A technique in which an ultrasonic transducer, in transmit mode, emits a high-frequency acoustic pulse towards the borehole wall, where it is reflected back to the same transducer operating in receive mode. The measurement consists of the amplitude of the received signal, the time between emission and reception, and sometimes the full waveform received. Tools that use this technique either have multiple transducers, facing in different directions, or rotate the transducer while making measurements, thereby obtaining a full image of the borehole wall. Pulse-echo techniques are used in the borehole televiewer. In cased hole, the waveform is analyzed to give indications of cement-bond quality and casing corrosion.