Clearance of 141Ce-labeled microspheres from blood and distribution in specific organs following intravenous and intraarterial administration in beagle dogs

The clearance of 141Ce-labeled polystyrene divinylbenzene microspheres in the 3–12-μm diameter size range following intravascular administration was found to be size dependent, with the larger spheres clearing the circulation most rapidly. With spheres of high specific activity, dynamic distribution in various organs was determined by continuous whole-body scanning for the 1st hr after administration and by static imaging at selected times thereafter up to 4weeks. The 7- and 12-μm spheres were filtered mechanically and retained for prolonged periods in the lungs, while the 3- and 5-μm spheres localized and were retained in the liver and spleen. Localization of these smaller spheres appeared to be due to phagocytosis by cells of the reticuloendothelial system; with the 12-μm spheres, there was no evidence of phagocytosis by the pulmonary macrophages of the reticuloendothelial system within 4weeks postadministration. Intraarterially administered larger microspheres did not show any significantly different distribution patterns from those administered intravenously. Histological examination revealed occasional vascular engorgement about the site of multiple-sphere lodgment, but no destructive tissue phenomenon was apparent in relation to the lodgment of the microspheres.