[Gate-users] Fixed Forced Detection algorithm: de-noising required?

[Simon Rit]

Interpolation is a good choice, I always use it in practice. I would not
consider denoising because the result is quite smooth already if you only
measure the object scatter.
Thanks, I would not have guessed it but it's a "small" object. Compton
scatter should take over at this energy with larger objects (intuitively).
Simon

On Wed, Jun 28, 2017 at 1:26 PM, Triltsch, Nicolas <nicolas.triltsch at tum.de>
wrote:

> Hi,
>
> Okay, this information is very helpful, because it shows possibilities for
> acceleration, for example, using interpolation or de-noising if the
> detector resolution is chosen very coarse (20 x 20, as an example.)
>
> You are right, maybe that's the reason. But then I wonder how they can use
> very little number of photons even for more complex test objects in later
> sections of their paper.
>
> This might be interesting for you: I simulated the scatter signal behind a
> water cylinder of 5cm diameter at 60keV and the coherent scatter signal
> (0.4% I_0) exceeded the incoherent scatter signal (around 0.1% I_0).
>
> Cheers,
>
> Nico
>
> On 06/28/2017 11:41 AM, Simon Rit wrote:
>
> Hi,
> There is no denoising and no interpolation. It gives the result of
> Poludniowski before intepolation which I think can easily be done out of
> Gate.
> I don't know why you need more photons... Are you sure you have tested the
> same test case? For example, they have used 60 keV monoenergetic photons
> which is very favorable because there is little elastic scattering at this
> energy (which takes longer to converge). I also note that they only look
> behind a (simple) cubic phantom where it converges faster in my experience.
> Simon
>
> On Wed, Jun 28, 2017 at 11:27 AM, Triltsch, Nicolas <
> nicolas.triltsch at tum.de> wrote:
>
>> Hello Gate community, hallo Simon Rit,
>>
>> I have a general question to the implementation of the fixed forced
>> detection algorithm.
>>
>> Is there a de-noising step performed at the end of one simulation run (as
>> reported by  Colijn & Beekman 2004 or Mainegra-Hing & Kawrakow 2008) or
>> does the implementation follow the fixed forced scheme ( Poludniowski et
>> al. 2009) where no de-noising step is required, because scatter is
>> registered at nodal points at the detector followed by linear interpolation.
>>
>> If the latter is used, then I wonder why 10^5 to 10^6 photons are
>> required to obtain low uncertainty images, because in the mentioned paper
>> they use only 10^3 to 10^4 photons to gain reasonable results.
>>
>> Cheers and I appreciate any help!
>>
>> Nico
>>
>> --
>> B.Sc. Nicolas Triltsch
>> Masterand
>>
>> Technische Universität München
>> Physik-Department
>> Lehrstuhl für Biomedizinische Physik E17
>>
>> James-Franck-Straße 1
>> 85748 Garching b. München
>>
>> Tel: +49 89 289 12591
>>
>> nicolas.triltsch at tum.de
>> www.e17.ph.tum.de
>>
>> _______________________________________________
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>
>
>
> --
> B.Sc. Nicolas Triltsch
> Masterand
>
> Technische Universität München
> Physik-Department
> Lehrstuhl für Biomedizinische Physik E17
>
> James-Franck-Straße 1
> 85748 Garching b. München
>
> Tel: +49 89 289 12591 <+49%2089%2028912591>
> nicolas.triltsch at tum.dewww.e17.ph.tum.de
>
>
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