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Physics - Common Equipment > Chapter 12 > Flashcards

Chapter 12 Flashcards

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1
Q

Scatter, in diagnostic x-ray is primarily due to _________ effect

A

Compton

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2
Q

What two major factors affect scatter production?

A

Tissue volume and kVp

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3
Q

Tissue volume is dependent on:

A

Part thickness and field size

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4
Q

What causes fog?

A

Scatter (unwanted radiation)

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5
Q

What two things does beam restriction do?

A

Limits patient dose
Reduces scatter production

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6
Q

True/False: Beam restriction and collimation are interchangable terms

A

True

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7
Q

What is the relationship between collimation and field size?

A

Inverse proportional

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8
Q

How does collimation affect contrast?

A

Less collimation = more scatter

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9
Q

How does collimation affect mAs?

A

The more collimation = the more mAs needed

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10
Q

Beam restricting devices

A

Aperture Diaphragms
Cones/Cylinders
Collimators

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11
Q

Flat peice of lead with a small hole in it, it attaches to the collimator

A

Aperture diaphragms

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12
Q

Long tube/cone that attaches to the collimator; most often used for dental imaging or small parts such as nasal bones and fingers

A

Cones/cylinders

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13
Q

Most used form of beam restriction

A

Collimator

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14
Q

How many lead shutters are in a collimator?

A

2-3 that can be adjusted using collimator controls

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15
Q

Automatically sets the field size depending on what exam is being completed

A

Positive Beam-limiting Device (PBL)

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16
Q

When was the grid invented?

A

1913

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17
Q

Who invented the grid?

A

Gustave Bucky

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18
Q

Drawback of using a grid

A

Requires more mAs

19
Q

What is grid frequency?

A

Number of lead strips per unit length

20
Q

What is grid ratio?

A

Ratio of the height of the lead strips and the distance between them

21
Q

Two types of linear grids

A

Long
Short

22
Q

These grids have lead lines that run parallel with the long axis of the grid

A

Long

23
Q

These grids have lead lines that run perp to the long axis of the grid

A

Short

24
Q

What is grid pattern?

A

Linear pattern of the lead lines within a grid

25
Q

2 types of grid patterns

A

Linear
Cross-hatched

26
Q

Difference between linear and cross-hatched grids

A

Linear - lines running in one direction

Cross hatched - lines running in two different directions, perp to each other

27
Q

What type of grid removes more scatter - linear or cross hatched?

A

Cross-hatched

28
Q

What is grid focus?

A

Refers to the orientation of the lead lines to one another

29
Q

2 types of grid focus

A

Parallel
Focused

30
Q

Difference between parallel and focused grids?

A

Parallel - lines are parallel and used primarily in fluoro and mobile x-ray

Focused - lines are angled to match beam divergence - designed to be used at specific distances

31
Q

Type of grid that is stationary, same size as IR, and usually taped to secure it to IR

A

Wafer grid

32
Q

Type of grid that is stationary, IR with a permanent grid mounted to the front surface

A

Grid cassette

33
Q

Type of grid that is stationary, designed to hold the IR so no tape is needed - most common type

A

Grid cap

34
Q

This type of grid moves slightly while the image is being taken

A

Reciprocating grid

35
Q

The decrease in the number of transmitted photons that reach the IR due to grid misalignment

A

Grid cutoff

36
Q

Grid cutoff caused by the grid being placed upside down

A

Upside-down focused

37
Q

Most common type of grid cutoff - the IR with grid is tilted and CR is not

A

Off-level

38
Q

What type of cutoff can occur with both focused and parallel grids?

A

Off-level

39
Q

Grid cutoff caused when the CR is not aligned to the center of the IR

A

Off-center

40
Q

Grid cutoff occurs when SID is outside of the focal range of the focused grid

A

Off-focus

41
Q

Zebra stripe pattern that occurs when the grid frequency of a stationary grid used in CR imaging is similar to the laser scanning frequency of the CR reader

A

Moire Effect

42
Q

How to eliminate the Moire effect

A

Use higher frequency grids or moving grids

43
Q

What is the Air Gap Technique

A

By increasing OID, we able to limit the amount of scatter that reaches the IR

44
Q

Increasing OID also increases:

A

Magnification

Physics - Common Equipment (7 decks)

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