Carr-Purcell-Meiboom-Gill train times

Ti reports on fast dynamics on a timescale of ps-ns, whereas T2 relaxation depends on both fast and slower dynamics (ps-ns and xs-ms). The experimentally measured T2 relaxation times include an exchange contribution that can be measured by a Carr-Purcell-Meiboom-Gill (CPMG) pulse train (25, 26) or an effective spin-lock field (27-29). The combination of T2 and Tip measurements allows determination of the contribution of chemical exchange to the relaxation time. Eurthermore, relaxation dispersion experiments have been developed to measure slow time-scale xs-ms dynamic processes (30-35). 

Carr-Purcell-Meiboom-Gill (CPMG) experiment. An experiment wherein the net magnetization is allowed tipped into the xy plane, and subjected to a series (or train) of RF pulses and delays to refocus the net magnetization. Maintaining the net magnetization in the xy plane allows the measurement of the T2 relaxation time. 

Figure 7.22 The NMR-MOUSE (a) Schematic. The NMR sensor consists of an u-shaped permanent magnet with a solenoidal rf coil placed in the gap. (b) Photo of the NMR-MOUSE testing a tyre, (c) Example of a train of successive Hahn echoes generated according to Carr, Purcell, Meiboom and Gill (CPMG echo train) for carbon-black filled SBR measured by the NMR-MOUSE. The time constant of the echo-envelope defines T...

The CPMG pulse sequence was first proposed by Carr and Purcell (1954) and modified by Meiboom and Gill (1958). It is composed of a P90 pulse and a train of Pjgo pulses as P tP/go 2TP,go 2TP7go 2x, etc. (Figure 7.16). The T value is, by NMR convention, the time between the middle of the initial P90 and the middle of the next pulse of the sequence, as in Figure 7.16. ... 

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