Not sure if you're doing an engineering type of thesis or a humanities type of thesis. But if it's engineering:
I just went with my wife to have an ultrasound (it's a boy!), and I was very impressed with what the ultrasound machine did, and how (relatively) simple the concept is: send pulses of vibration and listen for the timing of the echoes, very quickly, as to see what's inside of something. You'd need awfully fast circuitry to do it, but I'm imagining there's all kinds of creative applications of this basic concept that haven't been explored. Kind of like the ping sensor, but taken to the next level.
-Paul