THK5351 is primarily used in medical imaging, particularly in positron emission tomography (PET) scans for the diagnosis and study of neurodegenerative diseases. It is a radiotracer that binds to tau protein aggregates, which are associated with conditions like Alzheimer's disease. This allows for the visualization and quantification of tau pathology in the brain, aiding in early diagnosis and monitoring disease progression. Additionally, THK5351 helps researchers understand the underlying mechanisms of tau-related disorders and evaluate the efficacy of potential therapeutic interventions. Its application is crucial in advancing both clinical diagnostics and neuroscience research.