False-colour Magnetic Resonance Image (MRI) of an axial section through a human head, showing the division of the brain into left & right cerebral hemispheres - the dividing line runs from top to bottom in the centre of the image. MRI (also called NMR - nuclear magnetic resonance - imaging) distinguishes between the grey & white matter components of brain tissue. Here, the outer grey matter is coloured red & yellow, and the inner white matter coloured green. The layer of fat under the skin of the scalp appears as the outer blue border to the image. Bone of the skull and the cerebro-spinal fluid which bathes the brain appear black.