Patent ID: 7799947

Claim:
A compound of formula (Ia) or a salt thereof, wherein R 1 is selected from hydrogen, C 1-6 alkyl, C 2-6 alkenyl, C 2-6 alkynyl, C 5-12 aryl, and C 5-12 hetaryl; R 2 is selected from hydrogen, C 1-6 alkyl, C 2-6 alkenyl, C 2-6 alkynyl, C 5-12 aryl, and C 5-12 hetaryl; L is C 1-6 alkylene; one or two of the groups R 3 to R 7 are independently selected from halo, C 1-6 alkyl, C 1-6 haloalkyl, C 1-6 alkoxy, C 1-6 haloalkoxy and the remaining groups R 3 to R 7 are hydrogen; two, three, or four of the groups R 8 to R 12 are independently selected from halo, C 1-6 alkyl, C 1-6 haloalkyl, C 1-6 alkoxy, C 1-6 haloalkoxy and the remaining groups R 8 to R 12 are hydrogen and at least one of the groups R 8 to R 12 comprises a radiolabel selected from 11 C, 18 F, 123 I, 124 I, and 122 I.