There are "small animal" MRI machines, which are mostly intended for research.

The bores are really small: 55mm or so is not uncommon, so a mouse would fit, but nothing much bigger. Other animals are usually scanned on a machine meant for humans (sometimes even the exact same ones, very early in the morning or late at night).

Tend to be, but it's not that rare for someone to have a dog that's a hundred pounds and five feet long. That's in the range for an adult human.

My dad, a radiologist once had patient that was so large that they couldn't fit them on a conventional CT scanner. Luckily this was a university town, so they were able to access the vet's large animal scanner.

Makes sense. Horses and cows get much larger than humans!

I suppose that does make sense.

Re: the large patient, yikes!