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VetRad Boards prep > WAR MACHINE- Testable trivia > Flashcards

WAR MACHINE- Testable trivia Flashcards

1
Q

What is the primary purpose of the envelope?

A

to maintain a vacuum

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2
Q

Why is a vacuum needed?

A

To allow the amount and speed of the electrons to be controlled independently

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3
Q

What is the purpose of a focusing cup?

A

to help the electron beam strike the target anode in an acceptable size

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4
Q

What is the purpose of a rotating anode?

A

to spread the heat produced over a larger surface area to prevent melting

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5
Q

What focal spot size do general x-ray machines use?

A

0.6 and 1.2 mm

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6
Q

What causes differential x-ray attenuation?

A

steeper (smaller) anode angle

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7
Q

What are ways to reduce heel effect?

A
  • large anode angle
  • put thicker tissues toward cathode side
  • smaller plate
  • larger focal spot to film distance (FFD)
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8
Q

What is the minimum aluminim filter thickness?

A

2.5 mm

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9
Q

In Bremsstrahlung, what dictates the highest achievable energy x-ray?

A

Dictated by the original energy of the electron

Max energy (max keV)= Max kVp

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10
Q

Is Bremsstrahling more likely with higher or lower Z?

A

higher - more protons to make the electrons break

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11
Q

In nuc med, why are low Z materials used to shield Beta emitting particles?

A

to minimize Bremsstrahlung production - lead makes this worse

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12
Q

what is the K-shell binding energy of tungsten?

A

-69.5 keV

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13
Q

How is the energy of characteristic x-rays determined?

A

determined by the specific/characteristic binding energies of the element of the target atom (not determined by voltage)

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14
Q

80% of x-rays produced are what type?

A

Brensstrahlung

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15
Q

How to kVp and mAs effect quantity and quality?

A
  • mAs only affects QUANTITY
  • kVp influences both QUANTITY and QUALITY
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16
Q

What is the 15% rule?

A

If you increase kVp by 15%, youn decrease mAs by 1/2 to maintain the same x-ray density on the film

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17
Q

How do single and triple phase generators compare as far as voltage ripple and quality and quantity?

A

Single phase: more ripple = less quality and quantity

Triple phase: less ripple = more quantity and quality

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18
Q

What is HVL (half value layer)?

A

amoutn of material required to attenuate an x-ray photon to 1/2 the original output

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19
Q

What does increasing kVp do to the spectrum/spectrum diagram?

A
  • incr total quantity of x-rays
  • incr average energy
  • incr max energy
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20
Q

What are a few important characterisitc of Coherent/Classic scatter?

A
  • Do NOT result in ionization
  • Do NOT result in net transfer of energy - changes direction without loss of energy
  • Does NOT contribute to image
  • Adds tiny dose to patient
  • Seen at LOW energies (less than 10keV)
21
Q

What occurs with Compton interactions?

A
  • high energy incident x-ray strikes and frees outter shell electron - ejects as “compton” electron
    • thus ionizes the atom
  • deflects the incident x-ray as “scattered photon”
22
Q

What are some negative characteristics about Compton scatter?

A
  • dominant force contributing to scatter/image fog
  • major source of occupational exposure
  • materials rich in hydrogen have higher risk of Compton scatter - e/g animals
  • does not depend on z of atom
23
Q

Describe photoelectric interactions

A
  • Occurs throughout the diagnositc ranges but dominates at lower energy
  • x-ray strikes inner chell electron and transfers all its energy (is absorbed)
  • all or nothing - either rleases the k-shell electron or it doesn’t
  • atom is ionized - as electrons shift down, either release characeristic x-rasy or Auger electrons
    • Auger dominates in biologic tissues
24
Q

Describe the probability of photoelectric effect in relation to incident photon (IP) energy and atomic number

A
  • inversely proportional to the IP energy cubed: 1÷E3
  • directly proportional to Z cubed: Z3
25
Q

How do you describe/define K-edge?

A

P.E. peaks right around the binding energy of the inner shell electron - this peak is K-edge

26
Q

What influences attenuation in tissue?

A
  • effective atomic number in tissue
  • x-ray beam quality
  • tissue density
27
Q

What is linear attenuation coefficient?

A

Measure of the probability of the material to attenuate an x-ray beam over a set distance

28
Q

What is mass attenuation coefficient?

A

Measure of the rate of energy loss by an x-ray as it travels through a material

29
Q

How are LAC and MAC related?

A

MAC = LAC/density

30
Q

What factors determine entrance skin dose?

A
  • Tube current (mA) - proportional relationship
  • Time of exposure (s) - proportional relationship
  • Peak kilovoltage - square
  • Distance - inverse square law (double the distance, dose reduced by 4)
31
Q

What is radiographic density?

A

syonomous with optical density and film density - essentially a description of how dark the film is; more x-rays on the film = darker = more radiographic denisty

32
Q

What leads to more scatter?

A
  • Higher kVp
  • thicker parts/animals
  • larger field of view
33
Q

What does a grid do to dose?

A
  • using a grid increases dose
  • using a higher grid ratio also increases dose
34
Q

If trying to decrease noise, do you increase mA, kVp, or both?

A
  • increase mAs
    • will reduce mottle with more photons
    • in incr kVp too much, will lead to more Compton scatter and thus more noise
35
Q

What is the mathmatical relationship between mA and noise?

A

quadrupling x-ray photons will cut mottle in half

36
Q

How do you calculate magnification factor?

A

Source to image(detector) distance ÷ Source to object distance

37
Q

What is DQE?

A

an estimate of the required exposure levelthat will be necessary to create an optimal image (prediction of dose)

38
Q

What is the relationship between spatial resolution and pixel denisty and spacing(pitch)?

A
  • Increased pixel density = better spatial resolution
  • Decreased pixel pitch = better spatial resolution
39
Q

How does kVp relate to contrast?

A

High kVp = low contrast

Low kVp = high contrast

40
Q

What is the fill factor for Direct flat panels?

A

nearly 100%

41
Q

Describe the DQE for direct and intirect

A

High DQE for direct

Moderate DQE for indirect

42
Q

What are the major limiting factors for spatial resolution of each type of detector system?

A
  • Screen films = screen thickness
  • CR = light spread/ scatter and pixel size
  • DR = spread of light photons (indirect) and the size of the detector
43
Q

What determines slice thickness in single slice and multi slice CT?

A
  • Single slice: determined by collimation
  • Multi slice: determined by the width of the detector rows
44
Q

What are theadvantages of axial scanning?

A
  • less partial volume artifact - e.g. skull
  • better spatial resolution along the z-dimension
45
Q

What are the advantages of helical acquisition?

A
  • faster
    • less motion artifact
  • picture overlap - allow for better reconstruction
  • less stair-step artifact
46
Q

What is pitch?

A

the distance the table moves during the time of a single revolution of the tube divided by the beam width

Pitch = Table movement/beam width

47
Q

What does a pitch of 1 mean?

A

There is no overlap between slices

48
Q

What does a pitch less than 1 indicate?

A

table moved slow and slices overlap, thus increased spatial resolution but increased dose

49
Q
A

VetRad Boards prep (11 decks)

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