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BRL Abstracts Database |
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Your search for ultrasound produced 3296 results. Page 227 out of 330
| Title |
Shear wave elasticity imaging: a new ultrasonic technology of medical diagnostics. |
| Author |
Sarvazyan AP, Rudenko OV, Swanson SD, Fowlkes JB, Emelianov SY. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1998 |
| Abstract |
Shear wave elasticity imaging (SWEI) is a new approach to imaging and characterizing tissue structures based on the use of shear acoustic waves remotely induced by the radiation force of a focused ultrasonic beam. SWEI provides the physician with a virtual "finger" to probe the elasticity of the internal regions of the body. In SWEI, compared to other approaches in elasticity imaging, the induced strain in the tissue can be highly localized, because the remotely induced shear waves are attenuated fully within a very limited area of tissue in the vicinity of the focal point of a focused ultrasound beam. SWEI may add a new quality to conventional ultrasonic imaging or magnetic resonance imaging. Adding shear elasticity data ("palpation information") by superimposing color-coded elasticity data over ultrasonic or magnetic resonance images may enable better differentiation of tissues and further enhance diagnosis. This article presents a physical and mathematical basis of SWEI with some experimental results of pilot studies proving feasibility of this new ultrasonic technology. A theoretical model of shear oscillations in soft biological tissue remotely induced by the radiation force of focused ultrasound is described. Experimental studies based on optical and magnetic resonance imaging detection of these shear waves are presented. Recorded spatial and temporal profiles of propagating shear waves fully confirm the results of mathematical modeling. Finally, the safety of the SWEI method is discussed, and it is shown that typical ultrasonic exposure of SWEI is significantly below the threshold of damaging effects of focused ultrasound. |
| Title |
Shock-wave measurement using a calibrated interferometric fiber-tip sensor. |
| Author |
Koch C, Molkenstruck W, Reibold R. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1997 |
| Abstract |
The results of shock-wave measurements using a calibrated fiber-tip sensor based on a Michelson interferometer are presented. A transfer function, obtained by an. independent experiment that describes the properties of the sensor system, was used to correct the measured shock-wave data in the Fourier frequency domain. The phase. of the transfer function was determined from its amplitude by a fitting procedure using minimum-phase terms. As an example of application, the acoustic output field of. an electromagnetic lithotriptor was investigated, and the shock-wave source was reliably characterized. The measured data provide a basis for estimating the hazard to. which a patient is exposed during shock-wave treatment and for optimizing a lithotriptor system to produce a sharply localized and effective acoustic field. |
| Title |
Short- and long-term risks after exposure to diagnostic ultrasound in utero. |
| Author |
Stark CR Orleans M Haverkamp AD Murphy J. |
| Journal |
Obstet Gynecol |
| Volume |
|
| Year |
1984 |
| Abstract |
A total of 425 children exposed to diagnostic ultrasound at three Denver hospitals during the period May, 1968, through August, 1972, and 381 matched control children were studied for adverse effects at birth and again at a special examination.between seven and 12 years of age. Apgar scores, gestational age, head circumference, birth weight, length, congenital abnormalities, neonatal infection, and congenital infection were measured at birth. At seven to 12 years of age, measurements included conductive and nerve measurements of hearing, visual acuity and color vision, cognitive function, behavior, and a complete and detailed neurologic examination. No biologically significant differences between exposed and unexposed children were found. |
| Title |
Should there be upper limits to intensities for diagnostic ultrasound equipment? A panel discussion. |
| Author |
Nyborg WL, Buxbuam C, Carson PL. Carstensen EL, O'Brien WD Jr, Rooney JA, Stratmeyer ME, Taylor KJW. |
| Journal |
Reflections |
| Volume |
|
| Year |
1978 |
| Abstract |
No abstract available. |
| Title |
Signal processing strategies that improve performance and understanding of the quantitative ultrasound SPECTRAL FIT algorithm. |
| Author |
Bigelow TA, O'Brien WD Jr. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
2005 |
| Abstract |
Quantifying the size of the tissue microstructure using the backscattered power spectrum has had limited success due to frequency-dependent attenuation along the propagation path, thus masking the frequency dependence of the scatterer size. Previously, the SPECTRAL FIT algorithm was developed to solve for total attenuation and scatterer size simultaneously [Bigelow et al., J. Acoust. Soc. Am. 117, 1431?1439 (2005)]. Herein, the outcomes from signal processing strategies on the SPECTRAL FIT algorithm are investigated. The signal processing methods can be grouped into two categories, viz., methods that improve the performance of the algorithm and methods that provide insight. The methods that improve the performance include compensating for the windowing function used to gate the time-domain signal, averaging the spectra in the normal frequency domain rather than the log domain to improve the precision of the scatterer size and attenuation estimates, improving the selection of the usable frequency range for the SPECTRAL FIT algorithm, and improving the compensation for electronic noise. The methods that provide insight demonstrate that the anomalous rapid fluctuations of the backscattered power spectrum do not affect the SPECTRAL FIT algorithm, and accurate attenuation estimates can be obtained even when the correct scatterer geometry (i.e., form factor) is not known. |
| Title |
Signal processing techniques for improving b-mode echoencephalography. |
| Author |
Smith SW, Miller EB, von Ramm OT, Thurstone FL. |
| Journal |
Proc First Ultrasound Med Conf - Seattle |
| Volume |
|
| Year |
1974 |
| Abstract |
Lateral resolution, which can be described by the system point spread function, is a function of the relative phase variation introduced across the transducer aperture by the presence of the skull. A technique has been described (ibid., p.395-404) whereby this phase aberration can be measured by a secondary transducer and compensated for in a phased array imaging system. An alternative technique is described which requires no such a priori knowledge of the skull phase variation. This is accomplished by optimizing the transducer frequency and size, and by signal processing of the returning echoes. |
| Title |
Silicon micromachined ultrasonic immersion transducers. |
| Author |
Soh HT, Ladabam I, Atalar A, Quate CF, Khuri-Yakub BT. |
| Journal |
Appl Phys Lett |
| Volume |
|
| Year |
1996 |
| Abstract |
Broadband transmission of ultrasound in water using capacitive, micromachined transducers is reported. Transmission experiments using the same pair of devices at 4, 6, and 8 MHz with a signal‐to‐noise ratio greater than 48 dB are presented. Transmission is observed from 1 to 20 MHz. Better receiving electronics are necessary to demonstrate operation beyond this range. Furthermore, the same pair of transducers is operated at resonance to demonstrate ultrasound transmission in air at 6 MHz. The versatile transducers are made using silicon surface micromachining techniques. Computer simulations confirm the experimental results and are used to show that this technology promises to yield immersion transducers that are competitive with piezoelectric devices in terms of performance, enabling systems with 130 dB dynamic range. The advantage of the micromachined transducers is that they can be operated in high‐temperature environments and that arrays can be fabricated at lower cost. |
| Title |
Simulation of elastic wave scattering in cells and tissues at the microscopic level. |
| Author |
Doyle TE,Tew AT,Warnick KH,Carruth BL. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
2009 |
| Abstract |
The scattering of longitudinal and shear waves from spherical, nucleated cells and three-dimensional tissues with simple and hierarchical microstructures was numerically modeled at the microscopic level using an iterative multipole approach. The cells were modeled with a concentric core-shell (nucleus-cytoplasm) structure embedded in an extracellular matrix. Using vector multipole expansions and boundary conditions, scattering solutions were derived for single cells with either solid or fluid properties for each of the cell components. Tissues were modeled as structured packings of cells. Multiple scattering between cells was simulated using addition theorems to translate the multipole fields from cell to cell in an iterative process. Backscattering simulations of single cells indicated that changes in the shear properties and nuclear diameter had the greatest effect on the frequency spectra. Simulated wave field images and high-frequency spectra (15–75 MHz) from tissues containing 1211–2137 cells exhibited up to 20% enhancement of the field amplitudes at the plasma membrane, significant changes in spectral features due to neoplastic and other microstructural alterations, and a detection threshold of ~8.5% infiltration of tumor cells into normal tissue. These findings suggest that histology-based simulations may provide insight into fundamental ultrasound-tissue interactions and help in the development of new medical technologies.©2009 Acoustical Society of America
|
| Title |
Simulation of ultrasonic pulse propagation, distortion, and attenuation in the human chest wall. |
| Author |
Mast TD, Hinkelman LM, Metlay LA, Orr MJ, Waag RC. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
1999 |
| Abstract |
A finite-difference time-domain model for ultrasonic pulse propagation through soft tissue has been extended to incorporate absorption effects as well as longitudinal-wave propagation in cartilage and bone. This extended model has been used to simulate ultrasonic propagation through anatomically detailed representations of chest wall structure. The inhomogeneous chest wall tissue is represented by two-dimensional maps determined by staining chest wall cross sections to distinguish between tissue types, digitally scanning the stained cross sections, and mapping each pixel of the scanned images to fat, muscle, connective tissue, cartilage, or bone. Each pixel of the tissue map is then assigned a sound speed, density, and absorption value determined from published measurements and assumed to be representative of the local tissue type. Computational results for energy level fluctuations and arrival time fluctuations show qualitative agreement with measurements performed on the same specimens, but show significantly less waveform distortion than measurements. Visualization of simulated tissue-ultrasound interactions in the chest wall shows possible mechanisms for image aberration in echocardiography, including effects associated with reflection and diffraction caused by rib structures. A comparison of distortion effects for varying pulse center frequencies shows that, for soft tissue paths through the chest wall, energy level and waveform distortion increase markedly with rising ultrasonic frequency and that arrival-time fluctuations increase to a lesser degree. |
| Title |
Simulations of scanned focused ultrasound hyperthermia: The effects of scanning speed and pattern on the temperature fluctuations at the focal depth. |
| Author |
Moros EG Roemer RB Hynynen K. |
| Journal |
IEEE Trans UFFC |
| Volume |
|
| Year |
1988 |
| Abstract |
A transient three-dimensional simulation program has been developed to investigate the effects of scanning speed, scanning pattern, blood perfusion, and transducer choice on the temperature fluctuations that occur during scanned focused ultrasound hyperthermia treatments. The model uses the bioheat transfer equation with uniform tissue properties to solve for the temperature field. The results show that the largest temperature fluctuations are always located on the scanning path in the acoustical focal plane and that the temperature fluctuation pattern and magnitudes are essentially the same, regardless of the focal depth. The results also show that the magnitude of these temperature fluctuations increases linearly with increasing scan times (decreasing scanning speeds) and increases as a weak exponential with the magnitude of the blood perfusion rate. Moreover, the smaller the diameter of the focus of the power field, the larger the temperature fluctuations. To avoid temperature fluctuations inside the scanned volume, scan time of 10 s of less were needed when single 2-cm-diameter circular scans were simulated at practical blood flow values. The general trends predicted by the simulations agree with the trends present in previously reported experiments, indicating that the simulations could be an important tool in patient treatment planning and temperature field approximations. |
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