Effect of off-resonance on T saturation recovery measurement in inhomogeneous fields.

Saturation-recovery measurements with Carr-Purcell-Meiboom-Gill sequences are commonly employed to measure the longitudinal relaxation time constant, T, in grossly inhomogeneous fields. We show that in general the off-resonant effect generates unexpected extra signals in the T measurement. In the present study, we derive a modified T kernel that accounts for this off-resonance effect quantitatively. The new kernel has been tested with numerical simulations and experiments, and excellent agreement is found.