Here’s a good video about breast MRI.
It was made in 2007 so some aspects of the technology have already advanced. For instance, in the video they say that MRI can detect a tumor at 5 – 6 mm but we are now talking about detecting tumors of only 2 mm.
The video is brief (less than 3 minutes) and shows the breast coil. It also shows some images taken with the MRI.