Abstract As angiogenesis inhibitors have proven to be valuable agents in oncology there is a need to measure changes in vasculature for these and other related agents. Many of the angiogenesis inhibitors, though reducing tumor volume by reducing nutrient access to the tumor, do not always show decreased density of vasculature. This paradox, however, may be attributable to the difficulties of measuring the vasculature. One reason for this problem has been the heterogeneity of vessels in the tumor. With the ability to now scan 360o by 3D microCT imaging of the tumor, all image captured vessels can be measured. Another problem is the limitation of vessel size measured by microCT scanning resolution. Vessels smaller than ∼20 microns cannot be distinguished by size at scan parameters of 10 micron voxel resolution. In addition, agents used for imaging have their own limitations. Microfil is a polymer based radiopaque imaging reagent whereas AltaBlu is a proprietary formulation of a non-soluble radiopaque colloid suspension. For reasons not entirely clear, we do not believe Microfil enters capillaries since we have not observed it in the venous side of an arterial infusion. We believe AltaBluTM, can pass into smaller vessels since we have occasionally seen small amounts on the venous side, but these smaller vessels cannot be adequately measured in diameter by microCT scanning. We hypothesized that even though we may not be able to see smaller vessels by AltaBluTM, we might be able to see more of the smaller vessels due to improved reagent penetration and would therefore be more sensitive to changes in small vessel populations. Herein, we have compared perfusion of tumors via AltaBluTM and Microfil to determine the benefits/detractions of the various agents and used a variety of measuring parameters such as vessel radius, average vessel length, vessel density, tortuosity, and vessel branching factors in AltaViewerTM software to determine the sensitivity of each agent to vascular imaging. Citation Format: Daniel Small, David Weinstein, Christine O'Day, Glenn Knitter, Naveen Ouellette, Liane Pinkos, Sergio X. Vasquez, Neha Shah. AltaBluTM and Microfil 3D imaging of tumor vasculature. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3903. doi:10.1158/1538-7445.AM2013-3903