[Castor-users] Issues about the List-mode normalization

[Thibaut Merlin]

  Hi Zipai,

You will get the error described in 1. when you try to reconstruct the
list-mode with a datafile containing normalization correction factors
without providing a normalization datafile containing these factors. The
normalization correction factors must be included in both the regular
datafile (using -df option) and the normalization datafile (using -norm
option). Is it what you did ?

Regarding 2., the factors in your normalization datafile will contribute to
the correction in the image (through the sensitivity image which is
generated before the reconstruction itself), while the correction factors
in the datafile are used to normalize the additive background
(scatter/random) during reconstruction. As your data does not contain
scatter or random correction factors (and as you use a precomputed
sensitivity image), there will be no difference in the resulting image.

Hope this helps!

Best regards,
Thibaut

Zipai Wang <zipai.wang at stonybrook.edu> a écrit :

> Dear CASToR developers and users,       
>    I am trying to apply normalization to a simulated PET scanner but
> meet some issues, any help is highly appreciated!
>     
>    First I successfully applied the normalization by feeding the
> normalization file (all LORs with norm&attenuation factors) into the
> CASToR for the computation of the sensitivity image. The CASToR gives me
> artefact free images in this way.
>     
>    However, the normalization doesn't work when I embed the factors into
> the List-mode binary datafile:
>     
>    1. When I feed the list-mode data (with normalization factors and
> flag on) to CASToR, it give me the following error:
>    /oSensitivityGenerator::InitializeNormalizationFiles() ->
> Normalization correction is included in the data file while it is not in
> the sensitivity computation!/
>    In order to bypass this error, I use /-sens/ to provide a precomputed
> sensitivity image (Not normalized) to CASToR. Is this the proper way to
> do it? If not, what should I feed to CASToR instead?
>     
>    2. After feeding precomputed sensitivity image, the CASToR can run
> reconstruction with no issues, but the image with embedded LM
> normalization factors is identical to the image without normalization
> factors. Then I assign all the events with the same normalization factor
> of 0.1,1,10, respectively. But the reconstructed images have the same
> pixel intensities, which means I did something wrong and the LM
> normalization factors is not doing its job at all in my case.
>     
>    The version I am using is CASToR v 3.0.1.
>     
>    Here is one of the header files:
>    Data filename: PET_Sim_LMNorm.Cdf
> Number of events: 13755984
> Data mode: list-mode
> Data type: PET
> Start time (s): 0
> Normalization correction flag: 1
> Duration (s): 1500
> Scanner name: D04_sim_1ring
> Calibration factor: 1
> Isotope: unknown
>     
>    Here is some examples of the I generated list-mode data: (I
> assgin all the time frames to 0 and  norm factors to 1)
> 0000 0000 0000 803f ba22 0000 c005 0000
> 0000 0000 0000 803f 9a15 0000 9e19 0000
> 0000 0000 0000 803f e20e 0000 fa0b 0000
> 0000 0000 0000 803f f51f 0000 6a05 0000
> 0000 0000 0000 803f 971a 0000 1203 0000
> 0000 0000 0000 803f e91f 0000 d719 0000
> 0000 0000 0000 803f 211d 0000 3721 0000
> 0000 0000 0000 803f f906 0000 7105 0000
> 0000 0000 0000 803f 4c20 0000 f014 0000
> 0000 0000 0000 803f 8e1e 0000 a607 0000
> 0000 0000 0000 803f a821 0000 1a19 0000
> 0000 0000 0000 803f e81a 0000 8514 0000
>    0000 0000 0000 803f 6913 0000 e525 0000
>     
>     
>    Thank you very much!
>    --
>                                           Zipai Wang
>          Biomedical Engineering PhD student                    Stony
> Brook University 
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