<Table> <Tr> <Td> </Td> <Td> This article includes a list of references, but its sources remain unclear because it has insufficient inline citations . Please help to improve this article by introducing more precise citations . (May 2014) (Learn how and when to remove this template message) </Td> </Tr> </Table> <Tr> <Td> </Td> <Td> This article includes a list of references, but its sources remain unclear because it has insufficient inline citations . Please help to improve this article by introducing more precise citations . (May 2014) (Learn how and when to remove this template message) </Td> </Tr> <P> In X-ray tubes, the heel effect or more accurately, the anode heel effect is a variation of the intensity of X-rays emitted by the anode depending on the direction of emission . Due to the geometry of the anode, X-rays emitted towards the cathode are in general more intense than those emitted perpendicular to the cathode--anode axis . The effect stems from the absorption of X-ray photons before they leave the anode in which they are produced . The probability of absorption depends on the distance the photons travel within the anode material, which in turn depends on the direction of emission . </P> <P> The distance from the anode (source of X-rays) to the image receptor greatly influences the apparent magnitude of the anode heel effect . The shorter the distance, the less space the beam has to diverge . The effect is less noticeable at larger source - image distances (SID). </P>

The prominent heel effect in mammography is due to a