An electronic system for acoustic imaging of vapor bubbles in a liquid filled steel pipe is described. An array of 20 acoustic transducers is attached around the pipe. They are fired one at a time by a programmable sequencer. The same transducers are in turn used as receivers of echoes reflected back from the bubbles. Analog and digital circuits and logic is described for fast processing of received signals. The majority of unwanted echoes are eliminated by a memorized "mask" frame, made with the water-filled pipe free from bubbles, enabling a high rate on-line data transfer to the computer. Unlike the earlier systems, this one makes possible the real time imaging of live bubbles.