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Radiation Physics > Final Exam Review > Flashcards

Final Exam Review Flashcards

1
Q

______ is energy in transit, either as particles or electromagnetic waves…

A

Radiation

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2
Q

______ is the characteristic of various materials to emit ionizing radiation…

A

Radioactivity

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3
Q

______ is the removal of electrons from an atom and the essential characteristic of high energy radiations when interacting with matter…

A

Ionization

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4
Q

T/F, Electromagnetic energy of different sources and their ionizing ability are directly proportionate to their wavelength. As the wavelength decreases, the energy and ionizing potential will decrease…

A

FALSE: Electromagnetic energy of different sources and their ionizing ability are inversely proportionate to their wavelength. As the wavelength decreases, the energy and ionizing potential increases.

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5
Q

What is the largest man made source of ratiation?

A

Medical imaging (x-rays) 11%

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6
Q

What is the largest naturally occurring source of radiation?

A

Radon Gas (55%)

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7
Q

T/F: X-rays represent a form of man-made electromagnetic radiation…

A

TRUE

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8
Q

The cathode is what charge, and the anode is what charge?

A

Cathode -

Anode +

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9
Q

What are 5 characteristics of X-rays?

A 
1 - Penetrate most matters
2 - Invisible
3 - No charge
4 - Cause ionization and biological changes
5 - Make compounds emit light
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10
Q

The x-rays produced include _____ and ____ radiation…

A

Bremsstrahlung, characteristic

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11
Q

How are Bremsstrahlung x-rays made?

A

Bremsstrahlung x-rays are produced due to sudden deceleration of fast moving electrons when they collide and interact with the target anode’s nucleus

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12
Q

In the process of Bremsstrahlung x-rays being made how much of the energy is actually converted to usable x-rays?

A

In the process of deceleration more than 99% of the electron energy is converted into heat and less than 1% of energy is converted into x-rays

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13
Q

T/F: Bremsstrahlung x-rays represent majority in the x-ray spectrum produced at the anode

A

TRUE

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14
Q

How is characteristic radiation made?

A

When a fast moving electron collides with a K-shell electron, the electron in the K-shell is ejected (provided the energy of incident electron is greater than the binding energy of K-shell electron) leaving behind a “void” The void left behind is filled by an outer shell electron (from the L-shell, M-shell etc.) with an emission of a single x-ray photon, called characteristic radiation

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15
Q

X-rays can interact with matter by what 5 ways?

A 
1 - PE effect
2 - Compton effect
3 - Classical/Coherent, Thompson Scatter
4 - Photodisintegration
5 - Pair production
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16
Q

This statement describes which interaction with matter: Relatively low energy x-ray photons interact with the atomic electron and removes it from its shell and the energy of the x-photon is equal to or just greater than the binding energy of the electron in its shell…

A

Photoelectric effect

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17
Q

T/F: The probability of the photoelectric effect increases when the kVp is decreased…

A

TRUE

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18
Q

Contrast is increased when kVp has (increased/decreased)?

A

Decreased

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19
Q

During the PE effect the electron that is removed is then called a ______

A

Photoelectron

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20
Q

During the PE effect the incident photon is completely absorbed in the process thus the reason for the _____ of x-ray beam as it passes through different matter…

A

Attenuation

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21
Q

T/F: IN the PE effect a secondary characteristic radiation photon is also produced in the process…

A

TRUE

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22
Q

What happens to the PE effect when the atomic mass is increased?

A

If atomic number (Z) increases, PE will increase

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23
Q

As x-ray energy increases what three things take place relative to the PE effect?

A

1 - increased penetration through tissue without interaction
2 - Less PE effect relative to compton effect
3 - Reduced absolute PE effect

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24
Q

As mass density increases what happens to the photoelectric effect?

A

As mass density of absorber increases it leads to a proportional INCREASE in PE absorption

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25
Q

T/F: The pgotoelectric effect is most likely to occur with outer-shell electrons, loosely bound electrons, and when x-ray energy is just higher than electron-binding energy…

A

FALSE: The PE effect is most likely to occur with inner shell electrons, tightly bound electrons and when x-ray energy is just higher than electron-binding energy

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26
Q

Compton scatter is most likely to occur with (outer/inner) - shell electrons?

A

Outer

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27
Q

AS x-ray energy increases what happens to the Compton effect?

A

Increased penetration through tissue without interaction (decrease in compton effect), however, there is increased compton scattering relative to PE effect

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28
Q

As atomic number of absorber increases what happens to compton scattering?

A

No effect on compton scattering

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29
Q

As mass density of absorber increases what happens to compton scattering?

A

Proportional increase in Compton scattering

30
Q

T/F: Compton scatting has no useful contribution to the radiographic image and creates fogging, lowering image contrast…

A

TRUE

31
Q

How does Differential Absorption occur?

A

DIfferential Absorption occurs because of compton scattering, PE effect, and x-rays transmitted through the patient

32
Q

Define radiopaque…

A

Radiopaque - or opaque, the relative capacity of matter to obstruct the transmission of radiant energy. When x-rays are obstructed the film appears light. (Ex. Bone or metal or soft tissue radiopacity)

33
Q

Define radiolucent…

A

Radiolucent - or non-opaque, being permeable to radiation or penetrable by x-rays. When x-rays are not absorbed and obstructed the film is dark.

34
Q

What is the difference between the radiopaque and the radiolucent areas of the body, these areas give _____ or differential absorption of the image.

A

Contrast

35
Q

Differential absorption (contrast) increases as the kVp (energy) is ________ (increased/reduced)

A

Reduced

36
Q

As x-ray energy increases what happens to each of the following:

1) compton scattering
2) PE effect
3) Exposure of the film

A

1) fewer compton interactions
2) Many fewer PE interactions
3) More transmission through tissue exposing (blackening) the film

37
Q

As atomic mass density increases what happens to each of the following:

1) compton scattering
2) PE effect
3) Exposure of the film

A

1) Proportional increase in Compton interactions
2) Proportional increase in PE interactions
3) Proportional reduction in x-ray transmission “whitening” the film more

38
Q

The process by which radiation loses power as it travels through matter and interacts with it is known as….

A

Attenuation

39
Q

T/F: Beam attenuation is the basis of the contrast observed in all x-ray based imaging methods…

A

True

40
Q

The x-ray tube contains two principal elements. The _________ which provides electrons, while the _________ acts as the target for electrons and releases x-rays whilst dissipating heat.

A

Cathode (+)

Anode (-)

41
Q

T/F: The anode expels the electrons from the circuit and focus them in a beam towards the focal spot of the cathode…

A

False, The cathode expels the electrons from the circuit and focuses them in a beam towards the focal spot of the anode….

42
Q

The electrons are produced by heating the filament, i.e., a coil of wire made from __________, placed within the focusing cup that provides electrostatic focusing of the beam on the anode’s focal spot (can be Large or Small)

A

Tungsten

43
Q

In order to expel the electrons they need to be given the energy. Heat is used to expel the electrons from the cathode, this process is called…

A

Thermionic emission

44
Q

T/F: In the Cathode the filament is heated with the high electric current passing through it, reaching glowing temperature and the electrons are then expelled from the cathode…

A

FALSE: Cathode is heated with the LOW electric current passing through it…

45
Q

T/F: Positron Emission refers to the collection of electrons which are emitted from the metal filament surface, after the application of tube current, at a short distance away from the metal surface…

A

FALSE: SPACE CHARGE refers to the collection of electrons which are emitted from the metal filament surface, after the application of tube current, at a short distance away from the metal surface…

46
Q

Electrons collect and form a could of (-) charge which forms around the metal surface of the cathode. This space charge limits the further emission of electrons from the surface and is referred to as what?

A

Space Charge effect

47
Q

The ___ of an x-ray tube represents the component in which the x-rays are produced?

A

Anode (+)

48
Q

The whole anode is not included in the x-ray production. The x-rays are produced at small rectangular surface called the…

A

Focal spot

49
Q

There are _____ focal spots chosen according to the image procedure and (mAs) selected by the radiologist, and choosing the wrong focal spot may contribute to heat-related damage of the anode…

A

Two focal spots (Large/Small)

50
Q

Describe the Anode Heel Effect…

A

The x-ray beam consists of a central ray and a diverging beam. The x-rays towards the cathode end of the tube have more intensity. This is because, in a diverging beam, the rays which are parallel or near parallel to the inclined/angulated anode get absorbed by the anode itself. Thus in radiographic positioning, thicker patient’s part should be positioned to the cathode (-) end of the tube and vice versa

51
Q

T/F: A patients thicker parts should be placed towards the Anode (+) end of the tube…

A

FALSE: Thicker parts should be placed towards the cathode end of the tube…

52
Q

mAs = milliamps x seconds (time) = mAs milliamp (1/1000 of ampere) times (x) TIME (in seconds). This is what controls the ______ (quantity/quality) of electrons and x-ray photons produced…

A

Quantity/Amount

53
Q

T/F: mAs controls the BLACKENING or DENSITY on the x-ray film…

A

TRUE

54
Q

kVp: kilovolt Peak is the component that controls the _____ of the x-ray beam produced…

A

Quality

55
Q

kVp is what controls the _____ or ______ in the produced x-ray film…

A

Contrast, Gray Scale

56
Q

T/F: the higher the kVp the higher the contrast…

A

FALSE: the higher the kVp the lower the contrast

57
Q

T/F: When the kV is set on the control console, the maximum kilovolt that will be achieved is 33% of the number you have selected. For example, if you set the kVp at “60”, the maximum kilovolt that will be produced is 20kV, or 20,000 volts.

A

FALSE: When the kV is set on the control console, the maximum kilovolt that will be achieved is the number you have selected. For example, if you set the kVp at “60”, the maximum kilovolt that will be produced is 60kV, or 60,000 volts…

58
Q

Change in 10-15 kVp an equivalent change in mAs could be ____%?

A

50% mAs

59
Q

The __________ is the width of a material required to reduce the x-ray or gamma-ray beam to half its original value…

A

Half Value Layer (HVL)

60
Q

T/F: The HVL is a direct measure of photon energy or the hardness of a beam…

A

FALSE: The HVL is an INDIRECT measure of photon energy or the hardness of a beam…

61
Q

HVL is measured in millimeters of what type of material?

A

Aluminum

62
Q

T/F: Filters are metallic sheets that are used to absorb the low energy x-ray photons from the spectrum thus reducing the patient dose…

A

TRUE

63
Q

What are the two types of filtration?

A 
Inherent filtration (tube and housing)
Added filtration (aluminum and copper)
64
Q

Select the false statement (dealing with Collimators):

1) Collimators are devices that are used in the x-ray tube housing in such a way that the light and x-ray fields match each other
2) They are made of aluminum shutters which completely absorb the photons
3) Thus reduce patient dose as well as focus the radiation accordingly to the area of interest
4) They allow different projections of x-ray fields

A

2) They are made of LEAD shutters which completely absorb the photons

65
Q

Select the false statement (dealing with Grids):

1) Grids are placed between the patient and the image receptor to reduce the scattered radiation (produced mainly by Compton effect) and thus improve image contrast
2) Grids are made of parallel strips of lead with an interspace having an aluminum or organic spacer
3) The strips can be oriented either linear or crossed in their longitudinal axis
4) Grids are useful as the scatter radiation is decreased in “thinner” patients and when the field size is left small (poor collimation or a type of view)
5) Grids are very useful in such scenarios to improve image contrast

A

4) Grids are useful as the scatter radiation is INCREASED in “THICKER” patients and when the field size is left LARGE (poor collimation or a difficult type of view)

66
Q

T/F: Grid ratio of 8:1 or 10:1 is generally used for 70-90 kVp technique and 12:1 is used for >90 kVp technique

A

TRUE

67
Q

When are Grids most commonly used?

A

Grids are mostly used for: Abdomen, Pelvis and Spine (except lateral cervical, this uses air-gap technique) imaging…

68
Q

T/F: The higher the grid ratio, the worse the image contrast (less scatter clean up) but at a benefit of reduced patient dose…

A

FALSE: The higher the grid ratio, the better the image contrast (more scatter clean up) but at a cost of increased patient dose

69
Q

What are 5 typical problems radiographers run into with grids?

A

1) Off-level: cut-off across entire image, LIGHT image
2) Off-centre: cut-off across entire image, LIGHT image
3) Off-focus: cut-off towards the edge of the image
4) Upside-down grid: severe cut-off towards the edge of the film
5) Off-focus and off-centre grid: DARK on one side and LIGHT on the other side

70
Q

As tissue mass density increases what happens to each of the following:

1) compton scatter
2) PE effect
3) Exposure of the film

A

1) Proportional INCREASE in compton interactions
2) Proportional INCREASE in PE interaction
3) Proportional reduction in x-ray transmission “whitening” the film more

Radiation Physics (5 decks)

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