Infographics / Digital Radiography

Intensifying Screen Physics

Cross-section of a phosphor intensifying screen. Incident x-rays are absorbed in the phosphor and re-emitted as visible light that spreads laterally before reaching the film. A thin, slower screen gives a narrow light spread and a sharper image but less dose saving; a thicker, faster screen absorbs more x-rays for greater dose saving but the light spreads wider, causing more unsharpness. Rare-earth phosphors convert x-rays to light more efficiently than calcium tungstate.

Intensifying screen: x-ray to light conversion, spread and the speed / sharpness trade-off Cross-section of a phosphor intensifying screen. Incident x-rays are absorbed in the phosphor and re-emitted as visible light that spreads laterally before reaching the film. A thin, slower screen gives a narrow light spread and a sharper image but less dose saving; a thicker, faster screen absorbs more x-rays for greater dose saving but the light spreads wider, causing more unsharpness. Rare-earth phosphors convert x-rays to light more efficiently than calcium tungstate. Intensifying screen: the phosphor absorbs x-rays and re-emits many visible-light photons that expose the film, greatly amplifying exposure (large intensification factor) so a much lower patient dose is needed. incident x-rays absorption (x-ray to light) emitted light phosphor film narrow spread, sharp thin / slower screen sharper image, less dose saving thicker phosphor film wide spread, blurred thick / faster screen more dose saving, more unsharpness Rare-earth phosphors (e.g. gadolinium oxysulfide) convert absorbed x-rays to light more efficiently than calcium tungstate: more light per x-ray means a faster screen and lower patient dose for the same film density.
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