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2403 Physics > Comprehensive Exam > Flashcards

Comprehensive Exam Flashcards

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1
Q

What occurs if the number of pixels in a matrix increases and the field of view remains the same?

A

spatial resolution increases

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2
Q

What occurs if the number of pixels in a matrix decreases and the field of view remains the same?

A

spatial resolution decreases

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3
Q

What is the pixel size in millimeters of a 256 x 256 matrix with a 10-cm2 field of view?

A

0.39

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4
Q

spatial resolution calculation

A

FOV (cm) / matrix (mm)
change FOV cm to mm

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5
Q

To alter image brightness (density), the __________ is changed.

A

window level

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6
Q

What adjusts the range of densities displayed on the monitor?

A

window width

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7
Q

Making the digital image appear with low contrast, many shades of gray, is done by

A

increasing the window width (wide WW)

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8
Q

Why can an acceptable image be produced with computed radiography (CR) or digital radiography (DR) equipment even when the input exposure was underexposed or overexposed?

A

wide dynamic range of the digital detector

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9
Q

The range of exposures that produce acceptable information to be used in image formation is

A

exposure latitude

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10
Q

The range of exposure intensities that an IR can respond to and acquire image data is

A

dynamic range

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11
Q

The distance from the center of one pixel to the center of the one next to it is

A

pixel pitch

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12
Q

Spatial resolution can be increased by:

  1. Increasing the pixel pitch
  2. Increasing the pixel density
  3. Decreasing the pixel pitch
A

Increasing the pixel density and decreasing the pixel pitch only

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13
Q

What is pixel density?

A

Number of pixels in a given area

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14
Q

The number of visible shades of gray available per pixel in a digital image is determined by _____.

A

bit depth

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15
Q

If a pixel has a bit depth of 10, this means that:

A

It can produce 2^10 shades of gray

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16
Q

Which of the following is a method of describing the strength of the radiation exposure compared with the amount of noise apparent in a digital image?

A

signal-to-noise ratio

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17
Q

Does increasing or decreasing SNR improves the quality of digital image?

A

increasing
this means that the strength of the signal is high in comparison with the amount of noise

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18
Q

Does increasing or decreasing the SNR mean that there is increased noise compared with the strength of the signal, which decreases the quality of the image?

A

decreasing

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19
Q

Which of the following is correct regarding spatial frequency?

  1. small objects have lower spatial frequency
  2. small objects have higher spatial frequency
  3. large objects have lower spatial frequency
A

small objects have higher spatial frequency and large objects have lower spatial frequency only.

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20
Q

The number of lead lines per inch or centimeter is the grid

A

frequency

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21
Q

Differential absorption occurs because different tissues have varying amounts of

A

photoelectric interactions

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22
Q

Varying anatomic parts do not absorb the primary beam to the same degree. Anatomic parts composed of bone absorb more x-ray photons than parts filled with air

A

Differential absorption

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23
Q

Increasing the thickness of the part being imaged results in

A

increased attenuation

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24
Q

Decreased attenuation results in

A

more x-ray photons reaching the image receptor.

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25
Q

A high-energy beam results in

A

decreased attenuation

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26
Q

Total photon absorption depends on the energy of the incoming x-ray photon and the atomic number of anatomic tissue

A

Photoelectric absorption

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27
Q

do you increase or decrease kVp to have a greater chance of PE absorption?

A

decrease

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28
Q

What is bright on a radiograph? Why?

A

Bone, metal, or contrast are brighter on an x-ray because of their higher Z#

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29
Q

The thicker the part the more beam attenuation
X-rays are reduced by ___% for each _____cm of tissue thickness

A

50%, 4-5cm

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30
Q

the higher the Z# the ____ beam attenuation

A

more

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31
Q

How should mAs be adjusted for increased pt thickness?

A

Increase mAs by 2 for every 5cm of extra thickness

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32
Q

Need higher spatial frequency for _____ objects

A

small

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33
Q

Because it reduces spatial resolution, it is always best to minimize shape distortion in radiographic imaging. (Think about it before you answer the question)

A

false

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34
Q

Misalignment of the central ray among these three factors - tube, part, or image receptor - alters the shape of the part recorded

A

distortion

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35
Q

Scattering in the diagnostic range is due to

A

the Compton effect

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36
Q

What does scatter radiation do?

A

decreases the visibility of anatomic structures.

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37
Q

the loss of some energy of the incoming photon occurs when it ejects an outer-shell electron from a tissue atom. The ejected electron is called the Compton electron and it changes direction and may leave the anatomic part to interact with the image receptor

A

Compton scatter

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38
Q

an interaction that occurs with low-energy x-rays, typically below the diagnostic range. The x-ray does not lose energy but changes direction. Doesn’t ionize atom

A

Coherent scatter

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39
Q

What is the result of under-penetration?

A

quantum noise

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40
Q

Quantum noise is a result of

A

too few x-ray photons reaching the image receptor.

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41
Q

With digital imaging using AEC, what factor is increased if an AP thoracic spine is imaged using an outside instead of the center detector? (Assume all other factors are appropriate.)

A

quantum noise

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42
Q

When the image is distorted, spatial resolution is also decreased

A

true

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43
Q

A measurement of the efficiency of an image receptor in converting the x-ray exposure it receives to a quality radiographic image
The higher this is, the lower the radiation exposure to produce a quality image, thereby decreasing patient exposure

A

Detective Quantum Efficiency (DQE)

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44
Q

The resolution of the monitor used to display the digital image has an enormous effect on spatial resolution

A

true

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45
Q

Increased matrix of detector = _________ sharpness/spatial resolution

A

increased

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46
Q

The ideal expression of digital detector image resolution is the

A

modulation transfer function (MTF)
values range between 0-1.0

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47
Q

modulation transfer function (MTF) calculation

A

MTF = (maximum intensity - minimum intensity) / (maximum intensity + minimum intensity)

48
Q

Which of the following imaging systems uses a cassette, a photostimulable phosphor plate, a plate reader, and a computer workstation?

A

Computed Radiography

49
Q

The histogram is

A

a graphic representation of a data set

50
Q

The values of interest (VOI)

A

determine what section of the histogram data set should be included in the displayed image

51
Q

Digital imaging preprocessing includes

A

rescaling and histogram analysis

52
Q

The value that indicates exposure to the IR with a DR imaging system is the

A

dose-area product (DAP)

53
Q

Depends on the exposure factors and field size and is expressed in centigray-meter squared (cGY-m2)

A

Dose Area Product (DAP)

54
Q

The primary factor influencing contrast with digital imaging is the

A

lookup table (LUT)

55
Q

Digital imaging quality control focuses on

A

the display monitors and the viewing environment

56
Q

__________ allows for the acquisition, display, and storage of digital images

A

PACS

57
Q

__________ is the standard format for digital medical images

A

DICOM

58
Q

Whenever magnification is increased

A

spatial resolution is decreased

59
Q

Grids are typically used when:

  1. Part measures more than 10 cm
  2. At least 60 kVp needed for the exam
  3. Part transmits little scatter radiation
A

part measures more than 10 cm and at least 60 kVp needed for the exam only

60
Q

Increasing tube filtration

A

increases the beam energy

61
Q

mAs is directly proportional to ______ ______ reaching the patient and the amount of ________ radiation reaching the IR

A

radiation quantity, remnant

62
Q

mAs calculation

A

mA x seconds = mAs

63
Q

Increasing the kVp

A

increases the quantity of x-ray photons
increases the penetrating power of x-ray photons.
increases the energy of the x-ray photons
(all of these)

64
Q

Decreasing kVp results in

A

better contrast

65
Q

The relationship between kVp and the quantity of remnant radiation is known as the

A

15% rule

66
Q

Increasing the kVp by 15% has the same effect as

A

doubling the mAs

67
Q

When the intensities of radiation exiting the patient are very similar, the resulting radiographic image has

A

low contrast, long-scale contrast

68
Q

a radiograph with few densities but great differences among them is said to have high contrast

A

Short-scale contrast

69
Q

a radiograph with a large number of densities but little differences among them is said to have low contrast

A

Long-scale contrast

70
Q

Increasing the kVp has what affect on wavelength and frequency?

A

decreases wavelength and increases frequency

71
Q

As photon energy increases wavelength _______ and frequency _______

A

decreases, increases

72
Q

Standard radiographic x-ray tubes have small focal spots that measure approximately

A

0.5–0.6 mm

73
Q

Focal spot size is determined by and what does it effect?

A

cathode filament size
sharpness

74
Q

Which of the following is the correct formula for the inverse square law?

A

I1/I2 = (D2)^2/(D1)^2

75
Q

Using a longer SID

A

decreases magnification

76
Q

Which of the following is the formula to determine magnification factor?

A

MF = SID/SOD

77
Q

Restriction of the primary beam to the anatomy of interest does what?

A

reduces patient exposure and reduces the amount of scatter produced

78
Q

The unrestricted primary x-ray beam is

A

round

79
Q

The most effective and often used radiographic beam-restriction device is the

A

collimator

80
Q

The device used to absorb scatter radiation in the radiation leaving the patient before it reaches the image receptor is the

A

grid

81
Q

Which of the following is the correct formula to determine how mAs should be adjusted when different ratio grids are used?

A

mAs1/mAs2 = grid conversion factor1/grid conversion factor2

82
Q

Grids absorb scatter radiation because the scattered photons

A

travel at an angle to the transmitted photons

83
Q

The material between the lead strips of a grid must be

A

radiolucent

84
Q

The relationship between the height of the lead strips and the distance between them is the grid

A

ratio

85
Q

Which of the following is the formula used to determine grid ratio?

A

Grid ratio = height of the lead strips/distance between the lead strips

86
Q

Using a higher the grid ratio will

  1. increase spatial resolution
  2. increase scatter clean up
  3. increase radiographic contrast
A

increase scatter clean up and increase radiographic contrast only.

87
Q

To determine the amount of mAs to be increased when making grid changes, it is necessary to use the GCF (calculation)

A

GCF = mAs with grid/mAs without grid

88
Q

The formula to use when changing from one grid to another is

A

mAs1/mAs2 = GCF1/GCF2

89
Q

The air gap technique is based on creating a gap by increasing the ______

A

OID

90
Q

With digital imaging using AEC, what factor is increased if an AP thoracic spine is imaged using an outside instead of the center detector? (Assume all other factors are appropriate.)

A

quantum noise

91
Q

With digital imaging using AEC, what factor is decreased if an AP thoracic spine is imaged using an outside instead of the center detector? (Assume all other factors are appropriate.)

A

exposure time

92
Q

The primary purpose of AEC is to

A

control the amount of radiation reaching the IR

93
Q

The predetermined level of radiation exposure needed to terminate the exposure when using AEC is set by

A

the equipment service personnel

94
Q

The two types of detectors used in AEC are

A

phototimers and ionization chambers

95
Q

Ionization chamber AEC detectors are entrance-type devices because the x-rays must

A

enter the detector before getting to the IR

96
Q

When the x-rays enter the ionization chamber

A

atoms give up electrons
atoms become ions
electrons become electricity
(all of the above)

97
Q

These can be adjusted to increase or decrease the amount of radiation needed to terminate the exposure using AEC

A

exposure adjustment

98
Q

With digital imaging using AEC, if an AP thoracic spine is imaged with the exposure adjustment changed from 0 to +2, the exposure time is _______________________. (Assume all other factors are appropriate.)

A

longer

99
Q

Anatomically programmed technique is a system in which the radiographer selects

A

preset settings based on the part being imaged

100
Q

Pre-established guidelines used by the radiographer to select standardized manual or AEC exposure factors for each type of radiographic examination are called

A

exposure technique charts

101
Q

What information during fluoroscopy should be documented in the patient’s record?

  1. Total amount of fluoroscopy time
  2. Cumulative air kerma
  3. Dose-area product
A

total amount of fluoroscopy time, cumulative air kerma, and dose-area product

102
Q

______________ refers to how long each exposure lasts

A

Pulse width

103
Q

Which of the following is an advantage of flat panel detectors used in fluoroscopy?

A

60 times larger operational dynamic range because they do not exhibit veiling glare.
Less electronic noise.
Much lighter and more compact.
Produce a digital signal directly
(all of the above)

104
Q

The fiber optic bundle or optical lens system is used to

A

link the output phosphor and camera or CCD

105
Q

On fluoroscopic units that have an image intensifier, magnification of the fluoroscopic image results in improved

A

spatial resolution

106
Q

Each capacitor in a CCD represents a(n)

A

pixel

107
Q

A light-sensitive semiconducting device that generates an electrical charge when stimulated by light and stores this charge in a capacitor is the

A

charge coupled device (CCD)

108
Q

The Charge Coupled Device (CCD) is light-sensitive device that generates an electrical signal when stimulated by visible light

A

true

109
Q

When a CCD is exposed to light, it generates and briefly stores light energy

A

true

110
Q

Increasing the mA is the way to correct a fluoroscopic image that has

A

noise

111
Q

When operated in magnification mode, the electrostatic lenses have ________ of a negative charge

A

more

112
Q

The ________________ is (are) found along the entire length of the image intensifier

A

electrostatic focusing lenses

113
Q

The electrostatic focusing lenses have a ___________ charge

A

negative

114
Q

The term that means an expression of the degree to which the image is made smaller from input phosphor to output phosphor is the

A

minification gain

115
Q

This part of the image intensifier absorbs light and produces electrons

A

photocathode

116
Q

What is the relationship between kVp and subject contrast?

A

high kVp creates low subject contrast

117
Q

Which of the following contribute to subject contrast?

A

Effective atomic number
Differences in tissue density
Differences in tissue thickness
(all of the above)

2403 Physics (8 decks)

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