**Voxelotor** is a medicine for people with **sickle cell disease** (SCD), a genetic blood disorder that affects the brain. SCD causes the small blood vessels in the brain to widen to deliver enough oxygen to the brain. But, if blood flow is not enough, it can cause serious issues because the brain can't adapt well. Voxelotor helps by increasing **hemoglobin** (a protein in red blood cells that carries oxygen), potentially reducing stress on the brain. In this study, children aged 4 to 30 with SCD will take voxelotor daily for 12 weeks. Researchers will check how voxelotor affects brain blood flow and oxygen use using a special light technique. Participants must be available for the whole study and able to take oral medicine.

• **Study Duration:** 12 weeks with measurements at the start, week 4, and week 12.
• **Participation Requirements:** Ages 4-30, willing to take medicine daily and attend all assessments.
• **Exclusions:** Recent serious medical issues, ongoing infections, pregnancy, or other conditions affecting study results.