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AJT Physics > PHYSICS - X-ray > Flashcards

PHYSICS - X-ray Flashcards

1
Q

Relationship of frequency and wavelength to photon energy

A

frequency is proportional, wavelength is inversely proportinal; via Planck’s equation

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2
Q

Effect of higher Z on K-shell binding energy

A

increased K-shell binding energy (stronger nuclear attraction with higher Z)

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3
Q

Specific ionization (SI) relationships

A

SI is proportional to charge and inversely proportional to velocity

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4
Q

Specific ionization definition

A

number of ion pairs generated per unit path length

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5
Q

Inverse square law

A

beam intensity is proportional to 1 / d^2; beam intensity is x-rays produced PER SECOND

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6
Q

Projection naming related to source or detector

A

source (e.g. PA = source is posterior to patient, LAO = source is left-anterior to patient)

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7
Q

X-ray tube leakage limit

A

<1 mGy per 1 hour at 1 meter

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8
Q

Ideal anode characteristics

A

good conductor of heart and electricity, high melting point, high Z

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9
Q

Thermionic emission definition

A

process of electrons boiling off filament and moving toward anode

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10
Q

Primary x-ray-generating interaction in tungsten

A

Bremsstrahlung

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11
Q

Primary electron interaction in tungsten

A

excitation (release of heat)

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12
Q

K-shell binding energy of Ag

A

-25 keV; Ag = silver

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13
Q

K-shell binding energy of iodine

A

-33 keV

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14
Q

K-shell binding energy of barium

A

-37 keV

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15
Q

Change in position of characteristic peaks

A

target material has been changed

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16
Q

Bremsstrahlung radiation is the result of electron interaction with…

A

nucleus

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17
Q

Effect of increased Z material on Bremsstrahlung production

A

increased Bremsstrahlung production (vs. characteristic x-ray production)

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18
Q

Majority of x-rays in general radiology are…

A

Bremsstrahlung

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19
Q

Majority of x-rays in mammography are…

A

characteristic x-rays

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20
Q

Relationship of target material Z to Auger electron production

A

lower Z material => more Auger electron production (vs. characteristic x-rays)

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21
Q

mA is proportional to…

A

number of x-rays produced PER SECOND (mAs is obtained by multiplying by the # of seconds of the exposure)

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22
Q

mAs is proportional to…

A

total number of x-rays produced

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23
Q

Increase number of photons by 2x by…

A

doubling mAs or increasing kVp by 15%

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24
Q

Result of using a kVp less than the K-shell binding energy

A

no characteristic x-ray production (from the K-shell)

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25
Q

Average beam energy with a tungsten target

A

approximately 1/2 of kVp

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26
Q

3 ways to increase average beam energy

A

increase kVp, use target material with a higher Z, beam filtration (“hardening”)

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27
Q

How to: lower dose while maintaining a constant exposure

A

increase kVp by 15%, half mAs

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28
Q

Standard kVp for a chest radiograph (with grid)

A

120 kVp; with grid = not portable

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29
Q

Reduce voltage ripple by…

A

using a “three-phase generator” or “high frequency inverter generator”

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30
Q

2 standard deviations encompass what percentage?

A

95%

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31
Q

Primary contributor to patient dose (amongst photon interactions)

A

photoelectric effect

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32
Q

End-result of photoelectric absorption

A

original photon absorbed, photoelectron produced, characteristic x-ray or Auger electron production

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33
Q

Relationship of Compton scatter to Z of patient tissue

A

Compton scatter is independent of Z (only affected by 1/E and material density)

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34
Q

End-result of Compton scatter

A

free electron (Compton electron), new direction and lower energy of photon (which may cause more Compton interactions)

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35
Q

Major determinant of image contrast

A

photoelectric absorption

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36
Q

Dominant photon interaction at higher kVp

A

Compton scatter (photoelectric effect dominates at lower kVp; e.g. mammo)

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37
Q

How to: decrease scatter (creation or reaching detector)

A

collimation (smaller FOV), thinner object, air gap, grid

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38
Q

Delta rays

A

x-rays created when ejected electrons have enough energy to cause additional ionizations

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39
Q

Ideal kVp for a DSA

A

70 kVp

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40
Q

Ideal kVp for a CTA

A

100 kVp

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41
Q

Ideal kVp for barium fluoro

A

90-110 kVp

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42
Q

Half value layer definition

A

thickness of a material at which beam intensity (or air kerma) is reduced by one-half; expressed in mm

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43
Q

Effect of higher average beam energy on HVL

A

larger HVL (and vice-versa for lower average beam energy)

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44
Q

For a given kVp, monoenergetic or polyenergetic beams have a higher HVL?

A

monoenergetic beams have a higher HVL at a given kVp

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45
Q

Determinants of focal spot size

A

filament length, focusing cup charge, anode angle

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46
Q

How to: decrease heel effect

A

larger anode angle, increase SID, smaller FOV

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47
Q

Inherent filtration definition

A

attenuation occurring within the anode itself

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48
Q

Added filtration definition

A

attenuation occurring with the use of a filter

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49
Q

Most common situations for use of a copper filter

A

pediatrics and IR

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50
Q

Effect of collimation

A

smaller FOV (area of exposure) => fewer photon-patient interactions => lower dose, less scatter => increased contrast

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51
Q

Standard grid ratio for general radiography

A

10:1

52
Q

Standard grid ratio for mammography

A

5:1

53
Q

Typical Bucky factor

A

5 for general radiography; therefore a grid typically increases dose 5x

54
Q

Effect of adding a grid

A

reduced scatter => increased contrast, higher dose, longer exposure required

55
Q

Artifact: radiograph overpenetrated centrally and underpenetrated peripherally (left and right sides)

A

grid cutoff artifact (upside-down)

56
Q

Linear attenuation coefficient

A

describes attenuation per unit length of tissue; varies with kVp and tissue properties (Z and density); expressed in cm^-1; different for ice, water, and water vapor

57
Q

Effect of increasing kVp on _ (LAC)

A

smaller _ (less beam attenuation per unit length of tissue)

58
Q

Effect of increasing tissue Z on _ (LAC)

A

larger _ (more beam attenuation per unit length of tissue)

59
Q

Effect of increasing tissue density on _ (LAC)

A

larger _ (more beam attenuation per unit length of tissue)

60
Q

_ (LAC) for photon energies at the k-edge is increased or decreased?

A

increased _ (more beam attenuation per unit length of tissue at the k-edge)

61
Q

Relationship between _ (LAC) and HVL

A

inversely related; materials with a higher _ have a smaller HVL

62
Q

Mass attenuation coefficient

A

describes attenuation per unit mass of tissue; expressed in g^-1; same for ice, water, and water vapor

63
Q

Effect of decreasing SOD (same SID)

A

increased magnification, increased blurring, smaller FOV, decreased scatter (air gap); results in increased contrast (less scatter) and decreased spatial resolution

64
Q

Area of exposure (FOV) is proportional to…

A

SOD^2

65
Q

Kerma area product (KAP)

A

equal to AK * area exposed; independent of distance (SOD)

66
Q

Quantum mottle increases with…

A

SID (greater SID => increased quantum mottle; inverse square law)

67
Q

Flat panel detector (FPD) systems

A

indirect DR and direct DR; does NOT include CR and photon counting systems

68
Q

Effects of using a screen in film screen (vs. no screen)

A

increased speed (sensitivity) => decreased dose, decreased spatial resolution

69
Q

Components of film and screen layers

A

film layer contains a base and a single or double emulsion; screen layer contains a phosphor and a reflective layer

70
Q

Size and shape of silver halide crystals influences…

A

speed, contrast, and resolution

71
Q

Emulsion type, general radiography vs. mammography

A

general uses a double emulsion, mammo uses a single emulsion

72
Q

Photostimulable phosphor

A

used in CR; activated electrons are excited into a metastable state; composed of oxysulfides (e.g. GdOS)

73
Q

Effect of decreasing laser spot size (CR)

A

increased spatial resolution

74
Q

Spatial resolution in CR systems is dependent on…

A

laser spot size, phosphor density and thickness, rate of light sampling

75
Q

Scintillator properties in indirect DR

A

thallium-doped CsI (or NaI)

76
Q

Role of photodiodide in indirect DR

A

converts light into charge separation (which can be measured by TFT array)

77
Q

Drawback of CCDs

A

requires demagnification (minification) because size is limited to a few cm^2

78
Q

aSi vs. aSe

A

aSi is used in indirect DR, TFT array exists within aSi; aSe is used in direct DR, converts x-ray into charge separation

79
Q

Number of possible grayscale values per pixel

A

2^n, where n = # of bits per pixel

80
Q

Penetration is related to…

A

kVp; extent to which x-rays penetrate through the patient

81
Q

Exposure is related to…

A

mAs; total number of photons used to image patient

82
Q

Image is too white and spine is not visible

A

under-penetrated

83
Q

Image is too black and spine is too easily seen

A

over-penetrated

84
Q

Impact of increasing pixel density on fill factor

A

decreased fill factor => higher dose required

85
Q

Determinants of spatial resolution

A

focal spot size, geometric magnification/blurring, motion blur, detector properties

86
Q

Limitations of spatial resolution in film screen and digital systems

A

film screen is focal spot size; digital systems is pixel size

87
Q

Modulation transfer function (MTF)

A

measure of spatial resolution for an imaging system

88
Q

Detector quantum efficiency (DQE)

A

measure of signal to noise for an imaging system

89
Q

Effect of a higher DQE system on patient dose

A

same image quality can be obtained using a lower dose in a higher DQE system

90
Q

DQE of direct DR, indirect DR, and film screen systems

A

direct DR > indirect DR > film screen; better DQE means a lower dose can be used to obtain the same image quality

91
Q

Modifications for pediatric imaging

A

no grid, lower kVp (thinner object), same or decreased mAs

92
Q

Typical kVp for chest x-ray (no grid)

A

90 kVp; no grid = portable

93
Q

Typical SID for a PA chest radiograph

A

72” (or 182 cm)

94
Q

Typical SID for AP CXR, AXR, skull, C-spine, or extremities

A

40” (or 100 cm)

95
Q

Typical SID for mammography

A

26” (or 65-70 cm)

96
Q

Spatial resolution for screen film mammo

A

13 lp/mm in parallel direction and 11 lp/mm in the perpendicular direction; relative to anode-cathode axis

97
Q

Spatial resolution for digital mammo

A

7 lp/mm

98
Q

Spatial resolution for screen film radiography

A

6 lp/mm

99
Q

Spatial resolution for digital radiography

A

3 lp/mm

100
Q

Artifact: focal area of darkening

A

fogging; addition of charge to detector by something other than the x-ray beam; may affect all or part of image; e.g. cassette left in x-ray room or bracytherapy seeds within patient

101
Q

Artifact: two superimposed images

A

double exposure a.k.a. twin artifact; cassette used twice without erasing the plate in between (or without changing screen film); part of image double exposed = incomplete erasure

102
Q

Artifact: decreased image density peripherally

A

delayed scanning (CR); image degradation begins peripherally

103
Q

Tube power formula

A

kVp * mA; measured in Watts (or Joules/second)

104
Q

Tube window material (general radiography)

A

pyrex glass (vs. beryllium in mammo)

105
Q

Major source of occupational exposure

A

Compton scatter

106
Q

Relationship of quantum mottle to SID

A

quantum mottle is proportional to SID^2 (inverse square law)

107
Q

Relationship between FOV and anode angle

A

increased anode angle => increased FOV (area of exposure)

108
Q

Artifact: one side of image appears more exposed than the other

A

grid cutoff artifact (off-level or not centered)

109
Q

Artifact: thin white line through image

A

dust/dirt on CR plate reader (“light guide”)

110
Q

Artifact: tiny focal white dot(s)

A

dust/dirt on imaging plate

111
Q

Artifact: alternating lines throughout image

A

Moire artifact; seen with stationary grids, low density grids, or misaligned in plate reader; use higher density grid or moving grid

112
Q

If question stem mentions “obesity”…

A

remember that scatter is increased in bigger patients

113
Q

Focused grid

A

septa diverge away from patient (vs. a parallel grid); optimized for a particular SID

114
Q

Subject contrast

A

determined by beam characteristics and tissue characteristics (basically the same stuff that determines PE effect probability); loss of subject contrast means decrease PE absorption

115
Q

Image contrast

A

determined by subject contrast, detector properties, post-processing

116
Q

Equilibrium between PE effect and Compton scatter (soft tissue and bone)

A

25 keV for soft tissue, 40 keV for bone

117
Q

DEXA (acronym)

A

Dual Energy X-ray Absorptiometry; 2 kVp’s utilized to quantify bone mineral density (70-100 and 140 kVp)

118
Q

DEXA: osteoporosis

A

T-score < or equal to -2.5

119
Q

DEXA: osteopenia

A

-2.5 < T-score < -1.0 (note that a score of -1.0 would be considered normal)

120
Q

DEXA: what is T-score?

A

compared to health 30 y/o adult

121
Q

DEXA: what is Z-score?

A

compared to an age-matched control

122
Q

K-shell electrons are in a low or high energy state relative to M-shell electrons?

A

low energy state (require greater energy to remove)

123
Q

Speed of light

A

3 x 10^8 m/s

124
Q

K-shell binding energy of Tungsten

A

70 keV

125
Q

RIS (acronym)

A

Radiology Information System; workflow management (order entry, preauth, billing, distribute reports, coding)

AJT Physics (7 decks)

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