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XRAY > Exposure Class > Flashcards

Exposure Class Flashcards

1
Q

dry plaster cast, wet plaster, fiberglass - mAs adjustment?

A

2x dry, 3x wet (or base exposure on thickness measurement), no change fiberglass

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2
Q

Controlling factor for contrast?

A

Kilovoltage

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3
Q

What are the influencing factors for contrast?

A

OID, Grid Ratio, Collimation (Part thickness, contrast media)

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4
Q

Controlling factor for density?

A

mA and seconds

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5
Q

For every change in part thickness of 4 cm, mAs adjustment?

A

x2

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6
Q

How is anode heel effect most visible?

A

w/ short SID and large field size

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7
Q

What is HIGH contrast?

A

Few densities w/ great differences between them (SHORT SCALE)

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8
Q

What is LOW contrast?

A

Many densities w/ few differences between them (LONG SCALE)

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9
Q

Film contrast vs Subject contrast?

A

Film contrast is inherent property manufactured into film and how it should be XRed, subject contrast is result of absorption char of tissue and kvp

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10
Q

How does increasing kvp change contrast?

A

inc kvp, Dec contrast: higher penetrating, lower absorption, more transmission and few density diffs in tissues…. also increases scatter: fog and unwanted density decrease contrast

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11
Q

Increasing tube filtration effect on contrast?

A

increases penetrating power of beam (kvp), inc scatter, dec constrast

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12
Q

exposure factor modifications for peds?

A

fast exposure times 0-5: 25% mas 6-12: 50% mas

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13
Q

exposure factors for soft tissue?

A

increase contrast to penetrate ST foreign bodies

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14
Q

Focal spot size range?

A

.5 - 1.2 mm

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15
Q

What factors effect geometric unsharpness?

A

focal spot size, SID, OID

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16
Q

Line pairs?

A

line pairs per mm : greater resolution and recorded detail

17
Q

What is resolution?

A

ability of digital imaging sys to distingusih between 2 adjacent structures

18
Q

Spatial resolution?

A

smallest detail that can be detected in an image

19
Q

Contrast resolution?

A

ability of imaging sys to distinguish between small objects having similar subject contrast

20
Q

compensation in mAs when significantly collimating?

A

increase 30-50%

21
Q

When to use grids?

A

when part is thicker than 9-10 cm, and more than 60 kvp needed

22
Q

Grid frequency?

A

number of lead lines per unit length (25-45 lines/cm or 60-110 lines/inch)

23
Q

Grid ratio?

A

ratio of height of lead strips to distance between them (4:1 to 16:1)

24
Q

Convergent point on grid?

A

on focused grid, if lines were drawn to focal point of grid … points drawn along imaginary line on length of grid: convergent line

25
Q

Focal distance?

A

distance between grid and convergent line/point; helps determine SID

26
Q

Focal range?

A

recommended SIDs to be used w/ focused grid

27
Q

Stationary grids?

A

wafer grid, grid cassette, grid cap

28
Q

Moving/reciprocating grids?

A

Potter-bucky diaphragm; moves during exposure laterally

29
Q

What is the contrast improvement factor?

A

K : contrast w/ grid / contrast w/o grid

30
Q

What is grid cutoff?

A

decrease in number of transmitted photons reaching IR bc of grid misalignment (higher grid ratio: higher potential for grid cutoff)

31
Q

Upside-down focused grid cutoff?

A

focused grid upside down on IR (loss of density on edges of film…grid lines opp angle of divergent beam)

32
Q

Off-level cut off?

A

XR beam angled across lead strips, tube or grid angled…happens w/ parallel or focused

33
Q

Off-center cutoff?

A

focused grid: lateral decentering: tube angled not aligned side/side w/ center of grid

34
Q

Off-focus cutoff?

A

loss of density on periphery of image when proper SID not used

35
Q

Photoelectric effect vs compton effect?

A

Photoelectric: incoming photon knocks inner-shell electron and is completely absorbed - secondary photon created (smaller percentage at higher kvp) Compton: incoming photon ejects outer shell electron and changes direction (greater percentage at higher kvp) (absorption vs scattering)

XRAY (14 decks)

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