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Pod Exam 1 > 6/7: Radiation Physics - Mahoney > Flashcards

6/7: Radiation Physics - Mahoney Flashcards

1
Q

ionizing

A

removes an electron from an atom

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2
Q

roentgen

A

quantity of exposure

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3
Q

Rad

A

quantity of absorbed dose

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4
Q

Rem or Sv sievert

A

quantity of effective dose equivalent received by radiation workers

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5
Q

curie or becquerel

A

quantity of radioactivity

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6
Q

amount of ionization that is produced when radiation passes through matter

A

exposure

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7
Q

amount of energy absorbed by matter when radiation passes through it

A

absorbed dose

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8
Q

measure of biological damage caused by radiation

A

dose equivalent

product of absorbed dose multiplied by quality factor that accounts different types of radiation causing different amounts of damage

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9
Q

measure of biological damage caused by radiation to a specific organ

A

effective dose equivalent

product of dose equivalent multiplied by measure of risk from exposure to that organ compared to risk from whole body exposure to same dose

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10
Q

1 Gy = _____ rad

A

100

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11
Q

1 Sv = _____ rem

A

100

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12
Q

1 rad = _____ rem

A

1

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13
Q

1 Gy = _______ Sv

A

1

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14
Q

smallest quantity of any type of EM radiation

A

photon

has high energy and short wavelength

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15
Q

results in dif. shades of gray on film

A

attenuation

matter that absorbs x rays = white
matter that is penetrated = black

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16
Q

inverse square law

A

light intensity from a source is inversely proportional to the square of the distance b/w object and source

x ray intensity is 1 rad at 2 ft and .25 rad at 4 ft

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17
Q

energy of x-ray beam

A

kVp kilovoltage peak

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18
Q

manipulates primarily the energy or quality of x-rays and to a lesser extent the quantity of x-rays

A

kVp

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19
Q

manipulates the quantity of x-rays

A

mA and Timer

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20
Q

mA range

A

10-30 mA

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21
Q

timer range

A

1/60th -1/100th of a second

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22
Q

tube current and controls the number of photons produced

A

mA milliamperage

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23
Q

negative electrode of x-ray tube

A

cathode

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24
Q

positive electrode of x-ray tube

A

anode

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25
Q

inherent v. added filtration

A

tube housing absorbs off-focus radiation that does not contribute to the useful x-ray beam

filters teh useful x-ray beam and absorbs low energy rays that cannot reach image receptor

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26
Q

collimation

A

shape dimensions of useful x-ray beam so that only the area of interest is x-rayed

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27
Q

x-ray production summary

A

electrons generated at the cathode end at the filament

focusing cup directs electrons toward the anode target

electrons interact with the target where x-rays are produced

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28
Q

characteristic v. bremsstrahlung radiation

A

x-rays produced as outer-shell electrons fill the inner shells

+ charged nucleus changes course of electron which causes it to lose energy in the form of x-ray photons

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29
Q

penetrability of the x-ray or how much energy it has

A

quality

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30
Q

range of x-ray energies present in a quantity of x-rays

A

x-ray emission spectrum

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31
Q

increasing mAs increases ___ but not _____

A

quantity

quality

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32
Q

increases kVp increases _____ and _______

A

quality

quantity

33
Q

decreases quantity and increases quality

A

filtration

34
Q

the quality is increased with an _______ in kVp or an _______ in filtration

A

increase for both

35
Q

why do you position the thicker portion of the part to be examined closer to the cathode?

A

heel effect - useful x-ray beam has greater intensity on the cathode side than the anode side which is a result of the line-focus principle

36
Q

x-rays produced by this process

A

bremsstralung radiation

37
Q

coherent scattering

A

as x-ray photons excite the target atom, a secondary photon of equal energy is released in dif direction which is absorbed by the pt but does not contribute to diagnostic image

38
Q

occurs primarily, but not the most useful: comptom scattering

A

occurs when x-ray photon interacting w/ matter ejects the outer-shell electron causing ionization

original x-ray continues in dif direction w/ decreased energy

creates FOG that impairs image quality by reducing its contrast

39
Q

produces the image: photoelectric effect

A

x-ray photon is totally absorbed and an inner-shell electron is ejected during ionization

process causes beam attenuation and image formation

also contributes to pt absorbed dose

40
Q

diagnostic image is formed by photoelectric effect and

A

remnant radiation (xprays that pass through pt and strike image receptor)

most x-rays interact w/ matter by comptom scattering which causes fog

41
Q

favors photoelectric effect but increases dose of radiation

A

low kVp

high kVp favors compton scattering (more radiation will make its way to x-ray film)

42
Q

differential absorption is manifested by ________ which is the ___________ as it is absorbed and scattered by matter

A

attenuation

reduction in x-ray beam intensity

43
Q

ability to separate and distinguish b/q 2 separate objects

A

resolution

44
Q

able to distinguish b/w two objects that are aligned closely together

A

high spatial resolution

45
Q

ability to distinguish b/w differences in density or intensity

A

contrast

46
Q

amount of darkening in radiograph

A

optical density

47
Q

primary controlling factor of optical density

A

mAs

as mAs increases, both xpray quantity and radiographic density increase proportionally

48
Q

law of reciprocity

A

as mAs increases, the image becomes darker

need 30% change in mAs for human eyes to see visisble change

49
Q

if you need to make an adjustement in density either increase the mAs by a factor of ____ to increase darkness or decrease by a factor of __ to increase lightness

A

2 - darker

1/2- lighter

change either the mA or the s but not both

50
Q

low kVp produces ____ contrast; high kVp produces ___ contrast

A

high
low

kVp governs the penetrating power of electrons and alters both quality and quantity of photons produced

51
Q

15% Rule

A

a 15% increase in kVp will cause the same change in radiographic density (darker) as doubling the mAs

a 15% decrease in kVp will cause image to look lighter to the same extent as halving the mAs

52
Q

source to image distance will alter…

A

number of photons striking film

53
Q

inverse square law

A

if tube is too far from film, too few photons strike film producing a lighter image

if too close to film, more photons produce a darker image

54
Q

the ____ the speed of the film/screen, the ____ radiation is necessary to produce an image, but the ____ image detail is produced

A

higher
less
less

55
Q

why do you need a compensation filter?

A

to balance unequal radiographic density b/w forefoot and rearfoot

56
Q

subject v. radiographic contrast

A

subject - result of attenuation dif as xrays pass through body

radiographic - result of dif in densities tha allows viewer to discern b/w two adj densities w/i same image

57
Q

scale of contrast used in pod

A

short

distinguishes bone margins from adjacent soft tissues

58
Q

*** primary factor controlling contrast

A

kVp

59
Q

higher kVps produce _____ contrast

A

lower

60
Q

to produce shortened contast ….

to produce lengthened contrast…

A

increase mAs by 2 and decrease kVp by 15%

decrease mAs by 1/2 and increase kVp by 15%

61
Q

the greater the SID distance, the _____ the image

A

sharper

but requires increased mAs to maintain the same radiiographic density

62
Q

slower speed produces __ image

A

sharper

but require more radiation

speed dependent on silver halide crystal size larger - faster- less exposure

63
Q

** to limit motion of a part (pediatrics/parkinsons) …

A

decrease exposure time by 1/2 and icnrease kVp by 15% to produce same radiographic density

64
Q

plaster cast modifications ***

A

increase mAs 2X normal or +10kVp

65
Q

fiberglass cast modifications ***

A

increase mAs 1.5X normal

66
Q

soft tissue masses, foreign bodies modifications ***

A

decrease kVp 15% and double mAs

67
Q

fixed kVp is typically 60, the mAs are then..

if fixed mAs, the kVp is…

A

varied per part thickness

typically lower than 60kVp and varies on thickness

68
Q

how do traditional xrays produce an image

A
  • emerging pattern of photons of differing energies affect the film emulsion to produce latent image
  • developing the film allows this image to become visible
  • film emulsion consists of gelatin containing finely dispersed grains of silver bromide or halide
  • absorption of xprays by silver bromide grains renders them developable
  • silver bromide grains which have been exposed to xrays will be turned black by developer
  • unexposed grains are dissolved and removed and leave a white area on film
69
Q

intensify screens

A

present w/i cassette on either side of film

contain materials which fluoresce when bombarded by xrays

using both visible light and xrays allows reduction of exposure times (90% of exposure comes from intensifying screen light)

not used when very fine detail required

70
Q

traditonal xray housed in cassett, digital screen housed in …

A

imaging plate

71
Q

how does digital xray work?

A
  • PSP electrons energized when exposed to xrays and form latent image
  • IP placed into PSP reader, phosphor screen removed and scanned by laser beam
  • laser stimulates excited electrons to their ground state and PSPs emit light
  • light collected and directed to photodetector via optical system
  • photodetector measures light signal, amplifies it and sends electrical signal to analog-to-digital converter
  • phosphor plate exposed to bright light which erases latent image, so IP can be used again
  • time to process image takes 1 min
72
Q

smallest unit in an image is a

A

pixel

a pixel is 2D representation that corresponds to 3D volume of tissue known as voxel

73
Q

a _________ signal-to-noise ratio correlates to higher contrast resolution

A

higher

noise - anything that interferes with image formation
signal- xrays that exit pt and correspond to anatomical attenuation

74
Q

used to determine sites of abnormal glucose metabolism

A

PET positron emission tomography

inflammatory cells increase uptake of FDG

75
Q

produces a SD image

A

SPECT single photon emission computed tomography

76
Q

uses xprays to produce real-time moving images

A

fluoroscopy

utilizes xray image intensifier to reduce radiation

77
Q

is exposure with fluoroscopy greater to thin or thick pt

A

thick

image intensifier automatically adjusts brightness by increasing kVp (penetration) and mA (intensity)

78
Q

Fluoroscopy Recommendation

A
  • image intensifier input should be positioned as close to pt as practical
  • use exposure pedal as sparingly as possible
  • use last image hold and pulsed fluoro whenever possible
  • use smallest field of view allowed
  • high dose or detail modes should be used only sparingly
  • magnification should be used only when necessary
    • for carm type fluoroscopy units, the pt should be positioned as FAR from the xray tube as practical to minimize pt entrance dose (xray tube should also be beneath pt)

Pod Exam 1 (16 decks)

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