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Radiology Physics > X-ray physics > Flashcards

X-ray physics Flashcards

1
Q

The greatest # of x-rays emitted is approximately how much of the maximum energy?

A

1/3rd

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2
Q

What are 4 factors that influence the shape of the x-ray emission spectrum?

A

1) Projectile electrons accelerated from cathode to anode do not all have the peak kinetic energy. Depending on type of rectification/high voltage generator, some will have low energies when striking the target.
2) Projectile electrons have multiple interactions w/ target, each successive one @ lower E.
3) Low E x-rays are more likely to be absorbed by target
4) External filtration selectively removes low E x-rays.

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3
Q

What factors will affect the x-ray emission spectrum?

A 
mAs
kVp
Added filtration
Target material
Voltage waveform/ripple
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4
Q

How does mAs affect the x-ray emission spectrum?

A

It increases the amplitude only.

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5
Q

How does kVp affect the x-ray emission spectrum?

A

It increases the amplitude and causes a right shift to the curve (mostly affects high energy x-rays).

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6
Q

What is the 15% rule?

A

A 15% increase in kVp, is equivalent to doubling the mAs.

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7
Q

How does filtration affect the x-ray emission spectrum?

A

Decrease in the amplitude (mostly at low E) and a right shift to the curve.

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8
Q

How does using a higher atomic number target affect the x-ray emission spectrum?

A

Increases the amplitude and causes a right shift to the curve.

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9
Q

How does increased voltage ripple affect the x-ray emission spectrum?

A

Causes a decrease in the amplitude (quantity) and a left shift of the curve (quality).

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10
Q

Using a 3-phase or high frequency equipment vs a single-phase is equivalent to what in terms of kVp/mAs?

A

A 12% increase in kVp or doubling of mAs

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11
Q

What is the relationship of kVp and x-ray quantity?

A

X-ray quantity is proportional to the square of ratio of kVp (eg. double kVp = increase x-ray intensity by x4)

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12
Q

What factors affect the x-ray QUANTITY?

A

a) mAs (proportionally)
b) kVp
c) distance (inverse square law)
d) filtration

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13
Q

What factors affect x-ray QUALITY?

A

a) kVp

b) Filtration

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14
Q

What produces more heat? A 3-phase system or a single phase?

A

3 phase

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15
Q

Coherent scattering occurs at what x-ray energy?

a) 10keV
b) 1.02MeV
c) 10.2MeV
d) can occur at any energy

A

10kev – very low energy x-rays

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16
Q

The probability of photoelectric interaction depends on:

A

1) photon E (inc. in photon E = dec. in probability of PE) = photon^3
2) atomic # (inc. atomic # = inc. probability of PE) = atomic number^3

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17
Q

An increase in atomic number does what to Compton’s effect?

A

No effect

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18
Q

What are 3 ways to reduce the anode heel effect?

A

1) Increase the SID
2) Decrease the field size
3) Increase the anode angle

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19
Q

At lower energies (kVp), most of the attenuation is due to what secondary interaction?

A

PE

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20
Q

At higher energies (kVp), most of the attenuation is due to what secondary interaction?

A

Compton’s

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21
Q

What is bucky factor?

A

Increased does to the patient d/t to the use of a grid.

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22
Q

What is stage 1 collimation?

A

Prevents off focus radiation – electrons that interact at positions on the anode other than the focal spot.

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23
Q

What is stage 2 collimation?

A

3mm thick lead shutter leaves

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24
Q

What is the function of a grid in terms of contrast?

A

Increases contrast.

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25
Q

Contrast improvement factor of 1 indicates what?

A

No improvement with the use of a grid.

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26
Q

At what kVp is contrast improvement factor measured at?

A

100kVp

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27
Q

What will cause a higher bucky factor?

A

1) Increased grid ratio

2) Increased kVp

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28
Q

Grid cut-off at the edges of the film most likely represents which grid abnormality?

A

Off-focus or upside-down

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29
Q

How does kVp affect the air gap technique and why?

A

Air gap technique doesn’t work with high kVp’s because, the scatter radiation is more forward directed towards the image.

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30
Q

What is the active ingredient of the emulsion?

A

Silver halide crystal (98% silver bromide; 2% silver iodide)

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31
Q

What holds the halide crystal in place in the emulsion?

A

gelatin

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32
Q

What is the sensitivity center/speck?

A

Imperfections in the crystals containing AgS (silver-gold sulfide) that attract photoelectrons & Ag ions to combine and form a latent image.

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33
Q

What is the supercoat?

A

Protects the emulsion from scratching, pressure and contamination.

34
Q

What is the purpose of a double emulsion?

A

Faster speed

35
Q

What is spectral matching?

A

Matching films to the spectrum of light emitted by the intensifying screens.

36
Q

What are orthochromatic films?

A

rare earth screens and blue & green sensitive films

37
Q

What are panchromatic films?

A

Films that are sensitive to the entire visible light spectrum.

38
Q

What is the name of the production of the latent image?

A

Gerney-Mott theory

39
Q

What are the reducing agents in a developer?

A

Hydroquinone & phenidone

40
Q

What does the developer do?

A

Provides electrons to the sensitivity center of the crystal to change Ag+ to metallic Ag.

41
Q

What controls the pH of the developer?

A

sodium carbonate & sodium hydroxide

42
Q

What is the hardener in the developer and what does it do?

A

gluteraldehyde –> controls swelling & softening of emulsion

43
Q

Which step is only used in manual processing?

A

Stop Bath – use acetic acid to stop development process

44
Q

What is the clearing agent in the fixer?

A

Ammonium thiosulfate

45
Q

What is the hardener used in the fixer?

A

potassium alum, aluminum chloride, chromium alum

46
Q

What is the cause of deterioration/browning of the films after time?

A

Retention of the fixer in the emulsion combines with the silver –> forms silver sulfide –> oxidizes and causes image to discolor

47
Q

What is the active layer in the cassette?

A

Phosphor layer (contains the phosphorous elements that glow)

48
Q

What is the role of the reflective layer?

A

Intercepts light headed in other directions and redirects back to the film.

FYI, NOT present in the rare earth screens!

49
Q

What is the relative speed of a par speed screen?

A

100

50
Q

What is the fast speed screen?

A

High speed rare earth (up to 1200)

51
Q

What is a disadvantage to the use of intensifying screens?

A

Image blur – decrease SPATIAL resolution (b/c light emitted activates a larger area of emulsion than direct x-rays)

52
Q

What is intensification factor?

A

Ratio of exposures required to produce the same OD of a film w/ and w/out screens.

53
Q

How is resolution quantitatively measured?

A

Line pair test = # line pairs/mm

Higher this number, smaller the object that can be imaged

54
Q

What is the relationship of quantum mottle with intensifying screens and why?

A

Intensifying screens = inc. quantum mottle

Quantum mottle is decreased when larger # of x-rays are used. Intensifying screens are “faster” screens and hence fewer mAs (x-rays) are used, which means more quantum mottle.

55
Q

What does an H&D curve plot? And what does it mean?

A

Density (y) to exposure (x)

Describes the change in optical density over each exposure interval.

56
Q

What happens to density at very small and very large exposures, according to an H&D curve?

A

Large variances results in only small changes to OD.

57
Q

What is the reciprocity law?

A

As long as the mAs is constant, it doesn’t matter if the exposure time is long or short. Therefore, the OD is only proportional to the total E imparted on the film.

58
Q

What is latitude?

A

Range of exposures in which an x-ray film will respond with optical density in a radiographically useful range.

59
Q

What is the relationship of latitude and contrast?

A

Inversely proportional –>
wide latitude = long grey scale
short latitude = short grey scale

60
Q

The slope of a H&D curve is equivalent to:

A

The contrast of the image receptor.

61
Q

What makes up radiographic contrast?

A

Image receptor contrast + subject (person) contrast

62
Q

What does is the relative speed of image receptor A compared to image receptor B, if A is to the left side on an H&D curve?

A

Image receptor A is faster.

63
Q

What increases penumbra?

A

1) large effective focal spots
2) short SID
3) large OID
4) geometry of object
5) greater on the cathode side

64
Q

What is the minimum total filtration that must be used?

A

2.5mm Al

65
Q

What is exposure linearity?

A

Ability of a unit to produce constant radiation output for multiple combinations of mA and exposure time. (Should be within +/-10%)

66
Q

What does linear stochastic dose response mean?

A

That there is no threshold to which a biological response can be observed (i.e. response can be seen regardless of the size of the dose). Example: leukemia

67
Q

What is linear energy transfer?

A

Measure of the rate @ which E is transferred from ionizing radiation to soft tissue.

68
Q

What does an increased LET mean?

A

Radiation has a greater ability to produce a biologic response.

69
Q

What are deterministic biological effects?

A

Non-stochastic (threshold response)

70
Q

What is photostimulable luminescence?

A

Process of receiving x-rays and storing the energy as trapped electrons and releasing them as light when exposed to a different light source.

71
Q

What do digital screens contain that allow them to store electrons and release them later?

A

photostimulable phosphors

72
Q

What type of light is aimed at photostimulable phosphors to cause them to release the electrons and emit light?

A

Infrared light –> causes metastable electrons to return back to ground state

73
Q

What color light is aimed at the photostimulable phosphor screens?

A

Red

74
Q

What color light is emitted from the released electrons in a storage phosphor screen?

A

Blue (shorter wavelength)

75
Q

What causes the latent image in CR?

A

Electrons being stored in a metastable state in the photostimulable phosphor screen.

76
Q

How is the photostimulable phosphor erased?

A

Exposed to intense white light that returns any remaining metastable electrons back to ground state.

77
Q

What is the active ingredient in a photostimulable phosphor screen?

A

Europium-activated barium fluorohalide

78
Q

Grid cut-off on one side of image?

A

Grid off centered and off focus

79
Q

Grid cut-off across entire image?

A

Either off centered or off level

80
Q

List the different forms of energy along the electromagnetic spectrum, starting from smallest wavelength to greatest wavelength.

A

ia) gamma ray
ib) x-ray
ii) ultraviolet
iii) visible light
iv) infrared
v) microwave
vi) radiowave

81
Q

List the imaging modalities from best spatial resolution to worst.

A 
Radiography -- BEST
Fluoroscopy
CT
MRI
US
Gamma camera --WORST
82
Q

What is the maximum permissible dose for an adult occupational worker?
For an occupational worker under 18?
For a pregnant woman/fetus?
For the general public (not including medically required doses)?

A 
All of these are annual:
Adult occupational worker = 50mSv
Child occupational worker = 1mSv
Pregnant (and fetus) worker = 5mSv
General public worker = 1mSv

Radiology Physics (5 decks)

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