Hyperechoes

Abstract

A novel spin‐echo‐based refocusing strategy called a hyperecho mechanism is introduced by which the full coherence of magnetization submitted to a sequence of arbitrary RF pulses can be reinstalled. First implementations illustrate the potential of hyperecho formation—especially for Rapid Acquisition with Relaxation Enhancement (RARE) imaging, in which the full image intensity can be retrieved using a fraction of the RF power of a fully refocused sequence. The contribution of stimulated echo pathways to the hyperecho signal leads to an increased signal intensity at a given refocusing time for tissues with T₁ > T₂. For identical T₂ contrast, longer echo times have to be used. Further possibilities for using hyperechoes in gradient‐echo sequences and for spin selection are discussed. Magn Reson Med 46:6–12, 2001.