Magnetic Resonance Imaging of Water Content and Flow Processes in Natural Soils by Pulse Sequences with Ultrashort Detection

Haber‐Pohlmeier, Sabina; Caterina, David; Blümich, Bernhard; Pohlmeier, Andreas

doi:10.3390/molecules26175130

Cited by 6 publications

(1 citation statement)

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“…The internal magnetic field gradient is dependent of the external magnetic field (B 0 ) magnitude. Gradient echo sequences generally do not work due to inherently short T ⇤ 2 [144]. For spin-echo based sequences, short T 2 relaxation times reduce the echo intensity and decrease SNR, and short T ⇤ 2 decreases the effective resolution.…”

Section: Introductionmentioning

confidence: 99%

Advanced NMR methods and applications: diffusion, velocimetry and relaxation

Wang¹

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Since nuclear magnetic resonance (NMR) was developed, it has been widely applied in various areas, especially in chemistry, biology, medical imaging etc. It is also a very important method in the petrol industry, food science, material science etc. Nevertheless, the new and advanced NMR methodologies and their potential applications are still under exploration. In this thesis, we further developed the application of NMR in ultra-slow measurements of underground plant roots and the dynamics of fluids in nano-scale pores. As to the ultra-slow flow measurements, a composited pulse sequence was developed to fast scan 3D water flow in plants, during which the effect of plant growth was minimized. In addition, a mathematical model was also explored to quantify the detection limit for fluid displacements and their uncertainty. By this method, an ultra-slow counter-flow of approximately 8 μm/s was spatially resolved in the xylem and phloem of bean seedling roots. This work provides strong evidence of the capability of pulsed-field gradient (PFG) NMR to capture flow less than the diffusion rates. It also lays a foundation for the study of metabolic dynamics in the roots of plants in vivo. The mobility of molecules confined in nano-scale pores is greatly reduced because of strong host-guest interactions, resulting in very short T2 and thus poor spectral resolution. The short T2 also limits the duration of applied pulsed field gradients, reducing the sensitivity of diffusion NMR for molecules with low mobility. Therefore, the magic angle spinning (MAS) method was applied to elongate T2 by averaging the dominant dipole-dipole interaction and improve spectral resolution. Combined with MAS, many common pulse sequences can also be applied, providing a range of experiments for the study of molecular dynamics. In this thesis, the spectrally resolved dynamics of ionic liquid in carbon black (CB) were obtained, revealing the ionic liquid’s different environments. As to the dynamics of benzene and hexane inside the Metal-Organic-Framework(MOF) NU-1000 MOF, combining with pulse sequences, such as PFG NMR, inversion recovery (IR) and diffusion-diffusion exchange spectroscopy (DEXSY) pulse sequence etc, were successfully implemented. Experimental results suggest fast exchange between absorbed and bulk benzene molecules. Furthermore, no preferential adsorption sites for molecules in MOF NU-1000 have been found. These findings are essential for further design and tailoring of MOF structures.

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Section: Introductionmentioning

confidence: 99%