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Radiologic Exposures > Final Review: Grids > Flashcards

Final Review: Grids Flashcards

1
Q

-improves radiographic contrast in image
-absorbs scatter radiation before it reaches IR
-patient is primary source of scatter radiation
-scatter radiation has no diagnostic value

A

purpose of grid

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2
Q

responsible for dark images

A

transmission

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3
Q

responsible for light areas

A

absorption

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4
Q

lowers contrast

A

scatter

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5
Q

-recommended in patients with part thickness greater than 10 cm
-kvp greater than 60

A

Grids

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6
Q

Order
grid, IR, patient

A

patient, grid, IR

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7
Q

Why do we use a gride when decreasing atomic number

A

less absorption, more transmission

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8
Q

produces nice image because it cleans it up and less scatter

A

Grids

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9
Q

What material is in the grid

A

Lead

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10
Q

Why do you use a grid when increasing field size

A

because of increasing scatter

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11
Q

created by radiologist, Dr.Gustav Bucky

A

Grids

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12
Q

Grid contruction

A

-radiopaque lead strips
-separated by radiolucent interspace material (aluminum and carbon fiber-low dose grids)
-encased in aluminum or plastic for protection

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13
Q

this individual took Gustav Bucky’s design and made it better, made a grid that moves so it blurs out the grid lines, making them invisible

A

Potter Bucky

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14
Q

Grid Ratio

A

H/D
Height of radiopaque strips over distance between strips

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15
Q

Higher grid ration

A

more effective it is cleaning up scatter and higher the technique needed (increasing pt. dose)

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16
Q

Higher grid ratio

A

more black and white

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17
Q

lower grid ratio

A

more shades of gray

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18
Q

primary disadvantages of grid use:

A

-grid lines on film
-some absorption of primary radiation if not used properly

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19
Q

-allow primary radiation to reach image receptor
-absorbs most scattered radiation

A

Grids

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20
Q

what grid ratio is more efficient in removing scatter and requires more exposure

A

Higher grid ratio

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21
Q

typical grid range

A

5:1 to 17:1

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22
Q

Practice grid ration examples

A
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23
Q

number of lead strips per inch or cm, how often it is occuring

A

grid frequency

24
Q

high lead count

A

high grid ratio and low frequency

25
Q

as lead content increases, removal of scatter increases
therefore what happens to contrast

A

contrast increases

26
Q

is the undesirable interception of primary beam photons, by the grid strips

A

grid cut off

27
Q

artifact for grids

A

grid cut off

28
Q

most important factor in grids efficiency

A

lead content

29
Q

grid lines running in one direction only

A

Linear

30
Q

two parallel grids; one on top of the other

A

criss-cross or cross hatched

31
Q

two types of grid patterns

A

parallel and focused

32
Q

parallel

A

non focused, strips are just parallel to one another, not canting

33
Q

what happens to receptor exposure when you increase grid ration

A

receptor exposure will decrease

34
Q

as you increase grid ration, decrease receptor exposure, increase contrast, what happens to the patient dose

A

patient dose increases

35
Q

has canting lines to go with the divergence of the beam

A

focused grid

36
Q

which grid cant be angles

A

crosshatched

37
Q

what happens if you are below or above a certain SID

A

you will get a grid cut off

38
Q

allows primary beam to be angled along directions that lines are running

A

linear grid

39
Q

-grid lines across short axis of grid
-useful for portable chest procedures when ir is placed crosswise

A

short axis grids

40
Q

grids that can be attached to image receptor cassette

A

stationary grids

41
Q

Grid is incorporated into cassette structure

A

Grid cassettes

42
Q

small motor drives grid back and forth during exposure

A

reciprocating

43
Q

electromagnet pulls grid to one side
releases it during exposure and spring activated

A

Oscillating

44
Q

Practice grid conversion factor

A
45
Q

K factor

A

comparing contrast

46
Q

grid erros

A

-off level
-central ray angulation across grid lines
-off center
-off focus
-upside down
-moire effect

47
Q

grid lines parallel to scan lines
same grid lines in the same direction of sampling frequency

A

moire effect

48
Q

how to prevent moire effect

A

using high frequency grids designed for computer raduography

49
Q

-alternative to grid use
-scatter radiation lost in air space between patient and receptor
-10 inch air gap has simialr clean up of 15:1 grid
-SID needs to increase equal amount to maintain image resolution

A

AIR gap technique

50
Q

off leveling

A

receptor exposure only on one side

51
Q

off centering

A

not centering correctly, not lining up with divergence of the beam

52
Q

off focus and off radius

A

not within the SID range that it needs to be

53
Q

only has receptor exposure in the center

A

upside down grid

54
Q

creating oid (6in of oid) cleaning up scatter, increasing contrast and increasing oid because scatter is not reaching ir

A

Air gap

55
Q

Final nimage contrast principle determined by:

A

Look up table

56
Q

recomended technique wirh digital receptors

A

high kvp and reduction in mAs

57
Q

Grid conversion factor for
No grid
5:1
6:1
8:1
12:1
16:1
33334443

A

none=1
16:1=6
5:1=2
6:1=3
8:1=4
12:1=5

Radiologic Exposures (11 decks)

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