Neurodegenerative diseases including Alzheimer's disease (AD) are common causes of death in developed countries. Neurofibrillary tangles composed of hyperphosphorylated tau proteins are one of pathological hallmarks of neurodegenerative diseases. Neurofibrillary lesions strongly corelated with cognitive deficits in neurodegenerative diseases. Recent advance of in vivo imaging techniques has opened a window to capture a real time event during brain aging. Our group recently established the positron emission tomography (PET) imaging of tau lesions using 18FPM-PBB3 PET tracer to diagnose not only AD also non-AD tauopathies (e.g., Progressive supranuclear palsy, Corticobasal degeneration, and Chronic traumatic encephalopathy). In addition to clinical research, this tracer is a feasible to visualize tau pathologies in mouse models of tauopathy. Therefore, tau PET imaging is a translatable research tool between human and mouse tauopathies. Currently, investigating early detection of tauopathies during a transition from physiological tau proteins to pathological tau aggregates is one of our research achievements.