The development and application of new NMR methods for measuring diffusion in biological and non-biological heterogeneous systems
thesisposted on 15.12.2014, 10:35 by Simon Andrew. Clark
The aim of this work has been to design and develop a series of new NMR tools and data analysis techniques to measure diffusion, and in particular, restricted diffusion within heterogeneous systems. This area of research has many different applications in medicine and the pharmaceutical, oil-recovery, food, and chemicals industries. The information about fluid filled structures, be they cells, rock pores, or emulsions, and how these may alter under different conditions, is of great interest.;The work covered in this thesis is grouped into three sections, where in all cases constant, static magnetic field gradients are used, either by choice or necessity, for encoding diffusion.;The first section covers the design and development of a technique to isolate the signal of restricted diffusing spins from that of freely diffusing spins. This results in a more accurate and robust technique for quantifying restriction parameters relating to the size and structure of the restricting barrier.;The second study approaches the problem of measuring diffusion in heterogeneous environments where differences in magnetic susceptibility of the constituent parts gives rise to strong internal magnetic field gradients. Traditional techniques try to overcome these gradients in a manner of different ways. Here, the intrinsic gradients are poacher turned game-keeper, and used themselves as the diffusion encoding gradients.;The final study again uses large constant magnetic field gradients. Here, the fringe field of a superconducting magnet is used. Different pulse sequences and techniques are modelled and used experimentally to demonstrate how liquid diffusion coefficients may be measured, and it is shown that simple pulse sequences which do not allow for relaxation lead to inaccuracies.