Two dimensional spatially resolved T₂ map implemented on compact Halbach magnet

Heterogeneity is an important property of porous media such as biological materials and rock samples. Spatially resolved NMR is a suitable method to extract heterogeneous information and structure information from porous materials. Recently 1D and 2D Laplace NMR were combined with spatially resolved NMR to examine the detailed structure of heterogeneous samples. For example, the local T₂ relaxation time distributions can be obtained by combining 1D and 2D phase-encode imaging with CPMG method [1, 2]. Spatially resolved D-T₂ and G_int²D-T₂ correlation maps were measured using back-projection method to retrieve abundant structure information of porous media [3, 4].

However, these experiments were implemented using pulsed field gradients which need bulky and heavy gradient amplifiers. Here, we present a way of imaging fluid-filled macroscopic objects with functional microscopic contrast that can be applied to cylindrical samples without the conventional need of pulsing magnetic gradient fields but by rotating the sample instead. This means that images with diffusion, relaxation or diffusion-relaxation correlation contrast can be measured with compact NMR equipment by only using a motor to rotate the cylindrical sample inside the magnet, a simple way well suited for rugged service on a drilling platform or in a geophysical testing laboratory. The experiments were implemented on a 10 MHz home-made Halbach with Kea2 spectrometer (Magritek). The T₂ contrast is introduced by CPMG method and the samples were rotated by a motor in 16 steps. The diffusion-relaxation correlation contrast will be introduced in the future by implementing fast imaging method such as compressed sensing to save measurement time.