[Castor-users] CASToR TOF reconstruction

tmerlin Thibaut.Merlin at univ-brest.fr
Wed Apr 28 18:47:55 CEST 2021 

Hi Maxime,


Just for precision, the TOF resolution has to be set by the user. It is 
the TOF range which is automatically converted from GATE files (from the 
coincidence window value, and only if not set by the user).


You are right about the warnings though.


Best,
Thibaut


On 26/04/2021 17:09, Maxime Toussaint wrote:
> Greetings,
>
> Oh, you included optical photons in your simulation. I am less 
> familliar in how GATE deal with that case.
>
> In a basic simulation, without optical photons, the time registered 
> for Singles/Coincidences is directly the time of interaction of a 
> gamma with a "CrystalSD". It does not correspond to reality but it is 
> the best GATE can do when it does not emulate a photodetector and it 
> is good enough, as you said, with TOF resolution >100 ps*.
>
> I believe that some users of GATE + CASToR might not have your insight 
> about the correct manipulation of ultra-fast timing resolution (i.e. 
> adapting GATE timing). As such, it might be usefull to add a comment 
> on that part in the documentation of GATE-to-CASToR model conversion 
> tool since CASToR extract TOF resolution from GATE mac file. It might 
> even be usefull to add a warning in the documentation about the TOF 
> kernel with ultra-fast timing since it can become non-Gaussian in 
> those cases.
>
> Best,
> Maxime Toussaint
>
> * For typical detectors
>
> ------------------------------------------------------------------------
> *De :* Castor-users <castor-users-bounces at lists.castor-project.org> de 
> la part de COMTAT Claude <claude.comtat at cea.fr>
> *Envoyé :* 26 avril 2021 05:30
> *À :* castor-users at lists.castor-project.org 
> <castor-users at lists.castor-project.org>
> *Objet :* Re: [Castor-users] CASToR TOF reconstruction
>
> It was vGATE 9.0, and we analysed the root output (time difference). 
> The result as such is not surprizing. As far as I understood, the time 
> is set according to the very last interaction resulting from the 
> detection of the single photon in the detector. It includes obviously 
> the effect of variable depth of interaction. We measured a value of 72 
> ps FWHM. When we added a time resolution of X [ps] 
> (/gate/digitizer/Singles/timeResolution/setTimeResolution X), the 
> measured coincidence time resolution fitted nicely with SQRT(X^2 + X^2 
> + 72^2).
>
> Now, if you wish to simulate ultra-fast timing resolution (< 100 ps), 
> you need to modify how the time is set in GATE (for example, consider 
> the detection of the first photoelectron).
>
> Best,
>
> *Claude COMTAT*
>
> Laboratoire d’Imagerie Biomédicale Multimodale Paris Saclay
>
> Université Paris-Saclay, CEA, CNRS, Inserm
>
> Service Hospitalier Frédéric Joliot
>
> 91401, Orsay, France
>
> biomaps.universite-paris-saclay.fr 
> <https://can01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.biomaps.universite-paris-saclay.fr%2F&data=04%7C01%7Cmaxime.toussaint%40usherbrooke.ca%7C713f31b848a8477acafd08d908961a03%7C3a5a8744593545f99423b32c3a5de082%7C0%7C0%7C637550263043966069%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=%2BvVQy9ju26qii6p85Yr45f%2FbFA%2FWKWGT2qylP48oqIs%3D&reserved=0>
>
> BIOMAPS
>
> *De :*Castor-users <castor-users-bounces at lists.castor-project.org> *De 
> la part de* Maxime Toussaint
> *Envoyé :* dimanche 25 avril 2021 00:03
> *À :* castor-users at lists.castor-project.org
> *Objet :* Re: [Castor-users] CASToR TOF reconstruction
>
> Greetings,
>
> On which version of GATE and which type of data file (root, binary, 
> ascci) did you observe this behavior? In the past, I tested a range of 
> TOF resolution with Gate v8.0 using binary output and I did not 
> observe this behavior.
>
> Are you peharps referring to the effect of depth of interaction on 
> coincidence timing resolution? For typical detectors, the effect on 
> timing resolution would indeed be less than 100 ps.
>
> Best,
>
> Maxime Toussaint
>
> ------------------------------------------------------------------------
>
> *De :*Castor-users <castor-users-bounces at lists.castor-project.org 
> <mailto:castor-users-bounces at lists.castor-project.org>> de la part de 
> COMTAT Claude <claude.comtat at cea.fr <mailto:claude.comtat at cea.fr>>
> *Envoyé :* 24 avril 2021 10:05
> *À :* castor-users at lists.castor-project.org 
> <mailto:castor-users at lists.castor-project.org> 
> <castor-users at lists.castor-project.org 
> <mailto:castor-users at lists.castor-project.org>>
> *Objet :* Re: [Castor-users] CASToR TOF reconstruction
>
> Hello,
>
> just a comment: for a GATE simulation, the effective coincidence 
> resolution is not just SQRT(2*/X/^2). If you set /X/ to zero in GATE 
> and draw the ToF histogram for a perfectly centred point source, you 
> will see that the width of the distribution is not zero. There is an 
> intrinsic coincidence time resolution /E/ in GATE, related to the way 
> the time information is stored. So, the effective coincidence 
> resolution is SQRT(2*/X/^2 + /E/^2). Now, /E/ is typically less than 
> 100 ps. So, depending on X, it can be negligible.
>
> Best,
>
> Claude
>
> *Claude COMTAT*
>
> Laboratoire d’Imagerie Biomédicale Multimodale Paris Saclay
>
> Université Paris-Saclay, CEA, CNRS, Inserm
>
> Service Hospitalier Frédéric Joliot
>
> 91401, Orsay, France
>
> biomaps.universite-paris-saclay.fr 
> <https://can01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.biomaps.universite-paris-saclay.fr%2F&data=04%7C01%7Cmaxime.toussaint%40usherbrooke.ca%7C713f31b848a8477acafd08d908961a03%7C3a5a8744593545f99423b32c3a5de082%7C0%7C0%7C637550263043966069%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=%2BvVQy9ju26qii6p85Yr45f%2FbFA%2FWKWGT2qylP48oqIs%3D&reserved=0>
>
> BIOMAPS
>
> *De :*Castor-users <castor-users-bounces at lists.castor-project.org 
> <mailto:castor-users-bounces at lists.castor-project.org>> *De la part 
> de* Maxime Toussaint
> *Envoyé :* vendredi 23 avril 2021 20:05
> *À :* castor-users at lists.castor-project.org 
> <mailto:castor-users at lists.castor-project.org>
> *Objet :* Re: [Castor-users] CASToR TOF reconstruction
>
> Greetings,
>
>
> The profiles remind me of a nice paper that studied the consequences 
> of over/under estimation of the TOF kernel. Since you use GATE, is it 
> possible that you have made a slight error in setting the TOF 
> resolution? The command in GATE 
> "/gate/digitizer/Singles/timeResolution/setTimeResolution X" defines 
> the *single* resolution as X. As such, the *coincidence* resolution is 
> sqrt(2) * X.
>
> Note: My memory tells me that CASTOR extract the coincidence TOF 
> resolution directly from the .mac, so this should not happen. However, 
> you "set it by hand", which makes it a possibility.
>
> Bests,
>
> Maxime Toussaint
>
> ------------------------------------------------------------------------
>
> *De :*Castor-users <castor-users-bounces at lists.castor-project.org 
> <mailto:castor-users-bounces at lists.castor-project.org>> de la part de 
> Philip Kalaitzidis <kalaitzidis.philip at gmail.com 
> <mailto:kalaitzidis.philip at gmail.com>>
> *Envoyé :* 23 avril 2021 12:54
> *À :* castor-users at lists.castor-project.org 
> <mailto:castor-users at lists.castor-project.org> 
> <castor-users at lists.castor-project.org 
> <mailto:castor-users at lists.castor-project.org>>
> *Objet :* [Castor-users] CASToR TOF reconstruction
>
> Dear CASToR developers and users,
>
> I have a question regarding an issue with CASToR TOF reconstruction.
>
> I will give a brief background of the issue: I have modelled the G.E. 
> Discovery MI (DMI) PET/CT with GATE and simulated a PET acquisition 
> with the NEMA IQ phantom. I have converted the data to the CASToR 
> list-mode format and so far, there are generally no problems. However, 
> when including TOF in the data file I get an increased signal in the 
> reconstructed image in places where I do not expect, e.g., in the lung 
> insertion, but also a quite reduced signal in the spheres.
>
> The TOF information for each event that I write to the binary file I 
> simply take the arrival time difference between crystal1 and crystal2, 
> i.e., time1-time2 and then multiply the difference by 1e+12 to get the 
> delta time in ps. I then save the crystals in the binary file as 
> Crystal ID1 (c1) corresponding to GATE crystal1 and Crystal ID2 (c2) 
> corresponding to GATE crystal2 (since it is mentioned in the general 
> documentation that the TOF delta time is positive when the emission 
> occurs closer to c2.) In the header file I set the TOF resolution to 
> 380 ps and the TOF measurement range to 4900 ps. I decided to only 
> write the true coincidences in the binary file (together with 
> attenuation, normalization, and the inclusion of a span of 2 for 
> indirect slices for segment 0) so that I could efficiently look at the 
> effect of TOF without having to bother with random- and scatter 
> correction.
>
> If I then reconstruct the data, I notice an increased signal in the 
> insertion compartment, as well as a notable reduction in signal 
> between some of the spheres (especially visible between the largest 
> spheres), as opposed to if I reconstruct the data using the 
> /-ignore-TOF /option (or without including TOF information in neither 
> the binary- nor the header file.) If I reconstruct the same data but 
> increase the TOF resolution to, e.g., 700 ps, the signal in the 
> insertion compartment is reduced and the reduced signal between 
> spheres are no longer present. (I also tested using the 
> GATERootToCastor converter with the TOF resolution to 380 ps yielding 
> similar results.)
>
> I have attached images showing a slice of the three examples that I 
> mentioned (TOF included with 380 ps TOF resolution, TOF included with 
> 700 ps TOF resolution, and with the /-ignore-TOF /option used.) I have 
> also included profiles through the same slices passing through two of 
> the spheres and the insertion compartment.
>
> Intuitively, this seems to yield erroneous results (with 380 ps TOF 
> resolution), but I cannot seem to understand why this effect occurs. I 
> was hoping someone could help me understand what the issue might be, 
> if I have missed something, or whether I am on the wrong track and 
> have misunderstood the /“TOF-induced”/ results.
>
> I hope to hear from you.
>
> Best regards,
> /Philip/
>
>
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-- 
Thibaut MERLIN -- PhD

Docteur en Imagerie Médicale au Laboratoire de Traitement de l'Information Medicale (LaTIM - INSERM UMR 1101)
Institut Brestois de recherche en Bio-Santé (IBRBS)
12 Avenue Foch, 29200 Brest, FRANCE
Tel: 06.75.12.24.90

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