Calculations

Question 1

Half life formula

Answer 1

Ln (Xo/X) = kt
Where k = ln2 / t 1/2

Question 2

Radioactive Decay

Answer 2

• dN / dt = ¥N
  dN / dt is the change in number of atoms (N) per change in time
  decay constant

Question 3

Common pediatric dose based on weight

Answer 3

Kg x 0.14 mCi/kg

Question 4

Pediatric dose calculation
Young’s formula (age)

Answer 4

Age (yrs) / age + 12 x adult dose

Question 5

Pediatric dose calculation
Websters formula (age)

Answer 5

Age (years) + 1 / age + 7 x adult dose

Question 6

Pediatric dose calculation
Clarks formula (weight)

Answer 6

(child weight lbs) (adult dose) / 150 lbs

Question 7

Specific volume

Answer 7

Activity desired / specific concentration

Question 8

Specific activity

Answer 8

Concentration x volume

Question 9

Specific concentration

Answer 9

Activity / volume

Question 10

Well counter efficiency

Answer 10

%efficiency = counts per unit time (cpm/cps) / (disintegrations per unit time)(mean # of disintegrations) x 100

Question 11

Effective half life

Answer 11

Te = Tp x Tb / Tp + Tb
Te = effective half life
Tp = physical half life
Tb = biological half life

Question 12

Calculate change in exposure rate due to shielding

Answer 12

I = Io x e ^-(0.693)(x/HVL)

Question 13

Inverse square law

Answer 13

(I1)(D1)^2 = (I2)(D2)^2
I1 = intensity at original distance D1
I2 = intensity at new distance D2

Question 14

Convert cpm to dpm

Answer 14

Gross cpm - bkg cpm / efficiency expressed as a decimal

Question 15

Correction factor

Answer 15

Expected activity / actual activity

Question 16

Calculation of percent error or percent difference

Answer 16

(Expected -actual / expected) x 100

Question 17

CT number

Answer 17

(U tissue - u water) / u water x 1000

Question 18

Pitch

Answer 18

Table movement in one rotation / single slice thickness

Question 19

Volume pitch

Answer 19

Table movement in one rotation / total slice volume

Question 20

LBM (male)

Answer 20

(1.1 x body weight (kg) - 120 (body weight kg / body height cm) ^2)

Question 21

LBM (female)

Answer 21

(1.07 x body weight kg - 148 (body weight kg / body height cm)^2)

Question 22

SUV LBM (lean body mass)

Answer 22

Roi tracer concentration (mCi/cc) / tracer dose (mCi) / LBM (kg)

Question 23

BSA (m^2)

Answer 23

0.007184 x body weight (kg)^ 0.425 x body height (cm)^0.725

Question 24

SUV BSA (body surface area)

Answer 24

Roi tracer concentration (mCi/cc) / tracer dose (mCi) / BSA (m^2)

Question 25

SUV bw (body weight)

Answer 25

Roi tracer concentration (mCi/cc) / tracer dose (mCi) / patient weight (kg)

Question 26

NECR
Noise equivalent count rate

Answer 26

T^2 / (T + S + R)

Question 27

Decay calculation using half life (post)

Answer 27

At = Ao x e ^ -0.693 x (t / t1/2)