Non-invasive imaging of roots with high resolution X-ray micro-tomography

X-ray micro-tomography is a well-established technique for non-invasive imaging and evaluation of heterogeneous materials. An inexpensive X-ray micro-tomography system has been designed and built for the specific purposes of examining root growth and root/soil interactions. The system uses a silver target X-ray source with a focal spot diameter of 80 m, an X-ray image intensifier with a sampling aperture of about 100 m, and a sample with a diameter of 25 mm. Pre-germinated wheat and rape seeds were grown for up to 8–10 days in plastic containers in a sandy loam soil sieved to < 250 m, and imaged with the X-ray system at regular intervals. The quality of 3 D image obtained was good allowing the development and growth of both root axes and some first-order laterals to be observed. The satisfactory discrimination between soil and roots enabled measurements of root diameter (wheat values were 0.48–1.22 mm) in individual tomographic slices and, by tracking from slice to slice, root lengths were also measured. The measurements obtained were generally within 10% of those obtained from destructive samples measured manually and with a flat-bed scanner. Further developments of the system will allow more detailed examination of the root:soil interface.     

Fluorescence imaging of the activity of glucose oxidase using a hydrogen-peroxide-sensitive europium probe

A method for optical imaging of the activity of glucose oxidase (GOx) using a fluorescent europium(III) tetracycline probe for hydrogen peroxide is presented. A decay time in the microsecond range and the large Stokes shift of 210 nm of the probe facilitate intensity-based, time-resolved, and decay-time-based imaging of glucose oxidase. Four methods for imaging the activity of GOx were compared, and rapid lifetime determination imaging was found to be the best in giving a linear range from 0.32 to 2.7 m Unit/mL. The detection limit is 0.32 m Unit/mL (1.7 ng mL(-1)) which is similar to that of the time-resolved (gated) imaging using a microtiterplate reader. Fluorescent imaging of the activity of GOx is considered to be a useful tool for GOx-based immunoassays with potential for high-throughput screening, immobilization studies, and biosensor array technologies.     

Structural heterogeneity leads to functional homogeneity in A. marina phycocyanin

The major light harvesting antenna in all cyanobacterial species is the phycobilisome (PBS). The smallest PBS identified to date is that of Acaryochloris marina (A. marina), composed of a single four-hexamer rod. We have determined the crystal structure of phycocyanin (AmPC), the major component of the A. marina PBS (AmPBS) to 2.1?Å. The basic unit of the AmPC is a heterodimer of two related subunits (α and β), and we show that the asymmetric unit contains a superposition of two α and two β isoforms, the products of the simultaneous expression of different genes. This is the first time to our knowledge that isolated proteins crystallized with such identifiable heterogeneity. We believe that the presence of the different isoforms allows the AmPBS to have a significant bathochromic shift in its fluorescence emission spectrum, allowing, in the total absence of allophycocyanin, a better overlap with absorption of the chlorophyll d-containing reaction centers. We show that this bathochromic shift exists in intact AmPBS as well as in its disassembled components, thus suggesting that AmPC can efficiently serve as the AmPBS terminal emitter.     

Lung tumors on multimodal radiographs derived from grating-based X-ray imaging – A feasibility study

PurposeThe purpose of this study was to assess whether grating-based X-ray imaging may have a role in imaging of pulmonary nodules on radiographs.Materials and methodsA mouse lung containing multiple lung tumors was imaged using a small-animal scanner with a conventional X-ray source and a grating interferometer for phase-contrast imaging. We qualitatively compared the signal characteristics of lung nodules on transmission, dark-field and phase-contrast images. Furthermore, we quantitatively compared signal characteristics of lung tumors and the adjacent lung tissue and calculated the corresponding contrast-to-noise ratios.ResultsOf the 5 tumors visualized on the transmission image, 3/5 tumors were clearly visualized and 1 tumor was faintly visualized in the dark-field image as areas of decreased small angle scattering. In the phase-contrast images, 3/5 tumors were clearly visualized, while the remaining 2 tumors were faintly visualized by the phase-shift occurring at their edges. No additional tumors were visualized in either the dark-field or phase-contrast images. Compared to the adjacent lung tissue, lung tumors were characterized by a significant decrease in transmission signal (median 0.86 vs. 0.91, p = 0.04) and increase in dark-field signal (median 0.71 vs. 0.65, p = 0.04). Median contrast-to-noise ratios for the visualization of lung nodules were 4.4 for transmission images and 1.7 for dark-field images (p = 0.04).ConclusionLung nodules can be visualized on all three radiograph modalities derived from grating-based X-ray imaging. However, our initial data suggest that grating-based multimodal X-ray imaging does not increase the sensitivity of chest radiographs for the detection of lung nodules.     

2010年中国植物科学若干领域重要研究进展

2010年中国植物科学研究继续快速发展。中国科学家在植物科学各领域中取得了大量的具有原创意义的研究成果,尤其是在水稻产量决定的遗传机制和作物基因组研究方面获得了一系列突破,农业生态学研究等方面也取得了重大进展,获得国内外的高度评价。该文对2010年中国本土植物生命科学若干领域取得的重要研究进展进行概括性评述,旨在全面追踪当前中国植物科学领域发展的最新前沿和热点事件,并展现我国科学家所取得的杰出成就。     

光学相干层析分子成像方法初探

介绍了分子对比剂在光学相干层析成像(optical coherence tom ography,OCT)技术中的研究现状,概述了迄今出现的几种不同的光学相干层析分子成像方法(m olecu lar contrast OCT,简称为MCOCT),讨论了MCOCT的几个重要的实际问题:对比剂的选择范围、激发光强的限制、各种方法灵敏度比较以及MCOCT应用于临床与生物学领域需要考虑的因素。     

声聚焦层析增强的三维微波热声成像

本文提出了一种提高微波热声断层成像层析能力的方法和装置.基于热声成像原理和声聚焦理论,搭建了由超短脉冲微波源、384阵元环形探测器、声聚焦透镜、384-64通道采集切换系统、精密扫描位移平台构成的微波热声三维成像系统,并实现了模拟样品的断层成像.实验结果表明该系统能够实现亚毫米级分辨率的热声成像,通过声聚焦方法成倍地提高了其层析分辨率.这对推动微波热声CT技术走向临床具有重要的意义.     

The correlation of single-particle diffraction patterns as a continuous function of particle orientation

A statistical model for X-ray scattering of a non-periodic sample to high angles is introduced. It is used to calculate analytically the correlation of distinct diffraction measurements of a particle as a continuous function of particle orientation. Diffraction measurements with shot-noise are also considered. This theory provides a general framework for a deeper understanding of single particle imaging techniques used at X-ray free-electron lasers. Many of these techniques use correlations as a measure of diffraction-pattern similarity in order to determine properties of the sample, such as particle orientation.     

支气管扩张症的X线平片、CT和HRCT对照分析

目的:对支气管扩张的X线平片、CT和HRCT表现做一对比分析,以提高诊疗水平。方法:取病理证实支扩20例,分别摄有胸正侧位片,常规CT扫描和HRCT扫描。HRCT选薄层,大矩阵和高分辨率算法。结果:显示X光平片漏诊率高(8/20),特异性低(3/20)。CT较平片显示肺“盲区”效果好,有粘液嵌塞者,常规CT像上有时不易与血管性病变鉴别,HRCT可显示部分含气的支气管腔存在。结论:HRCT扫描诊断支扩特异性高,可与支气管造影相媲美,它不仅显示支扩范围、程度和部位。还能显示小叶中央性改变。常规CT较平片显示率高。     

7例肺类癌的CT影像报道及文献复习

目的:分析肺类癌的CT影像表现,结合文献复习以提高对该病的认识.方法:回顾性分析7例经病理证实的肺类癌的CT表现,其中3例行胸部CT平扫检查,4例行胸部CT平扫及增强扫描.结果:7例患者中有6例为典型类癌,1例为非典型类癌.6例典型类癌中:1例为微瘤型类癌,表现为右侧肺门旁支气管扩张、结石及条片状影;1例为硬化性血管瘤...