The dynamics of spin system coupled by chemical exchange between two sites with different chemical shifts during periodic radiofrequency (RF) irradiation was here investigated. When the instantaneous π-flip of effective frequency during the course of frequency sweep was applied, a significant increase of exchange-induced relaxation rate constants was observed for small tip angle of magnetization in the laboratory frame of reference. This increase of the rate constants corresponds to the side bands generated by the periodic irradiation during the RF pulses. The exchange - induced relaxation rate constants depend on the exchange conditions, the RF power and the irradiation period. The described phenomenon promises applications for studying protein dynamics and for generating exchange specific relaxation contrasts in MRI.
Bibliographical noteFunding Information:
The authors would like to thank following funding sources for financial support Instrumentarium Science Foundation (HL) , EU H2020 Marie Skłodowska RISE project #691110 (MICROBRADAM), Academy of Finland grants #275453 and #298007 , NIH grants U01-NS103569 , 1R01AG055591 , BTRC , P41 EB015894 , P30 NS057091 . SM was supported by Fulbright-Saastamoinen Foundation Grant in Health and Environmental Science.
- Bloch - McConnell equations
- Chemical exchange
- Periodic RF irradiation