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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.

Basic Proportion vs Multiplication Formula Setup

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

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Ex: 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

Grid Conversion Factors
(mas 1/mas 2) = (SID1^2 / SID2^2)
mAs Distance

1 / (2 x pi x f x c)

f = frequency, c = Farads

XC – Capacitive Reactance

2 x pi x f x I

f = frequency, I = Inductance (Henry)

XL – Inductive Reactance
(I1/I2) = (SID2^2/SID1^2)
Inverse Square Law
(mas x kVp^2) / (SID^2)
PE – Density

(FS x OID) / (SOD)

SID – OID = SOD

GU – Geometric Unsharpness
Flux Gain x Minification Gain
Brightness Gain
V (or E) = IR
EMF/Voltage

(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

Speed Class Conversion

15% of kVp

If increase, half mAs.
If decrease, double mAs.
Density remains the same but contrast changes!

15% Rule

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)

Heat Unit
1 Gy = 100 rad
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)
Gray Sieverts Conversions
SOD = SID – OID
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.

Entrance Skin Exposure
EqD = (D or Gy) x (W_r)
(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!!!

Equivalent Dose
EfD = (D or Gy) x (W_r) x (W_t)
(W_r) = weighted radiation
(W_t) = weighted tissueAnswer will be in Sieverts!!!

Effective Dose

ColEfD = EfD x # of people exposed

Answer will be in Sieverts!!!

Collective Effective Dose

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

To get mA minutes/week divide answer by 60.

Workload (W)

(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

Matrix File Size
1 Kilobyte (KB) = 1000 bytes
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
Storage Sizes

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

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

Calculating the number of 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

Max Resolution (lp/mm)
Ex: 1000/180(um) = 5.56 pixels/mm
PIxel size in microns (um); solve for pixels/mm
divide mAs by two
Single Phase to High Frequency
multiply mAs by two
High Frequency to Single Phase
Vp/Vs = Np/Ns = Is/Ip
V = volts, N = number of turns, I = amps/currentex: Ratio 1:800, Primary voltage: 80V -> 80/X = 1/800 -> x= 64,000 voltage = 64kV

Primary to Secondary & Autotransformers
Factors Affecting Density
Factors Affecting Density
Factors Affecting Contrast
Factors Affecting Contrast
Factors Affecting Details
Factors Affecting Details
Factors Affecting Distortion
Factors Affecting Distortion

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

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Half Value Layer
divide by 3 plus 1
Tomogram Fulcrum Level Calculation
Spine Positions for Z-Joints & Intervertebral Foramina
Spine Positions for Z-Joints & Intervertebral Foramina
add up all of the resistors
Simple Series

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

Parallel Series (Reciprocity)
Image Size/Object Size = SID/SOD
Image Size
Image Size/Object Size
Magnification Factor

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Radiology Formulas & References
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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.
Basic Proportion vs Multiplication Formula Setup
2018-10-20 00:28:39
2018-10-20 00:28:39
Radiology Formulas & References
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