Effect of incidence angle and wave mode conversion on transcranial ultrafast Doppler imaging

Real-time measurement of cerebral hemodynamics can provide valuable information for assessing neurovascular function in patients with acute brain injury or ischemic stroke. In transcranial ultrasound imaging, the skull supports both shear and compressional wave modes. Wave mode conversion occurs at the interface between the skull and the surrounding tissue. Since the incidence angle affects the wave mode conversion at the skull-brain interfaces, the quality of the transcranial Doppler image, including the resolution and the detectability of vessels, is also expected to be affected by the angle of incidence. In this study, we experimentally evaluate the effect of the angle of incidence on the image quality of ultrafast transcranial Doppler imaging. Results indicate that when imaging through the temporal bone window, a large angle of incidence could decrease the localization error. When imaging outside the temporal bone window, a normal angle of incidence could ensure a high rate of blood vessel detection.