Primary Radiation exit from tube

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

• Break easily
• Difficulty in storage
• Expensive

• 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)

• Not as efficient
• Not used as often

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