[Insight-users] waiting for help---confused by muti-scale frame work with physical space processing in ITK

[Luis Ibanez]

Hi Baoyun,


The use of image spacing in the ITK  Level Set framework only
matters for the purpose of correcting for anisotropic images.


That is, what matters is the relative values of the spacing
across each direction, not their absolute values.


     Regards,


         Luis


-----------------
Baoyun Li wrote:
> 
>  
> Dear All:
>  
> I am confused by muti-scale frame work with physical space processing in 
> ITK. Let take Level set for segmenation as example, the original data is 
> 1mm, and I will do the 3 reolution level for level set (4,2,1 mm) 
>  
> 1 I fully understand what happen in voxle space. we have intial level 
> set, at high resolution, the distance of initial levels set may be too 
> far to the true contour( let say 10mm or 10 voxle), then we go to 4mm, 
> and the distance is only 2.5 voxels. So muti-scale processing help the 
> level set to converge to the truth quickly.
>  
> 2. But if we process it in the ITK framework or say physical space, even 
> at low resolution, the distance is still 10mm and is not reduced. How 
> this muti -scale scheme helps to speed up the algorithm?
>  
> 3 I guess, even we say ITK is in physical space, but in real processing, 
> e.g, (at 4mm level), the program will only work on the grid point. But 
> the programm knows clearly that is 4mm voxle distance. The step is 4 
> time bigger than high resolution case.( I guess).
>  
>  
> I understand this question may be too naive, but I am really confused.
>  
>  
> Thanks
>  
> Baoyun
> 
>