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CORE > Physics Ch 2 XR Interactions > Flashcards

Physics Ch 2 XR Interactions Flashcards

1
Q

XR –> interact w ppl –> 5 ways?

A
  • classical
  • compton
  • photoelectric
  • pair production
  • photodisintegration
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2
Q

what is classical (elastic, coherent, thomson) interaxn?

A

xray –> strike orbital electron –> bounce off –> change direction

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3
Q

classical (elastic, coherent, thomson) –> what energy level?

A

low energy –> <10 keV

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4
Q

classical (elastic, coherent, thomson) –> cause ionization –> T/F?

A

F: too low energy

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5
Q

classical (elastic, coherent, thomson) –> how much contribute to…

  • image?
  • pt rad dose?
A

image: no sig

pt rad dose: tiny/small

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6
Q

Compton scatter –> what energy level?

A

high

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7
Q

what is compton scatter?

A

XR –> strike outer shell electron –> eject electron –> XR lose some energy –> change direction

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8
Q

compton scatter interaxn –> main results? (3)

A
  • freed electron –> compton electron
  • atom ionized
  • XR –> lose energy & change direction –> “scattered photon”
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9
Q

compton scatter interaxn –> what happen to…

  • image?
  • pt rad dose?
A

image –> foggy

rad dose: increase

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10
Q

diag energy (>100keV) –> soft tissue –> MC interaxn?

A

compton

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11
Q

diag energy range –> what can decrease compton scatter?

A

inc XR energy

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12
Q

image –> scatter/fog –> MC contributor?

A

compton scatter

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13
Q

occupational exposure –> MC source?

A

compton scatter

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14
Q

inc atomic# (Z) –> decrease compton scatter –> T/F?

A

F: compton scatter not depend on Z

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15
Q

inc materal density –> inc compton scatter –> T/F?

A

T

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16
Q

photoelectric interaxns –> occur at what energy?

A

diag range (20-120)

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17
Q

low energy –> photoelectric interaxn vs compton scatter –> which predominates?

A

photoelectric

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18
Q

photoelectric interaxns –> MOA?

A

xray –> strike inner shell electron –> eject electron

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19
Q

photoelectric interaxns –> what 3 products?

A
  • charact xrays or Auger electron
  • ejected electron (photoelectron)
  • positive ion (original atom –> now missing 1 electron)
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20
Q

photoelectric interaxns –> highest probability –> at what energy level?

A

near binding energy

21
Q

probability of photoelectric interaxn relative to kVp energy (incident photon energy) –> formula?

A

1/E^3

22
Q

probability of photoelectric interaxn relative to atomic# –> formula?

A

Z^3

23
Q

which interaxn develops image contrast?

A

photoeletric

24
Q

probability of photoelectric interaxn –> affected by what 2 factors?

A
  • kVp

- Z

25
Q

which interaxn contributes most to pt rad dose?

A

photoeletric

26
Q

general practice –> select highest kVp possible –> why?

A

photoelectric interaxn:

  • higher kVP –> less absorbed –> less rad dose to pt
  • but not too high kVp –> enough image contrast –> diagnostic image
27
Q

more photoelectric interaxn –> what happen to contrast?

A

increase

28
Q

what is K-edge?

A

energy at which there is peak photo-electric

29
Q

to visualize low-contrast tissues –> how to change…

  • kVp
  • mA
A
  • kVp constant

- mA inc

30
Q

to lower dose but maintain constant exposure –> how to change…

  • kVp
  • mA

why?

A
  • kVp inc 15%
  • mA dec 1/2

higher kVp –> more penetrate –> less absorbed by pt (less photoelectric)

31
Q

iodine –> K-edge 33 keV –> minimum kVp should be?

A

66 kVp

32
Q

barium –> K-edge 37 keV –> minimum kVp should be?

A

74 kVp

33
Q

classic (coherent, elastic) –> causes ionization –> T/F?

A

F

too low energy to cause ionization

34
Q

differeniate: probability of photoelectric vs compton –> at <30 keV?

A
  • PE: high prob

- compton: low

35
Q

differeniate: probability of photoelectric vs compton –> at 30 keV?

A

PE & compton –> equal prob

36
Q

differeniate: probability of photoelectric vs compton –> at >30 keV?

A
  • PE: sig dec prob (1/E^3)

- compton: dec prob (but not as much as PE)

37
Q

differeniate: probability of photoelectric vs compton –> inc tissue mass density?

A
  • PE: inc

- compton: inc

38
Q

differeniate: probability of photoelectric vs compton –> inc Z?

A
  • PE: inc

- compton: no change

39
Q

relationship bw mass attenuation & linear attenuation –> formula?

A

mass attenuation coefficient = linear atten coeff / density

40
Q

what is linear attenuation coefficient?

A

material’s probability to attenuate XR beam over a set distance

41
Q

what is mass attenuation coefficient?

A

rate of XR energy loss as travel thru material

42
Q

linear attenuation coefficient –> affected by what factor? (1)

A

material density

43
Q

mass attenuation coefficient –> affected by what factor? (2)

A
  • Z

- photon energy

44
Q

inc kVp –> what happen to…

  • linear atten coeff
  • half value layer
A
  • linear atten coeff –> dec

- half value layer –> inc

45
Q

inc density of tissue –> what happen to…

  • linear atten coeff
  • half value layer
A
  • linear atten coeff –> inc

- half value layer –> dec

46
Q

entrance skin dose –> affected by what factors? (4) by how much?

A
  • mA –> proportional
  • time of exposure (s) –> proportional
  • kVp –> ^2
  • distance –> 1/^2
47
Q

if dose = 28 mR at 25mA –> what is dose at 35mA?

A

28 x 35 / 25

48
Q

if dose = 20mR at 75kVp –> what is dose at 125kVp?

A

20 x 125^2 / 75^2

CORE (33 decks)

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