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BRL Abstracts Database |
Your search for ultrasound produced 3296 results. Page 180 out of 330
Title |
Morphostatic effect of ultrasound on limb regeneration in the newt Triturus (Diemictylus) viridescens. |
Author |
Wolsky A, Pizzarello DJ. |
Journal |
Am Zoo |
Volume |
|
Year |
1973 |
Abstract |
No abstract available. |
Title |
Motion compensation algorithm for non-invasive two-dimensional temperature estimation using diagnostic pulse-echo ultrasound. |
Author |
Simon C, VanBaren P, Ebbini E. |
Journal |
SPIE |
Volume |
|
Year |
1998 |
Abstract |
The feasibility of real-time non-invasive spatio-temporal temperature estimation from pulse-echo diagnostic ultrasound data has been previously demonstrated in stationary phantoms. The method is based on first estimating the axial shifts of the RF-echo data due to local changes in the speed of sound and thermal expansion in the propagating medium, and then differentiating these estimates along axial direction to obtain the temperature rise map. In a clinical setup, however, translation, rotation and deformation affect the estimates. In this paper we introduce an algorithm to compensate for tissue translation and uniform deformation along the axial and lateral directions of the ultrasonic imaging plane. This is achieved by separating the components of the time-shift map due to temperature rise (a local effect, occurring within the vicinity of the heated region) from the component due to translation and deformation (effect observed over a larger region). A rubber phantom experiment was designed where high intensity focused ultrasound was used to generate localized heating while motion was applied to the phantom and/or imaging transducer. Temperature profiles were successfully estimated while the phantom was translated by 30 mm and axially deformed by 13%. |
Title |
Mouse embryo heart in organ culture visualized by the acoustic microscope. |
Author |
Eggleton RC, Kessler LW. |
Journal |
Ultrasound Med |
Volume |
|
Year |
1974 |
Abstract |
No abstract available. |
Title |
Mouse lung damage from exposure to 30 kHz ultrasound. |
Author |
O'Brien WD Jr, Zachary JF. |
Journal |
Ultrasound Med Biol |
Volume |
|
Year |
1994 |
Abstract |
Two hundred and seventy mice were evaluated at three exposure durations (5, 10 and 20 min) and at six peak acoustic pressure levels (0, 65, 80, 87, 100 and 145 kPa) with 15 mice per exposure condition, at an ultrasonic frequency of 30 kHz modulated at 120 Hz. Threshold acoustic pressure levels for hemorrhage in mouse lung exposed for the three exposure durations appear to be in the range of 100 kPa. There did not appear to be a strong dependency on exposure duration. When compared to a study with mice in the megahertz frequency range (Child et al. 1990), it appeared that the threshold values followed a square root of frequency dependency, suggesting that the concept of the Mechanical Index (AIUM/NEMA, 1992), although developed for pulsed ultrasound conditions, may be extended to frequencies well below the diagnostic ultrasound frequency range. |
Title |
MR imaging-guided focused ultrasound surgery of fibroadenomas in the breast: a feasibility study. |
Author |
Hynynen K, Pomeroy O, Smith DN, Huber PE, McDannold NJ, Kettenbach J, Baum J, Singer S, Jolesz FA. |
Journal |
Radiology |
Volume |
|
Year |
2001 |
Abstract |
To test the feasibility of noninvasive magnetic resonance (MR) imaging–guided focused ultrasound surgery (FUS) of benign fibroadenomas in the breast.
Eleven fibroadenomas in nine patients under local anesthesia were treated with MR imaging-guided FUS. Based on a T2-weighted definition of target volumes, sequential sonications were delivered to treat the entire target. Temperature-sensitive phase-difference–based MR imaging was performed during each sonication to monitor focus localization and tissue temperature changes. After the procedure, T2-weighted and contrast material–enhanced T1-weighted MR imaging were performed to evaluate immediate and long-term effects.
Thermal imaging sequences were improved over the treatment period, with 82% (279 of 342) of the hot spots visible in the last seven treatments. The MR imager was used to measure temperature elevation (12.8°–49.9°C) from these treatments. Eight of the 11 lesions treated demonstrated complete or partial lack of contrast material uptake on posttherapy T1-weighted images. Three lesions showed no marked decrease of contrast material uptake. This lack of effective treatment was most likely due to a lower acoustic power and/or patient movement that caused misregistration. No adverse effects were detected, except for one case of transient edema in the pectoralis muscle 2 days after therapy.
MR imaging–guided FUS can be performed to noninvasively coagulate benign breast fibroadenomas. |
Title |
MR imaging-guided focused ultrasound surgery of uterine leiomyomas: A feasibility study. |
Author |
Tempany CMC, Stewart EA, McDannold N, Quade BJ, Jolesz FA, Hynynen K. |
Journal |
Radiology |
Volume |
|
Year |
2003 |
Abstract |
The feasibility and safety of magnetic resonance (MR) imaging–guided focused ultrasound surgery for uterine leiomyomas is reported. Sequential sonications were delivered to nine targets. Temperature-sensitive phase-difference MR imaging monitored the location of the focus and measured tissue temperature elevations, ensuring therapeutic dose. MR images and hysterectomy specimens were evaluated. Six leiomyomas received full therapeutic doses, and 98.5% of the sonications were visualized. MR thermometry was successful in all sonications and cases. Focal necrotic lesions were seen in all cases at MR, and five were pathologically confirmed. MR imaging-guided focused ultrasound causes thermocoagulation and necrosis in uterine leiomyomas and is feasible and safe, without serious consequences. |
Title |
MR monitoring of focused ultrasonic surgery of renal cortex: experimental and simulation studies. |
Author |
Hynynen K, Damianou CA, Colucci V, Unger E, Cline HH, Jolesz FA. |
Journal |
J Magn Reson Imaging |
Volume |
|
Year |
1995 |
Abstract |
The aim of the study was to test the hypothesis that magnetic resonance (MR) imaging-guided and -monitored noninvasive ultrasonic surgery can be performed in highly perfused tissues from outside the body. A simulation study was performed to evaluate the optimal sonication parameters. An MR-compatible positioning device was then used to manipulate a focused ultrasound transducer in an MR imager, which was used to sonicate kidneys of five rabbits at various power levels and different durations. Temperature elevation during sonication was monitored with a T1-weighted spoiled gradient-echo sequence. The simulation study demonstrated that a sharply focused transducer and relatively short sonication times (30 seconds or less) are necessary to prevent damage to the overlying skin and muscle tissue, which have a much lower blood perfusion rate than kidney. The experiments showed that the imaging sequence was sensitive enough to show temperature elevation during sonication, thereby indicating the location of the beam focus. Histologic evaluations showed that kidney necrosis could be consistently induced without damage to overlying skin and muscle. The study demonstrated that highly perfused tissues such as the renal cortex can be coagulated from outside the body with focused ultrasound and that MR imaging can be used to guide and monitor this surgery. |
Title |
MRI monitoring and control of focused ultrasound surgery. |
Author |
Mcdannold KH, Daum TF. |
Journal |
J Acoust Soc Am |
Volume |
|
Year |
1998 |
Abstract |
The clinical and animal tests of focused ultrasound surgery have shown significant variation between the effectiveness of the same power sonications. Therefore, it has become important to seek methods to monitor the in vivo ultrasound exposures. One of the most promising methods is the use of magnetic resonance imaging (MRI) to detect the temperature elevation. In this paper the calibration and accuracy of MRI thermometry will be presented. The in vivo mapped temperature distributions allow the thermal exposure of the tissue to be estimated. These estimates have been compared with the tissue coagulation produced in muscle and brain tissues in vivo. The results show that the lesion boundary is predicted with the resolution of the MRI voxels. This has significant clinical value since the MRI thermometry can be used to control the treatment on‐line. |
Title |
MRI-guided gas bubble enhanced ultrasound heating in in vivo rabit thigh. |
Author |
Sokka SD, King R, Hynynen K. |
Journal |
Phys Med Biol |
Volume |
|
Year |
2003 |
Abstract |
In this study, we propose a focused ultrasound surgery protocol that induces and then uses gas bubbles at the focus to enhance the ultrasound absorption and ultimately create larger lesions in vivo. MRI and ultrasound visualization and monitoring methods for this heating method are also investigated. Larger lesions created with a carefully monitored single ultrasound exposure could greatly improve the speed of tumour coagulation with focused ultrasound. All experiments were performed under MRI (clinical, 1.5 T) guidance with one of two eight-sector, spherically curved piezoelectric transducers. The transducer, either a 1.1 or 1.7 MHz array, was driven by a multi-channel RF driving system. The transducer was mounted in an MRI-compatible manual positioning system and the rabbit was situated on top of the system. An ultrasound detector ring was fixed with the therapy transducer to monitor gas bubble activity during treatment. Focused ultrasound surgery exposures were delivered to the thighs of seven New Zealand while rabbits. The experimental, gas-bubble-enhanced heating exposures consisted of a high amplitude 300 acoustic watt, half second pulse followed by a 7 W, 14 W or 21 W continuous wave exposure for 19.5 s. The respective control sonications were 20 s exposures of 14 W, 21 W and 28 W. During the exposures, MR thermometry was obtained from the temperature dependency of the proton resonance frequency shift. MRT2-enhanced imaging was used to evaluate the resulting lesions. Specific metrics were used to evaluate the differences between the gas-bubble-enhanced exposures and their respective control sonications: temperatures with respect to time and space, lesion size and shape, and their agreement with thermal dose predictions. The bubble-enhanced exposures showed a faster temperature rise within the first 4 s and higher overall temperatures than the sonications without bubble formation. The spatial temperature maps and the thermal dose maps derived from the MRI thermometry closely correlated with the resulting lesion as examined by T2-weighted imaging. The lesions created with the gas-bubble-enhanced heating exposures were 2-3 times larger by volume, consistently more spherical in shape and closer to the transducer than the control exposures. The study demonstrates that gas bubbles can reliably be used to create significantly larger lesions in vivo. MRI thermometry techniques were successfully used to monitor the thermal effects mediated by the bubble-enhanced exposures. |
Title |
MRI-guided noninvasive ultrasound surgery. |
Author |
Hynynen K, Darkazanli A, Unger E, Schenck JF. |
Journal |
Med Phys |
Volume |
|
Year |
1993 |
Abstract |
In this study, the feasibility of using magnetic resonance imaging (MRI) to detect tissue necrosis induced by focussed ultrasound beams was investigated. It was shown that lesions produced in dog's thigh muscle in vivo were clearly visible in T2-weighted images and that the lesion dimensions measured from the images correlated with the postmortem measurements of the visible tissue damage. It was also shown that the sonications can be done in the magnet and that the lesions are visible immediately after the sonications with increasing image contrast as a function of time. These results showed that MRI can be used to direct and monitor on-line noninvasive ultrasound surgery. This may have a major impact in future patient treatments. |
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