Hounsfield Unit

What is Hounsfield Unit?

• CT number
• Unit used to measure attenuation of tissue on CT
• A representative of relative attenuation coefficient of tissues, using water as a reference
  
• Water is defined as zero Hounsfield unit
• Matters with higher physical density (g/cm3), higher electron density (e/cm3) than water will have higher HU; and vice versa
• HU depends on kV peak (used in CT image acquisition) and filtration technique (used in CT image reconstruction)
• HU values on an image are only approximate (because it will change if kV changes)
  

Who is Hounsfield?

• Godfrey Hounsfield is a British electrical engineer
• He shared a 1979 Nobel Prize in physiology or medicine with Allan Cormack for the development of computed tomography (CT)

Reference:
Huda W, et al. Review of radiology physics. 2003
www.wikipedia.com