Described herein are compounds, compositions, and methods for diagnosing and/or monitoring pathogenic disease using positron emission tomography. Also described are conjugates of the formula B-L-P, wherein B is a radical of a targeting agent selected from vitamin receptor binding ligands (such as folate), PSMA binding ligands, or PSMA inhibitors; L is a divalent linker comprising aspartic acid, lysine, or arginine, and P is a radical of an imaging agent or radiotherapy agent, such as a radionuclide or radionuclide containing group, or a radical of a compound capable of binding a radionuclide, such as a metal chelating group.