A novel continuous arterial spin labeling approach for CBF measurement in rats with reduced labeling time and optimized signal-to-noise ratio efficiency

Objective  To develop a continuous arterial spin labeling (CASL) perfusion imaging method for cerebral blood flow (CBF) measurement in rats with reduced spin-labeling length and optimized signal-to-noise ratio (SNR _f ) per unit time. Materials and methods  In the proposed method, the longitudinal magnetization of brain tissue water in the imaging slice is prepared into a proper state before spin-labeling, and a post-tagging delay is employed after spin-labeling. The method was implemented on a 4.7 T small animal scanner. Numerical simulations and in vivo experiments were used to evaluate the performance of the method proposed. Results  With the proposed method, absolute CBF could be measured accurately from normal rat with a spin-labeling pulse as short as 400 ms, and yet employing the same formula as that used in the conventional CASL perfusion imaging method for calculation. The method also showed improved SNR _f per unit time over the conventional CASL perfusion imaging method and the pulsed arterial spin labeling perfusion imaging method FAIR. Conclusion  Compared to the conventional CASL perfusion imaging method, the proposed method would be advantageous for CBF measurement in small animals having short vascular transit time in terms of SNR _f per unit time and other benefits brought by shortened spin-labeling pulse.     

Regional proton nuclear magnetic resonance spectroscopy differentiates cortex and medulla in the isolated perfused rat kidney

Volume-localized proton nuclear magnetic resonance spectroscopy was used as an assay of regional biochemistry in the isolated perfused rat kidney. This model eliminated artifacts caused by respiratory and cardiac motion experiencedin vivo. Immersion of the kidney under its venous effluent reduced the susceptibility artifacts evoked by tissue-air interfaces. The rapid acquisition with relaxation enhancement imaging sequence was used for scout imaging. This gave excellent spatial resolution of the cortex, outer medulla, and inner medulla. Spectra were then acquired in 10 minutes using the volume-selective multipulse spectroscopy sequence from voxels with a volume of approximately 24 μL located within the cortical or medullary regions. Spectral peaks were assigned by the addition of known compounds to the perfusion medium and by comparison with spectra of protein-free extracts of cortex and medulla. The medullary region spectra were characterized by signals from the osmolytes betaine, glycerophosphorylcholine, and inositol. The spectra from the cortex were more complex and contained lesser contributions from osmolytes.     

Use of spin echo T2 BOLD in assessment of cerebral misery perfusion at 1.5 T

Inadequate blood supply relative to metabolic demand, a haemodynamic condition termed as misery perfusion, often occurs in conjunction with acute ischaemic stroke. Misery perfusion results in adaptive changes in cerebral physiology including increased cerebral blood volume (CBV) and oxygen extraction ratio (OER) to secure substrate supply for the brain. It has been suggested that the presence of misery perfusion may be an indication of reversible ischaemia, thus detection of this condition may have clinical impact in acute stroke imaging. The ability of single spin echo T₂ to detect misery perfusion in the rat brain at 1.5 T owing to its sensitivity to blood oxygenation level dependent (BOLD) contrast was studied both theoretically and experimentally. Based on the known physiology of misery perfusion, tissue morphometry and blood relaxation data, T₂ behaviour in misery perfusion was simulated. The interpretation of these computations was experimentally assessed by quantifying T₂ in a rat model for cerebral misery perfusion. CBF was quantified with the H₂ clearance method. A drop of CBF from 58 ± 8 to 17 ± 3 ml/100 g min in the parieto-frontal cortex caused shortening of T₂. from 66.9 ± 0.4 to 64.6 ± 0.5 ms. Under these conditions, no change in diffusion MRI was detected. In contrast, the cortex with CBF of 42 ± 7 ml/100 g min showed no change in T₂. Computer simulations accurately predicted these T₂, responses. The present study shows that the acute drop of CBF by 70% causes a negative BOLD that is readily detectable by T₂ MRI at 1.5 T. Thus BOLD may serve as an index of misery perfusion thus revealing viable tissue with increased OER.     

Reduced purine catabolite production in the postischemic rat heart: a31P NMR assessment of cytosolic metabolites

Ischemia can cause release of adenosine and purine catabolites from the heart, through the breakdown of ATP. If repeated periods of ischemia are induced, the efflux of purines is markedly reduced, although it is not clear if this is beneficial for the long-term survival of the heart. We have investigated changes in high-energy phosphates and purine release in the isolated perfused rat heart using³¹P NMR spectroscopy and high-performance liquid chromatography. Hearts were subjected to one of the following protocols: Group A—1 min of total global ischemia (TGI) after 40 min, 60 min, and 85 min of perfusion (a total of 3 × 1 min ischemia); Group B—1 min of TGI after 40 min of perfusion, 10 min of TGI after 50 min of perfusion, and a final 1 min of TGI after 85 min of perfusion. The profile of high-energy phosphate metabolites, P_i accumulation and purine release was similar for each 1-min period of TGI in Group A, whereas phosphocreatine content was increased and ATP content reduced by an extended period of TGI in Group B, leading to a less severe acidosis and purine efflux in the final 1 min of TGI at 85 min of perfusion. In conclusion, the reduced purine release observed in Group B may be related to the preischemic ATP pool size and accessibility and the increased myocardial energy reserve in the form of phosphocreatine.     

Numerical modelling for simulation and treatment planning of prostate thermal therapy

A 2D transmission line matrix model is used to study thermal transfer in living tissues exposed to laser energy. Damage size because of thermal coagulation in thermal treatment of benign prostate hyperplasia is determined quantitatively. Results show a quasilinear dependency of blood perfusion on temperature at the beginning of coagulation. Immediately thereafter, blood perfusion decreases considerably until it shuts down when the tissue under investigation has been coagulated. Increase in perfusion rate (ω) leads to high values of t₁₀₀, which is the time required to reach a primary zone temperature of about 100 °C, and reflects the increased cooling created by perfusion. The transmission line matrix numerical model predicts the coagulation damage contours; that way, it has a clinical interest in therapy as an aid for clinicians because damage cannot be easily measured within patients. Results are validated through comparison with other researches. Copyright © 2014 John Wiley & Sons, Ltd.     

Simulation of Absorption Spectra of Metal Nanoparticles Embedded in Organic Media

Metal nanoparticles, silver and gold, of different sizes and shapes are actively being researched in a variety of different fields such as solar cells. The unique plasmonic properties of these particles, especially in the visible and NIR-region ranging from 400-1200 nm, are the basis for most of these applications. The absorption spectra are calculated using the discrete dipole approximation (DDA) in the wavelength region of 300 to 1200 nm. The modeled samples for calculating are planar array nanoparticles, basically two particles and more than two particles. The influences of the nanoparticle size, interparticle distance and polarization direction of excited light on the absorption spectra are investigated. Moreover, the optical absorption can be tuned by adjusting sizes and shape of nanoparticles to obtain the enhanced absorption. The influence of the surrounding medium is also presented.     

Efficient optical coupling between a polymeric waveguide and anultrafast silicon MSM photodiode

One task of the integration of optoelectronic functions with silicon devices is the construction of an optical waveguide on Si and the optical coupling of this waveguide to a silicon photodetector. We have fabricated polymeric strip waveguides on Si and demonstrate a very efficient design for the optical coupling between the polymeric waveguide and an ultrafast Si-based metal-semiconductor-metal (MSM) mesa-type photodetector. This detector uses high-quality epitaxial Si as the sensitive layer, which is sandwiched between two metallic contacts. If these MSM detectors are excited by a vertically incident free beam of λ=840 nm and pulses of 100-fs full-width at half-maximum (FWHM), they respond with electrical pulses of 3, 5-ps length (FWHM, T=300 K)     

纳米SiO2/低密度聚乙烯复合介质的击穿特性

聚合物纳米复合介质的击穿强度与纳米填充颗粒的质量分数、粒径和表面处理密切相关。以不同表面处理的纳米SiO2颗粒为填料,制备了不同填充质量分数、粒径的纳米SiO2/低密度聚乙烯(low density polyethylene,LDPE)复合介质,测试了其在交流、直流正极性和直流负极性3种不同类型电场下的击穿场强。结果表明:在所研究范围内,填充纳米SiO2颗粒可以提高低密度聚乙烯的击穿场强,并且随着填充质量分数的增加,复合介质的击穿场强有升高的趋势。纳米颗粒填充质量分数相同时,在12~16 nm粒径下,复合介质的击穿场强有随纳米SiO2粒径的升高而降低的趋势;在7 nm小粒径下,可能由于纳米颗粒容易团聚,导致击穿场强较粒径大时要低。另外,纳米SiO2颗粒表面经疏水性处理后,能够有效提高复合介质的击穿场强。     

Tunable optical and magneto-optical properties of nickel-polymer nanoparticles

Abstract

The optical and magneto-optical (MO) properties of composites containing magnetic nanoparticles were experimentally as well as theoretically found to be dependent on the interparticle spacing, surrounding medium and particle size of the constituent nanoparticles. In this work, the optical and MO properties of composites consisting of two nickel (Ni) nanoparticles (NP) and embedded in polymethyl methacrylate were theoretically investigated in the wavelength range of 400–900?nm using the discrete dipole approximation method, which accounts for optical coupling between Ni NPs. The theoretical calculations suggest that the shifts in spectral peak position depend on both interparticle distance and particle size corresponding to the experimental results. In addition, the observed optical spectra of Ni NPs showed the plasmon resonance in the visible light range in the electromagnetic wave. The basic results of this study might be used for fabricating optical and MO devices.     

网络控制系统稳定性分析和控制方法

随着大规模集成电路技术的提高,网络通讯技术的成熟及对大规模系统和远程式控制系统的需要,网络控制系统越来越受到人们的青睐。网络控制系统具有高的性价比和很大的灵活性,因此它逐渐被应用于工业控制中。在网络控制系统中不可避免地存在网络时延,它降低系统的性能或使系统变得不稳定,要设计控制器使系统具有期望的性能,是一件具有挑战性和吸引力的工作。为了给初步进入网络控制系统研究的人员提供一些必要的知识,分析了网络控制系统的结构、原理,网络控制系统中延时的来源及近年来有关网络控制系统的一些控制和稳定性分析方法。     

应用蒸汽相变机理脱除燃煤可吸入颗粒物实验研究

应用蒸汽相变机理促进细颗粒凝结长大，然后用湿式洗涤塔脱除长大后的含尘液滴，对燃煤可吸入颗粒物作为凝结核在过饱和蒸汽中凝结长大及湿式洗涤塔对凝结长大颗粒的脱除效果进行了实验研究，考察了蒸汽添加量、颗粒粒径及洗涤塔操作条件的影响。用电称低压冲击器(ELPI)实时测量凝结洗涤脱除前后的颗粒数量浓度和粒径分布。实验结果表明：蒸汽添加量的增加，能够迅速提高小粒径颗粒的脱除效率，蒸汽添加量为0.17kg/m3时，对平均粒径为0.3μm的颗粒的脱除效率超过80%；随着颗粒粒径增大，脱除效率提高；此外，洗涤塔液气比的增加，有利于燃煤可吸入颗粒物的脱除。研究表明蒸汽相变是脱除燃煤可吸入颗粒物的重要预调节措施之一。     

Measurement of arterial input function of <Superscript>17</Superscript>O water tracer in rat carotid artery by using a region-defined (REDE) implanted vascular RF coil

A method of determining arterial input function (AIF) by continuously detecting the ¹⁷O MR signal changes of ¹⁷O-labeled water tracer in the rat carotid artery using a region-defined (REDE) implanted vascular RF coil at 9.4 Tesla is reported. This coil has a compact physical size of 1 mm inner diameter, 3 mm outer diameter and 11 mm in length. It can be readily implanted into the rat neck and wrapped around the rat carotid artery for achieving adequate MR detection sensitivity for determining AIF with minimal surgical trauma. Water phantom and in vivo MR experiments were conducted for validating the coil's performance. A signal-to-noise ratio of ~20:1 was achieved for the ¹⁷O signal acquired from naturally abundant H₂ ¹⁷O in a small amount of blood (~7 μl) inside the rat carotid artery with an acquisition time of 11 s. The REDE RF coil design electromagnetically isolates the rat carotid artery from surrounding tissues and ensures that the MR signal detected by the RF coil is only attributable to the artery blood. It also minimizes the electromagnetic coupling between the implanted RF coil and a head surface coil tuned at the same operating frequency (two-coil configuration). This configuration allowed simultaneous measurements of dynamic changes of ¹⁷O MR signal of the H₂ ¹⁷O tracer in both rat carotid artery and brain. Compared to most contemporary MR approaches, the REDE implanted RF provides a simple, accurate, and promising solution for determination of AIF in small experimental animals.     

In vivo imaging of cardiac related impedance changes

Electrical impedance tomography (EIT) produces cross-sectional images of the electrical resistivity distribution within the body, made from voltage or current measurements through electrodes attached around the body. The authors describe a gated EIT system to image the cardiogenic electrical resistivity variations and the results of in vivo studies on human subjects. It is shown that the sensitivity of EIT to tissue resistivity variations due to blood perfusion is good enough to image blood flow to the lungs; hence, abnormalities in pulmonary perfusion, such as pulmonary embolism, should appear in EIT images. In addition, more valuable information related to the cardiac activity can be gained from EIT images than from impedance cardiography. It is thus likely that a cardiac output index may be calculable from the average resistivity variations over the ventricles, but considerable research is required before the images can be understood in detail.     

电容层析成像系统径向电极对传感器性能及敏感场分布的影响

电容层析成像系统传感器的敏感场分布受多相流介质分布的影响,软场特性给图像重建带来很大困难.该文以8电极油水两相流电容层析成像为研究对象,采用有限元仿真的方法,分析了径向电极及其嵌入尺寸对电容层析成像系统电容值及敏感场分布的影响.通过仿真分析,确定了径向电极的嵌入尺寸,从而能够在缩小测量电容值的动态变化范围,减轻数据采集电路设计难度的同时,提高电容响应的灵敏度,改善传感器敏感场的分布,提高电容层析成像系统的性能.     

Clinical assessment of myocardial viability using MRI during a constant infusion of Gd-DTPA

This study assessed the accuracy and feasibility of magnetic resonance imaging (MRI) during a constant infusion of gadolinium diethylenetriaminepentaacetic acid (Gd-DTPA) for the determination of myocardial viability in patients with recent acute myocardial infarction (AMI). Nine patients were studied within 10 days of AMI. Rest-redistribution 201Thallium (201Tl) single photon emission computed tomography (SPECT) was used as a gold standard for viability. Using MRI, regional perfusion was assessed using dynamic imaging during a bolus injection of Gd-DTPA and viability was assessed during a continuous infusion. Finally, cine MR images were acquired at baseline, during low-dose dobutamine infusion and after recovery. To assess viability, the left ventricle was divided into 16 segments and signal intensity in corresponding MRI and redistribution SPECT segments were compared. Wall thickening index (WTI) was determined at each step during the dobutamine study. The results revealed that in five patients, reduced perfusion in infarcted regions was observed qualitatively during dynamic first pass imaging. There was a significant inverse correlation between 201Tl uptake and MRI signal intensity, i.e. infarcted tissue (low 201Tl uptake) had increased MR signal intensity. Segments were separated into normal (201Tl uptake > 90%) and infarcted (< 601%). lnfarcted MRI segments had greater signal intensity than normal segments (179 +/- 50 vs. 102 +/- 14%; P < 0.0001). WTI in normal segments increased by 18 +/- 8.5% (P < 0.0001) from baseline to 10 microg/kg per min of dobutamine while infarcted tissue WTI decreased 2.8 +/- 7.2% (P = 0.17). Thus regions of myocardium that were infarcted as defined by reduced 201Tl uptake and absent contractile reserve showed greatly increased MRI signal intensity during a constant infusion of Gd-DTPA. The use of MRI during a constant infusion of Gd-DTPA is accurate and feasible for the determination of myocardial necrosis in a clinical setting.     

Fault detection for a class of nonlinear networked control systems

In this paper, an observer‐based fault detection (FD) method is presented for a class of nonlinear networked control systems (NCSs) with Markov transfer delays. Firstly, based on Euler approximate method, a nonlinear NCS model with uncertainty is proposed using the Takagi‐Sugeno (T‐S) fuzzy model. Some geometric conditions are given to transfer the NCS model into an output‐feedback form. Then, the H_∞ FD observer is designed such that the estimation error (residual) converges to zero, if there exist no fault and uncertainty in the system, or the residual is minimized in the sense of H_∞ norm, when system contains fault and uncertainties. Furthermore, to simplify the model, the approximate model without uncertainty is considered. Then, sufficient conditions for the existence of FD observer gain and the sampling time of NCSs are given to achieve the semiglobal practical property. An inverted pendulum example is used to illustrate the efficiency of the developed techniques. Copyright © 2009 John Wiley & Sons, Ltd.     

烧结温度对纳米复相SmFeO_3/γ-Fe_2O_3材料组织结构及磁性的影响

采用溶胶-凝胶法制备了纳米晶SmFeO_3/γ-Fe_2O_3复合粉体,然后经压制和高温烧结制备了SmFeO_3/γ-Fe_2O_3块体样品.研究了烧结温度对样品组织结构与磁性能的影响,结果表明,干凝胶经450℃预烧后,粉体样品中出现SmFeO_3相,但仍有部分非晶相存在.烧结温度对块体材料晶粒尺寸及磁性能有着显著的影响,在保温时间为1h的情况下,当烧结温度从800℃升高到1100℃时,烧结块体中SmFeO_3和γ-Fe_2O_3两相的平均晶粒尺寸分别由51nm和48nm长大到79nm和76nm,样品致密度由56%增大到72%,比饱和磁化强度从51A·m~2/kg升高到76A·m~2/kg,矫顽力从215kA/m下降到187kA/m.     

网络控制系统的通信机制分析与应用

对基于通信网络的控制系统展开研究,提出网络控制系统NCS(NetworkedControlSystem)的概念,描述其结构特点及功能分配,指出它是控制与信息的和谐统一。对NCS的通信机制进行重点研究,分析了信息的流动过程,时延的产生及构成。对由于通信网络的参与引起的控制系统性能的变化进行了讨论。结合水力发电机组状态监测的实际,提出了一种具有LonWorks 交换式以太网结构的NCS,并对其进行了阐述。     

空间电荷与直流电导联合测试技术用于纳米MgO抑制XLPE中空间电荷的研究

粒径70nm的MgO以不同浓度与交联聚乙烯(XLPE)共混制成聚合物纳米复合介质。采用自主研发的四电极系统同时测量复合介质的高场电导特性和空间电荷分布。通过强场电导实验发现,在室温下,XLPE及纳米MgO/XLPE复合介质的电导机理不是单纯的空间电荷限制电流(SCLC)。此外,添加纳米MgO可以明显地提高空间电荷的注入阈值,并且在低于空间电荷注入阈值的电场下,复合介质的电导电流密度随纳米MgO浓度的增加,先减小后增大。最后从空间电荷的实验数据验证了纳米MgO能有效抑制XLPE中空间电荷,并进一步定性地认为纳米Mgo的添加提高了电子注入的电场强度阈值。     

纳米SnO2/C微球材料的制备及电化

采用化学沉淀法,并通过进一步的水热反应,制备得到纳米二氧化锡颗粒,通过TEM分析知纳米二氧化锡颗粒的粒径约为5 nm;通过2,4-二羟基苯甲酸和甲醛之间的缩合反应,在体系中加入纳米二氧化锡颗粒,再通过水洗和热处理等步骤制备了纳米SnO2/C碳包覆微球,控制加入二氧化锡纳米颗粒的质量制备了不同样品来探究其对材料形貌及性能的影响.研究表明,当添加纳米二氧化锡含量为40％时,纳米SnO2/C复合材料的电化学性能最佳.在电流密度为100 mA/g充放电时,首次可逆比容量为825.2 mAh/g,第100次循环的可逆比容量为593.2 mAh/g,容量保持率达71.9％.