X-Ray Imaging

Question 1

What is the purpose of the vacuum glass tube?

Answer 1

To allow electrons to travel unimpeded.

Question 2

What is the purpose of the rotating anode?

Answer 2

• To spread the heat over a larger area

- To emit x-rays when hit

Question 3

What is the purpose of the filament lamp?

Answer 3

To produce electrons by thermionic emission.

Question 4

What is the purpose of the lead casing?

Answer 4

To prevent x-rays escaping in unwanted directions.

Question 5

Why does the X-ray spectrum have a maximum photon energy and state the circumstances in which a photon of energy is produced.

Answer 5

• Maximum photon energy is determined by an accelerating voltage.
• Corresponds to all electron kinetic energy.
• Converted to a single photon
• Only one electron can contribute to the production of an X-ray photon

Question 6

Explain why the X-ray spectrum has lines?

Answer 6

• Line spectra which is characteristic of the target material
• The frequencies correspond to allowed transitions of inner electrons of target atoms
• Produced by de-excitation of excited electrons of target atoms

Question 7

State the steps taken to reduce the dose of X-rays a patient will receive.

Answer 7

• Use an image intensifier screen
• Low intensity X-rays can be used can be used as the image is enhanced by conversion of X-ray photons into light photons by fluorescent materials

Question 8

Define the half value thickness of a material.

Answer 8

The distance an X-ray travels through a material by which point it’s intensity has been reduced to 50%

Question 9

Define the linear attenuation coefficient for a material.

Answer 9

The fraction of X-rays removed per unit thickness of the material.

Question 10

Explain why the anode is rotated.

Answer 10

• Heat is spread over a greater area

- Thus allowing more energetic X-rays to be produced

Question 11

Explain why the anode is bevelled.

Answer 11

• It gives a larger target area

- But a small source area (to produce a sharp image)