Pulsed Field Gradients in Simulations of One- and Two-Dimensional NMR Spectra

Meresi, Ghirmai; Cuperlovic, Miroslava; Palke, William E.; Gerig, J. T.

doi:10.1006/jmre.1998.1665

Cited by 17 publications

(15 citation statements)

References 32 publications

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“…1, requires, in addition to the RF pulses, the incorporation of three independent sets of gradients, namely, slice selection, echo, and mixing gradients. To our knowledge only two other groups have addressed such inclusions numerically (19,20). Schematically, the interpulse evolution of coherence types that are influential in causing the STEAM output variability is illustrated in Fig.…”

Section: Steam Sequencementioning

confidence: 99%

Response of metabolites with coupled spins to the STEAM sequence

Thompson¹,

Allen²

2001

Magn. Reson. Med.

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This article demonstrates that a numerical solution of the full quantum mechanical equations for all metabolites with coupled spins is an efficient and accurate means, first, of predicting the optimum STEAM sequence design for quantifying any target metabolite in brain, and, second, for providing the basis lineshapes and yields of these metabolites to facilitate their accurate quantification. Using as illustrations the weakly coupled AX 3 system of lactate, the ABX aspartyl group of N-acetylaspartate, which has only two strongly coupled spins, and the much larger strongly coupled AMNPQ glutamyl group of glutamate, the numerical solutions for the response to STEAM highlight the principal source of response variability, namely, the evolution of and transfer between zero quantum terms during the mixing time, TM. These highlights include the rapid oscillations of zero quantum terms due to the chemical shift difference of the coupled spins, the proliferation of oscillating zero order terms due to strong coupling, and the serendipitous smoothing of the response as the number of strongly coupled spins increases. The numerical solutions also demonstrate that the design of the selective 90°pulses is a far less critical factor in determining the response than was the case for the selective 180°pulses Metabolite detection and quantification in vivo with proton spectroscopic methods is most commonly carried out using the spatial localization provided either by the single voxel PRESS (point resolved spectroscopy) (1,2) or STEAM (stimulated echo acquisition mode) (3,4) sequences. When both sequences are available, the sequence of choice is often determined by the metabolite target. For example, the observation of uncoupled singlet resonances in brain, namely, N-acetylaspartate (NAA) at 2.02 ppm, creatine (Cr) at 3.05 ppm, and choline (Cho) at 3.2 ppm, are routinely observed with a long-echo PRESS sequence. This stems from the factor of two advantages in uncoupled-spin signal yield over STEAM and the relatively long T 2 s of these resonances compared with either the macromolecular signals or the J-modulation envelopes of coupled spins. However, when the target metabolites contain coupledspin systems, short-echo STEAM spectroscopy has gained popularity in the clinical setting, due principally to its robustness at echo times from ϳ10 to ϳ50 ms. Nonetheless, the response of certain key, coupled-spin metabolites to the STEAM sequence, not to mention the background metabolite spectrum, exhibit significant variability. The purpose of this article is to demonstrate the efficacy of numerical calculations in the determination of the sources of that variability. The range of echo and mixing times considered (TE and TM, respectively) is that which is typically regarded as falling into the short-echo experimental range, namely, TE and TM less than ϳ50 ms.The short-echo-time limit is regarded as desirable for the observation of coupled spins because the longer echo-time modulations of the metabolite lineshapes lead, more often than not, to...

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Section: Steam Sequencementioning

confidence: 99%

Response of metabolites with coupled spins to the STEAM sequence

Thompson¹,

Allen²

2001

Magn. Reson. Med.

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“…They are now frequently used (42) as they allow to suppress many phase cycles, thus leading to faster experiments. Computer simulation of gradient enhanced sequences mainly follow two different paths: dividing the sample into a number of slices (18,43) or analytic propagation of operators (18,44). Recently, Edwards proposed a powerful alternative approach, using superoperators (45).…”

Section: Pulsed Field Gradientsmentioning

confidence: 99%

Spin algebra andNMRtheory using numerical software

Grivet

2015

Concepts Magnetic Resonance

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A simple method to execute spin algebra computations is presented. It uses the high-level numerical program Scilab and its large and convenient set of linear algebra routines. The techniques thus developed are applied to various nuclear magnetic resonance (NMR)-related simulations. Static spectra of AB and ABC spin systems are computed. Free precession of single or multispin systems are simulated using the density matrix formalism. Magnetization transfer under simple pulse sequences is examined. Matrices representing product operators are displayed and coherence orders are explained. COSY correlation maps for two and three spins are obtained without approximation. The simulation of a DQF-COSY spectrum, with its eight-step phase program, is explained. Two simple pulsed field gradient experiments are described. Computation times are under 100 s on a 1.66-GHz laptop computer. The approach is elementary, requiring only a basic knowledge of spin quantum mechanics.

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“…Introduced in 1994 [36], the GAMMA C++ library is a flexible and efficient tool for describing and simulating MR experiments. Since the early 1990s, there have been reports of a number of other NMR simulation libraries [5,16,22] and application tools [1,2,15,17,27,29,32,49] which have sought to provide similar functionality in either a more optimized or user friendly fashion. The growth in available tools reflects the consensus among MR scientists that simulation methods are a necessary and desirable step in the development of increasingly sophisticated data acquisition/analysis methods for viewing complex molecular systems.…”

Section: Introductionmentioning

confidence: 99%

GAVA: Spectral simulation for in vivo MRS applications

Soher

Young

Bernstein

et al. 2007

Journal of Magnetic Resonance

113

102

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An application that provides a flexible and easy to use interface to the GAMMA spectral simulation package is described that is targeted at investigations using in vivo MR spectroscopic methods. The program makes available a number of widely used spatially-localized MRS pulse sequences and NMR parameters for commonly-observed tissue metabolites, enabling spectra to be simulated for any pulse sequence parameter and viewed in an integrated display. The application is interfaced with a database for storage of all simulation parameters and results of the simulations. This application provides a convenient method for generating a priori spectral information used in parametric spectral analyses and for visual examination of the effects of difference pulse sequences and parameter settings.

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Pulsed Field Gradients in Simulations of One- and Two-Dimensional NMR Spectra

Cited by 17 publications

References 32 publications

Response of metabolites with coupled spins to the STEAM sequence

Response of metabolites with coupled spins to the STEAM sequence

Spin algebra andNMRtheory using numerical software

GAVA: Spectral simulation for in vivo MRS applications

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