X-Ray Production & Equipment

Question 1

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

Answer 1

Anode, cathode, glass envelope.

Question 2

What are the 2 components of the cathode ?

Answer 2

Filament and focussing cup.

Question 3

What are the 2 components of anode ?

Answer 3

Target and heat dissipating block.

Question 4

What is the filament ?

Answer 4

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.

Question 5

What is the filament made out of ?

Answer 5

Tungsten.

Question 6

Why is the filament made out of tungsten ?

Answer 6

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

Question 7

What is the focussing cup ?

Answer 7

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

Question 8

What is the focussing cup made of ?

Answer 8

Molybdenum.

Question 9

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

Answer 9

Poor thermionic emitter.
Withstands high temperatures.

Question 10

Explain the relationship between the cathode and anode.

Answer 10

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.

Question 11

What is the anode ?

Answer 11

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

Question 12

What is the anode made of ?

Answer 12

Tungsten - as it produces x-ray photons.

Question 13

Define focal spot.

Answer 13

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

Question 14

What is the function of the heat dissipating block ?

Answer 14

Prevents over heating by causing heat dissipation via thermal conduction.

Question 15

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

Answer 15

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

Question 16

What is the 2 important reasons for focal spot angulation ?

Answer 16

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.

Question 17

Explain the penumbra effect.

Answer 17

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

Question 18

What is the glass envelope made of ?

Answer 18

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

Question 19

What is the 2 functions of the glass envelope ?

Answer 19

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

Question 20

What are the 5 components to the tube head ?

Answer 20

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

Question 21

What is the function of filtration ?

Answer 21

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.

Question 22

What material is used for filtration in tube head ?

Answer 22

Aluminium.

Question 23

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

Answer 23

1.5mm.

Question 24

What is the normal voltage of x-ray machine ?

Answer 24

60-70kV.

Question 25

What is the function of the spacer cone ?

Answer 25

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

Question 26

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

Answer 26

200mm for >60kV.

Question 27

What are the 3 fates of electrons ?

Answer 27

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

Question 28

What is a collimator ?

Answer 28

Diaphragm attached to end of spacer.

Question 29

What is the collimator made out of ?

Answer 29

Lead.

Question 30

What is the function of the collimator ?

Answer 30

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

Question 31

What cross-section of collimator is preferred ?

Answer 31

Rectangular.

Question 32

Why is a collimator highly recommended ?

Answer 32

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

Question 33

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

Answer 33

<45mm x 35mm.

Question 34

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

Answer 34

Heat production. X-ray production.

Question 35

Define the consequence of continuous radiation ?

Answer 35

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.