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5th Semester: DI (Preeti) > Physics of Diagnostic Imaging 1 & 2 > Flashcards

Physics of Diagnostic Imaging 1 & 2 Flashcards

1
Q

Amount of energy is inversely proportional to _________

A

wavelength

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2
Q

T/F: Longer wavelength = higher energy

A

FALSE!

Longer wavelength = LESS energy

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3
Q

The basic unit of energy in electromagnetic radiation

A

eV (electron volt)

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4
Q

EM radiation > ____ eV

can ionize living cells

A

15 eV

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5
Q

The _________ potential is what makes xrays dangerous

A

ionization potential

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6
Q

An electron ejected from the shell of an atom

A

ION

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7
Q

T/F: Ionization of DNA (caused by xrays) can increase

the risk of cataracts

A

TRUE

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8
Q

What is a roentgen?

A

A unit of exposure to radiation

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9
Q

What is a Rad/Gray?

A

A unit of absorbed dose of radiation

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10
Q

What is a Rem/Sievert?

A

A unit of dose equivalent

1 Rem = 1,000 mRem

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11
Q

The typical person is exposed to _______ mRem/year

A

360 mRem/year

(1 mRem/day)

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12
Q

1 chest x-ray is equivalent to a dose of ____ mRem

A

10 mRem

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13
Q

T/F: There is an increased risk of radiation exposure when flying in an airplane

A

TRUE!

About 2.5 mRem dose for a 1-way flight across the US

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14
Q

T/F: Lead protective gear is great for protection against all types of radiation

A

FALSE!

Lead protective gear ONLY protects from SCATTER RADIATION

not the primary beam!

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15
Q

A voltage potential (Vp) is

electrically _________ at the Anode, and

electrically _________ at the Cathode

A

POSITIVE at the Anode (target)

and

NEGATIVE at the Cathode (filament)

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16
Q

Milliamperes (mA) is the unit of measure for

A

Electric current

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17
Q

The more electric current passed through the cathode (filament)

the ____ electrons produced

A

MORE

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18
Q

Increased Voltage Potential = Increased speed of electrons

= ______ energy of x-ray

A

INCREASED

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19
Q

How is voltage potential (energy of the xray) adjusted on

the xray machine?

A

Using kVp!

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20
Q

What are filaments and anodes usually made of?

A

Tungsten

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21
Q

kVp = the _______ of the xray

mAs = the ________ of the xray

A

kVp= quality of xray

mAs= quantity of xray

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22
Q

Increasing kVp increases the ______ of the xray

A

energy

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23
Q

Increasing mAs or time of exposure

increases the _______ of xrays produced

A

number

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24
Q

This principle is responsible for image generation from an x-ray

A

Photoelectric Effect

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25
Q

Due to this effect, the x-ray photon (energy)

is completely absorbed, and NO scatter is produced

A

Photoelectric Effect

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26
Q

The probability of photoelectric interaction is

directly proportional to Z3, which provides a

differential between _______

A

tissues

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27
Q

The higher the value of Z3, the _______ the image,

because there is better absorption with a higher value.

A

WHITER

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28
Q

If energy is too high, photoelectric effect is reduced,

resulting in ___________

A

Contrast Loss

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29
Q

This effect is responsible for nearly all scatter radiation in

diagnostic radiology

A

Compton Effect

30
Q

How is the the Compton Effect different from the Photoelectric Effect in regards to the incoming photon energy?

A

In the Photoelectric Effect, incoming energy is COMPLETELY absorbed.

In the Compton Effect, not all energy is absorbed –> SCATTER!

31
Q

Which effect contributes to film fogging?

A

The compton effect (scatter radiation)

32
Q

What happens when photographic emulsion (silver halide crystals)

is exposed to xrays?

A

Silver halide crystals precipitate as elemental silver- black dot

33
Q

Increasing kVp and mAs would _____ film blackness

34
Q

______ focal spot to film distance would increase film blackness

A

decreasing FS-FD would increase film blackness

35
Q

The Heel Effect contributes to _______ film blackness

36
Q

Doubling the mAs will _____ the film blackness

37
Q

Increasing the kVp by ____% will double the film blackness

38
Q

What is the standard FS to FD length?

A

40 - 60 inches

39
Q

This is the effect caused due to a portion of the xray beam

being absorbed by the Anode. It results in increased

film blackness due to an xray beam that is less intense on

the Anode side and more intense on the Cathode side.

A

The Heel Effect

40
Q

Why would you want to place thicker body parts under the

cathode side of an xray machine?

A

To combat the Heel Effect and give a uniform exposure across

the radiograph

41
Q

Motion results in decreased image sharpness.

What factors can be put in place to combat this?

A

Decrease the exposure time

Decrease the grid ratio

Decrease the FS to FD

42
Q

A long FS to FD _____ detail

A

INCREASES detail

but more mAs is needed

43
Q

Magnification occurs as object-film distance ______

44
Q

Screen convert xrays into visible light via _______

A

phosphorescence

45
Q

Screen vs. Non-screen Technique:

Which has superior detail but greater exposure?

A

Non-screen

(greater kVp and mAs)

46
Q

Screen vs. Non-screen Technique:

Information from this technique is spread over a larger area

A

Screen Technique

47
Q

Collimators, Grids, and Shielding all function to

limit _________

A

SCATTER radiation

48
Q

Grids are characterized by a ratio.

The ______ the ratio, the more effective at reducing scatter

A

higher

(But must increase mAs to compensate!)

49
Q

A Bucky is a device that moves the grid during exposure.

What does this prevent?

A

Moving the grid prevents lines (due to the lead strips in the grids) that would otherwise occur with a stationary grid

50
Q

Scatter radiation ________ as patient size (thickness) increases

51
Q

How do you determine if a grid needs to be used?

A

If the patient is over 10 cm in thickness, use a grid!

52
Q

The opacity difference between adjacent areas on a radiograph

is known as

53
Q

The number of density gradations between the

lightest radiograph shadow and the darkest radiograph shadow

is known as

A

The Scale of Contrast

54
Q

A radiograph with a high contrast and few shades of gray

between the lightest and darkest areas on the radiograph

is said to have a _______ Scale of Contrast

55
Q

A radiograph with LOW contrast and many shades of gray

between the lightest and darkest areas of a radiograph

is said to have a _______ Scale of Contrast

56
Q

Another name for Long Scale of Contrast (low contrast)

57
Q

How is Short Scale of Contrast achieved?

A

High mAs and Low kVp

58
Q

How is Long Scale of Contrast achieved?

A

Low mAs and High kVp

59
Q

Abdominal radiographs are taken with a

______ Scale of Contrast

60
Q

Thoracic radiographs are taken with a

________ Scale of Contrast

61
Q

Why would you want to avoid using expired film?

A

Film will fog spontaneously when too old

62
Q

A visual cue or signal that is produced by a pathologic change

in tissue and may be detected in a medical image

A

Roentgen (Imaging) Signs

63
Q

What are the 5 opacities?

A

Gas

Fat

Soft Tissue = Fluid Opacity

Mineral = Bone Opacity

Metal

64
Q

False white or black lines that appear at sharp boundaries

are due to this phenomenon

A

Mach Phenomenon

65
Q

Continuous scale from black to white

A

Analog Gray Scale

66
Q

An area of increased radiopacity (whiteness)

that occurs when 2 overlapping objects are in the

path of the xray beam and are not in contact with one another

67
Q

When the margins of two objects cannot be distinguished

or are difficult to distinguish

because of similar opacities and their margins are

in contact with one another

A

Silhouetting

68
Q

What is happening in radiograph A?

A

Silhouetting

69
Q

What is happening in radiograph B?

70
Q

What is happening in radiograph D?

71
Q

The blackest shade on a radiograph is most likely

_______

72
Q

The whitest shade on a radiograph is most likely

_______ or ________

A

dense bone or metal

5th Semester: DI (Preeti) (13 decks)

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