Single-Sided Tomography

Abstract

MRI is one of the most powerful non-invasive techniques to assess material heterogeneities [1, 2]. It allows the generation of images contrasted by a variety of parameters that enhance the discrimination of regions with different molecular structure and dynamics for a wide range of materials. In recent years special effort has been made to achieve spatial localization in the presence of the strongly inhomogeneous magnetic fields generated by open magnet geometries, a capability that converts single-sided NMR probes into truly open tomographs. These sensors were originally intended to scan the surface of large objects by simply repositioning the probe across a region of interest. This procedure provides a crude lateral spatial resolution of the order of the centimeter with a pixel size defined by the size of the sensitive volume, which is mainly determined by the extension of the rf coil. Although the resolution can be improved by decreasing the size of the rf coil, this approach leads to a considerable reduction of the maximum penetration depth of the sensor. To achieve finer resolution inside the sensitive volume, Fourier imaging proved to be the right approach. In this way, by combining pulsed gradients along the two lateral directions with the static gradient of the magnet along the depth full 3D localization has been achieved. The next sections describe the steps needed to implement this imaging techniques at maximum sensitivity.