I just wanted to post this in case somebody else is looking for this. There are 2 ultrasound machines in the government hospital on Koh Phangan. This is the only hospital on Koh Phangan that has them.
We had an emergency in the middle of the night (appendicitis symptoms). Not only they did a basic scan, but they also arranged a cheap CT scan at a partner private hospital in the middle of the night. (probably cheaper than if we ordered it directly from that other private hospital).