Counting Unique Names based on Criteria

I have attached a document that I need a formula for. In column B16, I need a formula that will count the number of unique people who are in radiology. As you can see, Adam, Ben, and Susan have radiology next to their name. I want the count to come out to 3 versus 7, since only 3 people have radiology in their name versus the amount of times their name come up.