SPATIALLY RESOLVED HOMONUCLEAR SOLID-STATE NMR .3. MAGIC-ECHO AND ROTARY-ECHO PHASE-ENCODING IMAGING

Two novel magic-echo pulse sequences are reported which are suitable for solid-state NMR imaging using the phase-encoding Fourier transform principle. With the magic-echo phase-encoding solid imaging (MEPSI) technique, ordinary gradients of the external magnetic field are employed. The rotary-echo phase-encoding solid imaging (REPSI) method, on the other hand, is based on gradients of the amplitude of the radiofrequency irradiated to the sample during the magic sandwich pulse in a certain analogy to rotating-frame zeugmatography. The use of magic echoes in solid-state NMR imaging experiments has two crucial advantages. The signal intensity in principle is recovered without incoherence losses. Second, the intervals during which the phase-encoding evolution takes place can be chosen much longer than with ordinary solid-echo experiments. Total encoding times in the order of milliseconds are feasible even with rigid solids. Thus the encoding efficiency of liquid-state imaging is approached. With given gradients, be they main field gradients in the case of MEPSI or gradients of the radiofrequency amplitude in the case of REPSI, therefore, a much better spatial resolution can be achieved than with other phase-encoding techniques. Theoretical treatments and test experiments are presented. © 1992.