一种新的磁共振成像技术

一种新型的磁共振成像技术(MRI)可望获得肺部的图像,用于详细研究肺部疾患部位和肺部的神经组织,为医生提供详细资料。 这种技术是普通MRI技术的一种延伸。通用的MRI技术使用强大的超导磁铁来极化人体中水和脂肪分子的氢核,可以得到人体某些区域,例如脊髓、大脑或眼球内部的图像,但不能得到充满气体的肺部图像。 新方法检测出的是氦核,这种氦核在进入人体之前已经极化了。这种极化了的氦核进入     

医学上的磁共振成像与激光成像

医学上的磁共振成像与激光成像张新明（华侨大学医院泉州市３６２０１１）关键词磁共振成像激光成像对比分辨率临床应用ＭｅｄｉｃａｌＭａｇｎｅｔｉｃＲｅｓｏｎｃｍｃｅａｎｄＬａｓｅｒＩｍａｇｉｎｇｓＺｈａｎｇＸｉｎｍｉｎｇ（ＨｏｓｐｉｔａｌｏｆＨｕａＱｉａｏ...     

医学领域的磁共振成像革命——2003年诺贝尔生理及医学奖主要工作介绍

在磁场中 ,自旋的原子核会吸收频率与其自旋频率相同的电磁波 ,使自身能量增加 ,发生能级跃迁 ,当原子核迁移回原能级时 ,就会把多余的能量以电磁波的形式释放出来 ,称为核磁共振 (NMR) .磁共振成像(MRI)利用这一原理 ,依据所释放的能量在物质内部不同结构环境中不同的衰减 ,通过外加梯度磁场检测所发射出的电磁波 ,即可得知构成这一物体原子核的位置和种类 ,据此可以绘制成物体内部的结构图像 .将这种技术用于人体内部结构的成像 ,就产生出一种革命性的医学诊断工具 .快速变化的梯度磁场的应用 ,大大加快了磁共振成像的速度 ,使该技术在临床诊断、科学研究的应用成为现实 ,极大地推动了医学、神经生理学和认知神经科学的迅速发展     

金红石型氧化钛覆膜热解碳的制备及血液相容性研究

用离子束增强沉积 (IBED)方法 :即在氧气氛中 ,通过惰性气体Xe+离子轰击和Ti的电子束蒸发进行了氧化钛薄膜的合成 .X射线衍射分析表明 ,用离子束增强沉积技术合成的薄膜为金红石结构 ,具有 ( 10 0 )择优取向 .用背散射技术分析了薄膜的成分 ,发现薄膜的O/Ti基本上接近 2∶1.薄膜中含有一定量的Ti2 +和Ti3+.体外试验及动物体内试验结果表明 ,金红石型氧化钛薄膜具有比目前临床应用的热解碳更好的血液相容性 .并认为 ,金红石型氧化钛覆膜热解碳极可能成为新的人工心脏瓣膜材料 .     

脊髓磁共振成像技术：方法与应用

脊髓磁共振成像是将磁共振成像应用于脊髓部分(主要是颈髓)的先进研究技术,在人体感觉、运动等基础科学研究,以及脊髓损伤、脊髓炎、慢性疼痛等疾病的临床应用中均已逐渐得到使用。脊髓磁共振成像的发展相比脑成像而言仍处于起步阶段,这主要受限于目前的磁共振成像技术和数据分析方法。本文以认知神经科学和医学领域的基础研究为主,聚焦于脊髓磁共振成像技术的方法与应用。首先介绍了常用多模态脊髓磁共振成像技术的成像原理、成像方法、测量指标及其应用现状,具体包括脊髓定量磁共振成像(结构成像、弥散成像、波谱成像、髓磷脂水分数成像、磁化转移成像和化学交换饱和转移成像等)和脊髓功能磁共振成像等;其次从噪声控制、数据处理流程优化以及可重复性与可信度三个维度介绍了脊髓磁共振成像在数据分析上所面临的技术挑战以及应对策略;最后对脊髓磁共振成像的应用现状和发展前景进行了总结与展望。     

磁敏感加权成像在帕金森病中的应用研究

目的:探索帕金森病(PD)的磁敏感加权成像(SWI)的表现。方法:34例帕金森病患者作为病例组和30例正常人作为对照组,采用GE1.5T磁共振成像系统,行常规的快速自旋回波T1、T2加权像后,加扫三维磁敏感加权成像覆盖基底节区及中脑。使用SWI后处理软件在校正相位图上两次测量双侧尾状核头、苍白球、壳核、黑质、红核的相位值,最终的相位值取两次测量的平均值。结果:病例组患者黑质、壳核的相位值较对照组明显降低,差异具有统计学意义(P<0.05),PD患者黑质及壳核铁沉积增加。病例组壳核的相位值与PD病程之间存在负相关。对照组中尾状核头、壳核、黑质相位值左侧低于右侧。结论:SWI是显示PD患者脑内铁沉积的有效的检查方法。     

磁敏感加权成像在帕金森病中的应用研究

目的：探索帕金森病（PD）的磁敏感加权成像（SWI）的表现。方法：34例帕金森病患者作为病例组和30例正常人作为对照组。采用GEL5T磁共振成像系统,行常规的快速自旋回波T1、T2加权像后,加扫三维磁敏感加权成像覆盖基底节区及中脑。使用SWI后处理软件在校正相位图上两次测量双侧尾状核头、苍白球、壳核、黑质、红核的相位值,最终的相位值取两次测量的平均值。结果：病例组患者黑质、壳核的相位值较对照组明显降低,差异具有统计学意义（P〈0．05）,PD患者黑质及壳核铁沉积增加。病例组壳核的相位值与PD病程之间存在负相关。对照组中尾状核头、壳核、黑质相位值左侧低于右侧。结论：SWI是显示PD患者脑内缺沉积的有效音白枪杏方法．     

用于可视化光治疗的Mn3O4@CuS纳米粒的制备研究

摘要 目的：本研究旨在制备用于肿瘤可视化光治疗的多功能Mn₃O₄@CuS核壳型纳米粒,在磁共振成像的引导下,使用近红外光定点辐照,实现局部光热消融治疗。方法：（1）采用高温热解法制备油胺稳定的Mn₃O₄纳米粒,在其表面构建CuS壳层,并进行聚乙二醇修饰,得到分散于水相中的Mn₃O₄@CuS核壳型纳米粒。（2）通过透射电镜、紫外可见近红外吸收光谱等方法对该纳米粒进行理化性质表征,并研究其体外磁共振成像、光热升温等性能。结果：制备的水相分散的Mn₃O₄@CuS纳米粒,粒径均一且分散性较好,形态为近圆形,粒径为9.30±2.29 nm;紫外可见近红外吸收光谱图表明Mn₃O₄@CuS纳米粒在近红外区有较强吸收,最大吸收峰位于1100~1200 nm范围;磁共振成像分析结果可计算出Mn₃O₄@CuS纳米粒的纵向弛豫率r1为1.662 mM^-1s^-1,表明其具有较好的磁共振增强造影效果;光热升温曲线显示Mn₃O₄@CuS纳米粒可在785 nm近红外激光下升温至73.5 ℃,具备较好的光热治疗潜力。结论：本文成功制备出水相分散的Mn₃O₄@CuS核壳型纳米粒,具有良好的磁共振造影成像性能和光热升温效应,有望应用于磁共振成像引导下的肿瘤可视化光治疗。     

磁共振功能成像在监测乳腺癌新辅助化疗中的应用和进展

近年来,新辅助化疗在原发乳腺癌治疗中运用越来越广泛。影像学手段在评价新辅助化疗疗效、指导临床治疗方案的制定中发挥重要作用。磁共振功能成像的引入,可以加深对恶性乳腺肿瘤的病理生理活动及分子生物学特性的了解,监测化疗疗效,提高早期预测的准确性。本文总结功能学MRI(磁共振成像)探测乳腺癌患者生物标志物的研究现状及发展情况,描述各种生物学标志物特性,评价其潜在的临床应用价值和局限性。以下将对动态增强磁共振成像、弥散加权成像、血氧水平依赖成像以及波谱成像等几种磁共振功能学成像方法的原理进行描述,重点对其在监测乳腺癌新辅助化疗中的应用进行综述。     

磁共振弥散加权成像在检测短暂性脑缺血责任病灶的临床价值

目的:探讨磁共振弥散加权成像显示短暂性脑缺血责任病灶的敏感性及其临床应用价值.方法:对连续的39例资料完整的住院TIA患者进行了常规磁共振成像和弥散加权磁共振成像(diffusion-weighted MRI,DWI)检查,对比不同成像序列对短暂性脑缺血责任病灶的检出率.结果:在39例TIA患者中,快速自旋回波序列(FSET1WI和FSET2WI)检出TIA责任病灶9例(9/39);翻转恢复序列(FLAIR)检出11例(11/39);弥散加权序列检出15例(15/39).不同序列检出率比较运用单因素的方差分析显示有明显差异(P=0.001),弥散加权序列检出率最高.结论:DWI序列对TIA责任病灶的检出率明显高于常规MR,可为TIA患者的临床处理提供可靠诊断信息.     

Peptide-mediated cellular uptake of cryptophane

Cryptophane-A has generated considerable interest based on its high affinity for xenon and potential for creating biosensors for (129)Xe nuclear magnetic resonance (NMR) spectroscopy. Here, we report the cellular delivery of three peptide-functionalized cryptophane biosensors. Cryptophanes were delivered using two cationic cell penetrating peptides into several human cancer and normal cell lines. An RGD peptide targeting alpha(v)beta(3) integrin receptor was shown to increase specificity of cryptophane cell uptake. Labeling the peptides with Cy3 made it possible to monitor cellular delivery using confocal laser scanning microscopy. The peptido-cryptophanes were determined to be relatively nontoxic by MTT assay at the micromolar cryptophane concentrations that are required for (129)Xe NMR biosensing experiments.     

Distribution of hyperpolarized xenon in the brain following sensory stimulation: preliminary MRI findings

In hyperpolarized xenon magnetic resonance imaging (HP (129)Xe MRI), the inhaled spin-1/2 isotope of xenon gas is used to generate the MR signal. Because hyperpolarized xenon is an MR signal source with properties very different from those generated from water-protons, HP (129)Xe MRI may yield structural and functional information not detectable by conventional proton-based MRI methods. Here we demonstrate the differential distribution of HP (129)Xe in the cerebral cortex of the rat following a pain stimulus evoked in the animal's forepaw. Areas of higher HP (129)Xe signal corresponded to those areas previously demonstrated by conventional functional MRI (fMRI) methods as being activated by a forepaw pain stimulus. The percent increase in HP (129)Xe signal over baseline was 13-28%, and was detectable with a single set of pre and post stimulus images. Recent innovations in the production of highly polarized (129)Xe should make feasible the emergence of HP (129)Xe MRI as a viable adjunct method to conventional MRI for the study of brain function and disease.     

Interaction of laser plasmas with noble gases

The interaction of a noble gas jet (Xe, Kr, He) with a laser plasma at a distance of ～1 cm from a solid target (Mg, (CH₂)_n, LiF, or CF₄) was studied for the first time. The line spectra that were excited in the course of charge exchange of multicharged ions with noble gas atoms in the interaction region were recorded. A clean (debris-free) soft X-ray source excited by laser pulses focused into a xenon jet was designed and investigated.     

Hyperpolarized Xenon for NMR and MRI Applications

Nuclear magnetic resonance (NMR) spectroscopy and imaging (MRI) suffer from intrinsic low sensitivity because even strong external magnetic fields of ~10 T generate only a small detectable net-magnetization of the sample at room temperature ¹. Hence, most NMR and MRI applications rely on the detection of molecules at relative high concentration (e.g., water for imaging of biological tissue) or require excessive acquisition times. This limits our ability to exploit the very useful molecular specificity of NMR signals for many biochemical and medical applications. However, novel approaches have emerged in the past few years: Manipulation of the detected spin species prior to detection inside the NMR/MRI magnet can dramatically increase the magnetization and therefore allows detection of molecules at much lower concentration ².Here, we present a method for polarization of a xenon gas mixture (2-5% Xe, 10% N₂, He balance) in a compact setup with a ca. 16000-fold signal enhancement. Modern line-narrowed diode lasers allow efficient polarization ⁷ and immediate use of gas mixture even if the noble gas is not separated from the other components. The SEOP apparatus is explained and determination of the achieved spin polarization is demonstrated for performance control of the method.The hyperpolarized gas can be used for void space imaging, including gas flow imaging or diffusion studies at the interfaces with other materials ^8,9. Moreover, the Xe NMR signal is extremely sensitive to its molecular environment ⁶. This enables the option to use it as an NMR/MRI contrast agent when dissolved in aqueous solution with functionalized molecular hosts that temporarily trap the gas ^10,11. Direct detection and high-sensitivity indirect detection of such constructs is demonstrated in both spectroscopic and imaging mode.     

Hyperpolarized 129Xe MR Imaging of Alveolar Gas Uptake in Humans

Background

One of the central physiological functions of the lungs is to transfer inhaled gases from the alveoli to pulmonary capillary blood. However, current measures of alveolar gas uptake provide only global information and thus lack the sensitivity and specificity needed to account for regional variations in gas exchange.

Methods and Principal Findings

Here we exploit the solubility, high magnetic resonance (MR) signal intensity, and large chemical shift of hyperpolarized (HP) ¹²⁹Xe to probe the regional uptake of alveolar gases by directly imaging HP ¹²⁹Xe dissolved in the gas exchange tissues and pulmonary capillary blood of human subjects. The resulting single breath-hold, three-dimensional MR images are optimized using millisecond repetition times and high flip angle radio-frequency pulses, because the dissolved HP ¹²⁹Xe magnetization is rapidly replenished by diffusive exchange with alveolar ¹²⁹Xe. The dissolved HP ¹²⁹Xe MR images display significant, directional heterogeneity, with increased signal intensity observed from the gravity-dependent portions of the lungs.

Conclusions

The features observed in dissolved-phase ¹²⁹Xe MR images are consistent with gravity-dependent lung deformation, which produces increased ventilation, reduced alveolar size (i.e., higher surface-to-volume ratios), higher tissue densities, and increased perfusion in the dependent portions of the lungs. Thus, these results suggest that dissolved HP ¹²⁹Xe imaging reports on pulmonary function at a fundamental level.     

In vivo MR imaging of pulmonary perfusion and gas exchange in rats via continuous extracorporeal infusion of hyperpolarized 129Xe

Background

Hyperpolarized (HP) ¹²⁹Xe magnetic resonance imaging (MRI) permits high resolution, regional visualization of pulmonary ventilation. Additionally, its reasonably high solubility (>10%) and large chemical shift range (>200 ppm) in tissues allow HP ¹²⁹Xe to serve as a regional probe of pulmonary perfusion and gas transport, when introduced directly into the vasculature. In earlier work, vascular delivery was accomplished in rats by first dissolving HP ¹²⁹Xe in a biologically compatible carrier solution, injecting the solution into the vasculature, and then detecting HP ¹²⁹Xe as it emerged into the alveolar airspaces. Although easily implemented, this approach was constrained by the tolerable injection volume and the duration of the HP ¹²⁹Xe signal.

Methods and Principal Findings

Here, we overcome the volume and temporal constraints imposed by injection, by using hydrophobic, microporous, gas-exchange membranes to directly and continuously infuse ¹²⁹Xe into the arterial blood of live rats with an extracorporeal (EC) circuit. The resulting gas-phase ¹²⁹Xe signal is sufficient to generate diffusive gas exchange- and pulmonary perfusion-dependent, 3D MR images with a nominal resolution of 2×2×2 mm³. We also show that the ¹²⁹Xe signal dynamics during EC infusion are well described by an analytical model that incorporates both mass transport into the blood and longitudinal relaxation.

Conclusions

Extracorporeal infusion of HP ¹²⁹Xe enables rapid, 3D MR imaging of rat lungs and, when combined with ventilation imaging, will permit spatially resolved studies of the ventilation-perfusion ratio in small animals. Moreover, EC infusion should allow ¹²⁹Xe to be delivered elsewhere in the body and make possible functional and molecular imaging approaches that are currently not feasible using inhaled HP ¹²⁹Xe.     

Theoretical study of the NMR chemical shift of Xe in supercritical condition

In this work we investigate the level of theory necessary for reproducing the non-linear variation of the ¹²⁹Xe nuclear magnetic resonance (NMR) chemical shift with the density of Xe in supercritical conditions. In detail we study how the ¹²⁹Xe chemical shift depends under supercritical conditions on electron correlation, relativistic and many-body effects. The latter are included using a sequential-QM/MM methodology, in which a classical MD simulation is performed first and the chemical shift is then obtained as an average of quantum calculations of 250 MD snapshots conformations carried out for Xe _n clusters (n =?2 ? 8 depending on the density). The analysis of the relativistic effects is made at the level of 4-component Hartree-Fock calculations (4c-HF) and electron correlation effects are considered using second order Møller-Plesset perturbation theory (MP2). To simplify the calculations of the relativistic and electron correlation effects we adopted an additive scheme, where the calculations on the Xe _n clusters are carried out at the non-relativistic Hartree-Fock (HF) level, while electron correlation and relativistic corrections are added for all the pairs of Xe atoms in the clusters. Using this approach we obtain very good agreement with the experimental data, showing that the chemical shift of ¹²⁹Xe in supercritical conditions is very well described by cluster calculations at the HF level, with small contributions from relativistic and electron correlation effects.     

Detection and characterization of xenon-binding sites in proteins by 129Xe NMR spectroscopy

Xenon-binding sites in proteins have led to a number of applications of xenon in biochemical and structural studies. Here we further develop the utility of 129Xe NMR in characterizing specific xenon-protein interactions. The sensitivity of the 129Xe chemical shift to its local environment and the intense signals attainable by optical pumping make xenon a useful NMR reporter of its own interactions with proteins. A method for detecting specific xenon-binding interactions by analysis of 129Xe chemical shift data is illustrated using the maltose binding protein (MBP) from Escherichia coli as an example. The crystal structure of MBP in the presence of 8atm of xenon confirms the binding site determined from NMR data. Changes in the structure of the xenon-binding cavity upon the binding of maltose by the protein can account for the sensitivity of the 129Xe chemical shift to MBP conformation. 129Xe NMR data for xenon in solution with a number of cavity containing phage T4 lysozyme mutants show that xenon can report on cavity structure. In particular, a correlation exists between cavity size and the binding-induced 129Xe chemical shift. Further applications of 129Xe NMR to biochemical assays, including the screening of proteins for xenon binding for crystallography are considered.     

Programming xenon diffusion in maltose-binding protein

Protein interiors contain void space that can bind small gas molecules. Determination of gas pathways and kinetics in proteins has been an intriguing and challenging task. Here, we combined computational methods and the hyperpolarized xenon-129 chemical exchange saturation transfer (hyper-CEST) NMR technique to investigate xenon (Xe) exchange kinetics in maltose-binding protein (MBP). A salt bridge ～9 Å from the Xe-binding site formed upon maltose binding and slowed the Xe exchange rate, leading to a hyper-CEST ¹²⁹Xe signal from maltose-bound MBP. Xe dissociation occurred faster than dissociation of the salt bridge, as shown by ¹³C NMR spectroscopy and variable-B₁ hyper-CEST experiments. “Xe flooding” molecular dynamics simulations identified a surface hydrophobic site, V23, that has good Xe binding affinity. Mutations at this site confirmed its role as a secondary exchange pathway in modulating Xe diffusion. This shows the possibility for site-specifically controlling xenon protein-solvent exchange. Analysis of the available MBP structures suggests a biological role of MBP’s large hydrophobic cavity to accommodate structural changes associated with ligand binding and protein-protein interactions.