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BRL Abstracts Database |
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Your search for ultrasound produced 3296 results. Page 40 out of 330
| Title |
Animal toxicity studies with ultrasound at diagnostic power levels. |
| Author |
Smyth MG Jr. |
| Journal |
Diagn Ultrasound |
| Volume |
|
| Year |
1966 |
| Abstract |
No abstract available. |
| Title |
Anisotropy of high-frequency integrated backscatter from aortic valve cusps. |
| Author |
Khan Z, Boughner DR, Lacefield JC. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
2008 |
| Abstract |
The biaxial anisotropy of integrated backscatter from aortic valve cusps was characterized ex vivo as an initial assessment of the suitability of high-frequency ultrasound for nondestructive evaluation of fiber alignment in tissue-engineered heart valves. Apparent integrated backscatter (AIB) from eight fresh, intact porcine cusps was measured over an 80 degrees range of insonification angles using a 40-MHz ultrasound system. Angular dependence of backscatter was characterized by fitting a sinusoid to plots of AIB versus insonification angle for data acquired while rotating the transducer about the cusps in the circumferential and radial directions. Angular variations in backscatter were detected along both directions in individual specimens, although the mean amplitude of the fitted sinusoid was significantly greater for the circumferential data (12.1 +/- 2.6 dB) than the radial data (3.5 +/- 3.1 dB, p = 0.002). The higher angular variation of backscatter in the circumferential direction implies that collagen fibers in the fibrosa layer are the most prominent source of high-frequency scattering from porcine aortic valve cusps. The ability to characterize anisotropic backscattering from individual specimens demonstrates that high-frequency ultrasound can be used for nondestructive evaluation of fiber alignment in heart valve biomaterials. |
| Title |
Anisotropy of the ultrasonic backscatter of myocardial tissue: II. Measurements in vivo. |
| Author |
Madaras EI, Perez J, Sobel BE, Mottley JG, Miller JG. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
1988 |
| Abstract |
The purpose of this investigation was to determine the angular dependence of the backscatter from canine myocardial tissue in vivo and to compare it with the variation of backscatter over the cardiac cycle that has been recognized and reported previously. The backscatter was measured from regions of left ventricular wall in canine hearts in which the fibers of the muscle lay parallel to the surface of the heart and were oriented predominantly in a circumferential fashion. Because of.technical considerations, the angle of insonification was varied systematically through two cycles in which the angle relative to the muscle fiber axes ranged from 60 degrees-120 degrees. Backscatter was maximum at angles of interrogation.perpendicular to the myocardial fibers and minimum at those most acute (60 degrees) relative to the orientation of the fibers. The previously observed variation of integrated backscatter over the heart cycle was evident at each angle of interrogation. At end systole, the average maximum-to-minimum angular variation of integrated backscatter as 5.0 +/- 0.4 dB. At end diastole, the average maximum-to-minimum angular variation was 3.2 +/- 0.4 dB. Thus, even though angular dependence of the backscatter from tissues with directionally oriented structures is substantial, the anisotropy does not account for cardiac-cycle-dependent variation of backscatter. Accordingly, the angular dependence should be incorporated in approaches to quantitative tissue characterization with ultrasound. |
| Title |
Anisotropy of ultrasonic backscatter and attenuation from human calcaneus: Implications for relative roles of absorption and scattering in determining attenuation. |
| Author |
Wear KA. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
2000 |
| Abstract |
Although bone sonometry has been demonstrated to be useful in the diagnosis of osteoporosis, much remains to be learned about the processes governing the interactions between ultrasound and bone. In order to investigate these processes, ultrasonic attenuation and backscatter in two orientations were measured in 43 human calcaneal specimens in vitro at 500 kHz. In the mediolateral (ML) orientation, the ultrasound propagation direction is approximately perpendicular to the trabecular axes. In the anteroposterior (AP) orientation, a wide range of angles between the ultrasound propagation direction and trabecular axes is encountered. Average attenuation slope was 18% greater while average backscatter coefficient was 50% lower in the AP orientation compared with the ML orientation. Backscatter coefficient in both orientations approximately conformed to a cubic dependence on frequency, consistent with a previously reported model. These results support the idea that absorption is a greater component of attenuation than scattering in human calcaneal trabecular bone. |
| Title |
Annual progress report on research on the effect of ultrasound on nerve tissue. |
| Author |
Fry WJ, Dunn F, Kelly-Fry E. |
| Journal |
Rep Univ Ill - Urbana/Champaign Eng Exp Station |
| Volume |
|
| Year |
1957 |
| Abstract |
A) Since start of project. Ultrasonic instrumentation has been design and developed for the purpose of quantitatively irradiating tissue in the central nervous system. This apparatus, which is of a high precision nature, represents a considerable advance in acoustic instrumentation for use at high sound levels. This apparatus includes: 1) Multiple beam focusing irradiators capable of producing small focal spots. 2) Positioning systems for accurate placing of the focal region of the sound beams in the tissue. 3) Electronic equipment providing accurate reproducibility of ultrasonic dosages. 4) Equipment for studying the physical mechanism of the action of the sound. This apparatus enables the preparation to be irradiated at a variety of temperatures under a range of hydrostatic pressures and at various frequencies. A new laboratory which houses the prototype instrument for human neurosonicsurgery was completed and put into operation. This four room laboratory constitutes a complete unit of the most advanced type for precision neurological studies using high intensity ultrasound as a basic research tool. A technical movie illustrating the complete instrumentation in operation, the preparation of the animal for irradiation, the calibration of the sound field, the technique of irradiation, and stained tissue sections illustrating ultrasonic lesions, was prepared and exhibited at number of scientific meetings and has been shown to scientific audiences in several countries. Extensive histological studies of ultrasonically produced lesions in the brains of cats have furnished information concerning the time course of changes produced in various tissue components of the central nervous system by exposure to high level ultrasound. |
| Title |
Annular and Cylindrical Phased Array Geometries for Transrectal High-Intensity Focused Ultrasound (HIFU) using PZT and Piezocomposite Materials |
| Author |
R. Seip, W. Chen, R. Carlson, L. Frizzell, G. Warren, N. Smith, K. Saleh, G. Gerber, K. Shung, H. Guo, N.T. Sanghvi |
| Journal |
AIP Conf Proc |
| Volume |
|
| Year |
2004 |
| Abstract |
This paper presents engineering progress and the latest in‐vitro and in‐vivo results obtained with a 4.0 MHz, 20 element, PZT annular transrectal HIFU array and several 4.0 MHz, 211 element, PZT and piezocomposite cylindrical transrectal HIFU arrays for the treatment of prostate cancer. The geometries of both arrays were designed and analyzed to steer the HIFU beams to the desired sites in the prostate volume using multi‐channel electronic drivers, with the intent to increase treatment efficiency and reliability for the next generation of HIFU systems. The annular array is able to focus in depth from 25 mm to 50 mm, generate total acoustic powers in excess of 60W, and has been integrated into a modified Sonablate®500 HIFU system capable of controlling such an applicator through custom treatment planning and execution software. Both PZT‐ and piezocomposite cylindrical arrays were constructed and their characteristics were compared for the transrectal applications. These arrays have been installed into appropriate transducer housings, and have undergone characterization tests to determine their total acoustic power output, focusing range (in depth and laterally), focus quality, efficiency, and comparison tests to determine the material and technology of choice (PZT or piezocomposite) for intra‐cavity HIFU applications. Array descriptions, characterization results, in‐vitro and in‐vivo results, and an overview of their intended use through the application software is shown. © 2005 American Institute of Physics |
| Title |
Annular array design and logarithmic processing for ultrasonic imaging. |
| Author |
Melton HE Jr., Thurstone FL. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1978 |
| Abstract |
The design of an annular array for electronic focal scanning depends upon the frequency of operation, a suitable limit of lateral resolution and the number and size of the elements of the array. The frequency is determined by considering (1) the frequency dependent attenuation caused by the tissues of interest, (2) the limiting characteristic of the receiver and (3) its equivalent input noise. The array size is determined by (1) the operating frequency, (2) the method of scanning and (3) a suitable limit of lateral resolution. Unusual resolution capability is realized with only five elements, equally spaced in the array, and with logarithmic signal processing in the receiver. |
| Title |
Anthropomorphic breast phantoms for assessing ultrasonic imaging system performance and for training ultrasonographers: part II. |
| Author |
Madsen EL, Zagzebski JA, Frank GR, Greenleaf JF, Carson PL. |
| Journal |
J Clin Ultrasound |
| Volume |
|
| Year |
1982 |
| Abstract |
Three prototype anthropomorphic breast phantoms are discussed. The phantoms were.constructed using ultrasonically tissue-mimicking materials; these materials mimic various tissue parenchymae in terms of attenuation, speed of sound, density, and.scatter level. Realistic artifacts related to refraction and reflection at interfaces between.different simulated parenchymae are produced. The phantoms represent.premenopausal breasts, and they complement one another. Two of them represent the.dense breasts of women under 30 years of age, and one represents that of a woman.between 35 and 40 years of age. Of the former two, one produces what is apparently.above-average refraction effects in the region of the peripheral fat layer; the other.produces more typical refraction effects. Simulated tumors, cysts, and calcifications.of various sizes are suspended in the glandular regions. Such phantoms are valuable.for use in developmental testing of state-of-the-art ultrasound machines, quality.assurance testing of clinical machines, and training of sonographers in breast.imaging. |
| Title |
Anthropomorphic phantoms for assessing systems used in ultrasound imaging of the compressed breast. |
| Author |
Madsen EL, Kelly-Fry E, Frank GR. |
| Journal |
Proc Ultrason Symp IEEE |
| Volume |
|
| Year |
1988 |
| Abstract |
Two anthropomorphic phantoms, simulating the breast as it is compressed against the chest wall during ultrasonic imaging, are described in detail regarding structural configurations and distributions of ultrasonic properties. The external shape of each phantom is that of a rectangular parallelepiped; this simple shape is consistent with the breast in the compressed configuration and also facilitates the inclusion of a considerable variety of simulated lesions including comparisons of imaging as a function of depth. One of the phantoms was completed about 4 1/2 years prior to this writing, and images made with scanners which were state-of-the-art in late 1983 and 1984 are compared with images made with two current state-of-the-art imagers. Improvements in imager quality over that period are apparent. The more recently produced phantom contains a simulated tumor with a complex structure as well as realistic simulated calcifications of various sizes. The tumor has a necrotic core and an irregularly shaped boundary. This boundary possesses a roughness intended to give rise to diffuse reflection. |
| Title |
Aortic compliance measurements using Doppler ultrasound: in vivo biochemical correlates. |
| Author |
Lehmann ED, Hopkins KD, Gosling RG. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1993 |
| Abstract |
A noninvasive Doppler ultrasound technique for the assessment of aortic compliance based on the in vivo measurement of pulse wave velocity along the thoraco-abdominal aortic pathway is described. An approach for correcting for the effect of blood pressure on aortic distensibility is considered. The derivation of an index of intrinsic distensibility, Cp, which is independent of blood pressure, is provided and applied to data collected from normal, healthy volunteers. Overviews are provided of studies utilising the technique to determine aortic compliance in medical disorders, which are known to predispose to premature cardiovascular disease, such as diabetes mellitus, familial hypercholesterolaemia and growth hormone deficiency. The significance of correlations between in vivo aortic compliance measurements and plasma concentrations of total cholesterol, low-density-lipoprotein cholesterol, high-density-lipoprotein cholesterol and insulin-like growth factor-I are discussed. It is proposed that the measurement of aortic compliance in normal, healthy individuals may potentially be a useful in vivo research tool for investigating the effects of biochemical factors on the biophysical properties of the aortic wall. Furthermore, we believe that the routine measurement of blood pressure-corrected aortic distensibility may prove a useful, noninvasive clinical tool for assessing patients' susceptibility to atherosclerosis, as well as for monitoring their response to therapeutic interventions. |
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