In vivo imaging of cerebral hemodynamics using high-frequency micro-ultrasound

Assessment of cerebral vascular response is important in neuroscience research. Some imaging modalities that are commonly used to detect flow and/or vessel diameter changes in the brain include magnetic resonance imaging, positron emission tomography, and optical intrinsic signal imaging. Ultrasound has not typically been used to assess neurovascular response but recent advances in the technology have led to the development of micro-ultrasound systems with significant potential for this application. The state of the art in high frequency (15-50 MHz) micro-ultrasound is based on linear arrays specifically designed for small animal imaging. These systems can achieve axial resolution ranging from 30 to 200 microm. They are capable of quantifying brain hemodynamics in terms of red blood cell (RBC) velocity, flow, and vascular density in real time, up to 35 mm below the cortical surface, and can achieve temporal resolution of up to 1000 frames per second. This protocol describes imaging of the rat brain using various ultrasound imaging modes (power Doppler, color Doppler, pulsed-wave Doppler, and nonlinear contrast-enhanced imaging) to assess the state of cerebral microcirculation.