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.

This study enrolls patients with refractory, progressive, or relapsed solid tumors. The purpose of this study is to find out whether a drug called PEEL-224 ("the study drug") is safe and effective when given as monotherapy (a drug given by itself) and as part of a combination therapy together with other chemotherapy drugs.