The purpose of this study is to identify tumor biomarkers in individuals with Neurofibromatosis type 1 (NF1). Biomarkers are signals that the investigator can measure that tell us about a process such as progress of a disease or treatment. Individuals with this diagnosis are at an elevated risk of developing a type of tumor called a plexiform neurofibroma. Currently, detecting the risk factors of these tumors in children is difficult and requires whole body imaging. The NF1 team at Lurie Children's established a way of using blood plasma in mice with neurofibromatosis type 1 to identify biomarkers that might signal the presence of tumors in people with NF1. This study is an effort to create biomarker profiles of patients with NF1 with known tumors. The study team will utilize whole-body MRI and mass spectrometry (a method for identifying unknown compounds and the properties of molecules). The ultimate goal of this study is to better understand the tumor biomarkers in patients with NF1.