Signal Optimization for Unilateral NMR Magnet Design.

摘要

In this thesis, we propose a method of signal optimization for an adjustable unilateral NMR (nuclear magnet resonance) permanent magnet design. Unilateral NMR magnets have many advantages over the conventional MRI (magnetic resonance imaging) bore design, including mobility, cost and open access geometry, but have not been adopted on a large scale for use in major fields varying from medical to industrial applications due to limitations such as poor SNR (signal noise ratio), low static magnetic field strength and field inhomogeneities. Attempts to improve these parameters have shown that a tradeoff occurs, i.e. increasing field strength reduces field homogeneity and vice versa. We introduce a model of a simple NMR magnet design where field strength and homogeneity can be controlled by an adjustable central magnet shim unit. We derive analytical expressions that are used to model the experimental sensitivity as a function of magnet geometry. We then present experimental data of a physical prototype of the model design that supports simulation results. In addition we show that field homogeneity is a more dominant factor in SNR optimization than field strength, perhaps indicating the future direction of unilateral magnet design.