[Rtk-users] Questions about xim / fdk

[Simon Rit]

Hi Greg,
- rtk can convert these files in any ITK file format. Run
rtkprojections -p DIRECTORY -r FILENAME -o test.mha --nolineint
- They are not already dark and flood corrected. See the converting class
https://github.com/RTKConsortium/RTK/blob/main/include/rtkVarianObiRawImageFilter.h#L35-L38
- The FDK output are in 1/length unit. The length unit are a user choice,
so if you set all ditances (spacings in image meta information and lengths
in RTK geometry) in mm, then you reconstruct in 1/mm.
- Conversion to HU requires a linear conversion after calibrating the value
for air and water. We don't do that usually but I believe there is an ITK
filter for this conversion.
- If you want to use a subset of projections, you can use our tool
rtksubselect :
srit at srit-Precision-5480:~$ rtksubselect -h
RTK 2.7.0, git hash 5e5929a510fc5940dccba9a96eec70aa6597f2fc

Subselects a few projections from a list of projection files and a geometry
file.

Usage: RTK [OPTIONS]... [FILES]...

  -h, --help                 Print help and exit
  -V, --version              Print version and exit
  -v, --verbose              Verbose execution  (default=off)
  -g, --geometry=STRING      XML geometry file name
      --out_geometry=STRING  Output geometry file name
      --out_proj=STRING      Output projections stack file name
  -f, --first=INT            First projection index  (default=`0')
  -l, --last=INT             Last projection index
  -s, --step=INT             Step between projections  (default=`1')
      --list=INT             List of projection indices to keep (0-based)

Good luck with all this,
Simon



On Mon, Mar 16, 2026 at 7:51 PM Sharp, Gregory C. <gcsharp at mgb.org> wrote:

> Hi all,  I have a few questions:
>
> Is there any viewer for these files and/or can I convert them into mha?
>
> Are the xim files already dark and flood corrected?
>
> What are the units for the fdk output?  Can they be scaled into something
> like HU?
>
> Is there a way to specify subsets of gantry angles to be used in the fdk
> recon?
>
> Thank you,
> Greg
>
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