Bubble presence within a region is monitored to determine if a predetermined condition is met such as whether the presence is of sufficient magnitude, the bubbles being subject to energizing (240). In some embodiments, the energizing only occurs when time- wise preceded by the determination (S508, S510). The determining can include measuring a grayscale value (104), or assessing the energy carried by a frequency component of the echo signal, in the region in real time. The energizing may occur region-by-region, automatically and without need for user intervention, in a treatment pass (S428) over the regions. The regions (232) in the pass might be subject to respective instances of the energizing without intervening monitoring, or, in another embodiment, to both the determining and the responsive energizing. The determining can be subject to, automatically and without need for user intervention, interruption (S408) and concurrent switching to a next region.