Composition for diagnosing amyloid-related diseases

A composition for diagnosing amyloid-related diseases, which comprises a compound represented by the following general formula (Ia) or a pharmaceutically acceptable salt thereof:

• wherein each of R1, R2, R3, and R4 independently represents a hydrogen atom, a halogen atom, a hydroxyl group, a carboxyl group, a sulfone group, a dimethylamino group, a methylamino group, an amino group, a nitro group, an alkyl group containing 1 to 4 carbon atoms, an alkoxy group containing 1 to 4 carbon atoms, a 2-fluoroethoxy group, a 3-fluoropropoxy group, a 4-fluorobutoxy group, or a 5-fluoropentoxy group;
• R5 represents an aryl group that is optionally substituted with one or two or more substituents selected from the following substituent group A, an aromatic heterocyclic group that is optionally substituted with one or two or more substituents selected from the following substituent group A, or a group represented by the formula:
• —CH═CH—R6 (wherein R6 represents an aryl group that is optionally substituted with one or two or more substituents selected from the following substituent group A, or an aromatic heterocyclic group that is optionally substituted with one or two or more substituents selected from the following substituent group A);
• and the substituent group A is a group consisting of a halogen atom, a hydroxyl group, a carboxyl group, a sulfone group, a dimethylamino group, a methylamino group, an amino group, a nitro group, an alkyl group containing 1 to 4 carbon atoms, and an alkoxy group containing 1 to 4 carbon atoms;
• wherein the compound represented by general formula (Ia) is labeled with a radionuclide.