[Castor-users] Possible problem with geom creation for Cylindrical Pet scanner with DOI layer

[tmerlin]

Hi Maxime,

Thank you for the work. There was indeed mismatches with the positioning 
in the layers. Additionally, even with a single layer the code assumes 
that the rsector face corresponds to the detector faces, which is not 
necessarily true. I made some quick fixes (code in attached), which 
should correct the issue. They will be included in the next code update.

Many thanks,
Thibaut M.


On 31/03/2019 17:12, Maxime Toussaint wrote:
> Greetings,
>
> We discovered a mismatch between the LUT generated by CASToR in 
> castor-recon and Gate detector center position for a scanner defined 
> as a Cylindrical Pet with DOI layer. After some investigation, the 
> mismatch was shown to be mostly radial and due to an "error" in 
> defining the scanner layer radius.
>
> From our understanding, Gate defines a detector position relative to 
> the detector center while CASToR defines it, at least temporally, 
> relative to its front face. While they can be made equivalent, the 
> current conversion of Gate "layer translation" to "scanner layer 
> radius" seems to be at fault. Currently, the layer translation, 
> defined in Gate relative to the center of its Parent, is applied 
> directly to the "layer front face radius" which is not equivalent.
>
> Following this email, we propose a solution which work for our case. 
> However, it is not perfect. For example, one of its limitation, if my 
> understanding is correct, is that it assume that the face of the first 
> DOI layer correspond to "block_pos_{X/Y}" which is "near enough" but 
> not exactly true most of the time.
>
> Best,
> Maxime Toussaint
>
>
>
> In src/management/gDataConversionUtilities.cc
>
> +         if ( l == 0)
> +         {
> + vec_scanner_radius.push_back( toString(scanner_radius) );
> +         }
> +         else
> +         {
> + vec_scanner_radius.push_back( toString(stod(vec_scanner_radius[l-1]) 
> + layers_size_depth[l-1]) );
> +         }
> -      vec_scanner_radius.push_back( 
> toString(scanner_radius+layers_positions[l][0]) );
>
>
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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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