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BRL Abstracts Database |
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Your search for ultrasound produced 3296 results. Page 125 out of 330
| Title |
Feasibility of using ultrasound phased arrays for MRI monitored noninvasive surgery. |
| Author |
Hynynen K, Chung A, Fjield T, Buchanan M, Daum D, Colucci V, Lopath P, Jolesz F. |
| Journal |
IEEE Trans UFFC |
| Volume |
|
| Year |
1996 |
| Abstract |
The purpose of this paper was to evaluate the in vivo feasibility of using phased arrays for MRI guided ultrasound surgery. Two different array concepts were investigated: a spherically curved concentric ring array to move the focus along the central axis and a spherically curved 16 square element array to make the focus larger. Rabbit thigh muscles were exposed in vivo in a 1.5 T MRI scanner to evaluate the array performance. The results showed that both of the arrays performed as expected, and the focus could be moved and enlarged. In addition, adequate power could be delivered from the arrays to necrose in vivo muscle tissue in 10 s. This study was the first implementation of phased arrays for MRI guided ultrasound surgery. The results demonstrate that phased arrays have significant potential for noninvasive tissue coagulation. |
| Title |
Fetal depth and ultrasound path lengths through overlying tissues. |
| Author |
Carson PL, Rubin JM, Chiang EH. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1989 |
| Abstract |
Measurements of minimum thicknesses, in a four-layer, overlying tissue model, on 22 pregnancies between 15 and 20 weeks gestation, yielded a global minimum and a mean of the minimum total thickness per patient of 1.7 and 2.9 cm, respectively, and a minimum and mean subcutaneous fat thickness of 0.7 and 1.4 cm. Conservative calculations of the minimum attenuation per patient, at 3.5 MHz indicated that less than 2.5% of 15 to 20 week pregnancies should fall below the lower 95% prediction line of: Attenuation (dB) = 0.10 x Maternal Weight (kg) - 3.0. The smallest calculated attenuation for any of the 21 subjects was 0.8 dB/MHz indicating just under a factor of two protection at 3.5 MHz of proximal fetal tissues compared with ultrasound intensities measured in water. This value is lower than those generally used in the past. The knowledge of distributions of transducer-to-fetal distances and thicknesses of overlying tissues is also important for improvement of image quality. Measurement of minimum depth of the anterior fetal thorax in 57 examinations of 25 to 40 week fetuses yielded minimum and mean values of 2.5 and 4.1 cm, respectively. |
| Title |
Fetal portraiture helps to align ultrasound with traditional medicine. |
| Author |
Birnholz JC. |
| Journal |
Diagn Imaging |
| Volume |
|
| Year |
1986 |
| Abstract |
No abstract available. |
| Title |
Fetal response to ultrasound. |
| Author |
Ruzinsky B. |
| Journal |
Appl Radiol |
| Volume |
|
| Year |
1980 |
| Abstract |
No abstract available. |
| Title |
Fetal ultrasound: How safe? |
| Author |
Arehart-Treichel J. |
| Journal |
Sci News |
| Volume |
|
| Year |
1982 |
| Abstract |
Diagnostic ultrasound exposure before birth doesn't seem to pose any immediate major health problems. However, the possibility of it exerting subtle or long-range health problems remains to be ruled out. |
| Title |
Fetal umbilical artery flow velocity waveforms and placental resistance: pathological correlation. |
| Author |
Giles WB, Trudinger BJ, Baird PJ. |
| Journal |
Br J Obstet Gynaecol |
| Volume |
|
| Year |
1985 |
| Abstract |
Placental microvascular anatomy was correlated with antenatal assessment of the umbilical circulation in 106 patients to further validate the measurement of the A/B ratio (the ratio of peak systolic to least diastolic flow velocity) of the umbilical artery flow velocity time waveforms as an index of blood flow resistance. Three groups of patients were studied: a normal group of 38 uncomplicated pregnancies, a control group of 33 potentially 'at risk' pregnancies with a normal A/B ratio matched by risk factors and gestation with the third group of 35 pregnancies with a high A/B ratio. Placental arterial resistance was quantitated by counting the number of small muscular arteries (less than 90 micron diameter) in the tertiary stem villi in a standard microscopic field (mean 18.5 fields/placenta). The modal small arterial vessel count was shown to be significantly less in the group with a high fetal risk and a high A/B ratio (1-2 arteries/field) than in both the normal and control groups (7-8 arteries/field). The tertiary villus count did not vary between groups. Antenatal studies of umbilical artery flow velocity waveforms with Doppler ultrasound identify a specific microvascular lesion in the placenta characterized by obliteration of small muscular arteries in the tertiary stem villi. |
| Title |
Fetal umbilical venous flow measured in utero by pulsed Doppler and B-mode ultrasound. I. Normal pregnancies. |
| Author |
Gill RW, Trudinger BJ, Garrett WJ, Kossoff G, Warren PS. |
| Journal |
Am J Obstet Gynecol |
| Volume |
|
| Year |
1981 |
| Abstract |
Umbilical venous blood flow was measured with a pulsed Doppler unit, which was used in combination with a B-mode ultrasonic imaging system to permit location of the umbilical vein and measurement of its cross-sectional area. The accuracy and limitations of the method are discussed. Forty-seven normal fetuses with gestational ages ranging from 22 weeks to term were studied on a total of 61 occasions. Flow increased with gestational age until 36 weeks, was maximal between 37 and 38 weeks, then decreased during the last 2 weeks of pregnancy. Flow per unit of fetal weight was constant during pregnancy until 36 to 37 weeks, when a reduction occurred. |
| Title |
Field conjugate acoustic lenses for ultrasound hyperthermia. |
| Author |
Lalonde RJ, Worthington A, Hunt JW. |
| Journal |
IEEE Trans UFFC |
| Volume |
|
| Year |
1993 |
| Abstract |
Ultrasonic phased arrays are capable of producing both simple foci and complex, multipoint foci using the pseudo-inverse field conjugation method [1]. We have synthesized multipoint foci by applying the field conjugation method to a single transducer coupled to a polystyrene lens. The lens design is based on phased array calculations, then fabricated on a computer-controlled milling machine. The measured beam patterns from the lenses agree closely with the beam patterns predicted from theory for the equivalent phased arrays. Temperature distributions from thermal modeling and measured in tissue equivalent phantoms show the lens system is capable of generating strongly localized, controlled temperature fields for hyperthermia. |
| Title |
Field measurements of ultrasonic diagnostic equipment. |
| Author |
Masao I. |
| Journal |
Proc Second Joint Meet ASA ASJ |
| Volume |
|
| Year |
1988 |
| Abstract |
Recent progress and popularization of ultrasonic diagnostic equipment are remarkable, and the standardization of this equipment, especially of its acoustic output which is related to bioeffects, has become important. IEC began by dealing with the standardization the measuring methods of acoustic fields. Studies on methods of measuring acoustic fields of diagnostic equipment have been made by such researchers as R.C. Preston, G.R. Harris, P.A. Lewin, and M. Ide, and others [IEEE Trans. Ultrason. Ferroelec. Freq. Contr. 35(1988)].. Since the field irradiated from the diagnostic equipment is pulsed ultrasound, method, at present, is the planar scanning method using a small hydrophone. Using this method, the values of the main parameters can be obtained relatively easily. This paper mainly shows this type of measuring relatively easily. This paper mainly shows this type of measuring method in the laboratory. By scanning a small hydrophone in water in three dimensions, the acoustic pressure the spatial and temporal parameters are computed. Examples of measured acoustic data from ultrasonic diagnostic equipment merchandised in Japan are shown. |
| Title |
Filter-based coded-excitation system for high-speed ultrasonic imaging. |
| Author |
Shen J, Ebbini ES. |
| Journal |
IEEE Trans Med Imaging |
| Volume |
|
| Year |
1998 |
| Abstract |
We have recently presented a new algorithm for high-speed parallel processing of ultrasound pulse-echo data for real-time three-dimensional (3-D) imaging. The approach utilizes a discretized linear model of the echo data received from the region of interest (ROI) using a conventional beam former. The transmitter array elements are fed with binary codes designed to produce distinct impulse responses from different directions in ROI. Image reconstruction in ROI is achieved with a regularized pseudoinverse operator derived from the linear receive signal model. The reconstruction operator can be implemented using a transversal filter bank with every filter in the bank designed to extract echoes from a specific direction in the ROI. The number of filters in the bank determines the number of image lines acquired simultaneously. In this paper, we present images of a cyst phantom reconstructed based on our formulation. A number of issues of practical significance in image reconstruction are addressed. Specifically, an augmented model is introduced to account for imperfect blocking of echoes from outside the ROI. We have also introduced a column-weighting algorithm for minimizing the number of filter coefficients. In addition, a detailed illustration of a full image reconstruction using subimage acquisition and compounding is given. Experimental results have shown that the new approach is valid for phased-array pulse-echo imaging of speckle-generating phantoms typically used in characterizing medical imaging systems. Such coded-excitation-based image reconstruction from speckle-generating phantoms, to the best of our knowledge, have not been reported previously. |
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