Functional micro-ultrasound imaging of rodent cerebral hemodynamics

High-frequency ultrasound imaging has been developed to the point where it can be used to quantitatively image changes in the hemodynamic state of the rat brain upon stimulation. We used a nonlinear contrast imaging mode on a commercial micro-ultrasound system to image a microbubble contrast agent in the microvasculature of the living rat brain through a cranial window. Electrical stimulation of the forepaw resulted in quantifiable changes in local cerebral blood flow, both spatially (100 μm in-plane resolution) and temporally (40 ms resolution) in the imaging slice. We also show initial data on three-dimensional ultrasound imaging of blood flow in the mouse brain using color Doppler imaging. The experimental paradigm and data analysis methods we developed will be used in a study of microvascular malformation in a mouse model of Alzheimer´s disease and should be useful for studies of neurodegenerative and neurovascular diseases in small animal models in general.