Advances in NMR spectroscopy and imaging: Low-power rf-excitation and MRI of soils

Nuclear Magnetic Resonance (NMR) techniques have proliferated in many fields of science and technology like bio-sensing, chemical reaction monitoring and material characterization. Since the inception of NMR as an analytical tool, improving the sensitivity by increasing the field strength has been the primary development goal. However, in order to reduce cost and environmental impact, the trend to miniaturized NMR devices and its diverse application fields enjoys increasing interest. The first part of this thesis introduces novel insights into low-power rf-excitation, which is one crucial aspect for enabling further development in this direction, by employing Frank sequences. Based on experimental data, a detailed evidence of the power savings by excitation in the linear regime is given aiming at future elimination of the rf-amplifier from the NMR spectrometer so as to allow further mobility improvements. Selective excitation by colored Frank-sequence is reported, which bears promise for solvent signal suppression and motion tagging in magnetic resonance imaging (MRI). To this end, spectroscopic quality as well as image resolution with Frank excitation was significantly improved. The aim of the second part is to provide quantitative 3D moisture content patterns of natural soil samples on the microscale, which are essential for improving geological simulations on the field scale. In the course of this, the standardized imaging sequences ’zero echo time’ (ZTE) and ’ultra-short echo time’ (UTE) were employed but also Frank-sequence excitation was implemented, reflecting its first genuine application. In order to characterize water-retention behavior of the soil samples, ZTE experiments were combined with standardized geological methods like Multi-Step Outflow (MSO) and tensiometric measurements. Compared to the established way of acquiring water-retention data, the introduced method provides a fast and precise method with low effort.