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BRL Abstracts Database |
Your search for ultrasound produced 3296 results. Page 142 out of 330
Title |
Human pituitary irradiation with focused ultrasound: An initial report on effect in advanced breast cancer. |
Author |
Hickey RC, Fry WJ, Meyers R, Fry FJ, Bradbury JT. |
Journal |
Arch Surg |
Volume |
|
Year |
1961 |
Abstract |
No abstract available. |
Title |
Hybrid spectral domain method for attenuation slope estimation. |
Author |
Kim H, Varghese T. |
Journal |
Ultrasound Med Biol |
Volume |
|
Year |
2008 |
Abstract |
Attenuation estimation methods for medical ultrasound are important because attenuation properties of soft tissue can be used to distinguish between benign and malignant tumors and to detect diffuse disease. The classical spectral shift method and the spectral difference method are the most commonly used methods for the estimation of the attenuation; however, they both have specific limitations. Classical spectral shift approaches for estimating ultrasonic attenuation are more sensitive to local spectral noise artifacts and have difficulty in compensating for diffraction effects because of beam focusing. Spectral difference approaches, on the other hand, fail to accurately estimate attenuation coefficient values at tissue boundaries that also possess variations in the backscatter. In this paper, we propose a hybrid attenuation estimation method that combines the advantages of the spectral difference and spectral shift methods to overcome their specific limitations. The proposed hybrid method initially uses the spectral difference approach to reduce the impact of system-dependent parameters including diffraction effects. The normalized power spectrum that includes variations because of backscatter changes is then filtered using a Gaussian filter centered at the transmit center frequency of the system. A spectral shift method, namely the spectral cross-correlation algorithm is then used to compute spectral shifts from these filtered power spectra to estimate the attenuation coefficient. Ultrasound simulation results demonstrate that the estimation accuracy of the hybrid method is better than the centroid downshift method (spectral shift method), in uniformly attenuating regions. In addition, this method is also stable at boundaries with variations in the backscatter when compared with the reference phantom method (spectral difference method). Experimental results using tissue-mimicking phantom also illustrate that the hybrid method is more robust and provides accurate attenuation estimates in both uniformly attenuating regions and across boundaries with backscatter variations. The proposed hybrid method preserves the advantages of both the spectral shift and spectral difference approaches while eliminating the disadvantages associated with each of these methods, thereby improving the accuracy and robustness of the attenuation estimation. |
Title |
Hyperthermia by low-frequency synthesized ultrasound. |
Author |
Shina T, Saito M. |
Journal |
Proc Tenth Ann Int Conf IEEE Med Biol Soc |
Volume |
|
Year |
1988 |
Abstract |
In ultrasonic hyperthermia, hot spots are usually generated by focusing the ultrasonic beams. However, it is difficult to heat regions other than gas and bones owing to the attenuation and scattering of the ultrasonic beams. The authors propose an ultrasonic heating method in which low-frequency ultrasound is used to heat the depths of the body, and heat generation is localized by synthesizing an acoustic field from several incident waves. The heat generation and temperature distribution are analyzed using models with properties similar to tissue. |
Title |
Hyperthermia by ultrasound. |
Author |
Lele PP |
Journal |
Proc Int Symp Cancer Ther Hyperthermia Radiat - Washington D.C. |
Volume |
|
Year |
1975 |
Abstract |
No abstract available. |
Title |
Hysteresis as an interaction mechanism of ultrasound and tissues. |
Author |
Johnston RL, Dunn F. |
Journal |
Proc Second Meet World Fed Ultrasound Med Biol - Miyazaki |
Volume |
|
Year |
1979 |
Abstract |
No abstract available. |
Title |
ICARUS: Imaging pulse compression algorithm through remapping of ultrasound. |
Author |
Biagi E, Dreoni N, Masotti L, Rossi I, Scabia M. |
Journal |
IEEE Trans UFFC |
Volume |
|
Year |
2005 |
Abstract |
In this work, we tackle the problem of applying to echographic imaging, those synthetic aperture focusing techniques (SAFT) in the frequency domain commonly used in the field of synthetic aperture radars (SAR). The aim of this research is to improve echographic image resolution by using chirp transmit signals, and by performing pulse compression in both dimensions (depth and lateral). The curved geometry present in the unfocused radio-frequency (RF) ultrasonic image is the main cause of inaccuracy in the direct application of frequency domain SAFT algorithms to echographic imaging. The focusing method proposed in this work, after pulse compression in the depth dimension, performs lateral focusing in the mixed depth-lateral spatial frequency domain by means of a depth variant remapping followed by lateral pulse compression. This technique has the advantage of providing a resolution that is uniform in nonfrequency selective attenuation media, and improved with respect to conventional time domain SAFT, without requiring the acquisition and processing of channel data necessary for the most advanced synthetic transmit aperture techniques. Therefore, the presented method is suitable for easy real-time implementation with current generation hardware. |
Title |
Identification of mechanisms responsible for fetal weight reduction in mice following ultrasound exposure. |
Author |
Barnett SB, Williams AR. |
Journal |
Ultrasonics |
Volume |
|
Year |
1990 |
Abstract |
This study challenges existing interpretations of the effects of ultrasound on fetal development. The results demonstrated that a lower mean fetal weight in mice observed after intrauterine exposure to 2 MHz ultrasound resulted from maternal distress, and was not simply a direct effect of ultrasound interaction with the fetuses. At day 8 of gestation continuous wave ultrasound was applied to different regions of the maternal abdomen at spatial average intensities between 0.5 and 5.5 W cm-2 for 3 min. Insonating the uterus directly resulted in resorptions, abortions and gross developmental abnormalities, with rare instances of fetal weight reduction which were apparently associated with maternal distended bladder syndrome (DBS). When the ultrasound beam deliberately avoided the uterus, by a dorsal approach centred on the vertebral column, mean fetal weight at day 18 was significantly lower in all mothers showing DBS. Fetuses of insonated mothers not affected by DBS were not significantly different from the sham-insonated group whether the uterus was directly exposed or not. The fetal weight reduction endpoint was therefore found to be more closely correlated with maternal damage (DBS) than with ultrasound intensity. |
Title |
Identifying acoustic scattering sources in normal renal parenchyma from the anisotropy in acoustic properties. |
Author |
Insana MF, Hall TJ, Fishback JL. |
Journal |
Ultrasound Med Biol |
Volume |
|
Year |
1991 |
Abstract |
Acoustical and histological properties of dog kidney parenchyma are examined in vitro to determine sources of acoustic scattering in the normal kidney. The speed of sound, attenuation, backscatter, effective scatterer size and scattering strength were measured within the frequency range 1-15 MHz and at eight angles of incidence with respect to the predominant nephron orientation. Significant angular dependence, or anisotropy, was observed in backscatter coefficient and scattering strength estimates; attenuation was found to be weakly anisotropic. All three parameters, each measured at 19 degrees C, exhibited values that were maximum for perpendicular incidence and minimum for parallel incidence. Speed of sound and scatterer size estimates were observed to be independent of scanning angle. Comparisons between these data for renal cortex and histological observations suggest that the glomerulus is the principal scatterer at low frequencies, and renal tubules and blood vessels at high frequencies. |
Title |
Identifying acoustic scattering sources in normal renal parenchyma in vivo by varying arterial and ureteral pressures. |
Author |
Insana MF, Wood JG, Hall TJ. |
Journal |
Ultrasound Med Biol |
Volume |
|
Year |
1992 |
Abstract |
Ultrasonic backscatter properties of normal dog kidney parenchyma are examined in vivo to determine sources of acoustic scattering. We systematically varied the renal perfusion and ureteral pressures to obtain detailed information about scattering sources that could not be seen under in vitro conditions. These data suggest that in normal parenchyma the principal sources of backscatter are Bowman's capsule at low frequencies (2.5-5.0 MHz) and glomerular arterioles at high frequencies (5.0-15.0 MHz). We found that the integrated backscatter coefficient (IBC) in normally perfused kidney cortex is approximately half that measured in the ischemic organ at all frequencies. Ischemia was found to reduce scatterer size estimates (D) by 10% at low frequencies and increase D54% at high frequencies. Acute obstruction of the kidney, under diuresis, produced an 11% increase in D at low frequencies, and no significant change in D at high frequencies. These variations in backscatter measurements are explained in terms of changes in the microscopic anatomy of the kidney. .. |
Title |
Identifying ultrasonic scattering sites from three-dimensional impedance maps. |
Author |
Mamou J, Oelze ML, O'Brien WD Jr, Zachary JF. |
Journal |
J Acoust Soc Am |
Volume |
|
Year |
2005 |
Abstract |
Ultrasonic backscattered signals contain frequency-dependent information that is usually discarded to produce conventional B-mode images. It is hypothesized that parametrization of the quantitative ultrasound frequency-dependent information (i.e., estimating scatterer size and acoustic concentration) may be related to discrete scattering anatomic structures in tissues. Thus, an estimation technique is proposed to extract scatterer size and acoustic concentration from the power spectrum derived from a three-dimensional impedance map (3DZM) of a tissue volume. The 3DZM can be viewed as a computational phantom and is produced from a 3D histologic data set. The 3D histologic data set is constructed from tissue sections that have been appropriately stained to highlight specific tissue features. These tissue features are assigned acoustic impedance values to yield a 3DZM. From the power spectrum, scatterer size and acoustic concentration estimates were obtained by optimization. The 3DZM technique was validated by simulations that showed relative errors of less than 3% for all estimated parameters. Estimates using the 3DZM technique were obtained and compared against published ultrasonically derived estimates for two mammary tumors, a rat fibroadenoma and a 4T1 mouse mammary carcinoma. For both tumors, the relative difference
between ultrasonic and 3DZM estimates was less than 10% for the average scatterer size. |
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