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BRL Abstracts Database |
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Your search for ultrasound produced 3296 results. Page 140 out of 330
| Title |
High‐intensity focused ultrasound transducer design for surgical and hemostatic applications. |
| Author |
keilman GW, Kaczkowski PJ. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
1998 |
| Abstract |
A resurgence in interest in the application of high‐intensity focused ultrasound (HIFU) to surgical problems is due in part to significant improvements in imaging modalities for targeting the delivery of ultrasound. The wide variety of potential applications under consideration necessitates a refinement of transducer design to accommodate often conflicting constraints. The need to deliver substantial power to a small target zone requires high focal gain to minimize collateral damage, and yet must be balanced with the need for small transducers in many procedures. In general, the choice of operating frequency, transducer aperture and focal depth, convenient acoustic coupling methods, waveform selection, and amplifier characteristics must all be adjusted to best fit the application. This presentation will discuss such tradeoffs in any HIFU transducer design, and will also address particular techniques for coupling and cooling transducers which deliver hundreds of watts of acoustic power. Transducer efficiencies of over 85% have been routinely achieved by judicious selection of matching layers and tuning networks, while maintaining over 50% relative bandwidth, for center frequencies spanning the range from 1 to 10 MHz. Transducer requirements for array‐based systems, motivated by clinical needs, will also be discussed. [Work funded by DARPA/ONR.] |
| Title |
Higher order spectra based deconvolution of ultrasound images. |
| Author |
Abeyratne UR, Petropulu AP, Reid JM. |
| Journal |
IEEE Trans UFFC |
| Volume |
|
| Year |
1995 |
| Abstract |
We address the problem of improving the spatial resolution of ultrasound images through blind deconvolution. The ultrasound image formation process in the RF domain can be expressed as a spatio-temporal convolution between the tissue response and the ultrasonic system response, plus additive noise. Convolutional components of the dispersive attenuation and aberrations introduced by propagating through the object being imaged are also incorporated in the ultrasonic system response. Our goal is to identify and remove the convolutional distortion in order to reconstruct the tissue response, thus enhancing the diagnostic quality of the ultrasonic image. Under the assumption of an independent, identically distributed, zero-mean, non-Gaussian tissue response, we were able to estimate distortion kernels using bicepstrum operations on RF data. Separate 1-D distortion kernels were estimated corresponding to axial and lateral image lines and used in the deconvolution process. The estimated axial kernels showed similarities to the experimentally measured pulse-echo wavelet of the imaging system. Deconvolution results from B-scan images obtained with clinical imaging equipment showed a 2.5-5.2 times gain in lateral resolution, where the definition of the resolution has been based on the width of the autocovariance function of the image. The gain in axial resolution was found to be between 1.5 and 1.9. |
| Title |
Higher order versus second order statistics in ultrasound image deconvolution. |
| Author |
Abeyratne UR, Petropulu AP, Reid JM, Golas T, Conant E, Forsberg F. |
| Journal |
IEEE Trans UFFC |
| Volume |
|
| Year |
1997 |
| Abstract |
We recently proposed a method for the estimation of imaging distortions associated with ultrasound images, based on the higher-order statistics (HOS) of radio frequency data. In this correspondence, we utilize the HOS-based estimated distortions to deconvolve ultrasound images of the breast. WE also estimate imaging distortions based on the second-order statistics (SOS) of radio frequency ultrasound data and subsequently utilize them to deconvolve the same breast images. Both subjective and objective measures suggest that deconvolution with HOS-based distortion estimates led to significantly higher resolution gains as compared to the gains achieved when SOS-based distortion estimates were used. |
| Title |
Highly efficient sonochemical reaction with a switched spiral focal field. |
| Author |
Kawabata K, Umemura S |
| Journal |
Ultrasonics |
| Volume |
|
| Year |
1993 |
| Abstract |
This paper describes an efficient method of inducing sonochemical reactions with focussed ultrasound. A sector-vortex transducer (a phased array transducer with multiple sectors and a geometric focus) is used to produce focal ultrasound fields with spiral-shaped wavefronts. Clockwise and counter-clockwise spiral focal fields, with basically the same ultrasound power distribution but having different wavefront angles, are produced by using the same array transducer. The oxidation of the iodide ions induced from the periodic switching between such a pair of spiral focal fields is investigated at an ultrasound frequency of 750 kHz. The oxidation rate at the optimum switching period (3 ms) is about ten times higher than that at switching periods of 1 s. The optimum switching period and the sonochemical reaction rate are unchanged when the viscosity was adjusted to that of human blood. |
| Title |
Histologic changes in porcine eyes treated with high-intensity focused ultrasound. |
| Author |
Burgess SEP, Iwamoto T, Coleman DJ, Lizzi FL, Driller J, Rosado A. |
| Journal |
Ann Ophthalmol |
| Volume |
|
| Year |
1987 |
| Abstract |
High-intensity focused ultrasound (HIFU) has recently been described in the treatment of patients with glaucoma. However, despite previous studies in animal and mathematical models, the mechanisms of action are not completely understood. We therefore undertook a histologic study of 15 porcine eyes to evaluate the effect of HIFU and, in particular, the changes seen after sequential insonification on previously treated areas of sclera. We demonstrated initial scleral swelling that was followed by scleral thinning. The scleral thinning could be maximized by a second superimposed course of HIFU. The most consistent change in the ciliary body was necrosis of the pars plana. Some treated animals developed a hemorrhagic retinal detachment that we believe to be due to the presence of a circumferential blood vessel, which runs in the ora serrata of the pig but which is not present in humans. Based on our observations, possible mechanisms of action of this treatment are discussed. |
| Title |
Histologic effects of contact ultrasound for the treatment of glaucoma. |
| Author |
Polack PJ, Iwamoto T, Silverman RH, Driller J, Lizzi FL, Coleman DJ. |
| Journal |
Invest Ophthalmol Vis Sci |
| Volume |
|
| Year |
1991 |
| Abstract |
The histologic effects of a contact ultrasound applicator were compared with those of the immersion applicator that is currently used clinically for the treatment of glaucoma. The applicator coupling cone uses a distensible rubber membrane that can be inflated to control stand-off distance relative to the surface of the eye. This feature allows the focal point of the therapeutic beam to be placed at selective depths. Histologic comparisons of lesions in rabbit and pig eyes showed lesions in the sclera and ciliary body that were similar to those produced by the immersion transducer when the same focal position was used. Moving the focal point to a greater depth resulted in less superficial damage, yet still produced ciliodestruction. Damage to the blood supply of the ciliary body, as found in human cadaver eyes, may be an additional mechanism of action of therapeutic ultrasound, and perhaps of other transscleral high-energy modalities. |
| Title |
Histologic studies following exposure of bone to ultrasound. |
| Author |
Bender LF, Janes JM, Herrick JF. |
| Journal |
Arch Phys Med Rehabil |
| Volume |
|
| Year |
1954 |
| Abstract |
No abstract available. |
| Title |
Histological analysis of healthy epithelium of Wistar rats in vivo irradiated with different intensities of therapeutic ultrasound. |
| Author |
De Bem DM, Maciel CD, Zuanon JA, Neto CB, Parizotto NA. |
| Journal |
Rev Bras Fisioter |
| Volume |
|
| Year |
2010 |
| Abstract |
BACKGROUND:
Ultrasound (US) is a widely used and studied resource for physical therapy treatments. Given the scarcity of studies on the effects of US on healthy tissue, many physical therapy professionals make unfounded decisions regarding its methods and parameters of application.
OBJECTIVES:
The possible histological and morphometric changes in the healthy tissue of Wistar rats in vivo irradiated with different intensities of US were evaluated.
METHODS:
Thirty Wistar rats, randomly distributed among five groups of six animals each, were treated on the right side of the dorsal region, over an area of 4 cm(2). The left side served as a control. The treatment was applied over a four-day period, with two mins. of daily irradiation. The output intensity was checked using a precision dosimeter before the applications. Histological and morphometric analyses were performed using the Image Tool software.
RESULTS:
There were slight inflammatory infiltration and thinning of the dermis fibers, particularly in the groups irradiated with 1.5 and 2 W/cm(2). There was also thickening of the epidermis in the samples from the irradiated animals. To evaluate the quantitative results, the statistical analyses consisted of one-way ANOVAs with the post-hoc Tukey tests. There were significant differences in epidermis thicknesses between the control group and the groups irradiated with 1.0, 1.5 and 2.0 W/cm(2).
CONCLUSIONS:
Higher doses of US produced changes in the epidermis and dermis, i.e. increased thickness and collagen fiber thinning and proliferation, respectively. These results serve as a warning of the possible implications of therapeutic ultrasound use in esthetics. |
| Title |
Histological and cytological study of the effects of ultrasound on the tail of the salamander. |
| Author |
Goessens G |
| Journal |
Arch Biol (Liege) |
| Volume |
|
| Year |
1966 |
| Abstract |
No abstract available. |
| Title |
Histological observation of Islet hemorrhage induced by diagnostic ultrasound with contrast agent in rat pancreas. |
| Author |
Miller DL, Dou C, Sorenson D, Liu M. |
| Journal |
PLoS One |
| Volume |
|
| Year |
2011 |
| Abstract |
Contrast enhanced diagnostic ultrasound CEDUS has been shown to induce capillary hemorrhage in heart and kidney. This study characterized the capillary hemorrhage induced in rat pancreas. The pancreata of anesthetized hairless rats were accessed by laparotomy. A 1.5 MHz diagnostic ultrasound probe with 2.3 MPa peak rarefactional pressure amplitude and 1 s intermittent trigger was used to scan the pancreas, located at the focus (3.8 cm), through saline coupling. The probe was swept to expose the entire organ in 5 min during infusion of Definity® contrast agent at 10 µL/kg/min, and this was repeated in a reverse sweep. The entire pancreas was removed, spread flat for fixation and histological slides were prepared from the mid-plane. Slides were scored blind for islet hemorrhage over the entire area of the organ. Intra-islet microlesions were evident and hemorrhage surrounded many islets. The hemorrhage often impacted nearby acini, and expanded into inter-lobular septa. In CEDUS pancreata removed soon after scanning, 76.2±11.8% (n = 6) of islets had evidence of hemorrhage and/or islet microlesions compared to 1.1±2.5% (n = 5) for sham CEDUS (P<0.001). In pancreata removed after 4 hr, fibrin formation was detected by immunohistology in the hemorrhage and intra-islet microlesions. Diagnostic ultrasound with contrast agent induced substantial capillary hemorrhage in rat pancreas, concentrated particularly in the islets. |
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