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2. inhomogeneities Medium can be of varying material
(different elemental composition
d Z ff) an e
ACE scales attenuation and absorption
voxel wise according to: Th i i li -
sc b
m
sc m bmb 1
, 1 

 

  







e same recurs ve equat on app es
BUT:
• additional input is required to calculate
m
sc en m
w
w
1  

 




  η1sc , χ1sc : the energy spectrum of 1sc
photons generated at each point.
This is taken from calculations in water so:
sc b
w
w
BmB 1
, 

    





• the scaling is APPROXIMATE and its
accuracy deteriorates as materials yield
different 1sc spectrum from water (as Z
increases due to coherent & photoelectric
phenomena-x ray fluorescence and S(x,Z))