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Radiology Physics > Contrast Ch. 27 > Flashcards

Contrast Ch. 27 Flashcards

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1
Q

Contrast is

A

the difference between adjacent densities that enables the visibility of anatomy detail

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2
Q

Which is better? Low contrast or high contrast?

A

Depends on the part being imaged

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3
Q

When would you want low contrast?

A

When imaging an abdomen since there is a lot of soft tissue that needs to be visualized

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4
Q

When would you want high contrast?

A

When you need to see bone in detail.

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5
Q

Low contrast has more..

A

gray

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6
Q

High contrast = _____ scale

A

short

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7
Q

Low contrast = ______ scale

A

long

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8
Q

Long scale has ____ shades of gray

A

more

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9
Q

Short scale has ____ shades of gray

A

less

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10
Q

Subject contrast is AKA

A

patient contrast

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11
Q

Subject contrast has a difference in..

A

tissue thickness, density eff. atomic number & differences in amount of attenuation

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12
Q

Does the amount of absorption affect subject contrast?

A

yes

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13
Q

What has a medium amount of shades of gray?

A

muscle/fat

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14
Q

Bone has a high atomic # and therefore..

A

more absorption, less shades of gray (more black and white)

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15
Q

Air has a low atomic # and therefore…

A

low density, darker shades of gray

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16
Q

What is the controlling factor for contrast in F/S?

A

kVp

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17
Q

If kVp is the controlling factor for contrast in F/S, then it should also be the controlling factor for digital. T or F?

A

False!! kVp is an influencing factor for contrast in digital

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18
Q

Does higher kVp increase or decrease contrast? (digital)

A

Decreases….higher kVp=lower mAs

19
Q

Does collimation increase or decrease contrast?

A

Appropriate collimation increases contrast and reduces scatter.

20
Q

Do grids increase or decrease contrast?

A

increases contrast and reduces scatter, gives fewer shades of gray

21
Q

Does the air gap technique increase or decrease contrast?

A

increases contrast b/c scatter doesn’t reach the IR.

22
Q

If there was an increase in lead content in a grid, would that increase or decrease contrast?

A

increase contrast cause it cleans up more scatter

23
Q

How many shades of gray can our eyes see?

A

about 32

24
Q

How many shades of gray are displayed on a computer screen?

A

about 4,000

25
Q

What does LUT stand for?

A

Look up table

26
Q

What does the LUT do?

A

it is a part of the software that gets appropriate contrast for the part being images (preset contrast)

27
Q

What could happen if you image a knee and run it in the LUT as a chest?

A

It will be overexposed and you will need to manually change it in the computer.

28
Q

What is display contrast?

A

ambient light in viewing area (on the computer’s display)

29
Q

For digital…brightness is emission of light from where?

A

the computer monitor

30
Q

WL & WW do what?

A

adjust the range of densities visible

31
Q

Window level =

A

brightness

32
Q

Window width =

A

contrast

33
Q

Too much or too little mAs can do what to an image/contrast

A

over or under expose it which would decrease the contrast either way

34
Q

F/S IRs effect image contrast how?

A

the design, use of screens, film density & issues related to processing - especially reduced time and temperature of the developer - all reduce contrast

35
Q

What is film contrast?

A

the range of densities that the film is capable of recording

36
Q

Increasing film developer time, temp or replenishment rate will increase…

A

the chemical fog on the film & decrease contrast

37
Q

What is the controlling factor of contrast in digital?

A

software…window width

38
Q

The proper _____ is important for the desired differential attenuation through the patient for a given examination

A

kVp

39
Q

In post-processing, what can affect the final image contrast that is displayed?

A

the histogram and LUT

40
Q

What is the primary controller of subject contrast?

A

kVp

41
Q

Why does low kVp give high subject contrast

A

because more low energy photons are being absorbed by thicker body parts and penetrate thinner body parts

42
Q

As kVp increases, the % of compton interactions increase which means what?

A

more scatter, less contrast

43
Q

When overall body thickness increases or field size increases what happens?

A

the amount of scatter will increase and decrease subject contrast

Radiology Physics (10 decks)

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