[Gate-users] Dose uncertainty

[Florian Bretin]

Dear Gaters, 

I sent an email already a few month back, but I still couldn't solve my
issue (although a friendly GATE user replied!). 

I am running a CT simulation of multiple field of views with a phantom. I
shift the phantom to simulate the translational source movement and
therefore have several dose maps and dose uncertainties per scan. I would
like to combine the uncertainty maps to form one single file expressing the
overall uncertainty of the simulation. All files are Analyze75 images (with
header .hdr and image .img).

I read in all files (dose squared map, "squared" in the equation; dose map,
"mean" in the equation and N being the overall emitted photons) in MATLAB
and fail to compute the final uncertainty or even reproduce the single
uncertainty.
I am using the following equation given in the manual (and in the file:
GateImageWithStatistic.cc, line 346, after Chetty et al. from 2006):

    // Chetty2006 p1250 : relative statistical uncertainty
    // exactly same than Ma2002
    if (mean != 0.0 && N != 1 && squared != 0.0){
      *po = sqrt( (1.0/(N-1))*(squared/N - pow(mean/N, 2)))/(mean/N);
    }
    else *po = 1;

All I get is a uncertainty map with complex numbers in MATLAB.
Did anyone face a similar problem?
Does anyone have a tool to compute the uncertainty or the final uncertainty
of several dose maps? 

Any help would be much appreciated, deadlines are approaching! ;) 

Kind regards,
Florian


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