The invention provides compounds of formula (I) radiolabelled with 18F, 123I, 76Br, 124I or 75Br and salts thereof, and a method of imaging translocator protein (18 kDa) (TSPO) in a subject comprising administering a compound of formula (I) radiolabelled with 18F, 123I, 76Br, 124I or 75 Br or a pharmaceutically acceptable salt thereof. The invention further provides fluoro-substituted compounds of formula (II) and salts thereof, and a method of treating a neurodegenerative disorder, inflammation or anxiety in a subject comprising administering a compound of formula (II) or a pharmaceutically acceptable salt thereof.
