Primary Radiation exit from tube



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tarix20.05.2018
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Primary Radiation exit from tube

  • Primary Radiation exit from tube

  • 100 % enters patient

  • 1% of the exit radiation forms image on cassette below

  • REMNANT Radiation-

    • Attenuated Beam
    • Scatter Radiation-Compton


Exit radiation interacts with IMAGE RECEPTOR to capture the image.

  • Exit radiation interacts with IMAGE RECEPTOR to capture the image.

  • radiographic image- permanent record of radiation exposed in image receptor

  • latent image -the undeveloped, unprocessed image formed by exit radiation



FIRST “FILM”

  • FIRST “FILM”

  • Glass plates

  • Cellulose acetate

    • Highly flammable
    • Easily torn




Standard “inches”:

  • Standard “inches”:

  • 8” x 10”

  • 10” x 12”

  • 11” x 14”

  • 14” x 17”



Two basic parts:

  • Two basic parts:

  • 1. Base

  • 2. Emulsion and Topcoat



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)

  • Uniform lucency

  • 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-topcoat, supercoat

  • Emulsion is a gelatin containing the film crystals---THE HEART OF THE FILM



Emulsion :

  • Emulsion :

    • Gelatin with silver halide crystals imbedded
    • Single or double emulsion, coated on one or both sides of
    • polyester base
  • Topcoat:

    • Protective layer
    • AKA supercoat








Made of mixture of gelatin & silver halide crystals

  • Made of mixture of gelatin & silver halide crystals

  • Silver halide crystals made of silver bromide (90%) and silver iodide (10%)

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



Gelatin- comprised of mostly bone, suspends grains (crystals) easily, easily penetrated by processing agents, can be varied in thickness

  • Gelatin- comprised of mostly bone, suspends grains (crystals) easily, easily penetrated by processing agents, can be varied in thickness

  • Silver Halide Crystals- x-ray (silver iodide) and light sensitive (silver bromide) crystals, contains sensitivity speck that reacts to both light and x-ray, this is where latent image is formed, crystals are varying in size, shape, density













  • More silver halide crystals = faster film

  • Less silver halide crystals= slower film





Parallax

  • Parallax











Light

  • Light

  • X-rays

  • Gamma Rays

  • Gases

  • Fumes





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













Direct x-ray exposure to film:

  • Direct x-ray exposure to film:

  • Requires 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

  • Very large dose to the patient



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



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)



Gadolinium

  • Gadolinium

  • Lanthanum

  • Yttrium

  • Found in low abundance in nature





DISADVANTAGES:

  • DISADVANTAGES:

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

    • Reduce patient exposure
    • Increase x-ray tube life






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.



  • Blue – UV light sensitive film – CALCIUM TUNGSTATE screens

  • Green, Yellow-Green light sensitive film -

  • RARE EARTH screens











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





1% of x-ray photons that leave patient

  • 1% of x-ray 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





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





























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