MRI scan for surgical brain modelling. Patient undergoing an MRI (magnetic resonance imaging) scan for stereotaxy. Stereotaxy is the use of three-dimensional measurements to model areas that will be operated on during surgery. Note the white markers on the patient's scalp. Magnetic resonance imaging uses a powerful magnetic field and radio waves to form images of slices through the body. Photographed at the Val de Grace military hospital, Paris, France.