From Jean Perilhou's patent "US3577772: DEVICE FOR DIAGNOSTIC EXAMINATION BY ULTRASONIC OSCILLATIONS" filed on May 8, 1967:

An ultrasonic device for examining the internal parts of the body comprising a plurality of ultrasonic transmitters mounted along a horizontal line on a movable carriage and triggered sequentially. A plurality of receivers is mounted on the carriage along a vertical line that intersects the horizontal line at right angles. The movement of the carriage is synchronized with the deflection of an electron beam in a PPI cathode-ray tube to provide a visual display of the surface contour of the internal body part under investigation.

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