ABSTRACT
The T1 and T2 relaxation processes are governed by uctuating magnetic elds associated with the molecular motions; both relaxations are assumed to be rst-order processes. T1 relaxation is an enthalpic process, because this process involves energy absorption. A temporal evolution of a transversal relaxation (T2) process differs from the longitudinal
foundation. It is equivalent to the loss of the coherence phase between individual magnetic moments on precession, and results in an increase in entropy (Gidley and Bociek, 1985; Cheng, 1991; Stejskal and Memory, 1994; Bovey and Mirau, 1996; Silva et al., 2002; Souza and Tavares, 2002; Tang and Hills, 2003; Tavares, 2003; Conte, Spaccini, and Piccolo, 2004; Nascimento, Tavares, and Nascimento, 2007; Costa et al., 2007a,b). These relaxation times are measured in distinct ways: T1 is determined through an inversion-recovery pulse sequence, occurring along the z axis and depending on a strong magnetic eld, the MHz frequency observation scale, whereas T2 is determined by pulse sequence, occurring in the xy plane and is also dependent on the external magnetic eld.
