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BDS3 Radiology > Physic Basics > Flashcards

Physic Basics Flashcards

1
Q

what are radiographs

A

images produced by x-rays passing through an object and interacting with a receptor

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2
Q

what do the different shades of grey on a radiograph correspond to

A

how dense the tissue it has passed through is

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3
Q

what are the common intraoral radiographs

A

periapical
bitewing
occlusal

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4
Q

what are the common extraoral radiographs

A

panoramic
lateral cephalograms

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5
Q

what are x-rays a form of

A

electromagnetic radiation

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6
Q

what is electromagnetic radiation

A

flow of energy created by simultaneously varying electrical and magnetic fields

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7
Q

what are the properties of electromagnetic radiation

A

no mass
no charge
always travels at speed of light
can travel in vacuum

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8
Q

how do you calculate wave length

A

the length of the cycle divided by how many sine waves there are

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9
Q

how do you calculate frequency

A

cycles divided by the amount of time its taken

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10
Q

what is frequency and how is it measured

A

how many times the waves shape repeats per unit time and measured in hertz

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11
Q

what is wavelength and how is it measured

A

the distance over which the wave’s shape repeats measured in metres

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12
Q

what is the calculation of speed

A

speed = frequency x wavelength

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13
Q

how does energy move in electromagnetic radiation

A

via photons

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14
Q

what are the types of x-ray

A

hard and soft

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15
Q

what are hard x-rays

A

able to penetrate through human tissues

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16
Q

what are soft x-rays

A

easily absorbed

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17
Q

what separates x-rays from gamma rays

A

x-rays are man made

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18
Q

what is ionisation

A

displacement of electrons from atoms

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19
Q

how are x-rays produced

A

electrons are fired at atoms at very high speeds and when they collide the kinetic energy of the electrons is converted to electromagnetic radiation and heat - the x-ray photons released are aimed at the subject

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20
Q

what do atoms consist of

A

protons
neutrons
electrons

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21
Q

what is the relative charge, mass and location of a neutron

A

charge - 0
mass - 1
nucleus

22
Q

what is the relative charge, mass and location of a proton

A

charge - +1
mass - 1
nucleus

23
Q

what is the relative charge,, mass and location of an electron

A

charge - -1
mass - 0
shells

24
Q

what does the atomic number relate to

A

number of protons

25
Q

what does the mass number relate to

A

the number of protons and neutrons

26
Q

what is the most inner shell in an atom called

A

K - then proceeds through the alphabet from K

27
Q

how do you calculate the maximum number of electrons a shell can hold

A

2 x the shell number squared

28
Q

how are electrons held within their shell

A

electrostatic force

29
Q

what is the binding energy

A

the energy required to exceed electrostatic force (eg remove an electron from its shell)

30
Q

where is the electrostatic force greatest

A

the shells closest to the nucleus
when there is a higher atomic number (aka more protons)

31
Q

how does an electron move to a more outer shell

A

energy that equals the difference in the binding energies of the two shells

32
Q

how does an electron move to an inner shell

A

energy is released

33
Q

what two values do you need to be able to calculate the energy needed to move an electron

A

binding energy of atom A
binding energy of atom B

34
Q

what are the x-ray equipments for dental x-ray units made up of

A

tubehead
collimator
positioning arm
control panel
circuitry

35
Q

what is current

A

the flow of electric charge usually by movement of electrons - measured in amps

36
Q

what are the two forms of current direction

A

direct current - constant unidirectional flow
alternating current - flow repeatedly reverses direction

37
Q

what is an alternating current cycle

A

the reverse and reverse back time (eg mains electricity)

38
Q

what does x-ray require the current to do

A

be flowing in one direction

39
Q

since x-rays are powered by mains electricity which is AC but x-rays require DC how does this come about

A

X-ray units have generators that modify the AC so it mimics a constant DC

40
Q

what is rectification

A

X-ray units have generators that modify the AC so it mimics a constant DC

41
Q

what is voltage

A

difference between negatively charged points in one place and positive in another
aka potential difference

42
Q

what voltages does x-ray units require

A

high as 10s of thousands of volts
one as low as 10 volts

43
Q

how do we get two difference voltage values from mains (240) voltage

A

through the use of transformers

44
Q

what are transformers

A

alter the voltage and current from one circuit to another

45
Q

how many transformers are required for an x-ray unit

A

mains - x-ray tube (cathod-anode)
mains - filament

46
Q

what two transformers are there

A

step-up transformer which increases the voltage
step down transformer which dcreases the voltage

47
Q

what is x-ray beam made up of

A

millions of photons directed in a same general direction

48
Q

what is x-ray beam made up of

A

millions of photons directed in a same general direction
but they diverge away from x-ray source and do not travel parallel

49
Q

what is the x-ray beam intensity

A

quantity of photon energy passing through a cross-sectional area of the beam per unit time

50
Q

how can you increase intensity of an x-ray

A

increasing number or energy of photons

51
Q

how does divergence of x-ray beam affect the dose given

A

the further away, dose decreases

52
Q

what is the inverse square law

A

the intensity of the x-ray beam is inversely proportional to the square of the distance between the x-ray source and the point of measurement (doubling distance = quarter dose)

BDS3 Radiology (9 decks)

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