During the injection of contrast media for cerebral angiography, high-intensity ultrasound reflections can be recorded by Doppler sonography and B-mode scanning. This phenomenon was examined during carotid angiography and by in vitro experiments in tube models. Our results show that these high-intensity reflections are caused by: (1) transient interfaces of impedance between small compartments of contrast medium and blood and (2) small gas bubbles, which are always present in freshly aspirated contrast medium. Therefore, intraarterially injected contrast medium acts as an ultrasound contrast medium as well.