Abstract: The present invention relates to a diagnostic substance, containing at least one complex of lipophilic anions and metal ions, wherein the lipophilic anions are selected from the group comprising: triethylene tetramine dihydrochloride (TETA), ethyl cysteinate dimer (ECD), methoxyisobutylisonitrile (MIBI), HMPAO (d,l-hexamethylpropylene aminoxime), ethylenediamine N,N,N?,N?-tetraacetanilide (EDTAN), dimethyldithiocarbamate (DMC) and diethyldithiocarbamate (DDC) and glycine N,N?-[1,2-ethanediylbis(oxy-2,1-phenylene)]bis [N-(carboxymethyl)-1,1?-bis[2-(octadecyloxy)ethyl]ester (DP-109), and wherein the metal ions are selected from the group comprising thallium isotopes, lead isotopes, cobalt isotopes and manganese isotopes, together with solvents, adjuvants and/or vehicles. The diagnostic substance is used for investigating metabolic processes in the brain and/or central nervous system (CNS).