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Chapter 11 Flashcards

1
Q

define 15% rule

A
  • The 15% rule states that changing the kVp by 15% has the same effect as doubling the mAs or reducing the mAs by 50%
  • Maintaining or adjusting exposure to the IR can be accomplished with kVp
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2
Q

define body habitus

A

the general form or build of the body, including size

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3
Q

what are the 4 different types of body habitus

A
  • sthenic
  • hyposthenic
  • hypersthenic
  • asthenic
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4
Q

define sthenic

A
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5
Q

define hyposthenic

A
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6
Q

define hypersthenic

A
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7
Q

define asthenic

A
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8
Q

define direct square law

A

provides a mathematical calculation for adjusting the mAs when changing the SID.

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9
Q

define exposure maintenance formula

A

provides a mathematical calculation for adjusting the mAs when changing the SID.

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10
Q

define inverse square law

A
  • states that the intensity of the x-ray beam is inversely proportional to the square of the distance from the source
  • The relationship between distance and x-ray beam intensity
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11
Q

define magnification factor (MF)

A
  • indicates how much size distortion or magnification is demonstrated on a radiographic image.
  • MF = SID / SOD
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12
Q

define object to image receptor distance (OID)

A
  • When distance is created between the object radiographed and the IR
  • decreased beam intensity may result
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13
Q

define source to image receptor distance (SID)

A
  • The distance between the source of the radiation and the IR
  • affects the amount of radiation reaching the patient
  • the intensity of the radiation varies at different distances
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14
Q

define source to object distance (SOD)

A
  • the distance from the x-ray source (focal spot) to the object being imaged
  • SOD = SID - OID
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15
Q

what are the 3 primary exposure factors?

A
  • mA
  • seconds
  • kVp
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16
Q

does mAs control quality or quantity?

A
  • quantity
  • controls the number of electrons boiled off the filament
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17
Q

does mAs and exposure value have a direct or indirect relationship?

A

direct

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18
Q

What happens to the exposure value when mAs is increased?

A
  • exposure increases
19
Q

what happens when the exposure value when mAs is decreased?

A
  • exposure decreases
20
Q

true or false: In order to get a certain mAs, the milliamperage or time can be adjusted to get the same byproduct

A

true
- when we look for a mAs of 20, different methods can be applied:
100 mA x 0.2s = 20 mAs
200 mA x 0.1s = 20 mAs

21
Q

what type of relationship does milliamperage and exposure time have?

A
  • indirect
  • when adjusting mAs and time, they have an indirect relationship in order to get a specific mAs
  • 50 mA x 200ms (0.2s) = 10 mAs
  • 200 mA x 50ms (0.05s) = 10 mAs
  • the variables depend on the type of examination being done and the type of tissue density (pediatrics, elders, etc.)
22
Q

Can mAs control brightness level when using digital IR?

A
  • no
  • need to make sure your exposure is correct in order for the Image to be diagnostic
23
Q

How is the brightness level affected when thr mAs is too low?

A
  • image is bright, but there’s an increased on quantum noise
24
Q

How is the brightness level affected when the mAs is too high?

A
  • exposes the patient with too much radiation
25
Q

define kVp

A
  • affects the exposure to the IR because it alters the amount and penetrating ability of the x-ray beam
  • more kVp increases kinetic energy
26
Q

true or false: Increasing or decreasing the kVp changes the amount of radiation exposure to the IR and the subject contrast produced within the image.

A

true

27
Q

Can kVp control brightness level when using digital IR?

A

-no
- has the same affect as mAs

28
Q

what controls image brightness?

A
  • computer processing
29
Q

What is the formula to increase kVp by 15%?

A
  • multiply kVp by 1.15
  • divide mAs by 2
30
Q

what is the formula to decrease kVp by 15%?

A
  • multiply kVp by 0.85
  • multiply the mAs by 2
31
Q

what is a disadvantage of high kVp?

A
  • increase of scatter
  • higher chances of photoelectric
  • possible lower contrast (due to scatter)
32
Q

what is a desired technique when doing examinations?

A
  • a high kVp and a law mAs
  • helps reduce patient dose
33
Q

name the secondary factors

A
  • focal spot size
  • SID
  • OID
34
Q

define focal spot size

A
  • affects the sharpness of the beam
  • small filament = increased spatial resolution (lower mA setting)
  • large filament = decreased spatial resolution (higher mA setting)
35
Q

what focal spot size is desirable?

A
  • large focal spot
  • spreads out heat better
36
Q

true or false: Modern radiographic x-ray generators are equipped with safety circuits that prevent an exposure from being made if that exposure exceeds the tube-loading capacity for the focal spot size selected.

A

true

37
Q

whats the formula for inverse square law?

A
  • I1/I2 = D2^2/D1^2
38
Q

true or false: Increasing the SID requires that the mAs be increased to maintain exposure to the IR, and decreasing the SID requires a decrease in the mAs to maintain exposure to the IR.

A

true

39
Q

what are the standard SID distances?

A

40, 48, 72 inches

40
Q

what other components does SID effect?

A
  • image distortion (magnification)
  • spatial resolution
41
Q

true or false: As SID increases, size distortion (magnification) decreases and spatial resolution increases; as SID decreases, size distortion (magnification) increases and spatial resolution decreases.

A

True

42
Q

what does it mean when the MF is greater than 1?

A

there is a percentage of magnification

43
Q
A

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