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BRL Abstracts Database |
Your search for ultrasound produced 3296 results. Page 277 out of 330
Title |
Thresholds for ultrasonically induced lung hemorrhage in neonatal swine. |
Author |
Baggs R, Penney DP, Cox C, Child SZ, Raeman CH, Dalecki D, Carstensen EL. |
Journal |
Ultrasound Med Biol |
Volume |
|
Year |
1996 |
Abstract |
The threshold for generation of lung hemorrhage in adult mice by pulsed.ultrasound has been shown to be approximately 1 MPa at the surface of the lung.(10-microseconds pulse and a carrier frequency of 2 MHz). This investigation.used neonatal swine to determine if the findings for mice can be generalized to.other species. After exploratory observations, the inverse sampling method was.used in a primary study (22 animals, 88 exposure sites) to determine the.threshold for lung hemorrhage in neonatal swine. The primary study was.followed by a separate confirmation study (13 animals, 48 exposure sites),.testing the conclusions of the first study and comparing damage at subthreshold.levels with sham-exposed animals. A separate investigation explored the.histological nature of tissue damage at suprathreshold levels. A 2.3-MHz focused.transducer (10 microseconds at 100-Hz pulse-repetition frequency) was.incremented vertically for a distance of 2 cm over the chest of the subject for a.total exposure period of 16 min. Animals were euthanized and lungs were scored.by visual inspection for numbers and areas of gross hemorrhages. The threshold.level for hemorrhage was approximately 1.5 MPa peak positive pressure in water.at the surface of the animal or, at the surface of the lung, 1.1 MPa peak positive.pressure, 1 MPa fundamental pressure, 0.9 MPa maximum negative pressure, 25.W cm-2 pulse average intensity or a mechanical index of 0.6. These values are.essentially the same as those reported for adult mice. |
Title |
Time lapse and microscopic examinations of insonated in vitro cells. |
Author |
Miller MW, Church CC, Ciaravino V. |
Journal |
Ultrasound Med Biol |
Volume |
|
Year |
1990 |
Abstract |
A fibroblast cell line (Balb/c 3T3) was sham/exposed to ultrasound (2.2 MHz resonant frequency, 35.4 W/cm2 SPTP, 3 microseconds pulse duration, 200 Hz prf) for 30 min and subsequently scored for cell motility and alterations in cell morphology. Cell motility was assessed by computerized tracking of cells..Cell morphology ("normal" or "abnormal") was determined blindly by three independent scorers. A positive control (1-4 Gy) yielded statistically significant alterations in cell motility and morphology; no such differences were observed for the ultrasound regimen. The results thus fail to confirm an earlier report by.Liebeskind et al. (Brit. J. Cancer 45(Suppl. V):176-186; 1982) of ultrasound-induced alterations in cell motility and morphology. |
Title |
Time to threshold (TT), a safety parameter for heating by diagnostic ultrasound. |
Author |
lubbers J,Hekkenberg RT,Bezemer RA. |
Journal |
Ultrasound Med Biol |
Volume |
|
Year |
2003 |
Abstract |
Activities in the standardisation of medical ultrasonic imaging and monitoring devices have been undertaken to ensure the safe application and to provide the user with tools to perform risk-to-benefit analysis. Internationally, agreement has not been reached to implement a system based on a physical quantity such as temperature rise. Therefore, recently, the IEC Standard 60601-2-37 has adopted the thermal index (TI) as a safety parameter. TI indicates conditions that are more likely than others to produce thermal effects. The models used to calculate TI are based on the equilibrium temperature rise for a stationary transducer. Ultrasound (US) is often applied during a short time at one place. To characterise the situation before equilibrium is reached, this study proposes a new parameter: TT (time to threshold). TT indicates the time after which a threshold temperature rise is exceeded. TT is calculated for some tissue models to illustrate the meaning of TT. TT indicates how long one piece of tissue can be insonated safely, provided the safe threshold is known. Using TT, higher intensities can be applied safely during a limited time. This paper illustrates the effects of short insonation times and the influence of the beam diameter. Questions that are critical to the introduction of TT as a safety parameter are discussed. (E-mail: j.lubbers@med.rug.nl)
Keywords: Ultrasound; Heating; Safety; Thermal index; TI; Temperature; Time to threshold; TT
|
Title |
Time-domain optimized near-field estimator for ultrasound imaging: Initial development and results. |
Author |
Viola F, Ellis MA, Walker WF. |
Journal |
IEEE Trans Med Imaging |
Volume |
|
Year |
2008 |
Abstract |
For nearly four decades, adaptive beamforming (ABF) algorithms have been applied in RADAR and SONAR signal processing. These algorithms reduce the contribution of undesired off-axis signals while maintaining a desired response along a specific look direction. Typically, higher resolution and contrast is attainable using adaptive beamforming at the price of an increased computational load. In this paper, we describe a novel ABF designed for medical ultrasound, named the time-domain optimized near-field estimator (TONE). We performed a series of simulations using synthetic ultrasound data to test the performance of this algorithm and compared it to conventional, data independent, delay and sum beamforming (CBF) method. We also performed experiments using a Philips SONOS 5500 phased array imaging system. CBF was applied using the default parameters of the Philips scanner, whereas TONE was applied on per channel, unfocused data using an unfocused transmit beam. TONE images were reconstructed at a sampling of 67 m laterally and 19 m axially. The results obtained for a series of five 20-m wires in a water tank show a significant improvement in spatial resolution when compared to CBF. We also analyzed the performance of TONE as a function of speed of sound errors and array sparsity, finding it robust to both. |
Title |
Time-domain ultrasound diffraction tomography. |
Author |
mast TD, Lin F, Waag RC. |
Journal |
Proc IEEE Ultrasonic Symposium |
Volume |
|
Year |
1999 |
Abstract |
No Abstract Available. |
Title |
Timing of exposures in ultrasonic hemorrhage of murine lung. |
Author |
Raeman CH, Child SZ, Carstensen EL. |
Journal |
Ultrasound Med Biol |
Volume |
|
Year |
1993 |
Abstract |
Pressure thresholds for lung hemorrhage by exposure to.low-temporal-average-intensity, pulsed ultrasound are of the order of 1 MPa..Earlier evidence suggested that ultrasound modifies the tissue over short periods.of time in such a way that the nonthermal action of ultrasound is enhanced..Measurements of thresholds (1) for hemorrhage and (2) for penetration of the.hemorrhage through the murine lung in which a given "on-time" was presented to.the tissue over periods of time up to 3 min support the hypothesis. |
Title |
Tissue ablation in benign prostatic hyperplasia with high intensity focused ultrasound. |
Author |
Madersbacher S, Kratzik C, Susani M, Marberger M. |
Journal |
J Urol |
Volume |
|
Year |
1994 |
Abstract |
In a phase I clinical trial the morphological impact and safety of high intensity focused ultrasound administered transrectally for tissue ablation in prostates from 22 patients undergoing subsequent prostatectomy were evaluated. Location and size of the tissue lesions correlated well with the predefined target area and revealed sharply delineated coagulative necrosis in all cases. Intervening tissues, such as the rectal wall and posterior prostate capsule, were invariably intact. In a subsequent phase II clinical trial the effectiveness of transrectal high intensity focused ultrasound as a novel minimally invasive treatment modality for 50 patients with symptomatic benign prostatic hyperplasia was determined. The maximum urinary flow rate (ml. per second) increased from 8.9 +/- 4.1 to 12.7 +/- 6.4 at 3 months in 44 patients, 12.4 +/- 5.6 at 6 months in 33 and 13.1 +/- 6.5 at 12 months in 20. During the same period the post-void residual volume (ml) decreased from 131 +/- 120 to 48 +/- 41, 59 +/- 42 and 35 +/- 30, respectively, and the American Urological Association symptom score (points) decreased from 24.5 +/- 4.7 to 13.3 +/- 4.4, 13.4 +/- 4.7 and 10.8 +/- 2.5, respectively. These data demonstrate that transrectal high intensity focused ultrasound is capable of inducing coagulative necrosis in the human prostate via a transrectal approach while preserving intervening and adjacent tissue. A 47% (+4.2 ml. per second) improvement in uroflowmetry and a 53% (-13.7 points) decrease in the American Urological Association symptom score 1 year after treatment clearly prove that transrectal high intensity focused ultrasound is a novel and safe minimally invasive treatment option for benign prostatic hyperplasia. |
Title |
Tissue as a Voigt body for propagation of ultrasound. |
Author |
Ahuja AS. |
Journal |
Ultrason Imaging |
Volume |
|
Year |
1978 |
Abstract |
No abstract available. |
Title |
Tissue characterisation using acoustic microscopy. |
Author |
Sinclair DA, Smith IR. |
Journal |
Proc Twelfth Int Symp Acoust Imaging - London |
Volume |
|
Year |
1982 |
Abstract |
It has been recognised for some time in clinical ultrasound that the speckle-like appearance of regions of relatively homogeneous tissue in B scans can provide significant diagnostic information-particularly in the case of diffuse disease. Improved understanding of the scattering and diffractive processes experienced by an acoustic wave propagating through such tissue regions can be expected to enhance the clinical assessment of the corresponding B scans. The scanning acoustic microscope provides a suitable method for imaging variations in the acoustic properties of in vitro samples with a resolution comparable to the acoustic wavelength. We discuss here techniques for the derivation of quantitative values for velocity and impedance from acoustic microscope image data. In particular we demonstrate the validity of a paraxial theory of microscope operation and show that enhanced sensitivity can be achieved by careful selection of the microscope coupling liquid. Maps of acoustic velocity and impedance are derived for human liver. |
Title |
Tissue characterization from ultrasound B-scan data. |
Author |
Nicholas D, Nassiri DK, Garbutt P, Hill CR. |
Journal |
Ultrasound Med Biol |
Volume |
|
Year |
1986 |
Abstract |
An approach to ultrasonic tissue characterization, using textural features of the B-scan image, is described. Portions of a B-scan image, 64 X 64 pixels spatially by 8 bits deep, are acquired from regions of interest and subjected to computer analysis. A systematic approach to defining a set of 93 textural features of a B-scan is described and methods and criteria for selecting optimum combinations of.these are discussed. As a test of its power, the approach has been applied to the discrimination between the B-scan textures corresponding to livers and spleens of normal humans and various measures of "success" have been quantified both on a "training set only" and on a "training set plus test set" basis. The overall test probability of success of 82% on a single image and 94% on a subject yielding multiple images indicates the potential of the techniques for conditions where a subtle but uniform change in parenchymal texture may be present. |
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