> I also think you're seriously underestimating the computational cost of converting the measured signal to a usable image. No way is an RPi fast enough to produce a live image with decent quality. There are quite a few papers in the literature about using high-end GPUs to speed up ultrasound imaging and denoising, for commercial vendors I'm guessing it's custom ASIC territory.

Really? Medical ultrasound has a long history predating high-end GPUs. Maybe that kind of computing power is required for modern high-resolution/low-lag devices, but my guess is you could get something usable with a computer as powerful as a RPi.

http://www.ob-ultrasound.net/history1.html

I can confirm that you can turn ultrasound data into a 2D image using a simple mid 2000's era ARM processor and an FPGA. So a RPi can even be overkill for that purpose.

But basic ultrasound machines have been with us for decades. From a quick check, since the sixties! I have no hard data yet, but I would be surprised if a Pi couldn't do it.

3D scans are another matter, but this is a thread about low cost scanners, so that's out of the picture.