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Radiation Physics And Safety > Midterm 2 > Flashcards

Midterm 2 Flashcards

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1
Q

List the darkroom essentials

A 
Film processors
Loading bench
Film bin
Film identification printer
Safelights
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2
Q

Safelights must not exceed ___ watts

A

15

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3
Q

Safelights must be at least ___ feet away from work area

A

4

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4
Q

Undeveloped film must not be exposed to safelights more than ___ minutes

A

3

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5
Q

Safelights usually only allows light from the ____ end of visible light spectrum?

A

Red (GBX filter)

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6
Q

_______ consists of incrementally exposing undeveloped film to dark room conditions in 30 sec intervals for up to 3 minutes.

A

Safe light test

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7
Q

What are the steps of film development?

A 
Exposure
Development
Fixing
Washing
Dry
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8
Q

What part of film development/image creation is when the film is exposed to light?

A

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

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9
Q

Exposure of the film causes silver bromide crystal to what?

A

Separate into a silver ion and a bromine ion

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10
Q

What step of film development is the latent image created?

A

Exposure

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11
Q

What does the developer do in film development?

A

Donates electrons that create elemental silver

Note: black in color

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12
Q

Between developer and fixer, what happens?

A

Wash stop bath to remove excess developer

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13
Q

What does fixer do in film development?

A

Remove unexposed silver halide crystals from emulsion.

Permanently stops exposure beyond what has been done prior to developer

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14
Q

What does the final wash do in the film development process?

A

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.

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15
Q

What happens in the film development process if washing was not good enough?

A

Overtime the film degrades: brown color, acetic acid smell, etc

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16
Q

What pH is developer?

A

pH 10-11.5, strong base

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17
Q

What is in developer?

A

Activator
Reducing agents
Preservative
Restrainer

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18
Q

What does “activator” do in developer solution and what is it?

A

Sodium carbonate

Softens gelatin protective cover on film, Makes alkaline pH at >7

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19
Q

What do the “reducing agents” do in developer solution and what is it?

A

Hydroquinone or Phenidone (Metal or Elon)

Reduces EXPOSED silver halide to black metallic silver

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20
Q

What does the “preservative” do in developer solution and what is it?

A

Sodium sulfite

Prevents oxidation

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21
Q

What does the “restrainer” do in developer solution and what is it?

A

Potassium bromide, acetic acid

Prevents chemical fog in new developer

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22
Q

What is in the fixer solution?

A

Clearing agent
Tanning agent
Activator

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23
Q

What does the “clearing agent” do in fixer solution and what is it?

A

Ammonium thiosulfate

Dissolves undeveloped silver halide, removes it from emulsion

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24
Q

What does the “tanning agent” do in fixer solution and what is it?

A

Potassium alum

Shrinks, hardens, preserves emulsion

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25
Q

What does the “activator” do in fixer solution and what is it?

A

Acetic acid

Neutralizes developer, stops the development process, maintains acid pH

26
Q

Processing is a function of 3 T’s

A

Time
Temp
Titration (chemicals)

27
Q

What causes film overdevelopment?

A

Increased time, temp or titration.

Note: overdevelopment = darker film

28
Q

Film overdevelopment is caused by processor-induced fog which is the forced development of

A

unexposed silver halide crystals by too much processing

29
Q

Manual processing: ___˚F, and list time for development, fixer, wash, dry

A 
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

30
Q

Automatic processing: temp ____ ˚F and ave. time ____ mins

A

92-96˚F

1.5-3 mins

31
Q

Benefit of automatic developer vs manual

A

Faster, constant agitation, consistency

32
Q

If you don’t take many films, but you keep your processor running all day, your machine requires [more/less] chemical replenishment

A

More

Because chemicals degrade more quickly when they are sitting at higher temps

33
Q

Under-replenishment of automatic developer chemicals causes (in regards to contrast and film density)

A

Loss of contrast (appears gray)

Loss of film density

34
Q

Over-replenishment of automatic developer chemicals causes (in regards to contrast and film density)

A

Loss of contrast (increased fog)

Chemical waste

35
Q

Every 1-2 months you should do what to your developer system (4)

A
  • Completely change chemicals
  • Clean tank
  • Check replenished rates
  • Check cycle time
36
Q

Causes of lower contrast on a film is caused by these (5) adverse conditions in the dark room:

A
  • safe light fog
  • night room temp/humidity
  • chemical fog from processor too hot
  • chemical fog from chemicals too concentrated
  • film past expiration date
37
Q

How does penumbra increase most rapidly?

A

Increasing OID

38
Q

How do you get shape distortion?

A

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.

39
Q

What is the machine that exposes film to a step wedge of known densities?

A

Sensitometer

40
Q

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?

A

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)

41
Q

The H&D curve consists of 3 parts of the curve named

A

Toe, body, shoulder

42
Q

The toe of the H&D curve measures what

A

Light absorbed by the film base, plus any fog

43
Q

The length of toe indicates

A

Sensitivity of film to fog

44
Q

The body of the H&D curve is the straight line component of the curve. It determines

A

The latitude of the film

45
Q

Short latitude vs. long latitude (body of the H&D curve)

A

Short lat has vertical rise and higher contrast film

Long lat has lower slope and lower contrast film, more shades of gray

46
Q

What does the shoulder of the H&D curve represent

A

The “D-max” or maximum optical density the film will achieve no matter how much mAs or kVp you throw at it

47
Q

What is a density meter?

A

Measures optical density of each step on a step wedge. Scale from 0 to 4

48
Q

What do the numbers on the densitometer represent?

A

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.

49
Q

What is the significance of the densitometer?

A

Measurements obtained track processor performance over time

50
Q

________ is established by finding the step on the sensitometric step wedge strip that has the closest optical density to 1.0

A

Speed index

51
Q

___________ 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

A

Contrast index

52
Q

Contrast index step should be between what 2 values for films used for skeletons

A

1.4 to 1.7

53
Q

Gross fog index is

A

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

54
Q

What is the usual value for optical density of fresh, unexposed film

A

0.15-0.20

55
Q

Faster films have a higher/lower gross fog index

A

Higher

Fast films = high gross fog index

56
Q

The longer the toe, the more/less sensitive to fog the film is

A

Less

Big toe = less sensitive to fog

57
Q

You should not see fluctuations greater than (3) on serial readings for speed, contrast, gross fog index

A

+/- 0.15 speed and contrast index

+/- 0.03 gross fog index

58
Q

What kind of crystals give you the slowest speed film but the best detail?

A

Small crystals in thin layers

And so: fast speed/lowest detail are large crystals in thick layers

59
Q

Term used to describe range of densities that can be recorded on the film

A

Latitude

  • Wide is best for low contrast e.g. chest
  • Short is best for high contrast
60
Q

How are contrast and latitude related (for film)?

A

Inversely

As contrast decreases, latitude increases.

61
Q

Double mAs, double

A

Density

Radiation Physics And Safety (8 decks)

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