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Radiographic Exposure > Grids > Flashcards

Grids Flashcards

1
Q

Who built the first grid?

A

Gustave Bucky 1913. Built the first lead foil strips on the standing edge of the grid in order to trap scatter radiation.

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2
Q

Who is Hollis E. Potter?

A

Created the first wire grid in 1915-1917. Shares the credit with Bucky on creating the grid

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3
Q

When looking at the image, what does dark area represent?

A

Transmission of x-rays passing through the body and striking the IR.

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4
Q

What does light areas on the image represent?

A

Absorption of x-ray or absence of x-ray striking the IR.

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5
Q

As a general rule, use a grid when body parts exceed ___

A

10 cm

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6
Q

As a general rule, use a grid when kVp is above ___

A

60

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7
Q

Name the term that explains the height of the grid divided by interspace width.

A

Grid Ratio.

GR = (h/D)

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8
Q

What is radiopaque material made from?

A

inexpensive lead and has high atomic #

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9
Q

What does radiolucent material made from

A

interspaced materal, thicker than lead, either aluminum or plastic fiber, absorbs low energy scatter.

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10
Q

If height were to stay the same and width were to decrease, ____

A

the ratio would increase. Inverse relationship.

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11
Q

Grid ratios can range from ___ to ___.

A

4:1 to 16:1. The most common is the 8:1 to 10:1

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12
Q

Which type of grid ratio will remove most of the scatter radiation?

A

Higher grids

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13
Q

True or False: The higher the grid ratio, the higher the Bucky factor?

A

True

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14
Q

What is a bucky factor?

A

to measure the penetration of primary and scatter radiation through the grid

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15
Q

Which type of grid ratio will improve the contrast?

A

higher ratios

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16
Q

What is a grid frequency?

A

the # of lead strips per inch or cm. Most common lays between 60 to 110 lines

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17
Q

General rule: typically higher frequency grid has ___ lead strips.

A

thinner

18
Q

How much scatter does 5:1 cleans up?

A

85%

19
Q

How much scatter does 16:1 clean up?

A

97%

20
Q

In grid frequency, as contrast increases, ___

A

scatter decreases

21
Q

The simplest type of grid, easiest to manufacture, and absorbs scatter in one direction.

A

Parallel grid

22
Q

The undesirable absorption of primary x-ray by the grid.

A

gird cutoff

23
Q

More efficient than parallel grid in cleaning up scatter radiation, manufacturing is not excessively expensive.

A

crossed grids

24
Q

Name the three disadvantages of crossed grids

A

1) positioning is critical
2) Tilt-table techniques are possible if tube and table are aligned
3) Exposure technique requires higher PT radiation dose.

25
Q

Difficult to manufacture but has the same properties of parallel grids expect when positioned properly exhibit no grid cutoff.

A

Focused Grid

26
Q

Three characteristics of focused linear grids

A

1) Proper centering
2) Preset SID
3) Careful alignment

27
Q

What is a reciprocating grid?

A

a moving grid that is motor-driven. The total distance of the drive is 2 cm.

28
Q

What is an oscillating grid?

A

A powerful electromagnet pulling the grid to one of the four sides. The gird moves (oscillates) in a circular motion for 20 to 30 seconds.

29
Q

Disadvantages of moving grids

A

Distance between patient and image receptor is increased.

Magnification and image blur due to increasing distance.

30
Q

True or False: Moving grids are the technique of choice and widely used

A

True

31
Q

As a general rule, below 90 kVp use a grid of ___. About 90 kVp use a grid of ___.

A

below - 8:1

above - 10:1

32
Q

As grid ratio increases, ______

A

radiographic density decreases. (inverse relationship)

33
Q

What is a grid selectivity?

A

describe grid’s ability to allow primary radiation to reach image receptor and prevent scatter.

k = (contrast with grid/contrast without grid)
Ranges of 1.5 or 3.5 (times better with grids)

34
Q

Commonly seen in mobile or beside radiography grid error.

A

Off-center and off-focus

35
Q

Grid problems results in ____

A

underexposed image or underexposed edges of images

36
Q

What is an off-level grid error?

A

Grid or tube was tilted. Cutoff happens around the image.

37
Q

what is an off-center grid error?

A

A lateral detent problem, One side of the image was cut-off.

38
Q

What will a off focus grid error look like?

A

Image appears blurry with some grid cutoff around the sides

39
Q

What is an air technique?

A

IR is moved 10 to 15 cm away from the patient. A portion of the scatter radiation will never hit the IR.

40
Q

What are the disadvantages with air technique?

A

increase mA 10% for every centimeter of air gap. Technique is about the same for 8:1 grid.
Higher dose of PT, increase SID and OID, image blur a bit.

Radiographic Exposure (2 decks)

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