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