Lecture 8

Question 1

What factors will influence the amount of attenuation that will occur in a tissue?

Answer 1

1. Tissue thickness
2. Density of the tissue
3. Beam energy kV - PE (photoelectric effect)
4. Atomic number of the tissue

Question 2

What are the two method of attenuation that can occur?

Answer 2

1. Absorption (photoelectric effect)
2. Scatter (compton scatter)

Question 3

What is the significance of the photoelectric effect?

Answer 3

1. Results in an increased patient dose
2. Results in decreased beam penetration
3. Increased image contrast

Question 4

What are the two factors that influence the photoelectric effect?

Answer 4

1. Beam energy (kV)
2. Tissue atomic number

Question 5

What causes comptom scatter?

Answer 5

Interactions with the outer shell electrons

Question 6

Why is comptom scatter significant?

Answer 6

• Results in increased scatter production
• Decreased film quality
• Increased worker dose

Question 7

What are the factors that will influence compton scatter?

Answer 7

1. Tissue thickness (greater thickness increases the likelyhood of outer shell interactions and hence increases Compton scatter)
2. Tissue Density (means the atoms are closer together and hence Compton scatter increases)
3. Beam energy (kV) (greater beam energy increases reactions with outer shell electrons)