Automated production of [¹¹C]butyrate for keto body PET imaging

The report describes an updated, fully automated method for the production of [¹¹C]butyrate, validated for use in clinical studies. A commercially available GE Tracerlab FX_M synthesis module was reconfigured to allow for air-free introduction of n-propyl magnesium chloride and to incorporate Sep-Pak cartridges to simplify and shorten the purification process, as compared to purifying the product using traditional HPLC. The method takes 20 min from end-of-bombardment and reliably produces injectable doses of [¹¹C]butyrate (8029 ± 1628 MBq (217 ± 44 mCi), 14 % radiochemical yield based on [¹¹C]CO_2, non-decay corrected) in high radiochemical purity (>97 %), n = 3. With radiotracer in hand, PET scans of rats confirmed uptake of the radiopharmaceutical in the brain. Rat biodistribution data was obtained and used in conjunction with OLINDA software to determine an estimated human total body effective dose of 3.20 × 10^-3 mSv/MBq (1.19 × 10^-2 rem/mCi), along with preliminary rodent PET imaging that confirmed brain uptake. Lastly, our first human [¹¹C]butyrate PET studies using a dynamic bolus injection technique (n = 5), with a graphical Logan analysis using a white matter reference region, confirmed good radiotracer uptake in the brain and with relatively more prominent uptake in the cerebellar hemispheres, vermis, cingulum cortex and the thalami.