Basics 2

Question 1

What is Classical/Coherent interaction with matter?

Answer 1

When X ray hits outer electron and bounces off

• Very Low energy= No ionization or significant contribution to image
• Minimal dose to patient

Question 2

What is Compton Scatter?

Answer 2

X ray hits outer electrons and knocks them loose (ionization)–> photo released

• Increases dose to patient
• Increases Noise/Fog in the image

Question 3

What determines the probability of Compton Scatter?

Answer 3

• Depends on the Density of the material

- NOT dependent on the Z

Question 4

What is the probability of Photoelectric Effect occuring?

Answer 4

• Occurs when the incident energy is close (but higher) than the inner shell binding energy
• Equals 1/Incident Energy Photon Cubed (Larger Energy= less PE Effect)
• Equals Z Cubed

Question 5

Why is Photoelectric effect so important?

Answer 5

Helps develop contrast in images

Question 6

What has the highest atomic number in the body?

Answer 6

Calcium

Question 7

What is the K edge?

Answer 7

Where the most Photoelectric effects will occur

K edge should be picked approximately 1/3 to 1/2 the KVP

Question 8

How do you increase absorption?

Answer 8

Increase the Photoelectric effect

• KVP closer to K Edge (Energy of Beam)
• Higher Z (atomic number)
• More Tissue Density

Question 9

What is linear attenuation?

Answer 9

Fraction of attenuated photons per unit thickness

-Different for ice, water and vapor

Question 10

What is mass attenuation?

Answer 10

Fraction of attenuated photons per mass (g)

-Same for Ice, water an vapor

Question 11

How do linear attenuation and HVL relate?

Answer 11

They are inversely related

• Increased Energy= Increased HVL= Lower LAC
• Increased Density= Lower HVL=Higher LAC