lesson 6

Question 1

refers to the height of the lead strips
divided by the

Answer 1

GRID RATIO

Question 2

formula 1

Answer 2

GR = h/D

h= height
D= thickness

Question 3

refers to the number of grid strips or grid lines per inch or per centimeter.

Answer 3

GRID FREQUENCY

Question 4

formula 2

Answer 4

GF = 10,000 µm/cm /
(T + D) µm/line pair

T= lead strips thickness
D = interspace thickness

Question 5

Advantages of Moving Grids:

Answer 5

1. No grid lines ( motion blurs out lead strip shadows)
2. Reduces secondary or scatter radiation
3. Radiographic contrast is improved

Question 6

Disadvantages of Grid:

Answer 6

1. Vibration potential cause by moving grid. 2. Limit minimum exposure time
2. Increases patient dose
3. Lateral decentering from motion
4. Up to 20% loss of primary radiation
5. Stationary grid makes interspace gaps darker for
   same amount of radiation
6. Increased OID, more geometric unsharpness
7. Misalignment of grid and image receptor
8. Can cause underexposure
9. Mechanical problems
10. Expensive