Radiographic Intensifying Screens Flashcards
What are Intensifying Screens?
A device that converts the x-ray beam energy into visible light
What converts the x-ray beam into visible light?
Intensifying Screens
What are some advantages of Intensifying Screens?
- Shorter Exposure times
- Extend the life of the tube
- Improved image contrast
- Smaller focal spot size
What are some disadvantages of Intensifying Screens?
- Wear (they are not long term)
- Blurring
- Magnification
How much of the latent image is formed by the fluorescence of the screens?
99%
By amplifying the incoming x-ray beam, what happens to the patent dose?
It is decreased
What is the purpose of the reflective layer?
To intercept light that has interacted with the phosphor and redirects it to the film
What does the Base of the intensifying screen do?
Serves as mechanical support for the active phosphor layer
Describe the Base of the intensifying screen:
- Polyester or cellulose triacetate
- Rugged, moist layer (does not absorb water)
- Chemically inert
- Flexible
- Does not discolor with age
- Does not suffer from radiation damage
What is Luminescence?
The emission of visible light
Where is the protective coating layer located?
Layer closest to the film (actually touches the film)
What is the protective layer useful for?
To prevent Abrasions and Stains
- Abrasions
- Fingernails, Jewelry
- Pick off
What is pick off?
White line artifacts caused by watches, bracelets fingernails etc.
What prevents static electricity build up?
The Protective Layer
What are two things the protective layer must be?
- Transparent to light (for fluorescence)
- Have a durable surface for cleaning
What is another name for the phosphor layer?
The Active Layer
Where are the rare earth elements that create the glow located?
In the active layer
What creates the glow of the intensifying screen?
The rare earth elements within the active layer when exposed to radiation
What impacts the quality and amplification of the phosphor/ active layer?
- Thickness of layer
- Concentration of phosphor crystals
- Size of crystals
- Type of phosphor
What are the two types of rare earth elements used at the phosphor layer?
- Yttirium Tantalate
- Gadolanium (used in MRI contrast)
What do phosphors do?
Convert x-ray beam to light
What is minimal afterglow?
All light stops after exposure
What are the Favorable Properties of a Radiographic Intensifying screen phosphor
- Should have high atomic #, so absorption is high
- Should emit large amount of light when struck by x-rays
- Minimal afterglow
- Must have proper wavelength (spectral matching)
- Not affected by heat, humidity or other elements
What happens when x-rays interact with the reflective layer?
It emits light and reflects back to the film (shiny white surface)
What is the most important property of the reflective layer?
To intercept light and redirect it
What is the goal of the reflective layer?
To get as much light from the phosphor layer to the film
What typically degrades a film?
The way we handle them
What is an important thing about Fluorescence?
Light is distributed Isotropically (evenly)
What is Fluorescence?
Visible light emitted when phosphor is stimulated
What is Phosphorescence?
- Long periods of visible light emission after stimulation of phosphor
- Screen lag or after glow (still giving off light)
- Missed the return
Is Phosphorescence wanted or unwanted?
Unwanted
What is screen speed?
A number used to identify the efficiency of conversion of x-rays to usable light
What are effecting factors of screen speed?
Increase in:
- Phosphor size
- Thickness of layer
- Concentration
In terms of film speed, what will an increase in temperature do?
Give you a decrease in screen speed
What are the (3) screen speed classes?
- Fast
- Slow
- Medium
Describe the characteristics of Fast Screens:
Thick Layer
Large Crystals
Describe the characteristics of Slow Screens:
Thin Layer
Small Crystal size
Describe the characteristics of Medium Screens:
Medium Layers
Medium Crystal size
What speed film will give you better detail, but requires more radiation?
Slow Screens
The faster the intensifying screen the more…
Light emitted for the same x-ray exposure
What two speeds are typically used?
Fast and Slow
Fast screen film will give you speed, but what does it sacrifice?
Quality and Detail
Using intensifying screens greatly reduces what?
The amount of x-rays needed and patient dose
Are rare earth screens widely used?
Yes
Test
Lanthanum and Gadolinium are faster and more efficient than what?
Calcium Tungstate
What does RESC stand for?
Rare Earth Screen Cassettes
What is Quantum Mottle
Speckles; Defects in the image
like rain drops on a sidewalk
RESC are manufactured to perform at…
Increased speeds without effecting resolution
-but show effects of quantum mottle
RESC has increased sensitivity. What are some examples?
- Higher x-ray absorption
- More efficient conversion of x-ray energy into light
What must be spectrally matched with film?
RESC
What is responsible for absorption of x-rays in the screen
Photoelectric effect
What is K-shell absorption edge?
- When x-ray energy= K shell electrons
- Can bind and become available for photoelectric interactions
What is the K-shell?
The only shell that produces characteristic x-rays (69.5)
The probability of photoelectric absorption in RESC is higher when the x-ray energy in K-shell electron binding energy is…
Matched
What is the Intensification Factor (IF)?
The ratio of the exposures required to produce the same optical density with and without screens
IF=
Exposure required without screens
_____________________________
Exposure required with screens
If you are imaging a hand on a direct exposure cassette at 100 mAs, and at 4 mAs with an intensifying screen, what is your IF?
100
____ = 25
4
IF= 25 times higher
Intensification Factor is directly proportional to what?
Screen speed
What is Conversion Efficiency?
- The ability of the phosphor to emit as much light per x-ray photon interaction as possible
- Ideally x-ray photon is converted into visible light
True /False
In Conversion Efficiency, the higher it is the better?
True
As CE increases, patient dose does what?
Decreases
What is Quantum (x-ray photons) Mottle?
Insufficient quantity of photons striking the intensifying screen
What does an intensifying screen with a reflective layer do?
Provides focus onto the film for high conversion
What is spacial resolution?
- Ability to accurately image an object
- Image Detail
- How well you see the detail of the image
T/F
With the use of Intensifying screens you get a loss of Spatial resolution?
True
But less patient dose
Spacial Resolution is effected by what?
Focal Spot size
- Size
- Thickness
- Concentration
What does a greater concentration of crystals do?
Gives you better resolution; improved screen speed
What are ways spatial resolution are affected?
- OID
- SID
- Focal Spot size
- Motion
What does film screen combination decrease?
Decreases:
- Patient dose
- Occupational Exposure
- Tube heat production
- X-ray exposure time
- X-ray tube mA
- Focal spot size
What do film screen combinations Increase?
Increases:
- Variability of kVp selection
- Contrast adjustment
- Spatial resolution
- Ability to magnify image
What are the parts of a cassette?
- Front cover
- Contact felt
- Front screen (intensifying screen)
- Film
- Back screen (intensifying screen)
- Contact felt
- Back cover
Describe the front cover:
- Made of carbon fiber
- Low atomic #
- Minimal attenuation
Describe the back cover?
- Thicker
- Metal
- High atomic #
- Absorption of transmitted x-rays (image absorbed)
What are some cassette requirements?
- Low absorption front material
- Lead foil back (as a barrier)
- Provides tight film screen contact
What are some examples of the “ease of use” design for the cassettes?
- Easy to handle in the darkroom
- Will not accidentally open in daylight
- Not too heavy
What color is the front side of the cassette?
Brown
What is the reason for the felt in the primary barrier?
- To give a firm base for adequate pressure when closing
- Gives even contact
RESC exhibit a CE of…
15-20%
Resulting in increased sensitivity and speed
RESC emit a green light and the use of specially designed ________________ must be used to maintain speed
Green sensitive film
- Whatever the color, they must be matched
- (blue/ blue etc)
When opening, how much can you open the cassette?
2-3 inches
How do you store film?
On end
How are films cleaned?
With an electrostatic cleaning solution
DO NOT USE WATER
Why do you clean film with an electrostatic cleaning solution?
- Does not leave mineral stains
- Will not become sticky
How long will cassettes last with proper care?
10-15 years
When using gauze to clean screens, how do you wipe?
Side to side at right angles
What is poor screen film contact?
Loss of contact which degrades the film
What is the main cause of poor film screen contact?
Poor management of cassettes
When are film screens evaluated?
Every quarter or semi annually
What is the cause an exhausted cassette?
- Mishandling
- Lack of cleaning
- Age
