Colour-coded image of the skull produced by computed axial tomography, known as a CAT scan. The image shows the eyes and nose at top, details of the brain, & the bones of the skull. CAT images are produced by a 180-degree scan using fine X-ray beams, rotated around the body in steps of 1 degree or less; data relating to the degree of X- ray absorption is stored on computer, which converts it into a monochrome image that can then be enhanced by colour-coding. In this image, the vitreous humour inside the eyes appears yellow- green.