 This study will look at the feasibility of using magnetic resonance fingerprinting MRF in children, adolescents and young adults AYA with and without brain tumors. This study will also look at subjects with and without neurofibromatosis type 1NF1, a genetic disorder that affects the growth of nervous system cells. Further, it will explore potential ways of using of MRF signal measurements in children, adolescents, and young adults with brain tumors, including tissue characterization, looking at whether the treatment was effective, and finding metastasized tumors of unknown origin occult tumors. To explore the feasibility and potential applications of MRF, this study will recruit up to 80 subjects but will stop once 10 subjects have usable data in each of six groups. 