[Castor-users] artifacts in the reconstruction

[Alessandro Pilleri]

Dear All,
with the intent to include the normalization coefficients I was looking at
the data file created by castor-GATERootToCastor and I saw that It contains
an odd number of events (LORs), in which an event is identified by a pair
crystal1-crystal2. The scanner (with a coincidence scheme of 1vs3) has ~9.7
million LORs but the entries in the data file are more than 25 million.
This event includes LOR identified for example by crystals belonging to the
same module, even adjacent crystals, that are clearly not in coincidence.
The "amount" value for these events is equal to zero. If I remove all the
zero-amount events from the data file and create a new histogram, the
reconstruction shows no artefacts, even without the application of the
normalization correction. I attach the images, left with all the events,
right after removing the zero-amount LORs.

Is this normal behaviour?

Best
Alessandro


[image: image.png]






On Wed, Dec 16, 2020 at 1:31 PM Alessandro Pilleri <a.pilleri at gmail.com>
wrote:

>
> Dear Simon,
> thank you for your answer.
>
> I used the GateRoot converter to create the data file in histogram mode
> and to automatically generate the geometry (-geo parameter). It
> automatically added the 135 deg min angle difference in the .geom file.
> I thought the min angle difference was applied in the loop over the data,
> so I tried to change it in the .geom file.  By the way, now  I created two
> different data files changing the digitizer option in the gate macfile to
> change the coincidence scheme and the sensitivity images do look different.
>
> For the application of the normalization coefficients, in histogram mode,
> do I have to manually modify the datafile to change the normalization
> coefficients of the events from 1 to the appropriate coefficient?
>
> Alessandro
>
> On Wed, Dec 16, 2020 at 11:42 AM STUTE Simon <simon.stute at chu-nantes.fr>
> wrote:
>
>> Hi Alessandro,
>>
>>
>> The artifacts are totally normal if you do not apply a normalization
>> correction, especially with low number of detector panels.
>>
>>
>> As for the min angle difference, did you let CASToR compute the
>> sensitivity image in both cases (135 and 180) ? Are they different ?
>>
>> The min angle difference is not apply in the loop over the data, so it
>> should be applied by yourself when building the datafile.
>>
>> Also, how did you build the geometry of your scanner, from your own LUT
>> file or using the GATE converter ?
>>
>>
>> By the way, your emails successfully reached the mailing list.
>>
>>
>> Best
>>
>> Simon
>>
>>
>> ------------------------------
>> *De :* Castor-users <castor-users-bounces at lists.castor-project.org> de
>> la part de Alessandro Pilleri <a.pilleri at gmail.com>
>> *Envoyé :* mardi 15 décembre 2020 16:37
>> *À :* castor-users at lists.castor-project.org
>> *Objet :* [Castor-users] artifacts in the reconstruction
>>
>> Dear castor-users,
>> I give an update to my previous email.
>> I tried to change the min angle difference in the geometry file from 135
>> (meaning a coincidence schema 1vs3) to 180 (meaning a coincidence schema
>> 1vs1) and the two reconstructions provided exactly the same results.
>>
>> Could the artifact be related to some kind of bug (or a misuse by my
>> side) related to the "min angle difference"?
>>
>> Thank you
>> Alessandro
>>
>
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