Midterm 2 Flashcards
List the darkroom essentials
Film processors Loading bench Film bin Film identification printer Safelights
Safelights must not exceed ___ watts
15
Safelights must be at least ___ feet away from work area
4
Undeveloped film must not be exposed to safelights more than ___ minutes
3
Safelights usually only allows light from the ____ end of visible light spectrum?
Red (GBX filter)
_______ consists of incrementally exposing undeveloped film to dark room conditions in 30 sec intervals for up to 3 minutes.
Safe light test
What are the steps of film development?
Exposure Development Fixing Washing Dry
What part of film development/image creation is when the film is exposed to light?
Exposure
Note: 99% of the image is created by light emanated by screens. 1% or less comes from direct exposure of silver halide crystal by an x-ray photon
Exposure of the film causes silver bromide crystal to what?
Separate into a silver ion and a bromine ion
What step of film development is the latent image created?
Exposure
What does the developer do in film development?
Donates electrons that create elemental silver
Note: black in color
Between developer and fixer, what happens?
Wash stop bath to remove excess developer
What does fixer do in film development?
Remove unexposed silver halide crystals from emulsion.
Permanently stops exposure beyond what has been done prior to developer
What does the final wash do in the film development process?
Clears all chemicals on the film surface and emulsion.
Prevents fixer chemicals from continuing to cause chemical changes to emulsion after the finished product has been produced.
What happens in the film development process if washing was not good enough?
Overtime the film degrades: brown color, acetic acid smell, etc
What pH is developer?
pH 10-11.5, strong base
What is in developer?
Activator
Reducing agents
Preservative
Restrainer
What does “activator” do in developer solution and what is it?
Sodium carbonate
Softens gelatin protective cover on film, Makes alkaline pH at >7
What do the “reducing agents” do in developer solution and what is it?
Hydroquinone or Phenidone (Metal or Elon)
Reduces EXPOSED silver halide to black metallic silver
What does the “preservative” do in developer solution and what is it?
Sodium sulfite
Prevents oxidation
What does the “restrainer” do in developer solution and what is it?
Potassium bromide, acetic acid
Prevents chemical fog in new developer
What is in the fixer solution?
Clearing agent
Tanning agent
Activator
What does the “clearing agent” do in fixer solution and what is it?
Ammonium thiosulfate
Dissolves undeveloped silver halide, removes it from emulsion
What does the “tanning agent” do in fixer solution and what is it?
Potassium alum
Shrinks, hardens, preserves emulsion
What does the “activator” do in fixer solution and what is it?
Acetic acid
Neutralizes developer, stops the development process, maintains acid pH
Processing is a function of 3 T’s
Time
Temp
Titration (chemicals)
What causes film overdevelopment?
Increased time, temp or titration.
Note: overdevelopment = darker film
Film overdevelopment is caused by processor-induced fog which is the forced development of
unexposed silver halide crystals by too much processing
Manual processing: ___˚F, and list time for development, fixer, wash, dry
68˚ F 5 min development 10 min fixer 20 min washing 20-40 min drying
Summary: estimated 1 hour total for each film in manual processing
Automatic processing: temp ____ ˚F and ave. time ____ mins
92-96˚F
1.5-3 mins
Benefit of automatic developer vs manual
Faster, constant agitation, consistency
If you don’t take many films, but you keep your processor running all day, your machine requires [more/less] chemical replenishment
More
Because chemicals degrade more quickly when they are sitting at higher temps
Under-replenishment of automatic developer chemicals causes (in regards to contrast and film density)
Loss of contrast (appears gray)
Loss of film density
Over-replenishment of automatic developer chemicals causes (in regards to contrast and film density)
Loss of contrast (increased fog)
Chemical waste
Every 1-2 months you should do what to your developer system (4)
- Completely change chemicals
- Clean tank
- Check replenished rates
- Check cycle time
Causes of lower contrast on a film is caused by these (5) adverse conditions in the dark room:
- safe light fog
- night room temp/humidity
- chemical fog from processor too hot
- chemical fog from chemicals too concentrated
- film past expiration date
How does penumbra increase most rapidly?
Increasing OID
How do you get shape distortion?
When x-ray tub is angled and object and film are parallel… unequal magnification creates shape distortion: e.g. increase OID of one end of a bone, it appears fatter and shortened.
What is the machine that exposes film to a step wedge of known densities?
Sensitometer
The sensitometric (H&D) curve is a graphic measure of how a film records density over a range of exposures. What is the vertical/Y axis measuring and what is the horizontal/X axis measuring?
Y axis — optical density
X axis — log relative exposure
Note: the Y axis goes from 0 to 4.0. 0 means 100% light transmission and 0 absorption of light (which isn’t truly possible)
The H&D curve consists of 3 parts of the curve named
Toe, body, shoulder
The toe of the H&D curve measures what
Light absorbed by the film base, plus any fog
The length of toe indicates
Sensitivity of film to fog
The body of the H&D curve is the straight line component of the curve. It determines
The latitude of the film
Short latitude vs. long latitude (body of the H&D curve)
Short lat has vertical rise and higher contrast film
Long lat has lower slope and lower contrast film, more shades of gray
What does the shoulder of the H&D curve represent
The “D-max” or maximum optical density the film will achieve no matter how much mAs or kVp you throw at it
What is a density meter?
Measures optical density of each step on a step wedge. Scale from 0 to 4
What do the numbers on the densitometer represent?
0 means 0% absorption of light through the film. So the film transmits 100% of light through itself.
4 means 100% absorption of light. The film is black and lets 0 light through it.
What is the significance of the densitometer?
Measurements obtained track processor performance over time
________ is established by finding the step on the sensitometric step wedge strip that has the closest optical density to 1.0
Speed index
___________ is the difference in optical density between the Speed Index step and the optical density reading of the step that is 2 steps darker on the sensimetric strip
Contrast index
Contrast index step should be between what 2 values for films used for skeletons
1.4 to 1.7
Gross fog index is
Base plus Fog
It’s the optical density of a film when its not been exposed and was run through processor blank. In a perfect world, it’d be clear. However there is no such thing so the usual value for optical density of fresh, unexposed film is 0.15-0.20
What is the usual value for optical density of fresh, unexposed film
0.15-0.20
Faster films have a higher/lower gross fog index
Higher
Fast films = high gross fog index
The longer the toe, the more/less sensitive to fog the film is
Less
Big toe = less sensitive to fog
You should not see fluctuations greater than (3) on serial readings for speed, contrast, gross fog index
+/- 0.15 speed and contrast index
+/- 0.03 gross fog index
What kind of crystals give you the slowest speed film but the best detail?
Small crystals in thin layers
And so: fast speed/lowest detail are large crystals in thick layers
Term used to describe range of densities that can be recorded on the film
Latitude
- Wide is best for low contrast e.g. chest
- Short is best for high contrast
How are contrast and latitude related (for film)?
Inversely
As contrast decreases, latitude increases.
Double mAs, double
Density
