Estimation of the in vivo decay rate of EPR signals for a nitroxide radical in rat brains by a region-selected intensity determination method

The region-selected intensity determination (RSID) method was proposed to obtain the temporal changes in electron paramagnetic resonance (EPR) signal intensity from a selected region by a stationary magnetic field gradient. To select the region, the subtraction field that was derived from the distance between the center and the projection of the selected region to the direction of the field gradient was applied to the main field. The directions of the stationary magnetic field gradient at a constant strength were systematically changed in a three-dimensional space after each acquisition of the spectrum. All spectra under the field gradient were accumulated and the resultant spectrum was deconvoluted by a spectrum without the field gradient. The center height of the deconvoluted spectrum indicates the signal intensity of the selected region. To verify this method, a phantom or in vivo study was conducted on a 700 MHz radio-frequency EPR spectrometer equipped with a bridged loop-gap resonator. In the temporal EPR measurements of phantoms including a nitroxide radical aqueous solution with and without ascorbic acid, the selected regions were alternatively changed at the position of the two phantoms. The signal intensity derived from the one phantom showed an exponential decay, and for the other phantom, no temporal changes. The spatial resolution of this method was estimated to be 2.7 mm by using a pinpoint phantom that included diphenylpicrylhydrazyl powder. In the in vivo temporal EPR measurements, the selected regions were alternatively changed at the cerebral cortex and the striatum of rats that had received a blood-brain barrier-permeative nitroxide radical. The decay rate of the signal intensity at each region obtained by this method was consistent with those previously reported.     

In vivo EPR imaging by using an acyl-protected hydroxylamine to analyze intracerebral oxidative stress in rats after epileptic seizures

EPR imaging by using an acyl-protected hydroxylamine, 1-acetoxy-3-carbamoyl-2,2,5,5-tetramethylpyrrolidine (ACP), in the head of a living rat after kainic acid (KA)-induced epileptic seizures was performed. ACP is a stable non-radical compound, but is easily deprotected with intracellular esterase to yield a hydroxylamine, which is oxidized by intracellular oxidative stress to yield an EPR-detectable nitroxide radical. From in vivo image data, the average values of EPR signal intensity from the hippocampus, striatum, and cerebral cortex were computed. There was no significant difference in cortical signal intensity between the control and KA-treated rats. The signal intensities from the hippocampus and striatum for the KA-treated rats were significantly higher than those for the control. The in vitro study showed that almost the same quantity of ACP moved into all regions of the brain of the control and KA-treated rats. These findings indicate that following a KA-induced seizure, the oxidative stress in the hippocampus and striatum is enhanced, but not so in the cerebral cortex.     

In vivo temporal EPR imaging of the brain of rats by using two types of blood-brain barrier-permeable nitroxide radicals

In vivo temporal EPR imaging was conducted on the brain of rats that received one of two kinds of blood-brain barrier-permeable nitroxide radicals via the tail vein-one is a water-soluble 3-hydroxymethyl-2,2,5,5-tetramethylpyrrolidine-1-oxyl (hydroxymethyl-PROXYL); and the other is a non-water-soluble 3-methoxycarbonyl-2,2,5,5-tetramethylpyrrolidine-1-oxyl (PCAM). From temporal EPR imaging data, temporal changes in the distribution of the nitroxide radical in the cerebral cortex, striatum, and hippocampus in the brain were investigated. It was found that the half-lives of the three parts in the brain of hydroxymethyl-PROXYL are longer and their EPR signal intensities are greater than those of PCAM.     

In Vivo Temporal EPR Measurements in the Lung of Mice by a Selected-Region Intensity Determination Method

Selected-region intensity determination (SRID) is a method for obtaining the temporal changes in electron paramagnetic resonance (EPR) signal intensity from a selected region without complicated procedures used in the previous imaging method. We used an in vivo 700 MHz radiofrequency EPR spectrometer equipped with a bridged loop-gap resonator and the SRID method to perform temporal EPR measurements of the lung area of mice which had received a nitroxide radical (3-carbamoyl-2,2,5,5-tetramethylpyrrolidine-1-oxyl) administration via the intravenous route. The half-life and initial level of nitroxide radical in the lung or the mediastinum were calculated from temporal changes in the signal intensity. A mathematical model was devised to determine the nitroxide radical concentration in the lung, which is connected to other organs via the circulatory system. Using this model and the results of the EPR measurements, the degrees of influence of the nitroxide reduction in the lung and other organs were simulated. It was found that the reaction rate (=log2/half-life) obtained from the lung mainly reflected the reduction of nitroxide radical there. Authors' address: Hidekatsu Yokoyama, National Institute of Advanced Industrial Science and Technology, 2266-98 Anagahora, Shimoshidami, Moriyama-ku, 463-8560 Nagoya, Japan     

Reaction kinetics analysis to estimate in vivo decay rate of EPR signals of a nitroxide radical in the brain and the inferior vena cava of rats

To clarify the degree of the influence of the peripheral organs on the temporal changes in the electron paramagnetic resonance (EPR) signal intensity of a nitroxide radical permeating the blood-brain barrier, 3-hydroxymethyl-2,2,5,5-tetramethylprrolidine-1-oxyl (hydroxymethyl-PROXYL), in the brain, temporal changes in the EPR signal in the brain or inferior vena cava of rats were measured by an in vivo 700 MHz radio-frequency EPR spectrometer equipped with a bridged loop-gap resonator or a surface-coil-type resonator. In all measurements, good linearity was observed on semilogarithmic plots of the signal intensity against time after the hydroxymethyl-PROXYL injection. From these plots, the reaction rate and the initial level of hydroxymethyl-PROXYL in the brain and the vena cava were calculated. A mathematical model expressing the nitroxide radical concentration in the brain, which is connected to other organs via the circulatory system, was made. With this model and the results of the EPR measurements, the degrees of influence of the nitroxide reduction in the brain and the other organs were simulated. It was found that the reaction rate (equal to log2/half-life) of hydroxymethyl-PROXYL observed in the brain reflected the reduction of hydroxymethyl-PROXYL there and was not influenced by the reduction in other organs.     

EPR imaging to estimate the in vivo intracerebral reducing ability of mature rats after neonatal hypoxic-ischemic brain injury

A rat model of neonatal hypoxic-ischemic encephalopathy (Rice's model) was obtained by unilateral ligation of the common carotid artery of 7-day-old rats with hypoxia (exposure to 8% oxygen). To estimate the in vivo intracerebral reducing ability of the mature rats (8 weeks old) of Rice's model, temporal electron paramagnetic resonance (EPR) imaging of the brain of a rat receiving a blood-brain barrier-permeable nitroxide radical, 3-hydroxymethyl-2,2,5,5-tetramethylpyrrolidine-1-oxyl, was performed. In this imaging technique, the decay rate of the EPR signal intensity in a selected region of the brain is indicative of region-specific reducing ability. The effect of neonatal treatment of an antioxidant agent, 3-methyl-1-phenyl-2-pyrazolin-5-one (MCI-186), after a hypoxic-ischemic insult was also tested. It was found that the reducing ability had been depleted in the contralateral hemisphere of Rice's model rats; this depletion was suppressed by administering MCI-186.     

Assessment of liver phagocytic activity using EPR spectrometry and imaging

The aim of the present study was to evaluate the usefulness of electron paramagnetic resonance (EPR) spectroscopy and imaging in assessing the phagocytic activity of the liver after administration of India ink. We conducted experiments on livers from control rodents and from rodents in which the Kupffer cell population had been depleted by pretreatment with gadolinium chloride. The EPR signal intensity recorded in liver homogenates was about two times lower in GdCl(3) treated rats than in control rats. EPR imaging carried out on precision-cut liver slices indicated a good correlation between the depletion of Kupffer cells and the EPR signal intensity.     

Real-time monitoring of ischemic and contralateral brain pO2 during stroke by variable length multisite resonators

Purpose

Electron paramagnetic resonance (EPR) oximetry using variable length multi-probe implantable resonator (IR), was used to investigate the temporal changes in the ischemic and contralateral brain pO₂ during stroke in rats.

Material and methods

The EPR signal to noise ratio (S/N) of the IR with four sensor loops at a depth of up to 11 mm were compared with direct implantation of lithium phthalocyanine (LiPc, oximetry probe) deposits in vitro. These IRs were used to follow the temporal changes in pO₂ at two sites in each hemisphere during ischemia induced by left middle cerebral artery occlusion (MCAO) in rats breathing 30% O₂ or 100% O₂.

Results

The S/N ratios of the IRs were significantly greater than the LiPc deposits. A similar pO₂ at two sites in each hemisphere prior to the onset of ischemia was observed in rats breathing 30% O₂. However, a significant decline in the pO₂ of the left cortex and striatum occurred during ischemia, but no change in the pO₂ of the contralateral brain was observed. A significant increase in the pO₂ of only the contralateral non-ischemic brain was observed in the rats breathing 100% O₂. No significant difference in the infarct volume was evident between the animals breathing 30% O₂ or 100% O₂ during ischemia.

Conclusions

EPR oximetry with IRs can repeatedly assess temporal changes in the brain pO₂ at four sites simultaneously during stroke. This oximetry approach can be used to test and develop interventions to rescue ischemic tissue by modulating cerebral pO₂ during stroke.     

Separation and Enrichment of the Active Component of Carbon Based Paramagnetic Materials for Use in EPR Oximetry

Carbon based paramagnetic materials are frequently used for EPR oximetry, especiallyin vivo,but the EPR spectra of these materials often have more than one paramagnetic center and/or relatively low signal intensity. To determine whether the multi-components of carbon based materials could be separated and enriched in the active component, we used density gradient centrifugation to separate the materials into several fractions. We studied two types of coals, gloxy and Pocahontas, and found these materials to have large density distribution. The separated density fractions had very different EPR spectra and intensities. The active component from the coal material had a more homogeneous EPR signal and significantly increased EPR signal intensity, whereas for India ink, only slight changes were observed. This result can be very useful in the development of better probes for EPR oximetry.     

Signal displacement in spiral-in acquisitions: simulations and implications for imaging in SFG regions

Susceptibility field gradients (SFGs) cause problems for functional magnetic resonance imaging (fMRI) in regions like the orbital frontal lobes, leading to signal loss and image artifacts (signal displacement and "pile-up"). Pulse sequences with spiral-in k-space trajectories are often used when acquiring fMRI in SFG regions such as inferior/medial temporal cortex because it is believed that they have improved signal recovery and decreased signal displacement properties. Previously postulated theories explain differing reasons why spiral-in appears to perform better than spiral-out; however it is clear that multiple mechanisms are occurring in parallel. This study explores differences in spiral-in and spiral-out images using human and phantom empirical data, as well as simulations consistent with the phantom model. Using image simulations, the displacement of signal was characterized using point spread functions (PSFs) and target maps, the latter of which are conceptually inverse PSFs describing which spatial locations contribute signal to a particular voxel. The magnitude of both PSFs and target maps was found to be identical for spiral-out and spiral-in acquisitions, with signal in target maps being displaced from distant regions in both cases. However, differences in the phase of the signal displacement patterns that consequently lead to changes in the intervoxel phase coherence were found to be a significant mechanism explaining differences between the spiral sequences. The results demonstrate that spiral-in trajectories do preserve more total signal in SFG regions than spiral-out; however, spiral-in does not in fact exhibit decreased signal displacement. Given that this signal can be displaced by significant distances, its recovery may not be preferable for all fMRI applications.     

Impact of High-Dielectric-Loss Materials on the Microwave Field in EPR Experiments

A dielectric material distorts the microwave field inside an EPR resonator, which results in distortion of the EPR signal from spins inside the material. In this paper, the effects of a spherical bulb filled with a dielectric liquid such as water or a water–ethanol mixture were examined. EPR spectra were recorded for small samples inside and outside of the sphere. The studies include CW and ESE experiments at two microwave frequencies, X band (9.2 GHz) and L band (1.03 GHz). The double integral (area) of an EPR signal depends on[formula]at the position of the sample, causing a large difference in EPR signal intensities between samples in regions of different dielectrics. The phase of the EPR signal also is affected by the presence of the dielectric. These results were compared with three methods of calculating electromagnetic fields (quasi-static method, plane-wave-superposition method, and numerical analysis). Good agreement was found between experimental and calculated results.     

Percept-related activity in the human somatosensory system: functional magnetic resonance imaging studies

In this paper, we review blood oxygenation level-dependent (BOLD) functional magnetic resonance imaging (fMRI) studies addressing the neural correlates of touch, thermosensation, pain and the mechanisms of their cognitive modulation in healthy human subjects. There is evidence that fMRI signal changes can be elicited in the parietal cortex by stimulation of single mechanoceptive afferent fibers at suprathreshold intensities for conscious perception. Positive linear relationships between the amplitude or the spatial extents of BOLD fMRI signal changes, stimulus intensity and the perceived touch or pain intensity have been described in different brain areas. Some recent fMRI studies addressed the role of cortical areas in somatosensory perception by comparing the time course of cortical activity evoked by different kinds of stimuli with the temporal features of touch, heat or pain perception. Moreover, parametric single-trial functional MRI designs have been adopted in order to disentangle subprocesses within the nociceptive system.

Available evidence suggest that studies that combine fMRI with psychophysical methods may provide a valuable approach for understanding complex perceptual mechanisms and top-down modulation of the somatosensory system by cognitive factors specifically related to selective attention and to anticipation. The brain networks underlying somatosensory perception are complex and highly distributed. A deeper understanding of perceptual-related brain mechanisms therefore requires new approaches suited to investigate the spatial and temporal dynamics of activation in different brain regions and their functional interaction.     

Changes in MRI signal intensity during hypercapnic challenge under conscious and anesthetized conditions

Most functional magnetic resonance imaging (fMRI) studies in animals are conducted under anesthesia to minimize motion artifacts. However, methods and techniques have been developed recently for imaging fully conscious rats. Functional MRI studies on conscious animals report enhanced BOLD signal changes as compared to the anesthetized condition. In this study, rats were exposed to different concentrations of carbon dioxide (CO(2)) while conscious and anesthetized to test whether cerebrovascular reactivity may be contributing to these enhanced BOLD signal changes. Hypercapnia produced significantly greater increases in MRI signal intensity in fully conscious animals (6.7-13.3% changes) as when anesthetized with 1% isoflurane (3.2-4.9% changes). In addition, the response to hypercapnia was more immediate in the conscious condition (< 30s) with signal risetimes twice as fast as in the anesthetized state (60s). Both cortical and subcortical brain regions showed a robust, dose- dependent increase in MRI signal intensity with hypercapnic challenge while the animals were conscious but little or no change when anesthetized. Baseline variations in MRI signal were higher while animals were conscious but this was off set by greater signal intensity changes leading to a greater contrast-to-noise ratio, 13.1 in conscious animals, as compared to 8.0 in the anesthetized condition. In summary, cerebral vasculature appears to be more sensitive to hypercapnic challenge in the conscious condition resulting in enhanced T2* MRI signal intensity and the potential for better BOLD signal changes during functional imaging.     

TiO2及其掺Fe材料的制备和EPR谱的研究

以钛酸四丁酯、无水乙醇、冰醋酸为原料,在室温下用溶胶-凝胶法制备得到二氧化钛及其掺Fe样品的湿凝胶,室温放置2天后,100 ℃干燥得到干凝胶,在500 ℃下焙烧得到二氧化钛及其掺Fe的粉末状样品. 利用X射线衍射、电子顺磁共振等测试手段对样品进行分析,结果显示所得样品均为锐钛矿,Fe被引入了二氧化钛晶格中,Ti³⁺氧化中心信号强度随Fe掺杂量的增加而增强,峰值向磁场减小方向小幅偏移. 在不同测试温度下, 含Fe量为0.1%的Fe-TiO₂样品中Ti³⁺氧化中心信号强度随温度升高而增强,峰值也向磁场减小方向小幅偏移. 根据电子顺磁共振理论以及二氧化钛在空气中与O₂的反应解释了这些现象.     

Importance of volume limitation for tissue redox status measurements using nitroxyl contrast agents: a comparison of X-band EPR bile flow monitoring (BFM) method and 300 MHz in vivo EPR measurement

Methods proposed for in vivo redox status estimation, X-band (9.4 GHz) electron paramagnetic resonance (EPR) bile flow monitoring (BFM) and 300 MHz in vivo EPR measurement, were compared. The spin probe 3-carbamoyl-2,2,5,5-tetramethylpyrrolidine-1-oxyl (carbamoyl-PROXYL) was utilized for both methods, due to its suitable lipophilicity. EPR signal decay of a nitroxyl spin probe in the bile flow and in the liver region (upper abdomen) of several rat groups with different selenium status were measured by both the BFM and the in vivo EPR method, respectively. The nitroxyl radical clearance measured with in vivo EPR method may be affected not only by the redox status in the liver but also by information from other tissues in the measured region of the rat. On the other hand, the time course of nitroxyl radical level in the bile flow of rats was found to be a reliable index of redox status. Measurement site and/or volume limitation, which was achieved by the BFM method in this paper, is quite important in estimating reasonable EPR signal decay information as an index of tissue/organ redox status.     

Mapping of the cerebral response to hypoxia measured using graded asymmetric spin echo EPI

Graded asymmetric spin echo-echo planar imaging (ASE-EPI) was used to measure transient alterations in cerebral oxygenation resulting from 60 seconds of anoxia in alpha-chloralose anaesthetised rats. The anoxic period induced a transient fall ( approximately 1 min) in signal intensity followed by a prolonged signal overshoot consistent with an autoregulatory response to oxygen deprivation. The magnitude of signal response, integrated over the entire brain, increased linearly with the echo asymmetry (t(ge)). However, that increase in sensitivity was offset by a reduced signal to noise ratio and quality of the image data. The responses of four regions of interest within the brain to the anoxic stimulus, and the effect of increasing the echo asymmetry, were compared. A comparable magnitude of signal decrease was observed in all brain regions except the superficial cortex that included pial vessels. As t(ge) was incremented differences in signal attenuation between regions became more pronounced. The signal overshoot observed upon restoration of normal breathing gases showed similar trends, producing similar normalised vascular responses for all regions of interest studied. Different regions of interest showed comparable time courses of the signal overshoot suggesting that similar autoregulatory vascular mechanisms operate in all brain regions. These findings additionally show that the use of graded ASE-EPI produced a characteristic profile of maximum signal change measured during and following the anoxic period for each brain region. They suggest that the shape of this profile was determined by the local vasculature within each region of interest; this feature could be exploited in activation studies to eliminate regions with significant signal changes originating from large draining vessels. Finally, the consistent physiological response observed, when the overshoot was compared to the magnitude of the signal drop, demonstrated that modification of the spin echo offset parameter did not mask or detrimentally alter the signal change resulting from the underlying physiological perturbation.     

EPR investigation of Mn(II), Fe(III) and free radical centers in green parts of living plants. Effects of environmental pollution

The needles of spruce and other conifers were investigated by using EPR spectroscopy. Contrary to previous studies, examples of weakened and diseased spruces exhibiting strong manganese(II) signals were found. This situation was found for trees damaged by acid rains in south-west Poland. For weakened spruces and pines from other regions the manganese(II) signal of decreased intensity and free radical signals were observed. Such trees also exhibited iron(III) signal, which appears to, be another indicator of reduced vitality. The influence of harmful agents on living plant parts was investigated on the basis of free radical EPR spectra.     

Correlations and dissociations between BOLD signal and P300 amplitude in an auditory oddball task: a parametric approach to combining fMRI and ERP

A parametric method is proposed to examine the relationship between neuronal activity, measured with event related potentials (ERPs), and the hemodynamic response, observed with functional magnetic resonance imaging (fMRI), during an auditory oddball paradigm. After verifying that the amplitude of the evoked response P300 increases as the probability of oddball target presentation decreases, we explored the corresponding effect of target frequency on the fMRI signal. We predicted and confirmed that some regions that showed activation changes following each oddball are affected by the rate of presentation of the oddballs, or the probability of an oddball target. We postulated that those regions that increased activation with decreasing probability might be responsible for the corresponding changes in the P300 amplitude. fMRI regions that correlated with the amplitude of the P300 wave were supramarginal gyri, thalamus, insula and right medial frontal gyrus, and are presumably sources of the P300 wave. Other regions, such as anterior and posterior cingulate cortex, were activated during the oddball paradigm but their fMRI signal changes were not correlated with the P300 amplitudes. This study thus shows how combining fMRI and ERP in a parametric design identifies task-relevant sources of activity and allows separation of regions that have different response properties.     

EPR study of porous silicon

An anisotropic EPR signal was observed in porous Si. According to its symmetry andg value, the EPR signal can be attributed to silicon dangling bonds located on the surface of a porous Si skeleton. The evolution of the EPR signal at room temperature in air was measured. The annealing temperature dependence of the EPR and the PL of porous Si in oxygen and the effects of gamma irradiation on the EPR and the PL spectra of porous Si were studied. The changes of the EPR signal and the PL intensity induced in atmosphere by ethyl alcohol and acetone were discovered. The dangling bond is only one of the factors which affect the PL.This project is supported by the National Natural Science Foundation of China.     

Background suppression for cloud clutter using temporal difference projection

To remove high intensity cloud clutter in infrared image sequence containing point target with high velocity, based on the optimal log-likelihood ratio detector test (LLRDT) together with exploratory temporal data analysis, a method called standardized maximum projection of temporal difference on adjacent frames (SMPTDAF) is proposed. First, cloud scenario is classified and analysis according to temporal features. Second, mathematical difference models of adjacent frames for all regions are presented. Third, to obtain the optimal temporal performance under LLRDT operator, based on the models, projection method after differencing and its simplified method for practical application are established. Finally in the paper, we compared the proposed method against classical temporal suppression method named Moving Target Indicator (MTI) and wavelet method by test image sequence. Experimental results show that the average SCR gain exceeds 11 when the target SCR is from 1.0 and 3, which is better than results of some representative multi-frame filters mentioned above.