Cassettes & Screens

Film Cassette

• rigid film holder to keep x-ray film & intensifying screen in close contact

• opaque to light

• radiolucent to x-ray

Front of Cassette

• sturdy & rigid

• radiolucent

• cleanable

• attaches to back with hinge & locks

Lead Blocker

• front of cassette

• usually in the corner

• prevents irradiation of film undrneath

• where radiograph label goes

Inside of Cassette

• lined with foam or felt pads

• ensures film doesn’t shift around

• keeps screen & film in close contact

Back of Cassette

• heavier material

• may be lined with lead

Cassette Care

• clean exterior monthly with soap & water

• limit physical damage

• put cassette in clear plastic bag if necessary

  • prevents leakage into cassette

Intensifying Screens

• sheet of luminescent phosphor crystals

• mounted on cardboard or plastic base

Screen Layers

• back seal (base)

• plastic base

• reflective layer

• phosphor layer

• protective coating

Function of Screens

• converts x-ray radiation to visible light

• light exposes film = latent image

• processing converts latent to visible image

Intensifying Screen Purpose

• reduce radiation needed to make image

• faster & more efficient image production

• enhancement of contrast

• 95% of exposure from light

• 5% from ionized photons

Phosphor Crystals

• crystals fluoresce - convert x-ray to visible light

• should have minimal afterglow

• should emit sufficient light of desired color

Calcium Tungstate

• emits light in blue range

• works with silver halide film

• 30-40% conversion efficiency

Rare Earth Elements

• emits light in green spectrum

• works with green receiving film

• 50-60% conversion efficiency

Screen Efficiency & Speed

• speed at which x-rays converted to light

• screens rated on efficiency - “screen speed”

• depends on:

  • x-ray absorption

  • conversion of x-ray to light

  • amount of afterglow

Factors Affecting Speed

• crystal size

  • larger crystal = faster, less detail

• phosphor layer thickness

  • increase thickness = increase x-ray absorption, detail decrease

• emulsion thickness

  • thin emulsion = slower speed

  • faster emulsion = faster speed

Screen Care

• clean every 3 months

• remove foreign material & debris

• do not use alcohol or abrasives

• use UV light to inspect screen

• completely dry before placing in cassette