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BRL Abstracts Database |
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Your search for ultrasound produced 3296 results. Page 193 out of 330
| Title |
Optical transducer for reception of ultrasonic waves. |
| Author |
Phillips PJ, vonRamm OT, Swartz JC, Guenther BD. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
1993 |
| Abstract |
A new optical transducer for the detection of acoustic pressure in the diagnostic ultrasound frequency range is described. This transducer is based on the modulation of an evanescent light field by the incident acoustic energy. Theoretical design considerations are presented for the purpose of developing the most sensitive transducer. Based on these considerations an experimental transducer was constructed. Although less sensitive than predicted this device was capable of transducing ultrasonic pulses with a 1.0-MHz center frequency at diagnostic ultrasound amplitude levels. The techniques developed here are applicable for two-dimensional transduction and may prove a viable alternative to piezoelectric array transducers. |
| Title |
Optimal beamforming in ultrasound using the ideal observer. |
| Author |
Abbey CK, Nguyen NQ, Insana MF. |
| Journal |
IEEE Trans Ultrason Ferroelectr Freq Control |
| Volume |
|
| Year |
2010 |
| Abstract |
Beamforming of received pulse-echo data generally involves the compression of signals from multiple channels within an aperture. This compression is irreversible, and therefore allows the possibility that information relevant for performing a diagnostic task is irretrievably lost. The purpose of this study was to evaluate information transfer in beamforming using a previously developed ideal observer model to quantify diagnostic information relevant to performing a task. We describe an elaborated statistical model of image formation for fixed-focus transmission and single-channel reception within a moving aperture, and we use this model on a panel of tasks related to breast sonography to evaluate receive-beamforming approaches that optimize the transfer of information. Under the assumption that acquisition noise is well described as an additive wide-band Gaussian white-noise process, we show that signal compression across receive-aperture channels after a 2-D matched-filtering operation results in no loss of diagnostic information. Across tasks, the matched-filter beamformer results in more information than standard delay-and-sum beamforming in the subsequent radio-frequency signal by a factor of two. We also show that for this matched filter, 68% of the information gain can be attributed to the phase of the matched-filter and 21% can be attributed to the amplitude. A 1-D matched filtering along axial lines shows no advantage over delay-andsum, suggesting an important role for incorporating correlations across different aperture windows in beamforming. We also show that a post-compression processing before the computation of an envelope is necessary to pass the diagnostic information in the beamformed radio-frequency signal to the final envelope image. |
| Title |
Optimal precision in ultrasound attenuation estimation and application to the detection of Duchenne muscular dystrophy carriers. |
| Author |
Berger G, Laugier P, Fink M, Perrin J. |
| Journal |
Ultrason Imaging |
| Volume |
|
| Year |
1987 |
| Abstract |
This paper deals with the measurement of the attenuation of ultrasound in muscle and its application to the detection of Duchenne Muscular Dystrophy (DMD) carriers. The precision obtained when measuring the attenuation is an important parameter to be considered. A statistical approach is taken on simulated data and compared to in vivo results. The results allow discussion for the minimum tissue volume needed for the estimation. Variations in muscle attenuation between normals were obtained from studies on 27 volunteers. These attenuation values were compared to those obtained from 19 carriers of DMD. Attenuation appears to be a potential clinical indicator of DMD carriers. |
| Title |
Optimal pulse-inversion imaging for microsphere contrast agents. |
| Author |
Reddy AJ, Szeri AJ. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
2002 |
| Abstract |
Microbubbles are used as contrast agents because they scatter incident ultrasound (US) efficiently. Pulse-inversion imaging makes use of the asymmetrical difference in response of a bubble to an US pulse and its symmetrical opposite to obtain improved contrast. In this theoretical work, the principle of pulse-inversion imaging is expanded upon by finding the optimal pulse shape to maximize the signal from a bubble. Given a limit on driving intensity, a suitable norm of the bubble response is maximized using optimal control theory to identify the proper pulse/antipulse driving protocol for a single bubble. The optimal pulse yields a several-fold increase in the normed response over the best sinusoidal pulse of the same driving intensity. It was found that the optimal driving for a single bubble also maximizes the nonlinear response of the cloud if its mean bubble size is the same as that of the single bubble.
|
| Title |
Optimal region-of-interest settings for tissue characterization based on ultrasonic elasticity imaging. |
| Author |
Tsuzuki K, Hasegawa H, Ichiki M, Tezuka F, Kanai H. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
2008 |
| Abstract |
Pathologic changes in arterial walls significantly influence their mechanical properties. We have developed a correlation-based method, the phased tracking method, for measurement of the regional elasticity of the arterial wall. Using this method, elasticity distributions of lipids, blood clots, fibrous tissue and calcified tissue were measured by in-vitro experiments of excised arteries (mean ± SD: lipids, 89 ± 47 kPa; blood clots, 131 ± 56 kPa; fibrous tissue, 1022 ± 1040 kPa; calcified tissue, 2267 ± 1228 kPa). It was found that arterial tissues can be classified into soft tissues (lipids and blood clots) and hard tissues (fibrous tissue and calcified tissue) on the basis of their elasticity. However, there are large overlaps between elasticity distributions of lipids and blood clots and those of fibrous tissue and calcified tissue. Thus, it was difficult to differentiate lipids from blood clots and fibrous tissue from calcified tissue by setting a threshold for a single elasticity value. Therefore, we previously proposed a tissue classification method using the elasticity distribution in each small region. In this method, the elasticity distribution of each small region of interest (ROI) (not a single pixel) in an elasticity image is used to classify lipids, blood clots, fibrous tissue and calcified tissue by calculating the likelihood function for each tissue. In the present study, the optimum size of the ROI and threshold To for the likelihood function were investigated to improve the tissue classification. The ratio of correctly classified pixels to the total number of classified pixels was 29.8% when the size of a small region was 75 μm × 300 μm (a single pixel). The ratio of correctly classified pixels became 35.1% when the size of a small region was 1,500 μm × 1,500 μm (100 pixels). Moreover, a region with an extremely low likelihood with respect to all tissue components was defined as an unclassified region by setting threshold To for the likelihood function to 0.21. The tissue classification of the arterial wall was improved using the elasticity distribution of a small region whose size was larger than the spatial resolution (800 μm × 600 μm) of ultrasound. In this study, the arteries used in construction of the elasticity databases were classified into each tissue using the constructed elasticity databases. Other arteries, which are not used for constructing the elasticity databases, should be classified in future work to thoroughly show the effectiveness of the proposed method |
| Title |
Optimization of exposure conditions for medical.ultrasound. |
| Author |
Nyborg WL. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1985 |
| Abstract |
Optimum exposure conditions are values of acoustic exposure parameters (e.g., intensity, pressure.amplitude, time) which yield maximum net medical benefit in a therapeutic or diagnostic procedure..It is generally agreed that if the exposure values are too low, the procedures are ineffective, while if.they are too high, harm will result. However, little quantitative information exists on what specific.values the parameters should have to give greatest net benefit in various applications. The.determination of optimum exposure conditions is an important goal, but the process is likely to be a.long one, requiring efforts by many individuals and groups. In this review several approaches to.the problem are discussed, and difficulties are pointed out. |
| Title |
Optimizing the beam pattern of a forward-viewing ring-annular ultrasound array for intravascular imaging. |
| Author |
Wang Y, Stephens DN, O'Donnell M. |
| Journal |
IEEE Trans UFFC |
| Volume |
|
| Year |
2002 |
| Abstract |
Intravascular ultrasound (IVUS) imaging systems using circumferential arrays mounted on cardiac catheter tips fire beams orthogonal to the principal axis of the catheter. The system produces high resolution cross-sectional images but must be guided by conventional angioscopy. A real-time forward-viewing array, integrated into the same catheter, could greatly reduce radiation exposure by decreasing angiographic guidance. Unfortunately, the mounting requirement of a catheter guide wire prohibits a full-disk imaging aperture. Given only an annulus of array elements, prior theoretical investigations have only considered a circular ring of point transceivers and focusing strategies using all elements in the highly dense array, both impractical assumptions. In this paper, we consider a practical array geometry and signal processing architecture for a forward-viewing IVUS system. Our specific design uses a total of 210 transceiver firings with synthetic reconstruction for a given 3-D image frame. Simulation results demonstrate this design can achieve side-lobes under -40 dB for on-axis situations and under -30 dB for steering to the edge of a 60/spl deg/ cone. |
| Title |
Optimum acoustic frequency for focused ultrasound surgery. |
| Author |
Hill CR. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1994 |
| Abstract |
A model is described that enables calculation of ultrasound lesioning rate (inverse of time to achieve a threshold lesion in the absence of thermal redistribution) as a function of acoustic frequency, tissue penetration depth, d, attenuation coefficient at specific frequency, mu, and power of dependence of attenuation on frequency, n. Two acoustic power conditions are considered: unlimited power, and power limited by the material properties of the transducer and the constraint that its dimensions be scaled to tissue penetration depth. Optimum frequencies for these two conditions are found to be, respectively, [(2 + n)/n mu d]1/n and [(3 - n)/n mu d]1/n. The tissue path attenuation, for both conditions, is independent of frequency, with a value of approximately 10 dB. Values of predicted lesioning rates under optimum frequency conditions are presented, and the likely constraints imposed by cavitation and propagation nonlinearity are considered.
|
| Title |
Optimum acoustic frequency for focused ultrasound surgery. |
| Author |
Hill CR. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1994 |
| Abstract |
A model is described that enables calculation of ultrasound lesioning rate (inverse of time to achieve a threshold lesion in the absence of thermal redistribution) as a function of acoustic frequency, tissue penetration depth, d, attenuation coefficient at specific frequency, mu, and power of dependence of attenuation on frequency, n. Two acoustic power conditions are considered: unlimited power, and power limited by the material properties of the transducer and the constraint that its dimensions be scaled to tissue penetration depth. Optimum frequencies for these two conditions are found to be, respectively, [(2 + n)/n mu d]1/n and [(3 - n)/n mu d]1/n. The tissue path attenuation, for both conditions, is independent of frequency, with a value of approximately 10 dB. Values of predicted lesioning rates under optimum frequency conditions are presented, and the likely constraints imposed by cavitation and propagation nonlinearity are considered. |
| Title |
Order selection criteria for detecting mean scatterer spacings with the AR model. |
| Author |
Varghese T, Donohue KD, Genis VI, Halpern EJ. |
| Journal |
IEEE Trans UFFC |
| Volume |
|
| Year |
1996 |
| Abstract |
This paper examines the detection of regular scatterer spacings from backscattered ultrasound using the autoregressive (AR) cepstrum. Monte Carlo simulations present a relationship between the probability of detection and the AR model order. An example using liver tissue data supports the observations made in the simulation. |
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