RESEARCH ARTICLE Imaging Tumor Necrosis with Ferumoxytol

Objective Ultra-small superparamagnetic iron oxide nanoparticles (USPIO) are promising contrast agents for magnetic resonance imaging (MRI). USPIO mediated proton relaxation rate enhancement is strongly dependent on compartmentalization of the agent and can vary depending on their intracellular or extracellular location in the tumor microenvironment. We compared the T1- and T2-enhancement pattern of intracellular and extracellular USPIO in mouse models of cancer and pilot data from patients. A better understanding of these MR signal effects will enable non-invasive characterizations of the composition of the tumor microenvironment. Materials and Methods Six 4T1 and six MMTV-PyMT mammary tumors were grown in mice and imaged with feru-moxytol-enhanced MRI. R1 relaxation rates were calculated for different tumor types and different tumor areas and compared with histology. The transendothelial leakage rate of fer-umoxytol was obtained by our measured relaxivity of ferumoxytol and compared betwee