Unit 27 - Medical Physics

Question 1

What does collimated mean?

Answer 1

Collimated Rays are parallel and have no reduction in intensity

Question 2

What does attenuate mean?

Answer 2

To weaken the value, amount or degree. To Absorb

Question 3

What is simple scatter?

Answer 3

• X-ray is deflected by an electron
• Happens a 1-20 KeV

Question 4

What is the photoelectric effect?

Answer 4

• X-ray gives an electron enough energy to leave the atom
• Happens at 30-100 KeV

Question 5

What is Compton scattering?

Answer 5

• X-ray photon gives enough energy to ionise an electron and extra energy gives out a reduced frequency X-ray
• Happens at 0.5-5 MeV

Question 6

What is pair production?

Answer 6

• The energy from X-ray changes into matter (Electron + Positron)
• Happens when energy is >1.02 MeV

Question 7

What is attenuation dependent on?

Answer 7

• Energy of photon
• Thickness of substance
• Type of substance

Question 8

What substance gives off visible light when hit by x-rays?

Answer 8

Sodium iodide

Question 9

How does a PET scanner work?

Answer 9

1) Radio isotopes that emit positrons are injected into the blood in a tracer (sugar to find cancer cells)
2) The annihilation of an electron and positron is used to produce a gamma ray pair
3) They are detected and an internal image of the body is produced

Question 10

What is the range for ultra-sound?

Answer 10

Sound with frequency higher than 20,000Hz

Question 11

What is the range for Infrasound?

Answer 11

Sounds with frequencies below 20Hz

Question 12

What is a coupling medium?

Answer 12

Used to ensure most of the sound produced is transmitted into the body, gel in ultrasound.