Biomedical Engineering, a specialty which normally is taught at the graduate level, after an initial engineering degree.
Most people who go to grad school for Biomedical engineering have initial degrees in electrical or chemical engineering.
For a Master's degree it would be at least 1 year after the initial degree and for a PhD or DEng you would need about 2-3 years after the Master's. Total: 4+1+3= 8 years.