Orbital drainage of different sizes of colloids in rabbits: a dynamic scintigraphic study.

Purpose: To investigate the drainage patterns of radiolabeled colloids of different sizes injected into the orbital cavity in an animal model.

Methods: Twenty-one orbits of 11 rabbits were included in the study. In group 1, human serum macroaggregates with particle sizes of 10 to 100 microm, labeled with 10 mL of 1480 MBq (40 mCi) technetium pertechnetate Tc 99m (99mTc), were used. In group 2, human serum albumin colloidal particles with particle sizes of 50 to 80 nm, labeled with 5 mL of 740 MBq (20 mCi) 99mTc, were used. In group 3, colloidal tin with particle sizes of 300 to 600 nm, labeled with 9 mL of 1665 MBq (45 mCi) 99mTc, were used. The dynamic acquisition of liver for 10 minutes (120 frames for 5 seconds) in a 128 x 128 matrix was acquired immediately after intraorbital injection and at the end of the second hour.

Results: The liver in groups 2 and 3 and the lung in group 1 were visualized in 10 seconds or less in six, five, and four rabbits, respectively. The injected activity persisted in the orbits in varying percentages in all rabbits at the end of acquisition.

Conclusions: Intraorbital injections have a great potential for systemic absorption and should not be considered as local pharmaceutical administration.