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BRL Abstracts Database |
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Your search for ultrasound produced 3296 results. Page 11 out of 330
| Title |
A new elastographic method for estimation and imaging of lateral displacements, lateral strains, corrected axial strains and poisson's ratios in tissues. |
| Author |
Konofagou E, Ophir J. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1998 |
| Abstract |
A major disadvantage of the current practice of elastography is that only the axial component of the strain is estimated. The lateral and elevational components are basically disregarded, yet they corrupt the axial strain estimation by inducing decorrelation noise. IN this paper, we describe a new weighted interpolation method operating between neighboring RF A-lines for high precision tracking of the lateral displacement. Due to this high lateral-tracking precision, quality lateral elastograms are generated that display the lateral component of the strain tensor. These precision lateral-displacement estimates allow a fine correction for the lateral decorrelation that corrupts the axial estimation. Finally, by dividing the lateral elastogram by the axial elastogram, we are able to produce a new image that displays the distribution of Poisson?s ratios in the tissue. Results are presented from finite-element simulations and phantoms as well as in vitro and inv vivo experiments. |
| Title |
A new generation of ultrasound contrast agents for echocardiography. |
| Author |
DeMaria AN. |
| Journal |
Clin Cardiol |
| Volume |
|
| Year |
1997 |
| Abstract |
The current supplement represents a series of articles directed toward examining the emerging role of contrast echocardiography in clinical cardiology. Navin C. Nanda, M.D., reviews the history of ultrasound contrast agents. Dr. Nanda describes the initial compounds used to produce microbubbles and highlights many of the new agents being developed for contrast echocardiography. Several ultrasound contrast agents are nearing approval and availability to the practicing community. One of these, perflenapent emulsion (EchoGen”, SONUS Pharmaceuticals, Bothell, Wash.) is the subject of two articles in this supplement. Paul Grayburn, M.D., reviews clinical experience
with perflenapent emulsion and offers his insight into the important future clinical role of contrast echocardiography. A companion article deals with the safety of perflenapent emulsion in both echocardiographic and radiologic
ultrasound applications and is coauthored by Steven C. Quay, M.D., Ph.D., the developer of the compound. Although the current advances in contrast echocardiography are primarily driven by the availability of new ultrasound contrast agents, developments in the instrumentation used to record images are also very important. Sanjiv Kaul, M.D., presents the technical developments of the ultrasound systems used to perform contrast echocardiography.
Dr. Kaul’s article includes both available technologies and those which are still being refined. The current role of contrast echocardiography in cardiovascular diagnostics is outlined by Julio Pkrez, M.D. Dr. Perez provides a comprehensive catalog of the many and varied applications for which ultrasound contrast i\ currently used in echocardiography laboratories.
Given the cost conscious healthcare environment in which we currently practice, some discussion of the economic considerations regarding contrast echocardiography is warranted. Leslee J. Shaw, Ph.D., who has been a leader in the field of cost effectiveness research, summarizes the pharmacoeconomic implications of contrast echocardiography as a diagnostic modality.
Together, these articles constitute a comprehensive review of the most important emerging aspects of contrast echocardiography and specifically examine one of the ultrasound contrast agents, perflenapent emulsion, that will
likely become available in the near future. |
| Title |
A new high intensity focused ultrasound applicator for surgical applications. |
| Author |
Brentnall MD, Martin RW, Vaezy S, Kaczkowski P, Forster F, Crum L. |
| Journal |
IEEE Trans Ultrason Ferroelectr Freq Control |
| Volume |
|
| Year |
2001 |
| Abstract |
Improved high-intensity focused ultrasound (HIFU) surgical applicators are required for use in a surgical environment. We report on the performance and characteristics of a new solid-cone HIFU applicator. Previous HIFU devices used a water-filled stand-off to couple the ultrasonic energy from the transducer to the treatment area. The new applicator uses a spherically-focused element and a solid aluminum cone to guide and couple the ultrasound to the tissue. Compared with the water-filled applicators, this new applicator is simpler to set up and manipulate, cannot leak, prevents the possibility of cavitation within the coupling device, and is much easier to sterilize and maintain during surgery. The design minimizes losses caused by shear wave conversion found in tapered solid acoustic velocity transformers operated at high frequencies. Computer simulations predicted good transfer of longitudinal waves. Impedance measurements, beam plots, Schlieren images, and force balance measurements verified strong focusing and suitable transfer of acoustic energy into water. At the focus, the -3 dB beam dimensions are 1.2 mm (axial) x 0.3 mm (transverse). Radiation force balance measurements indicate a power transfer efficiency of 40%. In vitro and in vivo tissue experiments confirmed the applicator's ability to produce hemostasis. |
| Title |
A new imaging technique based on the nonlinear properties of tissues. |
| Author |
Averkiou MA, Roundhill DN, Powers JE. |
| Journal |
Proc Ultrason Symp IEEE |
| Volume |
|
| Year |
1997 |
| Abstract |
Finite amplitude sound propagating in a medium undergoes distortion due to the nonlinear properties of the medium. The nonlinear distortion produces harmonic (and subharmonic) energy in the propagating signal. The amplitudes used by commercial medical scanners during routine diagnostic scanning are in most cases finite and thus within the range that produces nonlinear distortion. Thermoviscous absorption of tissue which is frequency dependent rapidly dissipates this harmonic energy. This has led to the widely held assumption that nonlinear distortion was not a significant factor in medical diagnostic imaging. However, the wide dynamic range, digital architecture, and the signal processing capabilities of modern diagnostic ultrasound systems make it possible to utilize this tissue generated harmonic energy for image formation. These images often demonstrate reduced nearfield artifacts and improved tissue structure visualization. Previously, those images were believed to be the result of transmitted second harmonic energy. It is shown that the nonlinear properties of tissue are the major contribution of harmonic images. |
| Title |
A new method for measuring small local vibrations in the heart using ultrasound. |
| Author |
Kanai H, Satoh H, Hirose K, Chubachi N. |
| Journal |
IEEE Trans Biomed Eng |
| Volume |
|
| Year |
1993 |
| Abstract |
In order to diagnose ventricular dysfunction based on the acoustic characteristics of the heart muscle of the ventricle, it is necessary to detect vibration signals from various parts of the ventricular wall. This is, however, difficult using previously proposed ultrasonic diagnostic methods or systems. The reason is that the amplitude of the cardiac motion is large during one.beat period which produces large fluctuations in the transit time required for ultrasonic waves to travel from the transducer to the heart and back. This paper proposes a new method for overcoming this problem and accurately measuring small vibrations of the ventricle wall using ultrasound. In this method, the demodulated ultrasound signal reflected at the heart wall is converted from analogue to digital (A/D) signal at a high sampling frequency; from the resultant digital signal, the velocity of the wall is accurately obtained over a wide dynamic range based on the Doppler effect. The proposed method is preliminarily applied to the detection of small vibrations on the aortic wall and the interventricular septum. The new method offers potential for research in acoustical diagnosis of heart and artery dysfunction. |
| Title |
A new motor-driven surgical probe and its in vitro comparison with the Cavitron Ultrasonic Surgical Aspirator. |
| Author |
Chan KK, Watmough DJ, Hope DT, Moir K. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1986 |
| Abstract |
The Cavitron Ultrasonic Surgical Aspirator (CUSA) has been applied in neurosurgery for several years, but its mode of action is not yet clear and its efficiency at removing soft tissue has not been quantified. We describe here how we have measured the rate of removing soft tissue per unit time, taking ox-liver tissue as the test material. A motor-driven vibrator/aspirator has been developed in our laboratory. It has permitted us to examine the effect of varying independently.frequency, amplitude of the vibration, and suction pressure on the removal rate. The results of this investigation show that beyond a certain tip acceleration amplitude (about 100 g) the removal rate does not increase significantly. Also the removal.rate is more or less independent of vibration amplitude within the range between 300 micron and 1 mm. Our in vitro experiments with the new probe show that a tip acceleration of about 100 g is enough to remove ox-liver tissue and then the.rate of removal is comparable to that obtained with the CUSA operating at maximum vibration amplitude. Analysis of the particle size of the debris collected from CUSA and from our motor-driven device shows that the particle size distribution is similar over the range of 0.5 micron less than d less than 250 micron. |
| Title |
A new perspective on hyperthermia-induced birth defects: The role of activation energy and its relation to obstetric ultrasound. |
| Author |
Miller MW, Miller HE, Church CC. |
| Journal |
Journal of Thermal Biology |
| Volume |
|
| Year |
2005 |
| Abstract |
This paper concerns the rate of birth defects that is induced by hyperthermic conditions during gestation. These defects occur with low rates under apparently normal physiologic conditions, but with substantially higher rates with appropriate timing of a hyperthermic event during gestation. The concept of ''free energy of activation'' is invoked to explain not only the background rate but also the effect of a short-term, acute (additive) thermal dosing at a highly heat-sensitive stage of embryogenesis. In this respect, this paper is both retrospective and prospective in approach. It briefly and retrospectively addresses the historical data in this area and then, following a novel mathematical procedure whereby the activation energy for a specific type of hyperthermia-induced birth defect is determined, prospectively applies this information to predict what the outcomes would be in a clinical situation such as obstetric diagnostic ultrasound where it is known that the clinical procedure can involve a temperature increment for a specific duration. A major outcome of this review is that there appear to be no thresholds for hyperthermic events, that any temperature elevation for any duration during pregnancy has some potential for inducing a deleterious effect. The paper includes an analysis that for the first time allows a calculation of risk for such defined thermal insults, with broader implications for any natural or other clinical situation in which the temperature of the embryo or fetus is raised above the normal physiologic level. The topic of hyperthermia-induced birth defects and related activation energies needs thorough, long-term testing of this prospective position. |
| Title |
A new three-dimensional ultrasound microimaging technology for preclinical studies using a transgenic prostate cancer mouse model. |
| Author |
Wirtzfeld LA, Wu G, Bygrave M, Yamasaki Y, Sakai H, Moussa M, Izawa JI, Downey DB, Greenberg NM, Fenster A, Xuan JW, Lacefield JC. |
| Journal |
Cancer Res |
| Volume |
|
| Year |
2005 |
| Abstract |
Prostate cancer is the most common cancer in adult men in North America. Preclinical studies of prostate cancer employ genetically engineered mouse models, because prostate cancer does not occur naturally in rodents. Widespread application of these models has been limited because autopsy was the only reliable method to evaluate treatment efficacy in longitudinal studies. This article reports the first use of three-dimensional ultrasound microimaging for measuring tumor progression in a genetically engineered mouse model, the 94–amino acid prostate secretory protein gene-directed transgenic prostate cancer model. Qualitative comparisons of three-dimensional ultrasound images with serial histology sections of prostate tumors show the ability of ultrasound to accurately depict the size and shape of malignant masses in live mice. Ultrasound imaging identified tumors ranging from 2.4 to 14 mm maximum diameter. The correlation coefficient of tumor diameter measurements done in vivo with three-dimensional ultrasound and at autopsy was 0.998. Prospective tumor detection sensitivity and specificity were both >90% when diagnoses were based on repeated ultrasound examinations done on separate days. Representative exponential growth curves constructed via longitudinal ultrasound imaging indicated volume doubling times of 5 and 13 days for two prostate tumors. Compared with other microimaging and molecular imaging modalities, the application of three-dimensional ultrasound imaging to prostate cancer in mice showed advantages, such as high spatial resolution and contrast in soft tissue, fast and uncomplicated protocols, and portable and economical equipment that will likely enable ultrasound to become a new microimaging modality for mouse preclinical trial studies.
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| Title |
A new time-gain correction method for standard B-mode ultrasound imaging. |
| Author |
Richard WD. |
| Journal |
IEEE Trans Med Imaging |
| Volume |
|
| Year |
1989 |
| Abstract |
Traditionally, there have been two distinct methods used to provide gain variation with received echo range to compensate for tissue attenuation in standard B-mode ultrasound imaging systems. The first technique uses a variable gain amplifier or multiplier capable of 60-70 dB gain variation. The second technique achieves signal multiplication by first logarithmically compressing the complete dynamic range of the received echo. The time-gain correction method described here is a modification of the second method. This method performs the time-gain correction operation digitally between the digital scan converter and the display. This method allows the overall system transfer function to be specified via a software interface without changing the characteristics of the analog front end. This interface can be automated to almost any degree, and it can include preset setting for typical imaging requirements. This method also allows the gain function to be changed even when new images are not being generated. |
| Title |
A new ultrasonic imaging system using time delay spectrometry. |
| Author |
Heyser RC, Le Croissette DH. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1974 |
| Abstract |
A new method of forming a visual image by ultrasound is described. A shadowgraphic transmission image similar to an x-ray radiograph is produced by the application of a technique known as Time Delay Spectrometry. The system uses a repetitive frequency sweep with a linear relationship between frequency and time and the transmitting and receiving crystal are scanned in raster fashion about the subject. By electronic processing, an image may be built up which represents the energy transmitted throught the specimen with a given time delay. An intensity modulated picture encompassing the full shades-of-gray capability of the recording system can be produced. A second type of image showing transmission time through the specimen may also be formed. Brightness changes in the displayed image in this case correspond to changes in the ultrasonic transmission time through the specimen. There is no analog for this type of image in current x-ray or ultrasonic practice. Examples of both types of images of specimens both in vitro and in vivo are shown. The advantages and potentials of this method for biomedical ultrasonic imaging and analysis are discussed. |
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