Invisalign and Braces at the Same Time?

I've been told that my bottom teeth are too crowded to correct with Invisalign so I would have to get Braces. I'm also told when you straighten your teeth you should move both top and bottom teeth to maintain a proper bite. Since my top teeth aren't bad, would I be able to use Invisalign to line up my upper teeth with my lowers, or would I need traditional braces for both?