Radiotracer compositions

A composition which comprises an imaging agent of Formula (I) together with one or more non-radioactive aryl derivatives of Formula (II):

• wherein:
• BTM is a biological targeting moiety;
• L1 is a synthetic linker group of formula -(A)m- wherein each A is independently —CR2—, —CR═CR—, —C≡C—, —CR2CO2—, —CO2CR2—, —NRCO—, —CONR—, —CR═N—O—, —NR(C═O)NR—, —NR(C═S)NR—, —SO2NR—, —NRSO2—, —CR2OCR2—, —CR2SCR2—, —CR2NRCR2—, a C4-8 cycloheteroalkylene group, a C4-8 cycloalkylene group, —Ar—, —NR—Ar—, —O—Ar—, —Ar—(CO)—, an amino acid, a sugar or a monodisperse polyethyleneglycol (PEG) building block, wherein each Ar is independently a C5-12 arylene group, or a C3-12 heteroarylene group;
• each R is independently chosen from H, C1-4 alkyl, C2-4 alkenyl, C2-4 alkynyl, C1-4 alkoxyalkyl or C1-4 hydroxyalkyl;
• m is an integer of value 1 to 20;
• Y is —O— or —NH—;
• X1 is 18F, —O(CH2)q18F or —OCH2—CH(OH)—CH218F, wherein q is 2, 3 or 4;
• X2 is —N+(CH3)3, —N(CH3)2, —OCH3, H, —CH3, —OH, —SCH3, —OC6H4CHO or 19F;
• wherein BTM, L1 and Y are the same in Formula (I) and (II);
• and wherein the total concentration of derivatives of Formula (II) present in the composition is less than 150 μg/mL.