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2. inhomogeneities Medium can be of varying material
(different elemental composition
and Zeff)
This affects cross sections
and hence Bθ ,bθ
2
) exp(
, 1
)
, 1
exp(
2
1
) 1(
)( 1
, 1
)
, 1
exp(
2
1
1
)( 1
1
) ,(
) ,( 1h
r
rb B
sc en r sc
dr en
sc dR
sc en r sc
dr R sc
sc dR
dV R sc
r
r sc
 











  

−
=
−

−
=
−

= =
 

 




, 1
, 1
1
) 1(
)( 1
sc b
sc en d en
sc dR
B
=

−
=
Can’t we scale the kernel?
Yes and different approaches have
appeared in the literature.
ACE scales attenuation and absorption
voxel-wise according to:
1 ,
1
1 ,
1
m
sc
m
b b b
m sc
w
w
m
en sc
m
B Bm sc
w
w

 

  
 

 

  
 
 
 
= =
 
 
 
 
= = 
 
 