Brisket is a very tough cut. As a result, you will not get good results trying to cook it as medium rare roast. Brisket has to be cooked slowly to an internal temperature of 93ºC to give the connective tissues etc. time to break down. Typically, you see briskets cooked in stews and pot roasts where this has a chance to happen.
"If you want to make an apple pie from scratch, you must first create the universe." -Carl Sagan