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Rad Phys > Exam 2 > Flashcards

Exam 2 Flashcards

1
Q

What does mAs control

A

The density of the film

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2
Q

What does kVp control

A

The Contrast and Density of the film

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3
Q

What increase in mAs will cause the first visual change to the film density

A

30%

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4
Q

Do you retake a film for the 30% rule

A

no, the difference is so slight it doesn’t make a difference

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5
Q

Other than manually changing the mAs how else can you increase the mAs?

A

Increase exposure time

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6
Q

What does doubling the mAs do to the density of the film

A

Doubles the density

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7
Q

If the film is too light but you can see structures what can you do to fix it (using mAs)

A

Double the mAs

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8
Q

If the film is too dark but you can see structures what can you do to fix it (using mAs)

A

1/2 the mAs

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9
Q

If the film is too dark or too light and you can see structures how can you fix it using kVp

A 
Dark = decrease kV 15%
Light = increase kV 15%
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10
Q

how much kV does it take to increase the density

A

4 kV

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11
Q

When changing the kV what should you keep in mind

A

Do not go over or under the optimal kV range

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12
Q

What happens if you need to decrease kV and mA but if you decrease kV it will be under the optimal range

A

1/2 the mA twice and leave kV alone

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13
Q

What can cause film fogging

A

Scattered rays
overhead lights
Increasing the developing time/temp
using an expired film

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14
Q

What does film fogging do to the density

A

increases the density (makes it darker)

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15
Q

If you use a spot shot what will happen to film density if the technique is not increased

A

The density will decrease (film will get lighter)

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16
Q

What are some factors that will decrease the density of the film

A 
Spot shot without changing technique
Too much filtration
Wrong film + screen combo
patient tissue and body build
decreased development  time and temp
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17
Q

What type of contrast is black and white

A

Short

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18
Q

What type of contrast scale has lots of greys

A

Long scale

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19
Q

How do you fix a film that has too high of contrast (short scale)

A

decrease kV 15%

double the mAs

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20
Q

How do you fix a film that has too low of contrast (long scale)

A

Increase kV 15%

1/2 the mAs

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21
Q

If the density of a film is good but there is too much grey how do you fix it

A

decrease kV 15%

Double the mAs

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22
Q

If the density of the film is good but there is not enough grey how do you fix it

A

increase kV 15%

1/2 the mAs

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23
Q

What is differential absorption

A

the differences in x-ray absorption of different tissues

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24
Q

How do the following appear on xrays

Air
Oil
Water
Bone

A 
Air = black
Oil = dark grey
water = grey
bone = white
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25
Q

What is the silhouette sign

A

If two structures of the same density are in contact you will not be able to see the boarders

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26
Q

How will thinner materials of the same density appear on a film compared to thicker

A 
Thin = less dense
thick = more dense
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27
Q

What are the different types of radiographic techniques

A

Variable kV
fixed kV
High kV

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28
Q

Which radiographic technique should be avoided

A

Variable kV

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29
Q

Which technique used a constant mAs and a varried kVp

A

Variable kV

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30
Q

Which technique only changes the kV depending on the size of the part of patient

A

Variable kV

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31
Q

What technique is most used today

A

Fixed kV

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32
Q

Which technique changes the mAs depending on the thickness of the part or person

A

Fixed kV

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33
Q

Which technique has a more constant contrast

A

Fixed kV

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34
Q

Which technique has a more varied contrast

A

Variable kV

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35
Q

Is the high kV technique used for bones

A

no

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36
Q

What is the high kV technique used for

A

Chest and contrast media studies

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37
Q

What type of Exposure control uses photocells behind the patient that will terminate the exposure once the desired density is achieved

A

Automatic Exposure Control

38
Q

When using a technique chart what is something to keep in mind about the values

A

The values are estimates, you should use your own judgement on whether or not to change these values depending on size and age or patient

39
Q

What is the name of the calculators used for determining x ray settings

A

Slide rule calculators

40
Q

What type of exposure control uses a computer chip that will calculate out the kV and mA depending on what film you are taking and the size of patient

A

Anatomicl Programmed Chips

41
Q

When using a chart how much will you decrease the mAs by when xraying a patient under 12 years olf

A

decrease by 30%-50%

42
Q

When using a chart how much will you have to decrease the mAs by when xraying an osteoporotic patient

A

decrease by 30-50%

same as a child under 12

43
Q

For more muscular or obese patients what will you have to change the mAs by

A

increase 30-50%

44
Q

How can you assure that contrast will be good with minimum patient exposure

A

Stay within the recommended kV ranges

45
Q

What is Quantum mottle

A

Visual defects in the film, ie; under/overexposed, too much/too little grey, grainy dots on film

46
Q

What causes Quantum mottle

A

Too fast of screens
too high kV and too low mA
dirty/poor screens
old screens

47
Q

What causes true Quantum mottle

A

Too high kV and too low mA

48
Q

What is unsharpness on a film called

A

Penumbra

49
Q

what is sharpness on a film called

A

numbra

50
Q

An increase or decrease in SID will do what to the film sharpness

A

Decrease SID = unsharp

increase SID = Sharper

51
Q

An increase of Decrease in OFD will do what to the film

A

Decrease OFD = Sharper

Increase OFD = unsharp

52
Q

What will a large or small focal spot do to the film

A 
Small = Sharper
Large = unsharp
53
Q 
What is the order of sharpest to least sharpest
Double screen
no screen
single screen
high speed screens
A

no screen = sharpest
single screen
double screen
high speed screen = least sharp

54
Q

What can cause motion blur

A

Patient motion

Equipment motion

55
Q

What can cause equipment motion

A

Faulty locks
unstable cassette holder
Heavy construction out side of office

56
Q

what type of unsharpness does magnification distortion cause

A

geometric unsharpness

57
Q

What causes magnification distortion

A

increased OFD

58
Q

How should the patient be positioned against the film

A

The part you want to xray should be as close to the film as possible

59
Q

a P-A film is best at showing what

A

Heart, anterior ribs, sinuses, frontal bone

60
Q

a A-P film is best at showing what

A

Spine, Occiput, Scapula, posterior ribs

61
Q

What is another name for Shape distortion

A

True distortion

62
Q

What causes Shape distortion/ True distortion

A

Angulation of the ray, film, or object

63
Q

What can happen to the X-ray when it enters a patient

A

Completely absorbed
Partially absorbed/deflected
Pass through patient

64
Q

X rays that are partially absorbed and pass through make up what type of radiation

A

Remnant radiation

65
Q

What are the rays that are deflected back to the tube called

A

Back scatter

66
Q

What xrays are undesirable

A

partially absorbed/deflected

67
Q

What produces the image on the film

A

Secondary xrays

68
Q

Explain secondary xrays

A

Primary Xrays hit patient and are absorbed, The extra energy sends another electron from the tissue out of its orbit. The secondary xray might hit the film, this will darken it and cause grey

69
Q

Secondary xrays that leave at a steep angle will do what on the film

A

No hit it, and create better contrast

70
Q

What is Comptons scatter effect

A

When an incoming phtons strikes the outter electron and dispalces it. The greater the angle the photon deflects at the more energy is lost

71
Q

What type of secondary radiation is more predominant when using recommended kV

A

Comptons Scatter effect

72
Q

What causes classic scatter

A

A weak photon (10keV) causes electrons to vibrate and give off another xray

73
Q

is there more or less scatter at higher kV

A

more scatter

74
Q

why does a higher kV cause more scatter

A

More penetration = less absorption = more graying from film fog

More x rays penetrate with no interaction

75
Q

How can you control scatter caused by kV

A

use optimate kV ranges

76
Q

How does beam size contribute to scatter

A

large beam = more scatter from patient tissue

77
Q

How does patient size affect scatter

A

More tissue = more scatter

Denser tissue = more scatter

78
Q

How can you help with removing scatter from patient tissue

A

Use a Grid infront or behind the patient

79
Q

What are grids made up of

A

Thin led or allumnium strips separated by interspacing material

80
Q

What is the recommended lines per inch grid frequency

A

103+

81
Q

What are the different types of grids

A

Stationany

moving grids

82
Q

What are the 3 types of stationary grids

A

Crossed
Parallel
Focused

83
Q

What is the problem with parallel grids

A

peripheral rays are attenuated this causes uneven exposure (sides of film are lighter)

84
Q

What is grid radius

A

The angle of the strips that match the divergence

85
Q

What is Grid cut-off

A

Unequal film density from strips absorbing primary radiation

86
Q

What causes grid cut-off

A 
Parallel grids
Grids that are out of range
malalignment of tube
backward installation
bent/warped grid
87
Q

What are grid lines

A

White lines there primary rays hit the led strips

88
Q

What is a moving grid also called

A

A reciprocating grid

89
Q

How can grid lines be avoided

A

by moving the grid during exposure

90
Q

What are some problems with a moving/reciprocating grid

A

They are thicker = increase OFD

can cause motion in film

Rad Phys (2 decks)

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