third Int Conf Med Electron |
| Volume |
|
| Year |
1960 |
| Abstract |
It was reported at the Second International Conference on Medical Electronics that localized intracellular movement of various kinds can be set up in plant cells via ultrasonic excitation of cell walls. Since that time more details have been obtained on the motions by employing high-speed cinematography. Events have been observed in cells of a variety of species, including ditchweed (Elodea sp.) leaves, onion (Allium cepa L.) epidermis, moss [Leptobryum pyriforme (L.) Schimper] protonemata, and Spirogyra sp. Filaments. Excerpts of the moving-picture films obtained were shown at the present Conference. The paper lists a few of the phenomena observed and discusses physical principles which appear to be involved. |
| Title |
Characteristics of the absorption of ultrasound by protein solutions. |
| Author |
Zaretskii AA, Zorina OM, Fursov KP, El'piner IE. |
| Journal |
Sov Phys Acoust |
| Volume |
|
| Year |
1972 |
| Abstract |
No abstract available. |
| Title |
Characteristics of the audio sound generated by ultrasound imaging systems. |
| Author |
Fatemi M, Alizad A, Greenleaf JF. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
2005 |
| Abstract |
Medical ultrasound scanners use high-energy pulses to probe the human body. The radiation force resulting from the impact of such pulses on an object can vibrate the object, producing a localized high-intensity sound in the audible range. Here, a theoretical model for the audio sound generated by ultrasound scanners is presented. This model describes the temporal and spectral characteristics of the sound. It has been shown that the sound has rich frequency components at the pulse repetition frequency and its harmonics. Experiments have been conducted in a water tank to measure the sound generated by a clinical ultrasound scanner in various operational modes. Results are in general agreement with the theory. It is shown that a typical ultrasound scanner with a typical spatial ?peak pulse-average intensity value at 2MHz may generate a localized sound-pressure level close to 100 dB relative to 20 ?Pa in the audible (<20 kHz) range under laboratory conditions. These findings suggest that fetuses may become exposed to a high-intensity audio sound during maternal ultrasound examinations. Therefore, contrary to common beliefs, ultrasound may not be considered a passive tool in fetal imaging. |
| Title |
Characteristics of the pulsed ultrasound field. |
| Author |
Wien KD, Harder D. |
| Journal |
Br J Cancer Suppl |
| Volume |
|
| Year |
1982 |
| Abstract |
Pulsed ultrasound fields show some quantitative differences from continuous fields. In order to support the analysis of bioeffects of pulsed ultrasound fields these differences are characterized. For each observation point, the sound pulse is.calculated by wavelet addition. The total pulse length has a maximum near the transducer surface, corresponding to large differences in acoustical pathlength from the surface elements. Accordingly, the spectrum varies strongly in the near field. In.the far field, pulse-length and spectrum are almost constant as long as frequency-dependent absorption is negligible. The radiation field at each point is described by the time integral of sound intensity over one pulse (energy transport per unit area) and by the corresponding "dose" (absorbed energy per unit volume in one pulse). Differences between the spatial distributions of these two quantities are mainly detectable in the near field, which is also the region where differences.between continuous and pulsed ultrasound (at the same centre frequency) are considerable. . |
| Title |
Characterization of benign and malignant solid breast masses: Harmonic versus nonharmonic 3D power doppler imaging. |
| Author |
Hsiao YH, Huang YL, Liang WM, Lin C, Kuo SJ, Chen DR. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
2009 |
| Abstract |
The aim of this study was to compare the diagnostic performance of nonharmonic ultrasound (US) and tissue harmonic imaging (THI) using three-dimensional (3D) power Doppler sonographic technique to classify benign and malignant breast tumors by vascularization. From January 2003 to February 2004, we evaluated 200 patients and one of lobular carcinoma in situ was excluded from the malignant category. One hundred and ninety-nine subjects were enrolled. All subjects with one or more breast masses were studied with 3D power Doppler US nonharmonic and harmonic technologies. Sixteen of 199 subjects were excluded because masses exceeded 3 cm limit of our US probe's footprint (n = 5) or no harmonic Doppler information (n = 11). A total of 97 benign and 86 pathologically proven malignant breast tumor images were analyzed. 3D power Doppler US imaging was performed using a Voluson730 US system. Three histogram indices, the vascularization index (VI), flow index (FI) and vascularization-flow index (VFI), on both nonharmonic and harmonic images were calculated for the intratumor and for shells with an outside thickness of 3 mm surrounding the breast lesion. A multilayer perception (MLP) neural network classifier used the vascularity indices to determine whether the breast tumors are benign or malignant. The receiver operating characteristic (ROC) curves are performed to estimate the diagnostic performances for nonharmonic and harmonic methods. ROC curve analysis used overall age, volume, VI, FI and VFI for both intratumor and shells with an outside thickness of 3 mm surrounding the breast lesions in nonharmonic US and THI. The area under the ROC curve (A(Z)) was 0.9086 and 0.9009 (p = 0.3770). The sensitivity was 90.7% and 83.7% (p = 0.72), respectively, and the specificity was 92.8% and 92.8% (p = 1.00), respectively. In conclusion, the performance of 3D power Doppler US with respect to the characterization of solid breast masses as benign or malignant was not significantly improved with tissue harmonic imaging.
|
| Title |
Characterization of cavitational activity in lithotripsy fields using a robust electromagnetic probe. |
| Author |
Pye SD, Dineley JA. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1999 |
| Abstract |
A robust electromagnetic probe has been used to investigate cavitational activity in vitro in the fields of two extracorporeal lithotripters and one intracorporeal lithotripter. Some aspects of the electromagnetic probe design and characteristics are described. A series of experiments have been carried out with results indicating that the probe head moves in response to the pressure gradient generated by radial motion of cavitation bubbles. Empirical expressions have been derived for the cavitational force acting on the probe head, and for the low-frequency sawtooth pressure wave generated by inertial cavitation. This is the first time that the existence of a low-frequency sawtooth wave produced by inertial cavitation has been described. A linear relationship exists between the negative pressure amplitude of the sawtooth wave and the lifetime of the bubbles. Close to the cavitation site, substantial negative pressure is maintained throughout bubble expansion. This can easily exceed the tensile strength of urinary calculi, and may be considered to be an important mechanism for disintegrating these relatively weak structures. A pilot study has also been carried out involving three patients treated by extracorporeal lithotripsy. Signals similar to those recorded during the in vitro cavitation experiments were detected. We conclude that the electromagnetic probe is capable of detecting and quantifying aspects of cavitational activity in vitro, and potentially also in vivo. The observation that the probe responds directly to the motion of cavitation bubbles, coupled with its ability to detect cavitation at a distance, give it the potential for use in a range of medical and industrial applications. |
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