Unit 5 (Radiographic Film & Intensifying Screens)
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Exposing the film to the ________ level makes the film insensitive.
Film that has emulsion on both sides:**
Film with emulsion on one side:
- Duplicating Film
- useful for making copies
List (in order from bottom to top) the components of radiographic film construction (4):**
- Adhesive Layer
- Supercoat (overcoat)
What is the foundation of radiographic film?
the film base
What are the thickness ranges for the radiographic film base?
- 150-200 micrometers
- (10-6 Mm)
Name some basic requirements for the radiographic film base (4):**
- flexible yet durable
- uniformly radiolucent
- must retain its size and shape
- made from thin sheets of polyester (Modern)
Before polyester, the radiographic film base was made of ___________(3, in order).
- glass plates coated with emulsion
- Cellulose Nitrate
- Cellulose Triacetate
What prompted the change from radiographic film bases being made from glass plates to being made from polyester?
glass plating shortage during WWI
What was the major drawback of using Cellulose Nitrate as a radiographic film base?
highly flammable (devastating hospital fires)
Name three disadvantages of using Cellulose Triacetate at a radiographic film base:
- Flammable (equal to paper's flammability)
- film would warp with age
- not as resilient
When was polyester as a radiographic film base first introduced?
Name two advantages of the specialization of blue tint in radiographic film bases:
- reduces eye strain
- increases diagnostic accuracy
What is crossover?
when light from one screen exposed the opposite emulsion
Does crossover increase or decrease recorded detail?
In a single emulsion film, should the emulsion side face toward or away from the intensifying screen?
In a single emulsion film, which side of the film is dull and which side is shiny?
- emulsion side is dull
- non-emulsion side is shiny
What type of film is most often used in mammography and why?**
- single emulsion film
- for better recorded detail/resolution due to lack of penumbra
Which type of film can be identified by a small notch in the lower left corner?
single emulsion film (copying film)
What binds the emulsion to the film base?
the Adhesive Layer
What can be described as the "heart" of the film?
What is the emulsion of radiographic film composed of?**
silver halide crystals suspended in gelatin
What is an important property of the silver halide crystals?
they are photosensitive
What is the thickness of the Emulsion layer in radiographic film?
Name some important attributes of the Gelatin that suspends the silver halide crystals (5):**
- allows even distribution of the crystals
- non-reactive (not sensitive to heat)
- penetrable by processing chemicals
- low atomic number
Name three types of Silver Halide Crystals:**
- Silver Bromide (most popular)
- Silver Iodide (also popular)
- Silver Chloride (not as popular as the other two)
Name the protective layer of gelatin on top of the radiographic film:
Name some important attributes of the Supercoat/Overcoat of radiographic film:**
- provides sturdiness
- reduces damage (scratches, pressure, etc)
If radiographic film folds, in the area of folding is the density increased or decreased?
increased (crystals are activated)
If radiographic film is scratched, is the scratch an area of increased or decreased density?
decreased (the emulsion is removed)
If hands with lotion handle radiographic film, will the touched areas show increased or decreased density?
decreased (crystals removed)
Name the four steps of manufacturing radiographic film:
- crystal production
What is an important aspect of all four steps of manufacturing radiographic film?
they all must take place in total darkness (crystals must remain un-activated)
What is the first step in silver halide crystal formation?
pure metallic silver is dissolved into nitric acid, forming silver nitrate.
What is silver nitrate combined with to form silver bromide and potassium nitrate?**
What do you get when you combine silver nitrate and potassium bromide?**
silver bromide and potassium nitrate
Which chemical element formed is water soluble and is washed away during production of the emulsion?**
When the potassium nitrate is washed away during silver halide crystal formation, what remains?
What are the two Crystal Classifications and shapes?
Name three advantages of tabular crystal formations:
- absorbs more photons
- can use thinner emulsion
- speeds up processing
What shape does the inner structure of a silver halide crystal take on?
cubic form (cubic lattice)
What charge does the sensitivity speck give to the ejected electron?**
What does the sensitivity speck attract and why?**
- the sensitivity speck is negatively charged (electrons), therefore it attracts silver which is positive.
What type of bond joins the elements of the crystal lattice (silver, bromide, iodide, sensitivity speck, etc)?**
Why does silver provide greater density?
because silver turns black
What impurity composes the sensitivity speck?**
What is the main purpose of the sensitivity speck?**
it allows for collection of many silver atoms in one area after being exposed to x-ray or light photons
What is the length of time the crystals need to grow?
When is ripening complete?
when the emulsion is cooled
What is the ripening time dependent on?
the size and emulsion (the size of the crystals)
With larger crystals, is the time needed for the ripening process increased or decreased?
If the crystals are larger, does the amount of penumbra increase or decrease?
increase (more divergence)
If the crystals are larger, does recorded detail increase or decrease?
decrease (more penumbra)
Will a pediatric screen or a detail screen require a longer ripening period?
pediatric (larger crystals, more divergence, less detail...but decreased dose)
What is happening during the Mixing period of manufacturing radiographic film?
- shredded emulsion is heated and melted
- (specific temperature)
- (sensitizes crystals)
Name some extra ingredients that might be added during the mixing process of manufacturing radiographic film
- dyes (i.e. blue tint)
- anti-fogging agents
How is a film that is sensitive to all wavelengths described?
How is a film that is not sensitive to red described?
orthochromatic (therefore, you can use a red light when developing and it won't expose the film)
How is the spectral sensitivity of the film determined?
by the dyes added during mixing (acting as filters)
Film is produced in what dimensions by the coating process?
40" rolls of film
When does Latent Image Formation take place?
prior to processing, after exposure
When was the Gurney-Mott Theory made?
1938 (concerning the theory that x-ray and light photons deposit energy into silver halide crystals: latent image formation)
The energy stored in silver halide crystals disrupts bonds in the crystal's atoms, causing (3 steps):
- an electron to be freed
- halide migrates into gelatin
- silver ion remains
Name three basic types of film:
- Direct exposure (nonscreen) film ex. cardboard
- Intensifying screen film
- Special applications ex. mammography
Special Application Films (7):
- Detail extremity radiography
- Contact surgical radiography
- CRT imaging
- Fluoroscopic spot
In the Duplication process, the film must undergo:
Prior to exposure, how should the film be stored?
- stored on end and upright
- according to age (oldest in front)
- below 68°F (20°C)
Prior to exposure, what should the humidity levels be?
Prior to exposure, what should you limit the film's exposure to?
What medical record information should each exposure include (6)?
- date of exposure
- full name of patient
- name of institution
- name of ordering physician
- patient identification number
- type of exam
What is the purpose of an intensifying screen?
it amplifies the beam to reduce patient dose
The image is produced by what percentages of what aspects of radiation?**
- 99% from light conversion (x-rays convert to light)
- 1% from direct interaction between x-rays and film
When was the Intensifying Screen developed and by who?
Name the elements that make up the construction of an intensifying screen (4):
- reflective layer
- phosphor layer
- protective coat
What is the base of an Intensifying screen made of and how thick is it?
- polyester plastic
- 1 mm thick
Name some basic requirements for the Intensifying Screen base (3):
- chemically inert
The reflective layer deals with what type of emission?
What is the intensifying screen's reflective layer made of?
a thin layer of magnesium oxide or titanium dioxide
What are the effects of the intensifying screen's reflective layer (3)?
- reflects light back to the film
- allows for reduction of patient dose
- loss of image sharpness/recorded detail due to increased penumbra
What is the "active layer" of the intensifying screen?
What is contained in the phosphor layer of the intensifying screen?
crystals that absorb x-rays and give off light
What conditions of the phosphors in the intensifying screen will result in emitting the most light?**
- larger size phosphors
- thicker layer
- higher concentration
What type of interactions can take place with high atomic number phosphors?**
- photoelectric absorption
- compton (lower energies interacting with the outer shell)
Name two aspects of the intensifying screen's protective coat:
- applied over the phosphor layer
- limits abrasions and staining from use
Name five important aspects concerning the phosphors in intensifying screens:
- atomic number
- conversion efficiency
- spectral emission
- rare earths
In dealing with the phosphors of the intensifying screen, is a higher or lower atomic number preferred, and why?
- high atomic number preferred
- increases the likelihood of x-ray photon absorption
*but you don't want it to be TOO high, or the photon will pass on through*
The precise wavelength of light emitted by the phosphor (in the intensifying screen) is the:
When considering the spectral emission of the intensifying screen, what must it do?
it must match the film screen's spectral sensitivity.
The ability of a substance to emit light in response to stimulation (radiation):**
Name two types of luminescence:
When light is emitted from a phosphor instantaneously, it is called:**
When light emitted from a phosphor is delayed, it is called:**
- (also, screen lag or "after glow")
What is screen lag?**
When the intensifying screen glows slightly after being exposed (occurs more as the phosphors age)...an "afterglow"
What is the average lifespan for an intensifying screen?**
Name four phosphor materials:
- Zinc sulfide
- Barium lead sulfide
- Calcium tungstate
- Rare earths (Modern, more efficient)**
Name three materials that rare earths are compounded with to be more efficient:
Name three ways in which rare earths as phosphor material are an improvement over calcium tungstate:
- greater absorption ability
- greater intensification factors (more light with every interaction)
- greater conversion efficiency
Do rare earths increase or decrease speed?
they increase speed (without compromising resolution), therefore decreasing patient dose
Compare Rare Earths conversion efficiency to the conversion efficiency of Calcium Tungstate:
- Rare Earths: 15-20% conversion efficiency
- Calcium Tungstate: 5% conversion efficiency
The ability of an imaging system to accurately image an object:
If a phosphor crystal size is smaller, will the resolution be increased or decreased?
If the phosphor layer is thicker, is the resolution increased or decreased?
If the concentration of the phosphor crystals is increased, is the resolutions increased or decreased?
increased (less penumbra)
Describe resolution's relationship to phosphor size, layer thickness, and concentration:
- phosphor size: Indirect relationship
- layer thickness: Indirect relationship
- concentration: Direct relationship
What can you do to decrease light emission on your screen?**
- small crystals
- thinner layer
- decrease concentration
- (making screen slower)
Resolution measurements for:
the naked eye:**
direct exposure film:**
- the naked eye: 10-20 lp/mm
- direct exposure film: 100 lp/mm
- detail screens: 15 lp/mm
- par speed: 10 lp/mm
- high speed: 7 lp/mm
What is Quantum Mottle (grainy appearance of image) most often caused by?**
- not enough mA
- also called noise
Describe speed's relationship to phosphor size, layer thickness, and concentration:
Direct relationship with all three
Temperatures of _______ will decrease speed:
100°F or above
Give the relative-speed number for the following:
Par speed =
High speed =
- Par speed = 100 RS
- High Speed = 200-1200 RS
- Fine/detail = 20-80 RS
Calcium tungstate absorbs _______% of the beam.
Rare Earths absorb _________% of the beam.**
- Calcium tungstate: 20-40%
- Rare earths: 50-60%
- (rare earths more efficient)
When does the K-shell absorption edge occur?
When the photon energy matches the K-shell binding energy of the phosphor
The rare earth's binding energy of the k-shell is around ___ keV, and the calcium tungstate's binding energy of the k-shell is around ____ keV.
- rare earth: 25 keV
- calcium tungstate: 75 keV
Due to the binding energies of the k-shells of rare earth and calcium tungstate, what can we conclude:
Fewer x-rays will be able to react with calcium tungstate because of its high atomic number. This is because we need energy ranges close to or slightly greater than the binding energy of the k-shell for a reaction to occur.
What are the atomic number ranges of rare earth?**
Name some important aspects of the cassette holding the film (4):
- the front must be uniformly radiolucent
- the back should be lead-lined
- front and back should be rigid
- there should be a foam pressure pad on both sides
What is the purpose of the foam pressure pads on both sides of the cassette containing the film?
- used for mounting intensifying screens
- ensures good film/screen contact
Without good film/screen contact, will density increase or decrease? Will detail increase or decrease?
- Density: decrease
- Detail: decreases
What is used to test for film/screen contact?**
Why should the front of the film cassette be uniformly radiolucent and the back of the film cassette be lead-lined?
- The front should be radiolucent so that the photons pass through it to interact with the phosphors.
- The back should be lead-lined to absorb backscatter.
How should film be loaded and unloaded from the cassette and why?
- DO NOT fully open the cassette, open it just enough to slide the film in/out
- This helps prevent the collection of dust and condensation
How should cassette's be stored:
- store on end (like a book)
- store empty (if storing for a long period of time)
Why are cassette's not to be stored in a flat position?
the screen is prone to warping eventually if stored in this position
Describe how to properly clean a cassette holder (5 steps):
- apply specially designed electrostatic cleaning solution to gauze
- wipe from side to side
- repeat at 90° to first application
- follow with dry gauze to absorb excess
- leave open (on end) until thoroughly dry
Name three means by which a phosphor may be activated, and what can they produce:
- these can all produce artifacts
Blocked light transmission can show up as ______ and is often caused by _______.
- a white spot on the image
- debris in the cassette
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