Hounsfield units

Hounsfield units

Hounsfield units

Hounsfield units are units universally used in


[B] CT Scan

[C] PET Scan

[D] Angiogram

Hounsfield units (HU) are a dimensionless unit universally used in computed tomography (CT) scanning to express CT numbers

Hounsfield units are obtained from a linear transformation of the measured attenuation coefficients This transformation is based on the arbitrarily-assigned radiodensities of air and pure water:

  • Radiodensity of distilled water at standard temperature and pressure (STP) equals 0 HU
  • Radiodensity of air at STP equals –1000 HU

Note: STP is defined as temperature of 0 °C and pressure of 105 pascals (i.e. sea-level)

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