CT Hounsfield Units

Godfrey N. Hounsfield
1979 Nobel prize
Award Winner –
Courtesy Wiki
Hounsfield’s sketch of the prototype CT scanner.
Original sketch from Hounsfield’s notebook. The picture was taken at the UKRC 2005 exhibition, Manchester G-Mex centre. 08:56, 20 July 2006 (UTC)
Courtesy Wiki

Shared 1979 Nobel Prize for Physiology or Medicine with Allan MacLeod Cormack

  • HU  Hounsfield Units
    • relative quantitative measurement of radio density
      • measured by  linear attenuation coefficient for each material at the selected effective energy
      • physical density of tissue is proportional to the absorption/attenuation of the X-ray beam.
      • Assigned numbers
      • 4096 values levels of gray (12 bit) and
        • ranges from
          • -1024 HU to 3071 HU
            • -1024 HU is black as in air
            • 0 HU represents water (
            • 3071 HU is white
              • represents the densest tissue in a human body,
              • tooth enamel.
        • All other tissues are somewhere within this scale; fat is around -100 HU, muscle around 100 HU and bone spans from 200 HU (trabecular/spongeous bone) to about 2000 HU (cortical bone).
      • Hounsfield scale is  displayed as
        • gray tones
          • dense tissue, with greater X-ray beam absorption,
            • has positive values
            • appears bright;
          • less dense tissue, with less X-ray beam absorption,
            • has negative values and
            • appears dark.
      • distilled water (at standard temperature and pressure) is arbitrarily defined to be zero HU
      • air defined as -1000 HU.
      • bones – 1000 for bones,
      • dense bones like the cochlea 2000,
      • metals like steel or silver more than 3000
    • Densities
      • For practical purposes in the body ie approximate
        • density of calcium +50 to +500
        • density of soft tissue  +50
        • density of lung-  -700 to -800
        • density of fluid  +5to +15
        • fat  -5 to -100
        • iodinated contrast  + 100 to +500

 

Links and References

DenOtter  TD et al  Hounsfield Unit