A sequence of pulses used for spin-echo experiments in nuclear magnetic resonance (NMR) in which the initial pulse is 90° followed by a series of 180° pulses. A CPMG sequence is designed so that the spin echoes die away exponentially with time. Spin-spin relaxation occurs characterized by a time constant T2, which can be determined from the decay signal. This sequence was devised by Herman Carr and Edward Purcell in 1954 and modified by Saul Meiboom and David Gill in 1958.