Always keep the collimated area smaller than the size of the cassette

ALWAYS KEEP THE COLLIMATED AREA SMALLER THAN THE SIZE OF THE CASSETTE

• ALWAYS KEEP THE COLLIMATED AREA SMALLER THAN THE SIZE OF THE CASSETTE

Primary Radiation exit from tube

• Primary Radiation exit from tube

• 100 % enters patient

• 1% exits for form image on cassette below

• REMNANT Radiation

FIRST “FILM”

• FIRST “FILM”

• GLASS PLATES

• CELLULOSE ACETATE

• HIGHLY FLAMMABLE
• EASILY TORN
• RESPONSIBLE FOR MANY FIRES IN HOSPITAL BASEMENTS

SIZES

• SIZES

• 14 X 17

• 11 X 14

• 10 X 12

• 8 X 10

Standard “inches”:

• Standard “inches”:

• 8” x 10”

• 10” x 12”

• 11” x 14”

• 14” x 17”

• Film is a media that makes a permanent record of the image.

• Image recorded on film is caused by exposure to photons.

X-ray photons converted to light photons

• X-ray photons converted to light photons

• Image before processing

• Latent image

• Made visible by chemical processing

• Manifest image

Radiographic film was most common image receptor

• Radiographic film was most common image receptor

• Two parts:

• 1. Base

• 2. Emulsion

Made of a polyester plastic

• Made of a polyester plastic

• Must be clear, strong, consistent thickness

• Tinted pale blue or blue-gray (reduces eye strain)

• COATED ON 1 OR 2 SIDES WITH EMULSION

Film emulsion can be on one side or both sides of base (single emulsion / double emulsion)

• Film emulsion can be on one side or both sides of base (single emulsion / double emulsion)

• Protective overcoat layered on top of emulsion

• Emulsion is a gelatin containing the film crystals

Made of mixture of gelatin & silver halide crystals

• Made of mixture of gelatin & silver halide crystals

• Most x-ray film emulsions made of :

• silver bromide (90%) silver iodide (10%)

• Photographically active layer – activated by light & radiation to create image

SINGLE OR DOUBLE EMULSION

• SINGLE OR DOUBLE EMULSION

• COATED ON A BASE

• EMULSION : GELATIN

• WITH SILVER HALIDE CRYSTALS

• BASE: SUPPORT

• POLYESTER

SINGLE EMULSION = BETTER DETAIL

• SINGLE EMULSION = BETTER DETAIL

• DOUBLE EMULSION = LESS DETAIL

• PARALLAX – single image

• With double emulsion – an image is created on both emulsions – then superimposed – slight blurring of edges

DARK SPOTS

• DARK SPOTS

• – SILVER HALIDE CRYSTALS THAT HAVE BEEN EXPOSED TO PHOTONS
• – TURN TO BLACK METALLIC SILVER AFTER PROCESSING

• LIGHT AREAS

• NO CRYSTALS EXPOSED
• SILVER HALIDE IS WASHED AWAY WITH PROCESSING

• Size of silver halide crystals & emulsion thickness determine speed of film and degree of resolution

• Speed – the response to photons

• Resolution – the detail seen

Larger crystals or Thicker crystal layer

• Larger crystals or Thicker crystal layer

• Faster response= less detail, and

• less exposure (chest x-ray)

• Finer crystals / thinner crystal layer

• Slower response, greater detail, more exposure (extremity)

• More silver halide crystals = faster film

• Less silver halide crystals= slower film

Clean, dry location

• Clean, dry location

• 40 – 60 % Humidity 70 º Fahrenheit

• Away from chemical fumes

• Safe from radiation exposure

• Standing on edge

• Expiration date clearly visible

Light

• Light

• X-rays

• Gamma Rays

• Gases

• Fumes

Unintended uniform optical density on a radiograph

• Unintended uniform optical density on a radiograph

• Get a long scale of contrast

Cassettes serve 3 important functions:

• Cassettes serve 3 important functions:

• Protect film from exposure to light

• Protect film from bending and scratching during use.

• Contain intensifying screens, keeps film in close contact to screen during exposure.

Direct x-ray exposure to film required

• Direct x-ray exposure to film required

• 25 to 400 times more radiation to create an image on the film

• BETTER DETAIL THAN FILM SCREEN (NO BLURRING OF IMAGE FROM LIGHT)

• ALL EXPOSURE MADE FROM X-RAY PHOTONS

• BIG DOSE TO THE PATEINT

The CASSETTE is used to hold the film during examinations.

• The CASSETTE is used to hold the film during examinations.

• It consist of front and back intensifying screens, and has a lead (Pb) backing.

• The cassette is light tight

Exposure side of cassette is the “front”.

• Exposure side of cassette is the “front”.

• Has the ID blocker (patient identification)

• Made of radiolucent material

• Intensifying screen mounted to inside of front.

Back made of metal or plastic

• Back made of metal or plastic

• Inside back is a layer of lead foil – prevents backscatter that could fog the film

• Inside foil layer is a layer of padding – maintains good film/screen contact

• Back intensifying screen mounted on padding

• MUST BE MATCHED WITH 1 OR 2 SIDED INTENSIFYING SCREENS

• Single emulsion film is used with single intensifying screen.

Polyester plastic base – support layer

• Polyester plastic base – support layer

• Phosphor layer – active layer

• Reflective layer – increases screen efficiency by redirecting light headed in other directions

• Protective coating

Flat base coated with fluorescent crystals called phosphors

• Flat base coated with fluorescent crystals called phosphors

• Active layer- (phosphors) give off light when exposed to photons (x-rays)

RARE EARTH – (emits green light)

• RARE EARTH – (emits green light)

• Developed in 1980’s
• Most efficient
• Most common in use today

• CALCIUM TUNGSTATE (blue light)

• Not as efficient
• Not used as often

Gadolinium

• Gadolinium

• Lanthanum

• Yttrium

• Found in low abundance in nature

DISADVANTAGES:

• DISADVANTAGES:

• less detail than direct exposure
• (detail better with rare earth than
• calcium tungstate screens)

• ADVANTAGES:

• Reduce patient exposure
• Increase x-ray tube life

• Blue – UV light sensitive film – CALCIUM TUNGSTATE screens

• Green, Yellow-Green light sensitive film -

• RARE EARTH screens

The light photons are emitted by phosphor crystals.

• The light photons are emitted by phosphor crystals.

• These crystals are significantly larger than the silver halide crystals in the film

• Screen reduces image sharpness

• Exams requiring extremely fine detail use screens with small crystals.

Efficiency of a screen in converting x-rays to light is Screen Speed.

• Efficiency of a screen in converting x-rays to light is Screen Speed.

Greater efficiency

• Greater efficiency

• less exposure - faster
• Standard screen speed class of 100
• 200 screen speed is twice as fast

• Speeds for routine work: 200 – 800

• Speeds for high detail: 50 - 100

• FASTER SPEED

• REDUCES PATIENT EXPOSURE

• FASTER SPEED –

• REDUCES IMAGE DETAIL (LIGHT BLURING AROUND IMAGE)

NO GAPS-

• NO GAPS-

• FOAM BACKING HELPS TO PLACE INTENSIFYING SCREENS IN DIRECT CONTACT WITH THE FILM

• IF GAPS

• MORE LIGHT CAN BE EMITTED IN SPACE, CAUSING THE IMAGE TO BE OF POOR DETAIL

1% of xray photons that leave patient

• 1% of xray photons that leave patient

• Interact with phosphors of intensifying screens

• 100’s of light photons created to make image on film

• Light photons expose silver halide crystals in the film emulsion –

• Turn black metallic silver after procession