Prime Factors

    Cards (50)

    • The x-ray beam
      Quantity
    • Quantity of the x-ray beam
      Determined by the number of photons in the useful beam
    • Exposure
      Measured in roentgens (R) or milliroentgens (mR)
    • Quantity of the x-ray beam
      Affected by: mAs, Kilovoltage, Distance, Filtration
    • Quantity of the x-ray beam
      • The primary influencer is mAs
    • Quality of the x-ray beam
      Measurement of the beam's penetrability
    • Quality of the x-ray beam
      • High energy/Short wavelength - more penetrability
      • Low energy/Long wavelength - less penetrability
    • Half-Value Layer (HVL)

      Amount of material needed to reduce x-ray intensity to half its original value; mm Al. Eq.
    • Energy, wavelength, & beam penetrability
      • High energy/Short wavelength = More penetrability
      • Low energy/Long wavelength = Less penetrability
    • Quality of the x-ray beam
      Affected by: kVp
    • Nature (quantity and quality) of the x-ray beam
      Controlled by: Inherent factors, Controllable factors
    • Inherent factors of the x-ray tube
      • Anode target material
      • Inherent filtration
      • Generator voltage waveform
    • Prime factors of imaging
      • Milliamperage
      • Time
      • Kilovoltage peak
      • Distance
    • Milliamperage
      Measurement of x-ray tube current
    • Tube Current
      The number of electrons travelling from the cathode towards the anode per second
    • Tube current & electron quantity
      Increase in tube current = Increase in electron quantity
    • Time
      Length of exposure, measured in seconds (s) and multiplied with milliamperage to find mAs
    • Time & electron quantity
      Increase in exposure time = Increase in electron quantity
    • mAs
      mA x s, where mA is milliamperage and s is exposure time in seconds
    • Different variations of mA and time can still result in the same mAs
    • Kilovoltage Peak (kVp)

      Controls both quantity and quality of the x-ray beam
    • kVp & quantity
      The change in the quantity of x-rays is approximately directly proportional to the square of the ratio of the change in kVp
    • Distance & x-ray intensity
      Increase in SID = Decrease in x-ray intensity to patient
    • Distance & x-ray intensity
      Inverse Square Law: the intensity of radiation at a given distance from the source is inversely proportional to the square of the distance
    • Distance & x-ray intensity
      Density Maintenance Formula: the exposure of radiation to the IR at a given distance from the source is directly proportional to the square of the distance
    • Distance & x-ray intensity
      Increasing OID: Increases distortion, Decreases detail, Decreases density, Decreases contrast
    • Law of Reciprocity
      The exposure of an image receptor should remain unchanged as long as the product of the intensity and the duration of the x-ray exposure remain unchanged
    • Radiographic density
      The overall blackness of an image
    • mAs & radiographic density/exposure
      Increasing mAs proportionally increases x-ray exposure, mAs is considered the primary controller of radiographic density/exposure
    • Density
      Density is considered to be exposure
    • kVp & density in film-screen
      Increasing kVp increases radiographic density, resulting in a decrease of contrast
    • kVp & density in digital imaging
      Increasing kVp does not affect brightness or darkness, but does still result in a decrease of contrast from scatter
    • Inherent factors - factors that are a part of the tube
    • Controllable factors - factors that a radiographer manages .
    • Three inherent factors of the x-ray tube :
      Anode target material
      Inherent filtration
      Generator voltage waveform
      These are not factors a radiologic technologist has control over .
    • Tube Current - the number of electrons travelling from the cathode towards the anode per second .
    • Increase of current = increase of electron quantity
    • When the exposure time is increase :
      More electrons are able to be created .
      More electron go from the cathode towards the anode.
    • Anode = positive
    • Cathode = negative
    See similar decks