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RAD > Lecture 4: x-ray equipment & specifications > Flashcards

Lecture 4: x-ray equipment & specifications Flashcards

1
Q

What 3 things must intra-oral equipment be, to get it as close to the patient?

A
  • small
  • light
  • manoeuvrable
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2
Q

What kind of electrical supply do x-ray machines require?

A

A dual electrical supply (for high voltage and low voltage components)

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3
Q

What is the electrical supply of the filament (cathode)?

A
  • low voltage (12v)

- high current supply (2-3mm thick)

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4
Q

What is the electrical supply of the tube circuit (cathode to anode)?

A
  • high voltage (60-70kV)

- low current (very thick HT cables)

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5
Q

Where are the high and low voltage supplies provided from?

A

From the mains supply

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6
Q

How is the available mains supply converted to the required voltage?

A

Using transformers

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7
Q

What does a transformer consist of?

How does voltage change work?

A
  • It consists of two sets of coils (windings)
  • Voltage change through a transformer will depend on the ratio between the number of turns on the primary winding to the number of turns on the secondary winding
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8
Q

How are the windings arranged on a step-down transformer?

What is the ratio of coils?

A
  • There are less turns on the secondary winding than there are on the primary winding
  • The ratio is 4:1
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9
Q

How are the windings arranged on a step-up transformer?

What is the ratio of coils?

A
  • There are more turns on the secondary winding than there are on the primary winding
  • The ratio is 1:4
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10
Q

What does the single tank construction model mean?

Why is this method used?

A
  • All the electrical components are contained within the tube head itself
  • It is used to overcome the flexibility and versatility problem dental x-ray tubes have.
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11
Q

What is total filtration made from?

A
  • Inherent (3 components)

- added (1 component)

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12
Q

What are the inherent filtration components of an x-ray tube?

A
  • mineral oil
  • boro-silicate glass envelope
  • berryllium exit port
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13
Q

What are the added filtration components of an x-ray tube?

A

-aluminium filter outside exit port

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14
Q

What are the 3 functions of the mineral oil?

A

1- provide electrical insulation
2-removes heat from the glass envelope to the tube casing through convection
3- filters off low energy photons

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15
Q

What are the legal minimum requirements for filtration?

A
  • Below 70kV there must be 1.5mm aluminium

- At of above 70kV there must be 2.5 mm aluminium

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16
Q

What is mA?

A

milliamps. It is the tube current.
There is a direct relationship between mA and intensity of the beam.
Double the mA gives double the number of photons, this decreases exposure time and reduces the possibility of patient movement

17
Q

What will higher mA cause to the image?

A

It will produce higher contrast images due to a higher intensity of the x-ray beam

18
Q

What is the relationship between the xray beam and kV?

A

The intensity of the x-ray beam is proportional to kV²

Small changes in kV will therefore cause large changes in the intensity of the beam

19
Q

What happens to penetrating power of beam if kV increases?

What type of scatter is produced and how does it affect the image quality?

A

-Increasing kV will increase penetrating power of the beam so all areas allow the passage of an increased number of photons.

-The scatter produced by xray interactions will be in a forward direction
This forward scatter reduces both contrast and sharpness of the image

20
Q

How does high and low kV scatter differ?

A

They both have the same amount of scatter, but their angles differ.

21
Q

What happens to low kV scatter (60kV)?

A

It scatters a long way from its original path

it produces wide angle scatter

22
Q

What happens to high kV scatter (70kV)?

A

It scatters close to its original path

it produces narrow angle scatter

23
Q

What are 2 advantages of high kV (70kV)?

A
  • narrow scatter produced, this means there is lower radiation dose for patient
  • less exposure time, so less patient movement
24
Q

What are the 2 disadvantages of high kV (60kV)?

A
  • low contrast

- low sharpness

25
Q

Why is high kV used to produce x-rays?

A

Although it reduces contrast and sharpness, the dose reduction is so much less it is worth the low sharpness and contrast

26
Q

How much less is the x-ray dose from high kV (70kV) compared to low kV (60kV)?

A

It is 60% less

27
Q

What does the external collimator of an xray machine do?

A

It strictly limits the beam to the required area

28
Q

What does the cone of the xray machine do?

A

It maintains the correct FFD

It shows the extent of the beam at the patient’s skin surface

29
Q

What does the rectangular collimator of the xray machine do?

A
  • It reduces the dose to the patient by up to 50% by limiting the total amount of radiation that impacts the patient
  • improves contrast and sharpness of image
30
Q

The ionising radiation regulations require a record is kept of the radiation doses delivered to patients.
What information is required?

A
  • kV
  • mA
  • filtration
  • FFD
  • total area exposed
  • exposure time
31
Q

What is the purpose of an OPG machine?

A

To produce an image of the whole mandible and maxilla with a single exposure in one image

32
Q

What are the advantages of an OPG?

A
  • it allows easy assessment of the relationship between all of the teeth and other anatomy
  • it is less time consuming for the operators
  • it is less invasive than whole mouth PAs
33
Q

What are the disadvantages of an OPG?

A
  • The exposure takes around 15 seconds, this can be a long time for a patient to sit still and can result in movement
  • The level of fine detail is much lower than a PA
34
Q

What is the focal trough set at?

A

2-3

35
Q

What is the purpose of the focal trough?

A

To ensure the anterior teeth 3-3 are in focus

36
Q

How can the focal trough be adjusted?

A
  • moving the patient in and out of the machine by moving the chin rest
  • changing the position of the central pivot/fulcrum point
37
Q

What is the field of focus like on an OPG machine that has an adjustable focal trough?

A

they have a narrow field of focus

38
Q

What is the field of focus like on an OPG machine that does not have an adjustable focal trough?

A

they have a wide field of focus, to accommodate all bite types

RAD (7 decks)

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