Coherence and Interference in Ultrafast RARE Experiments

The mechanisms of echo formation in U-FLARE experiments are described and the conditions for interference between echo pathways formulated. Three possible solutions to this problem are identified and demonstrated, namely coherent U-FLARE, in which all echoes add constructively, displaced U-FLARE, in which one echo parity is shifted out of the acquisition window, and phase-cycled U-FLARE, in which a two-step phase cycle is used to differentiate between echoes according to their parity. The relative merits and applications of each are discussed.