Introduction to RS

Question 1

Sketch a typical DR x-ray spectrum and explain how x-rays are generated? (5 marks)

Answer 1

• Characteristic radiation, discrete energy levels, electron knocks electron out of inner shell, electron drops from outer shell and releases x-ray.
• Continous Bremstrhalung, electron deflected by nucleus, via electronstatic interaction, releases energy.

Question 2

What is the anode made of and why? How efficient is it? (5 marks)

Answer 2

Usually tungsten, high Z and density to increase the stopping efficiency, high melting point so it does not melt. Very poor efficiency 99.9% energy goes to heat.

Question 3

Sketch an x-ray tube. (10 marks)

Answer 3

Sealed evacuated glass envelope.
Lead sheilding.
Berylium window.
HT cables.
Cathode filament (possibly two).
Focusing cup.
Anode and Cu stem.
Rotor and stator.
Surrounding oil.

Question 4

Sketch a Light Beam Diaphragm. (3 marks)

Answer 4

Filtration (Al) plus collimators plus light and mirror for showing the field.

Question 5

During fluoro, when considering the design of the fluoro unit, how might doses be reduced? (1 mark)

Answer 5

Use of a high speed switching grid to pulse the exposures can reduce the exposure as the beam is not constantly emitting radiation.

Question 6

Why is a small focal spot desirable? (1 mark)

Answer 6

It reduced penumbra, there-by increasing the resolution.

Question 7

What is a tube rating chart for? (1 mark)

Answer 7

It gives information regarding the maximal mAs allowed in a certain time period for the kVp set. This is to stop damaging the tube, by pitting the anode etc.