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BRL Abstracts Database |
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Your search for ultrasound produced 3296 results. Page 88 out of 330
| Title |
Difference-frequency ultrasound generation from microbubbles under dual-frequency excitation. |
| Author |
Ma QY, Qiu YY, Huang B, Zhang D, Gong XF. |
| Journal |
Chin Phys B |
| Volume |
|
| Year |
2010 |
| Abstract |
The difference-frequency (DF) ultrasound generated by using parametric effect promises to improve detection depth owing to its low attenuation, which is beneficial for deep tissue imaging. With ultrasound contrast agents infusion, the harmonic components scattered from the microbubbles, including DF, can be generated due to the nonlinear vibration. A theoretical study on the DF generation from microbubbles under the dual-frequency excitation is proposed in formula based on the solution of the RPNNP equation. The optimisation of the DF generation is discussed associated with the applied acoustic pressure, frequency, and the microbubble size. Experiments are performed to validate the theoretical predictions by using a dual-frequency signal to excite microbubbles. Both the numerical and experimental results demonstrate that the optimised DF ultrasound can be achieved as the difference frequency is close to the resonance frequency of the microbubble and improve the contrast-to-tissue ratio in imaging. |
| Title |
Differences in the attenuation of ultrasound by normal, benign, and malignant breast tissue. |
| Author |
Calderon C, Vilkomerson D, Mezrich R, Etzold KF, Kingsley B, Haskin M. |
| Journal |
J Clin Ultrasound |
| Volume |
|
| Year |
1976 |
| Abstract |
In quantitative measurements of the attenuation of ultrasound in 18 samples of variously normal, benign, and malignant breast tissue, we found significantly different ranges of attenuation. As observed in previous in vivo studies, with the.exception of medullary carcinoma, malignant tissue produces the most attentuation of ultrasound in the frequency range of 1.5 to 3.0 MHz we employed. The apparatus, measurement method, results, and the possible causes of the differences in.attenuation are presented. |
| Title |
Differential blocking of nerve conduction by vhf ultrasound. |
| Author |
Singer R. |
| Journal |
Thesis(MS):Massachusetts Institute of Technology |
| Volume |
|
| Year |
1971 |
| Abstract |
The relief of pain by differential blocking of peripheral nerves by ultrasonic irradiation,had previously been attempted at frequencies between 0.6 and 5.0 Mhz. In order to extend the range,an irradiation system is developed to insert 150 Mhz ultrasound into liquid media. This frequency has a wavelength intermediate between the 1μC fibers and the 10μC A fibers, and may therefore act on them discriminately when applied transversely.
The system is thermally calibrated in mineral oil. Its sonic efficiency is estimated from insertion loss measurements and verified by the comuputer solution of a mathematical model of the system.
Excised cat and monkey saphenous, and frog sciatic nerves are irradiated by 240 mW/cm2 in mineral oil. Differential blocking of the biphased detected C component of the compound action potential is observed,temporarily in all 25 nerves, and permanently in 8 of these specimens. The results although inconclusive,warrant further work. Improvements of the first generation system and additional experiments are proposed in detail.
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| Title |
Differential diagnosis of chronic spenomegly by grey-scale ultrasonography: Clinical observations and digital A-scan analysis. |
| Author |
Taylor JW, Milan J. |
| Journal |
Br J Radiol |
| Volume |
|
| Year |
1976 |
| Abstract |
Hitherto, ultrasound examination of the spleen has been limited to the determination of size and position. Grey-scale ultrasonography involves enhanced signal-to-noise ratio so that the soft-tissue texture is displayed, and this permits the recognition of diffusely abnormal consistency. This facility was used to predict lymphomatous involvement of the spleen in patients coming to laparotomy in whom an accuracy of 77-8 per cent was achieved. Three types of splenic consistency are described in a series of 60 patients presenting with chronic splenomegaly: Very low-level echoes emanate from malignantly involved spleens. Medium-level echoes are found in various benign conditions and high-level echoes occur in various chronic inflammatory conditions. These differences were confirmed and quantitated by computerized A-scan analysis. |
| Title |
Differentiation and characterization of rat mammary fibroadenomas and 4T1 mouse carcinomas using quantitative ultrasound imaging. |
| Author |
Oelze ML, O'Brien WD Jr, Blue JP, Zachary JF. |
| Journal |
IEEE Trans Med Imaging |
| Volume |
|
| Year |
2004 |
| Abstract |
Scatterer properties like the average effective scatterer diameter and acoustic concentration were determined in vivo using a quantitative ultrasound (QUS) technique from two tumor phenotypes grown in animal models. These tumor models included spontaneously occurring mammary fibroadenomas in rats and transplanted 4T1 mammary carcinomas in mice. The scatterer properties of average scatterer diameter and acoustic concentration were estimated using a Gaussian form factor from the backscattered ultrasound measured from both types of tumors. QUS images of the tumors were constructed utilizing estimated scatterer properties from regions in the tumors. The QUS images showed a clear distinction between the two types of tumors and a statistically significant difference existed between their estimated scatterer properties. The average scatterer diameter and acoustic concentration for the mammary fibroadenomas were estimated to be 105/spl plusmn/25 /spl mu/m and -15.6/spl plusmn/5 dB (mm/sup -3/), respectively. The average scatterer diameter and acoustic concentration for the carcinomas was estimated to be 28/spl plusmn/4.6 /spl mu/m and 10.6/spl plusmn/6.9 dB (mm/sup -3/), respectively. The distinctions in the scattering properties are clearly seen in the QUS images of the tumors and indicate that QUS imaging can be useful in differentiating between different types of mammary tumors. |
| Title |
Differentiation of breast tumors by ultrasonic tissue characterization. |
| Author |
Golub RM, Parsons RE, Sigel B, Feleppa EJ, Justin J, Zaren HA, Rorke M, Sokil-Melgar J, Kimitsuki H. |
| Journal |
J Ultrasound Med |
| Volume |
|
| Year |
1993 |
| Abstract |
The ability of ultrasonic tissue characterization to differentiate and classify benign and malignant breast tissues in vivo in patients with palpable breast masses and in vitro in excised breast tissue was evaluated. One-hundred and twenty-four in vivo and 89 in vitro studies were performed using a technique of UTC based on parameters from the power spectrum of backscattered echoes. Sensitivities and specificities for diagnosing carcinoma were 86 and 84% for in vivo studies and 94 and 92% for in vitro studies. These UTC parameters provided threshold values for color-coding breast lesion images. The results of this preliminary investigation suggest that UTC provides a basis for assessing more accurately lesions suspected of being malignant prior to biopsy and possibly for evaluating breast lesions noninvasively... |
| Title |
Differentiation of tumor types in vivo by scatterer property estimates and parametric images using ultrasound backscatter. |
| Author |
Oelze ML, Zachary JF, O'Brien WD Jr. |
| Journal |
Proc Ultrason Symp IEEE |
| Volume |
|
| Year |
2003 |
| Abstract |
Two kinds of solid tumors were acquired and scanned in vivo ultrasonically. The first tumor series consisted of spontaneous mammary tumors (fibroadenomas) in rats. The second tumor series were acquired by culturing a carcinoma cell line (4T1-MMT) in culture media. The scatterer properties of average scatterer diameter and acoustic concentration were estimated from a Gaussian form factor using the backscattered ultrasound measured from both kinds of tumors. Parametric images of the tumors were constructed utilizing the estimated scatterer properties for regions of interest inside the tumors. Differences between the two tumor types were clearly seen from the scatterer property estimates and the parametric images. Differences between the 10-MHz and 20-MHz estimates were due to the utilization of a more optimal ka range with the 20-MHz transducer in the estimator. Light microscopic evaluations of the fibroadenomas showed cellular structures of around 100 /spl mu/m in size, and carcinomas showed cell nuclei with an average size of approximately 15 /spl mu/m in diameter. |
| Title |
Differing hepatic lesions caused by the same dose of ultrasound. |
| Author |
Taylor KJ, Connolly CC. |
| Journal |
J Pathol |
| Volume |
|
| Year |
1969 |
| Abstract |
The liver is a convenient experimental organ for investigating the effects of ultrasound, since it is easily accessible without undue surgical trauma, it is homogeneous in its acoustic impedance, and yet is readily susceptible to injury by physical agents...Bell (1957), using focused ultrasound of frequency 1 MHz on liver, showed that lesions were produced selectively at the surface of the irradiated lobe opposite to the portal of entry. He concluded that this damage was due to a combination of thermal and physical effects. ..Curtis (1963, 1965), also using a frequency of 1 MHz on mouse livers, showed that an intensity of less than 10 W per cm2 was insufficient to cause infarction of the liver (as occurred at higher intensities), but produced evidence of liver damage of a characteristic distribution; it is this that is of particular interest here. This damage was especially around the central vein and spared the periphery of the lobule...The present work was undertaken to investigate the effects of ultrasound on liver in the 5-6 MHz range. There is already evidence that these intensities and frequencies break down macromolecules in malignant tissues (Connolly and Taylor, 1969). It is well established that the effects of ultrasound vary with the frequency, the intensity, and the duration of exposure, with the form (focused or planar) of the beams, and with the form (pulsed or continuous) of the radiation. This work describes two other important variables, namely the absolute length of the pulse and the method by which energy is delivered to the tissues. The effect on the red cell membrane of very short pulses of ultrasound separated by short intervals has been described (Connolly, 1969); there is no account of its effect on solid tissue. |
| Title |
Diffraction characterization of tissue using ultrasound. |
| Author |
Gramiak R, Hunter LP, Lee PP, Lerner RM, Schenk E, Waag RC. |
| Journal |
Proc Ultrason Symp IEEE |
| Volume |
|
| Year |
1976 |
| Abstract |
Wave interference has been applied to characterize tissue ultrasonically by measurement of scattered ultrasound intensity as a function of angle and frequency. Conditions of acoustic diffraction are compared with those of x-ray and electron diffraction to show similarities and differences. Model studies using diffraction gratings have provided information about beam width, alignment and nonuniformity on the ability to measure diffraction. Grating with regular spacings ranging from 0.51 to 1.52 mm were studied. Fourier analysis of experimental data collected with precise transducer alignment and the target in the far field produced results which were within 5% of those predicted by calculations for single scattering from points. Studies of a grating with random spacing inferred from measurements correlated with theory. Volume scattering measurements made on packed suspensions of spherical particles simulating tissue showed predicted changes in scattered intensity as a function of angle. A study of liver tissue obtained at autopsy shows scattering effects that suggest structure can be inferred from diffraction analysis. The capability of determining structure with ultrasound by employing the concepts of wave interference has been demonstrated. |
| Title |
Diffraction correction in pulse-echo attenuation measurements. |
| Author |
Cardoso JF, Fink M. |
| Journal |
Proc IEEE Ultrasonic Symposium |
| Volume |
|
| Year |
1983 |
| Abstract |
In the estimation of ultrasound attenuation in biological tissue,diffraction phenomena introduce bias due to their depth dependent filtering effect. The spectral high frequency composition is enhanced around the focal zone of a focused transducer( or in the far field of a plane transducer).
In order to understand,measure and correct this effect two approaches have been developed and compared: 1) The numerical calculations of the power spectrum of the roundtrip impulse response integrated over an isochronous system. The result gives the mean filiter introduced by diffraction at a given roundtrip time. 2) An experimental calibration of diffraction is obtained by measuring a gated back-scattered signal coming from a narrow slice slightly below the surface of a scattering test object,immersed in water. Calibration curves have been used to correct the running spectral moments and result in an important unbiasing of the attenuation estimate.
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