This study aims to explore a new type of magnetic resonance imaging (MRI) called Chemical Exchange Saturation Transfer (CEST) in children aged 6-18 years with brain tumors. An MRI is a machine that takes detailed pictures of the brain. The CEST MRI used in this study is still being tested and has not been approved by the FDA yet. The study wants to find out if this new type of MRI can help doctors evaluate brain tumors. CEST MRI creates images using water molecules and protons in the brain. Early research shows that CEST could be helpful in understanding brain tumor changes.

This study will enroll 5 participants.

The purpose of this research study is to determine if certain markers in your blood are increased over the duration of your chemotherapy, especially as you get sicker, such as developing a severe infection (sepsis) or severe respiratory failure (acute respiratory distress syndrome).

This study has two parts. Part A enrolls patients who have been diagnosed with a solid tumor, lymphoma or desmoid tumor that has either come back ("relapsed") or does not respond to therapy ("is refractory"). Part B enrolls patients with a relapsed or refractory Ewing sarcoma, desmoid tumor, osteosarcoma, liver tumor, Wilms tumor, or tumors with changes in a gene family known as the Wnt pathway. This study involves taking a study drug called tegavivint. The study will be testing different doses of the study drug to find the safest dose.