3-D MRI brain scan. Coloured three-dimensional magnetic resonance imaging (MRI) scan of a healthy human brain seen from above. The front of the brain is at top. Only the cerebrum, the largest section of the brain, can be seen. Conscious thoughts, emotions and movements are controlled within its two hemispheres. The surface of the cerebrum is folded into gyri and fissured with sulci. MRI scanners build images of the human body using pulses of radio waves. Successive slices" are compiled into a three-dimensional image by computer."