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ICS - RADIOLOGY > 3 - Production of X-rays > Flashcards

3 - Production of X-rays Flashcards

1
Q

tubehead components:

what does the lead shield do?

A

minimize radiation leakage

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2
Q

tubehead components:

what does oil do?

A

facilitate heat removal

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3
Q

tubehead components:

what does the aluminium filter do

A

removes low energy, damaging x-rays

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4
Q

tubehead components:

what does the collimator do? what is a device that may be part of the collimator?

A
  • restrict size & shape of beam

- beam indicating device (BID) or spacer cone

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5
Q

filament is heated by current due to?

A

filament is heated by current due to the excitation of electrons within wire

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6
Q

electrons lost from?
what is an electron cloud?
large potential difference between?

A
  • outer shell
  • free electrons surrounding the filament
  • large potential difference between cathode and anode
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7
Q

focusing cup points electrons towards?
-ve electrons attracted to?
how are they pulled across cathode and anode?
what does it mean when electrons have high energy?

A
  • focusing cup points electrons towards target/focal spot of anode
  • -ve charged electrons attracted to +ve charged electrons
  • pulled across by high kV between cathode and anode
  • they are fast moving
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8
Q

production of x-rays:

what happens once the electrons hit target?

A
  • they come to a sudden stop, and lose energy. the energy is then converted to 99% heat, and 1% x-rays
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9
Q

production of x-rays:
what happens to the heat produced? (what absorbs it and what dissipates it?)
where do the x-rays radiate? what is it absorbed by? how is a beam of radiation emitted?

A
  • the heat produced is absorbed by copper, and dissipated into the surrounding oil (facilitates heat removal)
  • the x-rays radiate in all directions, but most are absorbed by the leaded glass, which targets the x-ray towards the unleaded window, emitting a beam of radiation
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10
Q

what are the 2 types of x-ray spectra?

A
  1. continuous spectrum

2. characteristic spectrum

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11
Q

describe the continuous spectrum, i.e. brehmsstralung/braking radiation. what determines the amount of energy lost by the bombarding electron? what does this mean for the range of energy produced?

A
  • x-ray photons emitted by the rapid deceleration of bombarding electrons passing close to the nucleus of the tungsten atom is known as brehmsstralung or braking radiation
  • the amount of deceleration and degree of deflection determine the amount of energy lost by the electron
  • wide range or spectrum of photon energy is possible
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12
Q

describe the characteristic spectrum:
ionization or excitation leads to?
how do the electrons emit energy?

A
  • following ionization or excitation of tungsten atoms by bombarding electrons, the orbiting electrons rearrange themselves to return atom to neutral state.
  • electron jumps from one shell to another, resulting in emission of x-ray photons with specific energies.
  • loss of electrons from K and L shells
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13
Q

properties of x-rays?

  • how do they travel in free space?
  • what kind of beam formed?
  • travel through vacuum?
  • penetrate matter?
  • absorbed or scattered?
  • detectable by humans?
  • produce what kind of image?
  • causes what?
A
  • travel in straight lines
  • x-ray photons form divergent beam
  • can travel through vacuum
  • can penetrate matter
  • can be absorbed and scattered
  • not detectable by human senses
  • produces latent image on film emulsion
  • cause ionisation and biological damage
  • can cause certain sailts to fluoresce and emit light
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14
Q

define:

  • scattering
  • absorption
  • intensity
A
  1. random change in direction after hitting something
  2. deposition of energy in tissues
  3. number of xray photons in a defined area of beam
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15
Q

define:
- attenuation
- ionisation
- penetration

A
  1. reduction in intensity of beam due to scattering and absorption
  2. removal of electron from neutral atom to give -ve and +ve ions
  3. the ability of photons to pass through or into tissues/materials
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16
Q

what are the possible interactions of the x-ray beam?

A
  • completely scattered, with no loss of energy
  • absorbed, with total loss of energy
  • scattered, with some absorption and loss of energy
  • transmitted unchanged
17
Q

describe the mechanism of each interaction and state the 2 which are important in the x-ray energy range used in dentistry:

  • unmodified/rayleigh scattering
  • photoelectric effect
  • compton effect
  • pair production
A
  1. pure scatter
  2. pure absorption
  3. some absorption and loss of energy
  4. pure absorption

*photoelectric and compton effect are the 2 important ones

18
Q

photoelectric effect:

describe the process

A
  1. incoming xray photon interacts with inner shell (K) electron of tissue atom
  2. inner shell electron is ejected with energy into tissues, will undergo further interactions
  3. x-ray photon disappears after losing all its energy
  4. vacancy exists in inner electron shell, is filled by outer shell electrons dropping from one shell to another
  5. excess energy levels result in formation of very low energy radiation (light)
  6. atomic stability is achieved when the free electron is captured
19
Q

photoelectric effect: what happens to the high energy ejected photoelectron? what are these high energy electrons responsible for?

A

it behaves like the original xray photon, undergoing many similar interactions and ejecting other electrons as it passes through the tissues. they are responsible for the majority of the ionization interactions within tissue, and possible resulting damage caused by xrays

20
Q

compton effect: describe the process

A
  1. incoming xray photon interacts with loosely bound outer shell electron of tissue atom
  2. outer shell electron ejected (compton recoil electron), with some loss of energy from incoming photon (i.e. absorption). ejected electron undergoes ionizing interactions within tissues
  3. remainder of incoming photon energy is deflected or scattered from original path as a scattered photon
  4. scattered photon may undergo further compton reactions
  5. atomic stability is achieved by the capture of another free electron

ICS - RADIOLOGY (14 decks)

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