rCBF = Regional Cerebral Blood Flow — a neuroimaging measure tracking blood flow to specific brain areas, used to map neuronal activity and detect ischemia, stroke, or injury. Measured via PET or SPECT scans with tracers like xenon-133 or H₂[¹⁵O]. Higher flow = more active neurons; deficits signal tissue damage or vascular issues. Critical for diagnosing brain dysfunction and guiding treatment.