qaqc p2

intensifying screen

is a plastic sheet coated with fluorescent material called phosphors. Phosphors are materials which convert photon energy to light

luminescence

is the emission of light from a substancebombarded by radiation

fluorescence

means that luminescence is excited only during the period of irradiation and will terminate at completion of the X-ray exposure

protective coating/layer

• The layer of radiographic intensifying screen closest to the radiographic film

• This layer also helps eliminate the buildup of static electricity and provides a surface for routine cleaning without disturbing the active phosphor

phosphor lqyer

• The active layer of intensifying screen

• Emits light stimulation by x-rays

calcium tungstate

-    Used as an active phosphor in 1980 Rare Earth elements

reflective layer

• Found between the phosphor and base

• Made of magnesium oxide and titanium dioxide

• Light emits isotropically when interacted by x-ray

• Increases the efficiency of the intensifying screen, nearly doubling the number of light photons reaching the film

Detective quantum efficiency (DQE)

The phosphor should have a high atomic number so that x-ray absorption is high. This is called

Conversion Efficiency (CE)

The phosphor should emit a large amount of light per x-ray absorption. This is called

spectral matching

The light emitted must be of proper wavelength to match the sensitivity of the x-ray film. This is called

base

• Layer farthest from the film

• Approximately 1mm thick

• Serves principally as a mechanical support for the active phosphor layer

• Polyester is the popular base material in intensifying screen

fast screens

• Thick layer large crystals

• maximum speed is attained but with some sacrifice in definition

slow screens or high definition screens

• Thin layer Small crystals

• Detail is best but speed is slow necessitating a higher dose of ionizing radiation

intensification factor

The screens are used to reduce patient dose so one important characteristic of the screen is the magnitudeof dose reduction. This property is called _____ and is a measure of the speed of thescreen.

standard screens

use calcium tungstate phosphors

rare earth screens

use gadolinium or lanthanum phosphors

cassettes

A flat, light-tight container in which x-ray films are placed for exposure to ionizing radiation andusually backed by lead to eliminate the effects of back scatter radiation

phosphorescence

• “afterglow”

• phosphor material continues to emit light for a time after cessation of exposure to radiation and will continue to produce an image