The intensities of the Hahn spin echoes produced by a series of out of the bore of a superconducting magnet there is a huge 90Њ pulses applied to a sample in large static field gradients are gradient (ú1 T m 01 ), which is orders of magnitude larger calculated. Static gradients are important because they can be very than any of the normal pulsed field gradients used. STRAFI much larger than pulsed field gradients and echoes can be collected has the great advantage that the strong gradients dominate without recovery time problems. One application is for imaging almost all the other terms in the Hamiltonian, including nuusing the stray field of a magnet (STRAFI). The high strength of clear dipolar couplings, electron-nucleus interactions, and the gradients in the stray field allows the imaging of solids and quadrupole couplings in solids. Because the gradients are other systems with very broad lines. In an imaging pulse sequence static, there are no gradient transients and echoes can be consisting of pulses with phases 90 Њ x -(90Њ y ) n , the echoes (calcucollected within microseconds after the pulse. This allows lated in the absence of spin relaxation) have relative intensities of imaging of samples with very broad lines. The main disad-1: 3 2 : 3 2 :1 1 8 :1 1 8 , etc., whereas a 90Њ x -(90Њ x ) n pulse sequence produces
vantage is that STRAFI is a sensitive-plane technique. The echoes which have relative intensities of 1: 1 2 :0 1 2 :0 3 8 : 3 8 , etc. A simple way of calculating these intensities is presented, using an irreducsample is imaged by moving it through the sensitive plane ible tensor approach that has been termed the superspin formaland applying a back-projection technique. Almost any mateism. These numbers are for infinitely short pulses on resonance and rial can be imaged with this simple technique.
without relaxation or diffusion, but the extension to real systems is
In the course of experiments with the STRAFI technique, also discussed. In particular, it is shown that the attenuation down echo trains were generated by a series of 90Њ pulses, with the echo train is due to a varying contribution from both T 1 and each echo being acquired until the signal had decayed. Both T 2 processes, as well as diffusion. With long T 1 's and slow diffua 90Њ x -(90Њ x ) n sequence (top, Fig. 1) and the 90Њ x -(90Њ y ) n sion, the decay of the echoes approximates T 2 . ᭧ 1996 Academic sequence (bottom, Fig. 1) were used. The resulting 1D im-Press, Inc.
ages have been published elsewhere (9). The plots in Fig. 1 were made from a series of ''lines,'' each line being a compressed plot of a complete spin-echo train. The top im-