Magnetic resonance imaging (MRI) is an imaging technique used primarily in medical settings to produce high quality images of the inside of the human body. MRI is based on the principles of nuclear magnetic resonance (NMR), a spectroscopic technique used by scientists to obtain microscopic chemical and physical information about molecules. It is actually a Nuclear Magnetic Resonance signal in a thin slice throuch the human body. Then, several of these "slices" are put together to form a 3D layout of your insides. Kind of like the way an X-ray shows your bones. No blood is necessary.