" there's loads of standard free ones out there that work well."
Lol, go on then. Name me a free-to-use imaging format suitable for medical imagery. (there might be one I don't know).
I doubt it though. Even good digital cameras use proprietary formats for their RAW. And as above, jpeg aint going to cut it! "oh I'm sorry, it wasn't a tumour, it was a jpeg compression artifact".
I guess they might use TIFF or another lossless format. But that would be for display only, as the data captured by the devices won't be image data in the conventional sense.
To answer the OP, if there are hardcopies to hold onto you might be able to scan them, I did this with some x-rays I had.