X ray interaction with matter

Question 1

What 3 ways can photons in a diagnostic x-ray beam interact with matter?

Answer 1

• tramsission
• absorption
• scatter

Question 2

In reference to x-rays interacting with matter, what is meant by transmission?

Answer 2

photons pass through matter unchanged

Question 3

In reference to x-rays interacting with matter, what is meant by absorption?

Answer 3

• energy fully deposited into tissue
• photon cease to exist

Question 4

In reference to x-rays interacting with matter, what is meant by scatter?

Answer 4

• photon deflected by tissue
• partial deposition of energy into tissue
• photon continues in new direction to be transmitted, absorbed or scattered again

Question 5

What is attenuation?

Answer 5

• when x-rays are scattered or/and absorbed
• reduces intensity of x-ray beam

Question 6

what is the photoelectric effect?

Answer 6

• photon in x-ray beam interacts with inner shell electron in subject
• resulting in absorption of photon and creation of photoelectron
• occurs when energy of incoming photon is equal to or just greater than binding energy of inner shell electron

Question 7

How does absorption by the photoelectric effect affect a radiographic image

Answer 7

• prevents x-ray photons reaching the receptor
• therefore leads to a lighter area on the radiographic image

Question 8

Describe the Compton effect

Answer 8

photon in x-ray beam interacts with outer shell electron in subject, resulting in partial absorption and scattering of photon
- occurs when energy of incoming photon is much greater than binding energy of electron
- some photon energy transferred to electron to overcome binding energy and provide kinetic energy
- electron ejected - becomes recoil electron
- photon loses energy and changes direction

Question 9

Give 2 ways in which the photoelectric effect differs from the Compton effect

Answer 9

• deposition of all x-ray photon into tissue rather than some
• necessary for image formation, whereas Compton effect does not contribute usefully to image

Question 10

What is the rough effective dose of a periapical or bitewing radiograph?

Answer 10

4 uSv

Question 11

what is the effective dose of a maxillary occlusal radiograph?

Answer 11

8 uSv

Question 12

what is the effective dose of a panoramic radiograph?

Answer 12

20 uSv

Question 13

what is the effective dose of a lateral cephalogram?

Answer 13

3 uSv