Spatially resolved homonuclear solid-state NMR. II. Jeener-Broekaert and solid-echo phase-encoding imaging

Abstract

Phase encoding is a principle which is employed in several solid-state NMR imaging techniques. It is applicable to all kinds of spin echoes occurring in solid-state NMR. The exemplary density-operator theories for solid-echo as well as for Jeener-Broekaert phase-encoding imaging (JEPHI) are outlined, providing physical insight into the phase-encoding process with this type of experiment. At the same time, the basis for the theory of further solid-echo pulse sequences in the presence of magnetic field gradients is laid. The treatment is based on dipolar interaction although it is argued that the same pulse sequences work also in the presence of quadrupolar interaction. With ideally hard radiofrequency pulses the considered phase-encoding techniques permit the straightforward evaluation of image data. Artifacts appearing in images are suitably classified and physically explained. With softer RF pulses the tendency toward image artifacts increases. This can be alleviated by phase-cycling procedures. Corresponding pulse sequences and experiments are reported. A particularly favorable feature of this class of solid-state imaging techniques is that the pulse sequences can easily be implemented on standard tomographs.