MRI图像信噪比提高技术

MRI图像处理技术是数字图像处理在生物医学工程中的重要应用，是数字图像处理技术与核磁共振成像相结合的产物，不仅推动了核磁共振成像技术进一步的研究与发展，同时也为数字图像处理技术提出了新的挑战，由于MRI图像中的信息对医疗诊断特别重要，因此如何利用数字计算机与数字图像处理理论对被噪声污染的图像进行降噪处理便成籽MRI图像处理的中心任务，本文主要分析了MRI图像中的各种噪声源，以及各自降噪技术的研究进展。     

化学突触传递的数值模拟

为了进一步认识突触功能,构造了两个简单的突触连接模型,并对化学突触传递进行模拟,数值研究化学突触的传递功能.研究结果表明,神经信号通过化学突触进行传递时,存在明显的突触延搁现象;突触后膜上化学门控离子通道的开放比例与突触前膜电位呈正相关;化学突触传递存在阈电位.上述结果与神经生物学的相关理论基本吻合.本研究以数值模拟方法进一步认识和理解了神经元之间的信号传递过程,也为后续的神经网络的模拟仿真研究奠定基础.     

Effect of Cooling on Synaptic Transmission through the Cuneate Nucleus

The synaptic transmission through the cuneate nucleus was studied during local cooling of the dorsal column region. Field potentials, recorded from the surface as well as inside the nucleus, were greatly increased during moderate cooling (to 30–25^o C) but diminished rapidly if the cuneate temperature fell below about 20^o C. The increase was most evident for the afferent fibre volley potentials, but large changes of synaptic potentials (N-wave) were regularly seen as well. The increase (up to several hundred per cent) was partly rate-dependent since fast cooling gave larger increases than slower cooling did. In spite of the greatly increased N-wave, the transmission through the nucleus was always reduced. This was tested in various ways: measurement of the latency and probability of firing of single units, “killed end”–recording from lemniscal fibres as a measure of number of discharging cuneate neurones, and measurement of the size of thalamic and cortical field potential produced by impulses relayed through the cuneate nucleus. The reduced transmission was most likely due to a greatly increased synaptic delay, with slowing of conduction along the terminal branches of the afferent fibres as a contributing factor. On severe cooling blocking of conduction in these branches occurred. During moderate cooling the probability of firing of most relay cells remained strikingly high.     

高帧率超声成像系统中一种高信噪比扇形成像模式的实现

基于有限衍射波束的高帧率（High frame rate，HFR）成像系统能实现快速成像，但成像区域为矩形，使得远区成像的信息量受到一定的限制；同时由于通过一次发射事件成像，信噪比较低。本文提出一种方案有效地解决了这些问题。方案采用Golay互补序列作为激励信号及两次发射与接收过程，每个发射事件同时发射两个不同角度的平面波。在对接收信号进行处理时。利用Golay互补序列良好的正交性及其相关函数为冲击函数特征，不仅显著地提高了接收信号的信噪比，而且有效地分离出相对于不同发射角度的两个平面波的回波信号。然后分别用HFR成像方法重建不同区域图像，最后合成一帧扇形成像。     

Taurine-Induced Long-Lasting Enhancement of Synaptic Transmission in Mice: Role of Transporters

Taurine, a major osmolyte in the brain evokes a long-lasting enhancement (LLE_TAU) of synaptic transmission in hippocampal and cortico-striatal slices. Hippocampal LLE_TAU was abolished by the GABA uptake blocker nipecotic acid (NPA) but not by the taurine-uptake inhibitor guanidinoethyl sulphonate (GES). Striatal LLE_TAU was sensitive to GES but not to NPA. Semiquantitative PCR analysis and immunohistochemistry revealed that taurine transporter expression is significantly higher in the striatum than in the hippocampus. Taurine transporter-deficient mice displayed very low taurine levels in both structures and a low ability to develop LLE_TAU in the striatum, but not in the hippocampus. The different mechanisms of taurine-induced synaptic plasticity may reflect the different vulnerabilities of these brain regions under pathological conditions that are accompanied by osmotic changes such as hepatic encephalopathy.     

Actions of the Pro-Inflammatory Cytokine Il-1[beta] on Central Synaptic Transmission

It is now clear that IL-1 beta has profound and complex actions in the CNS. At pathophysiological concentrations it has an inhibitory effect on LTP in many regions of the hippocampus. There is also evidence emerging for a physiological role for IL-1 beta in the brain. Table 1 summarizes the effects of IL-1 beta and some other pro-inflammatory cytokines in the CNS.     

Systemic Hypoxia and the Depression of Synaptic Transmission in Rat Hippocampus after Carotid Artery Occlusion

The relationship between step reductions in inspired oxygen and the amplitude of evoked field excitatory postsynaptic potentials (fEPSPs) recorded from hippocampal CA1 neurons was examined in anaesthetized rats with a unilateral common carotid artery occlusion. The amplitudes of fEPSPs recorded from the hippocampus ipsilateral to the occlusion were significantly more depressed with hypoxia than were the fEPSPs recorded from the contralateral hippocampus. The adenosine A₁-selective antagonist, 8-cyclopentyl-1,3-dimethylxanthine (8-CPT), blunted the hypoxic depression of the fEPSP. Tissue partial pressure of oxygen ( P _tiss,O2) was measured in the ipsilateral and contralateral hippocampus using glass Clark-style microelectrodes. P _tiss,O2 fell to similar levels as a function of inspired oxygen in the ipsilateral and contralateral hippocampus, and in the ipsilateral hippocampus after administration of 8-CPT. Hippocampal blood flow (HBF) was measured using laser Doppler flowmetry. A decline in HBF was associated with systemic hypoxia in both hippocampi. HBF, as a function of inspired oxygen, fell significantly more in the ipsilateral than in the contralateral hippocampus. We conclude that endogenous adenosine acting at the neuronal A₁ receptor plays a major role in the depression of synaptic transmission during hypoxic ischaemia. The greater susceptibility of the fEPSP in the ipsilateral hippocampus to systemic hypoxia cannot be explained entirely by differences in P _tiss,O2 or HBF between the two hemispheres.     

人参皂苷对大鼠海马齿状回神经元突触传递功效及记忆行为的关系

人参皂甙可长时间显著提高大鼠海马齿状回颗粒细胞层PS的幅度,缩短其起始和蜂潜伏期,引起LTP现象。同时,促进大鼠的记忆能力。用APV阻滞NMDA受体或用多粘菌素B抑制PKC分别阻断或抑制人参皂甙诱发的LTP现象后,人参皂甙促进记忆效应也消失。说明人参皂甙促进记忆的神经机理之一是提高海马齿状回颗粒细胞层突触传递功效。PKC和NMDA受体是其作用的重要环节。