Quantitative two-photon imaging of blood flow in cortex

Abstract Cerebral blood flow plays a central role in maintaining homeostasis in the brain, and its dysfunction leads pathological conditions such as stroke. Moreover, understanding the dynamics of blood flow is central to the interpretation of data from imaging modalities, such as intrinsic optical signaling and functional magnetic resonance imaging, that rely on changes in cerebral blood flow and oxygen level to infer changes in the underlying neural activity. Recent advances in imaging techniques have allowed detailed studies of blood flow in vivo at high spatial and temporal resolutions. We discuss techniques to accurately measure cerebral blood flow at the level of individual blood vessels using two-photon laserscanning microscopy. By directing the scanning laser along a user-defined path, it is possible to measure red blood cell velocity, as well as vessel diameter, across multiple vessels near simultaneously. The combination of these measurements allows accurate assessment of total flux with sufficient time resolution to measure fast modulations in flux, such as those caused by heart-beat, as well as slower signals caused by vasomotion and hemodynamic responses to stimulus.