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The Attenuation Coefficients in CT: A Didactic Review

  • M. H. Gado
  • J. Eichling
Conference paper

Abstract

The density of a structure on a CT image depends on the CT number which in turn is derived from the linear attenuation coefficient (u) according to one of the following equations :
$$\frac{{ux - uw}}{{uw}} x 100 x 5 .................$$
(1)
$$\frac{{ux - w}}{{uw}} x 100 x 10 .................$$
(2)
where ux and uw are the attenuation coefficients for a certain material and water respectively. It has been suggested that CT numbers calculated by equation 1 are expressed in EMI units (EU), while those according to equation 2 as Hounsfield Units (HU). The scale of the EU ranges from — 500 to + 500 and the HU from — 1000 to + 1000. One HU is = 1/2 x EU. Attenuation of x-rays is determined by three factors : 1. Electron density 2. Physical Density 3. Atomic Number (Z).

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Copyright information

© Springer-Verlag Berlin Heidelberg 1980

Authors and Affiliations

  • M. H. Gado
  • J. Eichling

There are no affiliations available

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