The Experts below are selected from a list of 56760 Experts worldwide ranked by ideXlab platform
Howard J Halpern - One of the best experts on this subject based on the ideXlab platform.
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biological validation of Electron Paramagnetic Resonance epr image oxygen thresholds in tissue
The Journal of Physiology, 2021Co-Authors: Inna Gertsenshteyn, Mihai Giurcanu, Peter Vaupel, Howard J HalpernAbstract:Measuring molecular oxygen levels in vivo has been the cornerstone of understanding the effects of hypoxia in normal tissues and malignant tumors. Here we discuss the advances in a variety of partial pressure of oxygen ( P O 2 ) measurements and imaging techniques and relevant oxygen thresholds. A focus on Electron Paramagnetic Resonance (EPR) imaging shows the validation of treating hypoxic tumours with a threshold of P O 2 ≤ 10 Torr, and demonstrates utility for in vivo oxygen imaging, as well as its current and future role in cancer studies.
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optimization based image reconstruction from sparsely sampled data in Electron Paramagnetic Resonance imaging
Journal of Magnetic Resonance, 2018Co-Authors: Zhiwei Qiao, Zheng Zhang, Xiaochuan Pan, Boris Epel, Gage Redler, Dan Xia, Howard J HalpernAbstract:Electron Paramagnetic Resonance imaging (EPRI) can yield information about the 3-dimensional (3D) spatial distribution of the unpaired-Electron-spin density from which the spatial distribution of oxygen concentration within tumor tissue, referred to as the oxygen image or Electron Paramagnetic Resonance (EPR) image in this work, can be derived. Existing algorithms for reconstruction of EPR images often require data collected at a large number of densely sampled projection views, resulting in a prolonged data-acquisition time and consequently numerous practical challenges especially to in vivo animal EPRI. Therefore, a strong interest exists in shortening data-acquisition time through reducing the number of data samples collected in EPRI, and one approach is to acquire data at a reduced number of sparsely distributed projection views from which existing algorithms may reconstruct images with prominent artifacts. In this work, we investigate and develop an optimization-based technique for image reconstruction from data collected at sparsely sampled projection views for reducing scanning time in EPRI. Specifically, we design a convex optimization program in which the EPR image of interest is formulated as a solution and then tailor the Chambolle-Pock (CP) primal-dual algorithm to reconstruct the image by solving the convex optimization program. Using computer-simulated EPRI data from numerical phantoms and real EPRI data collected from physical phantoms, we perform studies on the verification and characterization of the optimization-based technique for EPR image reconstruction. Results of the studies suggest that the technique may yield accurate EPR images from data collected at sparsely distributed projection views, thus potentially enabling fast EPRI with reduced acquisition time.
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comparison of pulse sequences for r1 based Electron Paramagnetic Resonance oxygen imaging
Journal of Magnetic Resonance, 2015Co-Authors: Boris Epel, Howard J HalpernAbstract:Electron Paramagnetic Resonance (EPR) spin-lattice relaxation (SLR) oxygen imaging has proven to be an indispensable tool for assessing oxygen partial pressure in live animals. EPR oxygen images show remarkable oxygen accuracy when combined with high precision and spatial resolution. Developing more effective means for obtaining SLR rates is of great practical, biological and medical importance. In this work we compared different pulse EPR imaging protocols and pulse sequences to establish advantages and areas of applicability for each method. Tests were performed using phantoms containing spin probes with oxygen concentrations relevant to in vivo oxymetry. We have found that for small animal size objects the inversion recovery sequence combined with the filtered backprojection reconstruction method delivers the best accuracy and precision. For large animals, in which large radio frequency energy deposition might be critical, free induction decay and three pulse stimulated echo sequences might find better practical usage.
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in vivo po2 imaging of tumors oxymetry with very low frequency Electron Paramagnetic Resonance
Methods in Enzymology, 2015Co-Authors: Boris Epel, Howard J HalpernAbstract:For over a century, it has been known that tumor hypoxia, regions of a tumor with low levels of oxygenation, are important contributors to tumor resistance to radiation therapy and failure of radiation treatment of cancer. Recently, using novel pulse Electron Paramagnetic Resonance (EPR) oxygen imaging, near absolute images of the partial pressure of oxygen (pO2) in tumors of living animals have been obtained. We discuss here the means by which EPR signals can be obtained in living tissues and tumors. We review development of EPR methods to image the pO2 in tumors and the potential for the pO2 image acquisition in human subjects.
Angelika Bruckner - One of the best experts on this subject based on the ideXlab platform.
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in situ Electron Paramagnetic Resonance spectroscopy for catalysis
Nature Reviews Methods Primers, 2021Co-Authors: Shannon A Bonke, Alexander Schnegg, Thomas Risse, Angelika BrucknerAbstract:In situ catalysis studies seek insight into species present under reaction conditions to elucidate reaction mechanisms and understand the atomistic details of the active catalyst, both of which are key to optimizing catalyst reactivity and processes. Many reactions follow radical mechanisms, and many catalysts adopt Paramagnetic states within their catalytic cycles where the systems exhibit species with unpaired Electrons, which provide a sensitive handle to probe their geometric and Electronic structure. Electron Paramagnetic Resonance (EPR) spectroscopy directly probes these unpaired Electrons to characterize molecular radicals as well as determine transition metal ion oxidation states and coordination geometries. Here, we introduce the concept of EPR followed by the methodology for in situ EPR studies and discuss high-temperature gas–solid reactions, molecular catalysis, photocatalysis and electrocatalysis. The broad applicability of the approaches is demonstrated through case studies in each area, with a focus on unravelling catalytic mechanisms. We also discuss data sharing and reproducibility issues as well as limitations to the technique. Finally, we identify directions for development to guide interested researchers towards evolving areas including miniaturization and high-frequency analysis. This Primer on in situ Electron Paramagnetic Resonance spectroscopy describes various experimental set-ups to acquire spectral information on the Paramagnetic state of chemical species with unpaired Electrons present during catalytic reactions, with the goal of unravelling catalytic mechanisms and optimizing catalyst activity.
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in situ Electron Paramagnetic Resonance a unique tool for analyzing structure reactivity relationships in heterogeneous catalysis
Chemical Society Reviews, 2010Co-Authors: Angelika BrucknerAbstract:Electron Paramagnetic Resonance (EPR) offers widespread opportunities for monitoring catalytically relevant species that contain unpaired Electrons under conditions close to those of heterogeneous catalytic gas and liquid phase reactions. In this tutorial review, after introducing basic theoretical and experimental principles of the technique, selected examples of typical applications are discussed that comprise (1) transition metal ions in Paramagnetic valence states such as vanadium, (2) radical anions such as O˙− formed on oxide surfaces and (3) Electrons in ferromagnetic particles such as nickel as well as in conduction bands of organic conductors such as polyaniline.
Garnet Kinlic Chan - One of the best experts on this subject based on the ideXlab platform.
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Electron Paramagnetic Resonance g tensors from state interaction spin orbit coupling density matrix renormalization group
Journal of Chemical Physics, 2018Co-Authors: Elvira R Sayfutyarova, Garnet Kinlic ChanAbstract:We present a state interaction spin-orbit coupling method to calculate Electron Paramagnetic Resonance g-tensors from density matrix renormalization group wavefunctions. We apply the technique to compute g-tensors for the TiF3 and CuCl42- complexes, a [2Fe-2S] model of the active center of ferredoxins, and a Mn4CaO5 model of the S2 state of the oxygen evolving complex. These calculations raise the prospects of determining g-tensors in multireference calculations with a large number of open shells.
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Electron Paramagnetic Resonance g tensors from state interaction spin orbit coupling density matrix renormalization group
arXiv: Chemical Physics, 2017Co-Authors: Elvira R Sayfutyarova, Garnet Kinlic ChanAbstract:We present a state interaction spin-orbit coupling method to calculate Electron Paramagnetic Resonance (EPR) $g$-tensors from density matrix renormalization group wavefunctions. We apply the technique to compute $g$-tensors for the \ce{TiF3} and \ce{CuCl4^2-} complexes, a [2Fe-2S] model of the active center of ferredoxins, and a \ce{Mn4CaO5} model of the S2 state of the oxygen evolving complex. These calculations raise the prospects of determining $g$-tensors in multireference calculations with a large number of open shells.
S.d. Williams - One of the best experts on this subject based on the ideXlab platform.
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Electron Paramagnetic Resonance studies of silicon related defects in diamond
Physical Review B, 2008Co-Authors: Andrew M. Edmonds, P. M. Martineau, M E Newton, Daniel James Twitchen, S.d. WilliamsAbstract:We report the results of multifrequency Electron Paramagnetic Resonance studies at temperatures between 8 and 300 K on diamonds synthesized by chemical vapor deposition and intentionally silicon doped with isotopes in natural abundance or isotopically enriched. The $^{29}\text{S}\text{i}$ hyperfine structure has provided definitive evidence for the involvement of silicon in two Electron Paramagnetic Resonance centers in diamond that were previously suspected to involve silicon: KUL1 and KUL3. We present data that unambiguously identify KUL1 as an $S=1$ neutral silicon split-vacancy (${D}_{3d}$ symmetry) defect ${(V\text{-Si-}V)}^{0}$, while KUL3 is shown to be ${(V\text{-Si-}V)}^{0}$ decorated with a hydrogen atom, ${(V\text{-Si-}V:\text{H})}^{0}$.
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Electron Paramagnetic Resonance studies of silicon-related defects in diamond
Physical Review B - Condensed Matter and Materials Physics, 2008Co-Authors: Andrew M. Edmonds, P. M. Martineau, M E Newton, Daniel James Twitchen, S.d. WilliamsAbstract:We report the results of multifrequency Electron Paramagnetic Resonance studies at temperatures between 8 and 300 K on diamonds synthesized by chemical vapor deposition and intentionally silicon doped with isotopes in natural abundance or isotopically enriched. The Si-29 hyperfine structure has provided definitive evidence for the involvement of silicon in two Electron Paramagnetic Resonance centers in diamond that were previously suspected to involve silicon: KUL1 and KUL3. We present data that unambiguously identify KUL1 as an S=1 neutral silicon split-vacancy (D-3d symmetry) defect (V-Si-V)(0), while KUL3 is shown to be (V-Si-V)(0) decorated with a hydrogen atom, (V-Si-V:H)(0).
Daniel James Twitchen - One of the best experts on this subject based on the ideXlab platform.
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Electron Paramagnetic Resonance studies of silicon related defects in diamond
Physical Review B, 2008Co-Authors: Andrew M. Edmonds, P. M. Martineau, M E Newton, Daniel James Twitchen, S.d. WilliamsAbstract:We report the results of multifrequency Electron Paramagnetic Resonance studies at temperatures between 8 and 300 K on diamonds synthesized by chemical vapor deposition and intentionally silicon doped with isotopes in natural abundance or isotopically enriched. The $^{29}\text{S}\text{i}$ hyperfine structure has provided definitive evidence for the involvement of silicon in two Electron Paramagnetic Resonance centers in diamond that were previously suspected to involve silicon: KUL1 and KUL3. We present data that unambiguously identify KUL1 as an $S=1$ neutral silicon split-vacancy (${D}_{3d}$ symmetry) defect ${(V\text{-Si-}V)}^{0}$, while KUL3 is shown to be ${(V\text{-Si-}V)}^{0}$ decorated with a hydrogen atom, ${(V\text{-Si-}V:\text{H})}^{0}$.
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Electron Paramagnetic Resonance studies of the neutral nitrogen vacancy in diamond
Physical Review B, 2008Co-Authors: Solveig Felton, P. M. Martineau, M E Newton, Andrew M. Edmonds, D Fisher, Daniel James TwitchenAbstract:Despite the numerous experimental and theoretical studies on the negatively charged nitrogen vacancy center $({\mathrm{NV}}^{\ensuremath{-}})$ in diamond and the predictions that the neutral nitrogen vacancy center $({\mathrm{NV}}^{0})$ should have an $S=\frac{1}{2}$ ground state, ${\mathrm{NV}}^{0}$ has not previously been detected by Electron Paramagnetic Resonance (EPR). We report new EPR data on a trigonal nitrogen-containing defect in diamond with an $S=\frac{3}{2}$ excited state populated via optical excitation. Analysis of the spin Hamiltonian parameters and the wavelength dependence of the optical excitation leads to assignment of this $S=\frac{3}{2}$ state to the $^{4}A_{2}$ excited state of ${\mathrm{NV}}^{0}$. This identification, together with an examination of the Electronic structure of the NV centers in diamond, provides a plausible explanation for the lack of observation (to date) of an EPR signal from the ${\mathrm{NV}}^{0}$ ground state.
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Electron Paramagnetic Resonance studies of silicon-related defects in diamond
Physical Review B - Condensed Matter and Materials Physics, 2008Co-Authors: Andrew M. Edmonds, P. M. Martineau, M E Newton, Daniel James Twitchen, S.d. WilliamsAbstract:We report the results of multifrequency Electron Paramagnetic Resonance studies at temperatures between 8 and 300 K on diamonds synthesized by chemical vapor deposition and intentionally silicon doped with isotopes in natural abundance or isotopically enriched. The Si-29 hyperfine structure has provided definitive evidence for the involvement of silicon in two Electron Paramagnetic Resonance centers in diamond that were previously suspected to involve silicon: KUL1 and KUL3. We present data that unambiguously identify KUL1 as an S=1 neutral silicon split-vacancy (D-3d symmetry) defect (V-Si-V)(0), while KUL3 is shown to be (V-Si-V)(0) decorated with a hydrogen atom, (V-Si-V:H)(0).