We propose to develop a new and innovative method for the detection and classification of emboli flowing into the brain through Carotid arteries, specifically for situations involving space traveling. The present technique does not utilize Doppler technique, rather the advanced pulse-echo ultrasound technique based on detecting the nonlinear parametric scattered ultrasound pulse-echo wave from emboli. The proposed technique is predicted to have a resolution more than 10 times better than that of the Doppler technique, and to be able to exactly measure the size of and classify the type of emboli. Furthermore, the implementation of the proposed technique into a Holter-monitor type device is predicted to be much easier than the Doppler technique. This Phase I study propose to investigate the feasibility of the proposed technique in vitro.