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Imaging > Radiography Principles > Flashcards

Radiography Principles Flashcards

1
Q

What is a radiograph?

A

A photographic recording of shadows cast by differential absorption of x-rays directed through a patient.

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2
Q

Who discovered x-rays?

A

Wilhelm Conrad Roentgen

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3
Q

Radiation

A

propagation of energy through space and matter

  1. Particulate radiation
  2. Electromagnetic radiation
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4
Q

Where does the production of X-ray occur?

A

X-ray tube

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5
Q

Basic properties of X-rays

A
  1. Obey laws of light
    • cannot be reflected
  2. Dual nature
    • Electromagnetic waves
    • Photons/particles
  3. Short wavelength
    • 0.1 -1 angstrom
  4. Cause fluorescence
  5. Exposure photographic film
  6. Induce biologic effects
    • ionization
    • DNA damage
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6
Q

Difference btwn x-ray & gamma ray

A

?????

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7
Q

Describe the production of x-rays

A

Electrons from CATHODE (source of e-)

  • -> focused on target of Anode (+ charge)
  • -> 2% of energy converted to x-ray via Particulate radiation (e-)

energy w/in electromagnetic spectrum (x-rays)
• 1 of 2 types of radiation produced
1. general / bremsstrahlung radiation
2. Characteristic / line radiation

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8
Q

What setting on the X-ray machine controls the number of electrons emitted by the cathode?

A

mA setting

• Thermionic emissions

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9
Q

What does the focusing cup do in the cathode?

A

directs the electrons

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10
Q

Components of cathode

A

• Fine tungsten-rhenium wire filament

 - electrically negative
 - current runs thru it --> source of electrons

• Focusing cup
- directs electrons

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11
Q

Components of Anodes

A 
Target (made of:)
 • Tungsten
     - high atomic #  -- Important for ↑ energy (e- bend closer)
     - high melting point 
     - thermal conductivity
            - 98% of energy --> heat
            - 2% of energy --> x-rays
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12
Q

Types of anodes

• pros & cons

A
  1. Stationary
    • cheap
    • easily overheated
  2. Rotating
    - Expensive
    - dissipates he well
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13
Q

General/ Bremsstrahlung radiation

A

Main x-ray produced
• formed when e- from cathode comes close to the nucleus of an atom
–> “brakes”
–> releases x-rays
–> continues to produce more x-ray interactions

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14
Q

Characteristic / line radiation

A

minor component of x-rays
• formed when e- from cathode knocks an e- out of an orbit
–> produces energy equivalent to the binding energy
–> no more x-rays can be produced

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15
Q

What is Electrical phase?

Why is it important?

A 
Electrical phase
- cyclical phase of current coming from the wall
- Single phase 
         = power lines w/ 2 lines 
- Three phase 
         = power lines w/ 4 lines

Importance:
- x-rays can only be produced when the voltage is at its positive peak
- therefore, ↑ frequency (3phase) has a shorter exposure time.
(↑ radiation for ↓ time)

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16
Q

Name 3 controls on the x-ray machine

A

kVp (kilovoltage)
• high voltage circuit

mA (milliamperage)
• low voltage circuit

Time (sec)
• exposure time

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17
Q

Describe kVp

A

Controls photon energy
(therefore penetration)
• Major effect = Quality of radiation
• Minor effect = Quantity

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18
Q

Describe mA

A

Controls # of x-rays produced
• Major effect = Quantity

mA x time(sec) = mAs

  • there are multiple ways to get the same mAs
    • Use Highest mA w/ Shortest exposure time
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19
Q

2 ways to record a digital x-ray

A
  1. CR (Computed radiography)

2. DR (Digital radiography)

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20
Q

What is an intensifying screen?

Why is it important?

A

Fluorescent layer of Phosphorescent crystals
• When struck by x-ray –> converted to visible light
• Visible light –> exposes the film (at lower mAs values than non-converted x-rays)

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21
Q

Describe the comments of an x-ray film

A
  • Silver halide emulsion (AgBr/AgI) on each side
  • Polyester base in the middle

They can be exposed directly for ↑ resolution
(??)

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22
Q

Describe what is happening when an x-ray film is developed

A

Photon exposure
–> alters AgBr (↑ sensitivity to precipitation)

Developer

  • -> Precipitates Ag
  • -> leaves BLACK areas on film

Fixer

  • -> removes un-precipitated AgBr
  • -> leaving clear areas
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23
Q

Digital Radiography (DR)

A

• plate exposed w/ standard x-ray machine
• 3-5 sec
???????huh?

24
Q

Computed Radiography (CR)

A
  • cassette with medium that can be used thousands of times
  • processing time = 45sec
  • one film at a time
25
Q

What are the trade-offs of digital imaging

A

Standard rads

  • better spacial resolution
  • narrow margin for error (exposure can’t be changed)

Digital Rads

  • better contracts
  • wide margin for error (exposure can be changed)
  • ↑ mAs is better for resolution (but not for personnel health)
26
Q

What is Radiographic density?

A

referes to overall Blackness / Whiteness of finished rads
• Black = OVER exposed
• White = UNDER exposed
** Opacity is a better term!
- ability of tissue to absorb incident radiation

27
Q

Describe how Subject density affects radiodensity

A

Dense objects (bone)

  • -> ↓ Radiodensity
  • -> ↓ backness on film
28
Q

Basic radiopacity

A
  1. Air (Radiolucent - black)
  2. Fat
  3. H2O
  4. Bone
  5. Metal (Radiopaque - white)
29
Q

How does “Tissue atomic number” affect x-ray density?

A

Tissue w/ HIGH atomic number

  • -> ↑ x-ray absorption
  • -> Appear whiter

(Bone = 12 Vs Soft Tissue= 7)

30
Q

How does patient thickness affect radio density?

A

Thicker = ↑ xray absorption

–> whiter

31
Q

What factors affect it?

A

Patient
1 - Subject density
2- Atomic #
3- Thickness

Non-patient

  1. kVp
  2. mAs
  3. Distance btwn tube and recording
  4. Grids
  5. Beam restriction
  6. Processing time
32
Q

What is kVp & mAs affect on radiographic density?

A

20% ↑ in kV –OR– 2x mA

–> 2x radiodensity

33
Q

Factors affecting Detail (resolution)

A
  1. Motion
  2. Focal spot size
    • small = ↑ detail
  3. Object-Film Distance
    • Shorter/ closer to table = ↑ detail
  4. Intensifying screen
    • smaller crystals –> ↑ detail
    • Thiner screen –> ↑ detail
34
Q

Types of distortion

A
  1. Magnification
    • due to Object Film Distance
  2. Foreshortening
    • object angled
  3. Parallax
    • equal sized objects look longer at both ends (vertebrae)
35
Q

Contrast

A

AKA Gray scale

Refers to differences in film blackness (radiodensity) on a finished radiograph
• Affected by differential absorption
- tissue density OR thickness
- Fat helps create contrast

Digital&raquo_space; analog rads

36
Q

Appropriate ways of altering contrast?

A
  1. Adjust kVp and mAs
  2. Contrast media
    Positive
    -barium sulfate
    -organic iodide
    Negative
    -air
    -CO2
  3. Reduce scatter radiation – Grids, collimation
  4. Purchase a digital system
37
Q

Exposure factors

• Short scale vs long scale

A

Short scale
= only a few shades of gray
** ↓ kVp (16%) & ↑ mAs (2x)
–> ↓ subject contrast

Long Scale
= many shades of gray
** ↑ kVp (20%) & ↓ mAs (50%)
–> ↑ subject contrast

–These ##s are important!

38
Q

Secondary / scatter radiation

A

–> reduces subject contrast!

• occurs after photon interacts w/ subject
–> non-image forming radiation (can expose radiographer)

  1. Coherent scattering
  2. Photoelectrical absorption
  3. Compton scatter
39
Q

Coherent scattering

2° radiation

A
  • low kVp photons
  • w/o energy loss
  • photon –> excites atom
  • doesn’t cause ionization
40
Q

Photoelectric absorption

2° radiation

A

(Capture // photoelectron)
• enhances tissue contrast
• adds to exposure of patient
• ?? knocks electron from orbit –> positive ion ??

41
Q

Compton scatter

2° radiation

A

• responsible for worker exposure & “film fog”

• Recoil electron ??
–> positive ion
???

42
Q

Control of 2° radiation

A
  1. Beam Restrictor
  2. Grids
  3. Air Gap
  4. Small animal: compression
43
Q

Beam Restrictors

A

Devises that attach to opening in x-ray tube –> regulates the size/shape of exposure by 1° beam

  • Lead cone
  • Lead cylinder
  • collimator
44
Q

What is a Grid?

Is there a drawback?

A

Flat plate w/ a series of thin lead foil strips, separated by x-ray transparent spacers - btwn patient and film

• ↑s mAs requirement

45
Q

When to use a grid

A

Film
• > 10 cm thickness

Digital
• > 12-15 cm thickness

???

46
Q

Characteristics of a grid

A

2 types

 1. Focused grid  
         - specific focal distance
  2. Parallel grid
        - any focal distance

Grid frequency
• # of lead strips per inch

Grid ratio
• height/width to interspace distance
• No more ↓ scatter past 8:1

Grid Cutoff
• excessive amt of useful x-rays are prevented from reaching film
• high ratio & short grid-focus distance –> ↑ cut off

47
Q

Air gap

A

?

48
Q

Compression

A

?

49
Q

Errors before exposure

A
  1. want a fasted vomiting animal –> R/O FB

2. Wet fur artifact

50
Q

During exposure errors

A
  1. Personnel
  2. movement
  3. machine setting
  • Radiograph area too large/small
  • not enough views – need 2 minimum
51
Q

Best method for checking metastatsis

A

1 lateral view per side
- up side lung = imaged better
1 DV

52
Q

Errors after exposure

A
  1. Dark room

2. Personnel

53
Q

What is ALARA

A

As Low As Reasonably Achievable

• Good radiation safety practice

54
Q

Mechanisms of Radiation injury

A
  1. Direct damage to DNA
  2. Ionization of H2O –> Free Radicals –> indirect DNA damage
  • Absorption & Scatter is the main source of tissue interaction
  • Pass thru has no effect
55
Q 
Radiation dose limits
• occupational dose 
   - per year
   - over lifetime
• under 18
• embryo
A

Occupational dose per 1 yr
• 50mSv

Occupational (lifetime)
• age X 10mSv

None under 18yo

Embryo
• <0.5mSv

Imaging (2 decks)

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