Modified technique for manual synthesis of 68Ga-Citrate with high radiochemical purity

Objectives 67Ga-citrate is an established agent for imaging infection and inflammation. 68Ga being a short lived positron emitter (t1/2- 68min) has better imaging characteristics including high spatial resolution and quantitative features of PET compared with single photon emission tomography. The aim of this study was to synthesize 68Ga-citrate, with high radiochemical purity, as PET imaging agent for infection.

Methods The synthesis of 68Ga-citrate was performed manually on a semi automatic labeling module. Before starting the synthesis, the entire system was cleaned using ethanol, air, water and then air to avoid bacterial and pyrogen contamination. 68Ge/68Ga generator was eluted by 9mL of 0.1N HCl. Eluate was absorbed on cation exchange resin. 1 ml of Washing solution (0.15mol/l HCl in 80/20% acetone/water solution) was passed through resin which removed the impurities and was discarded. 0.5 ml Elution solution (0.05mol/l HCl in 98/2% acetone/water solution) was passed through resin which eluted 68Ga into reagent vessel already containing 3-4 ml sterile water. Reagent vessel was then heated at 90 degree celsius for 10 minutes. Solution from reagent vessel was aspirated through Sep-Pak Accell column (already activated with 2ml sterile water) which retained 68Ga. 1 ml Sodium citrate (0.08 mol/l) was passed through the column and 68Ga-citrate was obtained. It was passed through millipore filter. pH was measured using the standard pH meter.

Results It was found to be 6-7. Radiochemical purity was determined using ITLC-SG strip. Methanol/glacial acetic acid (9:1) was used as mobile phase. Rf value of 68Ga is 0 and Rf value of 68Ga-citrate is 1. Radiochemical purity of the labelled solution was found to be more than 98%. The product was found to be sterile and pyrogen free.

Conclusions 68Ga-citrate synthesized by this method had high radiochemical purity and was found to be suitable for human administration