Non-Invasive Brain Metabolic and Cytometric Imaging: Insights from Activity MRI [aMRI]

The first aMRI [activity MRI] maps of the awake, heathy human brain are presented. They show differences in cell density [ρ (cells/μL)], average cell volume [V (pL)], and on-going metabolic activity among different brain tissues. Metabolic activity is represented by the mean steady-state cellular water efflux rate constant [k_io], which reflects homeostatic cytolemmal Na⁺,K⁺-ATPase [NKA] enzymatic turnover. Cortical gray matter [GM] ρ is less than white matter [WM] ρ, while V_GM > V_WM. Most interesting is the quite large WM k_io, 30 s^-1. WM NKA activity per cell is considerably larger than in cortical GM.