How to convert Hounsfield Unit to mass attenuation coefficient

[dcze...@gmail.com]

Hi,

How to convert Hounsfield Unit to mass attenuation coefficient?

I know that HU can be converted to linear attenuation coefficent with
equation:
mi_x = mi_water * Hu / 1000 + mi_water,
where:
mi_x - linear att. for material with hounsfield unit = Hu
Hu - hounsfield unit of material
mi_water - linear att. for water
assuming that linear att. for air is 0

so:
if Hu = 800, and i want to know attenuation for energy 40 keV then:
mi_x = 0.2683 * 800 / 1000 + 0.2683 = 0.4821 [1/cm]

0.2683 is att for water in energy 40keV, (http://physics.nist.gov/
PhysRefData/XrayMassCoef/ComTab/water.html)

Now if i want to get mass att. coef. i have to use this equation:
mass_mi_x = mi_x / density_x

so:
Hu = 800 is for cortical bone (i found this somewhere if i'm incorrect
please let me know) and density for cortical bone is 1.65 [g/cm^3].
mass_mi_x = 0,4829 / 1.65 = 0.292 [g/cm^2]

And NIST (http://physics.nist.gov/PhysRefData/XrayMassCoef/ComTab/
bone.html) sais that value for mass att. coeficient for cortical bone
for energy 40keV is 0.6655

Where i have made a mistake?

Thanks.

Dominik

[dcze...@gmail.com]

On 26 Cze, 20:18, dczer...@gmail.com wrote:
[cut]

> 0.2683 is att for water in energy 40keV, (http://physics.nist.gov/
> PhysRefData/XrayMassCoef/ComTab/water.html)

assuming that density of water is 1 g/cm^3
[cut]

> mass_mi_x = 0,4829 / 1.65 = 0.292 [g/cm^2]

it should be in [cm^2/g]
[cut]

Dominik