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Clinical Pod Med Exam 1 > 6 - Radiation Physics and X-ray I > Flashcards

6 - Radiation Physics and X-ray I Flashcards

1
Q

What are x-rays?

A

X-rays are ionizing radiation

  • It removes an electron from an atom
  • It is also non-particulate and uncharged radiation
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2
Q

What are the ways we measure x-rays?

A
  • Roentgren (R) or Air Kerma
  • Rad or Gray (Gy)
  • Rem (r)
  • Curie or Becquerel
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3
Q

Roentgren (R) or Air Kerma

A

QUANTITY of exposure

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4
Q

Rad or Gray (Gy)

A

QUANTITY of absorbed dose

10-20 Gy is lethal to humans

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5
Q

Rem (r) or Sievert (Sv)

A

Rem = “roentgen-equivalent-man”

QUANTITY of effective dose equivalent received by radiation workers

4 Sv is lethal dose to humans

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6
Q

Curie or Becquerel

A

QUANTITY of radioactivity

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7
Q

Exposure

A

Amount of ionization that is produced when radiation passes through matter

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8
Q

Absorbed dose

A

Amount of energy absorbed by matter when radiation passes through it

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9
Q

Dose equivalent

A
  • Measure of biological damage caused by radiation
  • Product of absorbed dose multiplied by a quality factor that accounts for the observation that for the same amount of absorbed radiation, different types of radiation cause different amounts of biological damage
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10
Q

Effective dose equivalent

A
  • Measure of biological damage caused by radiation to a specific organ
  • Product of dose equivalent multiplied by the weighting factor that is a measure of the risk from exposure to that organ compared to the risk from whole body exposure to the same dose
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11
Q

What are the numbers of doses you need to know?

** KNOW THIS **

A
  • 1 Gy = 100 rad
  • 1 Sv = 100 rem

FYI - 1 rem = .01 Sv = 1cSv = 10 mSv

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12
Q

Describe what an x-ray is

A

X-rays, along with gamma rays, are also a form of electromagnetic radiation (another form of ionizing radiation) which have no mass or charge

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13
Q

Describe photons

A
  • Photon-smallest quantity of any type of electromagnetic radiation-has high energy and short wavelength
  • Photon energy is measured in electron volts
  • Diagnostic imaging uses 30 to 150 kVp (discussed later)
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14
Q

Attenuation

A
  • X-rays are partially absorbed by matter which is known as attenuation
  • Results in different shades of gray on film
  • Matter that absorbs x-rays appear white and are radiopaque ***
  • Matter that allows total penetration of x-rays appear black and are radiolucent***
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15
Q

Radiopaque

A
  • ABSORBS x-rays

- Shows up WHITE (bone)

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16
Q

Radiolucent

A
  • PENETRATION of x-rays

- Shows up BLACK (soft tissue)

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17
Q

Inverse square law

A

Inverse square law: light intensity from a source is inversely proportional to the square of the distance between the object and the source

Equation: [I₁/I₂ = (d₂/d₁)²]

Example: X-ray intensity is 1 rad at 2 feet and at 4 feet is 0.25 rad

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18
Q

Components of an x-ray unit

A
  • Control console
  • Transformer
  • High-voltage generator
  • Tubehead
  • Beam limitation device
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19
Q

What are the three factors under control of the x-ray operator?

** IMPORTANT **

A
  • kVp (kilovoltage peak)
  • mA (milliamperage)
  • Timer
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20
Q

Describe kVp (kilovoltage peak)

A
  • Energy of the x-ray beam
  • 50-70 kVp’s
  • Manipulates primarily the energy or QUALITY of x-rays and to a lesser extent the quantity of x-rays ***
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21
Q

Describe mA (milliamperage)

A
  • Tube current and controls the number of photons produced
  • 10-30 mA’s
  • Manipulates quantity of x-rays ***
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22
Q

Describe the timer

Listen to this for what he said will be on the test

A
  • Controls length of exposure
  • 1/60th to 1/100th of a second
  • Manipulates quantity of x-rays ** KNOW FOR EXAM **
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23
Q

What are the components of the tubehead?

A
  • Supporting arm: holds tubehead firmly in place and keeps the source-to-image distance (SID) constant and is at minimal 12 inches from the patient
  • X-ray tube
  • Beam limitation device
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24
Q

Describe the protective housing of the tubehead

A

Filled with oil, surrounds and insulates the x-ray tube

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25
Q

Describe the x-ray tube

A
  • Enclosed in glass or metal and maintains a vacuum
  • Has area which allows for passage of the x-rays called the useful beam

2 basic components

  • Cathode
  • Anode
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26
Q

Describe the cathode

A

Negative electrode of the x-ray tube

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27
Q

What does the cathode contain?

A
  • Filament: composed of tungsten and produces electrons when heated-the number of electrons produced is determined by the temperature of the filament and is measured in milliamperes
  • Focusing cup: directs the filament electrons to the anode
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28
Q

Describe the anode

A

Positive electrode of the x-ray tube

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29
Q

What does the anode contain?

A
  • Target: area to which electrons produced by cathode are directed and made of tungsten
  • Focal spot: area on target from which x-rays are emitted
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30
Q

Describe filtration

A
  • Inherent: tube housing absorbs off-focus radiation that does not contribute to the useful x-ray beam
  • Added: filters the useful x-ray beam and absorbs low energy x-rays that cannot reach the image receptor-usually made of 1.5 to 2.5 mm thick aluminum

Notes: Not every x-ray beam will be focused or used for diagnostics, so you want to filter out the x-ray beams that you don’t need. The lead will absorb some of the scatter radiation (INHERENT) and then just before it leaves, there is another filter that absorbs low-energy radiation and this will then never reach the patient (ADDED)

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31
Q

Beam limitation device

A

Shape the dimensions of the useful x-ray beam so that only the area of interest is x-rayed, a process called collimation

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32
Q

Describe the process of using a beam limitation device

A
  • First step is to turn on a light source which shines on the dimensions of the part to be examined and will correspond to the area exposed by the useful beam
  • The center of the light source has crosshairs or a circle to accurately position the central beam

Notes: Nothing more than a flashlight that allows you to control the length and width of the field you will expose the patient to - this field of exposure is called collimation

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33
Q

Choose the correct units that primarily determine the quantity of x-rays that reach the object during conventional x-ray of a foot.

1 - mA of 100
2 - kVp of 50
3 - mA of 50
4 - Timer of 1/70 of a second
5 - Timer of 1/30 of a second
A

What we are asking here is what PRIMARILY controls quality

Answer: Timer of 1/70 of a second

This is because it is a conventional foot x-ray (correct range)

34
Q

X-ray production summary

A
  • Electrons generated at the cathode end at the filament
  • Focusing cup directs electrons toward the anode target
  • Electrons interact with the target where x-rays are produced
35
Q

What are x-rays (photons) produced by?

A
  • Characteristic radiation

- Bremsstrahlung radiation

36
Q

Describe characteristic radiation

A
  • Electron interacts with atom’s inner shell electron and removes the electron which causes ionization
  • X-ray photons produced as outer-shell electrons fill the inner shells
37
Q

Describe Bremsstrahlung radiation

A
  • Electron slows down or “brakes” as it passes by + charged nucleus
  • Changes course of electron which causes it to lose energy in the form of x-ray photons
38
Q

Describe x-ray QUANTITY

A

X-ray quantity (output intensity, x-ray intensity, x-ray exposure) is the number of x-rays

39
Q

Describe x-ray QUALITY

A

X-ray quality is the penetrability of the x-ray or how much energy it has

40
Q

What do you need to know about x-ray contrast?

A
  • The more x-rays that strike the film, AND the more energy x-ray strikes the film, the blacker it makes the film and the less contrast there is (can’t tell white from black as well)
  • You WANT to have as much contrast as possible without exposing the patient to excess x-ray
  • More contrast means you can clearly tell white from balck
41
Q

Describe the x-ray emission spectrum

A
  • X-ray emission spectrum is the range of x-rays energies present in a quantity of x-rays-influenced by mAs, kVp, and added filtration
  • Increasing mAs increases quantity but not quality
  • Increasing kVp increases both quality and quantity
  • Filtration decreases quantity, increases quality
42
Q

What does increasing MAs do?

A
  • Increases quantity

- Does NOT increase quality

43
Q

What does increasing kVp do?

A
  • Increases BOTH quality and quantity
44
Q

What does decreasing filtration do?

A
  • Decreases quantity

- Increases quality

45
Q

Heel effect

A
  • Useful x-ray beam has greater intensity on the cathode side than the anode side which is a result of the line-focus principle
  • Position the thicker portion of the part to be examined closer to the cathode

The thicker part of the body part that you want to look at, put it closer to the cathode because it will be exposed to more x-rays

46
Q

Matching REVIEW:

* TEST QUESTION*

1 - X-rays are produced by this process…
2 - Place the thickest section of the object closest to the cathode…
3 - X-ray emission spectrum…
4 - Affect quality of x-ray…
5 - Affect quantity of x-ray…

A

Listen for the rest of the answers

1 - X-rays are produced by this process… Bremsstralung radiation

2 - Place the thickest section of the object closest to the cathode… Heel effect

3 - X-ray emission spectrum… Range of energies in x-ray beam

4 - Affect quality of x-ray… kVp, filtration

5 - Affect quantity of x-ray… kVp, mA, filtration, time of exposure, BUT mA PRIMARILY controls quantity

47
Q

X-ray interaction with matter occurs in three ways…

A

Occurs in 3 ways which have application to podiatric radiography:

  • Coherent scattering
  • Compton scattering
  • Photoelectric effect
48
Q

Describe coherent scattering

A

As x-ray photons excite the target atom, a secondary photon of equal energy is released in different direction which is absorbed by the patient but does not contribute to diagnostic image

49
Q

Describe Compton scattering

A
  • Occurs when x-ray photon interacting with matter ejects the outer-shell electron causing ionization
  • Original x-ray continues in different direction with decreased energy
  • This creates “fog” that impairs the image quality by reducing its contrast
50
Q

Describe the photoelectric effect

A
  • X-ray photon is totally absorbed and an inner-shell electron is ejected during ionization
  • This process causes beam attenuation and image formation
  • Also contributes to patient-absorbed dose
51
Q

What is the diagnostic formed by?

A

The diagnostic image is formed by the photoelectric effect and remnant radiation (x-rays that pass through patient and strike the image receptor)

52
Q

Describe what causes image fog

A

Most x-rays interact with matter by Compton scattering which causes image fog

Low kVp
- Favors photoelectric effect, but increases dose of radiation (more radiation is absorbed by the body)

High kVp
- Favors Compton scattering (more radiation makes its way to the x-ray film)

53
Q

Describe differential absorption

A
  • Differential absorption is manifested by attenuation which is the reduction in x-ray beam intensity as it is absorbed and scattered by matter
  • Bone absorbs x-rays to a greater degree (appears white) than fat and soft tissue (appear black)
54
Q

Matching REVIEW

* TEST QUESTION*

1 - Forms the diagnostic image…
2 - Forms image fog…
3 - Favors photoelectric effect…
4 - Favors Compton scattering …

A

1 - Forms the diagnostic image… Photoelectric effect

2 - Forms image fog… Compton scattering

3 - Favors photoelectric effect… Low kVp

4 - Favors Compton scattering… High kVp

55
Q

Describe what a high-quality x-ray should exhibit

A
  • Sufficient radiographic density
  • Acceptable contrast
  • Optimal detail
  • Minimal distortion
56
Q

Resolution

A

Ability to separate and distinguish between two separate objects

57
Q

Spatial resolution (image sharpness)

A
  • Ability to distinguish between two objects which are side by side and have different contrasts (bone vs. soft tissue)
  • High spatial resolution is able to distinguish between two objects that are aligned closely together
58
Q

Contrast resolution

A

Ability to distinguish between differences in density or intensity

59
Q

Radiographic density

A

The about of “darkness” or “blackness” on the film

AKA “optical density”

60
Q

Describe radiographic density

A
  • Amount of darkening in a radiograph
  • Along with contrast (adequate differences in density), are required to give visibility to the structural detail of a subject
61
Q

What is the primary controlling factor for radiographic density?

A
  • mAs is the primary controlling factor and is the product of milliampere multiplied by exposure time in seconds (mA x seconds)
  • Can have the same mAs but different milliamperes and seconds
62
Q

What happens as mAs increase?

A

Film becomes DARKER

Known as the law of reciprocity

63
Q

How do you make an adjustment?

A
  • If you need to make an adjustment in density either increase the mAs by a factor of 2 (to increase darkness) or decrease by a factor of ½ (to increase lightness)
  • Change either mA or s, but not both

Note that if you need to make an adjustment, you will need to increase or decrease mAs by at least 30% or the human eye cannot tell a difference

64
Q

What other things can effect the radiographic density other than mAs?

A
  • Kilovoltage (kVp)
  • Distance (SID)
  • Film/screen combinations
  • Compensation filter
  • Film processing
65
Q

Describe the characteristics of kVp

A
  • Governs penetrating power of electrons
  • Alters both quality (energy) of x-ray beam and quantity of photons produced
  • Abides by a 15% rule
66
Q

How does kVp govern the penetrating power of electrons

A
  • Low kVp produces high contrast (tissues appear black or white without much gray
  • High kVp produces low contrast (tissue appears uniformly gray)
67
Q

How much does kVp alter the quality (energy) of x-ray beams and quantity photos produced?

A

Need a 4% to 8% change in kVp (3 to 7 kVp) for the human eye to see a visible difference in the x-ray

68
Q

Give the 15% rule of kVp

A
  • A 15% increase in kVp will cause the same change in radiographic density (make image look darker) as doubling the mAs
  • A 15% decrease in kVP will cause image to look lighter to the same extent as will halving the mAs
69
Q

What does changing the distance between source to image do to the x-ray image?

A

Source-to-image distance (SID) will alter number of photons striking the film

Inverse square law:

  • If tube is too far from film, too few photons strike film producing a lighter image
  • If too close to film, more photons produce a darker image
70
Q

Film screen combinations

A
  • Film/screen speed-sensitivity of intensifying screen in cassette to the x-ray photons
  • The higher the speed of the film/screen, the less radiation is necessary to produce an image, but the less image detail is produced
71
Q

Compensation filter

A
  • Forefoot is thinner than rearfoot; as a result, radiographic density varies between toes and tarsus (toes are thinner than tarsus)
  • If exposure technique selected for toes, tarsus will be underexposed (look lighter)
  • If exposure technique selected for tarsus, toes will be overexposed (look darker)

*** Need compensation filter to balance unequal radiographic density between forefoot and rearfoot

72
Q

Film processing

A

As temperature and immersion time of film in developer increase, radiographic density increases (image darker), and vice versa

Don’t need to worry about this because you will never have to do this

73
Q

Contrast

A

Allows visibility of detail

Two types

  • Radiographic contrast
  • Subject contrast
74
Q

Radiographic contrast

A
  • Result of difference in densities that allows viewer to discern between two adjacent densities within the same image
  • Affected by type of intensifying screen, film’s density, characteristic curve, and processing
75
Q

Subject contrast

A
  • Result of attenuation differences as x-rays pass through body
  • Affected by tissue thickness, type, atomic number and density
76
Q

What are the two scales of contrast?

A
  • Short

- Long

77
Q

Short scale of contrast

A
  • Used in foot and ankle imaging

- Distinguishes bone margins from adjacent soft tissues

78
Q

Long scale of contrast

A
  • Used in abdomen

- Visualize different soft tissue structures that have more similar densities

79
Q

What is the PRIMARY factor in controlling contrast?

A

kVp

80
Q

Describe how kVp controls contrast

** KNOW THIS FOR EXAM **

A
  • Higher kVp’s produce low contrast and vice versa
  • To produce shortened contrast, increase mAs by 2 and decrease kVp by 15%
  • To produce lengthened contrast, decrease mAs by ½ and increase kVp by 15%

** NOTE: need to adjust mAs to maintain the same radiographic density (degree of “blackness”), so if your contrast is off, you need to change TWO things, you can’t just change the kVp **

If you don’t manipulate the mA you will either get a too-dark or too-light image

** KNOW THIS **

Clinical Pod Med Exam 1 (17 decks)

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