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exposures > unit 4 review > Flashcards

unit 4 review Flashcards

1
Q

why would an image be too dark

A

to many photons hitting IR, too dense

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2
Q

how to fix an image that is too dark

A

window level adjustment

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3
Q

why would an image appear too light

A

not enough photons hitting the IR, underexposed

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4
Q

how to fix an image that is too light

A

can’t , repeat image

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5
Q

controlling factor affecting density / IR exposure

A

mAs

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6
Q

influencing factor affecting density / IR exposure

A

kVp

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7
Q

more kVp =

A

more scatter

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8
Q

mAs must be changed from ____% to see a visible change in density

A

25-35

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9
Q

mAs & density are

A

directly proportional; BUT just because we double mAs does not mean density is doubled

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10
Q

in digital what are the graphic representations of the IR exposure

A

histograms

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11
Q

the width of the histogram

A

displays the range of exposures

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12
Q

the 2 ways kVp alters intensity

A

a change in kV alters the intensity of the beam when all other factors remain the same & affects the production of scatter

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13
Q

kVp being altered affects both

A

quality & quantity (scatter)

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14
Q

with a large focal spot

A

size bloom may occur , increases IR exposure

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15
Q

__% density variation from anode to cathode

A

45

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16
Q

as distance increases IR exposure

A

decreases

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17
Q

density / IR exposure decreases when filtration is

A

increased

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18
Q

compensating filters require an ____ in technique (mAs)

A

increase

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19
Q

beam restriction (collimation) reduces

A

the total # of photons, reducing IR exposure & density

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20
Q

air ( radiolucent contrast)

A

increases density/ IR exposure

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21
Q

barium / iodine (radiopaque contrast)

A

decreases density/ IR exposure

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22
Q

the more efficient the grid

A

the less density IR /exposure

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23
Q

high grid ratios will

A

decrease density / IR exposure

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24
Q

wide dynamic range “margin of error”

A

— higher latitude over film screen

25
Q

DQE - detective quantum efficiency is

A

how efficiently a system converts the incoming x ray into an image - determines the latitude

26
Q

contrast is

A

the difference in adjacent densities/ IR exposure

27
Q

dynamic range is the concept of

A

contrast as it is DISPLAYED on a monitor

28
Q

what is the digital processing function on the display that controls the range of brightness / contrast

A

window width

29
Q

contrast / dynamic range / window width all describe the

A

grayscale bit depth

30
Q

image contrast is

A

the amount of contrast acquired from the IR

31
Q

subject contrast

A

results from the anatomical part being radiographed ( NOT talking about IR)

32
Q

high contrast

A

black & white , fewer shades of gray (think extremities)

33
Q

low contrast

A

more shades of grays , long scale

34
Q

the # of useful visible density or shades of gray

A

scale of contrast

35
Q

short scale is

A

maximal differences (black & white)
high contrast

36
Q

long scale is

A

minimal differences between densities but maximal total number of densities
- low contrast

37
Q

the number of different shades of gray that can be stored and displayed by a computer system - monitor function

A

gray scale

38
Q

physical contrast

A

densities/ IR exposures that can be recorded by the IR

39
Q

visible contrast

A

total range of densities and IR exposure that can be perceived by the human eye

40
Q

term used to describe the ability of an IR to distinguish between objects having similar contrast

A

contrast resolution

41
Q

increased contrast, low kVp, short (narrow) dynamic range / window width

A

high contrast

42
Q

decreased contrast , high kVp, large wide dynamic range

A

low contrast

43
Q

kVp only affects

A

pre exposure

44
Q

kVp is controlled by

A

LUT

45
Q

Subject contrast is dependent on

A

kVp & tissue type/ thickness

46
Q

digital image receptor contrasts primary controller is

A

window width manipulations

47
Q

asses the range and quality of IR exposures

A

histogram

48
Q

will produce higher contrast because low energy photons will be absorbed by thicker parts — will not reach IR - more contrast

A

low kVp

49
Q

Will be able to penetrate more equally and reach IR, thus causing a more uniform image - less contrast

A

high kVp

50
Q

as body part thickness increases x-ray absorption

A

increases

51
Q

overall thicker part =

A

decreased subject contrast

52
Q

overall thinner part =

A

increased subject contrast

53
Q

mAs affecting contrast; if IR exposure is too high (overexposed) or to low ( underexposed)

A

contrast will be decreased

54
Q

influencing factors affecting contrast

A

mAs, focal spot size, anode heel effect, distance, filtration, beam restriction, anatomical part, grid

55
Q

SID - since IR exposure is affected by distance

A

so is contrast

56
Q

beam restriction

A

Reduces scatter therefore increases contrast

57
Q

images are improved with a

A

Larger matrix size with a larger number of pixels

58
Q

The square picture elements making the matrix - individual boxes

A

pixel

exposures (6 decks)

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