Potential lung perfusion imaging agent of synthetic origin

99mTc-labelled macroaggregated albumin (MAA) is the radiopharmaceutical routinely used for perfusion lung scans. However MAA formulations contain excipients of biological origin, that may potentially cause allergic hypersensitivity in patients. The aim of this study was to prepare a non-biological lung imaging agent, with physiological uptake based on a mechanism of colloid localisation in the pulmonary vasculature. To a frozen stannous fluoride cold kit (RAH Radiopharmacy) was added 99mTc-pcrtcchnetate (<2 GBq) in saline (1-4 mL), and the radioactive contents were mixed by rotation (90 rpm) at room temperature for 30-180 minutes. The preparative conditions were varied to control particle growth by: the addition of metal ions, halide ions, or oxidants; different mixing times; and temperatures. The 99mTc-products were analysed for % radiolabelling efficiciency (RE), radioactive particle size distribution (RPSD). qualitative and quantitative rat biodistribution studies. Results indicated that all radioactive particles were formed with >99% RE. and 1-47% were >8 um. The optimum radiotracer formulation containing the highest proportion of the largest particles, was prepared by mixing SnF2 and 99mTc-pertechnetate with a low [Na+] at room temperature for 50 minutes. Results from the quantitative organ assays gave 88+/-1% tracer in the lungs. 7+/-l% in the liver and l+/-0% in the spleen. The images showed excellent lung uptake with minimal interference from liver and spleen to the lower regions of right and left lobes. In conclusion, the synthetic radiopharmaceutical 99mTc-stan-nous fluoride colloid can be prepared with a large particle size, from a commercially available cold kit in a simple and practical manner, and it has high potential for use as a perfusion imaging agent in lung scans