Caption

Stroke: computed X-ray tomography (CT) scan of the brain of woman aged 48 years, revealing an area of cerebral infarction - the result of a stroke. The infarct - brain tissue starved of blood - appears as the dark rectangular area in centre. In CT, a narrow X-ray beam is directed through the subject towards a diametrically-opposed detector. A series of "slices" is made, with source & detector moving synchronously around the subject. Measurements of transmitted X-rays are processed by computer to reveal how elements of tissue in each "slice" affect the passage of X-rays & so construct an image of the section.