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Radiology 142 > Scatter Radiation Study Guide > Flashcards

Scatter Radiation Study Guide Flashcards

1
Q

What characteristics are important to image quality?

A

contrast and contrast resolution

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2
Q

What is contrast?

A

differences of light and dark on an x-ray image

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3
Q

What is the number of shades of gray on an image?

A

scale of contrast

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4
Q

The ability to image adjacent similiar tissues is defined as?

A

contrast resolution

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5
Q

What three factors contribute to the production of scatter radiation?

A

increased kVp
increased x-ray field size
increased patient thickness

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6
Q

What is designed to minimize the production of scatter by limiting field size to only the anatomy of interest?

A

Beam restricting devices

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7
Q

The three principle types of beam restricting devices are?

A

aperture diaphragms, cone or cylinders and collimators

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8
Q

What two types of x-rays are responsible for Optical Density and contrast on an image?

A
  1. those that pass through the patient without interacting (transmitted)
  2. those that are compton scatter within the patient
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9
Q

Define Remnant x-rays:

A

x-rays that exit the patient

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10
Q

Define Image forming x-rays:

A

x-rays that exit and interact with the image receptor

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11
Q

What does collimation do?

A

reduces patient dose and improves contrast resolution

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12
Q

As scatter radiation increases what happens to the image?

A

it loses contrast and becomes gray/dull

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13
Q

If kVp increases what happens to relative amount of scatter?

A

it increases

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14
Q

If kVp decreases what happens to patient dose?

A

it increases

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15
Q

As the thickness of the patient increases what happens to the probability of scatter?

A

it increases

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16
Q

One way to reduce the production of scatter is by imaging a thinner part by using?

A

constriction bands or compression paddles

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17
Q

If radiation field size increases what happens to the tissue being irradiated? Amount of scatter being produced?

A

it increases

it increases

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18
Q

What device helps to minimize the amount of scatter produced?

A

beam restrictors

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19
Q

What device helps clean up the scatter that has been produced?

A

grids

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20
Q

What type of beam restricting device is the simplest one that consists of a lead plate with a hole cut in it. The size of the opening determines the field size?

A

Aperture Diaphragms

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21
Q

X-rays being produced on other parts of the anode than the focal spot is called?

A

off- focus x-rays

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22
Q

What x-rays increase blur in the image?

A

off focus x-rays

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23
Q

What does positive beam limitation do?

A

automatically collimates to the size of the IR used.

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24
Q

Under NO circumstance should the x-ray beam?

A

exceed the size of the IR

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25
Q

When the beam is restricted the technique should? why?

A

increase to compensate for the loss of x-rays in the beam reaching the IR

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26
Q

Scatter makes?

A

Fog

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27
Q

Fog is?

A

Density

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28
Q

Removing scatter does what to the optical density?

A

decreases which makes the image lighter therefore mAs must increase

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29
Q

What is designed to transmit only x-rays whose direction is on a straight line to the IR?

A

Grid

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30
Q

Grids have three important dimensions:

A
  1. thickness of the lead strips (T)
  2. thickness of the interspace or interspace distance (D)
  3. height of the grid strip (h)
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31
Q

What is the Grid ratio equation?

A

Grid ratio=h/D

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32
Q

What grids are better at cleaning up scatter?

A

High ratio grids

33
Q

Why are high ratio grids better at cleaning up scatter?

A

because the angle of scatter allowed by high ratio grids is less than that of low ratio grids

34
Q

What happens to patient dose when using a high ratio grid?

A

increases because of the increased mAs needed to offset the loss of x-rays

35
Q

The number of grid strips per cm or per inch is known as

A

grid frequency

36
Q

If the grid strip width is constant, decreasing interspace distance will do what to grid frequency?

A

it will increase

37
Q

What has the purpose of maintaining precise separation between delicate lead strips?

A

interspace material

38
Q

The principle function of a radiographic grid is to?

A

increase contrast

39
Q

Who invented the grid and named after the bucky factor?

A

Gustave Bucky

40
Q

What measures how much technique will have to be increased to obtain the same optical density on a radiograph?

A

bucky factor

41
Q

What indicates how much of an increase to patient dose will result from form using a particular grid?

A

bucky factor

42
Q

For a grid ratio of 5:1 what is the bucky factor?

A

2

43
Q

For a grid ratio of 6:1 what is the bucky factor?

A

3

44
Q

For a grid ratio of 8:1 what is the bucky factor?

A

4

45
Q

For a grid ratio of 10:1 what is the bucky factor?

A

5

46
Q

For a grid ratio of 12:1 what is the bucky factor?

A

5

47
Q

For a grid ratio of 16:1 what is the bucky factor?

A

6

48
Q

The simplest type of grid is?

A

parallel grid

49
Q

What has grid strips that are straight up and down and run parallel to each other for the length of the grid?

A

Parallel grid

50
Q

The parallel grid is prone to what problem when manufactured?

A

grid cutoff

51
Q

What is the undesirable absorption of primary x-rays by the grid?

A

Cutoff

52
Q

Cutoff is demonstrated by a ______ in optical density toward the edges of the grid.

A

decrease

53
Q

Define grid radius

A

Distance to cutoff

54
Q

What grids have grid stips running in both the long dimension and short dimension of the IR?

A

crossed grids

55
Q

Crossed grids have a contrast improvement factor of ____ the grid ratio?

A

twice

56
Q

What grid is designed to minimized grid cutoff?

A

focused grid

57
Q

What grids are moving grids, just before exposure they move and will continue to move after the exposure is complete?

A

focused grid

58
Q

The device that moves the grid is called?

A

Potter-Bucky Diaphragm or “Bucky” for short

59
Q

Who came up with the simple idea of “move the grid during exposure blurs out the grid lines?”

A

Hollis Potter

60
Q

What grids move back and forth as driven by motor device?

A

reciprocating grids

61
Q

What grids move in circles?

A

oscillating grids

62
Q

What are some disadvantages to moving grids?

A
  1. increased magnification and blurring of image due to the motion which increases distance between the patient and the IR.
  2. Subject to failure resulting in grid lines on images
  3. motion of the grid may introduce motion in the IR causing motion blur
63
Q

Most grid problems occur because of?

A

improper positioning

64
Q

What are four problems with a focused grid?

A
  1. off level
  2. off-center
  3. off focus
  4. upside down
65
Q

What happens to an off-level grid?

A

cutoff across image

66
Q

What happens to an off-center grid?

A

cutoff across image

67
Q

What happens to an off-focus grid?

A

cutoff across image

68
Q

What happens to an upside down grid?

A

severe cutoff towards the edge

69
Q

Patient radiation dose ______ with ______ grid ratio?

A

increases, increases

70
Q

High ratio grids are used for _____ kVp exams

A

high

71
Q

Patient dose at high kVp is ____ than that for low kVp

A

less

72
Q

This technique is used to increase contrast without the use of a grid?

A

air gap technique

73
Q

One disadvantage of the air gap technique is?

A

magnification of the image with blur

74
Q

Total Filtration equation:

A

total filtration=inherent filtration+ added filtration

75
Q

Grid frequency equation:

A

Grid frequency=10,000cm/ (T+D) line pair

Don’t forget units

76
Q

Contrast improvement equation:

A

k=image contrast with grid/image contrast w/o grid

77
Q

Bucky factor equation:

A

B= incident remnant x-rays/transmitted image-forming xrays

=Patient dose with grid/patient dose without grid

78
Q

Grid cutoff equation:

A

Distance to cutoff= SID/Grid ratio

Radiology 142 (5 decks)

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