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BDS3 CDS Radiology > X-Ray Production & Equipment > Flashcards

X-Ray Production & Equipment Flashcards

1
Q

What are the 3 components of the X-ray tube ?

A

Anode, cathode, glass envelope.

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2
Q

What are the 2 components of the cathode ?

A

Filament and focussing cup.

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3
Q

What are the 2 components of anode ?

A

Target and heat dissipating block.

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4
Q

What is the filament ?

A

Coiled wire which low voltage and high current is passed through it to heat to 2200 degrees causing electrons to be released from the wire by thermionic emission causing a cloud of electrons to form around the wire.

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5
Q

What is the filament made out of ?

A

Tungsten.

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6
Q

Why is the filament made out of tungsten ?

A

Withstands high heat.
High atomic number - large amount of electrons to protons - 74.

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7
Q

What is the focussing cup ?

A

Metal plate around filament which is negatively charged and repells the electrons which is shaped to focus electrons at a point on the anode.

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8
Q

What is the focussing cup made of ?

A

Molybdenum.

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9
Q

What are the properties of molybdenum which makes it appropriate to be the focussing cup’s material ?

A

Poor thermionic emitter.
Withstands high temperatures.

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10
Q

Explain the relationship between the cathode and anode.

A

Electrons from filament are repelled and attracted to anode due to high potential difference created by electric current between cathode and anode.
Electrons accelerate at high speed causing increased kinetic energy on collision with anode.

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11
Q

What is the anode ?

A

Metal block which is a target for electrons accelerating from filament which produces photons and heat.

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12
Q

What is the anode made of ?

A

Tungsten - as it produces x-ray photons.

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13
Q

Define focal spot.

A

Target where photons (x-rays) are produced i.e. x-ray source.

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14
Q

What is the function of the heat dissipating block ?

A

Prevents over heating by causing heat dissipation via thermal conduction.

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15
Q

What is the heat dissipating block made of ? And why ?

A

Copper - good thermal conduction abilities and can withstand high temperatures.

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16
Q

What is the 2 important reasons for focal spot angulation ?

A

Increases actual surface area where electrons impact i.e. increases heat tolerance of anode.
Decreases apparent surface area from where x-ray beam is emitted i.e. reduce penumbra effect.

17
Q

Explain the penumbra effect.

A

Blurring of image due to focal point not being at one single point - minimised by shrinking focal spot area.

18
Q

What is the glass envelope made of ?

A

Lead glass - to absorb and maintain xrays only travelling in desired direction.

19
Q

What is the 2 functions of the glass envelope ?

A

Ensure electrons are only travelling in desired direction.
Vacuum to ensure electrons are unhindered by gas molecules.

20
Q

What are the 5 components to the tube head ?

A

Xray tube.
Metal shielding.
Aluminium filtration.
Oil.
Spacer cone.

21
Q

What is the function of filtration ?

A

Removes lower energy non-diagnostic x-rays which would ultimately be absorbed by patient tissues and would not contribute to the x-ray image produced.

22
Q

What material is used for filtration in tube head ?

A

Aluminium.

23
Q

What is the minimum thickness for aluminium filtration in tube head ?

A

1.5mm.

24
Q

What is the normal voltage of x-ray machine ?

A

60-70kV.

25
Q

What is the function of the spacer cone ?

A

Maintains reproducible and accurate distance between focal spot and patient - sometimes known as focus to skin distance (FSD).

26
Q

What is the minimum length of spacer cone required in tube head ?

A

200mm for >60kV.

27
Q

What are the 3 fates of electrons ?

A

Attenuated by lead shielding.
Attenuated by aluminium filtration.
Exit tube head and form x-ray beam.

28
Q

What is a collimator ?

A

Diaphragm attached to end of spacer.

29
Q

What is the collimator made out of ?

A

Lead.

30
Q

What is the function of the collimator ?

A

Reduced patient dose by matching x-ray beam’s size to size of the receptor.

31
Q

What cross-section of collimator is preferred ?

A

Rectangular.

32
Q

Why is a collimator highly recommended ?

A

Reduced irradiation by 50%.
Increases contrast of image by reduced photon scatter.

33
Q

What dimensions should the collimator be on x-ray tube head ?

A

<45mm x 35mm.

34
Q

What are the two consequences of bombarding the target with electrons ?

A

Heat production.
X-ray production.

35
Q

Define the consequence of continuous radiation ?

A

Bombarding electron passes close to target nucleus.
Causes it to deflect and decelerate causing loss in kinetic energy. Producing continuous range of x-ray photon energies.

BDS3 CDS Radiology (7 decks)

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