Shapes of Nuclear Induction Signals

Jacobsohn, Boris A.; Wangsness, Roald K.

doi:10.1103/physrev.73.942

Cited by 129 publications

(21 citation statements)

References 5 publications

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“…The spin remains mostly unaffected until nearly halfway through the pulse, when the sweep reaches resonance. There follow some transient oscillations in the z-magnetization that are reminiscent of the "ringing" observed in early slow passage experiments (27). Off-resonance trajectories are very similar, with a time shift that reflects the moment when the sweep passes through.…”

Section: Z- X- and Y-magnetization As A Function Of Offset For A mentioning

confidence: 92%

Adjustable, Broadband, Selective Excitation with Uniform Phase

Cano

Smith

Shaka

2002

Journal of Magnetic Resonance

106

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Section: Z- X- and Y-magnetization As A Function Of Offset For A mentioning

confidence: 92%

Adjustable, Broadband, Selective Excitation with Uniform Phase

Cano

Smith

Shaka

2002

Journal of Magnetic Resonance

106

View full text Add to dashboard Cite

“…Early in the development of NMR, transient effects, called ''wiggles,'' were observed after the magnetic field passed through resonance in a time that was short relative to T 1 and T 2 [1,2]. Since inhomogeneity over the sample causes the oscillations to damp out more rapidly, this effect was used in CW NMR to guide the shimming of the magnetic field to maximum homogeneity.…”

Section: Introductionmentioning

confidence: 98%

Rapid-scan EPR with triangular scans and fourier deconvolution to recover the slow-scan spectrum

Joshi

Ballard

Rinard

et al. 2005

Journal of Magnetic Resonance

108

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“…Contravention of the adiabatic condition leads not only to inefficient inversion. In addition, characteristic beats of the longitudinal magnetization become visible, which are analogous to the well-known "wiggles" of the transverse magnetization in continuouswave NMR (22). The wiggles represent beats at the difference of 1 ϭ ␥ B 1e and ⍀(t), where ⍀(t) is the time-dependent angular velocity of the change of the orientation of B 1e .…”

Section: Resultsmentioning

confidence: 90%

Efficiency of flow‐driven adiabatic spin inversion under realistic experimental conditions: A computer simulation

Trampel

Jochimsen

Mildner

et al. 2004

Magnetic Resonance in Med

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Continuous arterial spin labeling (CASL) using adiabatic inversion is a widely used approach for perfusion imaging. For the quantification of perfusion, a reliable determination of the labeling efficiency is required. A numerical method for predicting the labeling efficiency in CASL experiments under various experimental conditions, including spin relaxation, is demonstrated. The approach is especially useful in the case of labeling at the carotid artery with a surface coil, as consideration of the experimental or theoretical profile of the B 1 field is straightforward. Other effects that are also accounted for include deviations from a constant labeling gradient, and variations in the blood flow velocity due to the cardiac cycle. Assuming relevant experimental and physiological conditions, maximum inversion efficiencies of about 85% can be obtained. Perfusion imaging with magnetically labeled water as an endogenous tracer is capable of measuring regional cerebral blood flow (rCBF) (1,2). Continuous arterial spin labeling (CASL) can be achieved by velocity-driven adiabatic spin inversion in the carotid artery (2,3). This represents an effective method of spin labeling for absolute quantification of rCBF if the value of the inversion efficiency, ␣, is accurately known. The inversion efficiency is the percentage of (initially positive) longitudinal magnetization M z that becomes aligned with the negative z-axis at the end of the adiabatic fast passage:In velocity-driven adiabatic inversion, ␣ depends on the magnitude and spatial profile of both the RF magnetic field, B RF (z), and the frequency offset along the direction of flow (typically the z-axis), B G (z). The hemodynamics in the artery also affect ␣. Several approaches for theoretically analyzing the inversion efficiency by modeling the inversion process have been published (4 -8). Although the results of Refs. 4 -8 agreed with experimental data, some simplifications in their calculations did not match realistic conditions, especially if separate coils are used for CASL and image generation. The most valuable advantages of separating the radiofrequency (RF) irradiation for labeling and imaging by the use of two coils are the easy implementation of multislice imaging with arbitrary slice orientation, and the elimination of magnetization-transfer effects. Perfusion measurements with the dual-coil setup have been performed in animals (9,10) and humans (11,12). A recent study demonstrated the potential for functional magnetic resonance imaging (fMRI) by mapping rCBF changes in subjects performing a motor paradigm (13). In those experiments, the surface coil used for labeling provided a nonuniform RF field. Marro et al. (5) addressed in their model the influence of a nonuniform B RF profile, but did not consider different depths of the position of the artery. However, this might be relevant because the depth of the carotid artery can vary among subjects (especially children). Our numerical simulations of the inversion process explicitly consider such profiles. So...

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Shapes of Nuclear Induction Signals

Abstract: The various shapes of nuclear induction signals are discussed for small values of the r-f field. In the case of a linear variation with time of the strong magnetic field, numerical results are given for various values of the sweep rate and the total relaxation time.

Cited by 129 publications

References 5 publications

Adjustable, Broadband, Selective Excitation with Uniform Phase

Adjustable, Broadband, Selective Excitation with Uniform Phase

Rapid-scan EPR with triangular scans and fourier deconvolution to recover the slow-scan spectrum

Efficiency of flow‐driven adiabatic spin inversion under realistic experimental conditions: A computer simulation

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