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CORE > Physics Ch 3 Gen XR Concepts > Flashcards

Physics Ch 3 Gen XR Concepts Flashcards

1
Q

photons –> inc vs dec –> noise inc/dec?

A
  • inc photons –> dec noise

- dec photons –> inc noise

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2
Q

most important source of noise (quantum) noise?

A

quantum mottle –> XR beam is inhomogeneous –> not enough XR reach film/detector –> random noise

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3
Q

how to reduce quantum mottle? (2)

A
  • inc XR (mAs)

- inc efficiency detection

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4
Q

what factors inc scatter? (3)

A
  • inc kVp
  • inc thickness (body habitus)
  • inc field of view (lrger XR beam)
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5
Q

what is grid?

A

bw pt & image receptor –> device w mult thin lead stripes –> block scattered (angled) XRs

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6
Q

grid –> how affect contrast? scatter?

A

grid –> reduce scatter –> improve contrast

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7
Q

what is grid ratio? inc ratio –> how affect contrast?

A

ratio of lead ht to distance bw stripes

inc ratio –> dec scatter –> improve contrast

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8
Q

grid –> how affect dose?

A

inc grid ratio –> inc dose

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9
Q

tube-detector distance & noise –> relationship formula?

A

inc distance –> inc noise

inverse square law: inc distance 2x –> inc noise 1/4

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10
Q

noise & mottle –> relationship formula?

A

inc XR photons 4x –> dec mottle 1/2

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11
Q

to dec quantum mottle –> inc mA vs kVp?

A

correct answer: inc mA

inc kVp –> inc compton scatter –> inc noise

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12
Q

mAs -> most important factor for… sharpness vs contrast vs noise/mottle

A

noise/mottle

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13
Q

inc mA from 50 to 200 –> how change noise/mottle?

A

dec by 50%

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14
Q

which of following will reduce noise?

  • use grid
  • use air gap
  • inc mA
A

ALL reduce noise –> but correct answer is “inc mA”

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15
Q

what is signal to noise ratio? main concept?

A

quantitative method for compare signal vs noise

strong signal –> can tolerate more noise

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16
Q

contrast to noise ratio –> main concept?

A

high contrast –> can tolerate more noise

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17
Q

what happen to contrast to noise ratio?

  • inc mA?
  • automatic exposure control (AEC) –> dec kV?
A
  • inc mA –> dec noise –> improve contrast to noise ratio

- “fixed” noise –> dec kV –> inc contrast –> improve contrast to noise ratio

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18
Q

spatial resolution –> main concept? units?

A

how close 2 lines can be and still be seen as separate

line pairs per mm

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19
Q

what is spatial frequency?

A

spatial resolution

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20
Q

what is unsharpness?

A

loss of spatial resolution

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21
Q

what is motion unsharpness?

A

pt motion –> loss of spatial resolution

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22
Q

what is system unsharpness?

A

detector –> limiting factor –> max spatial resolution

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23
Q

geometric unsharpness:

  • small focal spot
  • dec source-object distance
  • dec object-detector distance
  • inc magnification

==> inc/dec blur?

A
  • small focal spot –> dec blur
  • dec source-object distance –> inc
  • dec object-detector distance –> dec
  • inc magnification –> inc
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24
Q

geometric unsharpness: small focal spot –> utilized in what exams? (2)

A
  • mammo

- extremity

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25
Q

inc magnification –> affected by what 2 factors?

A
  • source to obj distance –> dec

- object to detector distance –> inc

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26
Q

magnification –> formula?

A

source to detector (image) distance / source to obj (pt) distance

SID/SOD

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27
Q

what is modulation transfer fx? formula?

A

original perfect XR data that exited pt –> image that digital detector produced

MTF (image) = info recorded / info avail = <1.0

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28
Q

what is detective quantum efficiency (DQE)?

A

“prediction of dose” –> estimate required exposure level necess to create optimal image –> measure of efficiency of detector to convert XR energy to image signal –> better DQE –> less rad necess

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29
Q

detective quantum efficiency (DQE) –> relationship to…

  • MTF?
  • signal to noise ratio?
  • spatial resolution?
A
  • directly proportional to MTF
  • inversely proportional to signal to noise ratio
  • inversely proportional to spatial resolution
30
Q

digital imaging –> matrix –> contain pixels –> what is pixel density? pixel pitch?

A
  • pixel density: #pixels per unit area

- pixel pitch: “pixel spacing” –> distance from center or 1 pixel to next

31
Q

inc/dec pixel density –> better spatial resolution?

32
Q

inc/dec pixel pitch –> better spatial resolution?

33
Q

what kind of detector has best spatial resolution?

A

photoconductor

34
Q

lrger/smaller matrix –> smaller pixels?

A

larger matrix –> more pixels –> smaller pixels

35
Q

lrger/smaller matrix –> better spatial resolution?

36
Q

dec source to object distance (SOD) –> change what factor to compensate for blur inc?

  • inc kVp
  • dec focal spot size
  • inc focal spot size
A

dec focal spot size

37
Q

inc focal spot size –> what factor is improved? why?

  • noise (mottle)
  • contrast
  • blur (motion)
A
  • blur (motion)

inc focal spot size –> inc mA –> dec exposure time –> less time for pt to mv –> dec blur from motion

38
Q

dec/inc kVp –> dec/inc contrast?

A
  • dec kVp –> inc contrast

- inc kVp –> dec contrast

39
Q

inc scatter –> dec/inc contrast?

A

inc scatter –> dec contrast

40
Q

what factors improve contrast?

  • inc/dec kVp
  • inc/dec atomic number
  • inc/dec density
A
  • dec kVp
  • inc atomic number
  • inc density
41
Q

inc filtration –> what happen to avg energy beam (penetration power)? what happen to contrast?

A

inc filtration –> dec low energy XRs –> inc avg energy of XR beam –> dec contrast

42
Q

most important factor affecting contrast in digital system? in film system?

A
  • digital –> look up table (LUT)

- film –> kVp

43
Q

narrow vs wide window width –> inc contrast?

44
Q

window level –> determines what?

A

brightness

45
Q

which has wider dynamic range? –> digital imaging or film screen?

A

digital imaging

46
Q

window level –> inc vs dec –> good for looking at what?

A
  • inc –> inc pixel –> better for looking at dark –> ie lungs
  • dec –> dec pixel –> better for looking at light –> ie bones
47
Q

XR –> underexposed –> cause?

A

too low mA

48
Q

XR –> overexposed –> cause?

A

1 too high mA

49
Q

what kind of XRs usu DON’T have automatic exposure control (AEC)? (3)

A
  • portable XR
  • extremity XR
  • baby XR
50
Q

inc exposure time 4x –> what happen to mottle?

A

dec by 1/2

51
Q

inc exposure time –> what happen to patient motion/blur?

52
Q

tabletop extremity exam –> no automatic exposure control (AEC) –> inc exp time –> what happen…

  • contrast improve
  • motion artifact dec
  • image mottle/noise improve
A

image mottle/noise improve

53
Q

tabletop extremity exam –> automatic exposure control (AEC) –> inc exp time –> what happen…

  • pt dose inc
  • image sharpness worsen
  • image mottle/noise improve
A

image sharpness worsen

54
Q

filter –> thicker –> what happen to image contrast?

A

inc filtration –> higher energy XRs remain –> dec contrast

55
Q

tell XR tech to improve image contrast –> f/u XR shows no change –> what factor was changed?

  • kV
  • mA
  • grid ratio
A

mA –> NOT change contrast

56
Q

which of following uses highest kV?

  • abd
  • PA chest
  • extremity
57
Q

to inc penetration (exposure, “black”ness) –> should inc what factor? by how much?

A

mA

30% rule –> inc mA by at least 30% to make visible change in density

58
Q

obesity –> __cm pt tissue –> require __ inc in mA?

A

every 4cm of pt tissue –> 2x mA

59
Q

obesity –> lrg inc kV, small inc mA –> what happen to dose? contrast?

A
  • lower dose

- lower contrast

60
Q

obesity –> small inc kV, lrg inc mA –> what happen to dose? contrast?

A
  • higher dose

- higher contrast

61
Q

what is S/P ratio?

A

ratio of secondary XRs (scatter) to primary XRs (useful XRs)

62
Q

S/P ratio –> depend on what 2 factors?

A
  • thickness of body part: thicker –> more scatter –> inc S/P ratio
  • beam area: bigger –> more scatter
63
Q

reduce scatter & improve contrast –> 4 methods?

A
  • collimate: dec beam area
  • compress body part: dec thickness of body part
  • dec kVp: dec scatter, inc PE
  • use grid/airgap: dec scatter than strike detector
64
Q

infant XR –> how different from adult XR? (3)

A
  • no grid
  • lower kVp
  • lower mAs
65
Q

pediatric: how much mAs compared to normal adult mA?

  • 0-5yo
  • 6-12yo
A
  • 0-5yo: 25% mA of an adult

- 6-12yo: 50%

66
Q

fracture –> cast –> how change mA?

  • fiberglass cast
  • plaster cast
A
  • fiberglass: no change

- plaster: dry –> inc mA 2x, wet –> inc 3x

67
Q

XR:

  • h/o splenomeg –> should change what factor?
  • h/o ascites?
  • h/o sclerotic phase Paget’s?
  • h/o lytic phase Pagets?
  • h/o emphysema?
  • h/o osteoporosis?
  • soft tissue neck XR?
A
  • h/o splenomeg –> inc kVp
  • h/o ascites –> inc kVp
  • h/o sclerotic phase Paget’s –> inc kVp
  • h/o lytic phase Pagets –> dec kVp
  • h/o emphysema –> dec kVp
  • h/o osteoporosis –> dec kVp
  • soft tissue neck XR –> inc kVp
68
Q

radiographic density (blackness) –> controlled by kVp vs mAs?

69
Q

radiographic contrast –> controlled by kVp vs mAs?

70
Q

need to inc mAs by what% for noticeable difference in “density”?

71
Q

dec mA by 50% –> need to dec/inc kVp by how much% to maintain same density?

72
Q

4cm of tissue –> require how much more mA?

CORE (33 decks)

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