Formulas

Question 1

minification gain

Answer 1

input screen diameter² ÷ output screen diameter²

Question 2

brightness gain

Answer 2

minification gain x flux gain

Question 3

brightness gain

extended formula

Answer 3

(input screen diameter² ÷ output screen diameter²) x flux gain

Question 4

conversion factor

Answer 4

intensity of output phosphor ÷ mrad/sec

intensity of output phosphor = candela (Cd)

Question 5

increase in patient radiation dose

Answer 5

normal mode size² ÷ magnification mode size²

Question 6

vertical resolution (lp/mm)

Answer 6

number of horizontal lines ÷ (2 x diameter of object)

Question 7

Kell factor

Answer 7

vertical resolution ÷ number of scan lines

number of scan lines = horizontal lines

Question 8

Kell factor

extended fomrula

Answer 8

(number of horizontal lines ÷ (2 x diameter of object)) ÷ number of scan lines

Question 9

f-number

Answer 9

focal length ÷ lens diameter

Question 10

integral dose

Answer 10

absorbed dose x tissue weight

• absorbed dose = rad
• weight = g

Question 11

inverse square law

Answer 11

I₁(D₁)² = I₂(D₂)²

Question 12

photoelectric effect

Answer 12

I = I₀e⁻ᵘˣ

Question 13

half-valuue layer (HVL)

Answer 13

I = ½I₀

Question 14

approximate dose calculation to a fetus

Answer 14

2% of mother’s skin dose

- 1 Roentgen = 1 rad
- 1 rad = 1000 mrads