5. Radiographic grids and anti scatter grids Flashcards
What is Compton scatter?
When the primary beam interacts with electrons in the body and causes photons to change position
What would a higher grid ratio do to scatter?
It would decrease the scatter reaching the IR
How much scatter radiation do grids reduce to the IR
85-97%
What would increasing the height and decreasing the width demonstrate in a grid?
A higher grid ratio
What is grid frequency? What is the unit?
It is the # of grid strips or lines per cm (pb)-there’s 25-45 grid strips/cm
What is the contrast improvement factor? What is it usually stated with?
How much the grid increases the contrast on average, stated with either kVp, patient thickness or field size
What 3 factors does the contrast improvement factor depend on?
- kVp
- Patient thickness
- Field size
What is the bucky factor?
It tells us how much of an increase in technique will be required for a particular exposure compared to a non grid exposure.
What prime factor do we have to change when using grids?
mAs
What is the grid ratio when there’s no grid?
1
What is the grid ratio when using a 5:1 grid
2
What is the grid ratio when using a 6:1 grid
3
What is the grid ratio when using a 8:1 grid?
4
What is the grid ratio when using a 12:1 grid?
5
What is the grid ratio when using a 16:1 grid?
6
What are the 4 grid types?
- Linear parallel
- Crossed
- Linear focused
- Crossed focused
What are the pros and cons of linear focused grids?
Pros: loosing less good radiation
Cons: Have to centre in the middle of IR
What are the pros and cons of linear parallel grids?
Pros: Can center anywhere on IR
Cons: Loosing more good radiation at the peripheries
What is grid cut off?
What is it caused by?
An undesirable absorption of primary x-ray beams by grid strips, which prevents the useful x-rays from reaching the image receptor. Caused by grid errors or not being in detent
What are the benefits to grid line suppression software?
You only have to use a low grid ratio, and do not have to use a higher technique
