Constant time imaging approaches to NMR microscopy

Abstract

The resolution in nuclear magnetic resonance (NMR) microscopy is limited by a combination of the inherent low sensitivity of NMR, the destruction of spin magnetization gratings by molecular diffusion, and variations in the local magnetic field strength introduced by spatial variations of the bulk susceptibility. While none of these may be completely overcome, constant time imaging methods are the optimal approach to recording images when the above factors are important. This method aims to instantaneously create a spin magnetization grating and then to efficiently sample the spatially invariant portion of this - corresponding to a selected Fourier component of the sample distribution. The method is introduced, analyzed in the presence of molecular diffusion, and demonstrated to yield high-resolution images. To implement the method, a microscopy probe was constructed for a standard-bore 400-MHz NMR spectrometer (the latter was also implemented at 600 MHz), which is described. (C) 1997 John Wiley & Sons, Inc.