A potential lung perfusion imaging agent of synthetic origin

Abstract

Abstract99mTc‐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‐pertechnetate (⩽2 GBq) in saline (1–4 ml), and the radioactive contents were mixed by rotation (40 rpm) in a syringe at room temperature for 30–180 min. 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 efficiency (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 µm. 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 min. Results from the quantitative organ assays gave 88±1% tracer in the lungs, and less than 10% in the liver and spleen. The images showed excellent, uniform lung uptake with minimal interference from liver and spleen to the lower regions of right and left lobes. In conclusion, the synthetic radiopharmaceutical 99mTc–tin 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 good potential for use as a perfusion imaging agent in lung scans. Copyright © 2006 John Wiley & Sons, Ltd.