At this point the reading gradient of opposite polarity is applied, so as to compensate for the effect of the disparity gradient. When the area of the reading gradient is equal to that of the mismatching gradient, the spins will have a coherent new phase (except for the effects of T2* relaxation), and therefore a signal will be detectable again. This signal takes the name of echo or more specifically of gradient echo signal, because it is produced by rephasing due to a gradient (unlike the spin echo signal whose rephasing is due to a radiofrequency pulse).