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Radiographic Physics Exam 2 > Density 2 > Flashcards

Density 2 Flashcards

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1
Q

What concept is occurring when a 10 MeV x-ray invades a nucleus?

A

Photodisintegration

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2
Q

What happens to the energy during photo disintegration?

A

Is absorbed by the nucleus and nuclear fragments are emitted

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3
Q

What type of conditions contribute to scatter radiation production?

A

1 high kVp
2 thick soft tissue (water density)
3 large field size

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4
Q

What is the solution for a large field size that has the potential to produce a lot of scatter?

A

Collimation

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5
Q

What are some scatter control methods?

A 
1 optimum kVp
2 collimation to control field size
3 air-gap technique
4 scatter-absorbing grids
5 recumbent radiography
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6
Q

What is probably the best way to take an x-ray of a larger patient to ultimately reduce overall scatter?

A

Take it recumbent

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7
Q

What kind of filter is a grid?

A

Selective lead filter (between patient and film)

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8
Q

Who invented the scatter-absorbing grid?

A

Gustave Bucky in 1913

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9
Q

When is a grid needed?

A

When patient part measures greater than 10cm or when using techniques above 70 kVp

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10
Q

How does the grid affect the appearance of the film?

A

Improves contrast

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11
Q

What specific benefit does the grid NOT have?

A

Does NOT protect the patient

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12
Q

What is the orientation of the lead lines found in a grid?

A

Linear***, crosshatched, or rhombic crosshatched pattern

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13
Q

What separates the thin lead lines of the grid?

A

Thin strips of aluminum or carbon fiber

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14
Q

What are the two types of a linear grid?

A

Parallel and focused

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15
Q

Which type of grid design involves a grid cut-off and an underexposed appearance of the film?

A

Parallel

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16
Q

What is the benefit of a focused grid?

A

Grid cut-off is eliminated

17
Q

What is the grid ratio?

A

Measure of the height of the lead strips divided by the distance between them (h/d)

18
Q

When there is an increased grid ratio, what measurement must be increased to compensate?

A

mAs

19
Q

How does a higher grid ratio affect contrast?

A

Higher contrast

20
Q

What is the recommended grid ratio?

A

12: 1 focused grid used with a single phase generator
10: 1 focused grid used with high frequency generator

21
Q

What is grid frequency?

A

Measure of the number of lead lines per inch or centimeter

22
Q

What is the downside to a higher grid frequency?

A

Patient dose increases

23
Q

What is the benefit to a higher grid frequency?

A

Less grid lines on film

24
Q

How does the removal of scatter by a grid affect film density?

A

Decreases it (lighter film)

25
Q

If the film appears too light when using a grid to remove scatter, what measurement must be changed to compensate?

A

Increase mAs (to increase density)

26
Q

How does an increase in grid ratio affect film density?

A

Decreases it (lighter film)

27
Q

What effect does decreased film size have on density and why?

A

Decreased density (because scatter is eliminated)

28
Q

If you take a 14 x 17 and change it to a 5x5 via collimation, how is the appearance of the film changed?

A

Lighter film (decreased density)

29
Q

What is spot filming?

A

Using smaller films and tight collimation to improve contrast

30
Q

What technique can be a substitute for a grid?

A

Air-gap technique

31
Q

How big of an air-gap is comparable to a 7:1 grid ratio in a scatter clean-up?

A

4”-6”

32
Q

Why is the air-gap technique not recommended?

A

Changes must be then be made to technique, tube placement, etc.

33
Q

The air gap produces what kind of contrast: short or long scale?

A

Short scale

34
Q

What is the maximum distance for an air-gap due to magnification?

A

10”

35
Q

How does laying a patient recumbent prevent scatter?

A

Decreases diameter of the patient (lower kVp and mAs needed)

36
Q

What is the purpose of compression bands?

A

Compression of tissues to reduce scatter and improve contrast

37
Q

What is the purpose of lead vinyl blockers?

A

Cover areas of film on film cassettes where multiple exposures are made on a single film

Radiographic Physics Exam 2 (4 decks)

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