Principles and applications of differential tomography

A new tomographic method is described: the differential tomography. In this method, selective isolation of an element in the scanned sample is realized, when two X-ray beams are employed, which energies straddle a photoelectric discontinuity of the element. The CT-map exalts the presence of this element with respect to the matrix. The differential tomography can be employed in each case in which the presence of an element has to be enhanced, naturally present in the sample, or used as tracer, for medical and nonmedical applications.     

超声弹性显微镜成像系统开发与应用的初步研究

传统的超声弹性成像技术一般使用1MHz～10MHz的超声波,这一频段超声波的空间分辨率在毫米量级,它不能满足对生物组织中微细结构(如皮肤层,关节软骨等)的研究。文中介绍一套新开发的超声弹性显微镜成像系统,并将其初步应用于对关节软骨和老鼠表皮的成像研究中。该系统由加压系统和背向散射超声显微镜系统两部分组成,其中超声探头频率为50MHz。通过对关节软骨和老鼠表皮的成像实验表明,该系统可以清晰的对生物组织中微细结构成像,研究它们的机械特性。     

Channel defect detection in food packages using integrated backscatter ultrasound imaging

Hermetically-sealed flexible food packages require very effective seal integrity testing to extend the shelf stability of thermally processed food. The initial goal of this study was to estimate the detection limits of laboratory-generated channels which simulate defects in food packages using pulse-echo ultrasonic imaging techniques. Packages with well characterized (via transmission optical microscopy) laboratory-generated channels that simulate defects with diameters between 9 and 325 mum in the seal plane traversing the major axis of the heat seal were generated in heat-sealed microwavable retort-pouch plastic film (trilaminate). Pulse-echo techniques in the 13-17 MHz center frequency range were investigated. The samples were examined with a conventional B-mode imaging technique, which was found to be inadequate for subwavelength imaging of the types of typical channel defects found in shelf-stable food packages. Based on conventional B-mode image features, a new goal of this study was established to develop and evaluate an imaging technique which would exhibit subwavelength imaging capabilities. The new imaging technique called backscattered amplitude integral (BAI) is introduced here. It was observed that BAI-mode imaging has the ability for subwavelength detection of channel defects, e.g., detection of a 10-mum diameter channel defect at a center frequency of 13.1 MHz (lambda=182 mum).     

In-situ scanning electron microscopy and electron backscatter diffraction investigation on the oxidation of pure iron

Abstract

α-iron samples, with a 4 to 6 nm oxide layer on top of the surface due to preparation, were oxidised in situ within a scanning electron microscopy equipped with electron back-scatter diffraction. At 773 and 973 K, two different growth mechanisms during the initial stage of iron oxide formation could be observed, layer-by-layer growth at 773K and island growth at 973 K. The growth mechanism at 973K is correlated to the formation of a thin layer of Fe_1–XO (wüstite) prior to Fe₃O₄ (magnetite) crystallisation whereas at 773K only magnetite was found as newly grown oxide. Magnetite showed a strong epitaxial relationship to α-iron with its {111} plane growing preferentially on the {110} plane of iron.     

Protection circuits for ultrasound applications

A simple input protection circuit for ultrasound pulse-echo applications is described. Its performance is analyzed with regard to other widely used arrangements. Besides the primary function of showing high impedance during the transducer excitation time and a low impedance path to the amplifier in reception, issues of harmonic distortion, insertion losses, bandwidth, power dissipation, transient response, and noise are addressed. It is shown that the proposed circuit has many advantages, operating without any control signals or bias voltages. It is small and can be considered a good general-purpose protection circuit alternative.     

WOLD decomposition of the backscatter echo in ultrasound images of soft tissue organs

Deals with a method of detecting and estimating the scatterer spacing between the regularly spaced resolvable coherent scatterers in tissue. Scatterer spacing has been successfully used in classifying tissue structure, in differentiating between normal and cirrhotic liver, and in detecting diffuse liver disease. This paper presents a WOLD decomposition of the radio frequency (RF) field into its diffused and coherent components from which maximum likelihood estimates (MLE) or minimum mean square error (MMSE) estimates of the scattering spacing are easily computed. The MLE are efficient and for relatively long record are unbiased. They result in accurate estimates in low signal-to-noise (SNR) ratios. Unfortunately, they require nonlinear minimization and knowledge of the probability density associated with the RF backscatter echo. The MMSE estimates, on the other hand, are computationally simple, yield unique closed form solutions, do not require a-priori knowledge of the probability distribution function of the backscatter echo, and result in accurate estimates in low SNR ratios. This paper also presents an unbiased decision rule to detect whether or not an RF echo exhibits any specular scattering relative to the wavelength of the interrogating ultrasonic pulse. The approach has been tried on simulations as well as on in-vivo scans of liver data, and appears to perform well.     

A real-time measure of cavitation induced tissue disruption by ultrasound imaging backscatter reduction

A feedback method for obtaining real-time information on the mechanical disruption of tissue through ultrasound cavitation is presented. This method is based on a substantial reduction in ultrasound imaging backscatter from the target volume as the tissue structure is broken down. Ex-vivo samples of porcine liver were exposed to successive high-intensity ultrasound pulses at a low duty cycle to induce mechanical disruption of tissue parenchyma through cavitation (referred to as histotripsy). At the conclusion of treatment, B-scan imaging backscatter was observed to have decreased by 22.4 +/- 2.3 dB in the target location. Treated samples of tissue were found to contain disrupted tissue corresponding to the imaged hypoechoic volume with no remaining discernable structure and a sharp boundary. The observed, substantial backscatter reduction may be an effective feedback mechanism for assessing treatment efficacy in ultrasound surgery using pulsed ultrasound to create cavitation.     

Predicting backscatter characteristics from micron- and submicron-scale ultrasound contrast agents using a size-integration technique

In this paper, a computationally, inexpensive, size-integration method based on a modified Rayleigh-Plesset model is developed to predict backscatter spectra from groups of bubbles with various size distributions, incident acoustic amplitudes, and driving frequencies. The method was validated using experimentally measured spectra from contrast bubbles of various sizes: Optison, Levovist, ST68 microbubbles, and submicron bubbles. This method provides a computationally inexpensive means of examining backscatter spectrum from multiple bubbles, especially in predicting occurrence and relative amplitude of subharmonics and second harmonics.     

Improved scatterer property estimates from ultrasound backscatter using gate-edge correction and a pseudo-Welch technique

Quantitative ultrasound (QUS) techniques have been widely used to estimate the size, shape and mechanical properties of tissue microstructure for specified regions of interest (ROIs). For conventional methods, an ROI size of 4 to 5 beamwidths laterally and 15 to 20 spatial pulse lengths axially has been suggested to estimate accuracy and precision better than 10% and 5%, respectively. A new method is developed to decrease the standard deviation of the quantitative ultrasound parameter estimate in terms of effective scatterer diameter (ESD) for small ROIs. The new method yielded estimates of the ESD within 10% of actual values at an ROI size of five spatial pulse lengths axially by two beamwidths laterally, and the estimates from all the ROIs had a standard deviation of 15% of the mean value. Such accuracy and precision cannot be achieved using conventional techniques with similar ROI sizes.     

Scanning tomographic acoustic microscopy: Development and applications

The scanning tomographic acoustic microscope (STAM) is a device capable of performing subsurface imaging of microscopic specimens. Using ultrasonic energy to interrogate specimens, the STAM nondestructively obtains accurate two- and three-dimensional reconstructions of the internal structures of materials that are opaque to light. Applications include the nondestructive evaluation of integrated circuits and composite materials, characterization of the acoustical properties of substances, and examination of the condition of biological tissues. This article describes the design and development of the STAM, its capabilities, and applications using data obtained from a fully automated and integrated prototype. © 1997 John Wiley & Sons, Inc. Int J Imaging Syst Technol, 8, 255–262, 1997     

Metallurgical applications of scanning transmission electron microscopy

It is shown that scanning transmission electron microscopy (STEM) has followed two main lines of development, the pure STEM based upon a field emission electron source in which the emphasis is given to high resolution, and a combined system in which STEM is an attachment to a conventional transmission microscope (TEM + STEM). When used in combination with an energy dispersive X-ray spectrometer, the combined TEM + STEM system is shown to be extremely versatile and possibly the more useful for the applied metallurgist. The high vacuum requirements of pure STEM, however, make this system suitable to be used in conjunction with an Auger spectrometer. Examples of the various microanalysis facilities of STEM are given in the article, including micro-diffraction, rocking-beam channelling patterns, qualitative and quantitative X-ray spectroscopy analysis, particle analysis and in situ experimentation. The controversial subject of whether thicker specimens can be studied in STEM compared with conventional TEM is also discussed.     

超声背散射信息熵成像评价脂肪肝的新方法

提出超声背散射Tsallis信息熵成像评价脂肪肝的新方法。利用滑动窗口法,估算窗口内局部背散射包络信号的Tsallis信息熵参数值,对信息熵参数值矩阵进行扫描变换、颜色映射及感兴趣区域设置,叠加到超声B模式图像,实现Tsallis信息熵成像。分析72名肝脏捐献者和204名患者的超声背散射信号,参考标准分别为磁共振波谱测得的肝脏脂肪分数(Hepatic Fat Fraction, HFF)和肝活检组织学检查测得的脂肪肝程度。对于72名肝脏捐献者,Tsallis信息熵与lg(HFF)的相关系数r=0.67(P<0.000 1)。对于204名患者,受试者工作特征曲线下面积分别为0.82、0.88、0.89(≥轻度、≥中度、≥重度),而超声背散射零差K成像分别为0.76、0.82、0.82。超声背散射Tsallis信息熵成像可以直观定征并定量评价脂肪肝的严重程度,其诊断性能优于超声背散射零差K成像,可作为一种超声评价脂肪肝的新方法。     

Magnetorheological (MR) fluids: Principles and applications

In the relatively well established family of smart materials such as those based on ferroelectricity, piezoelectricity, magnetostriction, electrostriction and the shape memory effect, there resides another sub-set of materials known as ‘field responsive fluids’. These include magnetorheological (MR), magnetic liquids or ferrofluids and electrorheological (ER) fluids. This article provides a summary of the properties and applications and recent advances concerning MR fluids and devices. Applications of MR fluids in the automotive and other sectors of technology are also outlined.     

声成像技术及其在医学超声中的应用

由于声成像技术具有对材料内部力学特性进行成像检测的特点,它已成为医学超声中的重要研究领域。为了提高声成像的空间分辨力,近年来,又发展了光声成像,扫描电子声显微术和扫描探针声显微术等新的近场成像技术。结合同济大学声学研究所部分研究结果,对这些近场成像技术在医学超声中的应用作了简单介绍。     

Effect of red cell clustering and anisotropy on ultrasound blood backscatter: a Monte Carlo study

When flowing at a low shear rate, blood appears hyperechogenic on ultrasound B-scans. The formation of red blood cell (RBC) aggregates that also alters blood viscosity is the microscopic mechanism explaining this acoustical phenomenon. In this study, Monte Carlo simulations were performed to predict how RBC clustering increases ultrasound scattering by blood. A bidimensional Gibbs-Markov random point process parameterized by the adhesion energy epsilon and an anisotropy index nu was used to describe RBC positions for a hematocrit H = 40%. The frequency dependence of the backscattering coefficient chi(f) was computed using Born approximation. The backscattering coefficient chi0 at 5 MHz and the spectral slopes n(x) and n(y) (chi alpha f(nx) or f(ny)) measured, respectively, when the insonification is parallel and perpendicular with the RBC cluster axis were then extracted. Under isotropic conditions, chi0 increased up to 7 dB with epsilon and n(x) = n(y) decreased from 4.2 to 3.4. Under anisotropic conditions, the backscattering was stronger perpendicularly to aggregate axis, resulting in n(x) < n(y). The anisotropy in scattering appeared more pronounced when epsilon or nu increased. These two dimensional results generally predict that low-frequency blood backscatter is related to cluster dimension, and higher-frequency properties are affected by finer morphological features as anisotropy. This numerically establishes that ultrasound backscatter spectroscopy on a large frequency range is pertinent to characterize in situ hemorheology.     

超声谱法在颗粒两相流测量中的应用进展

颗粒两相流测量技术指对连续相中的颗粒粒度和浓度等参数进行测量,是两相流测量中非常重要的分支。它与化工、能源、动力、材料、食品等诸多行业都有着密切联系,随着近年来工业的高速发展,颗粒两相流测量技术获得越来越多关注。结合近几年超声谱法在颗粒测量中的研究现状,重点回顾超声谱法颗粒两相流测量技术的应用进展状况,并分析其发展前景。     

Analysis of the performance of a coherent pulsed fiber lidar for aerosol backscatter applications

The antenna and the Doppler estimation characteristics of a coherent pulsed lidar intended for short-range aerosol backscatter applications have been analyzed. The system used fiber-optic interconnects and operated at a wavelength of 1.548 microm. The range dependence of the signal for various bistatic and monostatic antenna configurations has been determined. The system operated in a low-pulse-energy, high-pulse-repetition-rate mode, and the Doppler estimates from the return signal were achieved with a multipulse accumulation procedure. The expected performance of the accumulation in this low-photocount regime was compared with the data obtained from the system, and a reasonable level of agreement was demonstrated.     

原子力显微镜及在膜科学技术研究中的应用

随着科学技术的进步 ,新型的观测仪器的出现为研究提供了先进的手段 .介绍了原子力显微镜的基本探测原理及在膜科学技术中的应用 ,由于原子力显微镜具有空前的高分辨率 ,为其在膜的表面形态与结构等的观测方面开启了一扇新的大门 .     

Regularized autoregressive analysis of intravascular ultrasound backscatter: improvement in spatial accuracy of tissue maps

Autoregressive (AR) models are qualified for analysis of stochastic, short-time data, such as intravascular ultrasound (IVUS) backscatter. Regularization is required for AR analysis of short data lengths with an aim to increase spatial accuracy of predicted plaque composition and was achieved by determining suitable AR orders for short data records. Conventional methods of determining order were compared to the use of trend in the mean square error for determining order. Radio-frequency data from 101 fibrous, 56 fibro-lipidic, 50 calcified, and 70 lipid-core regions of interest (ROIs) were collected ex vivo from 51 human coronary arteries with 30 MHz unfocused IVUS transducers. Spectra were computed for AR model orders between 3-20 for data representing ROIs of two sizes (32 and 16 samples at 100 MHz sampling frequency) and were analyzed in the 17-42 MHz bandwidth. These spectra were characterized based on eight previously identified parameters. Statistical classification schemes were computed from 75% of the data and cross-validated with the remaining 25% using matched histology. The results determined the suitable AR order numbers for the two ROI sizes. Conventional methods of determining order did not perform well. Trend in the mean square error was identified as the most suitable factor for regularization of short record lengths.     

Direct Z-scheme photocatalysts: Principles,synthesis, and applications

The properly designed semiconductor photocatalysts are promising materials for solving the current serious energy and environmental issues because of their ability of using sunlight to stimulate various photocatalytic reactions. Especially, the constructed direct Z-scheme photocatalysts, mimicking the natural photosynthesis system, possess many merits, including increased light harvesting, spatially separated reductive and oxidative active sites, and well-preserved strong redox ability, which benefit the photocatalytic performance. This review concisely compiles the recent progress in the fabrication, modification, and major applications of the direct Z-scheme photocatalysts; the latter include water splitting, carbon dioxide reduction, degradation of pollutants, and biohazard disinfection. It finishes with a brief presentation of future challenges and prospects in the development of direct Z-scheme photocatalytic systems.