The purpose of this study is to test whether and how a person's brain changes in the first few months after starting gender affirming hormone therapy (GAHT). The investigators want to know if GAHT changes: 1) cerebral blood flow (CBF), 2) brain structure, connectivity, and cognitive task performance, and 3) neurocognitive function (memory, attention, executive function, processing speed). 36 male at birth and 36 female at birth participants will conduct baseline studies prior to GAHT, with a second identical set of study visits 4-6 months after GAHT begins.