[0xfaded]

Trying to figure out how medical ultrasound works is a rabbit hole I'm still trying to claw my way out of. While there are phased arrays, most handheld imagers you would be familiar with are simply linear arrays of approx 100-150 transducer elements. While there is likely some simple phasing going on with adjacent elements firing together, a better model mental model for these would be the transducers firing one by one to produce a scan of individual beams. Before linear arrays, there was actually a single transducer that mechanically scanned back and forth to produce the same effect.

[nradov]

Air bubbles in the bloodstream show up clearly on medical ultrasound. Doctors use this to diagnose atrial septal defects.