[Castor-users] [Castor-devel] Fwd: Re: TR: SPECT reading Interfile

[Simon Stute]

Hi Michael,

To complete Thibaut's answer:
  - the scatter amount is given as a rate in counts/sec. The "counts" 
refer to a raw number of scatter counts for this given bin (directly 
comparable to the prompts). A rate is needed for the generalization when 
we reconstruct from a list-mode for which the time frames are not 
predefined, so it is flexible.
  - the normalization factor is optional and in SPECT it can be used for 
pixelated detectors like CZT-based detectors to normalize for variable 
efficiency from a pixel to another.

Finally, in CASToR, we took the decision to always consider additive 
contributions part of the model (added to the forward projection) and 
all multiplicative corrections are also combined within the system 
matrix elements. This corresponds to the "Ordinary Poisson" model. 
However, you are still allowed to provide any value in the "Amount of 
data in the bin" field.

Cheers
Simon

Le 28/04/2017 à 13:18, tmerlin a écrit :
>
> Hi Michael,
>
> The scatter rate is normalized by the frame/acquisition duration in 
> seconds (if provided) and added to the forward projection value. The 
> normalization factor is a multiplicative correction factor applied 
> during forward & backward projection.
>
> Best regards,
>
> Thibaut Merlin
>
>
> On 26/04/2017 18:53, Michael Ljungberg wrote:
>>
>> Hi all
>>
>> Look like my conversion program works now. I also got the attenuation 
>> correction to work. Simind and Castor has a different orientations so 
>> I solved this by starting at 180 degrees instead of flipping the end 
>> result. This also aligned to the orientation of the attenuation map.
>>
>> I have a question concerning the scatter. The value I add to the 
>> *.cdf file – is it added in the forward projector or is it subtracted 
>> in some way?  I assume the scatter value should be normalised to the 
>> total value I also add.
>>
>> Second question – what does the “ Normalization factor of the 
>> corresponding sinogram bin“ value actually do in SPECT histograms?
>>
>> Best regards
>>
>> Michael
>>
>>
>>
>> _______________________________________________
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>> Castor-users at lists.castor-project.org
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>
> -- 
> Thibaut MERLIN -- PhD
>
> Docteur en Imagerie Médicale au Laboratoire de Traitement de l'Information Medicale (LaTIM - INSERM UMR 1101)
> Bâtiment 1
> CHRU Morvan - 2, Av. Foch
> 29609 Brest CEDEX - FRANCE
> Tel: 06.75.12.24.90
>
>
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