Scatter

Question 1

What is secondary radiation?

Answer 1

· Radiation that is scattered or created as a result of the interaction between the primary beam and matter
· Travels in all directions and has less energy than primary beam

Question 2

What are 3 types of interactions of radiation and matter in the diagnostic range?

Answer 2

· Coherent Scattering
· Compton Effect
· Photoelectric Effect

Question 3

Coherent Scattering

Answer 3

an incident photon interacts with matter and excites an atom, causing it to vibrate. The vibration causes the photon to scatter

Question 4

Compton Effect

Answer 4

impact with outer orbital electron results in a lower energy photon with a new direction; majority of radiation interactions in the body; an incident photon interacts with an orbital electron, transferring some of its energy to that electron. The electron is ejected, and the photon is scattered.

Question 5

Photoelectric Effect

Answer 5

photon collides with inner orbital electron causing outer orbital electron to change shells, creating characteristic radiation

Question 6

What are the controlling factors of scatter?

Answer 6

· Volume of tissue irradiated: ↑ volume = ↑ interactions = ↑ scatter
· Thickness of subject
· kVp: ↑kVp = ↑ scatter
· Higher energy scatter radiation is better able to escape subject without being reabsorbed
· Field size: ↑ beam size = ↑ interactions = ↑ scatter
· mAs: ↑ photons = ↑ interactions = ↑ scatter

Question 7

What’s the visual effect of scatter?

Answer 7

· Exposes (fogs) radiograph
· Decreases contrast
· Reduces visibility of detail

Question 8

How to reduce scatter?

Answer 8

· Grid device – placed between patient and film to absorb scattering
· Air gap - ↑ OID = ↓ scatter intensity at film
· Minimize Field Size
· Decrease kVp