Hyperechoes

A novel spin-echo-based refocusing strategy called a hyperecho mechanism is introduced by which the full coherence of magnetization submitted to a seq uence of arbitrary RF pulses can be reinstalled. First implementations illu strate the potential of hyperecho formation- especially for Rapid Acquisiti on with Relaxation Enhancement (RARE) imaging, in which the full image inte nsify can be retrieved using a fraction of the RF power of a fully refocuse d sequence, The contribution of stimulated echo pathways to the hyperecho s ignal leads to an increased signal intensity at a given refocusing time for tissues with T-1 > T-2. For identical T-2 contrast, longer echo times have to be used. Further possibilities far using hyperechoes in gradient-echo s equences and for spin selection are discussed. (C) 2001 Wiley-Liss, Inc.