Bioacoustics Research Lab
University of Illinois at Urbana-Champaign | Department of Electrical and Computer Engineering | Department of Bioengineering
Department of Statistics | Coordinated Science Laboratory | Beckman Institute | Food Science and Human Nutrition | Division of Nutritional Sciences | College of Engineering
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William D. O'Brien, Jr. publications:

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Your search for ultrasound produced 3296 results.

Page 234 out of 330

Title Sound radiation of 3-MHz driven gas bubbles.
Author Grossmann S, Hilgenfeldt S, Lohse D, Zomack M.
Journal J Acoust Soc Am
Volume
Year 1997
Abstract The sound radiation of 3-MHz acoustically driven air bubbles in liquid is analyzed with respect to possible applications in second harmonic ultrasound diagnostics. devices, which have recently come into clinical use. In the forcing pressure amplitude P/sub a/=1-10 atm and ambient radius R/sub 0/=0.5-5 mu m parameter domain, a. narrow regime around the resonance radius R/sub 0/~1-1.5 mu m and relatively modest P/sub a/~2-2.5 atm is identified in which optimal sound yield in the second. harmonic is achieved while maintaining spherical stability of the bubble. For smaller P/sub a/ and larger R/sub 0/ hardly any sound is radiated; for larger P/sub a/ bubbles. become unstable toward nonspherical shape oscillations of their surface. The computation of these instabilities is essential for the evaluation of the optimal parameter. regime. A region of slightly smaller R/sub 0/ and P/sub a/~1-3 atm is best suited to achieve large ratios of the second harmonic to the fundamental intensity. Spherical. stability is guaranteed in the suggested regimes for liquids with an enhanced viscosity compared to water, such as blood.


Title Sound scattering and localized heat deposition of pulse-driven microbubbles.
Author Hilgenfeldt S, Lohse D, Zomack M.
Journal J Acoust Soc Am
Volume
Year 2000
Abstract The sound scattering of free microbubbles released from strongly driven ultrasound contrast agents with brittle shell (e.g., Sonovist) is studied numerically. At high peak pressure of the driving pulses, the bubbles respond nonlinearly with cross sections pronouncedly larger than in the linear case; a large portion of the energy is radiated into high frequency ultrasound. Subsequent absorption of these high frequencies in the surrounding liquid (blood) diminishes the effective scattering cross section drastically. The absorption results in highly localized heating, with a substantial temperature rise within the first few microm from the bubble surface. The maximum heating in 1 microm distance is strongly dependent on driving pressure. Temperature elevations of more than 100 K can be achieved for amplitudes of Pa approximately 30 atm, which coincides with the highest pressures used in ultrasound diagnostics. The perfectly spherical collapses assumed here occur rarely, and the heating is highly localized and transient (approximately 10 micros). Therefore, a thermal hazard would only be expected at driving pressures beyond the diagnostic range.


Title Source of double Doppler shift in blood flow.
Author Kremkau F.
Journal Ultrasound Med Biol
Volume
Year 1990
Abstract No abstract available.


Title Sparse random ultrasound array for focal surgery.
Author Frizzell LA, Goss SA, Kouzmanoff JT, Yang JM.
Journal Proc Ultrason Symp IEEE
Volume
Year 1996
Abstract The feasibility of using novel ultrasound phased arrays consisting of array elements larger than a wavelength and randomly located on a spherical shell have been investigated, both theoretically and experimentally, for surgical applications. Random placement of the sources minimizes grating lobes associated with the array. The size of the treatment volume, i.e., the region over which the focus of the array can be electronically scanned, is determined by the directive, overlapping beams from the circular sources that constitute the array elements. The treatment volume and the intensity at the focus have been determined for a range of frequencies and source dimensions. The source size and frequency determine the number of elements that are needed to generate the intensities required for tissue ablation. Gaussian sources were also evaluated for use in such an array. Results are presented for arrays consisting of 64 elements.


Title Sparse random ultrasound phased array for focal surgery.
Author Goss SA, Frizzell LA, Kouzmanoff JT, Barich JM, Yang JM.
Journal IEEE Trans Ultrason Ferroelectr Freq Control
Volume
Year 1996
Abstract Ultrasound phased arrays offer several advantages over single focused transducer technology, enabling electronically programmable synthesis of focal size and shape, as well as position. While phased arrays have been employed for medical diagnostic and therapeutic (hyperthermia) applications, there remain fundamental problems associated with their use for surgery. These problems stem largely from the small size of each array element dictated by the wavelength employed at surgical application frequencies (2-4 MHz), the array aperture size required for the desired focal characteristics, and the number of array elements and electronic drive channels required to provide RF energy to the entire array. The present work involves the theoretical and experimental examination of novel ultrasound phased arrays consisting of array elements larger than one wavelength, minimizing the number of elements in an aperture through a combination of geometric focusing, directive beams, and sparse random placement of array elements, for tissue ablation applications. A hexagonally packed array consisting of 108 8-mm-diameter circular elements mounted on a spherical shell was modeled theoretically and a prototype array was constructed to examine the feasibility of sparse random array configurations for focal surgery. A randomly selected subset of elements of the prototype test array (64 of 108 available channels) was driven at 2.1 MHz with a 64-channel digitally controlled RF drive system. The performance of the prototype array was evaluated by comparing field data obtained from theoretical modeling to that obtained experimentally via hydrophone scanning. The results of that comparison, along with total acoustic power measurements, suggest that the use of sparse random phased arrays for focal surgery is feasible, and that the nature of array packing is an important determinant to observed performance.


Title Spatial resolution enhancement of ultrasound images using neural networks.
Author Carotenuto R, Sabbi G, Pappalardo M.
Journal IEEE Trans UFFC
Volume
Year 2002
Abstract Spatial resolution in modern ultrasound imaging systems is limited by the high cost of large aperture transducer arrays, which require a large number of transducer elements and electronic channels. A new technique to enhance the spatial resolution of pulse-echo imaging systems is presented. The method attempts to build an image that could be obtained with a transducer array aperture larger than that physically available. We consider two images of the same object obtained with two different apertures, the full aperture and a subaperture, of the same transducer. A suitable artificial neural network (ANN) is trained to reproduce the relationship between the image obtained with the transducer full aperture and the image obtained with a subaperture. The inputs of the neural network are portions of the image obtained with the subaperture (low resolution image), and the target outputs are the corresponding portions of the image produced by the full aperture (high resolution image). After the network is trained, it can produce images with almost the same resolution of the full aperture transducer, but using a reduced number of real transducer elements. All computations are carried out on envelope-detected decimated images; for this reason, the computational cost is low and the method is suitable for real-time applications. The proposed method was applied to experimental data obtained with the ultrasound synthetic aperture focusing technique (SAFT), giving quite promising results. Realtime implementation on a modern, full-digital echographic system is currently being developed.


Title Spatial-resolution optimization of 3D high-frequency quantitative ultrasound methods to detect metastatic regions in human lymph nodes
Author Mamou J, Saegusa-Beecroft E, Coron A, Oelze ML, Yamaguchi T, Hata M, Yanagihara E, Machi J, Laugier P, Feleppa EJ
Journal 2013 Joint UFFC, EFTF and PFM Symposium
Volume
Year 2013
Abstract Proper staging and treatment of cancer require accurate detection of lymph-node metastases, but current histological methods fail to detect small, but clinically significant metastases. We used novel 3D quantitative ultrasound (QUS) methods to identify metastatic regions in freshly excised lymph nodes from cancer patients. Individual lymph nodes were scanned in 3D using a 26-MHz, single-element, F2 transducer with a 12-mm focal length. QUS methods quantified the backscatter coefficient to yield four estimates in cylindrical regions of interest (ROIs) having equal lengths and diameters ranging from 0.4 to 1 mm. To optimize the tradeoff between QUS-estimate quality and the spatial resolution of the estimates, the effect of ROI size on estimate bias and variance was investigated using a database of 101 lymph nodes of colorectal-cancer patients. Estimates were combined using linear-discriminant approaches and ROC curves were computed to assess classification performance. A Bayesian approach was used to convert the discriminant scores to 3D cancer-probability estimates throughout each lymph node. Analysis indicated that ROIs with a 0.8-mm length and diameter improved spatial resolution and minimally degraded estimate quality with an average variance increase of <20% for each estimate. The area under the ROC curve remained greater than 0.92 for all ROI sizes. Our QUS methods potentially can reduce the rate of false-negative determinations drastically by efficiently guiding pathologists to suspicious regions in lymph nodes, and having the best possible spatial resolution while retaining adequate estimate quality is critical.


Title Spatio-temporal analysis of molecular delivery through the blood-brain barrier using focused ultrasound.
Author Choi JJ, Pernot M, Brown TR, Small SA, Konofagou EE.
Journal Phys Med Biol
Volume
Year 2007
Abstract The deposition of gadolinium through ultrasound-induced blood–brain barrier (BBB) openings in the murine hippocampus was investigated. First, wave propagation simulations through the intact mouse skull revealed minimal beam distortion while thermal deposition simulations, at the same sonication parameters used to induce BBB opening in vivo, revealed temperature increases lower than 0.5 °C. The simulation results were validated experimentally in ex vivo skulls (m = 6) and in vitro tissue specimens. Then, in vivo mice (n = 9) were injected with microbubbles (Optison™; 25–50 µl) and sonicated (frequency: 1.525 MHz, pressure amplitudes: 0.5–1.1 MPa, burst duration: 20 ms, duty cycle: 20%, durations: 2–4 shots, 30 s per shot, 30 s interval) at the left hippocampus, through intact skin and skull. Sequential, high-resolution, T1-weighted MRI (9.4 Tesla, in-plane resolution: 75 µm, scan time: 45–180 min) with gadolinium (Omniscan™; 0.5 ml) injected intraperitoneally revealed a threshold of the BBB opening at 0.67 MPa and BBB closing within 28 h from opening. The contrast-enhancement area and gadolinium deposition path were monitored over time and the influence of vessel density, size and location was determined. Sonicated arteries, or their immediate surroundings, depicted greater contrast enhancement than sonicated homogeneous brain tissue regions. In conclusion, gadolinium was delivered through a transiently opened BBB and contained to a specific brain region (i.e., the hippocampus) using a single-element focused ultrasound transducer. It was also found that the amount of gadolinium deposited in the hippocampal region increased with the acoustic pressure and that the spatial distribution of the BBB opening was determined not only by the ultrasound beam, but also by the vasculature of the targeted brain region.


Title Specific characteristics of ultrasound contrast agents.
Author Jong ND, Frinking P, Cespedes I.
Journal J Acoust Soc Am
Volume
Year 1998
Abstract No abstract available.


Title Speckle coherence and implications for adaptive imaging.
Author Walker WF, Trahey GE.
Journal J Acoust Soc Am
Volume
Year 1997
Abstract Tissue speed of sound inhomogeneities cause significant degradation of medical ultrasound images. In certain cases these inhomogeneities can be modeled as a thin, spatially varying time delay screen located at the face of the transducer. Correction of such aberrators requires the addition of compensating time delays to the normal system focusing delays. These compensating delays are estimated from the arrival time differences between echoes received on different array elements. The accuracy with which these arrival time differences can be estimated is limited by the level of correlation between received speckle signals. This paper derives analytical expressions predicting the correlation between speckle signals acquired by a pulse echo system with either point or larger receive elements in the presence of near-field phase aberrations. Simulations are presented which are in good agreement with theoretical predictions. Similarities between the derived expressions and the Van Cittert-Zernike Theorem are discussed. These results indicate that near-field phase aberration correction may be far more difficult than previous analyses suggest because of the low correlation between echoes received by adjacent elements in elevation in 1.5-D arrays. Transmit aperture amplitude apodization and a new translating aperture technique are presented as methods for improving speckle correlation.


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