Apparent longitudinal relaxation in solutions with intermolecular dipolar interactions and slow chemical exchange

A modified CRAZED sequence with selective inversion before excitation was designed to investigate the longitudinal relaxation under the effects of slow chemical exchange and distant dipolar interactions in highly polarized spin systems. Analytical expressions for the apparent longitudinal relaxation time of such systems were derived from a combination of the dipolar field theory and product operator formalism. The result shows that the signal intensity follows a multi-exponential function of the inversion recovery time. Experimental results support the theoretical predictions.