超极化129Xe磁共振波谱和成像及在生物医学中的应用

文章简要介绍了磁共振波谱和成像的基本原理和对限制其灵敏度的挑战,详细阐述了为增强磁共振信号而制备超极化129Xe的物理机制,论述了129Xe在生物组织中的溶解性以及化学位移的特异性,综述了当前超极化129Xe在肺部、脑部成像领域的研究进展和在临床方面应用所取得的有代表性的研究成果,并讨论了基于超极化129Xe分子生物探针的超灵敏磁共振技术的研究前景,最后对超极化129Xe在生物医学领域的应用与发展作了展望.     

超极化129Xe磁共振分子影像学

磁共振分子影像学发展的主要瓶颈之一在于灵敏度的限制,基于激光光泵和自旋交换技术能获得增强4~5个量级的超极化¹²⁹Xe磁共振信号,因此超极化¹²⁹Xe磁共振分子影像学相对于传统MRI在灵敏度上表现出巨大的优势. 围绕提高灵敏度这一核心MRI问题及其在科学研究中的应用,该文介绍了目前基于超极化¹²⁹Xe的生物分子探针的基本结构和原理,阐述了与之相关的分子影像学方法和技术,同时评述了当前的最新研究进展和发展方向.     

超极化129Xe自动收集-升华装置研究

因其较高的核自旋极化度所提供的探测灵敏度,超极化¹²⁹Xe气体已被成功应用于动物和人体磁共振成像（MRI）.但是,在超极化¹²⁹Xe的收集-升华过程中,多种因素会导致¹²⁹Xe核自旋弛豫,进而限制其应用范围.本文通过理论模型分析和实验测量,验证了温度、磁场、螺旋冷阱材质等对冷冻恢复过程中超极化¹²⁹Xe弛豫的影响;同时,测量了自动收集-升华装置的稳定性.研究结果表明,升华方式和冷阱材质对¹²⁹Xe极化度损耗的影响显著;自制收集-升华装置的自动化程度高、长时间稳定,¹²⁹Xe极化度的恢复率可达到85.6% ± 4.7%.本研究非常有助于提升超极化¹²⁹Xe在动物和人体MRI中的使用效率.     

激光增强极化^129Xe和^3He的磁共振成像

当激光增强极化的＾１２９Ｘｅ或者＾３Ｈｅ被输送到一些感兴趣的生物体内组织中（例如：人或者动物的肺部），由于它们具有高的自旋密度对比度，可以给出大的核磁共振信号强度、高的成像空间分辨和数据率，有希望应用于质子成像不能达到的一些有意义的生物组织的成像。该文简述了激光增强极化＾１２９Ｘｅ和＾３Ｈｅ样品的制备、储存、输送方法和成像应用，以及相应过程中的物理量。     

频率校正方法在活体肝脏1H磁共振波谱中的应用

主要探讨频率校正技术在活体肝脏1H磁共振波谱的应用价值.肝脏单体素¹H 磁共振波谱采用PRESS序列,频率位移分析和校正基于频域谱的残余水峰. 结果表明,5例健康志愿者频率变化的标准偏差为7.92±4.12 Hz; 采用频率校正方法处理后, 残余水峰和脂肪峰(-(CH₂)_n-)的谱线明显变窄,信噪比得到一定程度的改善. 因此频率校正技术可以改善活体肝脏¹H磁共振波谱的谱质量,从而增加磁共振波谱在肝脏病变评价中的准确性.     

磁共振结构成像在自闭症研究中的应用

自闭症,又称作孤独症,是一种常发生在儿童中的广泛性发育障碍,表现为交流障碍、语言障碍以及重复刻板的行为和狭窄的兴趣爱好. 磁共振成像作为一种无损伤的和多参数的影像方法,其各种检测手段均被应用于自闭症实验研究,其中结构磁共振成像(sMRI)和功能磁共振成像(fMRI)研究居多. 研究表明自闭症患者脑部结构发生了显著性改变. 该文综述了当前世界上利用磁共振结构成像研究自闭症的主要成果,包括结构磁共振成像研究脑体积变化,扩散张量成像研究自闭症的脑白质损伤. 该文也说明磁共振成像是一种十分有用的研究工具,有望在将来更多被用于探索自闭症的未知领域.     

磁共振波谱及成像技术在纳米尺度物质生物效应研究中的应用

纳米尺度物质的生物效应研究是近年来在纳米科技发展过程中派生出来的一个崭新的、发展很快的且多学科高度交叉的领域,需要把纳米科学、物理学、化学以及生物医学等多学科的研究手段结合起来,进行综合研究.核磁共振波谱与成像,作为一种原位、无损、动态、实时、多信息的检测手段,在此领域的研究中将发挥不可或缺的重要作用.文章分3个方面简要介绍核磁共振波谱与成像技术在纳米尺度物质生物效应研究中的应用：(1)纳米尺度物质在生物组织及个体内的检测与分析;(2)纳米尺度物质与生物大分子相互作用的核磁共振波谱研究;(3)纳米尺度物质生物效应的核磁共振代谢组学研究.     

磁共振波谱及成像技术在纳米尺度物质生物效应研究中的应用

纳米尺度物质的生物效应研究是近年来在纳米科技发展过程中派生出来的一个崭新的、发展很快的且多学科高度交叉的领域，需要把纳米科学、物理学、化学以及生物医学等多学科的研究手段结合起来，进行综合研究．核磁共振波谱与成像，作为一种原位、无损、动态、实时、多信息的检测手段，在此领域的研究中将发挥不可或缺的重要作用．文章分3个方面简要介绍核磁共振波谱与成像技术在纳米尺度物质生物效应研究中的应用：（1）纳米尺度物质在生物组织及个体内的检测与分析；（2）纳米尺度物质与生物大分子相互作用的核磁共振波谱研究；（3）纳米尺度物质生物效应的核磁共振代谢组学研究．     

脑功能磁共振成像在人类嗅觉研究中的应用

在人类的5种主要感觉中,嗅觉是最广泛、古老、直接和内在的感觉.这些特性使人们对人类嗅觉的研究异常艰难,以致于直到今天人们对嗅觉的功能仍不清楚,而对大脑的功能机制所知更少.与其他基于物理原理的方法一样,磁共振成像技术的广泛应用极大地推动了整个生命科学的发展.脑功能磁共振成像的优势（高分辨率、高对比度、无损性和无放射性等）为人们研究嗅觉高级中枢以及与嗅觉相关行为的脑机制等提供了强有力的技术手段.文章在简单介绍嗅觉知识的基础上,着重讨论了近十年来,脑功能磁共振成像技术在人类嗅觉研究中所取得的成果.     

在体电子自旋共振(EPR)波谱和成像技术在生物医学中的应用

活性氧和氮自由基(ROS/RNS)在一系列的人类疾病中扮演着双重角色. 它们可以是氧化剂, 诱导氧化状态, 导致组织损伤. 它们又可以是信号传导因子, 诱发保护性反应, 使得被调节的组织器官经受得起更强的损伤. 鉴于它们在生物医学中的重要作用, 检测它们产生和分布的技术的研究因而变得必要和紧迫. 在体电子自旋共振(EPR)波谱和成像技术渐已被应用于活体生物体系中用以表针和显像ROS/RNS. EPR 波谱特性(包括线宽、强度和寿命)以及空间分布信息已为动物甚至人体病理模型中氧化还原状态和氧分布的检测提供不可缺少的依据. 该文将简单描述和讨论一系列在体EPR 波谱和成像技术在器官和组织中的应用, 其中包括活体组织氧化还原状态, 活体组织氧分布和时间演化, 自由基空间以及谱-空间成像等.     

NMR Study of Laser polarized ~(129) Xe in Low Pressure Natural Xenon Gas

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Nuclear spin resonance of (129)Xe doped with O(2)

Spin-lattice relaxation of (129)Xe nuclei in solid natural xenon has been investigated in detail over a large range of paramagnetic O(2) impurity concentrations. Direct measurements of the ground state magnetic properties of the O(2) are difficult because the ESR (electron spin resonance) lines of O(2) are rather unstructured, but NMR measurements in the liquid helium temperature region (1.4-4 K) are very sensitive to the effective magnetic moments associated with the spin 1 Zeeman levels of the O(2) molecules and to the O(2) magnetic relaxation. From these measurements, the value of the D[Sz(2)-(1/3)S(2)] spin-Hamiltonian term of the triplet spin ground state of O(2) can be determined. The temperature and magnetic field dependence of the measured paramagnetic O(2)-induced excess line width of the (129)Xe NMR signal agree well with the theoretical model with the spin-Hamiltonian D=0.19 meV (2.3 K), and with the reasonable assumption that the E[S(x)(2)-S(y)(2)] spin-Hamiltonian term is close to 0 meV. An anomalous temperature dependence between 1.4 K and 4.2K of the (129)Xe spin-lattice relaxation rate, T(1n)(-1)(T), is also accounted for by our model. Using an independent determination of the true O(2) concentration in the Xe-O(2) solid, the effective spin lattice relaxation time (which will be seen to be transition dependent) of the O(2) at 2.3 K and 0.96 T is determined to be approximately 1.4 x 10(-8)s. The experimental results, taken together with the relaxation model, suggest routes for bringing highly spin-polarized (129)Xe from the low temperature condensed phase to higher temperatures without excessive depolarization.     

Real-time functional magnetic resonance imaging: methods and applications

Functional magnetic resonance imaging (fMRI) has been limited by time-consuming data analysis and a low signal-to-noise ratio, impeding online analysis. Recent advances in acquisition techniques, computational power and algorithms increased the sensitivity and speed of fMRI significantly, making real-time analysis and display of fMRI data feasible. So far, most reports have focused on the technical aspects of real-time fMRI (rtfMRI). Here, we provide an overview of the different major areas of applications that became possible with rtfMRI: online analysis of single-subject data provides immediate quality assurance and functional localizers guiding the main fMRI experiment or surgical interventions. In teaching, rtfMRI naturally combines all essential parts of a neuroimaging experiment, such as experimental design, data acquisition and analysis, while adding a high level of interactivity. Thus, the learning of essential knowledge required to conduct functional imaging experiments is facilitated. rtfMRI allows for brain-computer interfaces (BCI) with a high spatial and temporal resolution and whole-brain coverage. Recent studies have shown that such BCI can be used to provide online feedback of the blood-oxygen-level-dependent signal and to learn the self-regulation of local brain activity. Preliminary evidence suggests that this local self-regulation can be used as a new paradigm in cognitive neuroscience to study brain plasticity and the functional relevance of brain areas, even being potentially applicable for psychophysiological treatment.     

A computer algorithm for the simulation of any nuclear magnetic resonance (NMR) imaging method

More than a dozen Nuclear Magnetic Resonance (NMR) imaging methods have been described using different radio-frequency pulse sequences, magnetic field gradient variations, and data processing. In order to have a theoretical understanding in the most general case, we have conceived a computer program for the simulation of NMR imaging techniques. The algorithm uses the solution of the Bloch equations at each point of a simulated object. The direction of every elementary magnetic moment is computed at each instant, and stored in an array giving the global signal to be processed, whatever the pulse and gradient sequence. To test the validity of this program, we have simulated some well-known experimental results. Some applications are presented which contribute to the understanding of image distortions and to techniques such as selective radio-frequency pulse or oscillating gradients. This program can be used to unravel physical and technological causes of image distortions, to have a "microscopic" look at any parameter of an experiment, and to study the contrast given by various NMR imaging techniques as a function of the three NMR parameters, i.e., the hydrogen nuclei density rho and the relaxation times T1 and T2.     

H Magnetic resonance imaging and P magnetic resonance spectroscopy in experimental filariasis

¹H Magnetic resonance imaging and ³¹P magnetic resonance spectroscopy (MRS) have been carried out in experimental rodent filariasis, i.e., Acanthocheilonema viteae infection in the rodent host, Mastomys coucha. The T₂-weighted image of the infected host shows fine hyperintense thread like structures of adult filariid nests in the cervical region. ³¹P MRS of normal and infected hosts, localized over the same region of interest, show seven major peaks corresponding to phosphomonoesters (including glucose-6-phosphate, fructose-6-phosphate, fructose-1-6-diphosphate, phosphorylcholine, and adenine monophosphate or AMP), inorganic phosphate, glycerophosphorylcholine, phosphoenolpyruvate, phosphocreatine and nucleoside di- and tri-phosphates. Concentrations of phosphomonoesters (PMEs) are higher in the normal rodent compared with the infected ones. In vivo ³¹P MRS provides a non-invasive assessment of tissue bioenergetics and phospholipid metabolism.     

脑功能磁共振成像在人类嗅觉研究中的应用

在人类的5种主要感觉中,嗅觉是最广泛、古老、直接和内在的感觉.这些特性使人们对人类嗅觉的研究异常艰难,以致于直到今天人们对嗅觉的功能仍不清楚,而对大脑的功能机制所知更少.与其他基于物理原理的方法一样,磁共振成像技术的广泛应用极大地推动了整个生命科学的发展.脑功能磁共振成像的优势(高分辨率、高对比度、无损性和无放射性等)为人们研究嗅觉高级中枢以及与嗅觉相关行为的脑机制等提供了强有力的技术手段.文章在简单介绍嗅觉知识的基础上,着重讨论了近十年来,脑功能磁共振成像技术在人类嗅觉研究中所取得的成果.     

Functional magnetic resonance imaging of tonic pain and vasopressor effects in rats

In functional magnetic resonance imaging (fMRI) studies, an elevation in blood pressure (BP) in individuals with a poor autoregulatory response may increase cerebral blood flow, potentially enhancing the blood oxygenation level dependent response. To investigate the role of BP changes, the cerebral activation to either tonic pain or the infusion of the vasopressor norepinephrine was correlated with the accompanying BP changes in alpha-chloralose anesthetized rats. Immediately after formalin (2%) injection into the forepaw, fMRI detected an activation that was correlated with the BP increase and additional activations that were independent of blood pressure changes 5–40 minutes later. The activation detected with the administration of the vasopressor norepinephrine, which does not cross the blood-brain barrier was correlated to both the amount and rate of increase in BP. The response ranged from being sparse, localized within cortex or widespread during modest, moderate or severe elevations in BP, respectively. The cerebral circulatory effects of hypertension should be considered as contributing to changes in cerebral blood oxygenation in fMRI studies involving increases in BP.