Magnetization transfer with echo planar imaging

The aim of magnetization transfer is to saturate the protons of the macromolecule pool with a radiofrequency (RF) pulse leading to differences in free water pool signal. Magnetization transfer (MT) contrast is difficult to achieve with the echo planar imaging (EPI) technique, although its short acquisition time would be most beneficial. Indeed, the RF saturation pulses can only be applied once before sampling the whole k-space in a single-short sequence. A possible solution to improve the sensitivity of EPI to magnetization transfer consists in applying a train of several saturation RF pulses before image acquisition. The different parameters of a RF pulse train and their influence on the MT rate have been tested to optimize an EPI clinical sequence. Our experimental procedure makes it possible to obtain a MT map in about 1 second. The technique is evaluated by multiple sclerosis lesion characterization. Supported by grants from the French research ministry and Siemens medical France.     

Real imaging and size values of Saccharomyces cerevisiae cells with comparable contrast tuning to two environmental scanning electron microscopy modes

The combined application of electron microscopy (EM) is frequently used for the microstructural investigation of biological specimens and plays two important roles in the quantification and in gaining an improved understanding of biological phenomena by making use of the highest resolution capability provided by EM. The possibility of imaging wet specimens in their "native" states in the environmental scanning electron microscope (ESEM) at high resolution and large depth of focus in real time is discussed in this paper. It is demonstrated here that new features can be discovered by the elimination of even the least hazardous approaches in some preparation techniques, that destroy the samples. Since the analysis conditions may influence the morphology and the extreme surface sensitivity of living biological systems, the results obtained from the same cultured cell with two different ESEM modes (Lvac mode and wet mode) were compared. This offers new opportunities compared with ESEM-wet/Lvac-mode imaging, since wet-mode imaging involves a real contrast and gives an indication of the changes in cell morphology and structure required for cell viability. In this study, wet-mode imaging was optimized using the unique ability of cell quantities for microcharacterization in situ giving very fine features of topological effects. Accordingly, the progress is reported by comparing the results of these two modes, which demonstrate interesting application details. In general, the functional comparisons have revealed that the fresh unprocessed Saccharomyces cerevisiae cells (ESEM-wet mode) were essentially unaltered with improved and minimal specimen preparation timescales, and the optimal cell viability degree was visualized and also measured quantitatively while the cell size remained unchanged with continuous images.     

Backscattered electron imaging of the undersurface of resin-embedded cells by field-emission scanning electron microscopy

In this study backscattered electron (BSE) imaging was used to display cellular structures stained with heavy metals within an unstained resin by atomic number contrast in successively deeper layers. Balb/c 3T3 fibroblasts were cultured on either 13-mm discs of plastic Thermanox, commercially pure titanium or steel. The cells were fixed, stained and embedded in resin and the disc removed. The resin block containing the cells was sputter coated and examined in a field-emission scanning electron microscope. The technique allowed for the direct visualization of the cell undersurface and immediately overlying areas of cytoplasm through the surrounding embedding resin, with good resolution and contrast to a significant depth of about 2 μm, without the requirement for cutting sections. The fixation protocol was optimized in order to increase heavy metal staining for maximal backscattered electron production. The operation of the microscope was optimized to maximize the number of backscattered electrons produced and to minimize the spot size. BSE images were collected over a wide range of accelerating voltages (keV), from low values to high values to give ‘sections' of information from increasing depths within the sample. At 3–4 keV only structures a very short distance into the material were observed, essentially the areas of cell attachment to the removed substrate. At higher accelerating voltages information on cell morphology, including in particular stress fibres and cell nuclei, where heavy metals were intensely bound became more evident. The technique allowed stepwise ‘sectional’ information to be acquired. The technique should be useful for studies on cell morphology, cycle and adhesion with greater resolution than can be obtained with any light-microscope-based system.     

The role of induced contrast in images obtained using the environmental scanning electron microscope

Generation of contrast in images obtained using the environmental scanning electron microscope (ESEM) is explained by interpretation of images acquired using the gaseous secondary electron detector (GSED), ion current, and the Everhart-Thornley detector. We present a previously unreported contrast component in GSED and ion current images attributed to signal induction by changes in the concentration of positive ions in the ESEM chamber during image acquisition. Changes in positive ion concentration are caused by changes in electron emission from the sample during image acquisition and by a discrepancy between the drift velocities of negative and positive charge carriers in the imaging gas. The proposed signal generation mechanism is used to explain contrast reversal in images produced using the GSED and ion current signals and accounts for discrepancies in contrast observed, under some conditions, in these types of images. Combined with existing models of signal generation in the ESEM, the proposed model provides a basis for correct interpretation of ESEM images.     

基于ARM内核的嵌入式肿瘤热疗系统

采用基于ARM内核的嵌入式系统开发小型超声热疗仪是肿瘤热疗系统开发领域中应用嵌入式技术的一个全新尝试，实现了上、下位机一体化设计。嵌入式肿瘤热疗系统包括组织温度采集与转换系统、超声功率控制信号发生模块、存储管理系统、人机交互系统（包括液晶显示及键盘输入）以及其他基本功能模块。根据热疗实际需要对PID控制算法进行改进与优化，提高了治疗中肿瘤组织温度的控制品质。实验结果表明，系统设计可靠，满足临床肿瘤热疗要求。     

齐次线性对数比模型的D—最优试验设计

讨论齐次线性对数比模型的D—最优设计问题。首先通过一个变换,将对数比换型变换为齐次线性模型,然后利用所得的模型求出设计的最优配置,最后证明相应的设计为D—最优设计。     

基于局部占优的自适应像素加权CT/MRI图像融合算法

针对传统基于像素加权平均图像融合算法存在加权因子难以确定的问题,根据CT/MR I图像信息在空间局部互补的特点,提出一种基于局部占优的自适应像素加权算法.根据CT/MR I在空间局部的亮度信息和细节信息的差异,定义并计算局部亮度对比度和局部细节对比度;根据局部亮度和局部细节对比度计算局部占优度矩阵,并进行中值滤波;接着根据局部占优度矩阵计算阈值K,并用阈值K对局部占优度矩阵进行阈值处理,从而得到自适应加权因子矩阵;根据自适应加权因子矩阵对CT/MR I图像进行融合.     

防毡缩整理对羊仔毛衫压缩性能的影响

通过对H2O2—酶HAP防毡缩整理后的羊仔毛衫片进行压缩性研究，得出处理后的衫片比原衫片压缩性能指标值小，而且随着反应条件的逐渐加剧，羊仔毛衫片的蓬松性、丰厚性及丰满性逐渐变弱。     

基于反衬度的钠光特征谱线实验研究

提出干涉条纹反衬度测量概念,在迈克耳逊干涉仪上对双黄线的波长与波长差进行测量的原理和方法,并对实验测量过程中波长和波长差数据进行了细致的计算.实验测量结果与理论值一致,达到了预期的效果.利用反衬度方法在迈克尔逊干涉仪上实现对钠光特征谱线一种快捷有效测量方法,所测的数据较精确,对研究钠原子的内部结构提供可靠的实验数据,该测量方法可进一步拓展为物理设计性、应用研究性实验.     

Color‐edge detection based on discrimination of noticeable color contrasts

Color‐edge detection is an important research task in the field of image processing. Efficient and accurate edge detection will lead to higher performance of subsequent image processing techniques, including image segmentation, object‐based image coding, and image retrieval. To improve the performance of color‐edge detection while considering that human eyes are ultimate receiver of color images, the perceptually insignificant edges should avoid being over‐detected. In this article, a color‐edge detection scheme based on the perceptual color contrast is proposed. The perceptual color contrast is defined as the visible color difference across an edge in the CIE‐Lab color space. A perceptual metric for measuring the visible color difference of a target color pixel is defined by utilizing the associated perceptually indistinguishable region. The perceptually indistinguishable region for each color pixel in the CIE‐Lab color space is estimated by the design of an experiment that considers the local property due to local changes in luminance. Simulation results show that the perceptual color contrast is effectively defined and the color edges in color images are detected while most of the perceptually insignificant edges are successfully suppressed through the proposed color‐edge detection scheme. © 2009 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 19, 332–339, 2009