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exposures > ch 15,17 & 18 > Flashcards

ch 15,17 & 18 Flashcards

1
Q

what is scatter

A

photons reaching the IR not part of the useful beam, impair image quality

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2
Q

what interaction causes scatter

A

compton interaction

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3
Q

what affect does scatter have on a radiograph

A

increases density , by increasing fog

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4
Q

what are the factors affecting scatter

A

kilovoltage & irradiated material

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5
Q

how does kVp affect scatter

A

as kVp increases scatter increases

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6
Q

how does the irradiated material affect scatter

A

as the volume increases the scatter increases

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7
Q

how do beam restrictors affect scatter

A

decrease scatter, as restrictions increase scatter decreases

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8
Q

name the types of beam restrictors

A

collimator, aperture diaphragms , lead impregnated rubber, cones/cylinders

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9
Q

inherent filtration is

A

built into the tube

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10
Q

what is the most common beam restrictor

A

collimator

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11
Q

what is PBL?

A

positive beam collimation device - automatic collimation of the beam size

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12
Q

what film size has the most scatter, why?

A

14 by 17 - increased volume

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13
Q

the bluriness around the edge of an image is called

A

penumbra

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14
Q

the difference between collimation & shuttering

A

collimation is a pre exposure reduction of beam, shuttering is post exposure

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15
Q

what is the type of beam limiting device that gets attached to the collimator tube housing, that has an opening cut in the middle

A

aperture diaphragms

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16
Q

what is a blocker used for

A

reduce scatter from patient reaching the IR

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17
Q

what is a mask used for

A

cut as a specific shape

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18
Q

who invented the grid

A

gustav bucky

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19
Q

who invented the bucky

A

hollis potter

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20
Q

what color is photoelectric on an IR

A

white

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21
Q

what is the purpose of a grid

A

improves contrast of image, absorbs scatter before reaching IR

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22
Q

what materials are grids made out of

A

lead, interspace made out of radiolucent material (plastic)

23
Q

define grid ratio

A

the height of the lead strips to the distance between the strips

24
Q

define grid frequency

A

the number of grid lines per inch or cm

25
Q

what is the formula for figuring grid ratio

A

grid ratio = h / d
height over distance

26
Q

when should a grid be utilized

A

imaging anatomy over 10 cm or above 60 kVp

27
Q

high grid ratios allow ___ scatter to pass thru to the IR

A

less

28
Q

lead strips are thicker in ___ frequency grids

A

low

29
Q

why is a high frequency grid used for digital

A

lead strips are thinner

30
Q

name the two types of grid patterns

A

linear & criss crossed

31
Q

name the three types of grids

A

parallel , focused, long or short dimension

32
Q

what grid type is used the most

A

focused

33
Q

what grid type is the easiest to use?

A

focused

34
Q

what grid type is the hardest to use

A

parallel

35
Q

what is a convergence line

A

the point where grid lines meet

36
Q

how much radiation does it take to make an exposure

A

1mR/ hr

37
Q

what does focal range mean

A

distance at which the divergence of the beam & grid lines will match

38
Q

types of grid movements

A

reciprocating & oscillating

39
Q

what is meant by grid selectively? the formula?

A

% of primary radiation transmitted
over—————————
% of scatter radiation transmitted

40
Q

what is meant by contrast improvement ability ? formula ?

A

how good the grid is at improving contrast

k = radiographic contrast with the grid
over ————————
radiographic contrast without the grid

41
Q

what is the alternate to using a grid

A

restrict beam size
air gap technique - increase OID

42
Q

main purpose of filtration

A

reduce patient dose by taking out low energy photons

43
Q

filtration works because

A

it removes soft x rays (low energy photons)

44
Q

filtration is measured in

A

HVL - half value layer

45
Q

material for filtration

A

aluminum & copper

46
Q

2 types of filtration

A

added & inherent

47
Q

they type of filtration the tech adds

A

added filtration

48
Q

total filtration is

A

sum of added and inherent filtration

49
Q

when above 70 kv you have to have

A

2.5 mm of aluminum equivalent

50
Q

largest producer of scatter

A

the patient

51
Q

what affects detail the most

A

OID ( magnification )

52
Q

photoelectric interaction adds to

A

the patient dose, passes through the body easier

53
Q

as scatter increases , absorption

A

decreases

exposures (6 decks)

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