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RTE 006 > Chapter 11:Full > Flashcards

Chapter 11:Full Flashcards

1
Q

What factors contribute to the production of scatter radiation?

A

kVp, field size, and patient thickness.

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2
Q

What is one method to control scatter radiation?

A

Using beam restrictors.

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3
Q

How does scatter radiation affect image quality?

A

It impacts image contrast.

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4
Q

What is the purpose of radiographic grids?

A

To improve contrast and reduce scatter radiation.

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5
Q

What is the Bucky factor?

A

A measure of the grid’s ability to improve contrast.

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6
Q

What are the types of grids mentioned?

A

Parallel grid, crossed grid, focused grid, and moving grid.

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7
Q

What are common grid problems?

A

Off level, off center, off focus, and upside down grid.

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8
Q

What considerations are important for grid selection?

A

Patient dose and air-gap technique.

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9
Q

What are remnant x-rays?

A

X-rays that exit from the patient.

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10
Q

What are image-forming x-rays?

A

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

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11
Q

What factors influence the production of scatter radiation?

A

Kilovoltage, field size, and patient thickness.

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12
Q

What is the importance of proper collimation?

A

It helps control scatter radiation.

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13
Q

What happens to the number of Compton interactions as x-ray energy is increased?

A

The absolute number of Compton interactions decreases.

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14
Q

How does the decrease in photoelectric interactions compare to Compton interactions as x-ray energy increases?

A

The number of photoelectric interactions decreases much more rapidly than Compton interactions.

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15
Q

What happens to the relative number of x-rays undergoing Compton scattering as x-ray energy increases?

A

The relative number of x-rays that undergo Compton scattering increases.

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16
Q

What is the effect of increased photoelectric absorption on patient radiation dose?

A

It results in a considerable increase in patient radiation dose.

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17
Q

What are the relative contributions of photoelectric effect and Compton scatter to the radiographic image?

A

They contribute differently, with photoelectric effect increasing absorption and Compton scatter affecting image contrast.

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18
Q

What is the significance of kilovoltage in skull radiographs?

A

It affects the quality of the radiographs and the resultant patient exposures.

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19
Q

How does field size influence scatter radiation?

A

Field size affects the level of scatter radiation and is controlled by the radiologic technologist.

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20
Q

What is the relationship between field size and optical density?

A

Field size can influence scatter radiation, which in turn affects optical density.

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21
Q

What is the recommended technique for lumbar spine radiography?

A

Collimation of the beam to the vertebral column.

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22
Q

What is the effect of the full-field technique on image contrast?

A

It results in reduced image contrast.

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23
Q

How does patient thickness affect scatter radiation?

A

Imaging thick parts of the body results in more scatter radiation than imaging thin body parts.

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24
Q

What types of tissue contribute to the production of scatter radiation?

A

Muscle, fat, and bone.

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25
Q

How does the size of body parts influence scatter radiation production?

A

Larger body parts have more tissue to interact with photons, resulting in greater scatter production.

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26
Q

What should be done to decrease scatter radiation?

A

Use the smallest possible field size.

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27
Q

How does patient thickness affect x-ray scattering?

A

More x-rays are scattered with increasing patient thickness.

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28
Q

What can be used to reduce scatter radiation to the image receptor?

A

Devices such as a compression paddle.

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29
Q

What are the benefits of compressing anatomy during radiography?

A

Improves spatial resolution, contrast resolution, and lowers patient radiation dose.

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30
Q

What is contrast in a radiographic image?

A

The degree of difference in optical density (OD) between areas of the image.

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31
Q

What does contrast resolution refer to?

A

The ability to image and distinguish soft tissues.

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32
Q

What happens to image contrast when only transmitted, unscattered x-rays are used?

A

The image would be very sharp, resulting in high contrast.

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33
Q

What is the result when only scatter radiation reaches the image receptor?

A

The image would be dull gray with very low contrast.

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34
Q

What do image-forming x-rays consist of?

A

Both transmitted and scattered x-rays, resulting in moderate contrast.

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35
Q

What are the two types of devices that reduce scatter radiation reaching the image receptor?

A

Beam restrictors and grids.

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36
Q

What is the simplest beam-restricting device?

A

Aperture diaphragm.

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37
Q

What is an aperture diaphragm?

A

A lead or lead-lined metal diaphragm attached to the x-ray tube head.

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38
Q

What is the design of the opening in an aperture diaphragm?

A

It usually covers just less than the size of the image receptor used.

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39
Q

What is the main disadvantage of the aperture diaphragm?

A

It does not provide a sharp demarcation of the edge of the x-ray beam.

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40
Q

How does a diaphragm affect edge penumbra?

A

With a diaphragm, off-focus is not controlled, resulting in a large area of penumbra at the edge of the exposed film area.

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41
Q

What advantage does a cylinder cone have over a diaphragm?

A

A cylinder cone controls off-focus radiation much better and decreases edge penumbra considerably.

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42
Q

What are radiographic extension cones and cylinders considered?

A

Modifications of the aperture diaphragm.

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43
Q

What shape is the useful beam produced by an extension cone or cylinder?

A

Usually circular.

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44
Q

What is a major drawback of using cones in radiography?

A

A different cone is required for each different field size and for every SID, making it impractical.

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45
Q

What issue arises from the circular cross-section of the x-ray beam when using cones?

A

It cannot be fitted to a rectangular film, leading to cone-cutting.

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46
Q

What is a major drawback of using cones in radiography?

A

It is impossible to correctly align the x-ray beam with the anatomical area of interest due to the lack of a centering light.

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47
Q

What does misalignment of the x-ray beam with the film receptor lead to?

A

It leads to poor image quality.

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48
Q

What is the most commonly used beam-restricting device in radiography?

A

The light-localizing variable-aperture collimator.

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49
Q

How does collimation benefit patients during radiography?

A

It reduces the patient radiation dose and improves contrast resolution.

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50
Q

What should the size of the x-ray beam be in relation to the image receptor?

A

The x-ray beam should not exceed the size of the image receptor.

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51
Q

What is a radiographic grid made of?

A

Alternating sections of radiopaque material (grid strip) and radiolucent material (interspace material).

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52
Q

What is the primary function of a radiographic grid?

A

To reduce the level of scatter radiation that reaches the image receptor.

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53
Q

Where is the grid positioned during radiographic imaging?

A

Between the patient and the image receptor.

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54
Q

Who first demonstrated the technique of using grids to reduce scatter radiation?

A

Gustave Bucky in 1913.

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55
Q

What does the grid design allow in terms of x-ray transmission?

A

It transmits only x-rays whose direction is on a straight line from the x-ray tube target to the image receptor.

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56
Q

How does the grid affect scatter radiation?

A

Scatter radiation is absorbed in the grid material.

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57
Q

Who made the Bucky grid practical and how?

A

Dr. Hollis Potter by moving it during the radiographic exposure to blur the grid lines out of the image.

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58
Q

What is the correct NEMA term for the grid developed by Dr. Hollis Potter?

A

Potter-Bucky diaphragm.

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59
Q

What happens to X-rays that strike the radiopaque grid strips?

A

They are absorbed and do not reach the image receptor.

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60
Q

How does a grid affect film density?

A

It decreases film density because it absorbs a small portion of the primary beam and most of the scattered radiation.

61
Q

What must be done to compensate for the decreased film density caused by a grid?

A

Increase the amount of incident radiation.

62
Q

What are the three important dimensions of a grid?

A

Thickness of the grid strip (T), width of the interspace material (D), and height of the grid (h).

63
Q

How is the grid ratio calculated?

A

By dividing the height of the grid by the interspace width.

64
Q

If a grid is constructed with 50-μm strips and a 350-μm interspace, what is being questioned?

A

What percentage of X-rays incident on the grid will be absorbed by its entrance surface?

65
Q

What is the grid ratio when the lead strips are 2.4 mm high and separated by 0.2 mm?

A

The grid ratio is 12:1.

66
Q

Why are high-ratio grids more effective in reducing scatter radiation?

A

Because the angle of scatter allowed by high-ratio grids is less than that permitted by low-ratio grids.

67
Q

What is the general range of grid ratios?

A

Grid ratios range from 5:1 to 16:1.

68
Q

What grid ratio is frequently used with general-purpose x-ray imaging systems?

A

An 8:1 to 10:1 grid.

69
Q

How much scatter radiation does a 5:1 grid reduce?

A

Approximately 85%.

70
Q

How much scatter radiation can a 16:1 grid reduce?

A

As much as 97%.

71
Q

What effect do high-ratio grids have on patient radiation dose?

A

They increase the patient radiation dose.

72
Q

What is grid frequency?

A

The number of grid strips per centimeter.

73
Q

How do high-frequency grids affect the appearance of grid lines on a radiographic image?

A

They show less distinct grid lines than low-frequency grids.

74
Q

What happens to the interspace of a grid as its frequency increases while keeping strip width constant?

A

The interspace must be thinner and the grid ratio must be higher.

75
Q

What is the effect of high-frequency grids on patient radiation dose?

A

They require high radiographic technique and result in a higher patient radiation dose.

76
Q

Why does increasing grid frequency lead to a higher patient radiation dose?

A

Because more grid strip is available to absorb x-rays, requiring a higher radiographic technique.

77
Q

What is the purpose of the interspace material in grids?

A

To maintain a precise separation between the delicate lead strips of the grid.

78
Q

What materials are commonly used for interspace material in grids?

A

Aluminum or plastic fiber.

79
Q

What is one advantage of using aluminum over plastic for grid interspace material?

A

Aluminum has a higher atomic number (Z), providing selective filtration of scattered x-rays.

80
Q

How does aluminum affect the visibility of grid lines on radiographs?

A

It produces less visible grid lines compared to plastic.

81
Q

What is a consequence of aluminum’s properties at low kVp?

A

It increases the absorption of primary x-rays in the interspace, resulting in higher mAs and a higher patient dose.

82
Q

What is a nonhygroscopic property of aluminum?

A

It does not absorb moisture like plastic fiber does.

83
Q

Why is aluminum easier to manufacture compared to plastic fiber?

A

Aluminum is easier to form and roll into sheets of precise thickness.

84
Q

What are the ideal characteristics of a grid strip?

A

It should be infinitely thin and have high absorption properties.

85
Q

Why is lead the most widely used material for grid strips?

A

Because it is easy to shape, relatively inexpensive, has a high atomic number, and high mass density.

86
Q

What materials have been tried for grid strips besides lead?

A

Tungsten, platinum, gold, and uranium.

87
Q

What does the contrast improvement factor reveal?

A

The ability of the grid to improve image contrast.

88
Q

How does the contrast improvement factor vary with grid ratio?

A

It is higher for high-ratio grids.

89
Q

What does a contrast improvement factor of 1 indicate?

A

No improvement in contrast.

90
Q

What is the typical contrast improvement factor range for most grids?

A

Between 1.5 and 2.5.

91
Q

How much does image contrast approximately increase when grids are used?

A

It is approximately doubled.

92
Q

What is the contrast improvement factor for a 12:1 grid if the average gradient without a grid is 1.1 and with the grid is 2.8?

A

The contrast improvement factor is 2.5.

93
Q

What must be increased when a grid is used in radiographic technique?

A

The radiographic technique must be increased to produce the same image receptor signal.

94
Q

What is the Bucky factor also known as?

A

The grid factor.

95
Q

Who is the Bucky factor named after?

A

Gustave Bucky, the inventor of the grid.

96
Q

What does the Bucky factor attempt to measure?

A

The penetration of primary and scatter radiation through the grid.

97
Q

How does the grid ratio affect the Bucky factor?

A

The higher the grid ratio, the higher the Bucky factor.

98
Q

What happens to the penetration of scatter radiation as grid ratio increases?

A

It becomes less likely, causing the Bucky factor to increase.

99
Q

How does increasing kVp affect the Bucky factor?

A

The Bucky factor increases with increasing kVp.

100
Q

Why does the Bucky factor increase at high voltage?

A

More scatter radiation is produced, which has a more difficult time penetrating the grid.

101
Q

What are the two types of linear/parallel grids?

A

Focused and non-focused.

102
Q

What is a key characteristic of parallel grids?

A

Lead strips run parallel to one another in one direction only.

103
Q

What must the X-ray beam be aligned with when using a parallel grid?

A

The center of the long axis.

104
Q

What is a common issue associated with parallel grids?

A

Grid cutoff, which is the undesirable absorption of primary X-rays by the grid.

105
Q

When is grid cutoff most pronounced?

A

When the grid is used at a short SID and with a large-area image receptor.

106
Q

What types of grids can be either moving or stationary?

A

All parallel grids.

107
Q

What is the easiest type of grid to manufacture?

A

Linear/parallel grid.

108
Q

Can angulation with the long axis be performed with parallel grids?

A

Yes, angulation with the long axis is possible.

109
Q

What is a characteristic of linear/parallel grids?

A

They do not coincide with the divergence of the x-ray beam, leading to some grid cutoff along the lateral edges.

110
Q

When is the parallel grid best employed?

A

At long SIDs, as the beam will be straighter and more perpendicular.

111
Q

What defines a cross-hatch/cross grid?

A

It consists of two sets of lead strips superimposed and running at 90° to one another.

112
Q

What is a key requirement when using a cross-hatch grid?

A

The beam must be aligned with the center of the grid

113
Q

How do cross-hatch grids compare to parallel grids in terms of efficiency?

A

Cross-hatch grids are more efficient in cleaning up scatter radiation.

114
Q

What is a significant disadvantage of using crossed grids?

A

Positioning the grid is critical

115
Q

What is a consequence of using crossed grids regarding patient radiation dose?

A

The exposure technique required is substantial, resulting in a higher patient radiation dose.

116
Q

What are the two types of grid focus?

A

Focused and Non-Focused.

117
Q

How are the lead strips arranged in a focused grid?

A

They are inclined inward, focusing at a predetermined point above the grid.

118
Q

What is the purpose of a focused grid?

A

To minimize grid cutoff.

119
Q

What does the convergence line represent in a focused grid?

A

The line in space where extended lead strips would intersect.

120
Q

What is the grid radius?

A

The distance from the face of the grid to the points of convergence of the lead strips.

121
Q

How are the lead strips arranged in a non-focused grid?

A

They are parallel and uniform to one another throughout.

122
Q

What are the three possible motions of reciprocating grids?

A
  1. Single-stroke (one-way), 2. Reciprocating (forward & backward), 3. Catapult.
123
Q

What usually causes an off-level grid?

A

An improperly positioned x-ray tube.

124
Q

When does an off-level grid occur during radiography?

A

When the grid tilts during horizontal beam radiography or when the image receptor sinks into the patient’s bed.

125
Q

What usually causes an off-level grid?

A

An improperly positioned x-ray tube.

126
Q

When does an off-level grid occur during radiography?

A

When the grid tilts during horizontal beam radiography or when the image receptor sinks into the patient’s bed.

127
Q

What is the result of a lateral shift of the grid?

A

Grid cutoff across the entire radiograph, producing lower optical density (OD).

128
Q

What is the term for the error caused by lateral shift of the grid?

A

Lateral decentering.

129
Q

What major problem arises when using a focused grid at unspecified SIDs?

A

Grid cutoff becomes more severe the farther the grid is from the specified focal distance.

130
Q

How does grid cutoff vary across the image receptor?

A

It is more severe at the edges.

131
Q

What major problem arises when using a focused grid?

A

It occurs when radiographs are taken at SIDs unspecified for that grid.

132
Q

What happens to grid cutoff as the distance from the specified focal distance increases?

A

The grid cutoff becomes more severe.

133
Q

Is grid cutoff uniform across the image receptor?

A

No, it is more severe at the edges.

134
Q

What effect does an upside-down focused grid have on a radiographic image?

A

It shows severe grid cutoff on either side of the central ray.

135
Q

What is the primary function of grids in radiography?

A

Grids absorb scatter radiation, which adds exposure to the image receptor.

136
Q

How does the efficiency of a grid affect exposure to the image receptor?

A

The more efficient a grid is at absorbing scatter, the less exposure will be received by the image receptor.

137
Q

What compensations must be made when using an efficient grid?

A

Compensations must be made to increase exposure, generally accomplished by increasing mAs.

138
Q

What is the relationship between grid efficiency and patient dose?

A

The better the grid cleans up scatter, the greater the dose given to the patient to achieve adequate exposure.

139
Q

What formula is used to calculate the amount of mAs needed when using a grid?

A

Grid Conversion Factor (GCF), also known as the Bucky factor.

140
Q

If a satisfactory chest radiograph is produced using 5 mAs without a grid, what is needed for a second image using a 12:1 grid?

A

The mAs needed can be calculated using the Grid Conversion Factor.

141
Q

What is a major disadvantage of using radiographic grids?

A

Increased patient radiation dose.

142
Q

How much more radiation may a patient receive when using a grid compared to not using one?

A

Several times more radiation.

143
Q

What is the approximate increase in patient radiation dose when using a moving grid instead of a stationary grid?

A

Approximately 15% more.

144
Q

What is the air gap technique?

A

An alternative to the use of radiographic grids that reduces scatter radiation and enhances image contrast.

145
Q

How far is the image receptor moved from the patient when using the air gap technique?

A

10 to 15 cm.

146
Q

How much should the mAs be increased for every centimeter of air gap in the air gap technique?

A

Approximately 10%.

147
Q

How does the patient dose associated with the air gap technique compare to that of a grid technique?

A

It is higher than that associated with the nongrid technique and approximately equivalent to that of an intermediate grid technique.

148
Q

What is one disadvantage of the air-gap technique?

A

Image magnification with associated focal-spot blur.

RTE 006 (6 decks)

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