Radiographic Cassette

Radiographic Cassette

A thin light-tight container, slightly larger than the film, intended to hold it

Front Cover of Cassette

Made of carbon fiber and other plastic materials

Front Cover of Cassette

Must be rigid and durable but radiolucent

Front Cover of Cassette

Has low atomic number to minimize attenuation

Back Part of Cassette

Made of steel or lightweight material like magnesium or lead

Felt Gaskets

Added to ensure light-proof edges of the cassette

Felt Gaskets

Also known as compression device

Felt Gaskets

Maintains low screen-film contact when cassette is closed and latched

Intensifying Screen

Enhances radiation effects for film blackening and contrast

Intensifying Screen

Converts x-rays into light

Intensifying Screen

Contains phosphors to convert x-ray energy into visible light

Intensifying Screen

Reduces patient dose compared to direct exposure radiography

Phosphors

Emit visible light when struck by radiation

Phosphors

Reduce patient dose by allowing lower mAs

Luminescence

Emission of light by intensifying screen when exposed to radiation

Fluorescence

Emission of light only during x-ray exposure

Phosphorescence

Emission of light after x-ray exposure has stopped

Types of Phosphor

Calcium Tungstate and Rare Earth

Protective Layer

Made of plastic to protect fragile phosphors

Reflecting Layer

Made of magnesium oxide or titanium dioxide

Reflecting Layer

Reflects light emitted by phosphors toward film

Absorbing Layer

Made of light-absorbing dye

Absorbing Layer

Absorbs light directed by phosphors

Base (Intensifying Screen)

Bottom layer, farthest from the film

Base (Intensifying Screen)

Made of polyester cardboard

Base (Intensifying Screen)

Provides support and stability to phosphor layer

Screen Speed

Ability of a screen to produce visible light

High-speed screens

produce more light but lower resolution

Low-speed screens

provide higher resolution

Conversion Efficiency

Calcium Tungstate ~5%, Rare Earth Screens ~20%

High-speed screens

used for dose reduction, mobile exams, high kVp, pediatric, and spot-film

Slow-speed screens

used for bone radiography and magnification techniques

Intensification Factor

Degree to which exposure and patient dose are reduced using IS

Intensification Factor Formula

IF = Exposure without screens / Exposure with screens

Light Emission & Patient Dose

Faster screen = more light, less dose

Light Emission & Patient Dose

Screen speed and density are directly proportional

mAs Conversion Formula

mAs₁ / mAs₂ = Relative Speed₂ / Relative Speed₁

Quantum Mottle

Statistical fluctuation in photon quantity per mm²

Quantum Mottle

Appears mottled or splotchy at very low exposures

Quantum Mottle

Occurs with very fast screen-film systems

Quantum Mottle

Reduced by increasing mAs or using slower screens