Hounsfield Units (Where do CT numbers come from?)

Hounsfield Units (a.k.a. CT numbers) express the values of all Computed Tomography (CT) images. This is a normalized scale of the X-ray attenuation values calculated during the CT scan.

This was produced by Brian Nett, PhD at https://howradiologyworks.com . See our site for more information on x-ray and CT physics.

Hounsfield Units are defines as:
HU= (mu_material - mu_water) / mu_water

This leads to HU values such as:

HU value of air: -1000
HU value of lung: -900 to -500
HU value of soft tissue/fat: -80 to 80
HU value of trabecular bone: 100 to 300
HU value of cortical bone: 300 to 1200



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