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Dental Radiography > LO1 > Flashcards

LO1 Flashcards

1
Q

What is the nature of X-rays?

A
  • Electromagnetic energy
  • Natural and produced by Sun
  • Absorbed by atmosphere
  • Travel in straight lines
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2
Q

What are the properties of X-rays?

A
  • Electromagnetic
  • X-ray beam has millions of photons of different energies
  • Travel in straight line
  • Energy carried can be attenuated by matter
  • X-rays capable of ionizing matter and causing biological damage in living tissue
  • X-rays undetectable by human senses
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3
Q

What is a photon?

A

Packet of energy (quantum)

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4
Q

What is the relationship between the wavelength and frequency?

A

Shorter wavelength:

  • Higher frequency.
  • Higher energy.
  • More penetrating radiation.
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5
Q

Define wavelength

A

Distance between 2 similar points on 2 successive waves.

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6
Q

Define frequency

A

No. of waves that pass given point per unit of time

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7
Q

Define velocity

A

Speed of wave

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8
Q

How are X-rays produced?

A
  1. X-ray machine turned on and length of exposure selected with timer.
  2. Activate low-voltage circuit – heat filament.
  3. Activate high-voltage circuit – pull electrons across tube.
  4. Electrons cross tube, strike target and produce x-rays.
  5. The X-rays pass through the filter and collimator before exiting through the PID.
  6. X-ray production stops when exposure time ends – release exposure button.
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9
Q

Why is the X-ray production process inefficient?

A

Only 1% of interactions result in X-rays and rest produces heat.

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10
Q

What happens to excess heat produced by X-rays?

A

Excess heat absorbed by high tungsten target, copper sleeve and cooling from oil surrounding X-ray tube.

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11
Q

What is the kVp – kilovoltage peak?

A

Maximum voltage across the tube between anode and cathode (70K).

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12
Q

What is the eV – electron volt?

A

Force applied to electrons.

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13
Q

What is the keV – kiloelectron volts?

A

Measures kinetic energy of electrons (70keV).

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14
Q

Name 3 X-ray interaction reactions

A
  1. Heat producing reaction
  2. Bremsstrahlung/braking reaction
  3. Characteristic reaction
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15
Q

Explain the heat producing reaction

A
  • Incoming electron is deflected by cloud of outer-shell tungsten electrons, with small loss of heat energy.
  • Incoming electron collides with outer shell tungsten electron, displacing it to more peripheral shell (excitation) or displacing it from the atom (ionisation) – small loss of heat energy.
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16
Q

Explain the Bremsstrahlung/braking reaction

A
  • High-speed electron from filament enters tungsten atom.
  • Electron slowed down by +ve charge of nucleus – energy released as X-ray.
  • Electron continues in different direction to interact with other atoms until all energy lost.
  • Maximum energy:
    • High-speed electron from filament enters tungsten atom – loses energy and disappears.
    • X-ray produced has energy equal to that of high-speed electron (maximum energy possible).
17
Q

Explain the characteristic reaction

A
  • Electrons aim towards the nucleus and collide with an inner-shell tungsten electron (K/L/M shell) and displaces it (ejected electron).
  • Electrons jump from one shell to another resulting with subsequent emission of X-ray photons with specific energies.
    • Electrons jump so the atom returns to its neutral state.
  • Photons that are only produced by X-ray tubes operating at no less than 70 kV (critical voltage (Vc)).
  • K lines are of importance since L lines have too little energy.
18
Q

What is attenuation?

A

Reduction in intensity of X-ray beam

19
Q

Name the 4 types of interactions of X-rays at atomic level

A
  • Pair production
  • Coherent scatter
  • Photoelectric effect
  • Compton/incoherent effect
20
Q

What is Pair production?

A

Pure absorption

21
Q

What is Coherent scatter?

A

Pure scatter

Unmodified/Rayleigh scattering

22
Q

How does Coherent scatter work?

A
  • Low energy X-rays (< 10keV).
  • Photons interact with matter without change in wavelength (unmodified).
  • No ionisation no energy transferred.
  • X-ray/photon is scattered in different direction unchanged – forward.
  • Contributes to fogging.
23
Q

What is photoelectric effect?

A

Pure absorption

24
Q

How does the photoelectric effect work?

A
  • Primary x-ray strikes an outer-shell electron, knocking it out of its orbit (ionisation).
  • X-ray loses all of its energy and disappears.
25
Q

What is the Compton effect?

A

Scatter and absorption

Thompson scattering

26
Q

How does the compton effect work?

A
  • Primary x-ray strikes an outer-shell electron, knocking it out of its orbit (ionisation).
  • Primary x-ray loses some energy and continues in a different direction as a scattered X-ray.
27
Q

What is background radiation?

A

Ionising radiation that is always present in our environment.

28
Q

What exposure factors regulate the energy and number of X-rays?

A
  • kVp control
  • mA setting
  • Exposure time
29
Q

What happens if exposure factors aren’t set properly?

A

Film may be too light/dark

30
Q

What are the 2 components of X-ray filtration?

A
  • Inherent filtration

- Added filtration

31
Q

What is inherent filtration?

A

It results from the materials present in the x-ray tube head.

  • Beryllium window of the x-ray tube.
  • Oil in the tube head.
32
Q

What is added filtration?

A

Addition of aluminum disks placed in the path of the x-ray beam.

They remove the x-rays that had enough energy to get through the inherent filtration but are still not energetic enough to contribute to image formation.

33
Q

What is a collimator?

A

Lead disk with hole in middle.

  • Shape of hole determines shape of X-ray beam.
  • Size of opening determines size of beam at end of BAD.

Collimation doesn’t change energy or no. of X-rays in X-ray beam that rach the film.

34
Q

What is quality and how is it increased?

A

The quality (average energy) of x-ray beam is increased with an increase in kVp or increase in filtration.

35
Q

What is quantity and how is it increased?

A

The quantity (no. of X-rays) is increased with an increase in kVp, mA and timer settings

36
Q

What is the mA (milliampere) setting and what does it determine?

A

Heating of the filament and no. of electrons.

- Doubling the mA setting results in twice as many X-rays.

37
Q

How does exposure time influence X-rays?

A

Increase in exposure time increases no. of X-rays.

- Exposure time has no effect on average or max. energy of X-ray beam.

Dental Radiography (5 decks)

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