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Physics > Test 4 Chapters 10-11 > Flashcards

Test 4 Chapters 10-11 Flashcards

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1
Q

Ability to image small objects

A

Spatial Resolution

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2
Q

Distinguish anatomy with similar subject contrast

A

Contrast Resolution

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3
Q

OID refers to

A

Size, magnification

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4
Q

You want OID as small or large as possible?

A

Small

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5
Q

Most CR/DR systems run between speeds of what?

A

200-400

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6
Q

Direct exposure means what in regard to patient exposure and intensifying screens?

A

No intensifying screens and TONS of patient exposure

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7
Q

Speed number is directly or indirectly related to patient exposure?

A

Directly

1-50 is a reduction by 50. 100-200 is a reduction by 100

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8
Q

Noise looks like what on an image?

A

Fuzzy, grainy

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9
Q

Noise is what?

A

Film graininess-actual piece of film NOT image
Structure Mottle
Quantum Mottle-number of photons controlled by mAs
Scatter

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10
Q

Image quality speed

A

How efficiently photons are converted to light. The faster the speed, the faster the conversion, the less mAs needed to convert, thus less exposure to patient

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11
Q

Spatial resolution improves as…

A

Screen blur decreases
Motion blur decreases
Geometric blur decreases

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12
Q

The random fluctuation in the OD (optical density) of the image

A

Radiographic Noise

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13
Q

The use of high-mAs, low-kVp and of slower image receptors reduces…

A

Quantum mottle

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14
Q

Fast image receptors have…

A

High noise
Low spatial resolution
Low contrast resolution

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15
Q

High spatial resolution and high contrast resolution require

A

Low noise

Slow image receptors

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16
Q

Low noise accompanies slow image receptors with

A

High spatial resolution

High contrast resolution

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17
Q

Exposure to film and the percentage of light transmitted through the processed film is

A

Sensitometry

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18
Q

Optical Density is referring to

A

How much % of light that gets through

-Degree of darkening of the image

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19
Q

Measurements in film exposure and % of light transmitted through describe what relationship?

A

Between OD (optical density) and Radiation Exposure

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20
Q

The relationship between OD and Exposure is called what?

A

Characteristic Curve

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21
Q

At low and high radiation exposure levels, what kind of variations in exposure result in only a small change in OD?

A

Large variations

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22
Q

At intermediate radiation exposure levels, what kind of changes in exposure result in large changes in OD?

A

Small variations

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23
Q

The portions of the characteristic curve that represent the large variations in exposure are called?

A

Toe and Shoulder

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24
Q

The region in which properly exposed radiographs appear is the

A

Straight-line portion

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25
Q

A densitometer

A

measures OD

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26
Q

Already on the film, built in density even with no exposure

A

Base and Fog

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27
Q

A characteristic curve that is more horizontal

A

Is a slower speed and has long scale contrast-more shades of gray-therefore higher kVp and higher mAs

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28
Q

A characteristic curve that is more vertical

A

Is a faster speed and has short scale contrast-fewer shades of gray-therefore lower kV and lower mAs

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29
Q

Latitude is referencing

A

Margin of error

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30
Q

Wide latitude means

A

Have room to play with, long scale contrast-more shades of gray, slower speed

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31
Q

Narrow latitude means

A

Less room to play with, short scale contrast-fewer shades of gray, faster speed

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32
Q

Optical density + 0.3 LRE does what to image?

A

Twice as much density, image will appear twice as dark

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33
Q

Base + Fog =

A

Base= 0.1 Fog= 0.1
Base + Fog = 0.10-0.30
How much density is already built into the film

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34
Q

Where do useful radiographic densities lie?

A

0.25-2.5

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35
Q

The HD curve (rise over run) is telling you what?

A

Numerical number for contrast

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36
Q

When does the reciprocity law fail for screen film?

A

When the mAs difference is extreme in either faster time or slower time:
less than 10 ms or greater than 2 seconds

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37
Q

Reciprocity law ALWAYS works for what kind of exposure of film?

A

Direct exposure

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38
Q

Inherent system (film/IR) contrast is designed to be what in relation to grey scale?

A

Shorter scale

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39
Q

Screen film or Digital systems ALWAYS have shorter scale than what?

A

Direct exposure

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40
Q

Contrast scale gets (blank) the faster the system (goes clear to black fast)

A

Shorter

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41
Q

Subject contrast is determined by what?

A

Size
Shape
Attenuating characteristics of subject

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42
Q

Latitude and contrast are (blank) related

A

Inversely

Wide latitude means you have long scale contrast

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43
Q

The wider the latitude the wider…

A

The range of acceptable exposures

44
Q

Processing includes:

A

Chemical concentration (strength)
Agitation
Time
Temperature

45
Q

What happens if the temperature is too hot during processing?

A

The image is going to convert to dark quicker-temperature will effect density AND contrast

46
Q

What happens during the fixing stage of processing?

A

You stop the image from processing-turning dark,and you remove the silver crystals that weren’t exposed

47
Q

If an image measures at the “toe” of an HD curve chart what does your image look like?

A

Light, way underexposed

48
Q

If an image measure at the “shoulder” of an HD curve chart what does your image look like?

A

Dark, way overexposed

49
Q

Objects will always be (blank) than my image if lined up properly. If object size is (blank) than image size-something is wrong. (especially in math problems)

A

Smaller

Bigger

50
Q

Shape distortion is what?

A

Unequal magnification of object

51
Q

If you have foreshortening/elongation this means what in relation to the object?

A

Object was not parallel to the image receptor

52
Q

How do you minimize distortion?

A

Keep you anatomy of interest in the center of your IR and keep the CR on the area of interest.

53
Q

If I decrease SID (get closer with the tube) I will do what with magnification?

A

Get MORE magnification.

54
Q

Chose a small focal spot for

A

Detail ie bone work

55
Q

Chose a large focal spot for

A

Heat loading capability concern

56
Q

If you’re using a small focal spot, do you use more or less mAs than with a large focal spot?

A

Less mAs for a small focal spot

57
Q

Unsharpness and loss of detail are worse with larger or smaller focal spots, shorter SID and longer OID

A

Larger
think of lateral c-spine:
You back tube up to 72 inches to reduce magnification, and because there’s an air gap between the neck and the image receptor.

58
Q

Focal spot blur is worse on Anode or Cathode side?

A

Cathode

More photons on the cathode side

59
Q

What is good to reduce magnification, is also good to reduce…

A

Focal Spot Blur

60
Q

In relation to focal spot blur you want to Minimize (blank) and Maximize (blank)

A

Min- OID

Max- SOD

61
Q

Most important influence on subject contrast is

A

kVp

62
Q

Low kVp gives what kind of scale

A

Short scale (absorption)

63
Q

High kVp gives what kind of scale

A

Long scale (scatter)

64
Q

Iodine gives us…

A

Differential Absorption

65
Q

You can enhance subject contrast with…

A

Contrast Media that has a relatively high atomic number-gives you photoelectric absorption

66
Q

What would a low atomic number contrast media be and what would it give you image wise?

A

Air, it’s radiolucent so blackness

67
Q

To help reduce motion blur what can you do?

A 
Good instructions
Immobilization devices
Comfortable positions
Short exposure times
Long SID
Short OID
68
Q

In screen film scenarios, image density is Directly or Indirectly proportional to mAs?

A

Directly

69
Q

In order to see a change in screen film density from one set of technical factors to another, what must you do?

A

Have a 30% change in mAs

70
Q

Between Direct exposure, Screen film and CR/DR-which has the longest scale of contrast, and then the next etc

A

Direct has longest scale of contrast, then Screen film, then CR/DR

71
Q

Which type of imaging has the highest patient dosage and therefore is unacceptable?

A

Direct exposure

72
Q

Contrast results from attenuation differences…which is

A

Differential Absorption

73
Q

As grid ratio increases, scale of contrast…

A

Decreases

74
Q

What happens to patient does when using a grid?

A

Goes up

75
Q

Increased collimation is a smaller or larger light field?

A

Smaller

76
Q

What makes detail visible?

A

Contrast

77
Q

What attributes to image sharpness?

A 
Recorded detail:
Small focal spot
Short OID
Long SID
Eliminate motion
Slowest acceptable imaging system
78
Q

What attributes to image visibility?

A

Reduce fog and scatter by restricting the beam, use grids

79
Q

What attributes to Distortion?

A

Control with tube, image receptor, part alignment and patient positioning

80
Q

What is scatters relationship with density?

A

It adds to Density

81
Q

If you remove scatter you do what to image density?

A

Decrease the image density

82
Q

Ways to reduce scatter

A

Beam restriction
Grids
kVp

83
Q

Beam restriction does what?

A

Remove off direction photons

Better image clarity and shorter scale of contrast

84
Q

When you use beam restriction you have to do what to mAs?

A

Increase, need more quantity to maintain image density.

85
Q

Low kVp gives you more of what kind of reaction?

A

More Photoelectric

86
Q

High kVp gives you more of what kind of reaction?

A

More Compton

87
Q

PBL stands for and does what?

A

Positive Beam Limitation

Automatic beam collimation, detects image receptor size and automatically collimates to that size.

88
Q

In relation to soft tissue, which interaction is most likely at less than 20 keV?

A

Mostly photoelectric

89
Q

In relation to soft tissue, which interaction is most likely at more than 20 keV?

A

Mostly compton

90
Q

In relation to bone, which interaction is most likely at less than 40 keV?

A

Mostly photoelectric

91
Q

In relation to bone, which interaction is most likely at more than 40 keV?

A

Compton

92
Q

How does grid use influence patient dose?

A

It increases it because you have to use more mAs to get the image you need

93
Q

What are the different grid parts usually made of and why?

A

Lead strips-to absorb the lower quality photons that produce scatter
Interstrip material that is radiolucent to allow photons to pass through to the IR

94
Q

Grid ratio is

A

Height divided by distance

95
Q

The higher the grid ratio…

A

The more sensative, more grid cut off etc. You must be more precise with positioning.

96
Q

As you go up in grid ratio the lead strips are packed more tightly giving you what kind of contrast scale? And causing what with patient exposure?

A

Shorter Scale

Go up

97
Q

Two most common grid patterns

A

Parallel and Focused

98
Q

What kind of a grid is in the wall bucky or table?

A

Reciprocating grid-moves to blur the lead lines.

99
Q

Focused-Grid misalignments:

Off Level

A

Cutoff across image; underexposed, light image

100
Q

Focused-Grid misalignments:

Off Center

A

Cutoff across image; underexposed, light image

101
Q

Focused-Grid misalignments:

Upside down

A

Severe cutoff toward edge of image

102
Q

Focused-Grid misalignments:

Off Focus

A

Cutoff toward edge of image

103
Q

The need for a grid is reduced with …

A

Increased OID

104
Q

Keep SID and SOD as (blank) as possible and OID as (blank) as possible

A

Long

Short

105
Q

Noise, what can you control?

A

Quantum Mottle

Very small amounts of mAs is when this comes into play

106
Q

Structure mottle is what?

A

Screen inherent-the way it’s made,nothing you can do about it

107
Q

Faster imaging systems have (blank) structure mottle

A

Worse

Physics (7 decks)

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