The spin echo effect was discovered by Erwin Hahn when he applied two successive 90° pulses separated by short time period, but detected a signal, the echo, when no pulse was applied. This phenomenon of spin echo was explained by Erwin Hahn in his 1950 paper,[1] and further developed by Carr and Purcell who pointed out the advantages of using a 180° refocusing pulse for the second pulse.[9] The pulse sequence may be better understood by breaking it down into the following steps: