Magnetic resonance imaging (MRI) used to detect and monitor pediatric brain tumors is subjective, can lead to misdiagnosis, and often requires long imaging times. Furthermore, MRI cannot distinguish between treatment-induced side-effects from disease progression. Therefore, to develop and test new treatments for pediatric brain tumors including immunotherapies, a critical need is to develop a non-invasive, reproducible, fast, imaging technique that improves MRI’s ability to detect and monitor response to therapy. Our team members pioneered a transformative MRI technology termed Magnetic Resonance Fingerprinting (MRF) that generates MRI assessments in as little as 11 seconds and is quantitative. MRF is now a product on human clinical MRI scanners and has shown superior accuracy and reproducibility in multi-center imaging trials. In pediatric brain tumor patients, MRF can: 1) distinguish tumor grade; and 2) differentiate tumor from normal brain not identifiable using conventional MRI. MRF can detect changes following treatment indicative of tumor recurrence. The goals of this study are to develop pediatric human in animal models of brain tumors, and to use these models to optimize preclinical MRF in order to find the best approach to assess response to immunotherapies. We will also add 3D MRF to our clinical imaging study to characterize human pediatric brain tumors prior to and following therapy.