{"chart":"radiography-formulas-chart","generatedFrom":"All Unit Conversions shared conversion library","tables":[{"title":"Inverse square law factors","headers":["Distance ratio d₂ ÷ d₁","Dose rate factor (d₁ ÷ d₂)²","mAs factor to keep exposure"],"rows":[["0.25","16","0.0625"],["0.5","4","0.25"],["0.75","1.778","0.5625"],["1","1","1"],["1.25","0.64","1.563"],["1.5","0.4444","2.25"],["1.75","0.3265","3.063"],["1.8","0.3086","3.24"],["2","0.25","4"],["2.5","0.16","6.25"],["3","0.1111","9"],["4","0.0625","16"],["5","0.04","25"],["10","0.01","100"]]},{"title":"Exposure and geometry formulas","headers":["Relationship","Formula","Worked example"],"rows":[["mAs","mAs = mA × exposure time (s)","200 mA × 0.1 s = 20 mAs"],["Exposure maintenance","mAs₂ = mAs₁ × (SID₂ ÷ SID₁)²","10 mAs at 100 cm → 32.4 mAs at 180 cm"],["15% rule","+15% kVp ≈ doubles exposure to the image receptor; −15% kVp ≈ halves it","70 kVp + 15% = 80.5 kVp with half the mAs"],["Grid conversion","mAs₂ = mAs₁ × (GCF₂ ÷ GCF₁)","5 mAs with no grid → 25 mAs with a 12:1 grid (GCF 5)"],["Magnification factor","MF = SID ÷ SOD","SID 100 cm, SOD 80 cm → MF 1.25"],["Object size","Object size = image size ÷ MF","50 mm image ÷ 1.25 = 40 mm"],["Heat units","HU = kVp × mA × s × c  (c = 1 single-phase, 1.35 three-phase, 1.4 high-frequency)","80 kVp × 200 mA × 0.1 s × 1.4 = 2,240 HU"]]},{"title":"Grid conversion factors (GCF)","headers":["Grid ratio","GCF"],"rows":[["No grid","1"],["5:1","2"],["6:1","3"],["8:1","4"],["12:1","5"],["16:1","6"]]},{"title":"Half-value layers: fraction transmitted","headers":["Number of HVLs","Fraction transmitted","Percent transmitted"],"rows":[["0","1","100"],["1","0.5","50"],["2","0.25","25"],["3","0.125","12.5"],["4","0.0625","6.25"],["5","0.03125","3.13"],["6","0.01563","1.56"],["7","0.007813","0.781"],["8","0.003906","0.391"],["10","9.766 × 10⁻⁴","0.0977"]]},{"title":"Dose limits compared","headers":["Limit (per year unless stated)","ICRP 103 (international)","US NRC 10 CFR 20","NCRP Report 116 (US guidance)"],"rows":[["Occupational, effective dose","20 mSv averaged over 5 years; at most 50 mSv in any year","50 mSv (5 rem)","50 mSv; cumulative 10 mSv × age in years"],["Lens of the eye","20 mSv averaged over 5 years; at most 50 mSv in any year (ICRP 118)","150 mSv (15 rem)","150 mSv"],["Skin, hands and feet","500 mSv","500 mSv (50 rem)","500 mSv"],["Public, effective dose","1 mSv","1 mSv (0.1 rem)","1 mSv continuous; 5 mSv infrequent"],["Embryo or fetus (declared pregnancy)","1 mSv for the rest of the pregnancy","5 mSv (0.5 rem) over the whole pregnancy","0.5 mSv per month"]]},{"title":"ALARA: time, distance, shielding","headers":["Principle","Rule of thumb"],"rows":[["Time","Dose = dose rate × time: halve the time, halve the dose."],["Distance","Inverse square law: double the distance, a quarter of the dose rate."],["Shielding","Each half-value layer halves the intensity; n HVLs transmit (½)ⁿ."]]}]}