You should take a look at Boston University's LEAP program (http://www.bu.edu/eng/academics/special-programs/leap/). It is tailored towards people who do not have undergraduate degrees in engineering, and their only requirements are a bachelor's degree (which you clearly have), and one semester of college level calculus with a grade of a B or better. I know in the US calculus is also a requirement for medical school, so you probably have that as well. LEAP offers a Phase 1 where you catch up on math/physics/engineering courses you missed as an undergraduate, and as long as you maintain a 3.2 GPA or better you are guaranteed admission to the M.Eng. program of your choice. You can also apply to their M.S. or Ph.D. programs, or apply to another school. People enter this program with degrees in psychology, literature, education, etc., so your background would certainly not be a hinderance. In fact, if you want to to biomedical engineering, I would expect an M.D. would be quite a useful degree to have.