Correlating Tumor Microstructure With Hypoxia Using Magnetic Resonance Imaging

Knowledge of oxygen concentration in tumors is important as hypoxic or oxygen deficient regions in tumors have been known to offer greater resistance to radiation treatment. Electron paramagnetic resonance oxygen imaging (EPROI) is an established technique for measuring absolute partial oxygen pressure (pO2) in tissues. Tumors also possess highly disorganized microstructure that can be measured using magnetic resonance imaging (MRI). Both these imaging modalities when used in conjunction, show the promise to create the opportunity for targeted radiation delivery to tumors. This work describes the initial pilot experiments that were done to correlate viscosity and fractional anisotropy with pO2 in FSa and MCa4 tumors in murine model. Using diffusion weighted MRI, the relationship between tissue viscosity and fractional anisotropy maps from MRI have been correlated to pO2 maps obtained using EPROI. EPROI is a functional imaging procedure, whereas MRI provides the best soft tissue contrast. Thus, further research in correlating structural information through MRI to oxygen information through EPROI will open the doors to create an effective targeted radiation delivery system, where areas inside a tumor can be differentiated based on their oxygen concentration and tissue microstructure, and subjected to different radiation treatment plans. This may lead to better post-treatment healing and minimize dysfunction by sparing healthy tissue structure with optimized radiation doses. The long-term goal of this study is to help create efficient intensity modulated radiation therapy (IMRT) treatment plan for solid tumors.