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



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tarix20.05.2018
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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



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

  • 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







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