Patent ID: 8022075

Claim:
A compound represented by formula (I): wherein X 1 is an optionally substituted benzothiazolyl, benzoxazolyl, imidazopyridyl, imidazopyrimidyl, or benzimidazolyl group, wherein when X 1 is an imidazopyridyl the imidazopyridyl is substituted with one to three substituents and said substituent is selected from the group consisting of a halogen atom, a hydroxy group, an alkyl group, an alkyltin group, a halogenoalkyl group, a halogenoalkylcarbonylamino group, and a chelate-forming group, X 2 represents a hydrogen atom, a halogen atom, or a chelate-forming group; ring A represents a benzene ring or a pyridine ring; and ring B represents an optionally substituted 5-membered aromatic heterocyclic group which is bonded to the benzene ring or the pyridine ring via a carbon atom of ring B, wherein X 1 and ring B are in a para position, and wherein X 1 , X 2 , or ring B has at least one radioactive nuclide, a salt thereof, or a transition metal coordination compound of any of these.