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S4: Radiographic Imaging > Chapter 18 Notes > Flashcards

Chapter 18 Notes Flashcards

1
Q

a grid is used to

A

improve image contrast

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2
Q

grids are made of

A

lead strips alternating with an interspace material (usually aluminum)

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3
Q

what grids are more efficient at removing scatter

A

grids with higher ratios and lead content

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4
Q

what technical factor should be increased when using a grid

A

mAs

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5
Q

alternative to use of a grid

A

air-gap technique or grid replacement software applications

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6
Q

what is the primary source of scatter radiation

A

the patient

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7
Q

scatter radiation has no _____

A

diagnostic value

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8
Q

transmission on a radiograph

A

dark areas of image

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9
Q

absorption on a radiograph

A

light areas of image

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10
Q

what does scatter do to contrast

A

lowers contrast

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11
Q

scatter increases as

A

kVp increases; field size increases; thickness of part increases; and atomic number decreases

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12
Q

grids are recommended in patients with

A

part thickness greater than 10 cm

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13
Q

grids are recommended with kVp setting

A

greater than 60

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14
Q

who created grids

A

Dr. Gustav Bucky

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15
Q

when were grids created

A

1913

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16
Q

what was the design of early grids

A

wide lead strips (2” apart) with a crosshatched design

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17
Q

who made improvements to the early grid

A

Dr. Hollis Potter

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18
Q

how did Dr. Hollis Potter improve the grid

A

realigned lead strips to run in one direction; thinner strips

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19
Q

grid ratio =

A

height of lead strips / thickness of interspace material
(h/D)

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20
Q

typical grid ratio range

A

5:1 to 17:1

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21
Q

grid frequency

A

number of lead strips per inch or cm

22
Q

grid frequency range

A

60-200 lines/in (lpi)

23
Q

most common grid frequency

A

85-103 lpi

24
Q

lead content measured in

A

mass per unit area
gcm(squared)

25
Q

as lead content increases, removal of scatter _____; therefore contrast _____

A

increases; increases

26
Q

linear grid pattern

A

grid lines running in one direction only

27
Q

cross-hatched grids

A

two parallel grids; one on top of the other

28
Q

the cross-hatched grid is not widely used due to

A

positioning limitations and dose

29
Q

a linear grid allows

A

primary beam to be angled along direction that lines are running (typically along long axis of table)

30
Q

short axis grids

A

grid lines run across short axis of grid

31
Q

a short axis grid is useful for

A

portable chest procedures when IR is placed crosswise

32
Q

focused linear grids

A

lead strips angled to match divergence of beam

33
Q

focused linear grids must be used within

A

range of SIDs

34
Q

what grid is least expensive but unpopular due to positioning limitations

A

parallel linear grids

35
Q

stationary grids

A

grids that can be attached to IR cassette

36
Q

Potter-Bucky diaphragm

A

moves grid during exposure

37
Q

reciprocating grid movement

A

small motor drives grid back and forth during exposure

38
Q

oscillating grid movement

A

electromagnet pulls grid to one side, releasing it during exposure

39
Q

GCF stands for

A

grid conversion factor

40
Q

GCF =

A

mAs with grid / mAs without grid

41
Q

GCF is _____ dependent

A

kVp

42
Q

grid conversion

A

mAs1/mAs2 = GCF1/GCF2

43
Q

contrast improvement ability

A

“K” factor

44
Q

K factor typically ranges between

A

1.5 and 3.5

45
Q

higher “K” factor grids offer

A

higher contrast

46
Q

Moire effect

A

grid lines parallel to scan lines

47
Q

how can Moire effect be prevented

A

by using high-frequency grids designed for computed radiography

48
Q

what air gap has similar clean-up of 15:1 grid

A

10”

49
Q

grid replacement software is designed to

A

produce a grid-like image with no grid use

50
Q

grid suppression software

A

removes grid lines from final image for review

S4: Radiographic Imaging (31 decks)

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