Magnetic Resonance for Nonrotating Fields

Bloch, F.; Siegert, A. J. F.

doi:10.1103/physrev.57.522

Cited by 1,146 publications

(674 citation statements)

References 2 publications

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“…During a spin-lock, the magnetization is locked in the rotating frame by an RF field, the socalled spin-lock field B 1lock . The effective resonance frequency in the rotating frame during the spin-lock condition is very close to ω 1lock = γB 1lock , deviating only by a potential BlochSiegert shift (Bloch and Siegert, 1940). This latter small shift in resonance frequency results from the counter-rotating field component of a linearly polarized time varying field.…”

Section: Introductionmentioning

confidence: 74%

“…The observed line width of the saturation spectra is about 6 Hz FWHM. The peak often appeared at a slightly (2 Hz) higher frequency than expected from the B 1lock level determined from the instruments standard transmit calibration, possibly due to the Bloch-Siegert shift (Bloch and Siegert, 1940) or a mis-calibrated B 1 level. For high dipole current strengths (400 μA), the rotary saturation effect achieved a 30% amplitude decrease.…”

Section: Rotary Saturation Spectramentioning

confidence: 86%

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Stimulus-induced Rotary Saturation (SIRS): A potential method for the detection of neuronal currents with MRI

et al. 2008

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Neuronal currents produce local transient and oscillatory magnetic fields that can be readily detected by MEG. Previous work attempting to detect these magnetic fields with MR focused on detecting local phase shifts and dephasing in T2 or T2* weighted images. For temporally biphasic and multiphasic local currents the sensitivity of these methods can be reduced through the cancellation of the accrued phase induced by positive and negative episodes of the neuronal current. The magnitude of the phase shift is also dependent on the distribution of the current within the voxel. Since spins on one side of a current source develop an opposite phase shift relative to those on the other side, there is likely to be significant cancellation within the voxel.We introduce a potential method for detecting neuronal currents though their resonant T1ρ saturation during a spin-lock preparation period. The method is insensitive to the temporal and spatial cancellation effects since it utilizes the multi-phasic nature of the neuronal currents and thus is not sensitive to the sign of the local field. To produce a T1ρ reduction, the Larmor frequency in the rotating frame, which is set by γB 1lock (typically 20 Hz -5 kHz), must match the major frequency components of the stimulus-induced neuronal currents. We validate the method in MRI phantom studies. The rotary saturation spectra showed a sharp resonance when a current dipole within the phantom was driven at the Larmor frequency in the rotating frame. A 7 minute block design experiment was found to be sensitive to a current dipole strength of 56 nAm, an approximate magnetic field of 1 nT at 1.5 mm from the dipole. This dipole moment is similar to that seen using the phase shift method in a similar experimental setup by Konn et.al. (2003), but is potentially less encumbered by temporal and spatial cancellation effects.

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Section: Introductionmentioning

confidence: 74%

Section: Rotary Saturation Spectramentioning

confidence: 86%

Stimulus-induced Rotary Saturation (SIRS): A potential method for the detection of neuronal currents with MRI

et al. 2008

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“…These are known to be proportional to the square of the strength of the rf field, and inversely proportional to the shift between the observed and irradiated spins. [21][22][23] To illustrate these coherent effects, some numerical simulations of dichromatic decoupling experiments are given in Fig. S1 of the ESI.…”

Section: Resultsmentioning

confidence: 99%

Homonuclear decoupling for spectral simplification of carbon-13 enriched molecules in solution-state NMR enhanced by dissolution DNP

Chinthalapalli

Bornet

Carnevale

et al. 2016

Phys. Chem. Chem. Phys.

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“…using an 83 kHz proton decoupling field to correct for the Bloch-Siegert effect. 15 The samples were packed at the center of the rotor with 2.5-mm thickness along the axis to ensure the homogeneity of the r.f. fields and sample temperature.…”

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confidence: 99%

Solid-state 19F MAS and 1H→19F CP/MAS NMR study of the phase-transition behavior of vinylidene fluoride–trifluoroethylene copolymers: 2. semi-crystalline films of VDF 75% copolymer

Aimi

Ando

2012

Polym J

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The changes in the crystalline structure and molecular mobility in the semi-crystalline vinylidene fluoride (VDF) and trifluoroethylene (TrFE) copolymer P(VDF 75 /TrFE 25 ) caused by the ferroelectric-paraelectric phase transition were analyzed using variable temperature solid-state 19 F magic angle spinning (MAS) and 1 H-19 F cross polarization/MAS nuclear magnetic resonance spectroscopy in the temperature range of 42-129 1C. The conformational exchange between trans and gauche at the VDF and VDF-TrFE head-to-head linkage gradually increases at temperatures above 77 1C, and the conformational exchange at the head-to-tail linkage has a key role in the ferroelectric-paraelectric phase transition. The anomalous decrease in the amorphous peak intensities and the presence of a T 1q F value similar to that of the crystalline domain at 122 1C indicate that cooperative motion occurs in both phases just above the transition temperature (T c ). The amorphous domain is assimilated by the crystalline domain upon lowering the temperature from 129 to 85 1C, which significantly increases the crystallinity to below T c , as indicated by the shape of the spectra, and identical T 1q INTRODUCTIONVinylidene fluoride (VDF)-trifluoroethylene (TrFE) copolymer (P(VDF x /TrFE 1 Àx )), where x is the VDF molar fraction, is a typical ferroelectric polymer that shows a ferroelectric-paraelectric phase transition, which has garnered much interest in the effort to clarify its mechanism. 1,2 Two types of ferroelectric phases have been reported at room temperature, that is, the low-temperature (LT) and the cooled phase, depending on the VDF content and preparation conditions of the copolymer. 2 In the LT phase, the CF 2 dipoles are arranged in parallel because of the planar zigzag formed by the all-trans polymer chains, which is the same arrangement as the PVDF form I (b-form), whereas in the cooled phase, long trans segments are connected by irregular trans-gauche linkages along their chain axis to form a type of super lattice. However, the stable crystal structure in the hightemperature (paraelectric) phase is hexagonal and is composed of statistically mixed chains with TG þ , TG -, T 3 G þ and T 3 Gconformations. These chains rotate about their axes via the onedimensional diffusion of the conformational defects along the chain.Several reports have shown that lamellar crystals grow in P(VDF/ TrFE) films at VDF contents of x ¼ 0.60 to 0.82 when annealed at temperatures above the Curie point (T c ). In particular, annealing such polymers at elevated temperatures in the paraelectric phase increases the integrated X-ray diffraction intensities of the 110 and 200 reflections, which correspond to the all-trans chains, and sharpen the differential scanning calorimetry (DSC) endotherms observed at T c . [3][4][5][6][7] The efficient growth of lamellar crystals in the paraelectric phase has been explained using a sliding diffusion model for the polymer chains. For instance, a polyethylene lamellar crystal can thicken at higher pressures through th...

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Magnetic Resonance for Nonrotating Fields

Cited by 1,146 publications

References 2 publications

Stimulus-induced Rotary Saturation (SIRS): A potential method for the detection of neuronal currents with MRI

Stimulus-induced Rotary Saturation (SIRS): A potential method for the detection of neuronal currents with MRI

Homonuclear decoupling for spectral simplification of carbon-13 enriched molecules in solution-state NMR enhanced by dissolution DNP

Solid-state 19F MAS and 1H→19F CP/MAS NMR study of the phase-transition behavior of vinylidene fluoride–trifluoroethylene copolymers: 2. semi-crystalline films of VDF 75% copolymer

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