31P Magnetization Inversion Transfer Study of Three-Site PCr←→ATP←→Pi Exchange System in Human Brain at 7T

Fei Du¹, Wei Chen¹

Magnetization inversion transfer (IT) NMR approach has been used for the studies of creatine kinase (CK) in human and animals. To date, IT approach was based on the two-site chemical exchange model and ATPase reaction was ignored. However, in principle, the chemical reactions of CK and ATPase constitute a three-site chemically coupled spin system i.e. PCr&[larr]&[rarr]ATP&[larr]&[rarr]Pi. In this work, we investigated the kinetics involving PCr&[larr]&[rarr]ATP&[larr]&[rarr]Pi in the human brain at 7T using the three-site chemical exchange model with full matrix Bloch equation analysis developed by our lab, and compared the results derived from the three-site and two-site chemical exchange model, respectively. This study reveals that CK reaction can be approximately treated as a two-site chemical exchange system when the ATPase reaction pool is relatively small. However, ATPase reaction must be treated as a three-site chemical reaction system in order to accurately measure its chemical reaction fluxes in the brain.