[Rtk-users] Iterative reconstruction

[Zhang, Zhehao]

Hi all,

I have used RTK for a while, first of all, thanks for providing this great software.

I am trying to perform some iterative CBCT reconstruction with a specifically defined regularization term recently. Since this regularization is not TV nor wavelet, I may not be able to directly use those RTK provided filters, like ‘ConjugateGradientConeBeamReconstructionFilter’. What I want is simply use gradient descent method and calculate the gradient of (1/2) ||(Rf - P)||^2 and my regularization term. I got some problems on how to get the gradient of  (1/2) ||(Rf - P)||^2 , which should be R*(Rf - p), f is the required results, p is measured projections and R is forward projections. Hope to get some hints for you.

Fow now, I tried to directly use  ‘JosephForwardProjectionImageFilter’ and ‘JosephBackProjectionImageFilter’ to achieve this goal, however, the acquired values seems to be really large after several iterations. I think I must made something wrong. Could you please give me some suggestions about this problem if I want to utilize RTF to get gradient? Or is there any implementation detail of CG/SIRT filters that we can access (I am not sure if it is public)? I put my current code here (https://drive.google.com/file/d/1GPuoYHk4ACe5VDnVwZlsIzK1OHrM2AdK/view?usp=sharing)

Thank you very much and best regards.

Zhehao
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