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1.
A numerical model for simulating nonlinear pulsed beams radiated by rectangular focused transducers, which are typical of
diagnostic ultrasound systems, is presented. The model is based on a KZK-type nonlinear evolution equation generalized to
an arbitrary frequency-dependent absorption. The method of fractional steps with an operator-splitting procedure is employed
in the combined frequency-time domain algorithm. The diffraction is described using the implicit backward finite-difference
scheme and the alternate direction implicit method. An analytic solution in the time domain is employed for the nonlinearity
operator. The absorption and dispersion of the sound speed are also described using an analytic solution but in the frequency
domain. Numerical solutions are obtained for the nonlinear acoustic field in a homogeneous tissue-like medium obeying a linear
frequency law of absorption and in a thermoviscous fluid with a quadratic frequency law of absorption. The model is applied
to study the spatial distributions of the fundamental and second harmonics for a typical diagnostic ultrasound source. The
nonlinear distortion of pulses and their spectra due to the propagation in tissues are presented. A better understanding of
nonlinear propagation in tissue may lead to improvements in nonlinear imaging and in specific tissue harmonic imaging.
Published in Russian in Akusticheskiĭ Zhurnal, 2006, Vol. 52, No. 4, pp. 560–570.
This article was translated by the authors. 相似文献
2.
Measures of overlap of labelled regions of images, such as the Dice and Tanimoto coefficients, have been extensively used to evaluate image registration and segmentation algorithms. Modern studies can include multiple labels defined on multiple images yet most evaluation schemes report one overlap per labelled region, simply averaged over multiple images. In this paper, common overlap measures are generalized to measure the total overlap of ensembles of labels defined on multiple test images and account for fractional labels using fuzzy set theory. This framework allows a single "figure-of-merit" to be reported which summarises the results of a complex experiment by image pair, by label or overall. A complementary measure of error, the overlap distance, is defined which captures the spatial extent of the nonoverlapping part and is related to the Hausdorff distance computed on grey level images. The generalized overlap measures are validated on synthetic images for which the overlap can be computed analytically and used as similarity measures in nonrigid registration of three-dimensional magnetic resonance imaging (MRI) brain images. Finally, a pragmatic segmentation ground truth is constructed by registering a magnetic resonance atlas brain to 20 individual scans, and used with the overlap measures to evaluate publicly available brain segmentation algorithms. 相似文献
3.
Objective: We have shown that High-Intensity Focused Ultrasound (HIFU) can effectively control bleeding from injuries to solid organs such as liver, spleen, and lung. Achievement of hemostasis was augmented when a homogenate of tissue and blood was formed. The objective of this study was to investigate quantitatively the effect of homogenate production on HIFU application time for hemostasis. Possible mechanisms involved in homogenate production were also studied.Methods: Ten anesthetized rabbits had laparotomy and liver exposure. Liver incisions, 15-25 mm long and 3-4 mm deep, were made followed immediately by HIFU application. Two electrical powers of 80 and 100 W corresponding to focal acoustic intensities of 2264 and 2829 W/cm2, respectively were used. Tissue and homogenate temperatures were measured. Smear and histological tissue sample analysis using light microscopy were performed.Results: In treatments with homogenate formation, hemostasis was achieved in 76 ± 1.3 s (Mean ± Standard Error Mean: SEM) at 80 W. In treatments without homogenate formation (at 80 W), hemostasis was achieved in 106 ± 0.87 s. At 100 W, hemostasis was achieved in 46 ± 0.3 s. The time required for homogenate formation, at 80 and 100 W were 60 ± 2.5 and 23 ± 0.3 s, respectively. The homogenate temperature was 83 °C (SEM 0.6 °C), and the non-homogenate tissue temperature at the treatment site was 60 °C (SEM 0.4 °C). The smear and histological analysis showed significant blood components and cellular debris in the homogenate, with some intact cells.Conclusion: The HIFU-induced homogenate of blood and tissue resulted in a statistically significant shorter HIFU application time for hemostasis. The incisions with homogenate had higher temperatures as compared to incisions without homogenate. Further studies of the correlation between homogenate formation and temperature must be done, as well as studies on the long-term effects of homogenate in achieving hemostasis. 相似文献
4.
Porter TM Crum LA Stayton PS Hoffman AS 《The Journal of the Acoustical Society of America》2004,116(2):721-728
The persistence of acoustic cavitation in a pulsed wave ultrasound regime depends upon the ability of cavitation nuclei, i.e., bubbles, to survive the off time between pulses. Due to the dependence of bubble dissolution on surface tension, surface-active agents may affect the stability of bubbles against dissolution. In this study, measurements of bubble dissolution rates in solutions of the surface-active polymer poly(propyl acrylic acid) (PPAA) were conducted to test this premise. The surface activity of PPAA varies with solution pH and concentration of dissolved polymer molecules. The surface tension of PPAA solutions (55-72 dynes/cm) that associated with the polymer surface activity was measured using the Wilhelmy plate technique. Samples of these polymer solutions then were exposed to 1.1 MHz high intensity focused ultrasound, and the dissolution of bubbles created by inertial cavitation was monitored using an active cavitation detection scheme. Analysis of the pulse echo data demonstrated that bubble dissolution time was inversely proportional to the surface tension of the solution. Finally, comparison of the experimental results with dissolution times computed from the Epstein-Plesset equation suggests that the radii of residual bubbles from inertial cavitation increase as the surface tension decreases. 相似文献
5.
A comparison of the fragmentation thresholds and inertial cavitation doses of different ultrasound contrast agents 总被引:6,自引:0,他引:6
Chen WS Matula TJ Brayman AA Crum LA 《The Journal of the Acoustical Society of America》2003,113(1):643-651
Contrast bubble destruction is important in several new diagnostic and therapeutic applications. The pressure threshold of destruction is determined by the shell material, while the propensity for of the bubbles to undergo inertial cavitation (IC) depends both on the gas and shell properties of the ultrasound contrast agent (UCA). The ultrasonic fragmentation thresholds of three specific UCAs (Optison, Sonazoid, and biSpheres), each with different shell and gas properties, were determined under various acoustic conditions. The acoustic emissions generated by the agents, or their derivatives, characteristic of IC after fragmentation, was also compared, using cumulated broadband-noise emissions (IC "dose"). Albumin-shelled Optison and surfactant-shelled Sonazoid had low fragmentation thresholds (mean = 0.13 and 0.15 MPa at 1.1 MHz, 0.48 and 0.58 MPa at 3.5 MHz, respectively), while polymer-shelled biSpheres had a significant higher threshold (mean = 0.19 and 0.23 MPa at 1.1 MHz, 0.73 and 0.96 MPa for thin- and thick-shell biSpheres at 3.5 MHz, respectively, p<0.01). At comparable initial concentrations, surfactant-shelled Sonazoid produced a much larger IC dose after shell destruction than did either biSpheres or Optison (p<0.01). Thick-shelled biSpheres had the highest fragmentation threshold and produced the lowest IC dose. More than two and five acoustic cycles, respectively, were necessary for the thin- and thick-shell biSpheres to reach a steady-state fragmentation threshold. 相似文献
6.
Hwang $^{}$ J. H. Zhou Y. Warren C. Brayman A. A. Crum L. A. 《IEEE transactions on bio-medical engineering》2010,57(1):37-40
7.
John S. McCloy Jarrod V. Crum S. K. Sundaram Ryan Slaugh Paul P. Woskov 《Journal of Infrared, Millimeter and Terahertz Waves》2011,32(11):1337-1349
Millimeter wave (MMW) radiometry can be used for simultaneous measurement of emissivity and temperature of materials under
extreme environments such as in slagging coal gasifiers, where sensors have been identified as a key enabling technology need
for process optimization. We present a dual-channel MMW heterodyne radiometer with active interferometric capability that
allows simultaneous measurements of sample temperature, emissivity, and flow dynamics. Interferometric capability at 137 GHz
is supplied via a probe signal originating from a local oscillator allowing monitoring of sample dynamics such as volume expansion
and thickness change. This capability has been used to monitor characteristic behavior between refractories and slag such
as slag infiltration, slag melting, viscous flow, foaming, and crucible corrosion by the molten slag. These results show the
promise of the MMW system for extracting process parameters from operating slagging coal gasifiers, providing valuable information
for process efficiency, control, and increased productivity. 相似文献
8.
Our objective was to investigate whether hemorrhage control can be achieved faster when high-intensity focused ultrasound (HIFU) is applied in the presence of ultrasound contrast agents (UCA) as compared to HIFU only application. Incisions (3 cm long and 0.5 cm deep) were produced in the livers of anesthetized rabbits. UCA Optison (0.18 ml/kg) was injected into the mesenteric vein. A HIFU applicator (5.5 MHz, 6800 W/cm2 in situ) was scanned at a rate of 1–2 mm/s in one direction over the incision (with multiple passes if needed), until hemostasis was achieved. Hemostasis times were 59 ± 23 s (n = 21) in the presence of Optison and 70 ± 23 s (n = 29) without Optison. The presence of Optison produced on average 37% reduction in hemostasis times normalized to initial bleeding rates (p < 0.05), as well as 60% faster formation of the coagulum seal over the incision (p < 0.05). Gross and histological observations showed similar appearance of HIFU lesions produced in the presence of Optison and HIFU lesions produced without Optison. Our results suggest potential utility of UCA for increasing efficiency of HIFU-induced hemostasis of solid organ injuries. 相似文献
9.
An experiment suitable for first-year students is reported. In this activity, students use a molecular modeling program to compute infrared spectra for a series of molecules. From the data obtained, students generate a group frequency chart and use it to identify unknowns. This provides students with an introduction to vibrational spectroscopy and the use of molecular modeling. 相似文献
10.
Lawrence A. Crum 《Ultrasonics sonochemistry》1995,2(2):S147-S152
Sonochemistry is an evolving field that has shown recent rapid growth and increasing interest. Although this field concentrates on chemistry and uses acoustics principally as a tool, the basic mechanism that gives rise to sonochemistry — acoustic cavitation — is often ignored or given little attention. This paper addresses some of the relevant aspects of cavitation and physical acoustics that apply to sonochemistry. 相似文献