BDS3 X-ray interaction with matter

Question 1

What direction do higher energy photons scatter?

Answer 1

Forward

Question 2

What direction do lower energy photons scatter?

Answer 2

Back

Question 3

Why does the controlled area need to completely surround the patient?

Answer 3

Scatter

Question 4

When does the compton effect occur?

Answer 4

Partial absorption and scatter
When the energy of the incoming photon is much greater than the bonding energy of the electron

Question 5

When does the photoelectric effect occur?

Answer 5

When the energy of the incoming photon is equal to or just greater than the binding energy of the inner shell electron

Question 6

What is the photoelectric effect?

Answer 6

Complete absorption of the x-ray photon

Question 7

What is the compton effect?

Answer 7

Partial absorption and scatter of phton

Question 8

What is the effect of FORWARD scatter on the radiographic image?

Answer 8

Photons scattered obliquely forward might reach receptor but interact with wrong area.
Causes darkening of image in the wrong place
Results in fogging of image - reduces image contrast/quality.

Question 9

What is the effect of backwards scatter on radiographic image?

Answer 9

Does not affect the image

Question 10

How do you reduce scatter and what is it?

Answer 10

Collimation - putting lead in the x-ray tube to restrict the x-ray beam to the area of interest.

Question 11

What are the 5 things that collimation does?

Answer 11

decreases:
SA irradiated
Volume of irradiated tissue
Number of scattered photons produced in tissue
Scattered photons interacting with receptor
Loss of contrast on radiographic image

Question 12

What is the negative effect of lowering kV on an X-ray unit?

Answer 12

Increased dose absorbed by patient
Lower kV makes the x-rays less penetrating.

Question 13

What is the negative effect of RAISING the kV on the X-ray unit?

Answer 13

Decreased contrast between tissues with different Z