Small-molecule ligands, amenable to positron emission tomography (PET) imaging of different types of neurodegenerative disease-associated amyloid deposits in the CNS of living patients, hold considerable promise for diagnostic purposes, as well as for monitoring disease progression and the effectiveness of treatments. The patent entitled 'Heterocyclic Compounds as Imaging Probes of Tau Pathology' (WO2013090497) discloses the identification of a novel class of tau imaging agents, the aminothienopyridazines. Selected compounds from this class are described that can stain selectively tau pathology in brain tissue sections. Moreover, examples of this class of compounds exhibit absorption, distribution, metabolism, excretion and pharmacokinetics (ADME-PK) properties that are appropriate for CNS PET ligands.