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Flashcards in Physics 1 Deck (82):
1

What are the 7 properties of X-rays?

  1. A type of electromagnetic radiation
  2. Product of electron interactions
  3. Travel at the speed of light
  4. Invisible
  5. Cannot be felt
  6. Can penetrate matter
  7. Can ionize atoms

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2

T/F: All electromagnetic (EM) radiations are energetic

TRUE

3

The amount of energy is _____ proportional to the wavelength

inversely

4

What is the basic energy unit?

Electron volt (eV)

5

EM that is greater than ___ can produce ionization in living cells

15 eV (low energy)

6

What makes an X-ray hazardous?

The ionization potential--most diagnostic X-rays in the kilovolt (keV) range. An ion is an electron ejected from the shell of an atom; the resulting ion pair within the affected molecule may have a functional or physical characteristic change.

7

What is our biggest concern with X-ray hazards?

The ionization of DNA

8

What might the ionization of DNA result in (an increased what)?

  • Rate of mutation
  • Rate of abortion or fetal abnormalities (utero) Susceptibility to disease
  • Risk of cancer
  • Risk of cataracts

9

What is the primary objective of radiation therapy? ALARA

"The primary objective is to obtain maximum diagnostic information with the minimum exposure of the patient, radiology personnel, and the general public." As Low As Reasonably Achievable

10

In the radiation dose perspective, what is the difference between acute injury and chronic injury?

Acute injury = nuclear meltdowns Chronic injury = small doses over time

11

Defining units:

  • Roentgen
  • Rad/Gray
  • Rem/Sievert
  • 1Rem 

  • Roentgen = a unit of exposure
  • Rad/Gray = a unit of absorbed dose
  • Rem/Sievert = a unit of dose equivalent
  • 1Rem = 1000mRem

12

How much radiation do you get from being alive?

360 mrem/year

13

What are the NRC dose limits?

Less than 5Rem/year in addition to non-occupational dose

14

T/F: Lead protective gear does not protect you from the primary beam, only weaker scatter radiation

TRUE

15

What happens during the production of an X-ray?

High speed electrons hurled at a metal target generate x-rays. The source of diagnostic x-rays is the x-ray tube

16

What are the components of an x-ray?

  1. Cathode/filament
  2. Anode/target
  3. Focal spot
  4. Generators

17

T/F: The cathode/filament is very similar to a light bulb

TRUE

18

The more electric current you pass through the filament (wire), the ___ electrons boil off

more

19

What is electron current measured in?

Milliamperes (mA)--is the mA setting on the machine

20

What is filament usually made of?

Tungsten

21

X-rays are produced at the ____.

anode

22

What is applied across the anode and cathode?

A voltage potential (Vp)

23

Which is negative and which is positive (anode/cathode)?

The potential is electrically positive at the anode and negative at the cathode

 

(Remember: cats are generally pretty negative. assholes)

24

Where does the Vp accelerate the e-cloud toward?

The anode

 

Remember: you MUST apply the kVp or nothing will happen  to electrons!

25

The energy of the x-rays produced at the anode is a function of what?

How fast the electrons strike it

26

What is the relationship between voltage potential, electron speed, and energy of the x-ray?

Increased Vp-->increased e- speed-->increased energy

27

What is the anode usually made of?

Tungsten

28

Whatchu know about electron interactions in x-rays (2 general aspects)?

  1. X-rays form via electron colliding with target atoms or radiative interactions
  2. Collisional interactions are responsible for a tiny fraction of diagnostic x-rays produced 

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29

Bremsstrahlung X-rays (3 facts)

  1. Radiative interactions are the main source of diagnostic x-rays
  2. Slowing or "breaking" of the electron as it passes by the atom
  3. Releases energy in the form of x-rays

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30

Understand Bremsstrahlung and collision radiation (diagram)

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31

To penetrate an object in order to detect the x-ray on the opposite side of the object we need an x-ray beam with what 2 things?

Adequate energy

Sufficient quantities

32

What does increasing the kVP do?

Increases the energy of the x-ray photon

Increases the number of x-rays generated

33

Why do the number of x-rays increase when kVP is increased?

Increased interactions in the anode (i.e. more breaking and collision radiation)

34

kVP = ____ of the x-ray

QUALITY

35

mA and s = _____ of the x-ray

QUANTITY

36

Increasing the time of the exposure also increases what?

The number of x-rays produced

37

What are the 5 types of radiation?

  1. Photoelectric effect
  2. Compton effect
  3. Coherent scattering
  4. Pair production
  5. Photodisintegration 

38

T/F: In the photoelectric effect, the x-ray photon (energy) is totally absorbed and scatter radiation is produced in excess.

FALSE--scatter raditiation is NOT produced

39

What happens to the electron in the photoelectric effect?

  • The electron is ejected from the orbit of an atom and produces a characteristic x-ray
    • electron results in subsequent ionizations within the body
    • the characteristic electron has low energy and absorbed locally

40

T/F: The photoelectric effect is primariy responsible for the patient's absorbed dose

TRUE

41

The photoelectric effect is the interaction that is key to what? 

Generation of the radiographic image

42

What is the probability of a photoelectric interaction directly proportional to? What does it provide?

Z3

Zprovides a differential between tissues

*VERY IMPORTANT--this principle is responsible for image generation

43

What are the different opacities of fat and bone, and what do they mean?

  • Fat--mostly carbon (C = 12)
  • Bone--mostly calcium (Ca = 20)
  • Zfor bone is much higher = bone has a better chance of having absorption of an x-ray

44

If the energy is too high, what happens to the photoelectric effect?

It is reduced-->contrast loss

45

Gimme 3 facts about Compton scattering.

  1. It is responsible for nearly all scattered radiation in diagnostic radiology
  2. Similar to photoelectric but the incoming photon energy is not completely absorbed
  3. An orbital electron is ejected and an energy reduced photon continues on

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46

What is the probability of the Compton effect proportional to?

Physical and electron density (it is independent of Z)

47

T/F: The Compton effect contributes to formation of the image but doesn't contribute to film fogging and exposure to patient/surrounding participants.

FALSE--The Compton effect DOESN'T contribute to formation of the image but DOES contribute to film fogging and exposure to patient/participants.

48

How is a 'radiograph' produced?

When x-ray beams pass through a target (patient) and expose photographic film

49

What makes the actual image?

Exposed photographic emulsion

50

Explain how the radiographic image is produced on the x-ray film.

  • X-ray film is similar to photographic film
  • The emulsion contains silver halide crystals
  • When exposed to x-rays the silver halide precipitates as elemental silver--black dot
  • Unexposed emulsion is washed away

51

What are the factors that contribute to increased film blackness?

  • Increased kVP
  • Increased mAs
  • Decreased focal spot--film distance
  • Heel effect

52

What is the relationship of focal spot to film distance?

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53

What is a high FS to FD chosen for? What is the standard value?

  • Avoid high mAs
  • Preserve radiographic detail
  • 40-60 inches

54

What is the Heel effect, what does it result in, and what is the clinical correlation?

  1. The Heel effect is due to a portion of the x-ray beam being absorbed by the anode
  2. Results in an x-ray beam that is less intense on the anode side and more intense on the cathode side
  3. Since the x-ray beam will be more powerful on the cathode side, always place thicker body parts under the cathode side to give a uniform exposure across the radiograph 

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55

What are the 7 factors affecting image detail?

  1. Motion
  2. Film speed
  3. Focal spot size
  4. Focal spot-film distance
  5. Object film distance
  6. Intensifying screens
  7. Grids

56

How does motion affect an x-ray? What are 5 things you can do to decrease the effect?

Motion results in reduced image sharpness

  1. Decrease exposure time
  2. Sedate or GA
  3. Use a regular (non-detail) screen/film combination
  4. Reduce grid ratio
  5. Reduce FS to FD

57

T/F: Most x-ray generators have 2 filaments: a small and a large one

TRUE

58

T/F: Large mA values would melt small filaments.

TRUE

59

How are large filaments able to produce a larger amount of x-rays?

  • Make larger effective focal spots
  • Decrease sharpness of the image

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60

T/F: A long FS to FD increases detail, but lower mAs are required

FALSE--higher mAs are required

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61

What 2 things occur as the object film distance increases?

  1. Magnification 
  2. Decrease in image detail

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62

How do intensifying screens work?

  • Film emulsion is insensitive to x-rays compared to visible light
  • Screens convert x-rays into visible light through phosphoresence
  • Various types of crystals exist based on thickness, composition, and size of crystal

63

T/F: Rare earth screens are less efficient at producing visible light.

FALSE--they are more efficient

64

What are 3 ways in which the non-screen technique differs from the screen technique?

  1. Non-screen has superior detail but greater exposure (i.e. greater kVP's and mAs)
  2. X-rays alone are used to expose silver halide crystals in the emulsion
  3. Information in the screen technique is spread out over a larger area

65

What are 3 other devices that limit scatter?

  1. Collimator
  2. Grids
  3. Shielding

66

What are grids? What is the ratio they are characterized by?

  • Plates with rows of lead strips that are placed between the patient and the cassette (film and screens)
  • The higher the ratio, the more effective at reducing scatter
    • Must increase the mAs to compensate (2-3x)

67

What is a "Bucky?"

A device that moves the grid during the exposure

68

What does a stationary grid result in?

Lines where the lead strips are located

69

Scatter radiation ______ as patient size (thickness) increases.

increases

70

When is a grid helpful?

When the thickness is over 10 cm;

Under 10 cm = no grid

71

What is contrast?

The opacity difference between adjacent areas on a radiograph

72

What is the scale of contrast?

The number of density gradations between the lightest radiograph shadow and the darkest radiograph shadow

73

An image with a lot of contrast is said to have a ____ scale of contrast. A high contrast image has ____ shades of gray between the lightest and darkest areas of the radiograph.

short

only a few

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74

___ mAs and ___ kVP's are one method of achieving short scale contrast. _____ radiographs are taken with a short scale contrast.

High; low

Abdominal

75

What is long scale contrast also referred to as?

Lattitude

76

Which radiographs are taken with a long scale contrast?

Thoracic

77

What are 3 factors affecting contrast?

  1. Subject contrast
  2. Film contrast
  3. Fog and scatter

78

What are the 4 areas of subject contrast?

  1. Thickness
  2. Density
  3. Atomic number differences
  4. X-ray beam energy

79

What is film contrast?

Inherent property of the film

80

What are 3 ways to reduce fog and scatter?

  1. Scatter radiation: use a grid
  2. Avoid high temperature, visible light or pressure
  3. Watch expiration dates--film fogs spontaneously 

81

What are the 3 stages of film processing?

  1. Developing (deposits)
  2. Fixing (removes)
  3. Washing

82

T/F: Conventional radiography is still the gold standard by which all digital methods are judged.

TRUE