Vessel Size Imaging with iron oxide and with gadolinium: a comparative study in rodent

Introduction Blood Volume fraction (BVf) and Vessel Size Index (VSI) MR imaging are powerful tools for characterizing tumor microvasculature and its evolution under therapy. BVf and VSI imaging are based on the measurement of the changes in R2 (ΔR2) and in R2* (ΔR2*) induced by a contrast agent (CA) [1]. In brief, two types of CA have been evaluated: iron oxide particles (USPIO), in animals, and Gd chelates (Gd), in humans [2,5]. Due to the difference in magnetic susceptibility between the two CA, experiments have been performed at steady-state for USPIO (i.e. imaging before and after USPIO injection) and during the first passage of Gd (ΔR2 and ΔR2* are measured at bolus peak). In this study, we compare VSI values obtained with dynamic and steady-state acquisition schemes with each CA in rats bearing C6 glioma.