A study of radiogallium aqueous chemistry: in vitro and in vivo characterisation of 67Ga‐hydrolysed‐stannous fluoride particles

The objective of this study was to explore the aqueous chemistry of gallium using ⁶⁷Ga‐chloride starting material, by radiolabelling hydrolysed(h)‐stannous fluoride particles and then characterising the optimal formulation for radiochemical purity (RCP) and radioactive particle size distribution in vitro. The pilot reactions determined stannous fluoride was added to ⁶⁷Ga‐acetate under nitrogen and then heated at 100 °C for 20 min to achieve ≥95% RCP and ⁶⁷Ga‐particles were >3 µm in diameter. A high radioactive concentration of ⁶⁷Ga‐h‐SnF₂ particles could be prepared similarly in ≥97% RCP with 74% as 3–5 µm and 26% >5 µm in diameter. The latter formulation had larger particles than ^99mTc‐h‐SnF₂ colloid (96% of 1–3 µm), and it resulted in a rat biodistribution of 41% in the lungs, 41% in the liver plus spleen and 18% in the carcass at 20 min after injection. The carcass activity was attributed to bone marrow and some ⁶⁷Ga‐transferrin formed in blood. Isolated mixed human leucocytes were radiolabelled with ⁶⁷Ga‐h‐SnF₂ particles in 100% efficiency, and the ⁶⁷Ga‐cells did not release soluble ⁶⁷Ga³⁺ at room temperature over 3 h. The ⁶⁷Ga‐h‐SnF₂ particle formulation could find a use in labelling leucocyte cells for in vivo homing studies when delayed animal imaging is required.