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X-rays Flashcards

1
Q

Discovery of x-rays

A

Wilhelm Conrad Roentgen Nov 8, 1895

won nobel prize in 1901

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2
Q

electormagnetic radiation relevant to DX

A

x-rays and gamma rays

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3
Q

Are gamma or x-rays more powerful?

A

trick question - depends on energy of electron interacting with atom

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4
Q

Velocity =

A

frequency x wavelength

= speed of light

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5
Q

Energy =

A

Planck’s constant x speed of light/wavelength

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6
Q

What is the changing factor with electromagnetic radiation energy?

A

wavelength

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7
Q

What level of energy required to produce x-ray?

A

15eV causes ionization of atoms

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8
Q

Equivalencies of roentgen rads gray sievert and rem

A

roentgen = 2.58X10^-4 C/kg

1Gy = 1 joule/kg or 100rads

1rem = 10mSv

1 rad = 100ergs/g

1 rem = dose x weighting factor

1 sievert = Gy x weighting factor

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9
Q

Does an equivalent dose of Gy cause the same biologic damage between alpha particles and x-rays?

A

No, higher ionization density of alpha particles causes more biologic damage

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10
Q

Gy to rads

A

1 Gy = 100 rads

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11
Q

Sv to rem

A

1Sv = 100rem

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12
Q

What is determinstic?

A

threshold of dose to severity

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13
Q

What is stochastic?

A

random and not dose dependent

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14
Q

Is cataract formation deterministic?

A

yes

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15
Q

Is the International Commision on Radiological Protection a government organization?

A

No, they are independent internationa organization that provide guidance and recommendations

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16
Q

Maximum mSv per year

A

20 mSv averaged over 5 years with max of 50 mSv in any one year

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17
Q

Allowable lifetime accumulation of mSV

A

10mSv x age in years

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18
Q

What is the nuclear regulatory commison

A

federal exposure standards

<50mSv/year which is 5 rem

<1mSv for public

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19
Q

Relation of distance to x-ray reduction of dose

A

logarithmic

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20
Q

Thickness of lead gowning should be?

A

0.5mm Pb equivalent

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21
Q

Film badge vs modern dosimetry badge

A

film with exposure vs. now radiation-sensitive aluminum oxide or lithium flouride

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22
Q

What does increasing mA do?

A

Increases electric current passing through filament from cathode to anode by increasing the amount of free electrons at the cathode

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23
Q

What does changing kVp do?

A

Changes voltage difference between filament so increases energy via velocity differential

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24
Q

What is binding energy?

A

Energy required to eject electron - specific to atom and orbit level

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25
Binding energy is related to characteristic x rays via radiative interaction?
False, via collisional interaction
26
What is radiative interaction? And what is another name for it?
Brehmsstrahlung or braking radiation Energy given off by "braking" of electrons near the positively changed Tungsten nucleus
27
Most x-rays arise from collisional or radiative interactions?
Radiative, and electrons can "brake" multiple times
28
kVp vs kEv?
kVp is the energy across the tube from cathode to anode at absolute peak in a revolving wave from -kVp to +kVp at maximum and minimum. Now this is not actually true because the tube never goes negative and "high frequency generators" keep the actual kVp very high but not always maximum kEv is the ACTUAL energy of the electron as it crosses the tube which is dependent on the relation of release from the cathode and wave of kVp.
29
Why is there a range of energy of electrons leaving anode?
Variance in kVp AND electrons must "brake" all at once to give off all their energy which is rare
30
Why is Tungsten used?
High melting point of 3422°C or 6192°F High elecrron number increasing efficiency by harder braking
31
Properties of anodes?
Small focal spot and rotating
32
When do you use a small filament?
Exotics or very small - decreased focal spot but limited mA
33
What is full-wave rectification?
Keeping kVp in a high positive energy High frequency generators
34
What is coherent scattering?
Photon interacting with object with no loss of energy or absorption Scatter 5% of x-rays produced
35
What is photoelectric effect?
Electron emitted after x-ray knocks one out of orbit
36
Is characteristic x-ray production in tissues the same energy as produced in the x-ray tube?
No because Tungsten has high energy binding and tissues have low energy binding of orbits
37
What is Compton scattering?
X-rays that hit outer shell electrons in tissues but still have energy to continue on at different angle and energy
38
Is Compton scatter dependent on atomic number?
No, only tissue density
39
How does the tube filter out low energy x-rays produced?
A filter before the collimator
40
What emulsion is present in film?
Silver halide
41
What factors change film blackness
kVp mAs Distance to plate
42
What mAs would be needed in this scenario. 10mAs at distance of 40inches X mAs at distance of 30inches
7.5mAs
43
Why lower mAs with smaller focal size?
Filament will overheat
44
What is the edge unhappiness with large focal spots called?
Penumbra
45
How can we make film more efficient?
Using an intensifying screen
46
What is an intensifying screen?
Flourescent material that converts x-rays to visble light which is more efficient at sensitivity the film emulsion
47
What is the relationship of intensifying screens to speed and detail?
Thick flourescent layer allows more x-ray absorption and conversion but also more diffusion before hitting film which decreases detail Speed and detail inversely related
48
How many intensifying screens are used?
Two, one on each side of film, slight decrease in image quality for large increase in efficiency
49
What is a way to decrease diffused light in a thick flourescent screen?
Light-absorbing dye
50
What are rare earth phosphors
Atomic numbers 57-71 These allow lower mAs settings as they produce more visible light in relation to the original phosphor used which was calcium tungstate
51
How to prevent fog?
Grids
52
What three things increase photon scattering?
Density if patient Amount of tissues Beam energy (kVp)
53
What is a grid composed of?
Alternate layers of absorbing (lead) and transparent (aluminum) material Aligns x-rays withpatient to prevent image degradation
54
How do you compensate for decreased x-rays getting to the patient with grids?
2-3x increase mAs
55
What thickness should you use grids
\>10cm
56
What is the name of an oscillating grid?
Bucky
57
Pros and cons of Bucky grid
Decreases chance of grid lines Loud when moves
58
What are the two things that can be changed in a grid?
Strips per linear inch - decreases grid lines Grid ratio - height to width ratio of strips (usually 5mm x 0.4mm)
59
T or F Higher grid ratio = less effective absorption of scatter radiation
False
60
How are grid strips aligned?
Diverging to match beam
61
What is a focused grid?
Peripheral divergence angulation to match beam Defined range of FFD's
62
How are grid strips aligned with x-ray table?
Parallel with long axis and centered
63
What is lateral decentering?
Loss of primary beam from central malalignment
64
When do you get distortion?
Closer to x-ray tube than plate
65
Biggest effects on contrast?
Relationship of kVp and mAs Fogging
66
What is the most important component on over or underexposure
kVp as it dictates energy
67
What is long scale vs short scale
Long scale is low contrast (more shades of gray) Short scale is high contrast (less shades of gray)
68
How to produce short scale?
Low kVp high mAs X-rays are absorbed or not and less range
69
What scale does high kVp low mAs produce?
Long scale Higher energy allows for variance in absorption
70
What radiographic technique allows predominance of photoelectric absorption?
High mAs low kVp More dependent on atomic number
71
What radiographic technique results in more Compton process?
High kVp low mAs Less absorption Independent of atomic numbers Less difference in soft tissue and bone
72
What can fog a film by environmental exposure?
Light Pressure High temperatures
73
What photoconductor are direct flat panel detectors made of?
Selenium
74
Is light intermediary necessary for charged couple device?
Yes Similar to camcorders and digital cameras
75
What is the difference between indirect and charged coupled?
Fiberoptics to focus light from intensifying screen
76
What is the difference between the relationship of intensity to distance and mAs to distance?
Intensity to distance is inversely proportional mAs to distance is directly proportional
77
Rayleigh scattering and coherent scattering are the same? T or F
True
78
What is a thin film transistor?
The screen that turns pixels on or off
79
Pixel size is related to resolution how?
Smaller pixel size = improved spatial resolution
80
Pixel depth is related to resolution how?
More bit depth = better contrast resolution
81
How many bits in a byte?
8 bits in a byte
82
Storage data for image dependent on?
Bit depth x matrix size

Physics (6 decks)

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