PET Molecular Probes for Neuroinflammation in Neurodegenerative Diseases: Progress and Prospects

Neuroinflammation is a central pathological process underlying neurodegenerative diseases, including Alzheimer disease (AD), Parkinson disease (PD), and amyotrophic lateral sclerosis. Positron emission tomography (PET) molecular probes now enable the noninvasive, quantitative visualization of neuroinflammatory processes in the living brain. This review surveys recent advances in PET probes targeting microglial activation markers─including the 18 kDa translocator protein (TSPO), the purinergic P2X7 receptor (P2X7R), colony-stimulating factor 1 receptor (CSF1R), and sphingosine-1-phosphate receptor 1 (S1PR1)─as well as astrocyte reactivity markers such as monoamine oxidase B (MAO-B) and imidazoline-2 binding sites (I2BS). I discuss the evolution from first-generation TSPO ligands to polymorphism-insensitive third-generation tracers, highlight emerging targets beyond TSPO, and evaluate the translational value of these probes for early diagnosis, disease staging, treatment monitoring, and drug development. Current challenges-including limited cellular specificity, genetic polymorphism effects, quantification difficulties, and clinical accessibility barriers─are analyzed alongside promising solutions. Integrating neuroinflammation PET into multimodal biomarker frameworks will be essential for advancing precision medicine in neurodegenerative diseases.