X-Ray Interaction with Matter

Question 1

How are radiographs produced?

Answer 1

• If we are going to produce a radiographic image we have to have a source of x-rays
• X-rays are directed at the patient
• When x-rays reach the patient there will be some kind of interaction to get an image
  Needs to be variable interaction depending on the tissues
• So the x-ray beam when it comes out of the patient will not have the same energy levels of x-ray photons as it had when it went in
• It is this variation throughout the beam in the number of x-ray photons and their energy and how that reaches the image receptor that will produce the radiographic appearance of the other tissues

Question 2

What are the possible outcomes of x-ray photos traversing tissues? (4)

Answer 2

The may:

• Pass through unaltered
• Change direction with no energy loss (scattered)
• Change direction loosing energy (scatter and absorption)
• Be stopped, depositing all energy within tissues (absorption)

Question 3

What is attenuation? (3)

Answer 3

• Reduction in number of photons (X-rays) within beam
• Occurs as a result of absorption and scatter)
• Affects the number of photons reaching image receptor (this impacts on what the image actually looks like)

Question 4

If all photons reach the film, what effect does this photon absorption have on the image?

Answer 4

Image looks black

Question 5

If there is partial attenuation, what effect does this photon absorption have on the image?

Answer 5

Image looks grey - this is what gives us detail and allows us to pick up pathology

Question 6

If there is complete attenuation, what effect does this photon absorption have on the image?

Answer 6

Image looks white - material which has completely absorbed the photon energy

Question 7

What is the structure of an atom? (4)

Answer 7

• Central nucleus
• Protons (positive charge)
• Neutrons (no charge)
• Orbiting electrons (negative charge)

Question 8

What does the atomic number equal?

Answer 8

• Number of protons (equivalent to the no. of electrons in a neutral atom)

Question 9

What does the atomic mass equal?

Answer 9

Equals the number of protons + the number of neutrons

Question 10

Where are electrons found in an atom?

Answer 10

• Electrons orbit the nucleus in shells (K,L,M…)

Question 11

Where is the maximum number of electrons in orbit greater?

Answer 11

• Greater in outer shells (2xn^2)

Question 12

Which electron shell has the highest binding energy?

Answer 12

K shells (requires more energy to eject electron from shell) 
- Outer shells have low binding energies

Question 13

How are electrons kept in their normal shells?

Answer 13

• The binding energy

Question 14

What are the 2 principle interactions of diagnostic x-rays in tissues that we need to know about?

Answer 14

• Photoelectric effect - absorption

- Compton effect - scatter, and absorption

Question 15

Just read the rest of the lecture

Answer 15

Too hard to make flashcards for