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BDS3 RADIOLOGY > 1 - Physics basics > Flashcards

1 - Physics basics Flashcards

1
Q

What is a radiograph?

A

Image created by x-rays projected through an object and interacted with a receptor

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2
Q

What are radiographs used for?

A
  • visualising structures within the body, particularly mineralised structures
  • aids diagnosis, treatment planning and monitoring
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3
Q

What are the common intra-oral radiographs?

A
  • periapical
  • bitewing
  • occlusal
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4
Q

What are the common extra-oral radiographs?

A
  • panoramic
  • lateral cephalograms
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5
Q

What are properties of EM radiation?

A
  • no mass
  • no charge
  • travel at 3x10^8 m/s
  • travel in a vacuum
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6
Q

What is the EM spectrum?

A
  • 7 groups with different properties based on energy, wavelength and frequency
  • gamma ray, x-ray, UV, visible, infrared, microwave and radio
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7
Q

What is frequency?

A
  • how many times a waves shape repeats per unit time
  • measured in hertz
  • 1Hz = one cycle per second
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8
Q

What is wavelength?

A
  • distance over which the wave’s shape repeats
  • measured in metres
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9
Q

How is energy proportional to frequency?

A
  • directly proportional
  • higher frequency = higher energy
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10
Q

How are frequency and wavelength related?

A

Higher frequency = shorter wavelength

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11
Q

What are photons?

A
  • “packets of energy”
  • measured in electron volts, eV
  • 1 eV = energy gained by an electron moving across a potential difference of 1 volt
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12
Q

What are the different types of x-rays?

A
  • photon energy varies between 124eV - 124keV
  • hard x-rays (>5keV)
  • soft x-rays
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13
Q

Which type of x-rays are used in medical imaging?

A

Hard x-rays >5keV

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14
Q

How are x-rays formed?

A
  • man made
  • electrons fired at atoms at high speed
  • on collision the kinetic energy is converted to EM and heat
  • x-ray photons are aimed at subject
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15
Q

What is an atom made up of?

A
  • protons
  • neutrons
  • electrons
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16
Q

What is the atomic number?

A
  • Z
  • number of protons
  • unique to each element
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17
Q

What is the mass number?

A
  • A
  • number of protons and neutrons
18
Q

What are the atomic and mass number of tungsten?

A

Z = 74
A = 184

19
Q

What is the ground state of an atom?

A

When number of electrons = protons

20
Q

What is ionisation?

A

Removing or adding of electrons to change the charge of an atom

21
Q

What is the innermost shell of an electron called?

A

K

22
Q

What is the maximum number of electrons in a K shell?

A

2

23
Q

What is the maximum number of electrons in a L shell?

A

8

24
Q

What is the maximum number of electrons in a M shell?

A

18

25
Q

What is the maximum number of electrons in a N shell?

A

32

26
Q

How do you calculate the maximum number of electrons in a shell?

A

2n^2

27
Q

How are electrons held in the shells?

A
  • negative charge of electrons attracted to positive nucleus
  • to remove electrons, binding energy must be broken
28
Q

What is binding energy?

A
  • energy required to exceed the electrostatic force of the attraction of the electrons to the nucleus
  • closer the electron is to the nucleus, the higher the binding energy
29
Q

What is the K shell binding energy of a tungsten atom?

A

69.5keV

30
Q

How does electrons moving between shells release energy?

A
  • an electron moving to a more outer shell releases binding energy
  • energy released is equal to difference in energy shells
31
Q

What is current?

A
  • flow of electric charge
  • movement of electrons
  • measured in amps, A
32
Q

What is direct current?

A

Constant unidirectional flow of electrons (eg batteries)

33
Q

What is alternating current?

A
  • electron flow repeatedly reverse direction (eg mains)
  • number of complete cycles per unit time = frequency
  • main frequency = 50Hz
34
Q

What type of current is used in x-ray machines?

A
  • DC
  • powered by AC source, therefore must be rectified
35
Q

What is voltage?

A
  • difference in electrical potential between 2 points
  • how forcefully a charge is push through an electrical field
  • measured in volts, V
36
Q

What voltage is required in an x-ray machine?

A
  • 2 different voltages
  • one as high as 10s of thousands of volts
  • one around 10V
37
Q

What is a transformer?

A

Alters voltage and current from one circuit to another

38
Q

What transformers are present in an x-ray machine?

A
  • step up transformer, mains to X-ray tube (cathode/anode)
  • step down transformer, main to filament
39
Q

How do x-ray beams travel?

A

Photons travel in straight lines but diverge from the source

40
Q

What is the inverse square law?

A
  • intensity of x-ray beam is inversely proportional to square of the distance between the source and point of measurement
  • “double the distance, quarter the dose”

BDS3 RADIOLOGY (9 decks)

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