INTENSIFYING SCREEN AND CASSETTE

Thomas Edison

developed intensifying screen in 1896

Micheal Pupin

first used a film/screen combination in radiography later that same year.

Crystal emitted within 10 s-8

Light emitted promptly

Used for Intensifying Screens

FLUORESCENCE

Crystal emitted after 10 -8 s

Delayed emission of light (Afterglow/lag)

Not desired to used for Intensifying Screens

PHOSPHORESCENCE

INTENSIFYING SCREEN SPEED

refers to the amount of light emitted by the screen for a given amount of x-ray exposure.

Intensification factor,

relative name,

speed value.

Screen Speed can be measure by

Intensifying Factor = Exposure without screens / Exposure with screens

INTENSIFYING FACTOR FORMULA

RELATIVE SPEED VALUE

is the most common method of designating screen speed and used for all screens with rare earth phospohor

New mAs = old mAs x old relative speed value / New relative speed value

RELATIVE SPEED VALUE FORMULA

Name of Screen

Ultra high or hi-plus 300

High or fast 200

Medium, par, or standard 100

Detail, slow, or high resolution 50

Ultradetail 25

Older Names for Screen Speed

• 2 category.

- rare earth

- nonrare earth

Type of Phosphor Material

Nonrare Earth

emit light in the blueviolet portion og the color spectrum.

Calcium tungstate,

barium strontium sulfite,

barium fluorochloride.

Nonrare Earth

Type of Phosphor Material

Thickness of phosphor layer

Size of Phosphor Crystal

Reflective layer

Light Absorbing Dyes

Ambient Temperature

Kilovolt (Peak) Selection

FACTOR AFFECTING SCREEN SPEED

150 to 300 um

The average range of phosphor thickness

GREATER CONVERSION EFFICACY

Ability of screen to convert x-ray energy into light energy

GREATER DETECTIVE QUANTUM

The ability to interact with x-ray

4 % to 5%

15% to 25%

Calcium tungstate screen -

Newer rare earth screens -

Rare Earth

developed in the early 1970s

• atomic numbers ranging 57 - 71 known as Lanthanide or rare earth.