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BRL Abstracts Database |
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Your search for ultrasound produced 3296 results. Page 70 out of 330
| Title |
Comparison of gene delivery techniques for therapeutic angiogenesis. |
| Author |
Kobulnik J,Kuliszewski MA,Stewart DJ,Lindner J R,Leong-Poi H. |
| Journal |
J Am Coll Cardiol |
| Volume |
|
| Year |
2009 |
| Abstract |
Objectives: This study was designed to compare the efficacy of angiogenic gene delivery by ultrasound-mediated (UM) destruction of intravenous carrier microbubbles to direct intramuscular (IM) injections.
Background: Current trials of gene therapy for angiogenesis remain limited by suboptimal, invasive delivery techniques.
Methods: Hind-limb ischemia was produced by iliac artery ligation in 99 rats. In 32 rats, UM delivery of green fluorescent protein (GFP)/vascular endothelial growth factor-165 (VEGF165) plasmid deoxyribonucleic acid was performed. Thirty-five animals received IM injections of VEGF165/GFP plasmid. Remaining rats received no treatment. Before delivery (day 14 after ligation) and at days 17, 21, and 28 and week 8 after ligation, microvascular blood volume and microvascular blood flow to the proximal hind limbs were assessed by contrast-enhanced ultrasound (n = 8 per group). Total transfection was assessed by reverse transcriptase–polymerase chain reaction, and localization of transfection was determined by immunohistochemistry.
Results: By day 28, both IM and UM delivery of VEGF165 produced significant increases in microvascular blood volume and microvascular blood flow. Whereas increases in microvascular blood volume were similar between treatment groups, microvascular blood flow was greater (p < 0.005) in UM-treated animals as compared with IM-treated animals, persisting to week 8. The VEGF165/GFP messenger ribonucleic acid expression was greater (p < 0.05) for IM-treated animals. A strong GFP signal was detected for both groups and was localized to focal perivascular regions and myocytes around injection sites for IM and to the vascular endothelium of arterioles/capillaries in a wider distribution for UM delivery.
Conclusions: Despite lower transfection levels, UM delivery of VEGF165 is as effective as IM injections. The UM delivery results in directed vascular transfection over a wider distribution, which may account for the more efficient angiogenesis. |
| Title |
Comparison of micronuclei induction for x-ray and ultrasound exposures of Vicia faba root meristem cells. |
| Author |
Miller MW. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1978 |
| Abstract |
X-irradiation (200R) but not ultrasound (1.1 MHz, 8 W/cm2 peak, 1 min continuous exposure) induced micronuclei formation in root meristem cells of Vicia faba 6-36 hr post-exposure. |
| Title |
Comparison of mouse and rabbit lung damage exposure to 30 khz ultrasound. |
| Author |
O'Brien WD Jr, Zachary JF. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1994 |
| Abstract |
Twenty-four mice and sixteen rabbits were evaluated at one exposure duration (10 min) and at three exposure acoustic pressure levels (0, 100 and 145 kPa) at an ultrasonic frequency of 30 kHz, continuous wave for the purpose of testing whether there was a species difference in the degree of sensitivity to ultrasound-induced lung damage. This study was undertaken because it was hypothesized that the mouse may not be an acceptable or suitable animal model for studies that examine the effects of ultrasound on lung tissue for purposes of extrapolating or estimating the degree of potential damage in other species. The rabbit was selected for comparison to the mouse because the rabbit exhibited sufficient physiological and morphological differences from those of the mouse to test this hypothesis. Using exactly the same exposure conditions and lung assessment criteria, it appeared that the mouse lung was more sensitive to ultrasound-induced damage than that of the rabbit by a factor of between 2.8 and 3.6. Lung lesions in mice and rabbits were similar in character, but were much more severe and extensive in mice. Lesions in both species consisted of intraalveolar hemorrhage that appeared as dark red to red-black areas that were visible on the pleural surfaces and that extend within the lung parenchyma. |
| Title |
Comparison of quantitative ultrasound parameters for fat content liver detection and monitoring. |
| Author |
Muleki-Seya P, Han A, Andre MP, Erdman JW Jr, O'Brien WD Jr. |
| Journal |
Proc IEEE Ultrason Symp |
| Volume |
|
| Year |
2017 |
| Abstract |
Quantitative ultrasound parameter estimates from the Lizzi-Feleppa (LF slope, intercept and midband) and quantitative ultrasound (mean BSC, mean AC, ESD and EAC) approaches were compared for in vivo and ex vivo mouse liver fat content monitoring. The quantitative ultrasound parameters having the higher correlations with fat content were EAC (R2=0.68), mean BSC (R2=0.60), mean AC (R2=0.60) and LF midband (R2=0.70) for ex vivo conditions and mean BSC (R2=0.45), LF midband (R2=0.44) and mean AC (R2=0.37) for in vivo conditions. By defining a threshold fat content of 11.6% between normal vs. fatty mouse livers, the parameters yielding the better sensitivities and specificities to differentiate normal and fatty liver ex vivo were the mean AC (sensitivity=1, specificity=1), then mean BSC and LF midband (sensitivity=0.87, specificity=1). In vivo, the parameters yielding the better sensitivities and specificities to differentiate normal vs. fatty liver were mean BSC and LF midband (sensitivity=0.93, specificity=0.87) and then the mean AC (sensitivity=0.67, specificity=0.93). |
| Title |
Comparison of sound fields generated by different coded excitations--experimental results. |
| Author |
Nowicki A Klimonda Z Lewandowski M Litniewski J Lewin PA Trots I. |
| Journal |
Ultrasonics |
| Volume |
|
| Year |
2006 |
| Abstract |
This work reports the results of measurements of spatial distributions of ultrasound fields obtained from five energizing schemes. Three different codes, namely, chirp signal and two sinusoidal sequences were investigated. The sequences were phase modulated with 13 bits Barker code and 16 bits Golay complementary codes. Moreover, two reference signals generated as two and sixteen cycle sine tone bursts were examined. Planar, 50% (fractional) bandwidth, 15 mm diameter source transducer operating at 2 MHz center frequency was used in all measurements. The experimental data were collected using computerized scanning system and recorded using wideband, PVDF membrane hydrophone (Sonora 804). The measured echoes were compressed, so the complete pressure field in the investigated location before and after compression could be compared. In addition to a priori anticipated increase in the signal to noise ratio (SNR) for the decoded pressure fields, the results indicated differences in the pressure amplitude levels, directivity patterns, and the axial distance at which the maximum pressure amplitude was recorded. It was found that the directivity patterns of non-compressed fields exhibited shapes similar to the patterns characteristic for sinusoidal excitation having relatively long time duration. In contrast, the patterns corresponding to compressed fields resembled those produced by brief, wideband pulses. This was particularly visible in the case of binary sequences. The location of the maximum pressure amplitude measured in the 2 MHz field shifted towards the source by 15 mm and 25 mm for Barker code and Golay code, respectively. The results of this work may be applicable in the development of new coded excitation schemes. They could also be helpful in optimizing the design of imaging transducers employed in ultrasound systems designed for coded excitation. Finally, they could shed additional light on the relationship between the spatial field distribution and achievable image quality and in this way facilitate optimization of the images obtained using coded systems. |
| Title |
Comparison of split-beam transducer geometries and excitation configurations for transrectal prostate HIFU treatments |
| Author |
Seip R, Sanghvi NT. |
| Journal |
Proc Ultrason Symp IEEE |
| Volume |
|
| Year |
2001 |
| Abstract |
Six split-beam transducer configurations have been examined using computer simulations and in-vitro experiments. The goal of this study was to identify a simple split-beam transducer configuration capable of reducing transrectal high intensity focused ultrasound (HIFU) prostate cancer treatment time without sacrificing treatment safety and efficacy. Lesion volume, lesion and rectal wall temperatures, sonication ON/OFF time, and total acoustic power parameters were used as comparison criteria. The most promising split-beam configuration generates necrosed tissue volumes 5 times larger than the single-element transducer with the same sonication time, while keeping maximum focal zone temperatures below 90°C. These parameters yield approximate overall treatment time reductions by a factor of 1.85 as compared to single-element transrectal HIFU PC treatments, mainly due to longer tissue cooling time required to maintain current safety levels. |
| Title |
Comparison of split-beam transducer geometries and excitation configurations for transrectal prostate HIFU treatments. |
| Author |
Seip R, Sanghvi NT. Uchida T, Umemura SI. |
| Journal |
Proc IEEE Ultrasonic Symposium |
| Volume |
|
| Year |
2002 |
| Abstract |
Six split-beam transducer configurations have been examined using computer simulations and in-vitro experiments. The goal of this study was to identify a simple split-beam transducer configuration capable of reducing transrectal high intensity focused ultrasound (HIFU) prostate cancer treatment time without sacrificing treatment safety and efficacy. Lesion volume, lesion and rectal wall temperatures, sonication ON/OFF time, and total acoustic power parameters were used as comparison criteria. The most promising split-beam configuration generates necrosed tissue volumes 5 times larger than the single-element transducer with the same sonication time, while keeping maximum focal zone temperatures below 90°C. These parameters yield approximate overall treatment time reductions by a factor of 1.85 as compared to single-element transrectal HIFU PC treatments, mainly due to longer tissue cooling time required to maintain current safety levels. |
| Title |
Comparison of techniques for in vivo attenuation measurements. |
| Author |
Parker KJ, Lerner RM, Waag RC. |
| Journal |
IEEE Trans Biomed Eng |
| Volume |
|
| Year |
1988 |
| Abstract |
The attenuation of an ultrasound pulse within tissue can be estimated from either the amplitude decay or the frequency downshift of returning echoes. The authors compare the results of both analyses as applied to ultrasound B scan echoes from the livers of 49 individuals. The amplitude decay of the backscattered signal Fourier components with depth was used to calculate attenuation coefficients. In addition, the frequency downshift of the same backscattered signals was estimated using both zero-crossing and spectral centroid methods. The results show that the frequency-domain estimators yield consistently higher attenuation coefficients, with higher variability compared to the amplitude decay method. Explanations for the apparent bias and variability of the frequency-shift estimators include both the assumptions regarding tissue and signal which may not be met in practice and the effects of low-frequency electronic noise on spectral estimates. |
| Title |
Comparison of the output display standard's TIS estimates with independently determined maximum temperature increase calculations. |
| Author |
O'Brien WD Jr, Ellis DS. |
| Journal |
Proc Ultrason Symp IEEE |
| Volume |
|
| Year |
1996 |
| Abstract |
The monopole-source solution was used to calculate the three-dimensional complex acoustic pressure field for focused circular apertures (diameters: 1, 2, 4 cm) and transmit f-numbers (radius of curvature/diameter values: 0.7, 1, 1.3, 1.6, 2, 3, 4, 5) for various ultrasonic frequencies (1, 2, 3, 4, 5, 7, 9, 12 MHz) from which the three-dimensional temperature distribution was calculated using the bio-heat transfer equation in homogeneous, perfused media (attenuation=absorption=0.3 dB/cm-MHz; perfusion length: 1.0 cm). For the 184 cases, the acoustic field was normalized to the derated spatial peak, temporal average intensity (ISPTA.3) of 720 mW/cm2 , the maximum value allowed by the FDA 510(k) diagnostic ultrasound equipment approval process, from which the axial temperature increase profile and the maximum temperature increase (ΔTmax ) were determined. Also, from the normalized acoustic field, the soft-tissue thermal index (TIS) was determined according to the procedures of the Output Display Standard from the normalized acoustic field. In general, TIS and ΔTmax increase with increasing transmit f-number and TIS tracks ΔTmax which allows for As Low As Reasonably Achievable (ALARA) Principle implementation. TIS mostly underestimates ΔTmax (TIS⩽ΔTmax) for f-numbers⩽1 and mostly overestimates ΔTmax (TIS⩾ΔTmax) for f-numbers⩾2. For the lower transmit f-numbers ⩽2, ΔT max does not exceed a value of 0.30°C (0.0060⩽ΔTmax⩽0.30°C for these 115 cases) and the maximum value of TIS does not exceed a value of 0.40 (0.00010⩽TIS⩽ 0.40 for these 115 cases). Therefore, for f-numbers ⩽2, the TIS display would never be available to the system operator since the TIS value does not equal or exceed 1.0. For the higher transmit f-numbers⩾3, TIS is generally within a factor of 2 of ΔTmax for predicting ΔTmax. These results generally confirm the applicability of the TIS estimation procedure but question the FDA ISPTA.3 intensity limit of 720 mW/cm2. |
| Title |
Comparison of ultrasound attenuation and backscatter estimates in layered tissue-mimicking phantoms among three clinical scanners. |
| Author |
Nam K, Rosado-Mendez IM, Wirtzfeld LA, Ghoshal G, Pawlicki AD, Madsen EL, Lavarello RJ, Oelze ML, Zagzebski JA, O'Brien WD Jr, Hall TJ. |
| Journal |
Ultrason Imaging |
| Volume |
|
| Year |
2012 |
| Abstract |
Backscatter and attenuation coefficient estimates are needed in many quantitative ultrasound strategies. In clinical applications, these parameters may not be easily obtained because of variations in scattering by tissues overlying a region of interest (ROI). The goal of this study is to assess the accuracy of backscatter and attenuation estimates for regions distal to nonuniform layers of tissue-mimicking materials. In addition, this work compares results of these estimates for “layered” phantoms scanned using different clinical ultrasound machines. Two tissue-mimicking phantoms were constructed, each exhibiting depth-dependent variations in attenuation or backscatter. The phantoms were scanned with three ultrasound imaging systems, acquiring radio frequency echo data for offline analysis. The attenuation coefficient and the backscatter coefficient (BSC) for sections of the phantoms were estimated using the reference phantom method. Properties of each layer were also measured with laboratory techniques on test samples manufactured during the construction of the phantom. Estimates of the attenuation coefficient versus frequency slope, α0, using backscatter data from the different systems agreed to within 0.24 dB/cm-MHz. Bias in the α0 estimates varied with the location of the ROI. BSC estimates for phantom sections whose locations ranged from 0 to 7 cm from the transducer agreed among the different systems and with theoretical predictions, with a mean bias error of 1.01 dB over the used bandwidths. This study demonstrates that attenuation and BSCs can be accurately estimated in layered inhomogeneous media using pulse-echo data from clinical imaging systems. |
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