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BRL Abstracts Database |
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Your search for ultrasound produced 3296 results. Page 317 out of 330
| Title |
Ultrasound scattering properties of Albunex microspheres. |
| Author |
de Jong N, Hoff L. |
| Journal |
Ultrasonics |
| Volume |
|
| Year |
1993 |
| Abstract |
Albunex is an ultrasound contrast agent used in echocardiography and in other areas, it consists of microspheres of which more than 95% have a diameter in the range 1-10 microns. The scattering properties of this agent as functions of ultrasound frequency and microsphere diameter and concentration are investigated. A model of the Albunex microspheres has been previously described, considering the individual microspheres as air bubbles surrounded by a thin elastic shell. In the present study this model is extended by including into it the internal friction in the shell when the microsphere vibrates. Acoustic scattering and transmission are measured in the frequency range from 700 kHz to 12.5 MHz. The measured transmitted power is used to estimate the two parameters in the theoretical model: the shell elasticity parameter, Sp and the shell friction, Sf. Introduction of the shell friction into the model improves the agreement between theory and measurements. For the scattered power, differences between measured and calculated values lie within 3 dB. It is concluded that for the frequencies 2.5 and 5 MHz, microspheres with a diameter between 5 and 12 microns are preferred as these deliver the most significant contribution to the total scattered power and cause relatively little attenuation. |
| Title |
Ultrasound speckle analysis based on the K distribution. |
| Author |
Weng L, Reid JM, Shankar M, Soetanto K. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
1991 |
| Abstract |
The departure of speckle magnitude from Rayleigh statistics was applied to examine insonated phantoms with both low and high concentrations of scatterers. A mathematical model, the K distribution of Jakeman, was used to characterize non-Rayleigh statistics. This model contains a parameter, alpha, which characterizes the clustering of the scattering sites in a medium. It is shown from phantom experiments that alpha is linearly proportional to the log-scaled scatterer concentration in a range from about 1 to 30 scatterers per sample volume. |
| Title |
Ultrasound speckle reduction by directional median filtering. |
| Author |
Czerwinski RN, Jones DL, O'Brien WD Jr. |
| Journal |
Proc IEEE ICIP |
| Volume |
|
| Year |
1995 |
| Abstract |
This paper presents a novel adaptation of the median filter to the problem of boundary-preserving speckle reduction in ultrasonic imaging. The technique involves applying a bank of oriented one-dimensional median filters to the image, and retaining at each point the largest value among all the filter bank outputs. The result is an operator which suppresses speckle noise while retaining the structure of the image, particularly the thin bright streaks, which tend to occur along boundaries between tissue layers. The technique is compared to a block median filter and an algorithm discussed by Loupas et al. (1989), and is shown to be far superior to the median filter, and noticeably better than the Loupas filter at enhancing thin lines. |
| Title |
Ultrasound speckle reduction using coded excitation, frequency compounding, and postprocessing despeckling filters. |
| Author |
Ullom JS, Oezle M, Sanchez JR. |
| Journal |
IEEE Int Ultrasonics Symp Proc |
| Volume |
|
| Year |
2010 |
| Abstract |
A technique for improvement of ultrasonic B-mode imaging that uses coded excitation, pulse compression, and frequency compounding was developed. A coded excitation and pulse compression technique known as resolution enhancement
compression (REC) was used to enhance the bandwidth of an imaging system by a factor of two. This bandwidth was subdivided into smaller subbands through the speckle-reducing technique known as frequency compounding (REC-FC).
Frequency compounded images were generated using various subband widths and then averaged to reduce speckle and to improve contrast while preserving spatial resolution, known as enhanced REC-FC (eREC-FC). In this study, further
improvements in contrast and reduction in speckle were obtained by applying post-processing despeckling filters. The following post-processing despeckling filters were explored and analyzed in regard to contrast improvement, speckle reduction, and image feature preservation: median, Lee, homogeneous mask area,
geometric, and speckle reducing anisotropic diffusion (SRAD). To quantify the performance of each filter, contrast-to-noise ratio was used. Data from thirty simulated phantoms and experimental data from a tissue-mimicking phantom were generated and filtered. Results demonstrated that post-processing despeckling
filters coupled with the eREC-FC technique could improve the image by up to 563%, in terms of the contrast-to-noise ratio, when compared to conventional ultrasonic imaging. |
| Title |
Ultrasound spectral investigations for tissue characterization. |
| Author |
Lizzi FL, Laviola MA. |
| Journal |
Ultrasound Med |
| Volume |
|
| Year |
1976 |
| Abstract |
No abstract Available. |
| Title |
Ultrasound spectroscopy applied to blood coagulation.studies. |
| Author |
Jacobs JE, Malinka AV, Haque P, Jhabvala MD. |
| Journal |
Ultrasonics |
| Volume |
|
| Year |
1976 |
| Abstract |
Two frequency scanning ultrasonic spectrographs utilizing time-delay signal processing techniques have been developed. These permit measurement of time delays (and hence velocity changes) in a sample in the order of 10(^-8) s. The present instruments allow such measurements to be made continuously over a frequency range of 1-10 MHz. These instruments have been used to monitor changes in velocity as a function of frequency during coagulation in purified human fibrinogen solution and human plasma. It was found that velocity dispersion occurred at discrete frequencies during the coagulation process. The frequency dependent data is reproducible, although this depends to some extent upon the samples used. The instruments which were calibrated using a fixed length of coaxial cable, exhibit a high degree of reproducibility. |
| Title |
Ultrasound termed superior to palpation for localizing breast cancer. |
| Author |
Unknown. |
| Journal |
The NewsMagazine of OB and Gynecology |
| Volume |
|
| Year |
1974 |
| Abstract |
No abstract available. |
| Title |
Ultrasound tissue characterization of breast biopsy specimens. |
| Author |
Edmonds PD, Mortensen CL, Hill JR, Holland SK, Jensen JF, Schattner P, Valdes AD. |
| Journal |
Ultrason Imaging |
| Volume |
|
| Year |
1991 |
| Abstract |
Results of measurements of ultrasound speed and absorption coefficients in the range 3 to 8 MHz in breast tissues at 37 C are reported and analyzed in attempts to identify a set of ultrasound parameters capable of discriminating normal, benign, and malignant tissues. We analyzed 118.tissue regions, comprising 47 normal, 55 benign, and 16 malignant by straight-line fitting of frequency dependence of attenuation. Data for ten additional regions, for a total of 128, became available and were added to the cohort when we subsequently fitted quadratic curves. Sound speed consistently emerged as the variable with greatest discriminating power, particularly for separating normal from benign and malignant tissue. Great difficulty was encountered in discriminating benign from malignant, even when the jackknife technique was used. More success was found with classification and regression trees (CART), although results were sensitive to assigned misclassification costs. Best results from straight-line fits were obtained when discriminating malignant from combined normal/benign data after randomly assigning 75 percent of the data to the learning set and 25 percent to the test set. Then, 23 out of 25 normal/benign and 4 out of 4 malignant cases in the test set were correctly classified. With quadratic fitting, best results were obtained in the three-class case--the false positive rate for malignancy was reduced to zero in the learning (0/31) and test (0/10) sets. Nevertheless, the false negative rate increased to 13 out of 31 (42 percent) in the learning set, while attaining zero (0/4)in the test set. |
| Title |
Ultrasound tissue displacement and tissue elasticity imaging. |
| Author |
Chen ECJ. |
| Journal |
Thesis(PhD): Univ of Illinois |
| Volume |
|
| Year |
1995 |
| Abstract |
In this dissertation, we investigate the feasibility of using high frequency ultrasound, to measure tissue motion and tissue elasticity for medical imaging applications. Ultrasound provides a means for non-invasive imaging of soft tissues, providing soft tissue contrast that cannot be achieved using conventional X-ray or tomographic imaging.
A two-dimensional correlation search algorithm is used to track local tissue displacement from radio frequency (RF) ultrasound echoes and from digitized ultrasound images. The accuracy of displacement imaging is investigated as a function of various imaging parameters such as ultrasound frequency and target size.
Ultrasound elasticity imaging consists of three basic steps: 1) measurement of tissue displacement, 2) estimation of tissue stresses and strains, and 3) recovery of tissue elasticity. Tissue strains and tissue elasticities are obtained from reconstructed tissue displacement fields and experimental measurements of applied stresses. Ultrasound elasticity measurements were compared with independent Instron load cell elasticity measurements.
Several examples of tissue displacement imaging of breast tumors in human breast cancer patients and ultrasound elasticity measurements of tissue phantoms (soft gels), and samples of bovine muscle and fat tissue are provided.
|
| Title |
Ultrasound tissue displacement imaging with application to breast cancer. |
| Author |
Chen EJ, Adler RS, Carson PL, Jenkins WK, O'Brien WD Jr. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1995 |
| Abstract |
A method for quantitative imaging of internal tissue motion based on speckle tracking is described. Tissue displacement images from eight patients with sonographically apparent breast masses are used to illustrate the technique. The local displacement response of tissues surrounding malignant and benign breast masses is compared, testing the hypothesis that altered mechanical properties may result in motion signatures for many soft tissue tumors relative to their host tissue. In addition, the potential or anticipated influence of various biological and physical factors on tissue motion response is discussed. |
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