可见/近红外光谱图像在作物病害检测中的应用

农作物病害严重影响了我国正常的农业生产,现代农业迫切需要快速、准确、高效的作物病害诊断方法。首先简单介绍了常用病害检测技术,如：聚合酶链式反应技术、人工感官判定技术、统计学方法等,这些方法或是比较费时、或是只能用于产生明显病斑后的病害诊断,而光谱技术在植物病害的快速检测方面有一定的潜力,目前已有大量的研究成果。主要围绕可见/近红外光谱图像在病害检测的应用展开分析和讨论,讨论了该技术所涉及的仪器,并从细胞、植物组织、冠层及更大尺度层面分析了该技术在病害检测中的现况。目前大部分与植物病害有关的可见/近红外光谱研究都以植物叶片为对象,而在更小尺度（细胞至显微尺度）和更大尺度（冠层至航空/航天遥感方面）上的研究较少,特别是单细胞级别的病害研究,只在动物细胞领域展开,而且以荧光、拉曼、红外光谱为主。可见/近红外在以植物叶片为主要研究对象的器官尺度上有大量的成功应用,目前的研究已涉及了大部分的常见作物及其主要病害,包括真菌性、细菌性等各种病原引起的病害的检测。植物叶片尺度的研究主要从以下三个方面展开：(1）基于计算机图像处理和模式识别的病害信息自动快速判断;(2）基于化学计量学方法的高光谱或高光谱图像病害程度模型;(3）建立与作物病害有关的叶片某些理化参数的光谱模型,从而量化病害的程度。在植物叶片这一尺度相关研究的主要问题是：研究过于碎片化,往往只研究了某一种或少数几种病害,所建的模型只能用于特定实验条件,无法直接自动判断任意田间样本的染病种类与程度。在近地冠层尺度,植株的三维形态对光谱模型有较大的干扰,有文献表明以植株近地冠层2D图像作为病害检测数据,偏差较大,所建模型不稳定,基于卫星影像的病害模型较少。还讨论了常用光谱及光谱图像建模与分类方法。目前可见/近红外光谱在农作物病害方面有一定的应用潜力,但存在研究内容的不平衡、研究系统性不够、各学科合作研究不够深入等几大问题。最后提出可见/近红外光谱在病害检测领域中应更注重多学科的深入合作,并急需相关的仪器设备、方法模型方面的突破。     

X射线光场成像技术研究

X射线三维成像技术是目前国内外X射线成像研究领域的一个研究热点.但针对一些特殊成像目标,传统X射线计算层析(CT)成像模式易出现投影信息缺失等问题,影响CT重建的图像质量,使得CT成像的应用受到一定的限制.本文主要研究了基于光场成像理论的X射线三维立体成像技术.首先从同步辐射光源模型出发,对X射线光场成像进行建模;然后,基于光场成像数字重聚焦理论,对成像目标场在深度方向上进行切片重建.结果表明:该方法可以实现对成像目标任一视角下任一深度的内部切片重建,但是由于光学聚焦过程中的离焦现象,会引入较为严重的背景噪声.当对其原始数据进行滤波后,再进行X射线光场重聚焦,可以有效消除重建伪影,提高图像的重建质量.本研究既有算法理论意义,又可应用于工业、医疗等较复杂目标的快速检测,具有较大的应用价值.     

基于随机场照射的最优微波成像

近年来,电磁计算成像的理论和技术得到了广泛的研究和发展,其中基于随机场照射的微波成像引起了诸多关注.与传统成像方法的连续波照射不同,基于随机场照射的成像方法以随机照射的方式获取多组非相关的目标散射测量值,经过反演计算就能提取散射目标体的轮廓和形状等信息.基于阵列天线理论,本文理论分析并实验验证了一种最优的二维微波成像系统,能够使用最少的天线单元实现随机照射,通过最少的测量次数完成矩阵求逆并得到重建图像.该系统主要有以下两个创新点:完全随机照射的获取和成像系统最优参数的选取.与基于超材料的成像系统相比,本文通过对1 bit相位调制器随机相位调制的方式获取随机场照射,使得每个天线单元都处于工作状态,因此整个系统的能量效率更高.此外,所述单频成像系统还具有频谱效率高、结构简单、成本低等优点,在安检、室内定位等不同场景中具有潜在的应用价值.     

基于细观混凝土模型的时间逆转损伤成像方法

提出了一种针对混凝土结构损伤检测的时间逆转损伤成像方法.以检测混凝土结构中与骨料尺寸相近的微小损伤为目的,引入细观混凝土随机骨料模型,该模型将混凝土结构视为由水泥浆基底、骨料及粘接层组成的三相复合材料,基于Monte Carlo随机样本原理并结合真实试件的骨料级配曲线建立.在数值模拟分析中,将生成含损伤的细观模型导入有限元分析软件进行超声波场模拟,同时采用自适应性强的时间逆转模型(time reversed model,TRM)进行损伤定位.TRM分为正向检测和逆时成像两个部分:正向检测过程得到包含损伤的一系列散射回波信号,从数值角度进行时间反演并作为逆时过程的输入信号;逆时成像过程选用等效弹性参数模型,几何尺寸与随机骨料模型相同,时反信号在相应几何位置同时加载形成时反波场,时反波场在损伤位置会发生干涉叠加从而导致能量峰值的出现,通过确定干涉峰值时刻,并获取该时刻对应原始波场以及小波变换能量场完成成像.与原始数据波场图相比,小波变换处理成像结果消除了杂波干扰,成像结果更加清晰.进一步对等效弹性参数的取值进行讨论,并且在骨料尺寸范围内调整损伤大小,结果显示成像结果匹配度高,对于非均质混凝土结构的损伤检测能很好满足损伤定位需求.由此证明,时间逆转成像方法对于具有复杂结构的混凝土材料的损伤检测具有较好的适用性.     

A protocol for searching the most probable phase‐retrieved maps in coherent X‐ray diffraction imaging by exploiting the relationship between convergence of the retrieved phase and success of calculation

Coherent X‐ray diffraction imaging (CXDI) is a technique for visualizing the structures of non‐crystalline particles with size in the submicrometer to micrometer range in material sciences and biology. In the structural analysis of CXDI, the electron density map of a specimen particle projected along the direction of the incident X‐rays can be reconstructed only from the diffraction pattern by using phase‐retrieval (PR) algorithms. However, in practice, the reconstruction, relying entirely on the computational procedure, sometimes fails because diffraction patterns miss the data in small‐angle regions owing to the beam stop and saturation of the detector pixels, and are modified by Poisson noise in X‐ray detection. To date, X‐ray free‐electron lasers have allowed us to collect a large number of diffraction patterns within a short period of time. Therefore, the reconstruction of correct electron density maps is the bottleneck for efficiently conducting structure analyses of non‐crystalline particles. To automatically address the correctness of retrieved electron density maps, a data analysis protocol to extract the most probable electron density maps from a set of maps retrieved from 1000 different random seeds for a single diffraction pattern is proposed. Through monitoring the variations of the phase values during PR calculations, the tendency for the PR calculations to succeed when the retrieved phase sets converged on a certain value was found. On the other hand, if the phase set was in persistent variation, the PR calculation tended to fail to yield the correct electron density map. To quantify this tendency, here a figure of merit for the variation of the phase values during PR calculation is introduced. In addition, a PR protocol to evaluate the similarity between a map of the highest figure of merit and other independently reconstructed maps is proposed. The protocol is implemented and practically examined in the structure analyses for diffraction patterns from aggregates of gold colloidal particles. Furthermore, the feasibility of the protocol in the structure analysis of organelles from biological cells is examined.     

Characterization of a sCMOS‐based high‐resolution imaging system

The detection system is a key part of any imaging station. Here the performance of the novel sCMOS‐based detection system installed at the ID17 biomedical beamline of the European Synchrotron Radiation Facility and dedicated to high‐resolution computed‐tomography imaging is analysed. The system consists of an X‐ray–visible‐light converter, a visible‐light optics and a PCO.Edge5.5 sCMOS detector. Measurements of the optical characteristics, the linearity of the system, the detection lag, the modulation transfer function, the normalized power spectrum, the detective quantum efficiency and the photon transfer curve are presented and discussed. The study was carried out at two different X‐ray energies (35 and 50 keV) using both 2× and 1× optical magnification systems. The final pixel size resulted in 3.1 and 6.2 µm, respectively. The measured characteristic parameters of the PCO.Edge5.5 are in good agreement with the manufacturer specifications. Fast imaging can be achieved using this detection system, but at the price of unavoidable losses in terms of image quality. The way in which the X‐ray beam inhomogeneity limited some of the performances of the system is also discussed.     

Targeting Upconversion Nanoprobes for Magnetic Resonance Imaging of Early Colon Cancer

Colon cancer (CC) is one of the most common intestinal malignancies and is difficult to detect in its early stage by magnetic resonance imaging (MRI) with currently used contrast agents (CAs). The development of targeted CAs contributes to the early diagnosis of CC and thereby enables early intervention and timely therapy. Considering the outstanding performance of upconversion nanoprobes (UCNPs) in high‐performance MR and fluorescence imaging, a new type of nanoprobes with considerably enhanced imaging performance is developed herein. Carcinoembryonic antigen (CEA) antibody is conjugated onto the surface of UCNPs to achieve the targeted imaging of early CC tumors, which overexpress CEA. Both toxicity tests and histological/hematological examinations demonstrate the excellent biocompatibility of these CC‐targeting nanoprobes, which possess great potential for clinical application in the early diagnosis of CC.     

Highly Bright and Photostable Li(Gd,Y)F4:Yb,Er/LiGdF4 Core/Shell Upconversion Nanophosphors for Bioimaging Applications

Intense green‐emitting Li(Gd,Y)F₄:Yb,Er/LiGdF₄ core/shell (C/S) upconversion nanophosphors (UCNPs) with a tetragonal bipyramidal morphology are synthesized. The morphology and UC luminescence of the Li(Gd,Y)F₄:Yb,Er UCNPs are significantly affected by the Li precursors, and bright UC green‐emitting Li(Gd,Y)F₄:Yb,Er UCNPs with a tetragonal bipyramidal shape, i.e., UC tetragonal bipyramids (UCTBs), are synthesized using LiOH·H₂O as a Li precursor. A LiGdF₄ shell is grown on the Li(Gd,Y)F₄:Yb,Er UCTBs, and the C/S UCNPs exhibit 4.7 times higher luminescence intensity than core UCTBs. The C/S UCNPs show a high absolute UC quantum yield of 4.6% under excitation with 980 nm near infrared (NIR) light, and the UC luminescence from the C/S UCNPs is stable under continuous irradiation with the 980 nm NIR laser for 1 h. The hydrophobic surfaces of the as‐synthesized C/S UCNPs are modified to hydrophilic surfaces by using poly(acrylic acid) (PAA) for bioimaging applications. They are applied to human cervical adenocarcinoma (HeLa) cell imaging and SK‐MEL‐2 melanoma cell imaging and in vivo imaging, including subcutaneous and intramuscular imaging, and UC luminescence images with high signal‐to‐noise ratio are obtained. Furthermore, sentinel‐lymph‐node imaging is successfully conducted with the PAA‐capped Li(Gd,Y)F₄:Yb,Er/LiGdF₄ C/S UCNPs under illumination with NIR light.     

Multifunctional Small Molecule Fluorophore for Long‐Duration Tumor‐Targeted Monitoring and Dual Modal Phototherapy

In this work, a specific tumor‐targeted small molecular fluorophore for synchronous long‐duration cancer imaging, photodynamic therapy, and photothermal therapy is synthesized. This novel fluorophore exhibits specific targeting ability in certain tumors (U87MG, MDA‐MB‐231, A549, etc.) based on its inherent structure and efficiently generates local hyperthermia and reactive oxygen species simultaneously for imaging‐guided precise cancer therapy combining the photothermic and photodynamic effects under laser irradiation. Meanwhile, compared to traditional near infrared fluorophore, this novel fluorophore with significantly enhanced stability against photobleaching can prolong the time of tumor imaging and improve the phototherapy efficiency. This work presents a potential strategy to develop small‐molecule‐based cancer theranostic agents for simultaneous cancer targeting, imaging, and therapy.     

纳米荧光探针用于核酸分子的检测及成像研究

核酸,包括脱氧核糖核酸和核糖核酸,在生物的生长、发育、突变、炎症、癌症等正常或异常的生命活动中发挥着重要的作用,它们的异常表达与多种疾病的发生、发展也密切相关.因此,发展准确、有效的方法实现核酸分子的检测,对深入探究核酸的功能调控以及相关疾病的早期检测与治疗都具有重要的意义.荧光检测法与荧光成像技术具有灵敏度高、时空分辨率高等优点,为实时、准确的检测核酸分子提供了有力的工具.本文着重综述了近年来发展的纳米荧光探针用于疾病相关核酸分子的检测与细胞和活体成像工作的研究进展,最后提出了进一步构建新型纳米荧光探针用于核酸检测面临的挑战、未来发展方向与展望.