Ultrafast two-photon fluorescence imaging of cerebral blood circulation in the mouse brain in vivo

Characterizing blood flow dynamics in vivo is critical to understand the
function of vascular network under physiological and pathological
conditions. Existing methods for hemodynamic imaging have insufficient
spatial and temporal resolution to monitor blood flow at cellular level in
large blood vessels. By employing an ultrafast line-scanning module based
on free-space angular chirped enhanced delay (FACED), we achieved
two-photon fluorescence imaging of cortical blood flow at 1,000 2D frames
and 1,000,000 1D line scans per second in the awake mouse. This
orders-of-magnitude increase in temporal resolution allowed us to measure
cerebral blood flow up to 49 mm/s and observe pulsatile blood flow at
harmonics of heart rate. Directly visualizing red blood cell (RBC) flow
through vessels down to >800 µm in depth, we characterized
cortical-layer-dependent flow velocity distributions of capillaries,
obtained radial velocity profiles and kilohertz 2D velocity mapping of
multi-file blood flow, and carried out RBC flux measurements from
penetrating blood vessels.