Background <p>[¹¹C]TGN-020 has been developed as a positron emission tomography (PET) tracer for imaging aquaporin-4 (AQP4) in the brain and used in clinical studies. Previously, [¹¹C]TGN-020 was synthesized through the acylation of [¹¹C]nicotinic acid, produced by the reaction of 3-bromopyridine and <i>n</i>-butyllithium with [¹¹C]CO₂, with 2-amino-1,3,4-thiadiazole. In this study, to enhance the automated radiosynthesis efficiency of [¹¹C]TGN-020, we optimized its radiosynthesis procedure using our in-house developed ¹¹C-labeling synthesizer.</p> Results <p>[¹¹C]TGN-020 was synthesized via direct [¹¹C]CO₂ fixation using <i>n</i>-butyllithium and 3-bromopyridine in tetrahydrofuran, followed by treatment of lithium [¹¹C]nicotinic acetate with isobutyl chloroformate and subsequent acylation with 2-amino-1,3,4-thiadiazole in the presence of <i>N</i>,<i>N</i>-diisopropylethylamine. The optimized process significantly improved the radiosynthesis efficiency of [¹¹C]TGN-020, achieving a high radiochemical yield based on [¹¹C]CO₂ (610‒1700&#xa0;MBq, 2.8 ± 0.7%) at the end of synthesis (<i>n</i> = 12) and molar activity (<i>A</i>_m) of 160–360&#xa0;GBq/μmol at the end of synthesis (<i>n</i> = 5). The radiosynthesis time and radiochemical purity were approximately 60&#xa0;min and &gt; 95% (<i>n</i> = 12), respectively. PET studies based on [¹¹C]TGN-020 with different <i>A</i>_m values were performed using healthy rats. The radioactive uptake of [¹¹C]TGN-020 with high <i>A</i>_m in the cerebral cortex was slightly higher than that with low <i>A</i>_m.</p> Conclusions <p>[¹¹C]TGN-020 with high <i>A</i>_m was obtained in reproducible radiochemical yield. Overall, the proposed optimization process for the radiosynthesis of [¹¹C]TGN-020 can facilitate its application as a PET radiopharmaceutical for clinical use.</p>