The way it usually works is, they'll introduce themselves first "Hi, I'm Dr. _____" then you say "Nice to meet you. I'm yummytummy." At the end of the interview, you can refer to them as whatever they introduced themselves as.
If you have to introduce yourself first, no biggie. "Hi, my name is yummytummy." Then they'll introduce themselves.
Just because you may know their name already doesn't mean you won't go through the whole introduction thing.