利用超声回波特征无创监测微波热疗的实验研究

寻找一种合适的方法区别正常组织与坏死组织,是癌微波热疗应用中所面临的重要难题.本研究探讨微波热疗过程中组织回波时域的变化,以寻找合适的参数,无创监测热疗组织状态的变化.在原理分析的基础上设计了实验系统,采用微波介入的加热方式,采集超声回波信号,对变性区域做回波幅值时域积分、幅值平方时域积分(能量)和损伤数字减影积分,并分析它们的变化趋势.实验结果表明:生物组织回波的不同方式积分值与加热过程中的组织变性具有相关性,微波热疗前后组织回波的幅值、能量、不均匀性均有增大的趋势.利用超声背向散射积分和反应不均匀度的参数进行监测,可得到较理想的结果.     

基于超声衰减系数的微波热疗无损测温

目的 热疗的引导、疗效及剂量控制都需要温度监测,本文旨在探索一种基于超声衰减系数的微波热疗无损测温新方法.方法 利用水浴加热实验系统,以新鲜体外猪肝组织为研究对象,通过采集不同温度下的超声原始回波信号,分析不同温度下组织的超声衰减系数,建立超声衰减系数与温度相关性模型,用于微波加热实验过程中温度的检测.结果 超声衰减系数与温度相关性模型为:超声衰减系数=0.513×温度-0.80.超声衰减系数在微波热疗低温段(≤50℃)测温误差较小(＜5℃),在高温段(＞50℃)测温误差较大(＞10℃).结论 超声衰减系数可用于常规热疗无损测温.微波热疗温度分布不均使得检测较为困难.利用正常与热凝固组织超声衰减系数的差异进行热凝固区的检测具有一定优势.     

组织超声回波时移温度相关性及其无创测温研究

研究生物组织超声回波时移的温度相关性,以期利用这种相关性实现癌热疗中组织温度的无创检测.以去气水和新鲜离体猪肝为实验研究对象,采集其在一定温度范围（20℃～50℃）内的组织背向反射超声回波信号,通过信号分析探寻超声回波时移与温度的相关性,并利用这种相关性进行无创测温.实验结果表明：①组织内超声声速随温度的变化而变化,它与加热区域内的组织热膨胀共同引起了回波时移的变化;②回波时移的变化与温度变化之间有明显的相关性,且具有较为稳定的线性相关函数;③利用组织超声回波时移的温度相关性进行无创测温是可行的.     

基于组织超声回波时移的无创测温技术及系统设计

寻找一种实时、无创的温度检测技术是目前癌热疗技术应用中面临的主要课题.在研究生物组织超声回波时移与其温度相关性的基础上,设计超声波高速数据采集与处理系统,利用这种相关性来无创检测癌热疗中组织温度的变化.该系统主要由超声发射接收器、高速AD采集卡和微型计算机组成,能检测不同温度下组织背向反射超声波的回波时间,实现了组织温度的实时测量与显示.     

癌热疗中超声无创测温方法的研究

癌热疗中组织温度的测控直接影响到热疗的效果 ,利用超声可以实现热疗中组织温度的无创检测。本文介绍了癌热疗中目前所采用的几种超声测温方法 ,对各种方法的原理及存在的问题进行了分析 ,概述了超声无创测温当前国内外的研究现状     

癌热疗中超声无创测温方法的研究

癌热疗中组织温度的测控直接影响到热疗的效果，利用超声可以实现热疗中组织温度的无创检测。本介绍了癌热疗中目前所采用的几种超声测温方法，对各种方法的原理及存在的问题进行了分析，概述了超声无创测温当前国内外的研究现状。     

利用超声射频实现肿瘤热疗实时无创测温方法

无创测温是肿瘤热疗的技术难题,超声射频测温技术是一种临床应用前景较好的无创测温方法。本文根据4种超声射频参数对超声射频测温方法进行了综述。诸多特征参数均与温度存在一定的相关性,测量方法中超声回波时移测温技术最为成熟,测温精度达到0．24℃。频移、能量、声衰减测温方法分别受不同因素的影响,定量测温尚存在一定困难。超声特征参数提取精度的提高将有效改善测温效果,多参数融合分析和凝固区定征识别也是超声无创测温技术的发展方向。     

微波热疗凝固区域超声回波信号的小波去噪方法

目的 针对用于监测微波热疗凝固区域的超声回波信号信噪比较低,强反射点较多,难以定位凝固区域边缘的特点,研究了一种基于小波分解的去噪方法.方法 在理论分析的基础上,对超声回波信号进行小波分解,根据不同频段信号的特征,进行局部分层小波阈值去噪,再通过小波重构得到去噪后的超声回波信号.结果 对比硬阈值去噪、软阈值去噪和本文所采用方法的效果,探讨了利用本文算法进行凝固区域边缘识别的可行性.结论 局部分层小波去噪算法可有效抑制噪声,保留信号的细节特征,达到优化超声回波信号的目的.     

肿瘤热疗无损测温技术研究进展及存在问题

肿瘤热疗是指用加热来治疗肿瘤的一类治疗方法。基本原理是利用物理能量加热人体全身或局部,使肿瘤组织温度上升到有效治疗温度,并维持一定时间。利用正常组织和肿瘤细胞对温度耐受能力的差异,达到既能使肿瘤细胞凋亡、又不损伤正常组织的治疗目的。肿瘤热疗已成为继手术、放疗、化疗和免疫疗法之后的第五大疗法,是治疗肿瘤的一种新的有效手段。本文分析了现阶段肿瘤热疗无损测温方法的基本原理和存在问题,对当今无损测温在肿瘤热疗方面的理论研究和技术进展进行了总结。     

基于分数阶Fourier变换的线性调频超声回波信号的滤波

编码超声发射技术已在高端超声成像仪中使用,其中线性调频信号是常用的编码信号。由于通过超声系统的回波会有较大衰减,接收信号通常比较微弱,并且带有强噪声,影响成像质量。分数阶Fourier变换应用在编码超声信号处理中,可以有效提高成像质量。本研究提出一种新的成像方法,先对回波信号进行分数阶Fourier变换,再经带通滤波器滤除大部分噪声,然后通过匹配滤波器处理,最后成像。该方法同时融合了信号在时域和频域的信息,并可以进一步降低发射功率。仿真结果表明,这种方法相对于传统的成像方法可以进一步增强系统的抗干扰能力,提高信噪比,从而改善超声成像质量。     

New method for the detection of thrombus formation in cardiovascular devices: optical sensor evaluation in a flow chamber model

We proposed a new method of detecting the onset of thrombus formation based upon the backscattered light intensity changes caused by the alteration of blood flow behavior in the cardiopulmonary devices. In an optical senor based upon the First Order Scattering theory, the relationship between the backscattered light intensity and hematocrit exhibited a monotonically decaying curve for the hematocrit level greater than 45%. To distinguish the effect either by thrombus formation or erythrocyte aggregation on the back-scattered light intensity with a flow chamber connected to a rabbit arterial-venous bypass model, we generated an oscillatory flow using a roller pump and analyzed the results using a Fast Fourier Transform (FFT) method. Our hypothesis was that the nonclotting blood flow would yield an unchanged fundamental spectral power density of the oscillation frequency generated by a roller pump, whereas the thrombus formation would attenuate its power. We measured the back-scattered light intensity in the flow chamber of high shear region and low shear region (n = 5). The blood flow rate was 40 ml/min with the roller pump. The activated clotting time and the hematocrit level were adjusted to 170 +/- 10 s with heparin and 35 +/- 5% with a phosphate buffered sulfate solution, respectively. As a result, the backscattered light intensity from the low shear rate region gradually diminished with time (p < 0.05; 0-5 minutes vs. more than 10-15 minutes), whereas that from the high shear rate region remained fairly constant. The experimental finding supported the hypothesis that the decrease of the backscattered light intensity and diminished spectral power density were caused by the aggregation or clotting erythrocytes. In conclusion, we found that the measurement of the average backscattered light intensity level together with FFT analysis of the backscattered light from the flowing blood is a valuable approach in detecting the onset of thrombus formation.     

Shear Rate Dependence of Ultrasound Backscattering from Blood Samples Characterized by Different Levels of Erythrocyte Aggregation

The objectives were (1) to determine the effect of the erythrocyte aggregation level (wide range of aggregation) and shear rate (which also affects aggregation) on the ultrasound backscattered power, and (2) to evaluate the reproducibility of the ultrasound method. Experiments were performed under steady flow (100–1250 ml/min) in a 12.7 mm diameter vertical tube. Doppler ultrasound at 10 MHz was used to measure simultaneously the velocity and the backscattered power across the tube. For each radial position, the shear rate was computed from the derivative of the velocity profile. The backscattered power decayed exponentially as a function of the shear rate, and for a given shear rate, the power increased monotonically with the level of aggregation measured by laser reflectometry. Using blood samples simulating hypo-, normal, and hyperaggregating erythrocytes, the power of the ultrasound signal varied respectively by –7.8, –13.2, and –16.1 dB as a function of the shear rate (from 0.4 to 50 s^–1). The reproducibility of the backscattered power was 5.5 dB, which is less than the variations observed as a function of the shear rate. In conclusion, ultrasound backscattering is sensitive to the level of erythrocyte aggregation. At a first glance, ultrasound seems less accurate when compared to laser reflectometry but it is suggested that this is because ultrasound backscattering may be sensitive to structural aggregate changes that are not detected by the laser method. © 2000 Biomedical Engineering Society. PAC00: 8718-h, 8719Tt, 8750Kk     

Modeling photon output caused by backscattered radiation into the monitor chamber from collimator jaws using a Monte Carlo technique

Dose per monitor unit in photon fields generated by clinical linear accelerators can be affected by the backscattered radiation into the monitor chamber from collimator jaws. Thus, it is necessary to account for the backscattered radiation in computing monitor unit setting for a treatment field. In this work, we investigated effects of the backscatter from collimator jaws based on Monte Carlo simulations of a clinical linear accelerator. The backscattered radiation scored within the monitor chamber was identified as originating either from the upper jaws (Y jaws), or from the lower jaws (X jaws). From the results of Monte Carlo simulations, ratios of the monitor-chamber-scored dose caused by the backscatter to the dose caused by the forward radiation, R(x,y), were modeled as functions of the individual X and Y jaw positions. The amount of the backscattered radiation for any field setting was then computed as a compound contribution from both the X and Y jaws. The dose ratios of R(x,y) were then used to calculate the change in photon output caused by the backscatter, Scb(x,y). Results of these calculations were compared with available measured data based on counting the electron pulses or charge from the electron target of an accelerator. Data from this study showed that the backscattered radiation contributes approximately 3% to the monitor-chamber-scored dose. A majority of the backscattered radiation comes from the upper jaws, which are located closer to the monitor chamber. The amount of the backscatter decreases approximately in a linear fashion with the jaw opening. This results in about a 2% increase of photon output from a 10 cm x 10 cm field to a 40 cm x 40 cm field. The off-axis location of the jaw opening does not have a significant effect on the magnitude of the backscatter. The backscatter effect is significant for monitor chambers using kapton windows, particularly for treatment fields using moving jaws. Applying the backscatter correction improves the accuracy of monitor-unit calculation using a model-based dose calculation algorithm such as the convolution method.     

A Monte Carlo technique for signal level detection in implanted intracranial pressure monitoring

Statistical monitoring techniques like CUSUM, Trigg's tracking signal and EMP filtering have a major advantage over more recent techniques, such as Kalman filtering, because of their inherent simplicity. In many biomedical applications, such as electronic implantable devices, these simpler techniques have greater utility because of the reduced requirements on power, logic complexity and sampling speed. The determination of signal means using some of the earlier techniques are reviewed in this paper, and a new Monte Carlo based method with greater capability to sparsely sample a waveform and obtain an accurate mean value is presented. This technique may find widespread use as a trend detection method when reduced power consumption is a requirement.     

The use of photoconductive cells in photoplethysmography

Photoplethysmography (p.h.p.l.) is a noninvasive method of monitoring changes in peripheral blood volume. The method consists of illuminating the skin with a light flux, and detecting transmitted or backscattered light from the vascular bed by a photosensor. Experience and measurements show that the photoconductor (p.h.c.) is among the most sensitive of photosensors, and it is also small, cheap, and does not require high voltages. The p.h.c., however, has the unfavourable characteristics of temperature and light-history dependence, which contribute to drift, and dynamic characteristics that change with different levels of ambient light and temperature level. This paper investigates these unfavourable electrical properties and shows how they can be dealt with so that the p.h.c. can be used with a high level of confidence, and photoplethysmograms obtained with minimum artefact.     

基于"WD倒谱"法分析人体脾组织的超声散射微结构特征

本文提出了一种对超声散射信号分析的新方法--“WD倒谱”法,并利用该方法对人体正常脾和脾增生组织的回波信号进行了分析,对软组织中散射子的平均间距进行了估计,结果表明：两种脾组织散射子的平均同距明显不同;“WD倒谱”能有效的反映软组织的微观结构特征,说明“WD倒谱”是软组织超声散射信号分析与软组织散射子平均间距定征的一种有效方法。     

Statistical distributions of potential interest in ultrasound speckle analysis

Compound statistical modelling of the uncompressed envelope of the backscattered signal has received much interest recently. In this note, a comprehensive collection of models is derived for the uncompressed envelope of the backscattered signal by compounding the Nakagami distribution with 13 flexible families. The corresponding estimation procedures are derived by the method of moments and the method of maximum likelihood. The sensitivity of the models to their various parameters is examined. It is expected that this work could serve as a useful reference and lead to improved modelling of the uncompressed envelope of the backscattered signal.