Interactions of X Rays with matter

Question 1

What is attenuation?

Answer 1

Is the reduction of the intensity of the primary beam as it passes through matter

Question 2

What is a) photoelectric effect and b) compton scatter?

Answer 2

They are the types of secondary radiation

a) the primary beam absorbed by the animal/equipment
b) parts of the primary beam that has enough energy to be deflected/scattered. It’s hazardous

Question 3

What does the degree of absorption of x ray photons depends on?

Answer 3

• The atomic number (Z) of a tissue
• SG of tissue
• Thickness of tissue

Question 4

Explain PE absorption in detail

Answer 4

• Low energy x ray photons are absorbed by the matter so they don’t reach the image receptor
• More PE at lower kVp levels
• PE effect adds to radiation dose of animal
• Good radiographic contrast at lower kVp

Question 5

Explain CS in detail

Answer 5

• Moves in random directions
• Can’t be seen, hazard
• Higher kVp inc. CS, reduces radiographic contrast

Question 6

Explain what a light beam diaphragm (LBD) is

Answer 6

An aluminum box placed beneath the exit window of the x ray tube to mimic primary beam
It limits the size of the area of irradiation and reduce the CS produced by patient

Question 7

What is LBD collimation?

Answer 7

Limit the primary beam within the borders of the image receptor, aim to have all images 100% collimated (reduces CS and improves image quality)

Question 8

What does kVp stand for? what happens if it is increased?

Answer 8

Kilovolt peak.

Inc in this will result in more CS produced by patient

Question 9

What is a compression band and what are they used for?

Answer 9

Reduces the volume of tissue resulting in reduced scatter by patient
ie: velcro band placed over abdomen to reduce the amount of tissue being radiographed

Question 10

What are grids used for?

Answer 10

They control the CS reaching the image receptor

• allows primary beam to pass through unaffected
• absorb secondary scattered radiation

Question 11

What are the types of stationary grids?

Answer 11

-Parallel
Composed of strips of lead
-Focussed
Lead strips are angled from the centre

Question 12

What is grid factor?

Answer 12

When the grid absorbs some of the primary beam so more exposure is needed
Use manufacturer guidelines/inc mAs by 20/30%

Question 13

What is a type of moving grid?

Answer 13

Potter-bucky grid

a mechanism that allows grid to move during exposure to blur grid lines

Question 14

When and how should grids be used?

Answer 14

When thickness of animal over 10cm
Between animal and image receptor
Use correct SID
Line up grid with centre of primary beam 
Inc exposure factors