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BRL Abstracts Database |
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Your search for ultrasound produced 3296 results. Page 183 out of 330
| Title |
New approaches to aberration correction in medical ultrasound imaging. |
| Author |
Haun MA. |
| Journal |
Thesis(PhD): Univ of Illinois |
| Volume |
|
| Year |
2003 |
| Abstract |
Medical ultrasound imaging is in widespread use today due to its low cost, portability,lack of side ef fects, and unique ability to probe the mechanical properties of tissue. As transducer apertures and operating frequencies grow, however, ultrasound's resolving power continues to be limited by variations in the speed of sound within tissue. Concepts borrowed from other imaging disciplines can provide new insights into the aberration problem in medical ultrasound; in particular, some of the same issues have been studied
for many years to improve acoustic imaging of the non homogeneous Earth.
The seismic imaging community has understood for some time that layered media may be approximated by constant-sound-speed media for beam forming purposes, leading to so-called time-migration algorithms. This raises the possibility of medical ultrasound applications|for example, brain imaging through the adult human skull. While our simulation results have been encouraging, experiments with animal skulls have been inconclusive due to the high attenuation of ultrasound in skull bone. Further research may validate the time-migration concept for brain imaging. Complete data sets are composed of the raw reflection data from every combination of one transmit element and one receive element in an array. The tremendous redundancy of a complete data set can be exploited for aberration correction by analyzing the time shifts on common-midpoint gathers. Until now, however, the wide-angle, random-scattering nature of medical ultrasound targets has limited the accuracy and robustness of this approach, particularly when estimating azimuth-dependent aberration pro files.
Pre filtering the data with two-dimensional fan filters largely solves this problem and produces an aberration-correction algorithm (OFF) that outperforms the most popular existing algorithms in almost all cases.The concept of focusing-operator updating, recently popular in seismic imaging, provides insight into iterative aberration-correction algorithms using a transmit focus. We develop a new updating procedure based on dynamic programming. With careful selection of initial focus points, the resulting algorithm outperforms existing algorithms in some experiments. Our aberration-correction results imply that imaging with single-valued focusing operators may be able to correct for most of the aberration encountered in soft tissues; that increasing aperture should not be viewed merely as a source of aberration, but as an opportunity to more fully correct it; and that the noise penalty for using complete data
sets may not be as serious a problem as commonly assumed. A diff erent kind of image-formation challenge is posed by small-diameter cylindrical imaging platforms. We derive a fast, three-dimensional, frequency-domain imaging algorithm for this geometry by making suitable approximations to the point spread function for wave propagation in cylindrical coordinates and obtaining its Fourier transform by analogy with the equivalent problem in Cartesian coordinates. For the most e ffective use of limited aperture, the focus of a transducer is treated as a virtual source, and the synthetic-aperture algorithm then forms images on deeper cylindrical shells. Computer simulations and experimental results show that this imaging technique attains the resolution limit dictated by the operating wavelength and transducer characteristics.
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| Title |
New approaches to nonlinear diffractive field propagation. |
| Author |
Christopher PT, Parker KJ. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
1991. |
| Abstract |
In many domains of acoustic field propagation, such as medical ultrasound imaging, lithotripsy.shock treatment, and underwater sonar, a realistic calculation of beam patterns requires treatment.of the effects of diffraction from finite sources. Also, the mechanisms of loss and nonlinear.effects within the medium are typically nonnegligible. The combination of diffraction,.attenuation, and nonlinear effects has been treated by a number of formulations and numerical.techniques. A novel model that incrementally propagates the field of baffled planar sources with.substeps that account for the physics of diffraction, attenuation, and nonlinearity is presented..The model accounts for the effect of refraction and reflection (but not multiple reflections) in the.case of propagation through multiple, parallel layers of fluid medium. An implementation of the.model for axis symmetric sources has been developed. In one substep of the implementation, a.new discrete Hankel transform is used with spatial transform techniques to propagate the field.over a short distance with diffraction and attenuation. In the other substep, the temporal.frequency domain solution to Burgers' equation is implemented to account for the nonlinear.accretion and depletion of harmonics. This approach yields a computationally efficient procedure.for calculating beam patterns from a baffled planar, axially symmetric source under conditions.ranging from quasilinear through shock. The model is not restricted by the usual parabolic wave.approximation and the field's directionality is explicitly accounted for at each point. Useage of a.harmonic-limiting scheme allows the model to propagate some previously intractable high-intensity nonlinear fields. Results of the model are shown to be in excellent agreement with measurements performed on the nonlinear field of an unfocused 2.25-MHz piston source, even in the near field where the established parabolic wave approximation model fails. Next, the model is used to compare the water path and in situ fields of a medical ultrasound device. Finally, the model is used to calculate the spatial heating rate associated with a nonlinear field and to simulate the phenomenon of saturation-induced beam broadening. |
| Title |
New approaches to nonlinear diffractive field propagation. |
| Author |
Christopher PT, Parker KJ. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
1991 |
| Abstract |
In many domains of acoustic field propagation, such as medical ultrasound imaging, lithotripsy shock treatment, and underwater sonar, a realistic calculation of beam patterns requires treatment of the effects of diffraction from finite sources. Also, the mechanisms of loss and nonlinear effects within the medium are typically nonnegligible. The combination of diffraction, attenuation, and nonlinear effects has been treated by a number of formulations and numerical techniques. A novel model that incrementally propagates the field of baffled planar sources with substeps that account for the physics of diffraction, attenuation, and nonlinearity is presented. The model accounts for the effect of refraction and reflection (but not multiple reflections) in the case of propagation through multiple, parallel layers of fluid medium. An implementation of the model for axis symmetric sources has been developed. In one substep of the implementation, a new discrete Hankel transform is used with spatial transform techniques to propagate the field over a short distance with diffraction and attenuation. In the other substep, the temporal frequency domain solution to Burgers' equation is implemented to account for the nonlinear accretion and depletion of harmonics. This approach yields a computationally efficient procedure for calculating beam patterns from a baffled planar, axially symmetric source under conditions ranging from quasilinear through shock. The model is not restricted by the usual parabolic wave approximation and the field's directionality is explicitly accounted for at each point. Useage of a harmonic-limiting scheme allows the model to propagate some previously intractable high-intensity nonlinear fields. Results of the model are shown to be in excellent agreement with measurements performed on the nonlinear field of an unfocused 2.25-MHz piston source, even in the near field where the established parabolic wave approximation model fails. Next, the model is used to compare the water path and in situ fields of a medical ultrasound device. Finally, the model is used to calculate the spatial heating rate associated with a nonlinear field and to simulate the phenomenon of saturation-induced beam broadening. |
| Title |
New clinical applications. |
| Author |
Kossoff G. |
| Journal |
Prog Med Ultrasound |
| Volume |
|
| Year |
1980 |
| Abstract |
The major new applications that were described in the literature in 1978 are reviewed. The author considers: B-mode imaging; water enema; the liquid filled stomach; continuous Doppler; pulsed Doppler; a combined technique; tissue characterisation; echographic appearance of fatty tissues; transmission reconstruction imaging. |
| Title |
New clinical applications. |
| Author |
Kossoff G. |
| Journal |
Prog Med Ultrasound |
| Volume |
|
| Year |
1981 |
| Abstract |
No abstract available. |
| Title |
New contrast-detail phantoms for improved precision in lesion detection measurements. |
| Author |
Smith SW, Insana MF, Lopez H. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1989 |
| Abstract |
The previous design of our ultrasound contrast-detail (C-D) phantom is limited in its ability to evaluate the quality of diagnostic ultrasound imaging systems. There is uncertainty in the contrast-detail measurements due to the single available viewing angle for each target and the resulting single realization of the ultrasound speckle pattern. Two new contrast-detail phantom designs are described which enable many independent realizations of the speckle noise for observer C-D experiments of improved precision. In the first design, a single tissue-mimicking cone is located on the axis of a tissue-mimicking cylinder. Cross-sectional images of the cone which simulate focal lesions can be obtained from any orientation by rotating the cylinder under the transducer. In the second new design, a tissue-mimicking cone is positioned in a tissue-mimicking slurry of agar/graphite spheres. Gentle stirring of the slurry and rotation of the cone produce many independent realizations of the speckle. In both new phantoms, the lesion contrast can be specified and is frequency/transducer independent. |
| Title |
New diagnostic tool employs ultrasound. |
| Author |
Unknown. |
| Journal |
Sci News Lett |
| Volume |
|
| Year |
1958 |
| Abstract |
No abstract available. |
| Title |
New doxorubicin-loaded phospholipid microbubbles for targeted tumor therapy: Part I--Formulation development and in-vitro characterization. |
| Author |
Tinkov S, Winter G, Coester C, Bekeredjian R. |
| Journal |
J Cont Rel |
| Volume |
|
| Year |
2010 |
| Abstract |
Despite high antitumor efficacy and a broad application spectrum, clinical treatment with anthracycline chemotherapeutics is often limited by severe adverse effects such as cardiotoxicity and myelosupression. In recent years, tumor drug targeting has evolved as a promising strategy to increase local drug concentration and reduce systemic side effects. One recent approach for targeting solid tumors is the application of microbubbles, loaded with chemotherapeutic drugs. These advanced drug carriers can be safely administered to the patient by intravenous infusion, and will circulate through the entire vasculature. Their drug load can be locally released by ultrasound targeted microbubble destruction. In addition, tumors can be precisely localized by diagnostic ultrasound since microbubbles act as contrast agents. In the present work a novel microbubble carrier for doxorubicin has been developed and characterized in-vitro. In contrast to many recent tumor-targeting MB designs the newly developed doxorubicin-loaded microbubbles possess a soft but stable phospholipid monolayer shell. Importantly, the active drug is embedded in the microbubble shell and is complexed to the phospholipids by both electrostatic and hydrophobic interactions. Despite their drug load, these novel microbubbles retained all important physical characteristics for ultrasound targeted microbubble destruction, comparable with the commercially available ultrasound contrast agents. In cell culture studies doxorubicin-loaded microbubbles in combination with ultrasound demonstrated an about 3 fold increase of the anti-proliferative activity compared to free doxorubicin and doxorubicin-loaded liposomes. For the first time in the literature the intracellular partition of free doxorubicin and phospholipid-complexed doxorubicin were compared. In conclusion, new doxorubicin-loaded microbubbles with ideal physical characteristics were developed. In-vitro studies show enhanced cytotoxic activity compared to free doxorubicin and doxorubicin-loaded liposomes. |
| Title |
New method for tracking fetal breathing movements using real-time pulsed Doppler.ultrasonographic displacement measurement. |
| Author |
Shinozuka N, Yamakoshi Y, Taketani Y..Department of Obstetrics and Gynecology, Faculty of Medicine, University of Toyko, Japan. |
| Journal |
J Ultrasound Med |
| Volume |
|
| Year |
1994 |
| Abstract |
To develop a clinical device for monitoring FBM with a simplified mechanism, the multichannel pulsed Doppler device was achieved.by modifying the ultrasonographic module and probe of a cardiotocograph. A new algorithm of signal processing with a.high-accuracy displacement estimation technique produced real-time and continuous displacement calculations. In vivo measurements.demonstrated that real-time output produced commendable quality in FBM tracking. The displacement of a few hundred micrometers.because of FBM was measured successfully. The results suggest that quantitative assessments of FBM should be possible with this.technique. |
| Title |
New piezoelectric transducers for therapeutic ultrasound. |
| Author |
Chapelon JY, Cathignol D, Cain C, Ebbini E, Kluiwstra JU, Sapozhnikov OA, Fluery G, Berriet R, Chupin L, Guey JL. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
2000 |
| Abstract |
Therapeutic ultrasound (US) has been of increasing interest during the past few years. However, the development of this technique depends on the availability of high-performance transducers. These transducers have to be optimised for focusing and steering high-power ultrasonic energy within the target volume. Recently developed high-power 1-3 piezocomposite materials bring to therapeutic US the exceptional electroacoustical properties of piezocomposite technology: these are high efficiency, large bandwidth, predictable beam pattern, more flexibility in terms of shaping and definition of sampling in annular arrays, linear arrays or matrix arrays. The construction and evaluation of several prototypes illustrates the benefit of this new approach that opens the way to further progress in therapeutic US. .. |
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