首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   18篇
  国内免费   1篇
  完全免费   6篇
  物理学   25篇
  2014年   1篇
  2013年   1篇
  2012年   2篇
  2011年   5篇
  2010年   4篇
  2009年   1篇
  2008年   3篇
  2007年   3篇
  2005年   3篇
  2001年   1篇
  2000年   1篇
排序方式: 共有25条查询结果,搜索用时 78 毫秒
1.
HIFU温度场可视化测量初探   总被引:3,自引:0,他引:3       下载免费PDF全文
本实验用蓖麻油模拟人体环境、热敏打印纸作为记录载体,测量高强度聚焦超声(HIFU)治疗系统焦点附近的温度分布情况。实验中热敏打印纸显影所指示的温度已经达到HIFU治疗所需要的温度,实验的结果对进一步研究HIFU温度场分布有借鉴作用。  相似文献
2.
自聚焦换能器的声场研究   总被引:3,自引:0,他引:3       下载免费PDF全文
高强度聚焦超声(HIFU)治疗局部肿瘤是一项无创伤的新技术,有着很好的应用前景,因此对其声场的研究是有实际的价值的。对声场的研究不仅有利于换能器的设计,提高治疗的效果;而且有助声场测量方案的设计,提高对治疗超声剂量的安全保证。本文采用时域有限差分法研究了自聚焦换能器的声场,分别对简谐波,脉冲波进行了研究。比较清楚地看出在焦区的声场可以认为是平面波,这对光纤端面法声场测量提供了有力的支持。  相似文献
3.
高强聚焦超声(HIFU)加热活体组织中的温度分布   总被引:2,自引:1,他引:1       下载免费PDF全文
钱祖文 《应用声学》2010,29(4):269-272
在高强聚焦超声(HIFU)加热的情况下,利用多针射频(RF)测温装置测量活体组织内的温度分布,结果表明,温度梯度依赖于局部温度,温度越高,梯度越大。此外,本文还研究了血流对温度梯度的影响,结果似乎证实了理论预测,即血流(或血液灌注)减缓了温度(梯度)的变化。  相似文献
4.
Higher perfusion of uterine fibroids at baseline is recognized as cause for poor efficacy of MR-guided high intensity focused ultrasound (HIFU) ablation, and higher acoustic power has been suggested for the treatment of high-perfused areas inside uterine fibroids. However, considering the heterogeneously vascular distribution inside the uterine fibroids especially with hyper vascularity, it is not easy to choose the correct therapy acoustic power for every part inside fibroids. In our study, we presented two cases of fibroids with hyper vascularity, to show the differences between them with different outcomes. Selecting higher therapy acoustic powers to ablate high-perfused areas efficiently inside fibroids might help achieving good ablation results. Volume transfer constant (Ktrans) maps from dynamic contrast-enhanced (DCE) imaging at baseline helps visualizing perfusion state inside the fibroids and locating areas with higher-perfusion. In addition, with the help of Ktrans maps, appropriate therapy acoustic power could be selected by the result of initial test and therapy sonications at different areas with significantly different perfusion state inside fibroids.  相似文献
5.
Medical implants are prone to colonization by bacterial biofilms. Normally, surgery is required to replace the infected implant. One promising noninvasive modality is to destroy biofilms with high-intensity focused ultrasound. In our study, Pseudomonas aeruginosa biofilms were grown on implant-mimicking graphite disks in a flow chamber for 3 days prior to exposing them to ultrasound pulses. Exposure time at each treatment location was varied between 5, 15 and 30 s. Burst period was varied between 1, 3, 6 and 12 milliseconds (ms). The pulses were 20 cycles in duration at 1.1 MHz from a spherically focused transducer (f/1, 63 mm focal length), creating peak compressional and rarefactional pressures at the graphite disk surface of 30 and 13 MPa, respectively. P. aeruginosa were tagged with green fluorescent protein, and killed cells were visualized using propidium iodide before determining the extent of biofilm destruction. The exposure-induced temperature rise was measured to be less than 0.2 °C at the focus, namely the interface between graphite disk and water. Then, the temperature rise was measured at the focus between the graphite disk and a tissue-mimicking phantom to evaluate therapy safety. Two thresholds, of bacteria destruction increase and of complete bacteria removal, respectively, were identified to divide our eight exposure conditions. Results indicated that 30-s exposure and 6-ms pulse period were sufficient to destroy the biofilms. However, the 15-s exposure and 3-ms pulse period were viewed as optimum when considering exposure time, efficacy, and safety.  相似文献
6.
Jeong JS  Chang JH  Shung KK 《Ultrasonics》2012,52(6):730-739
In an ultrasound image-guided High Intensity Focused Ultrasound (HIFU) surgery, reflected HIFU waves received by an imaging transducer should be suppressed for real-time simultaneous imaging and therapy. In this paper, we investigate the feasibility of pulse compression scheme combined with notch filtering in order to minimize these HIFU interference signals. A chirp signal modulated by the Dolph-Chebyshev window with 3-9 MHz frequency sweep range is used for B-mode imaging and 4 MHz continuous wave is used for HIFU. The second order infinite impulse response notch filters are employed to suppress reflected HIFU waves whose center frequencies are 4 MHz and 8 MHz. The prototype integrated HIFU/imaging transducer that composed of three rectangular elements with a spherically con-focused aperture was fabricated. The center element has the ability to transmit and receive 6 MHz imaging signals and two outer elements are only used for transmitting 4 MHz continuous HIFU wave. When the chirp signal and 4 MHz HIFU wave are simultaneously transmitted to the target, the reflected chirp signals mixed with 4 MHz and 8 MHz HIFU waves are detected by the imaging transducer. After the application of notch filtering with pulse compression process, HIFU interference waves in this mixed signal are significantly reduced while maintaining original imaging signal. In the single scanline test using a strong reflector, the amplitude of the reflected HIFU wave is reduced to −45 dB. In vitro test, with a sliced porcine muscle shows that the speckle pattern of the restored B-mode image is close to that of the original image. These preliminary results demonstrate the potential for the pulse compression scheme with notch filtering to achieve real-time ultrasound image-guided HIFU surgery.  相似文献
7.
Zhang D  Zhang S  Wan M  Wang S 《Ultrasonics》2011,51(8):857-869
To monitor HIFU-induced lesion with elastography in quasi-real time, a fast correlation based elastographic algorithm using tissue stiffness–dependent displacement estimation (SdDE) is developed in this paper. The high time efficiency of the proposed method contributes to the reduction on both the number of the displacement points and the computational time of most of the points by utilizing local uniformity of the tissue under HIFU treatment. To obtain admirable comprehensive performance, the key algorithm parameter, a threshold to densify the displacement points, is optimized with simulation over a wedge-inclusion tissue model by compromising the axial resolution (AR) and the computational cost. With the optimum parameter, results from both simulations and phantom experiments show that the SdDE is faster in about one order of magnitude than the traditional correlation based algorithm. At the same time, other performance parameters, such as the signal-to-noise ratio (SNRe), the contrast-to-noise ratio (CNRe) and the axial resolution (AR), are superior to or comparable with that obtained from the traditional algorithm. In vitro experiments on bovine livers validate the improvement on the time efficiency under the circumstances of real tissue and real radio frequency (RF) signal. This preliminary work implies potential of the SdDE in dynamic or close real time guidance and monitoring of HIFU treatment.  相似文献
8.
Enhancing cavitation activity with minimal acoustic intensities could be interesting in a variety of therapeutic applications where mechanical effects of cavitation are needed with minimal heating of surrounding tissues. The present work focuses on the relative efficiency of a signal combining two neighbouring frequencies and a one-frequency signal for initiating ultrasound inertial cavitation. Experiments were carried out in a water tank, using a 550 kHz piezoelectric composite spherical transducer focused on targets with 46 μm roughness. The acoustic signal scattered, either by the target or by the cavitation bubbles, is filtered using a spectral and cepstral-like method to obtain an inertial cavitation activity measurement. The ultrasound excitations consist of 1.8 ms single bursts of single frequency f0 = 550 kHz excitation, in the monofrequency case, and of dual frequency f1 = 535 kHz and f2 = 565 kHz excitation, in the bifrequency case. It is shown that depending on the value of the monofrequency cavitation threshold intensity the bifrequency excitation can increase or reduce the cavitation threshold. The analysis of the thresholds indicates that the mechanisms involved are nonlinear. The progress of the cavitation activity beyond the cavitation threshold is also studied. The slope of the cavitation activity considered as a function of the acoustic intensity is always steeper in the case of the bifrequency excitation. This means that the delimitation of the region where cavitation occurs should be cleaner than with a classical monofrequency excitation.  相似文献
9.
Experimental studies of thermal effects in high-intensity focused ultrasound (HIFU) procedures are often performed with the aid of fine wire thermocouples positioned within tissue phantoms. Thermocouple measurements are subject to several types of error which must be accounted for before reliable inferences can be made on the basis of the measurements. Thermocouple artifact due to viscous heating is one source of error. A second is the uncertainty regarding the position of the beam relative to the target location or the thermocouple junction, due to the error in positioning the beam at the junction. This paper presents a method for determining the location of the beam relative to a fixed pair of thermocouples. The localization technique reduces the uncertainty introduced by positioning errors associated with very narrow HIFU beams. The technique is presented in the context of an investigation into the effect of blood flow through large vessels on the efficacy of HIFU procedures targeted near the vessel. Application of the beam localization method allowed conclusions regarding the effects of blood flow to be drawn from previously inconclusive (because of localization uncertainties) data. Comparison of the position-adjusted transient temperature profiles for flow rates of 0 and 400 ml/min showed that blood flow can reduce temperature elevations by more than 10%, when the HIFU focus is within a 2 mm distance from the vessel wall. At acoustic power levels of 17.3 and 24.8 W there is a 20- to 70-fold decrease in thermal dose due to the convective cooling effect of blood flow, implying a shrinkage in lesion size. The beam-localization technique also revealed the level of thermocouple artifact as a function of sonication time, providing investigators with an indication of the quality of thermocouple data for a given exposure time. The maximum artifact was found to be double the measured temperature rise, during initial few seconds of sonication.  相似文献
10.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号