Full Recovery Time
INCORRECT. The T2* relaxation time describes the decay of Mxy, not the recovery of Mz.
Example recovery curve of Mz (time constant T1).
CORRECT. After a 90° rotation of M0, we must wait 5·T1. (T1 is the longitudinal relaxation time of the tissue in question.)
Magnitude of Mz is given by
Mz(t) = M0(1-exp(-t/T1))
At t=5·T1, this equals
Mz(t) = M0(1-exp(-5
Mz(t) = 0.993·M0
i.e. 99.3% recovery has occurred. Even after a 180° RF pulse, 98.7% recovery has occurred at t=5·T1.
Note that longitudinal recovery follows an exponential shape and thus is asymptotic to the equilibrium value (M0). So in effect you could say that the (classically described) spin system never returns to equilibrium!
INCORRECT. Although ten seconds is long enough for even the slowest recovering tissues in MRI (longest T1), this is not the rule.