[Castor-users] Siddon multiray returns prematurely (I think)

[tmerlin]

Dear Andreas,

You are definitely right about the implementation, this is indeed an 
oversight. The instruction should be continued instead of returned, and 
the nb_lines should be updated accodingly.

Many thanks for spotting it!

Best regards,
Thibaut

On 24/02/2021 18:01, Andreas Bolke wrote:
> Dear Castor Developers,
>
> first of all, thanks for making Castor open source and maintaining the 
> code in the first place. It has already helped me
> to find Bugs in my own reconstruction when I was comparing my results 
> to the castor result.
>
> Well I guess I get right to the point then.
> I use very simple GATE data to make PET reconstructions and compare 
> them to my own reconstruction.
> If I understand multiray correctly, then I think in 
> iProjectorIncrementalSiddonMulti::ProjectWithoutTOF() the line 282:
>
> / if( alphaMax <= alphaMin ) return 0;/
>
> will cause the function to return prematurely without having iterated 
> over all lines (I mean multiray lines, not oProjectionLine objects).
> This can cause for example low sensitivity values on the edges (I 
> added a screenshot to the attachment).
> When for example you use 16 lines, but because of the
> random position of each line, line no. 2 might not hit a voxel, the 
> function will return and stop iterating over
> the remaining 14 lines.
>
> Or am I missing something? If this is the case, I apologize in advance.
>
>
> Best regards,
> Andreas
>
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-- 
Thibaut MERLIN -- PhD

Docteur en Imagerie Médicale au Laboratoire de Traitement de l'Information Medicale (LaTIM - INSERM UMR 1101)
Institut Brestois de recherche en Bio-Santé (IBRBS)
12 Avenue Foch, 29200 Brest, FRANCE
Tel: 06.75.12.24.90

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