Abstract: Continuous wave ultrasonic sound waves from a transmitter and receiver are highly focused to a width of approximately 1 millimeter or less and are transmitted and received through intersecting paths within the tissue of a patient. A doppler flow detector produces an image of the moving blood within the vessel. The transmitter and receiver are systematically scanned over the subject and the detected images are converted into visually intelligible pictures.An improved circuit for more clearly defining the flow picture of the moving blood particles utilizes a conventional directional doppler circuit plus a multiplier-differentiator-low pass filter circuit to automatically eliminate venous flow signals. A grey scale oscilloscope provides brightness intensity on the visual picture proportional to the velocity and direction of the blood flow for detecting stenosis in the vessel.A recording technique is disclosed for detecting atherosclerotic thickening of the artery wall.