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RAD 354 Chapt . 8 X-ray emission

RAD 354 Chapt . 8 X-ray emission. X-ray output in AIR is measured in ROENTGENS and refers to x-ray QUANTITY 1 R = 2.58 X 10 -4 C/kg. 4 Factors affect the QUANTITY of RADIATION: mAs , kVp , distance & filtration. mAs – DIRECTLY proportional to the x-ray quantity

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RAD 354 Chapt . 8 X-ray emission

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  1. RAD 354 Chapt. 8 X-ray emission • X-ray output in AIR is measured in ROENTGENS and refers to x-ray QUANTITY • 1 R = 2.58 X 10-4 C/kg

  2. 4 Factors affect the QUANTITY of RADIATION: mAs, kVp, distance & filtration • mAs – DIRECTLY proportional to the x-ray quantity • kVp – x-ray quantity varies proportional to the SQUARE of the RATIO of the kVp • Distance – Inverse square law • Filtration – Absorbs/Attenuates the LOW energy LONG wavelength photons – INCREASES average hardness of the beam

  3. X-ray QUALITY = Penetrability • INCREASED hardness = INCREASED penetration and DECREASED wavelength • Measured via HALF VALUE LAYER (HVL = BEST measure of x-ray QUALITY) • Penetrometer/step wedge • Filtration – used to harden the beam and absorb the “useless, long wave photons” • Inherent (.5 mm al) Added = 2 mm al (70-80 kVp)

  4. “Special” Filters • Trough – for CXR’s • “Bow Tie” – for some generations of CT • Wedge – for use with an AP foot, etc. • Conic – for digital fluoro • Don’t reduce patient dose, but improve the image

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