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BRL Abstracts Database |
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Your search for ultrasound produced 3296 results. Page 45 out of 330
| Title |
Assessment of articular cartilage and subchondral bone: Subtle and progressive changes in experimental osteoarthritis using 50 MHz echography in vitro. |
| Author |
Saied A, Cherin E, Gaucher H, Laugier P, Gillet P, Floquet J, Netter P, Berger G. |
| Journal |
J Bone Miner Res |
| Volume |
|
| Year |
1997 |
| Abstract |
The main objectives of this work were to demonstrate the potential of 50 MHz echography for assessing initial and progressive morphological and structural changes of articular cartilage and bone developed in an experimental model of osteoarthritis (OA). Degenerative lesions were induced in rat knees by the unilateral intra-articular injection of a 3 mg dose of mono-iodo-acetic acid. To assess the lesion progression, the animals (n = 30) were sacrificed at different time intervals up to 8 weeks after the injection. Three-dimensional echographic data were acquired in vitro on patellar cartilage and bone at various stages of the remodeling process using a scanning ultrasound microscope. Changes involving the OA cartilage characteristics are discussed relative to those of the contralateral control joint which received a placebo. Images of control cartilage showed a smooth hyperechoic articular surface and an echoic matrix. The cartilage thickness was 266 ? 44 ?m (mean ? SD) in the central region of the tissue. The precision of ultrasonic thickness measurements was better than 1.3%. First changes in cartilage internal structure and subchondral bone appeared on ultrasound images 3 days after the injection and were even more evident by day 7. They resulted in a slight thinning of the cartilage, a 30% increase of its internal structure echogenicity, and the appearance of echoic zones in subchondral bone. Histologic findings confirmed chondrocyte depletion and degeneration, decrease of matrix proteoglycans, and fibrovascular connective tissue proliferation at the subchondral plate. Progressive and severe lesions at both bone and cartilage surface and internal structure were assessed and correlated to histologic features. These results show that high resolution echography is sensitive to subtle and progressive osteochondral remodeling. This technique has the potential to be used for intra-articular quantitative imaging and assessment of early changes in bone and cartilage structure associated with natural human disease. |
| Title |
Assessment of bone density using ultrasonic backscatter. |
| Author |
Wear KA, Garra BS. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1998 |
| Abstract |
The goal of this project was to investigate the utility of ultrasonic backscatter for the assessment of bone status. Ultrasound offers a low-cost, portable, nonionizing alternative or complement to common X-ray- or radioisotope (gamma ray)-based methods of bone densitometry. Ultrasonic backscatter may provide useful information not revealed by ultrasonic attenuation and sound-speed densitometers. Backscatter is sensitive to microstructural variations in acoustic impedance and should therefore provide information regarding architecture (which is related to.fracture risk), as well as density. Ultrasonic backscatter at 2.25 MHz and CT bone densitometric data have been acquired from 10 healthy human volunteers. The degree of correlation between CT and ultrasonic backscatter is high(r = 0.87, p < 0.001). The envelope signal-to-noise ratio was 1.81 +/- 0.08 (mean +/- standard deviation). This suggests that the number of scatterers per resolution cell is large, the radiofrequency signal approximately obeys circular Gaussian statistics, and the envelope obeys Rayleigh statistics. These results indicate promise for ultrasonic backscatter as a substitute for or an adjunct to other ultrasonic measurements (attenuation and sound speed) and X-ray measurements for the assessment of bone status. |
| Title |
Assessment of dystocia pelvis by ultrasound pelvimetry. |
| Author |
Nakano H. |
| Journal |
Acta Obstet Gynaecol Jpn |
| Volume |
|
| Year |
1981 |
| Abstract |
Following successful preceding studies, a quantitative analysis of the female pelvic cavity was made using contact compound scanning procedures. The subjects were seventy-seven, 3 day postpartum women and ultrasonic tomograms were obtained concerning the five pelvic transections in each individual. For the quantitative analysis, variables of binary digits were used. Such were based on the standard of "normopelvis" in the polar coordinate system plus the external criteria, normal progress of labor, protraction and arrest disorders. Characteristics of the dystocia pelvis included an abnormal side wall of the small pelvis as well as an increased resistance of the muscles of the pelvic floor. The efficiency of the discrimination was greatest when those variables were adopted from each transection (78.3%). Arrest disorders could be clearly distinguished from the normal cases, however, cases of protraction disorder presented more difficulty as the distribution was wide between normal and the arrest disorder. Here, the pelvic floor muscles contribute significantly. The newly developed numerical system should make feasible an early prediction of dystocia, assist in screening processes and pave the way for accurate assessments of the interaction of anatomical factors related to the mechanics and processes of labor. |
| Title |
Assessment of errors in intensity measurements of pulse echo ultrasound.using miniature hydrophones. |
| Author |
Fischella PS, Carson PL. |
| Journal |
Med Phys |
| Volume |
|
| Year |
1979 |
| Abstract |
Total transmitted power and intensity distributions from diagnostic ultrasound systems have been measured with a radiation.force balance and with a miniature hydrophone and instrumentation available in many medical centers. In assessing the.accuracy of absolute intensity and power determinations from measurements of acoustic pressure with a hydrophone,.ultrasonic power was computed from hydrophone measurements. This power value was compared with the power determined.by a radiation force technique. On five pulse echo ultrasound systems, the ratio of the power measured with a radiation force.balance to the power determined with the hydrophone varied from 0.25 to 5.5. These differences are attributed mainly to the.known large variations in hydrophone response as a function of frequency, and possible time, since several other possible.sources of error were evaluated and estimated to have a reasonably small net effect of 25%. The errors evaluated were those.dealing primarily with measurement procedures. |
| Title |
Assessment of high-intensity focused ultrasound treatment of rodent mammary tumors using ultrasound backscatter coefficients |
| Author |
Kemmerer JP, Ghoshal G, Karunakaran C, Oelze ML |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
2013 |
| Abstract |
Fischer 344 rats with subcutaneous mammary adenocarcinoma tumors were exposed to therapeutic ultrasound at one of three exposure levels (335, 360, and 502W/cm
(^2) spatial-peak temporal-average intensity). Quantitative ultrasound estimates were generated from ultrasound radio frequency (RF) data from tumors before and after high-intensity focused ultrasound treatment. Treatment outcome
was independently assessed by triphenyl tetrazolium chloride (TTC) staining, histological analysis by a pathologist, and thermocouple data. The average backscatter coefficient (BSC) and integrated backscatter coefficient (IBSC) were estimated before and after therapeutic ultrasound exposure for each tumor from RF data collected using clinical (Ultrasonix Sonix RP) and small-animal (Visualsonics Vevo 2100) array systems. Changes in the BSC with treatment were comparable to inter-sample variation of untreated tumors, but statistically significant differences in the change in the IBSCs were observed when comparing the exposures collectively (p<0.10 for Sonix RP, p<0.05 for Vevo 2100). Several exposure levels produced statistically significant differences in the change in IBSC when examined pair-wise, including two exposures having similar intensities
(p<0.05, Vevo 2100). A comparison of the IBSC results with temperature data, histology, and TTC staining revealed that the BSC was not always sensitive to thermal insult and that peak exposure pressure appeared to correlate with observed BSC increases. |
| Title |
Assessment of the effects of scatterer size distributions on effective scatterer diameter estimates. |
| Author |
Lavarello RL, Oelze ML. |
| Journal |
IEEE Int Ultrasonics Symp Proc |
| Volume |
|
| Year |
2010 |
| Abstract |
Scattering models used in most quantitative ultrasound studies assume distributions of identical scatterers.However, actual tissues may exhibit multiple levels of spatial scales. Therefore, the objective of the present study was to use both simulations and experiments to analyze the effects
of scatterer size distributions when using a fluid-sphere model for estimating effective scatterer diameter (ESD). Simulations were conducted with populations of scatterers with uniformly distributed sizes within [25, 100], [25, 50], [50, 100], and [50, 75]um. Simulated backscatter coefficients (BSCs) used as inputs for the ESD estimator were obtained using two methods: (1) using portions of the theoretical BSC with different center frequencies between 1 and 40 MHz and 100% fractional bandwidth, and(2) processing simulated radiofrequency data from computer phantoms using f/4 transducers with center frequencies of 3, 6,
12, 24, and 36 MHz and 100% fractional bandwidth. Experiments were conducted using a gelatin phantom with Sephadex spheres ranging in diameter from 30 um to 140 m and 3.5, 7.5, 10, and 13 MHz focused transducers. ESD estimates obtained with both simulation methods were approximately inversely proportional
to frequency and mostly independent of the underlying scatterer size distribution for sufficiently high analysis frequencies. For frequencies higher than 13 MHz the ESD estimates were below 50 um for all considered size distributions even though two of them had no scatterers smaller than 50 um. Further, the asymptotic behavior of ESD vs. frequency estimates was also observed experimentally. The results of this work highlight some of the effects of continuous scatterer size distributions when obtaining ESD estimates, and challenge the hypothesis that different frequency ranges are more sensitive to different spatial scales when using a single-size scattering model. Although the results presented here are not necessarily universal and most likely will be affected by the actual size distribution and frequency-dependent BSC of the individual scatterers, this work
suggests that caution must be exerted when interpreting ESD estimates at different frequency ranges. This work was supported by a grant from the NIH R21CA139095. |
| Title |
Attenuation and backscattering of ultrasound in freshly excised animal tissues. |
| Author |
Kadaba MP, Bhagat PK, Wu VC. |
| Journal |
IEEE Trans Biomed Eng |
| Volume |
|
| Year |
1980 |
| Abstract |
No abstract available |
| Title |
Attenuation and reflection of ultrasound in canine lung tissue. |
| Author |
Bauld TJ, Schwan HP. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
1974 |
| Abstract |
Canine lung tissue was investigated with short pulses of ultrasonic energy at frequencies of 2.4, 5.0, and 7.4 MHz. The objective was to determine the basic ultrasonic parameters of the tissue in the frequency range of present clinical ultrasonic apparatus and to assess the possibilities of using ultrasound as an aid in the diagnosis of diseases of the lung. Attenuation coefficients and reflection losses were measured for samples of fixed inflated tissue and collapsed freshly excised tissue. The reflection loss depended strongly on the degree of inflation and, unlike the results for other soft tissude, the reflection loss varied with the frequency. The attenuation coefficients increased linearly with frequency and were an order of magnitude greater than the values for other tissues. The fixation process did not substantially change the ultrasonic parameters. Because of the very high attentuation coefficients, the usefulness of ultrasound in diagnosis may be limited to conditions which are manifested at or near the periphery of the lung. The large variation of the reflection loss with frequency is felt to be potentially very important, although further experiments using samples with specific disorders are required to determine the sensitivity of the reflection loss to changes in the condition of the tissue. |
| Title |
Attenuation and scattering of ultrasonic waves in suspensions. |
| Author |
Kol'tsova IS, Mikhailov IG. |
| Journal |
Sov Phys Acoust |
| Volume |
|
| Year |
1974 |
| Abstract |
The attenuation and scattering of ultrasound has been measured by a pulse technique from 3 to 21 MHz in twelve stabilized suspensions. The scattering is measured in the near field of the scattering cluster by a finite detector. The dependence of the scattering on the concentration, scattering parameter, and acoustical properties of the particles is analyzed. The acoustic energy lost by the direct ultrasonic beam due to scattering is estimated. |
| Title |
Attenuation and size distribution measurements of definity and manipulated definity populations. |
| Author |
Goertz DE, de Jong N, van der Steen AF. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
2007 |
| Abstract |
The contrast agent Definity has recently been shown to have substantial nonlinear activity at high ultrasound frequencies (>10 MHz). In this study, measurements were performed to characterize the frequency dependent attenuation properties of Definity and populations of Definity that had been modified to preferentially isolate smaller bubbles through decantation or mechanical filtration. A narrowband pulse-echo substitution method was employed with a series of four transducers covering the frequency range from 2 to 50 MHz. "Native" Definity has peak in attenuation in the vicinity of 10 MHz and remains high until 50 MHz. This pattern is significantly different from other clinically approved agents and is consistent with recent reports of nonlinear activity at high frequencies. With increasing decantation times, the attenuation peak becomes more diffuse and occurs at progressively higher frequencies. By 3 h for example, attenuation continues to rise until 30 MHz. The bubble size distribution undergoes preferential skewing toward smaller bubbles with increasing decantation time. Between 30 s and 3 h, the mean bubble diameter goes from 3.99 to 0.98 micrometers. Mechanical filtration with 2 and 1 microm pores causes attenuation to rise until 15 and 40 MHz, respectively. Definity can therefore be manipulated to improve its relative activity at higher frequencies (>10 MHz), which has implications for ultrasound biomicroscopy and intravascular ultrasound applications. Further, these results suggest that agent handling can have a substantial impact on size distributions affecting lower frequency applications. Shell friction estimates derived from these data are lower than those reported for larger bubbles at lower frequencies. |
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