Calculations Flashcards
If the kV is increased by 10 what must be done to the mAs to keep the exposure the same?
The mAs must be halved
If the kV is decreased by 10 what must be done to the mAs to keep the exposure the same?
The mAs must be doubled
What does FFD stand for?
Focal Film Distance
How is the new mAs calculated when the FFD is changed?
New mAs = Old mAs x (New FFD² / Old FFD²)
What should be done to the mAs if the FFD is doubled?
The mAs should be multiplied by 4
What is Sante’s Rule?
A method of estimating kilovoltage in relation to area thickness: (2 x thickness in cm) + 40 = kVp
What is kVp more commonly referred to as?
kV
What does kVp stand for?
kilo voltage peak
mA x seconds = what?
mAs
A diagnostic radiograph is obtained using an mAs of 3 and a FFD of 75cm. If the tube head is raised to a FFD of 90cm, what new mAs is required?
Old mAs = 3
Old FFD = 75cm
New FFD = 90cm
Answer = 4.32mAs
A diagnostic radiograph is obtained using an mAs of 5 and a FFD of 75cm. If the tube head is raised to a FFD of 80cm, what new mAs is required?
Old mAs = 5
Old FFD = 75cm
New FFD = 80cm
Answer = 5.68mAs
A diagnostic radiograph is obtained using an mAs of 3 and a FFD of 75cm. If the tube head is reduced to a FFD of 60cm, what new mAs is required?
Old mAs = 3
Old FFD = 75cm
New FFD = 60cm
Answer = 1.92mAs
The exposure settings 70kV, 30mA and 0.2sec produce a diagnostic radiograph of the femur of a dog. If the kV is reduced to 60kV, what mAs is required to produce a similar picture?
First work out original mAs: 30mA x 0.2sec = 6mAs
Then: kV has been decreased by 10 so mAs is doubled.
Then: 6mAs x 2 = 12mAs
The exposure settings 50kV, 10mA and 0.4sec produce a diagnostic radiograph. If the kV is increased to 60kV, what mAs is required to produce a similar picture?
First work out original mAs: 10mA x 0.4sec = 4mAs
Then: kV has been increased by 10 so mAs is halved.
Then: 4mAs / 2 = 2mAs
Calculate the mAs for these exposure settings:
50kV, 0.2sec, 6mA
0.2sec x 6mA = 1.2mAs
