Physical sources of registration errors in pulse-echo ultrasonic systems

The sources of registration errors in ultrasonic-scanning systems are discussed. In a water bath, a ball-bearing target mounted on a micromanipulator was used to find the position of maximum echo amplitude in an ultrasonic beam. A target at this location will give rise to a point on the display along the axis of the beam, and therefore deviation of this point will produce a registration error. Considerable deviations were produced by the interposing of a normal living human calf. The effects of sound velocity and absorption in the sorrounding medium were investigated. The observed deviations were attributed to the mechanisms of refraction, reflection and differential absorption.