CONSTANT-TIME IMAGING APPROACHES TO NMR MICROSCOPY

The resolution in nuclear magnetic resonance (NMR) microscopy is limit ed by a combination of the inherent low sensitivity of NMR, the destru ction of spin magnetization gratings by molecular diffusion, and varia tions in the local magnetic field strength introduced by spatial varia tions of the bulk susceptibility. While none of these may be completel y overcome, constant time imaging methods are the optimal approach to recording images when the above factors are important. This method aim s to instantaneously create a spin magnetization grating and then to e fficiently sample the spatially invariant portion of this - correspond ing to a selected Fourier component of the sample distribution. The me thod is introduced, analyzed in the presence of molecular diffusion, a nd demonstrated to yield high-resolution images. To implement the meth od, a microscopy probe was constructed for a standard-bore 400-MHz NMR spectrometer (the latter was also implemented at 600 MHz), which is d escribed. (C) 1997 John Wiley & Sons, Inc.