Cavity- and waveguide-resonators in electron paramagnetic resonance, nuclear magnetic resonance, and magnetic resonance imaging

Webb, Andrew

doi:10.1016/j.pnmrs.2014.09.003

Cited by 19 publications

(23 citation statements)

References 68 publications

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“…1). This particular slot geometry has been proven to have a higher SNR compared to the other possible alternatives [19][20][21][22]. Tuning and matching capacitors (0-15 pF: Voltronics Co. Salisbury, MD, USA) were soldered directly onto the surface: five parallel ceramic capacitors (American Technical Ceramics, Huntington Station, NY, USA), four 15 pF capacitors, and one 3.9 pF capacitor were placed as shown in Fig.…”

Section: Coil Prototypementioning

confidence: 99%

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Surface coil with reduced specific absorption rate for rat MRI at 7 T

Solis-Najera

Martin

Vázquez

et al. 2015

Magn Reson Mater Phy

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Section: Coil Prototypementioning

confidence: 99%

“…This coil design is a scaled-down version of a previous coil prototype built for whole-body MRI of obese rats at 4 T [20]. Webb [21] has recently reviewed this coil design. Here, coil performance was studied both theoretically and experimentally using the SNR model reported in [22] and phantom image data.…”

mentioning

confidence: 99%

Surface coil with reduced specific absorption rate for rat MRI at 7 T

Solis-Najera

Martin

Vázquez

et al. 2015

Magn Reson Mater Phy

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“…And in 2013, Klaus Möbius and coworkers discussed in Progress high-field/high-frequency EPR experiments on membrane proteins thereby crossing the gap between EPR and NMR [1]. In 2014, Andrew Webb reviewed cavity-and waveguide-resonator constructions in EPR, NMR and MRI applications [8]. In the same year, 2014, Konstantin Ivanov and coworkers [9] discussed in their review in Progress the role of level anti-crossings in nuclear spin hyperpolarization, a phenomenon based on the interaction between nuclear and electron spins and related to Chemically Induced Dynamic Nuclear Polarization (CIDNP).…”

Section: Introductionmentioning

confidence: 99%

Biomolecular EPR Meets NMR at High Magnetic Fields

et al. 2018

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In this review on advanced biomolecular EPR spectroscopy, which addresses both the EPR and NMR communities, considerable emphasis is put on delineating the complementarity of NMR and EPR regarding the measurement of interactions and dynamics of large molecules embedded in fluid-solution or solid-state environments. Our focus is on the characterization of protein structure, dynamics and interactions, using sophisticated EPR spectroscopy methods. New developments in pulsed microwave and sweepable cryomagnet technology as well as ultrafast electronics for signal data handling and processing have pushed the limits of EPR spectroscopy to new horizons reaching millimeter and sub-millimeter wavelengths and 15 T Zeeman fields. Expanding traditional applications to paramagnetic systems, spin-labeling of biomolecules has become a mainstream multifrequency approach in EPR spectroscopy. In the high-frequency/high-field EPR region, sub-micromolar concentrations of nitroxide spin-labeled molecules are now sufficient to characterize reaction intermediates of complex biomolecular processes. This offers promising analytical applications in biochemistry and molecular biology where sample material is often difficult to prepare in sufficient concentration for NMR characterization. For multifrequency EPR experiments on frozen solutions typical sample volumes are of the order of 250 μL (S-band), 150 μL (X-band), 10 μL (Q-band) and 1 μL (W-band). These are orders of magnitude smaller than the sample volumes required for modern liquid- or solid-state NMR spectroscopy. An important additional advantage of EPR over NMR is the ability to detect and characterize even short-lived paramagnetic reaction intermediates (down to a lifetime of a few ns). Electron–nuclear and electron–electron double-resonance techniques such as electron–nuclear double resonance (ENDOR), ELDOR-detected NMR, PELDOR (DEER) further improve the spectroscopic selectivity for the various magnetic interactions and their evolution in the frequency and time domains. PELDOR techniques applied to frozen-solution samples of doubly spin-labeled proteins allow for molecular distance measurements ranging up to about 100 Å. For disordered frozen-solution samples high-field EPR spectroscopy allows greatly improved orientational selection of the molecules within the laboratory axes reference system by means of the anisotropic electron Zeeman interaction. Single-crystal resolution is approached at the canonical g-tensor orientations—even for molecules with very small g-anisotropies. Unique structural, functional, and dynamic information about molecular systems is thus revealed that can hardly be obtained by other analytical techniques. On the other hand, the limitation to systems with unpaired electrons means that EPR is less widely used than NMR. However, this limitation also means that EPR offers greater specificity, since ordinary chemical solvents and matrices do not give rise to EPR in contrast to NMR spectra. Thus, multifrequency EPR spectroscopy plays an important role in better understanding paramagnetic species such as organic and inorganic radicals, transition metal complexes as found in many catalysts or metalloenzymes, transient species such as light-generated spin-correlated radical pairs and triplets occurring in protein complexes of photosynthetic reaction centers, electron-transfer relays, etc. Special attention is drawn to high-field EPR experiments on photosynthetic reaction centers embedded in specific sugar matrices that enable organisms to survive extreme dryness and heat stress by adopting an anhydrobiotic state. After a more general overview on methods and applications of advanced multifrequency EPR spectroscopy, a few representative examples are reviewed to some detail in two Case Studies: (I) High-field ELDOR-detected NMR (EDNMR) as a general method for electron–nuclear hyperfine spectroscopy of nitroxide radical and transition metal containing systems; (II) High-field ENDOR and EDNMR studies of the Oxygen Evolving Complex (OEC) in Photosystem II, which performs water oxidation in photosynthesis, i.e., the light-driven splitting of water into its elemental constituents, which is one of the most important chemical reactions on Earth.

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“…Ultrahigh field [7 Tesla (T) and above] human MRI provides the impetus for new radiofrequency coil designs. Thus, in addition to modifications to existing designs (1) such as the birdcage coil (2), transverse electromagnetic mode resonator (3) and surface coil, new concepts such as travelling wave antennas (4)(5)(6)(7)(8), dipoles (9)(10)(11)(12), cavity resonators (13) and dielectric resonators (DRs) (14,15) have been shown, both for single coils as well as for transmit arrays. Transmit arrays (16)(17)(18) offer a high degree of flexibility in terms of shaping the transmit magnetic (B þ 1 ) field and are essential for body imaging at very high fields.…”

Section: Introductionmentioning

confidence: 99%

“…Musculoskeletal imaging (knee, ankle, wrist) and neuroimaging at very high field can be performed relatively successfully at high field using single coil structures which produce circularly polarized B þ 1 fields. Cavity-and dielectric-resonators (13,19,20) have the advantage that simple designs with intrinsically homogeneous modes can be used. DRs use high permittivity materials with the lower frequency modes being suitable for MRI (13).…”

Section: Introductionmentioning

confidence: 99%