In contrast to BOLD: signal enhancement by extravascular water protons as an alternative mechanism of endogenous fMRI signal change

Despite the popularity and widespread application of functional magnetic resonance imaging (fMRI) in recent years, the physiological bases of signal change are not yet fully understood. Blood oxygen level-dependant (BOLD) contrast — attributed to local changes in blood flow and oxygenation, and therefore magnetic susceptibility — has become the most prevalent means of functional neuroimaging. However, at short echo times, spin-echo sequences show considerable deviations from the BOLD model, implying a second, non-BOLD component of signal change. This has been dubbed “signal enhancement by extravascular water protons” (SEEP) and is proposed to result from proton-density changes associated with cellular swelling. Given that such changes are independent of magnetic susceptibility, SEEP may offer new and improved opportunities for carrying out fMRI in regions with close proximity to air–tissue and/or bone–tissue interfaces (e.g., the prefrontal cortex and spinal cord), as well as regions close to large blood vessels, which may not be ideally suited for BOLD imaging. However, because of the interdisciplinary nature of the literature, there has yet to be a thorough synthesis, tying together the various and sometimes disparate aspects of SEEP theory. As such, we aim to provide a concise yet comprehensive overview of SEEP, including recent and compelling evidence for its validity, its current applications and its future relevance to the rapidly expanding field of functional neuroimaging. Before presenting the evidence for a non-BOLD component of endogenous functional contrast, and to enable a more critical review for the nonexpert reader, we begin by reviewing the fundamental principles underlying BOLD theory.     

Magnetic resonance imaging of dissolved hyperpolarized Xe using a membrane-based continuous flow system

A technique for continuous production of solutions containing hyperpolarized ¹²⁹Xe is explored for MRI applications. The method is based on hollow fiber membranes which inhibit the formation of foams and bubbles. A systematic analysis of various carrier agents for hyperpolarized ¹²⁹Xe has been carried out, which are applicable as contrast agents for in vivo MRI. The image quality of different hyperpolarized Xe solutions is compared and MRI results obtained in a clinical as well as in a nonclinical MRI setting are provided. Moreover, we demonstrate the application of ¹²⁹Xe contrast agents produced with our dissolution method for lung MRI by imaging hyperpolarized ¹²⁹Xe that has been both dissolved in and outgassed from a carrier liquid in a lung phantom, illustrating its potential for the measurement of lung perfusion and ventilation.     

A contrast estimator for completely or partially observed hypoelliptic diffusion

Parametric estimation of two-dimensional hypoelliptic diffusions is considered when complete observations–both coordinates discretely observed–or partial observations–only one coordinate observed–are available. Since the volatility matrix is degenerate, Euler contrast estimators cannot be used directly. For complete observations, we introduce an Euler contrast based on the second coordinate only. For partial observations, we define a contrast based on an integrated diffusion resulting from a transformation of the original one. A theoretical study proves that the estimators are consistent and asymptotically Gaussian. A numerical application to Langevin systems illustrates the nice properties of both complete and partial observations’ estimators.     

Fast color contrast enhancement method for color night vision

The increasing availability and deployment of imaging sensors operating in multiple spectral bands has led to a large research effort in color image fusion, resulting in a plethora of pixel-level image fusion algorithms. In this study a simple and fast fusion approach for color night vision is presented. The contrast of infrared and visible images is adjusted by local histogram equalization. Then the two enhanced images are fused into the three components of a Lab image in terms of a simple linear fusion strategy. To obtain false color images possessing a natural day-time color appearance, this paper adopts an approach which transfers color from the reference to the fused images in a simplified Lab space. To enhance the contrast between the target and the background, a stretch factor is introduced into the transferring equation in the b channel. Experimental results based on three different data sets show that the hot targets are popped out with intense colors while the background details present natural color appearance. Target detection experiments also show that the presented method has a better performance than the former methods, owing to the target recognition area, detection rate, color distance and running time.     

动脉粥样硬化造影剂PGMA-EDA-g-PEG-g-DS@IO的合成及性能

利用乙二胺(EDA)对聚甲基丙烯酸缩水甘油酯(PGMA)进行开环反应, 制备了侧链多氨基聚合物PGMA-EDA; 再利用聚乙二醇(PEG-COOH)和硫酸葡聚糖钠盐(DS)分别对PGMA-EDA上氨基进行酰胺化反应和还原胺化反应, 制备含动脉粥样硬化斑块靶向分子DS的双亲性接枝共聚物PGMA-EDA-g-PEG-g-DS. 通过核磁共振(¹H NMR)谱和红外光谱(FTIR)表征了聚合物的结构. 利用凝胶渗透色谱(GPC)表征了聚合物的数均分子量M_n=16255, 多分散性指数PDI=1.54. 采用配体交换法, 利用该聚合物对油胺配体超顺磁性氧化铁纳米粒子进行修饰, 制备了水溶性氧化铁纳米粒子PGMA-EDA-g-PEG-g-DS@IO. 通过透射电镜(TEM)和动态光散射(DLS)表征了纳米粒子的形貌和粒度, 采用热重分析(TGA)和振动样品磁强(VSM)仪表征了纳米粒子的包覆率和磁强度. 采用细胞计数试剂盒(CCK)测定了纳米粒子的细胞毒性, 结果表明, 水溶性纳米粒子的生物相容性较好, 可作为动脉粥样硬化斑块的特异性磁共振检测用造影剂.     

Spatially resolved solid-state MAS-NMR-spectroscopy

A comprehensive account of spatially resolved solid-state MAS NMR of ¹³C is given. A device generating field gradients rotating synchronously with the magic angle spinner is described. Spatial resolution and sensitivity are compared for phase and frequency encoding of spatial information. The suppression of spinning sidebands is demonstrated for both cases. Prior knowledge about the involved materials can be used for the reduction of data from spatially resolved spectra to map chemical structure. Indirect detection via ¹³C NMR gives access to the information about mobility from proton-wideline spectra. Two-dimensional solid-state spectroscopy with spatial resolution is demonstrated for a rotor-synchronized MAS experiment which resolves molecular order as a function of space. By comparison of different experiments the factors affecting the spatial resolution are investigated.     

基于心理学的高中物理新旧教材对比分析——以人教版《物理·必修2》机械能守恒定律一章为例

以人教版的新旧教材必修2的机械能守恒定律为例,从心理学的角度对比分析新旧教材的知识呈现顺序和知识呈现方式,期望能帮助教师对新教材进行进一步地思考,从而更好地运用教材.     

聚酯—酰胺型MRI造影剂的合成及其弛豫性能研究

通过二乙三胺五乙酸双酸酐分别与乙醇胺、Ｌ—丝氨酸及其乙酯、Ｌ—酪氨酸及其甲酯、苄酯、正辛酯共聚，合成了七种大分子配体，制备了它们的Ｇｄ（Ⅲ）配合物，并进行了表征。测试其中五种水溶性配合物的弛豫性能。结果表明它们具有与Ｇｄ（ＤＴＰＡ）相当或更强的弛豫性能。     

Design of high-contrast blue top-emitting organic light-emitting device with color invariance

Organic light-emitting devices (OLEDs) with high contrast are highly in demand, particularly for outdoor applications. However, lowering the reflectance of OLEDs to enhance the contrast ratio can also reduce its efficiency. This study presents in detailthe design of high-contrast blue top-emitting organic light-emitting devices with relatively high efficiency and weak viewing angle dependence.     

Enumeration of Liposomes by Multinuclear NMR and Photon Correlation Spectroscopy

Diamagnetic dipalmitoylphosphatidylcholine (DPPC) liposomes dispersed in glucose solution as well as their paramagnetic analogs encapsulating a paramagnetic contrast agent used in magnetic resonance imaging (Gd-HPDO3A, ProHance ® ) were prepared and characterized. The vesicle diameter was assessed by photon correlation spectroscopy (PCS). 31 P NMR spectroscopy was used to measure the phospholipid content and to confirm the highly unilamellar character of the liposome membrane. For both types of liposome preparation, the internal water volume was evaluated below the phase transition temperature ( T m ) by natural abundance 17 O NMR spectroscopy in the presence of a shift reagent confined to the external compartment. For the paramagnetic vesicles, the internal water content was independently assessed by analysis of the biexponential decay of the proton transverse magnetization below T m . Knowing the unilamellarity of the vesicles ( 31 P NMR measurements), the number concentration of liposomes was assessed from the liposomal internal volume calculated from PCS data and the total internal water content obtained by 17 O NMR spectroscopy or 1 H relaxometry. The results obtained are in good agreement and validate these techniques as non invasive methods for the assessment of the number concentration of liposome in suspension.