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BRL Abstracts Database |
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Your search for ultrasound produced 3296 results. Page 251 out of 330
| Title |
The combined effect of ultrasonic exposure and protein restriction on maternal and fetal mice. |
| Author |
Kim HL, Picciano MF, O'Brien WD Jr. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1983 |
| Abstract |
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. |
| Title |
The concentric-ring array for ultrasound hyperthermia: Combined mechanical and electrical scanning. |
| Author |
Ibbini MS, Cain CA. |
| Journal |
Int J Hyperthermia |
| Volume |
|
| Year |
1990 |
| Abstract |
While two-dimensional phased arrays can be electronically focused and steered in three dimensions without physically moving the applicator, they generally require a relatively large number of small transducer elements and, consequently, complex drive electronics. A configuration that does not require a large number of elements is that of a concentric-ring array. The field conjugation method can be used to produce a focal spot (or multiple spots) along the array axis. The resulting focal regions are very small and need to be steered transversely to heat tumours of typical size. However, steering the focused beam away from the array axis results in annular heating patterns which are often associated with undesired secondary foci (hot spots). In this paper, a method based on combining electrical and mechanical scanning using a concentric-ring applicator is presented. Advantages of the new method over the mechanically scanned fixed-focus transducers, currently in use, are pointed out. Computer simulations are conducted to investigate the possibility of heating different size tumours by appropriately combining the two scanning techniques. The bioheat transfer equation is solved numerically and temperature distributions associated with relevant heating patterns are presented and discussed. The simulations demonstrate the possibility of the combined technique to produce useful heating patterns which cannot be produced by either technique separately. |
| Title |
The cooling effect of liquid flow on the focussed ultrasound-induced heating in a simulated foetal brain. |
| Author |
Vella GJ, Humphrey VF, Duck FA, Barnett SB. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
2003 |
| Abstract |
There is a need to investigate the thermal effects of diagnostic ultrasound (US) to assist the development of appropriate safety guidelines for obstetric use. The cooling effect of a single liquid flow channel was measured in a model of human foetal brain and skull bone heated by a focussed beam of simulated pulsed spectral Doppler US. Insonation conditions were 5.7 microseconds pulses, repeated at 8 kHz from a focussed transducer operating with a centre frequency of 3.5 MHz, producing a beam of −6 dB diameter of 3.1 mm at the focus and power outputs of up to 255 ? 5 mW. Brain perfusion was simulated by allowing distilled water to flow at various rates in a 2 mm diameter wall-less channel in the brain soft tissue phantom material. This study established that the cooling effect of the flowing water; 1. was independent of the acoustic source power, 2. was more effective close to the flow channel, for example, there was a marked cooling at a distance of 1 mm and negligible cooling at a distance of 3 mm from the channel; and 3. initially increased at low flow rates, but further increase above normal perfusion had very little effect. |
| Title |
The dependence of ultrasound Doppler bandwidth on beam geometry. |
| Author |
Newhouse VL, Furgason ES, Johnson GF, Wolf DA. |
| Journal |
IEEE Trans Sonics Ultrason |
| Volume |
|
| Year |
1980 |
| Abstract |
The output spectrum of ultrasound Doppler flowmeters contains information about flow parameters such as degree of turbulence, flow velocity gradient, and direction. This information can be extracted if the effects of the sound beam geometry on the Doppler spectrum can be understood and controlled. Equations for calculating the Doppler output signal bandwidth caused by constant velocity flow through the waist of focused transducers and through the intermediate and far field of unfocused transducers are derived and experimentally verified in this paper. The results presented show how to minimize the bandwidth caused by beam geometry and thus maximize the accuracy of flow parameter estimation. It is also shown that the angle between flow and beam can be estimated from the Doppler bandwidth if the velocity gradient in the range cell is small enough and if flow is laminar. |
| Title |
The design of an ultrasound fixed array controller for use in hyperthermia. |
| Author |
Grethen DC. |
| Journal |
Thesis(MS): Univ of Illinois |
| Volume |
|
| Year |
1985 |
| Abstract |
No abstract available. |
| Title |
The design of an ultrasound phased array controller for use in hyperthermia. |
| Author |
Silverman SG. |
| Journal |
Thesis(MS): Univ of Illinois |
| Volume |
|
| Year |
1984 |
| Abstract |
No abstract available. |
| Title |
The design of protection circuitry for high-frequency ultrasound imaging systems. |
| Author |
Lockwood GR, Hunt JW, Foster FS. |
| Journal |
IEEE Trans UFFC |
| Volume |
|
| Year |
1991 |
| Abstract |
Transmission line lengths in the protection circuitry of a high-frequency (>20-MHz) ultrasound imaging system have an important effect on the frequency, amplitude, and bandwidth of the pulse-echo response of the system. A model that includes the transmission line lengths between the pulser, transducer, and receiver and the electromechanical properties of high-frequency transducers is used to illustrate the importance of correctly choosing these line lengths. An iterative optimization procedure for designing the protection circuitry for a broadband system is proposed. A theoretical and experimental analysis of the validity of this approach is reported for a 45-MHz PVDF transducer. |
| Title |
The detection of breast microcalcifications with medical ultrasound. |
| Author |
Anderson ME, Soo MS, Bentley RC, Trahey GE. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
1997 |
| Abstract |
Microcalcifications are small crystals of calcium apatites which form in human tissue through a number of mechanisms. The size, morphology, and distribution of microcalcifications are important indicators in the mammographic screening for and diagnosis of various carcinomas in the breast. Although x-ray mammography is currently the only accepted method for detecting microcalcifications, its efficacy in this regard can be reduced in the presence of dense parenchyma. Current ultrasound scanners do not reliably detect microcalcifications in the size range of clinical interest. The results of theoretical, simulation, and experimental studies focused on the improvement of the ultrasonic visualization of microcalcifications are presented. Methods for estimating the changes in microcalcification detection performance which result from changes in aperture geometry or the presence of an aberrator are presented. An analysis of the relative efficacy of spatial compounding and synthetic receive aperture geometries in the detection of microcalcifications is described. The impact of log compression of the detected image on visualization is discussed. Registered high resolution ultrasound and digital spot mammography images of microcalcifications in excised breast carcinoma tissue and results from the imaging of suspected microcalcifications in vivo are presented. .. |
| Title |
The detection of temperature induced structural changes in T4B and T7 bacteriophages by means of high precision acoustic velocity measurements. |
| Author |
Shilnikov GV, Khusainov AA, Sarvazyan AP, Williams AR. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1986 |
| Abstract |
High precision measurements of the velocity of 7-7.5 MHz ultrasonic waves in suspensions of both T4B and T7 bacteriophages as a function of temperature revealed the presence of a distinct transition in the physiological range of 35-45 degrees C. Data from acoustic measurements, sedimentation analysis and electron microscopy enabled us to identify this transition as being caused by the protein component of the phage and not the DNA. This transition does not depend on the position of the long tail fibers and may be part of some normal physiological process within the bacteriophage which presumably enhances its recognition and attachment to its host cell. |
| Title |
The development and present status of ultrasonic.encephalography. |
| Author |
White DN. |
| Journal |
Biomed Eng |
| Volume |
|
| Year |
1973 |
| Abstract |
When the first successful attempts were made fifteen years ago to image with ultrasonic reflection techniques two-dimensional tomographic slices of the internal bodily structures, it was widely believed that this new technique, which did not use ionising radiation, might replace many conventional X-ray examinations. With the possible exception of the use of ultrasonic tomography in obstetrics, this development has not occurred and it may be opportune to consider the reasons for this. As the author of this article has stated in the introduction to this book Ultrasonic Encephalography: "Because of the skull's acoustic properties, the problems encountered in developing ultrasound for diagnostic purposes in medicine are seen to their greatest extent in encephalography." While these problems are greater in magnitude in applying ultrasonic techniques to the head, they are nevertheless the same as those that restrict its development for other bodily regions. For this reason a review of the development and present status of ultrasonic encephalography may be instructive; the restrictions the article's author describes and the lessons he has learned may be applicable to the development of ultrasonic techniques in other bodily regions that are not enclosed by a bony structure like the skull. |
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