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BRL Abstracts Database |
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Your search for ultrasound produced 3296 results. Page 93 out of 330
| Title |
Doppler color flow in echocardiography: analytical and in-vitro investigations of the quantitative relationship between orifice flow and color jet dimensions. |
| Author |
Holen J, Nanna M, Lockhart J, Waag R. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1990 |
| Abstract |
The goal of this investigation was to explore the relationship between orifice flow rate and the dimensions of the resulting color jet. Equations were derived which describe flow rate as a function of the color jet dimensions, instrument.characteristics, and a coefficient which represents the unknown velocity profile across the jet. Experiments in which fluid was injected at a variety of flow rates via an assortment of orifice sizes into a compliant, axisymmetric chamber were.performed for comparison with the analytical results. During each injection, orifice flow rate and color jet dimensions were recorded. The experimental results were closely predicted (r = 0.97) by an equation which expresses flow rate as a function.of the ratio of the color jet area and color jet length, and with a coefficient which approximates that of a parabolic velocity profile. |
| Title |
Doppler power variation from porcine blood under steady and pulsatile flow. |
| Author |
Paeng D,Cao P,Shung KK. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
2001 |
| Abstract |
Although a number of recent studies have demonstrated that the echogenicity of blood varies as a function of time under pulsatile flow, the fundamental mechanisms responsible for it are still uncertain. To better understand this phenomenon, the Doppler power from porcine blood and polystyrene microsphere suspensions was measured at the center of the tube as functions of two crucial parameters, flow velocity and stroke rate (for pulsatile flow), under steady and pulsatile flow in a mock flow loop. In the present study, the experimental results were obtained with a 10-MHz pulsed Doppler system with a frequency response estimated more accurately by electronic injection, and validated by comparing to the radiofrequency (RF) signal acquired from the same Doppler instrument. The results show that the Doppler power from microspheres and porcine red blood cell (RBC) suspensions did not vary appreciably (< 2 dB), with either the speed or stroke rate (for pulsatile flow only) under steady and pulsatile flow. It was found that the Doppler power from porcine whole blood under steady flow decreased with the speed by approximately 13 dB from 3 to 33 cm/s and was only 3 dB higher than that from RBC suspension at 33 cm/s, suggesting minimal RBC aggregation in whole blood at this speed. The apparent cyclic variation from whole blood was observed at 20 and 40 beats/min (BPM). The cyclic variation became more obvious as the speed and stroke rate decreased. The mean Doppler power over a cycle increased as the peak speed decreased. The Doppler power reached a maximum near peak systole and a minimum at late diastole at the center of the tube. This pattern cannot be explained by RBC aggregation due to the shear rate alone, and may be attributed to acceleration and deceleration along with aggregation. The cyclic variation was not observed at 60 BPM, probably because of a lack of time for aggregation to occur. (E-mail: paeng@psu.edu)
Keywords: Doppler power; Cyclic variation; Pulsatile flow; Aggregation; Acceleration; Shear rate
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| Title |
Doppler ultrasound and fetal activity. |
| Author |
David H, Weaver JB, Pearson JF. |
| Journal |
Br Med J |
| Volume |
|
| Year |
1975 |
| Abstract |
The possibility that Doppler ultrasound, as used in routine fetal monitoring by external cardiotocography, might stimulate fetal activity was investigated. A mean increase in fetal activity of over 90% was found, as judged by the fetal movement count. |
| Title |
Doppler ultrasound imaging detects changes in tumor perfusion during antivascular therapy associated with vascular anatomic alterations. |
| Author |
Gee MS, Saunders HM, Lee JC, Sanzo JF, Jenkins WT, Evans SM, Trinchieri G, Sehgal CM, Feldman MD, Lee WMF. |
| Journal |
Cancer Res |
| Volume |
|
| Year |
2001 |
| Abstract |
Noninvasive monitoring of antiangiogenic therapy was performed by serial power Doppler ultrasound imaging of murine tumors treated with recombinant interleukin 12, the results of which were correlated with assessments of tumor vascularity by microscopy. Growth of established K1735 tumors, but not of IFN-y-unresponsive K1735.N23 variants was suppressed by treatment. Serial Doppler imaging of K1735 tumor vascularity during treatment revealed a progressive change from a diffuse perfusion pattern to a more punctate distribution. Quantitative analysis of the images revealed that color-weighted fractional average, representing overall tumor perfusion, consistently decreased in these tumors, primarily because of a decrease in fractional tumor cross-sectional area carrying blood flow. In contrast, these parameters increased in nonresponsive tumors during treatment. Confocal microscopy of thick tumor sections revealed a reduction in the density and arborization of vessels labeled in vivo by fluorochrome-conjugated lectin with effective treatment. Immunohistological examination of thin tumor sections confirmed the preferential loss of small vessels with successful therapy. Similar changes in tumor vascular anatomy and perfusion were also observed during recombinant interleukin 12 treatment of two other responsive murine tumor types. These results indicate that power Doppler ultrasound is a sensitive noninvasive method for reporting functional consequences of therapy-induced vascular anatomical changes that can be used to serially monitor tumor perfusion and efficacy of antivascular therapy in clinical trials. |
| Title |
Doppler ultrasound in obstetrics. |
| Author |
Brown RE. |
| Journal |
JAMA |
| Volume |
|
| Year |
1971 |
| Abstract |
Since its first description in 1964, Doppler-principle ultrasound has been used for detection of fetal life, placental localization, and more recently detection of multiple pregnancies and fetal hear monitoring. Techniques and methods of interpretation as applied to 521 patients gave the following accuracy in each determined: detection of fetal life (single examination, 98.8%; double examination, 100%); placental localization for placenta praevia, 96% and diagnosis of multiple pregnancies, 99.7%. Two limitations of these techniques are (1) the fetal heart is not heard prior to 10 to 12 weeks gestation, and (2) experience is the key factor in placental localization, and thus it must be carried out by only one or two well-trained individuals in each hospital unit. On the other hand, accuracy, safety, and simplicity of the Doppler-principle ultrasound techniques far outweigh the limitations. |
| Title |
Dose parameters relevant to ultrasound bioeffects on cell growth. |
| Author |
Edmonds PD, Ross P. |
| Journal |
Proc Twenty-eighth Annu Meet AIUM - New York |
| Volume |
|
| Year |
1983 |
| Abstract |
No abstract available. |
| Title |
Dose-dependent effect of ultrasound on fetal weight in mice. |
| Author |
O'Brien WD Jr. |
| Journal |
J Ultrasound Med |
| Volume |
|
| Year |
1983 |
| Abstract |
Outbred non-Swiss albino mice (CF(1)) were time-mated, exposed on the eighth day of gestation to 1 MHz continuous wave ultrasound, and examined on the eighteenth day of gestation. Seven exposure conditions (spatial average intensity versus exposure time) were employed for the 272 litters: 0 w/cm(^2) (sham); 0.5 W/cm(^2), 300 sec; 0.7 W/cm(^2), 300 sec; 2.0 W/cm(^2), 20 sec; 3.0 W/cm(^2), 20 sec; 3.0 W/cm(^2), 10 sec; and 5.5 W/cm(^2), 10 sec. Relative to the sham group, every exposed group exhibited a reduced average fetal weight, ranging from 5.3 to 17.5 per cent, and the nonparametric Kruskal-Wallis one-way analysis of variance by ranks indicated that the average fetal weight varied significantly, at the 0.001 level, with exposure condition. In addition, a linear dose-effect dependence of exposure condition versus average fetal weight was observed, in which the dose parameter was defined as I2t, where I is the spatial average exposure intensity and t is the exposure time. |
| Title |
Dose-effect relationships for ultrasound irradiation of brain tissue. |
| Author |
Johnston RL. |
| Journal |
Thesis(PhD): Univ of Illinois |
| Volume |
|
| Year |
1979 |
| Abstract |
A series of experimental animals were irradiated using high-intensity focused ultrasound in the frequency range from 1 to 7 MHz to produce irreversible structural alterations in brain tissue (surgical focal lesions). A dose-effect relationship was demonstrated to exist between the calculated absorbed energy per unit volume, expressed as joules/mm cubed, and the volume of the produced lesions as measured on histologically prepared tissue sections. It was also shown that equal size lesions, produced at a given dose-rated or intensity, were obtained at two different ultrasound irradiation frequencies by equivalent values in absorbed dose...Another series of experiments were conducted to study the effects of the superior brain meninges (dura mater, arachnoid membrane, and pia mater) on the propagation of ultrasound to investigate the apparent frequency dependence, over the range of 1 to 9 MHz, in the minimum irradiation exposure required for the just discernable appearance of a brain lesion as evidenced by subsequent histological preparation and optical microscopy (an apparent threshold phenomenon). A model of the meningeal layers involving different propagation properties due to collagenous inclusions was found to fit the data of previous investigators and was found to predict behavior which was subsequently tested by irradiations at 7 MHz. This mathematical description provides a means to refine estimates of intensities delivered to the irradiation sites in brain tissues...Hysteresis associated with the non-linear stress-strain response of tissues subjected to high levels of stress at ultrasonic frequencies was considered as an ultrasound-tissue interaction mechanism for the production of the irreversible structural biological effects. Thus, hysteresis was found capable of describing accurately the previously observed "threshold" curve for this endpoint. This mechanism was considered in its relationship to other proposed tissue interaction mechanisms of ultrasound. Hysteresis effects in tissues include non-linear or intensity dependent acousticl absorption coefficient, linearly increasing absorption coefficient with increasing frequency, dispersion-free velocity, and harmonic production. Partial evidence for these effects were cited from works of other experimenters.. |
| Title |
Double passive cavitation detection of optison shell rupture. |
| Author |
Ammi AY, Cleveland RO, Mamou J, Wang GL, Bridal SL, O'Brien WD Jr. |
| Journal |
Proc Ultrason Symp IEEE |
| Volume |
|
| Year |
2005 |
| Abstract |
An improved understanding of ultrasound contrast agent (UCA) shell rupture is required to optimize therapeutic and diagnostic use. This experimental and theoretical study aims to explore the mechanism of UCA shell rupture by determining thresholds as a function of ultrasonic excitation parameters (driving frequency, pulse duration, and peak rarefractional pressure). The experimental setup is based on a passive cavitation detection system described in previous work. However, this system has been modified to allow simultaneous acquisition of the signals received with the 13-MHz passive receiver and the signals incident upon the lower frequency (0.9, 2.8 and 4.6 MHz) transmitting transducer functioning in the pulse-echo mode. Post-excitation signals were used to detect rupture thresholds. By allowing acquisition of the signals received by the insonifying transducer (pulse-echo during the excitation and passively at post-excitation) additional information is obtained within a frequency range and a transmission/reception configuration typical of ultrasonic diagnostic imaging. Data are analyzed to estimates the incident peak rarefactional pressure leading to 50% destruction. Comparison experimental results with microbubble dynamics predicted using the Modified Herring equation was used to explore microbubble rupture indices based on radical expansion and peak velocity. |
| Title |
Doubly Apodized Linear FM Chirp Signal and its Applications. [in Japanese] |
| Author |
Takeuchi Y. |
| Journal |
Technical Report of IEICE |
| Volume |
|
| Year |
1995 |
| Abstract |
Spread spectrum (SS) signals have been widely applied, not only for communication or cryptography but also for echo sounding for ranging or imaging. In this case range (or time) sidelobe level of the signaling design vastly determines the quality of the measurement or the obtained image. Here presented a family of doubly apodized linear chirp signals having -100dB or less autocorrelation sidelobe, found by author, during years of study of SS signals application for medical ultrasound echpgraphic imagers, in terms of insonification safety as well as detection performance. The signal has extra gaussian apodization upon well known cosine-square apodized linear chirp. Its autocorrelation sidelobe diminishes to less than -100dB range, for example, when chirp over 1:2 frequency range with 100 wavelength. This is virtually equivalent sidelobe performance as Golay code or complementary code family, yet having essential pulse to pulse Doppler-shift tolerance. |
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