Do microspheres with narrow or standard size distributions localize differently in vasculature? An experimental study in sheep kidney and uterus.

Purpose: To compare standard embolization microspheres (SMS) with microspheres of very narrow size distribution in terms of physical properties and relative distribution within sheep kidney and uterine artery models of embolization.

Materials And Methods: Standard microspheres (SMS; 500-700 mum and 700-900 mum) were compared with narrow microspheres (NMS) of the same material made with a microfluidic method that produced a much narrower size distribution (600 mum and 800 mum). Characterization of both microspheres was performed in vitro (ie, bead size, water content, and compressive modulus). In the sheep model of kidney and uterus embolization, histopathologic analysis was performed to determine the average vessel size occluded, the number of microspheres per vessel, and the deformation in vivo, with a focus on the localization of the products within the different vascular zones of the organ tissues.

Results: In vitro testing showed the physical properties of NMS to be similar to those of SMS. SMS and NMS also possessed the same degree of deformation in vivo. In both embolization models, there were no major differences in the localization of SMS compared with NMS of equivalent mean bead diameters.

Conclusions: Compared with SMS with a normal distribution in size range, NMS with a narrow size distribution did not exhibit a very different distribution within the vasculature of the sheep kidney or uterus.