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BRL Abstracts Database |
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Your search for ultrasound produced 3296 results. Page 207 out of 330
| Title |
Pulsed doppler accuracy assessment due to frequency-dependent attenuation and rayleigh scattering error sources. |
| Author |
Embree PM, O'Brien WD Jr. |
| Journal |
IEEE Trans Biomed Eng |
| Volume |
|
| Year |
1990 |
| Abstract |
It is pointed out that frequency-dependent attenuation and Rayleigh scattering are significant error sources for pulsed Doppler ultrasound, used for human blood flow measurement, because the transmitted ultrasound signal has a finite width spectrum. The former causes a frequency downshift and the latter a frequency upshift, both of which are independent of the actual Doppler frequency shift. These error sources were evaluated through computer simulation, and the computed error is compared with experimental data |
| Title |
Pulsed doppler with b-mode imaging for quantitative blood flow measurement. |
| Author |
Gill RW. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1979 |
| Abstract |
A technique is described, using the UI Octoson and a frequency-offset pulsed Doppler system, to obtain fully quantitative blood flow measurements in deep-lying vessels. By uniformly insonating the vessel and using a mean frequency. Doppler demodulator, average velocity is obtained regardless of the velocity profile. B-scan imaging provides the necessary anatomic information to calculate volume flow from this average velocity. Results of in vitro flow measurement tests indicate accuracies of ?14% rms error, ?32% maximum error. The causes of error appear to be well understood, and in a number of cases they can be corrected. Preliminary clinical measurements of fetal umbilical vein flow and adult right branch portal vein flow are also presented. |
| Title |
Pulsed enhancement of acoustic cavitation: a postulated model. |
| Author |
Ciaravino V, Flynn HG, Miller MW. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1981 |
| Abstract |
Iodine-131 labeled sodium iodid was used to demonstrate an iodine release reaction indicative of cavitation activity. Exposure of Na(131)I at varying pulsed regimes (1:1 duty cycle, 60 sec-60 microsec pulse duration) and intensities (10-30 W/cm(^2)) resulted in an increased efficiency of pulsed ultrasound to produce iodine release compared to continuous wave exposures. A model based on the concurrent operation of two mechanisms has been proposed to explain this phenomenon. |
| Title |
Pulsed enhancement of acoutic cavitation: A postulated model. |
| Author |
Church CC, Flynn HG, Miller MW, Ciaravino V. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1981 |
| Abstract |
No abstract available. Letter to editor. |
| Title |
Pulsed ultrasonic doppler blood-flow sensing. |
| Author |
Baker DW. |
| Journal |
IEEE Trans Sonics Ultrason |
| Volume |
|
| Year |
1970 |
| Abstract |
Doppler detection of pulsed ultrasound is being used to map fluid flows in models and transcutaneously in blood vessels in man. A device has been developed and is being evaluated using 1-ms bursts of 5 MHz ultrasound that are projected into the stream under study. The Doppler shift of the backscattered signals is sensed in a phase detector. This Doppler signal corresponds to the mean velocity over a smaller region in space defined by the ultrasonic beam dimensions, transmitted pulse duration, and transducer bandwidth. By using a comb-type gate and sequential sampling, the flow velocity profile can be mapped at selected intervals over one period of pulsatile flow in a model or in man. From this information, a three-dimensional surface is generated as a function of velocity, tube diameter, and time. Volume flow, stroke volume, and flow acceleration can be derived directly from the data. |
| Title |
Pulsed ultrasound and the hyperbarically exposed mouse fetus. |
| Author |
Child SZ, Hoffman D, Norton S, Carstensen EL, Cox C, Gates AH. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1991 |
| Abstract |
To enhance the likelihood of cavitation, pregnant mice were subjected to.hyperbaric conditions and quickly returned to atmospheric pressure. Following.this treatment, they were exposed to spatial average, pulse average intensities of.100 W/cm2 (2.2-MHz, 20-microseconds pulses with a duty cycle of 1/1000 or a.temporal average spatial average intensity of 0.1 W/cm2). Fetal weights, deaths.and malformations were scored. No statistically significant effects were observed.in the offspring. |
| Title |
Quality assurance in diagnostic ultrasound: A manual for the clinical user. |
| Author |
Goldstein A. |
| Journal |
Rep U S Dept HHS |
| Volume |
|
| Year |
1980 |
| Abstract |
No abstract available. |
| Title |
Quality assurance of RF and ultrasound cancer hyperthermia systems. |
| Author |
Bassen H, Allen S, Herman B, Kantor G, Robinson R. |
| Journal |
Proc IEEE Annu Conf of EMBS |
| Volume |
|
| Year |
1985 |
| Abstract |
Test instruments were developed to evaluate radiofrequency (RF) and ultrasound (US) deep-heating cancer therapy systems. Spatial distribution and the rate of temperature rise delivered by hyperthermia devices can be tested for proper performance with 1. An RF "torso" phantom composed of simulated fat and muscle material, with four embedded thermometer probes; 2. A cubical ultrasound phantom with tissue-simulating gel and fifteen embedded thermometer probes; 3. RF hazard monitors for stray radiation; 4. An ultrasound radiation force meter for total output power from US transducers; and, for precise recalibrations at the user's site; 5. An ultrasound reference transducer, plus; 6. A traveling thermometry inter-comparison standard. |
| Title |
Quantative ultrasound characterization of cancer radiotherapy effects in vitro. |
| Author |
Vlad RM, Alajez NM, Giles A, Kolios MC, Czarnota GJ. |
| Journal |
Int J Radiat Oncol Biol Phys |
| Volume |
|
| Year |
2008 |
| Abstract |
Purpose: Currently, no routinely used imaging modality is available to assess tumor responses to cancer treatment within hours to days after radiotherapy. In this study, we demonstrate the preclinical application of quantitative ultrasound methods to characterize the cellular responses to cancer radiotherapy in vitro. Methods and Materials: Three different cell lines were exposed to radiation doses of 2-8 Gy. Data were collected with an ultrasound scanner using frequencies of 10-30 MHz. As indicators of response, ultrasound integrated backscatter and spectral slope were determined from the cell samples. These parameters were corrected for ultrasonic attenuation by measuring the attenuation coefficient. Results: A significant increase in the ultrasound integrated backscatter of 4-7 dB (p < 0.001) was found for radiation-treated cells compared with viable cells at all radiation doses. The spectral slopes decreased in the cell samples that predominantly underwent mitotic arrest/catastrophe after radiotherapy, consistent with an increase in cell size. In contrast, the spectral slopes did not change significantly in the cell samples that underwent a mix of cell death (apoptosis and mitotic arrest), with no significant change in average cell size. Conclusion: The changes in ultrasound integrated backscatter and spectral slope were direct consequences of cell and nuclear morphologic changes associated with cell death. The results indicate that this combination of quantitative ultrasonic parameters has the potential to assess the cell responses to radiation, differentiate between different types of cell death, and provide a preclinical framework to monitor tumor responses in vivo. |
| Title |
Quantative ultrasound characterization of responses to radiotherapy in cancer mouse models. |
| Author |
Vlad RM, Brand S, Giles A, Kolios MC, Czarnota GJ. |
| Journal |
Clin Cancer Res |
| Volume |
|
| Year |
2009 |
| Abstract |
Purpose: Currently, no imaging modality is used routinely to assess tumor responses to radiotherapy within hours to days after the delivery of treatment. In this study,we show the application of quantitative ultrasound methods to characterize tumor responses to cancer radiotherapy in vivo, as early as 24 hours after treatment administration. Experimental Design:Three mouse models of head and neck cancer were exposed to radiation doses of 0, 2, 4, and 8 Gray. Data were collected with an ultrasound scanner using frequencies of 10 to 30 MHz. Ultrasound estimates calculated from normalized power spectra and parametric images (spatial maps of local estimates of ultrasound parameters) were used as indicators of response.
Results: Two of the mouse models (FaDu and C666-1) exhibited large hyperechoic regions at 24 hours after radiotherapy.The ultrasound integrated back scatter increased by 6.5 to 8.2 dB (P < 0.001) and the spectral slopes increased from 0.77 to 0.90 dB/MHz for the C666-1tumors and from 0.54 to 0.78 dB/MHz for the FaDu tumors (P < 0.05), in these regions compared with preirradiated tumors.The hyperechoic regions in the ultrasound images corresponded in histology
to areas of cell death. Parametric images could discern the tumor regions that responded to treatment.
The other cancer mouse model (Hep-2) was resistant to radiotherapy.
Conclusions:The results indicate that cell structural changes after radiotherapy have a significant influence on ultrasound spectral parameters. This provides a foundation for future investigations regarding the use of ultrasound in cancer patients to individualize treatments noninvasively based
on their responses to specific interventions. |
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