Advances in CNS imaging agents: Focus on PET and SPECT tracers in experimental and clinical use

The physiological functioning of the brain is not well-known in current day medicine and the pathologies of many neuropsychiatric disorders are still not yet fully understood. With our aging population and better life expectancies, it has become imperative to find better biomarkers for disease progression as well as receptor target engagements. In the last decade, these major advances in the field of molecular CNS imaging have been made available with tools such as functional magnetic resonance imaging (fMRI), magnetic resonance spectroscopy (MRS), single photon emission computed tomography (SPECT), and neuroreceptor-targeted positron emission tomography (PET). These tools have given researchers, pharmaceutical companies, and clinical physicians a better method of understanding CNS dysfunctions, and the ability to employ improved therapeutic agents. This review is intended to provide an update on brain imaging agents that are currently used in clinical and translational research toward treatment of CNS disorders. The review begins with amyloid and tau imaging, the former of which has at least three [¹⁸F] agents that have been recently approved and will soon be available for clinical use for specific indications in the USA and elsewhere. Other prevalent PET and SPECT neurotransmitter system agents, including those newly US FDA-approved imaging agents related to the dopaminergic system, are included. A review of both mature and potentially growing PET imaging agents, including those targeting serotonin and opiate receptor systems, is also provided.