Well, generally radiology is a common major in "high end" medical and technological schools. This means that majoring in radiology is as simple as calling up the college you are interested in and seeing if they offer the program you are interested in.
A quick google search shows that your second concern "ultrasound technician" is often a non accredited program at some technical schools. If you plan on doing this , make sure you go to a public (not private) university, also it is imperative to ask if the degree is locally and federally accredited (you don't want to waste you money do you?).
Dental hygienist , as your final concern, is a very common major at most 2-4 year colleges. However, you need to understand that hygienist jobs don't usually require more than a technical school degree, and the chances for promotion in this field seem saturated.