re phasing of the u03c61 term ensues whereas the u03c62 term continues to increase at time t 1 a refocusing radio frequency pulse rf2 is emitted to the spins again under the influence of a slice selection gradient gs3 it thereby must be taken into consideration that this pulse as a result of a non ideal 180 u00b0 rotational angle not only reverses the existing cross magnetization but also initiates the generation of a stimulated echo the phase in the stimulated echo path is indicted with dots in fig1 in the primary echo path the phase initially increases with respect to the term u03c61 as well as with respect to the term u03c62 in the first half 3 of the slice selection gradient gs3 and is then inverted the phase relation for both terms u03c61 u03c62 remains present in the stimulated path at time t 2 a spin echo system s1 arises as a purely primary echo having the overall phase u03c6 s1 equ7 a further refocusing radio frequency pulse under the influence of a slice selection gradient gs4 follows at time t 3 here the phase relation is inverted not only in the primary echo path but also in the stimulated echo path with respect to the linear gradient terms as well as with respect to the quadratic terms a second spin echo s2 thus arises at time t 4 this second spin echo s2 and all following spin echoes represent a superimposition of primary and stimulated echoes with various phase relations the phase relation for the primary component referenced with the superscript 34 p 34.