RAD 254 Chapter 13 Intensifying Screens Physical purpose: to convert x-ray photons into light photons (done at the phosphor layer)

Most – if not all in use are “rare earth” Rare earth crystals include (but are not limited to): –Gadloinium –Lanthanum –Yttrium

Desired Physical Properties of crystals High atomic number = high absorption (DETECTIVE QUANTUM EFFICIENCY {DQE} ) Phosphor should emit a LARGE # of light photons for each x-ray photon – CONVERSION EFFICIENCY (CE) Color of light should match the color light the film is sensitive to – SPECTRAL MATCHING ZERO/next to zero afterglow

Important terms Luminescence – process of giving off light when stimulated Fluorescence – giving off light ONLY when stimulated Phosphorescence – continuing to give off light after stimulation Intensification factor – amount of radiation reduction with screens vs NO screens

Screen speed Can be judged by intensification factor (IF) Increasing speed increases noise Increasing speed REDUCES spatial resolution Increasing speed INCREASES quantum mottle (line-pair test pattern)

Technologist CONTROLABLE items Screen attributes the tech can control: radiation quality; image processing and temperature (also screen care and cleaning)

Cassette Construction Rigid, light proof protective housing for the film and screens. Felt/rubber/sponge “compression” layer to assure good film-screen contact K-edge of crystals determines light spectrum

Screen cleaning Compare and contrast screen cleaning solutions (home made vs commercially made) Cotton vs 4 X 4’s

Screen – Film Contact Test Wire mesh test for screen-film contact and proper resolution/visibility of detail