Neurovascular Coupling Methods

Abstract

Measuring microvascular characteristics in cortical tissue and individual microvessels has important applications for functional imaging, biomedical research, and clinical diagnostics. Multiphoton fluorescence microscopy approaches are most effective and allow to reliably record red blood cell (RBC) velocity in individual vessels, but require injecting fluorescent tracers. Moreover, only one or few vessels in a small area can be imaged at a time. Wide-field CCD/CMOS-based optical imaging of intrinsic absorption or reflection changes in macroscopic vascular networks allows to overcome these shortcomings, by recording RBCs’ trajectories over several mm 2 of cortical surface. The RBC velocity can then be extracted from these wide-field data using specialized algorithms. Here, we describe two of those, which provide robust RBC velocity estimations that are independent and can thus be used as a control one for another. Although this approach can be used in any part of the body with optically accessible blood vessels, here we show its application in two cases: first the cerebral cortex and then the eye. In this latter application, we go into some more detail in describing the retinal function imager (RFI): a unique, noninvasive multiparameter functional imaging instrument that directly measures hemodynamic parameters such as retinal RBC velocity, oximetric state, and metabolic responses to photic activation. In addition, it allows capillary perfusion mapping without any contrast agent. These parameters of retinal function are degraded by retinal abnormalities. Here, we thus focus on the characterization of microvessels properties. Indeed, clinical studies suggest that knowing these properties should yield multiple clinical applications for early diagnosis of retinal diseases, possible critical guidance of their treatment, as well as implications for vascular diseases of cortex and eye.