# Radiology Formulas & References

Anything with (a/b) = (c/d) means you have to CROSS multiply. This would result in (ad) = (cb) and it is called proportion.

(a/b) x (c/d) means you multiply ACROSS. This would result in (ac)/(bd). Basic multiplication setup.

5:1 = x2, 6:1 = x3, 8:1 = x4, 10:1 = x4.5, 12:1 = x5, 16:1= x6

Order nowEx: 10 mAs non grid to 8:1. 10 * 4 = 40 mAs. To change it from 8:1 to 16:1. 40 / 4 = 10 mAs multiply that by 6 to get 60 mAs

1 / (2 x pi x f x c)

f = frequency, c = Farads

2 x pi x f x I

f = frequency, I = Inductance (Henry)

(FS x OID) / (SOD)

SID – OID = SOD

(mas1/mas2) = (SC2/SC1)

For <100SC = 25SC and CB = 2.5SC. Cross multiply as usual. If it is less than 100SC with an actual value like 54SC or 26SC, use those instead! Ex: 200SC @ 20 mAs to 100SC. 20/X = 100/200 -> 4000/100 = X = 40mAs

15% of kVp

If increase, half mAs.

If decrease, double mAs.

Density remains the same but contrast changes!

mAs x kVp x Efficiency Factor

Effiency Factor: type of electrical current that is being used

(1P: 1, 3P-6P: 1.35, 3P-12P & HF: 1.41)

1 Sv = 100 rem

1 rem = 1 rad = 10 mSv

1 cGy = 1 rad

1 Gy = 1 Sv

1 R = 0.00877 Gy or Sv = 8.77 mGy or mSv

(centi = 100: milli = 1000: micro = 100,000)

OID = PT Thickness + Bucky DistanceESE: (mr1/mr2) = (SOD^2/SID^2)

If kVp changes, use kVp formula first:

(mr1/mr2) = (kVp1^2/kVp2^2) then plug the new mR back into the ESE formula to get the new mR2.

If dealing with multiple shots, add up the ESE for each of the shots in the end with the appropriate rate times their mAs.

(W_r) = weighted radiationIf there are multiple radiation sources, just add it in:

EqD = (D or Gy) x (W_r) + (D or Gy) (W_r)

Answer will be in Sieverts!!!

(W_r) = weighted radiation

(W_t) = weighted tissueAnswer will be in Sieverts!!!

ColEfD = EfD x # of people exposed

Answer will be in Sieverts!!!

W = (avg mAs)(days per week)(avg # of pts)(avg images per pt)

To get mA minutes/week divide answer by 60.

(X-Axis) x (Y-Axis) x (Bit Depth) / 8

Ex: 2000×3200 pixel matrix with 10 bit depth :

(2000x3200x10)/8 = 8,000,000 bytes = 8MB = 8000 KB

1 Megabyte (MB) = 1,000,000 bytes = 1000 KB

1 Gigabyte (GB) = 1,000,000,000 bytes = 1000 MB

1 Terabyte (TB) = 1,000,000,000,000 bytes = 1000 GB

Ex: 2048×2048 pixel matrix, represents an image 35x35cm

35 x 10 = 350mm -> 2048/350 = 5.85 pixels/mm

Take pixels/mm, divide it by 2 and the answer will come out as lp/mm.

Ex: 5.85 pixels/mm / 2 = 2.9 lp/mm

V = volts, N = number of turns, I = amps/currentex: Ratio 1:800, Primary voltage: 80V -> 80/X = 1/800 -> x= 64,000 voltage = 64kV

Multiply the intensity by (1/2)^X. X = the amount of layer of walls.

For Tenth Value Layer (10th) use (1/10)^X.

Ex: 30 mR going through 6 leaded walls -> 30 x .5^6 = 0.469 mR

1/Rt = 1/R1 + 1/R2 + 1/R3 + 1/Rx….

Ex: 1/R(total) = 1/20 + 1/30 + 1/10 -> 3/60 + 2/60 + 6/60 = 11/60 -> 60/11 = 5.45 Ohms