QUANTITATIVE STUDIES OF MAGNETIZATION-TRANSFER BY SELECTIVE EXCITATION AND T-1 RECOVERY

Water proton longitudinal relaxation has been measured in agar and cro ss-linked bovine serum albumin (BSA) using modified selective excitati on (Goldman-Shen and Edzes-Samulski) pulse sequences. The resulting re covery curves are fit to biexponentials, The fast recovery rate gives magnetization transfer (MT) information, which is complementary to tha t given by steady-state saturation methods, TL ris rate provides an es timate of the strength of the coupling of the immobile proton pool to the mobile proton pool. Near their optimal pulse power values, the Gol dman-Shen and Edzes-Samulski sequences give fast recovery rates that a gree with each other, However, these measured fast recovery rates are dependent on the pulse power, an effect not predicted by the coupled t wo-pool model. For 8% agar and 17% BSA, both methods (at optimal pulse powers) give rates in the neighborhoods of 210 and 64 Hz, respectivel y, The Goldman-Shen and Edzes-Samulski pulse sequences have several ad vantages over those techniques based on steady state saturation: no lo ng saturating pulses, shorter measurement time, and reduced necessity for making lineshape or fitting technique assumptions. The principle d isadvantages are smaller effects on the NMR signal, less complete char acterization of the MT system, and, in the case of the Goldman-Shen se quence, greater pulse power.