⁶⁸ Ga-Ca-phytate particles: A potential lung perfusion agent of synthetic origin prepared in a cold kit format

The objective of this study was to investigate the radiosynthesis of ⁶⁸ Ga-Ca-phytate particles and then characterize the formulation for radiochemical purity, radioactive particle size distribution, and biodistribution in normal rats. This radiotracer was prepared using a commercial phytate cold kit after reconstitution with saline, ⁶⁸ Ga-chloride generator eluent, calcium chloride, and air, then heating at 100°C for 30 minutes to achieve 99% radiochemical purity of ⁶⁸ Ga-particles that were 21% 3-5 μm, 8% 5-15 μm, and 71% >15 μm in diameter. This optimal formulation was stable for 2 hours at room temperature. Intravenous administration of ⁶⁸ Ga-particles in rats resulted in an uptake of 93% in the lungs, 4% in the liver plus spleen, and 3% in the carcass after 20 minutes. Two-thirds of the carcass activity was radioactive blood, likely to be ⁶⁸ Ga-transferrin. The positron emission tomography image was superior than the ^99m Tc-MAA image because it displayed high lung uptake against a low background. Low uptake by the liver, spleen did not interfere with the diagnostic quality, and faint activity in the submandibular (salivary) glands was due to ⁶⁸ Ga-transferrin. The preclinical data so far indicate that ⁶⁸ Ga-Ca-phytate particles have good potential as a lung perfusion imaging agent.