Hounsfield unitThis is a featured page

The Hounsfield unit (HU) scale is a linear transformation of the original linear attenuation coefficient measurement in one in which the radiodensity of distilled water at standard pressure and temperature (STP) is defined as zero Hounsfield units (HU), while the radiodensity of air at STP is defined as -1000 HU.
For a material X with linear attenuation coefficient μX, the corresponding HU value is therefore given by where is the linear attenuation coefficient of water.
Thus, a change of one Hounsfield unit (HU) represents a change of 0.1% of the attenuation coefficient of water since the attenuation coefficient of air is nearly zero.
It is the definition for CT scanners that are calibrated with reference to water.
Tissue CT number (HU)
Bone 1000
Liver 40 - 60
White matter ~20-30 HU
Grey matter ~37-45 HU
Blood 40
Muscle 10 - 40
Kidney 30
Cerebrospinal fluid 15
Water 0
Fat -50 - -100
Air -1000

Latest page update: made by eliseleblanc , May 19 2012, 4:13 PM EDT (about this update About This Update eliseleblanc Moved from: CT - eliseleblanc

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