SENSITIVITY AND RESOLUTION OF CONSTANT-TIME IMAGING

A constant-time-imaging experiment is described in which the magnetization is created with a short RF pulse applied after the gradient is switched on. Only one magnetization measurement per RF pulse is made. All spatial information is obtained with phase-encoding gradients resulting in distortion-free images. Expressions for the resolution and signal-to-noise ratio of this technique are derived and compared to those of frequency-encoded-imaging techniques. Constant-time imaging provides superior signal-to-noise ratios when the gradient-switching time is longer than T-2. The resolution is not limited by the digitizer bandwidth or relaxation effects, and the diffusion-limited resolution is twice as fine as that of frequency-encoded techniques. This technique can be implemented on a standard liquid NMR spectrometer with a microimaging probe, to yield high-quality images of protons in rigid materials in a reasonable amount of time. Examples of 2D and 3D images of protons in Delrin are shown. (C) 1994 Academic Press, Inc.