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rad phys exam 3 > rad phys questions > Flashcards

rad phys questions Flashcards

1
Q

to double the density of a film by using mAs what would you do?

A

increase the mAs by 100%

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2
Q

of the choices below which is true about a reciprocating grid?

a. requires a 10:1 ratio
b. it requires 103 lines per inch
c. it is thicker than a stationary grid
d. it requires a faster exposure time
e. it is less expensive than a stationary grid

A

c. it is thicker than a stationary grid

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3
Q

when converting from a grid with low ratio to one with high ratio which of the following would be the best to do to maintain a good film quality?

a. increase kV
b. increase mAs
c. decrease kV
d. decrease mAs

A

b. increase mAs

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4
Q

which of the following is recommended for spinal radiography in the usual chiro office?

A

a focused grid

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5
Q

what effect does using a high kV have?

A

produces more scatter
more Compton compared to photoelectric effect
more penetration= less absorption
more graying from film fog
more x-rays pass through without interaction

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6
Q

what is the preferred grid focus range for a spinal radiography?

A

40” to 72”

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7
Q

how do you control scatter from a high kV?

A

use the optimal kV technique

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8
Q

what is the relationship of beam size and scatter?

A

the larger the beam the more scatter

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9
Q

what do you do to control the scatter from a large size beam?

A

collimate to film or part size

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10
Q

describe optimal kV

A

the lowest possible mAs with acceptable contrast on the film

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11
Q

how many lines per inch are recommended for a stationary grid?

A

100-103

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12
Q

diminished penetration at the periphery of a grid is called?

A

grid cut off

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13
Q

if a film is said to be burned out, what would it look like?

A

too dark

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14
Q

which choice below is the main reason why a “fixed kV technique is preferred?

a. contrast is consistent
b. less stress on the tube
c. patient exposure is reduced
d. faster exposure time can be used

A

a. contrast is consistent

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15
Q

scattered or primary rays that leave the patient and reach the grid is called?

A

remnant radiation

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16
Q

what are some common grid ratios and there max kV?

A

8: 1- 90 kV
10: 1- 100 kV
12: 1- 110 kV
16: 1

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17
Q

which grid ratios are recommended for spinal use?

A

10:1 or 12:1

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18
Q

grid frequency is the # of lead strips per in also called?

A

lines per inch LPl

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19
Q

what are the 3 types of stationary grids?

A

crossed- not practical for spinal
parallel
focused

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20
Q

with parallel strips there is an attenuation of the periphery of the beam due to an angle of diverging rays, what does this create?

A

uneven exposure with sides being lighter

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21
Q

which type of stationary grid has graduated angles to match the angle of divergence?

A

focused- the periphery of the beam is not attenuated

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22
Q

what is grid radius?

A

the angle of the strips that match the divergence extending from the grid to the focal spot

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23
Q

which type of grid will produce the least amount of grid lines?

A

moving grid because moving the grid during exposure can avoid the lines all together

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24
Q

when are grid lines more noticeable?

A

with lower frequencies and parallel grids

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25
Q

when are grid least noticeable?

A

with a 10:1 focused grid and 103 lines

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26
Q

what is another name for a moving grid?

A

reciprocating grid or Potter Bucky diaphragm

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27
Q

exceeding the optimal kV while still maintaining good density will yield what type of film?

A

long scale contrast

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28
Q

which of the following would increase patient exposure?

a. using high kV
b. using 10:1 stationary grid
c. using high speed screen
d. using air gap technique

A

b. using 10:1 stationary screen

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29
Q

about how much increase in mAs is required when going from a non grid technique to using a technique with a 12:1 grid?

A

12 times

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30
Q

what are some negatives to using a moving grid?

A

more expensive
can fail
thicker so increase OFD
can cause motion of film leading to blurring
can be too slow for fast exposures causing grid lines

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31
Q

to get through any grid what is needed?

A

more exposure

32
Q

when should grids normally be used?

A

when 70+ kVp is used or part is over 10-15cm thick

33
Q

what hold a grid in place?

A

grid cabinet

34
Q

true or false, the patient is more stable when they are in contact with the cabinet?

A

true

35
Q

which films need to use air gap technique?

A

lateral, flexion, extension and oblique cervical films

36
Q

if a part of separated from the cabinet some scatter will miss the film, what is this called?

A

air gap technique

37
Q

what is the term for attenuation of part of the beam by the grid?

A

grid cut off

38
Q

what is the main effect of using a grid with a patient?

A

reduces x-ray exposure to patient

39
Q

the higher the kVp the more ______ radiation is produced?

A

compton

40
Q

what is an advantage of a high kVp technique?

A

lowered patient radiation exposure

41
Q

if using high frequency with a chart made for single phase what do you do with the mAs?

A

cut the mAs in half

42
Q

what is a technique chart?

A

estimators that indicate what settings to use for what situation

43
Q

what is a mini phantom for measuring a unit’s output?

A

penetrometer

44
Q

which setting device fits in your pocket and is “super tech” that allows for more specific design

A

slide rule calculator

45
Q

it is more difficult to see what on films that are too light, too dark or to grainy? distortion or detail?

A

detail

46
Q

if no unsharpness is seen there is _____ detail?

A

good recorded

47
Q

penumbra =

A

unsharpness

48
Q

umbra=

A

sharpness

49
Q

with unsharpness the edges of a structure will be?

A

unclear or blurry

50
Q

what are the 3 basic causes of unsharpness?

A

geometric
screen
motion

51
Q

which cause of unsharpness relates to distance between the focal spot and object and film?

A

geometric unsharpness

52
Q

does INcrease in OFD increase or decrease unsharpness?

A

increases

53
Q

does DEcrease in SID increase or decrease unsharpness?

A

increases

54
Q

decrease in OFD increases_____

A

clarity or sharpness

55
Q

a small focal spot ________ sharpness

A

increase

56
Q

to decrease geometric unsharpness….

A

use short OFD
long SID
small focal spot

57
Q

single screen has _____ clarity than no screen and double screen has _____ clarity than single screen

A

less, less

58
Q

high speed screens have ___ clarity than slow speed screens

A

less; increase in size of crystals increases unsharpness

59
Q

to reduce screen unsharpness and maintain low patient exposure…

A

use 400 speed rare earth screens
maintain good film/ screen contact
change screens if warped

60
Q

what is the most common cause of image blur?

A

patient motion

61
Q

magnification distortion causes _______ _______

A

geometric unsharpness

62
Q

shape distortion is also known as?

A

true distortion

63
Q

distortion of a shape occurs from?

A

angulation of a ray, film or object

64
Q

what are the 3 things that happen when x-rays enter a body?

A
  1. total absorption- don’t reach film
  2. partial absorption and deflection- some rays reach film but aren’t desirable
  3. passing through patient with no interaction- image producers
65
Q

when rays actually reach a film it is called

A

remnant radiation

66
Q

to overcome the binding energy of an inner electron, the incoming photon’s energy is totally absorbed this is called

A

photoelectric effect

67
Q

dense tissue like bone _____ rays

A

absorbs

68
Q

less dense tissue like muscle and fat _____ as much

A

don’t absorb

69
Q

the contrast between structures of different densities is called?

A

differential absorption

70
Q

when an incoming photon strikes an outer shell electron displacing it its called?

A

compton scatter/effect

71
Q

the angle of photo deflection determines how much energy is lost, the greater the angle the _______ energy is lost

A

more

72
Q

when photons are scattered toward the tube it is called?

A

back scatter

73
Q

film fog=

A

graying of a film

74
Q

what are 2 causes of film fog?

A

secondary rays or scatter that reaches the film

75
Q

when a weak incoming photon doesn’t displace but vibrates an electron or atom its called

A

classical or coherent scatter

76
Q

classical scatter ___ energy to the atom which gives off x-ray in order to return to original balance

A

adds

77
Q

at 70 kVp what % of scatter is classical?

A

3-5%

rad phys exam 3 (1 decks)

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