Diffusion pore imaging with generalized temporal gradient profiles

TL;DR

This paper generalizes the methods for NMR diffusion pore imaging by demonstrating that a wide range of temporal gradient profiles, beyond previously used ones, can be employed to determine pore shapes in porous materials.

Contribution

It introduces a generalized framework for temporal gradient profiles in diffusion NMR, expanding the possibilities for pore imaging beyond traditional gradient designs.

Findings

Any number of short gradient pulses can be used under the short-gradient approximation.

Long gradient pulses of small amplitude can fulfill the rephasing condition.

Classical q-space gradients with two short pulses of opposite sign are not suitable due to phase loss.

Abstract

In porous material research, one main interest of nuclear magnetic resonance diffusion (NMR) experiments is the determination of the shape of pores. While it has been a longstanding question if this is in principle achievable, it has been shown recently that it is indeed possible to perform NMR-based diffusion pore imaging. In this work we present a generalization of these previous results. We show that the specific temporal gradient profiles that were used so far are not unique as more general temporal diffusion gradient profiles may be used. These temporal gradient profiles may consist of any number of 'short' gradient pulses, which fulfil the short-gradient approximation. Additionally, 'long' gradient pulses of small amplitude may be present, which can be used to fulfil the rephasing condition for the complete profile. Some exceptions exist. For example, classical q-space gradients consisting of two short gradient pulses of opposite sign cannot be used as the phase information is lost due to the temporal antisymmetry of this profile.