[191mIr: distribution and retention in animal experiments]

Ultrashort-lived tracer 191mIr (T1/2 = 4.92 s) can be obtained with a high yield from an 191Os/191mIr generator with a low 191Os breakthrough. It was eluated directly into the tail veins of Wistar rats. These animals were imaged dynamically (five frames/s) up to 40 s. The measurement was repeated five times on each animal. The whole-body retention and biodistribution of 191Os was studied by sacrificing the rats at one and four days, respectively, after injection. The activity retained was highest in the kidneys and the spleen, followed by the muscles and the liver. These values indicate that the breakthrough is by no means dangerous and that investigations can be repeated immediately with a radiation exposure of no significance. Furthermore, all investigations in the same animal were reproducible, suggesting that 191mIr might be a good tracer for nuclear angiograms.