Magnetic Resonance Pore Imaging: Overcoming the resolution limit of MRI for closed pore systems

Abstract

The structure of porous materials is important in many areas of basic and applied science. Various Nuclear Magnetic Resonance (NMR) techniques are applied to study porous media on different length scales. Among them, diffusive-diffraction Pulsed Gradient Spin Echo (PGSE) NMR is able to resolve features of the pore space on the micrometer scale. However, this technique only measures the modulus square of the structure factor, which leaves the exact pore structure obscured due to the lack of phase information. In this contribution, we present experimental evidence that it is possible to obtain the full structure factor with a recently suggested modification of the PGSE NMR experiment. Our adaptation which we call Magnetic Resonance Pore Imaging (MRPI), creates a hybrid between Magnetic Resonance Imaging (MRI) and PGSE NMR. This allowed us to obtain two-dimensional average pore images with an unprecedented resolution as compared to conventional MRI. Based on these advances we demonstrate that MRPI integrates well with proven concepts of MRI and offers great potential to characterize even heterogeneous porous structures by mapping the MRPI signal on MRI images.