Exposure Calculations Look at each question and calculate the new exposure factors Do not use a calculator The cards with red text provide examples of the equations that should be used

If the mA is 60 and the time is 0.5 seconds, what mAs is being used?

If the mA is 60 and the time is 0.5 seconds, what mAs is being used?   mAs = mA x sec = 60 x 0.5 = 30

What will be the new mAs if the FFD is changed from 75cm to 100cm, and the original mAs was 25?

New mAs = old mAs x new distance2 What will be the new mAs if the FFD is changed from 75cm to 100cm, and the original mAs was 25?   New mAs = old mAs x new distance2 old distance2 = 25 x 1002 ÷ 752 = 44

An exposure of 70kV and 25mAs is needed to radiograph a dog’s chest without a grid at 100cm. If a grid with a grid factor of 4 is used, what exposure and FFD is needed to produce a similar image?

An exposure of 70kV and 25mAs is needed to radiograph a dog’s chest without a grid at 100cm. If a grid with a grid factor of 4 is used, what exposure and FFD is needed to produce a similar image?   mAs = 25 x 4 = 100 No other factors change

Calculate the new mAs, if the FFD is changed from 75cm to 90cm with an original mAs of 30.

New mAs = old mAs x new distance2 Calculate the new mAs, if the FFD is changed from 75cm to 90cm with and original mAs of 30. New mAs = old mAs x new distance2 old distance2 = 30 x 902 ÷ 752 = 30 x 8100 ÷ 5625 = 43

If a mA of 20 and a time of 0.2secs are used to radiograph a dog carpus with a kV of 53, what exposure factors are used?

If a mA of 20 and a time of 0.2secs are used to radiograph a dog carpus with a kV of 53, what exposure factors are used? mAs = mA x time = 20 x 0.2 = 4mAs kV remains constant at 53kV

You are asked to radiograph a cat’s elbow following surgery and a vet wrap bandage has been applied. What exposures would be used if your original exposures were 45kV and 8mAs?

Vet wrap = multiply mAs by 1.5 Exposure factors 45kV 12mAs You are asked to radiograph a cat’s elbow following surgery and a vet wrap bandage has been applied. What exposures would be used if your original exposures were 45kV and 8mAs? kV remains constant Vet wrap = multiply mAs by 1.5 8 x 1.5 = 12mAs Exposure factors 45kV 12mAs

A radiograph is taken of a dogs abdomen using 55kv and 12mAs, if this was to be repeated using a grid, with a grid factor of 3, what exposure would now be needed to produce a diagnostic image?

Multiply mAs by grid factor A radiograph is taken of a dogs abdomen using 55kv and 12mAs, if this was to be repeated using a grid, with a grid factor of 3, what exposure would now be needed to produce a diagnostic image? kV remains constant Multiply mAs by grid factor 12 x 3 = 36mAs Exposure factors 55kV 36mAs

Multiply mAs by grid factor

mAs = mA x time

Vet wrap = Multiply mAs by 1.5

New mAs = Old mAs x new distance2 old distance2