THK5351 exhibits favorable pharmacokinetics and no defluorination in mice. ¹⁸F-THK5351 enters the brain immediately after intravenous injection and shows a fast washout from the brain. At 0.1 and 1 mg/kg, no animals died and no treatment-related changes in any animal are noted in clinical observations, body weight measurement, and pathologic examination^[1]. Autoradiography in the brain sections of patients with PSP demonstrates [³H]THK-5351 binding to tau deposits with a high selectivity. Although patients with PSP exhibits no remarkable [¹⁸F]THK-5351 retention in the temporal cortex, significantly higher tracer retention is observed in the globus pallidus and midbrain^[2].