In Vivo EPR For Dosimetry

As a result of terrorism, accident, or war, populations potentially can be exposed to doses of ionizing radiation that could cause direct clinical effects within days or weeks. There is a critical need to determine the magnitude of the exposure to individuals so that those with significant risk have appropriate procedures initiated immediately, while those without a significant probability of acute effects can be reassured and removed from the need for further consideration in the medical/emergency system. In many of the plausible scenarios there is an urgent need to make the determination very soon after the event and while the subject is still present. In vivo EPR measurements of radiation-induced changes in the enamel of teeth is a method, perhaps the only such method, which can differentiate among doses sufficiently for classifying individuals into categories for treatment with sufficient accuracy to facilitate decisions on medical treatment. In its current state, the in vivo EPR dosimeter can provide estimates of absorbed dose with an error approximately +/- 50 cGy over the range of interest for acute biological effects of radiation, assuming repeated measurements of the tooth in the mouth of the subject. The time required for acquisition, the lower limit, and the precision are expected to improve, with improvements in the resonator and the algorithm for acquiring and calculating the dose. The magnet system that is currently used, while potentially deployable, is somewhat large and heavy, requiring that it be mounted on a small truck or trailer. Several smaller magnets, including an intraoral magnet are under development, which would extend the ease of use of this technique.     

Visualization and Characterization of Atherosclerotic Plaques by Micro-MRI at 4.7 T In Vivo and 11.7 T Ex Vivo

The aim of this study was to evaluate the capability of using micro-magnetic resonance imaging (MRI) to visualize and characterize atherosclerotic plaques of mouse models. Twenty five apolipoprotein E-knockout mice were fed atherogenic diet, which enabled creation of aortic atherosclerotic plaques. Aortic plaques were examined in vivo by 4.7 T MRI and then characterized ex vivo by 11.7 T three-dimensional MRI. MR images were correlated with subsequent histological confirmation. In vivo 4.7-T MRI demonstrated unevenly thickened aortic walls due to formation of atherosclerotic plaques. Ex vivo 11.7-T MRI enabled not only to acquire full volume-rendered images of the entire vessels but also to characterize plaque components (such as lipid cores and fibrous caps) at any level and any projection, which were confirmed by histological correlation. Micro-MRI provides an excellent imaging tool for basic science to investigate atherosclerosis in small animal models, which may become a supplement to histopathology of atherosclerotic cardiovascular disease.     

In Vivo Magnetic Particle Targeting by Local Gradient Field of Interstitial Seeds Magnetized in an Ex Vivo Uniform Field

The possibility of in vivo magnetic particle targeting by the locally induced gradient field of interstitial ferro- magnetic implants, magnetized in an ex vivo uniform field, is evaluated by a modelling analysis. A simplified 3D model analogous to a torso size, with a continuous laminar flow through the volume with the typical velocity and viscosity values of in vivo blood flow and a ferromagnetic seed inserted in the volume center vertical to the flow, is used to evaluate the magnetic particle capturing efficiency by the seed, which is magnetized in a uniform field. The initial modelling results indicate that for 1-10μm iron oxide particles transporting with a blood flow of 0.5-5 mm/s, the seeds of tungsten steel, magnet steel and cast cobalt all present an effective particle capturing efficiency, which shows a fast initial increase and a slow saturation with the increasing magnetic field, a quasilinear increase with the increasing particle size, and a nonlinear decrease with the increasing blood velocity.     

共振拉曼光谱在体测量类胡萝卜素含量

类胡萝卜素是人体内重要的抗氧化剂,能够消除体内的自由基和其它有害氧分。研究表明类胡萝卜素含量与癌症、心血管疾病、老化等疾病发病率呈反比关系。目前检测方法为采用血清液相色谱检测方法,不能做到在体无损伤、实时测量。文章介绍了一种用于测量类胡萝卜素的新技术——共振拉曼光谱技术,具有在体无损伤、灵敏度高和实时检测等特点。该技术利用强度远小于美国ANSI Z136.1-2000标准的473 nm激光激发拇指中类胡萝卜素,产生强荧光和叠加在其上的弱共振拉曼光,通过测量拉曼散射光强度在体评估类胡萝卜素的含量。同时,利用组织通透技术,改善了测量信噪比。测量了不同饮食习惯志愿者的类胡萝卜素含量,说明其含量与其摄入量成正比。该技术在临床应用和科学研究等领域具有重要意义。     

Assessment of Nitrones as In Vivo Redox Sensors

Spin traps such as 5,5-dimethyl-1-pyrroline N-oxide, α-phenyl-tert-butyl nitrone, α-(4-pyridyl-1-oxide)-N-tert-butyl nitrone and newer generation 5-(diethoxyphosphoryl)-5-methyl-1-pyrroline N-oxide analogs have been known for years. What are the desired properties of good probes for measuring in vivo redox reactions in biological systems? These are specificity, sensitivity, rapid, high yield kinetics, low toxicity, high stability and easy to administer and target. Unfortunately, the nitrones perform poorly in almost all of these categories. Typical in vivo concentrations of spin trap approach 100 mM (assuming solubility and toxicity are not an issue), frequently yield 1% nitroxide or less stoichiometry, are typically unstable with time and frequently lack specificity. In vivo electron paramagnetic resonance (EPR) experiments need to have strong signals that correlate with redox chemistry. The resultant signal should be stable and not rapidly interconvert to other diamagnetic species. Fortunately, some newer probes of in vivo redox reactions in biological systems have come upon the horizon. In fact some have been around for a long time, but their virtues are becoming increasingly appreciated. This paper summarizes the disadvantages of nitrones versus the clear advantages of other probes of free radicals, redox state and the like by EPR. It also expands on the properties of nitroxides and nitrones as therapeutics.     

Resonators for In Vivo Imaging: Practical Experience

Resonators for preclinical electron paramagnetic resonance imaging have been designed primarily for rodents and rabbits and have internal diameters between 16 and 51 mm. Lumped-circuit resonators include loop-gap, Alderman–Grant, and saddle coil topologies and surface coils. Bimodal resonators are useful for isolating the detected signal from incident power and reducing dead time in pulse experiments. Resonators for continuous wave, rapid scan, and pulse experiments are described. Experience at the University of Chicago and University of Denver in design of resonators for in vivo imaging is summarized.     

MRI评价药物投递性能方法研究

采用MRI评价自制肝组织特异性非离子型高分子磁共振造影剂在小鼠体内药物投递效果. 分别在注射造影剂后0.1 h、6 h、12 h、24 h及7天采集磁共振T₁加权图像. 所有扫描均在1.5T临床磁共振成像仪上完成, 以固定体线圈为射频发射线圈, 三英寸圆形表面线圈为信号接收线圈. 数据分析前采用线圈非均匀性校正和信号非稳定性校正进行预处理. 实验结果显示,线圈空间敏感性校正使得小鼠组织图像信号强度空间更加均匀,稳定性校正后使得图像数据更加准确可靠,MRI是一种在体评价顺磁性标记高分子化合物药物投递效果的有效方法.     

二维核磁共振定域谱及其在活体中的应用

核磁共振定域谱(MRS)是获得活体生化定量信息和诊断信息的无损检测技术,是核磁共振成像强有力的补充技术,可为临床诊断和疾病预测提供重要的信息. 然而,活体1D ¹H MRS通常存在代谢物谱峰拥挤、分辨率较低和归属难等问题. 引入2D MRS可在较大程度上解决¹H MRS谱峰重叠和谱峰归属难的问题. 该文简述和分析了几种典型的2D MRS新方法及其优缺点,并讨论了它们在脑部、肌肉、乳腺、前列腺等活体组织中的应用. 虽然2D MRS存在着实验时间较长的局限,但最新研究表明其具有一些独特的优势及较好的发展前景.     

Two-Photon Excitation Fluorescence Microscopy of Rat Elastin Fiber In Vivo

Russian Physics Journal - The paper presents the results of two-photon excitation fluorescence microscopy of rat elastin fiber in vivo. It is shown that in approximating the fluorescence...     

Current Problems and Potential Techniques in In Vivo Glucose Monitoring

Accurate in vivo monitoring of glucose concentration would be a valuable asset, particularly for management of diabetes and preterm infants during critical care. In vivo glucose monitoring devices can be divided into two categories: implanted and non-invasive. Extensive research into in vivo glucose monitoring over recent decades has not resulted in the widespread use of clinically reliable monitoring systems. For implanted devices, poor biocompatibility of the materials used for fabrication remains a major challenge, whilst progress in the commercial development of non-invasive devices is hampered by the problem of multiple interference between the detected signals and the biological components. In this review, the methods available for in in-vivo glucose monitoring are described and the associated problems are discussed.     

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.     

In Vivo EPR Imaging of a Perfluoroalkyl Radical in Mouse Abdomen

Although it is thought that perfluoro-2,4-dimethyl-3-isopropyl-3-pentyl (PFR-2) is a candidate for electron paramagnetic resonance (EPR) imaging agents because of its high stability, no study has been made yet on the EPR imaging of PFR-2. In this study, EPR imaging of a phantom including PFR-2 and mice that had received PFR-2 was performed by an in vivo EPR imaging system operating at an EPR frequency of 700 MHz equipped with a bridged loop-gap resonator (inner diameter, 41 mm; axial length, 10 mm). Because PFR-2 is insoluble in water, it was dissolved in perfluorocarbon. The PFR-2 solution was put in cylindrical sample tubes with various inner diameters, and these sample tubes were placed together in a larger cylindrical sample tube filled with a physiological saline solution, which was used as a phantom. The spatial resolution was estimated to be about 3 mm on the basis of EPR imaging of the phantom. EPR images of mice that had received a PFR-2 injection via the intraperitoneal route indicated that PFR-2 remained in the peritoneal cavity even 2 days after the injection. This finding suggests that it is possible to perform EPR imaging of experimental animals using PFR-2 as an imaging agent which persists in a biological system. Authors' address: Hidekatsu Yokoyama, National Institute of Advanced Industrial Science and Technology, 2266-98 Anagahora, Shimoshidami, Moriyama-ku, Nagoya, Aichi 463-8560, Japan     

Comparison of In Vivo Optical Systems for Bioluminescence and Fluorescence Imaging

In vivo optical imaging has become a popular tool in animal laboratories. Currently, many in vivo optical imaging systems are available on the market, which often makes it difficult for research groups to decide which system fits their needs best. In this work we compared different commercially available systems, which can measure both bioluminescent and fluorescent light. The systems were tested for their bioluminescent and fluorescent sensitivity both in vitro and in vivo. The IVIS Lumina II was found to be most sensitive for bioluminescence imaging, with the Photon Imager a close second. Contrary, the Kodak system was, in vitro, the most sensitive system for fluorescence imaging. In vivo, the fluorescence sensitivity of the systems was similar. Finally, we examined the added value of spectral unmixing algorithms for in vivo optical imaging and demonstrated that spectral unmixing resulted in at least a doubling of the in vivo sensitivity. Additionally, spectral unmixing also enabled separate imaging of dyes with overlapping spectra which were, without spectral unmixing, not distinguishable.     

Nitronyl Nitroxides as a Spin Probe in EPR Tomography In Vivo

Recently, new water- and blood-soluble nitronyl nitroxides, 2-(5-methyl-1H-imidazole-4-yl)-4,4,5,5-tetramethyl-4,5-dihydroimidazole-3-oxide-1-oxyl (NN1) and 2-(1H-imidazole-4-yl)-4,4,5,5-tetramethyl-4,5-dihydroimidazole-3-oxide-1-oxyl (NN2), (Fig. 1), were synthesized and used as contrast agents for MRI (Savelov et al. Dokl Academ Nauk 416(4): 493–495, 2007). Taking into account the high rate constants of NN’s reduction by ascorbic acid and other biologically relevant reductants, it is not clear which factors helped with the use of these nitroxides in vivo as a contrast reagent. Moreover, due to high solubility in an aqueous solution and low toxicity (Ovcharenko et al. in Dokl Academ Nauk 404(2):198–200, 2005, Eriksson et al. in Drug Metab Dispos 15(2):155–160, 1987, Afzal et al. in Polyhedron 22(14):1957–1964, 2003) of NNs, it seems possible to use them as a spin probe for NO in vivo with EPR tomography. In this paper, we studied reduction of NN1 and NN2 in model conditions (by ascorbic acid) and in vitro. In addition, the possibility of NN1 and NN2 to be used as paramagnetic probes for L-band EPR imaging in vivo was investigated. Nitric oxide (NO) expression in vivo leads to the decrease in concentrations of NN1, 2 upon the injection in a mouse body, that can be explained by the reaction of studied radicals with NO and fast transformation of the reaction products to diamagnetic species. Pharmacokinetics of NN1, 2 and limitations of their application as contrast agents in MRI are discussed also. Finally, the results of EPR tomography were compared with MRI data. It is shown that the fast reduction of the reaction product of NN with NO—imino nitroxides—is the main obstacle to use NN as a spin probe in vivo.

In Vivo Monitoring of Neovascularization in Tumour Angiogenesis by Photoacoustic Tomography

Photoacoustic tomography （PAT） is presented to in vivo monitor neovascularization in tumour angiogenesis with high resolution and high contrast images in a rat. With a circular scan system, the photoacoustic signal, generated by laser pulses at a wavelength of 532nm from a Q-switched Nd：YAG laser is captured by a hydrophone with a diameter of 1 mm and a sensitivity of 850nV/Pa. The vascular structure around the rat tumour is imaged clearly, with optimal contrast, because blood has strong absorption near this wavelength. Serial noninvasive photoacoustic images of neovascularization in tumour angiogenesis are also obtained consecutively from a growing tumour implanted under the skin of a rat over a period of two weeks. This work demonstrates that PAT can potentially provide a powerful tool for tumour angiogenesis detection in cancer research. It will bring us closer to clinical applications for tumour diagnosis and treatment monitoring.