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BRL Abstracts Database |
Your search for ultrasound produced 3296 results. Page 286 out of 330
Title |
Ultrasonic attenuation and absorption in liver tissue. |
Author |
Parker KJ. |
Journal |
Ultrasound Med Biol |
Volume |
|
Year |
1983 |
Abstract |
A large range of values for ultrasonic attenuation and absorption coefficients of tissues are reported in the literature. An important distinction both practically and theoretically is the magnitude of the true absorption, which characterizes the rate of conversion of ultrasonic to thermal energy, as compared with the total attenuation of the ultrasonic signal as it propagates through tissue. The magnitudes of these quantities were studied in bovine liver. Total attenuation was measured, in the range of 1-6 MHz, by both phase sensitive and phase insensitive insertion loss techniques. Ultrasonic absorption was determined by two thermal techniques. The standard "transient thermoelectric" or rate-of-heating method, and a new measurement technique based on the temperature decay following a short ultrasonic pulse were employed for the determination of the ultrasonic absorption coefficient. The results demonstrate that the ultrasonic amplitude attenuation and absorption coefficients at low megahertz frequencies are not significantly different in liver. The mean values cluster around 0.05 nepers/cm/MHz (0.4dB/cm/MHz). The sample-to-sample variation is indicated by the standard deviation in the measurements of 0.01 nepers/cm/MHz (0.09dB/cm/MHz) or less. The results show that in liver tissue, absorption is the dominant feature of attenuation over this frequency range. |
Title |
Ultrasonic attenuation and propagation speed in mammalian tissues as a function of temperature. |
Author |
Bamber JC, Hill CR. |
Journal |
Ultrasound Med Biol |
Volume |
|
Year |
1979 |
Abstract |
Ultrasonic attenuation in the frequency range 1-7 MHz, and the speed of sound, were determined experimentally in both fresh and fixed bovine and human soft tissues for various temperatures in the range 5-65 C. At temperatures below 40 C the attenuation coefficient behaves similarly for fixed and fresh tissues where, at high frequencies, it has a negative dependence on temperature, the value at 20 C being about 21% higher than that at 37 C. As the frequency is reduced, the temperature coefficient of attenuation pregressively decreases until, after passing a transition frequency (this varies with the tissue specimens but is around 1-2 MHz), a positive dependence on temperature may be observed. At temperatures above about 40 C, the attenuation coefficient of freshly excised tissues increases with temperature, whereas for fixed tissues the attenuation coefficient continues to decrease. These observations help to resolve a possible discrepancy evident in previous reports of the temperature dependence of attenuation. The speed of sound in non-fatty tissues increases with temperature and exhibits a maximum at around 50 C, while for fatty tissues a negative dependence is observed. The implications of this result for improved diagnostic procedures is discussed. |
Title |
Ultrasonic attenuation estimation of the pregnant cervix: a preliminary report. |
Author |
McFarlin BL, Bigelow TA, Laybed Y, O'Brien WD, Oelze ML, Abramowicz JS. |
Journal |
Ultrasound Obstet Gynecol |
Volume |
|
Year |
2010 |
Abstract |
OBJECTIVE: Estimates of ultrasonic attenuation (the loss of energy as an ultrasonic wave propagates through tissue) have been used to evaluate the structure and function of tissues in health and disease. The purpose of this research was to develop a method to estimate ultrasonic cervical attenuation during human pregnancy using a clinical ultrasound system. METHODS: Forty women underwent a cervical scan once during pregnancy with the Zonare(R) z.one clinical ultrasound system using a 4-9-MHz endovaginal transducer. This ultrasound system provides access to radiofrequency (RF) image data for processing and analysis. In addition, a scan of a tissue-mimicking phantom with a known attenuation coefficient was acquired and used as a reference. The same settings and transducer used in the clinical scan were used in the reference scan. Digital data of the beam-formed image were saved in Digital Imaging and Communications in Medicine (DICOM) format on a flash drive and converted to RF data on a personal computer using a Matlab(R) program supplied by Zonare. Attenuation estimates were obtained using an algorithm that was independently validated using tissue-mimicking ultrasonic phantoms. RESULTS: RF data were acquired and analyzed to estimate attenuation of the human pregnant cervix. Regression analysis revealed that attenuation was: a predictor of the interval from ultrasound examination to delivery (beta = 0.43, P = 0.01); not a predictor of gestational age at time of examination (beta = - 0.23, P = 0.15); and not a predictor of cervical length (beta = 0.077, P = 0.65). CONCLUSIONS: Ultrasonic attenuation estimates have the potential to be an early and objective non-invasive method to detect interval between examination and delivery. We hypothesize that a larger sample size and a longitudinal study design will be needed to detect gestational age-associated changes in cervical attenuation. Copyright (c) 2010 ISUOG. Published by John Wiley & Sons, Ltd. |
Title |
Ultrasonic attenuation imaging in a rodent thyroid cancer model |
Author |
Zenteno O, Ridgway W, Sarwate S, Oelze M, Lavarello R |
Journal |
2013 Joint UFFC, EFTF and PFM Symposium |
Volume |
|
Year |
2013 |
Abstract |
The incidence of diagnosed thyroid cancer has increased significantly over the last decades. Although advances in ultrasonic imaging have increased the malignancy detection rate, current ultrasonic imaging markers do not provide a
sufficient level of diagnostic accuracy to replace biopsy. Recent studies suggest that ultrasound parameters derived from backscatter coefficients may allow differentiating among different types of thyroid tumors and normal tissues in a rodent model ex vivo. In this work, the potential use of attenuation
coefficient (AC) estimates for the same purpose was explored. A sample set of 24 excised mice thyroids were scanned using a 40-MHz, f/3 single element transducer. The experimental dataset contained six animals that developed papillary thyroid carcinoma (PTC), five that developed follicular variant papillary thyroid
carcinoma (FV-PTC), five that developed c-Cell adenoma (c-Cell) and eight that did not develop thyroid abnormalities (control). AC slope maps were generated with a spectral log difference method using 0.5mm by 0.5mm data blocks. Outliers of each slice due to artifacts in AC estimation were discarded using the
Thompson Tau method. Finally, a Kruskal-Wallis test was conducted to analyze if statistically significant differences in the mean AC slope among the four groups existed. The median and interquartile range for each group were 1.29 and 0.22 dB/cm-MHz for the control group, 1.64 and 0.09 dB/cm-MHz for c-Cell, 1.16 and 0.12 dB/cm-MHz for PTC and 1.33 and 0.08 dB/cm-MHz for FV-PTC, respectively. These values are consistent with previous reports of attenuation in thyroid tissues. The Kruskal-Wallis test reported statistically significant differences between the c-Cell group and the other groups of study and between the PTC and FV-PTC groups (p<0.05). These preliminary results suggest that the AC may be used to characterize thyroid tissues. |
Title |
Ultrasonic attenuation in human calcaneus from 0.2 to 1.7 MHz. |
Author |
Wear KA. |
Journal |
IEEE Trans UFFC |
Volume |
|
Year |
2001 |
Abstract |
Ultrasonic attenuation has been demonstrated to be a useful measurement in the diagnosis of osteoporosis. Most studies have employed ultrasound in a range of frequencies from about 200 kHz-300 kHz to 600 kHz-1 MHz, and many have assumed a linear dependence of attenuation on frequency. In order to investigate the attenuation properties of human calcaneus at higher frequencies, 16 defatted human calcanea were interrogated in vitro using two matched pairs of transducers with center frequencies of 500 kHz and 2.25 MHz. The linear dependence of attenuation on frequency seems to extend up to at least 1.7 MHz. The correlation between attenuation coefficient and frequency from 400 kHz to 1.7 MHz was r=0.999 (95% confidence interval, CI,=0.998-1.00). The measurements suggest that some deviations from linear frequency dependence of attenuation may occur at lower frequencies (below 400 kHz), however. |
Title |
Ultrasonic attenuation in human tissue. |
Author |
Chivers RC, Hill CR. |
Journal |
Ultrasound Med Biol |
Volume |
|
Year |
1975 |
Abstract |
A spectroscopic method of measuring attenuation is described and measurements of attenuation as a continuous function of frequency between 1.0 and 7.5 MHz presented for fixed human fat, liver, and spleen at 18 degrees C. These are compared with data from the literature, showing approximate agreement for liver, whilst for fat the values are significantly higher than those previously reported. |
Title |
Ultrasonic attenuation tomography based on log-spectrum analysis. |
Author |
Jirik R, Stotzka R, Taxt T. |
Journal |
Ultrason Imaging |
Volume |
|
Year |
2005 |
Abstract |
The paper presents a new ultrasonic attenuation imaging method which might be used as a new imaging modality, targeted at breast cancer diagnostics. Two approaches based on ultrasonic imaging are combined together, namely the estimation of ultrasound attenuation coefficients from pulse-echo B-mode imaging data and an ultrasound computer tomography imaging technique. A recently published method for estimation of the ultrasound attenuation coefficient using the log--spectrum analysis is applied to radiofrequency signals acquired by an ultrasound computer tomography system to estimate images of the attenuation coefficients. The examined volume (e.g. female breast) is enclosed by several thousand ultrasound transducers. Radiofrequency signals from all transducers using all sending positions are recorded. Compared to the known ultrasound attenuation tomography methods, not only the directly transmitted signal, but also the reflected and scattered signals are processed here, i.e. substantially more information is used. The method is presented in its initial stage. The applied algorithm is derived using simplifying assumptions which will be relaxed in further research. However, even at this stage the resulting attenuation image is of higher quality than the standard attenuation imaging methods applied to the same data set. |
Title |
Ultrasonic attenuation. |
Author |
Mackinnon L. |
Journal |
Contemp Phys |
Volume |
|
Year |
1962 |
Abstract |
Ultrasonic waves have been produced in the laboratory at frequencies up to 24 kMc/s. The mechanism of the absorption process is examined and the experimental measurement of attenuation coefficient is discussed. The types of research problem for which a study of ultrasonic attenuation may be useful are summarised. Particular attention is given to the low temperature absorption of megacycle ultrasound by electrons in metals; the magnetoacoustic effect and its usefulness in evaluating the Fermi surface are briefly described. |
Title |
Ultrasonic backscatter coefficients for weakly scattering, agar spheres in agar phantoms. |
Author |
King MR, Anderson JJ, Herd MT, Ma D, Haak A, Wirtzfeld LA, Madsen EL, Zagzebski JA, Oelze ML, Hall TJ, O'Brien WD Jr. |
Journal |
J Acoust Soc Am |
Volume |
|
Year |
2010 |
Abstract |
Applicability of ultrasound phantoms to biological tissue has been limited because most phantoms have generally used strong scatterers. The objective was to develop very weakly scattering phantoms, whose acoustic scattering properties are likely closer to those of tissues and then compare theoretical simulations and experimental backscatter coefficient (BSC) results. The phantoms consisted of agar spheres of various diameters (nominally between 90 and 212 microm), containing ultrafiltered milk, suspended in an agar background. BSC estimates were performed at two institutions over the frequency range 1-13 MHz, and compared to three models. Excellent agreement was shown between the two laboratory results as well as with the three models. |
Title |
Ultrasonic backscattering from human tissue: A realistic model. |
Author |
Gore JC, Leeman S. |
Journal |
Phys Med Biol |
Volume |
|
Year |
1977 |
Abstract |
The propagation of ultrasound pulses in inhomogeneous media is described, and it is shown that they are scattered by fluctuation in density and compressibility. It is proposed that some of the echoes recorded by diagnostic pulse echo equipment are produced in this way. The precise form of the acoustic field backscattered from tissues is calculated using realistic approximations about the nature of tissue inhomogeneities and the form of the pulses used. It is shown that only limited information about tissue structure is contained in these signals, and the restrictions imposed by the use of typical pulses are indicated. The implications of this analysis for methods of tissue characterization and clinical imaging are discussed. |
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