Pet imaging agents

A method for quantification of the percentage or change in percentage of unbound autotaxin in a subject after administration of a ligand binding to autotaxin, comprising:

• (i) administering a radiolabeled compound of formula (I)
• wherein R is halogen, —CF3, —OCF3, —OCH3, —CH3 or CN;
• A is a pyridinyl or oxazolyl group substituted with at least one substituent selected from halo-(C1-6-alkyl), halo-(C1-3-alkyl)oxy(C2-4-alkyl), or halo-(C1-3-alkyl)oxy(C2-4-alkyl)oxy(C2-4-alkyl), and
• wherein the carbon atom numbered “1” is chosen from 11C, 12C, or 14C;
• and compound comprises at least one 3H, 18F, 19F, 123I, 124I, 125I, 127I or 131I, or a pharmaceutically acceptable salt thereof, to said subject;
• (ii) detecting uptake of said radiolabeled compound administered in step (i) by in vivo PET or SPECT imaging;
• (iii) allowing a suitable amount of time to pass such that the compound administered in step (i) has radioactively decayed;
• (iv) administering of an effective amount of either (a) a non-radiolabelled autotaxin ligand, or (b) a non-radiolabelled agent influencing the endogenous level of autotaxin substrates, with contemporaneous administration of a radiolabeled compound of formula (I) or a pharmaceutically acceptable salt thereof as defined in step (i);
• and
• (v) detecting uptake of said compound of formula (I) administered in step (iv) by in vivo PET or SPECT imaging.