Siemens mMR NEMA example has scatter problems

[KrisThielemans]

With the default settings in our sample par file

STIR/examples/samples/scatter_estimation_par_files/scatter_estimation.par

Lines 78 to 79 in 420d598

	maximum scatter scaling factor := 2 ;10
	minimum scatter scaling factor := 0.4 ;0.1

(used by https://github.com/UCL/STIR/blob/master/examples/Siemens-mMR/scatter_and_recon.sh), the resulting scatter estimate oscilates wildy between scatter iterations. Reducing the minimum scale to 0.1, this problem disappears, and the resulting scatter estimate is fine. The estimates scale factors are around 0.25 (edit:) 0.16.

This is unexpected, as a scale factor of 1 means "single scatter only".

I don't know if this is a recent problem or an old one.

[KrisThielemans]

Profiles through unscaled sinograms (in extras) obtained via

python3 ~/devel/STIR/examples/python/plot_sinogram_profiles.py unscaled_[23456].hs

and amide screenshots of extras/recon_6.hv

• min-scale 0.4
  
  

• min-scale 0.1