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RTE1418 Introduction to Radiologic Technique > Image Contrast > Flashcards

Image Contrast Flashcards

(76 cards)

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1
Q

define image contrast

A

the degree of difference between the light and dark areas of a radiograph

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2
Q

What makes the blacks, whites, and grays on a radiograph?

A

differential absorption

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3
Q

subject contrast

A

component of image contrast determined by size, shape, and x-ray attenuating characteristics of the subject

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4
Q

define differential absorption

A

the difference between photons absorbed and those that penetrate the body

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5
Q

different body structures absorb x-ray photons to ____________ extents

A

different

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6
Q

bones are denser and ________ more x-ray photons than those filled with air such as lungs

A

absorb

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7
Q

attenuation

A

removal of any photons from the primary beam before striking the IR

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8
Q

attenuation is the reduction of:

A

the intensity of an x-ray beam

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9
Q

causes of attenuation:

A

differential absorption
scatter

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10
Q

absorption

A

x-ray photons that are attenuated by the body and do not reach the IR

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11
Q

transmission

A

x-ray photons that pass through the body and reach the IR

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12
Q

What terms describe the beam entering the patient?

A

primary
useful
entrance

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13
Q

primary beam

A

x-ray beam as it is upon exiting collimator and exposing patient

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14
Q

What terms describe the beam leaving the patient?

A

remnant
exit

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15
Q

remnant beam

A

x-ray beam that remains after interaction with patient when exiting the patient to the IR

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16
Q

the remnant beam is composed of what?

A

transmitted and scattered photons

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17
Q

radiopaque

A

body structures that absorb x-ray photons

(bones)

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18
Q

radiolucent

A

less dense body structures that have a lower probability of absorption

(air filled lungs)

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19
Q

photons absorbed show up as _______ on a radiograph

A

white

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20
Q

photons that pass through body and reach IR show up as _______ on a radiograph

A

black

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21
Q

technical term for absorption within the patient

A

Photoelectric Effect

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22
Q

denser tissue _________ the probability of photons being absorbed

A

increases

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23
Q

structures filled with air __________ the probability of absorption

A

decreases

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24
Q

what causes the shades of gray?

A

photons that aren’t completely absorbed or transmitted

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25
high contrast:
large differences in brightness
26
high contrast images have mostly:
areas of black and white only few shades of gray
27
a high contrast image is also referred as:
short-gray scale
28
short gray scale contrast
mostly black and white, few shades of gray
29
low contrast:
small differences in brightness
30
low contrast images have mostly:
areas of gray only few areas of black and white
31
a low contrast image is also referred as:
long gray-scale
32
long gray scale contrast
many shades of gray very little black and white
33
the total brightness levels that an imaging monitor is capable of displaying is referred to as:
bit depth
34
high contrast = ______ gray-scale
short
35
low contrast = ______ gray-scale
long
36
8 factors that affect image contrast
kVp differential absorption computer processing and display filtration Compton scatter grids OID beam restriction
37
high kVp =
low contrast long gray-scale
38
why does increasing kVp decrease contrast?
it creates a more penetrating beam = less differential absorption = longer gray-scale = low contrast image.
39
low kVp =
high contrast short gray-scale
40
Why does decreasing kVp increase contrast?
it creates a less penetrating beam, increasing differential absorption, which creates a shorter gray-scale, thus high contrast
41
higher levels of differential absorption =
higher levels of contrast
42
Look Up Table (LUT)
takes place after the exposure is made and image is processed by imaging system software
43
added filtration will result in:
decrease in differential absorption longer gray-scale thus lower contrast
44
filtration and image contrast has what kind of relationship?
indirect
45
higher filtration =
harder average beam lower contrast/long gray-scale
46
lower filtration =
softer average beam higher contrast/short gray-scale
47
Compton scatter
x-ray photon that interacts with the body and "scatters" off its original trajectory
48
Compton scatter contributes no useful:
information to the image
49
Compton scatter causes a uniform exposure on the IR, causing:
a loss of visible image contrast
50
radiographic grid
device used to reduce the intensity of scatter radiation in the remnant beam
51
grid clean up
ability of a grid to absorb scatter radiation
52
a grid _______________ the scattered photon before it can strike the IR and reduce image contrast
catches or attenuates
53
OID and image contrast share a _________ relationship
direct
54
increased OID =
increase image contrast
55
the most common type of beam restriction is:
use of collimation
56
increasing collimation:
reduces scatter, leading to a higher image contrast
57
Raw numbers (bar graph) of what is occurring in the body (absorption/transmission) will determine?
dose
58
Percentages of what is occurring in the body (absorption/transmission) will determine?
contrast
59
effects of kVp on the x-ray beam:
increasing kVp creates a more penetrating beam decreasing kVp creates a more less one
60
effects of kVp on patient dose and on absorption
increasing kVp causes a greater dose due to greater % of beam passing through patient, which has a decrease on absorption vice versa
61
why does increasing kVp increase dose?
increasing kVp creates a bigger beam
62
Why does increasing kVp create a bigger beam?
more electrons are called over which creates more photons
63
increasing kVp does what to dose and absorption?
increases dose, but decreases the percentage of absorption
64
will an increase in kVP cause an increase or decrease to the photoelectric?
decrease
65
describe the relationship between filtration and image contrast
indirect (greater the filtration the more low photons are removed)
66
a photon that does not strike the IR, what type of photon is this?
attenuating photon
67
in the digital age, what is the controlling factor for image contrast?
look up table (LUT)
68
a decrease in kVp will cause the average amount of transmission to increase or decrease?
decrease
69
why does beam restriction improve image contrast?
reduces amount of scatter (less matter = less scatter
70
what are the two different ways an x-ray photon can become attenuated?
scatter and absorption
71
what produces subject contrast?
differential absorption
72
using one word, describe why increasing OID improves image contrast
divergence
73
the total number of grays a system is capable of displaying in a radiograph image is referred to as what?
bit depth
74
decreasing kVp will have what effect on differential absorption?
increases
75
what is the controlling factor for subject contrast?
kVp
76
illustrate how an increase in kVp can cause an increase in dose and a reduction of contrast at the same time:
2 kvp lines with one slightly higher and fatter toward when it gets to the bottom dose is in middle section and contrast is in wider section near bottom

RTE1418 Introduction to Radiologic Technique (12 decks)

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