Evaluation of 18F-Fluciclovine Positron Emission Tomography - Magnetic Resonance Imaging (PET-MRI) in LGG

Inclusion Criteria 1. LGG including the brainstem and supratentorial only (WHO grade I-II), confirmed by biopsy unless in NF1 participants with classic appearance. 2. Participants must have evaluable disease (1x1 cm tumor on MRI) 3. Scheduled to receive systemic therapy for LGG 4. Performance Score: Karnofsky ≥ 50 for participants \> 16 years of age and Lansky ≥ 50 for participants ≤ 16 years of age. Participants who are unable to walk because of paralysis, but who are up in a wheelchair, will be considered ambulatory for the purpose of assessing the performance score. 5. Age: Participants must be ≥ 1 years but ≤21 years of age at registration 6. Being on a treatment regimen does not exclude a subject from enrollment. Exclusion Criteria 1. Inability to tolerate imaging procedures in the opinion of an investigator or treating physician 2. Pregnant participants 3. Participants who weigh less than 8 kg. 4. Participants who cannot avoid contact with a pregnant woman or infant for at least 12 hours following injection. 5. Participants with a history of abnormal kidney function or creatinine \>= CTCAE v5.0 grade 2 at time of study registration. 6. Participants with primary tumors of the spinal cord.