Frequency-swept pulses for ultrafast spatially encoded NMR

Abstract

Ultrafast NMR based on spatial encoding yields arbitrary multidimensional spectra in a single scan. The dramatic acceleration afforded by spatial parallelisation makes it possible to capture transient species and processes, and has notably been applied to the monitoring of reactions and the analysis of hyperpolarised species. At the heart of ultrafast NMR lies the spatially sequential manipulation of nuclear spins. This is virtually always achieved by combining a swept radio-frequency pulse with a magnetic field gradient pulse. The dynamics of nuclear spins during these pulse sequence elements is key to understand and design ultrafast NMR experiments, and can often be described by surprisingly simple models. This article describes the spatial encoding of relaxation, chemical shift and diffusion in a common framework and discusses directions for future developments.

Quadratic spacing of the effective gradient area for spatially encoded diffusion NMR

“…This derivation relies on the assumption of an instantaneous flip of the magnetisation during the frequency swept-pulse. While this approximation was found to give excellent results for the predicted phase variation in the case of a linearly swept pulse, [9,13] the result deserves to be investigated, with the help of numerical simulation that are free from this approximation.…”

“…[3,8] In UF NMR, spatial encoding is usually achieved by the combined application of a frequency-swept pulse and a magnetic-field gradient. [5,9,10] This results in the spatial parallelisation of the evolution delay of 2D spectroscopy experiments, the duration of the diffusion-encoding gradient in diffusion experiments, or the inversion recovery delay for relaxation experiments. Single-scan acquisition methods such as echo-planar spectroscopic imaging (EPSI) or a Carr-Purcell-Meiboom-Gill (CPMG) loop are then used to simultaneously read the spatially encoded information and to sample the direct dimension.…”

The exposome paradigm to predict environmental health in terms of systemic homeostasis and resource balance based on NMR data science

“…86 In spatial encoding and spatial selection methods, several sub-experiments are conducted in parallel in different spatial regions of the sample spectra. 87,88 As an example of spatial methods, magnetic resonance imaging (MRI) can be used for the noninvasive evaluation of spatial 1 H density, diffusion or relaxation, and chemical shi in biological and other samples. It is also put to practical use in the medical eld as a powerful technique for diagnostic imaging.…”

Measuring Protein–Ligand Binding by Hyperpolarized Ultrafast NMR

“…Here, we overcome this limitation for the measurement of spin–spin ( R 2 ) relaxation using single-shot hyperpolarization such as dissolution dynamic nuclear polarization (D-DNP) . The method is based on the principle of two-dimensional ultrafast NMR spectroscopy. − An ultrafast NMR pulse sequence (Figure ) encodes the chemical shift into a spatial dimension of the NMR sample using a combination of pulsed field gradients and adiabatic frequency-swept pulses. The encoded signals are read out in a spin–echo pulse train, also under the application of pulsed field gradients.…”