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C2 > CONTROL OF SCATTER RAD > Flashcards

CONTROL OF SCATTER RAD Flashcards

1
Q

What percentage of x-rays incident on the patient reach the image receptor?

A

Approximately 1%.

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2
Q

What does compression of anatomy improve in radiography?

A

It improves spatial resolution, contrast resolution, and lowers patient dose.

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3
Q

Why is compression particularly important in mammography?

A

It helps to achieve better image quality and lower patient dose.

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4
Q

Name two types of x-rays responsible for optical density and contrast on a radiograph.

A
  • X-rays that pass through the patient without interacting
  • scattered x-rays within the patient.
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5
Q

X-rays that exit from the patient.

A

Remnant xrays

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6
Q

X-rays that exit and interact with the image receptor.

A

image-forming xrays

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7
Q

Name one effect of proper collimation.

A

Less scatter radiation, reduced patient dose, and improved contrast resolution.

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8
Q

List three factors that increase scatter radiation.

A

kVp, field size, and patient thickness.

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9
Q

What is the effect of increased kVp on scatter radiation?

A

Increase scatter radiation, reduce image contrast.

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10
Q

What happens to patient dose when kVp is decreased?

A

Patient dose increases due to the need for higher mAs.

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11
Q

How does increased field size affect scatter radiation?

A

It increases scatter radiation.

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12
Q

What is used to reduce scatter radiation in thick body parts?

A

compression paddle

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13
Q

The visible difference between light and dark areas on an image.

A

image contrast

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14
Q

The ability to image and distinguish soft tissues.

A

contrast resolution

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15
Q

What effect does scatter radiation have on image contrast?

A

It reduces contrast, making the image appear dull or gray.

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16
Q

Name two devices used to reduce scatter radiation.

A

Beam restrictors, grids.

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17
Q

What is the primary purpose of collimation in radiography?

A

To reduce patient dose and improve contrast resolution.

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18
Q

What are the three types of beam restrictors?

A

Aperture diaphragm, cones or cylinders, and variable-aperture collimators.

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19
Q

What is the simplest beam-restricting device?

A

Aperture diaphragm.

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20
Q

Name one application of the aperture diaphragm.

A

Trauma and dental radiography

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21
Q

What is the primary advantage of using cones and cylinders?

A

They reduce scattered radiation and improve image contrast.

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22
Q

What is the most commonly used beam restrictor?

A

Variable-aperture collimator.

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23
Q

X-rays produced in the anode but not at the focal spot.

A

off-focus radiation

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24
Q

Collimators that automatically adjust the radiation field to the size of the image receptor.

A

positive-beam limiting (PBL) devices

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25
Q

What is the total filtration equivalent required in radiography?

A

2.5 mm Al.

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26
Q

A device used to reduce scatter radiation in the remnant x-ray beam.

A

grid

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27
Q

What is the principal function of a grid?

A

To improve image contrast.

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28
Q

Where is a grid placed in relation to the patient and image receptor?

A

Between the patient and the image receptor.

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29
Q

What material are grid strips typically made of?

A

Radiopaque material, usually lead.

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30
Q

What are the three important dimensions of a grid?

A

Grid strip thickness (T), interspace width (D), and grid height (h).

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31
Q

Who demonstrated the technique for reducing scatter radiation that reaches the image receptor?

A

Gustav Bucky in 1913.

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32
Q

What is the formula for grid surface x-ray absorption?

A

Width of grid strip / (width of grid strip + width of interspace) x 100.

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33
Q

The height of the grid divided by the interspace width (h/D).

A

grid ratio

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34
Q

What is an advantage of a high-ratio grid?

A

It is more effective in cleaning up scatter radiation.

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35
Q

What is a disadvantage of a high-ratio grid?

A

It increases patient dose.

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36
Q

What grid ratios are commonly used in general radiography?

A

8:1 to 10:1.

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37
Q

What grid ratios are used in mammography?

A

4:1 to 5:1.

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38
Q

The number of grid strips per centimeter.

A

grid frequency

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39
Q

It reduces the visibility of grid lines on the radiograph.

A

high-frequency grid

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40
Q

What range is typical for grid frequency?

A

25-45 lines per centimeter.

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41
Q

What is the formula for calculating grid frequency?

A

10,000 μm/cm ÷ (T + D) μm/line pair.

42
Q

What is the purpose of interspace material in a grid?

A

To maintain precise separation between the lead strips.

43
Q

What are two common interspace materials in grids?

A

Aluminum and plastic fiber.

44
Q

Name one advantage of using aluminum as interspace material.

A

It does not absorb moisture (nonhygroscopic).

45
Q

What is a disadvantage of using aluminum in grids?

A

It increases primary beam absorption, raising patient dose.

46
Q

What material is preferred for interspaces to minimize patient dose?

A

Plastic fiber.

47
Q

What characteristics are essential in grid strips?

A

They should be thin and have high absorption properties.

48
Q

What is the contrast improvement factor (k) in grid performance?

A

The ratio of radiographic contrast with a grid to that without a grid.

49
Q

What is the typical value of k for most grids?

A

Between 1.5 and 2.5.

50
Q

The ratio of incident to transmitted radiation through a grid.

A

Bucky factor in radiography

51
Q

What is a high Bucky factor indicative of?

A

Higher patient dose due to the grid’s increased scatter removal efficiency.

52
Q

How does increasing kVp affect the Bucky factor?

A

It increases the Bucky factor, requiring higher exposure.

53
Q

The simplest grid type, with parallel grid strips.

A

parallel grid

54
Q

The undesirable absorption of primary x-rays by the grid.

A

grid cutoff

55
Q

What causes grid cutoff in a parallel grid?

A

Occurs at short SID and large area IR.

56
Q

A grid made by sandwiching two parallel grids together at right angles.

A

crossed grid

57
Q

Name one advantage of a crossed grid.

A

It cleans up scatter radiation more effectively than a single parallel grid.

58
Q

What is a major disadvantage of a crossed grid?

A

It is susceptible to grid cutoff.

59
Q

A grid with strips parallel to the path of primary x-rays to minimize cutoff.

A

focused grid

60
Q

What is an off-level grid error?

A

When the central ray is not perpendicular to the grid, causing grid cutoff.

61
Q

What is an off-center grid error?

A

When the grid is shifted laterally, leading to partial grid cutoff.

62
Q

What is an off-focus grid error?

A

Occurs when the SID does not match the grid’s focal distance, causing edge cutoff.

63
Q

What is the effect of an upside-down grid?

A

Severe or complete grid cutoff at the edges of the image.

64
Q

A method where the image receptor is placed 10-15 cm away from the patient to reduce scatter.

A

air-gap technique.

65
Q

What is an advantage of the air-gap technique?

A

It reduces scatter radiation and enhances image contrast.

66
Q

What is a disadvantage of the air-gap technique?

A

It causes image magnification and focal spot blur.

67
Q

What is the mAs increase factor for a 5:1 grid?

A

2x

68
Q

What is the kVp increase for a 5:1 grid?

A

+8-10 kVp.

69
Q

What is the mAs increase factor for an 8:1 grid?

A

4x

70
Q

What is the kVp increase for an 8:1 grid?

A

+13-15 kVp.

71
Q

What is the mAs increase factor for a 12:1 grid?

A

5x

72
Q

What is the kVp increase for a 12:1 grid?

A

+20-25 kVp.

73
Q

What is the mAs increase factor for a 16:1 grid?

A

6x

74
Q

What is the kVp increase for a 16:1 grid?

A

+30-40 kVp.

75
Q

What is the main purpose of collimation in radiographic imaging?

A

To limit the x-ray beam to the area of interest.

76
Q

What happens if the x-ray beam size exceeds the IR?

A

Patient dose and scatter radiation increase.

77
Q

Why is a moving grid used?

A

To reduce visible grid lines on the radiograph.

78
Q

What are the two types of moving grids?

A

Reciprocating and oscillating grids.

79
Q

Who invented the moving grid?

A

Hollis Potter in 1920.

80
Q

A motor-driven grid that moves back and forth during exposure.

A

reciprocating grid

81
Q

A grid that oscillates in a circular fashion around the grid frame.

A

oscillating grid

82
Q

How does a moving grid affect patient dose?

A

It increases patient dose by about 15%.

83
Q

What is the preferred grid ratio for kVp below 90?

A

up to 8:1

84
Q

What grid ratio is recommended for kVp above 90?

A

Greater than 8:1.

85
Q

The x-ray that travels along the center of the useful beam.

A

central ray

86
Q

A type of off-center grid error due to improper alignment of the grid and x-ray tube.

A

lateral decentering

87
Q

What is the typical kVp range for chest radiography using the air-gap technique?

A

180-300 cm SID.

88
Q

How does grid ratio affect radiographic technique?

A

Higher grid ratios require higher technique and increase patient dose.

89
Q

What does SID stand for?

A

Source-to-image distance.

90
Q

What is the purpose of grid lines?

A

They reduce scattered radiation in specific directions but can appear as lines on the radiograph.

91
Q

What grid ratio generally requires no additional technique increase?

A

No grid ratio or 1x increase.

92
Q

What material in grids improves durability but increases primary absorption?

A

Aluminum interspace material.

93
Q

What is the effect of grid cutoff on image quality?

A

It reduces optical density and can cause underexposure.

94
Q

How does patient dose compare with a moving vs. stationary grid?

A

A moving grid increases patient dose.

95
Q

What is an advantage of focused grids over parallel grids?

A

Focused grids reduce grid cutoff.

96
Q

What is the purpose of a grid in mammography?

A

To enhance contrast while using low-ratio grids like 4:1 to 5:1.

97
Q

What technique can serve as an alternative to grid use?

A

Air-gap technique.

98
Q

How does compression improve radiographic imaging?

A

It reduces thickness, which lowers scatter and improves resolution.

99
Q

What is a disadvantage of crossed grids?

A

prone to grid cutoff and increase patient dose.

100
Q

What is required for the proper function of a focused grid?

A

Correct alignment with the x-ray tube focal distance and position.

C2 (7 decks)

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