Abstract: STUDIES OF TECHNETIUM CHEMISTRY Ⅶ.A STUDY ON THE RETENTION MECHANISM OF~99Tc~m-BRAIN IMAGINGSTU ZHUDE ;MENG ZHAOXING ;LIU BOLI（Department of Chemistry，Beijing Normal University,100875）ABSTRACT The retention mechanism of the brain imagings belonging to analogues of ~99Tc~m-PnAO and~99Tc~M-BAT is studied with the CNDO／ 2 methed of quantum chemistry and molecular gragphicmethed. The results show that the retention of these imagings in the brain is prqportional to the（E_LUMO－E_HOMO）of molecular orbitals of Tc-complexes，Using this index the retention mecha-nism of ~99Tc~m-brain imaging attacked by the glutanthione－SH could be illustrated reasonally.The results give some theoretical informations for designing new brain imaging molecules anduseful suggestion in improving and making brain imaging drugs.Key words~99Tc~m-brain imaging CNDO／ 2 method ~99Tc~m-PnAO ~99Tc~m-BAT