Hyperechoes

TLDR

The authors introduce a hyperecho mechanism, a spin‑echo refocusing strategy that restores full magnetization coherence under arbitrary RF pulse sequences. The mechanism achieves this by re‑installing coherence and is applicable to gradient‑echo sequences and spin‑selection techniques. Initial experiments show that hyperecho formation can recover complete image intensity in RARE imaging using only a fraction of the RF power, enhances signal for tissues with T1 > T2 via stimulated echo pathways, and requires longer echo times to maintain identical T2 contrast. Published in Magn Reson Med 46:6‑12, 2001.

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 T(1) > T(2). For identical T(2) 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.