E. Baguet et C. Roby, FAST INVERSION-RECOVERY MEASUREMENTS IN THE PRESENCE OF A SATURATING FIELD FOR A 2-SPIN SYSTEM IN CHEMICAL-EXCHANGE, Journal of magnetic resonance. Series A, 108(2), 1994, pp. 189-195
This work shows that a fast inversion-recovery sequence reliably measu
res longitudinal relaxation rates with slow chemical exchange in the p
resence of a saturating RF field. First, the coefficients of the compl
ete set of Bloch equations, obtained after a base transformation in th
e rotating frame, have been calculated for a two-site chemical-exchang
e spin system that is continuously irradiated. Then, with approximatio
ns, these results were used to analyze the usual case having one speci
es on resonance with a large resonance offset for the other one. This
led to the expression of the components parallel to the respective eff
ective magnetic fields of the two exchanging magnetizations as a funct
ion of time. The analysis of the time courses of the magnetizations du
ring the inversion-recovery sequence has been completed. The conclusio
n is drawn that the relaxation delay can be reduced to its minimum val
ue, annulling the transverse magnetizations without affecting the dete
rmination of the effective longitudinal relaxation time. The theoretic
al analysis has been confirmed by measurements relative to the exchang
ing protons of the N,N-dimethylacetamide molecule undergoing hindered
rotation around the amide bond at 40 degrees C. (C) 1994 Academic Pres
s, Inc.