[Castor-users] CASToR TOF reconstruction

Mon Apr 26 11:29:16 CEST 2021

Hello,

thank you for your quick response, Maxime. You are correct, I had set the
single time resolution incorrectly!

Thank you for the help in this matter, your assistance has been greatly
appreciated.

Best regards,
*Philip*

On Sun, Apr 25, 2021 at 12:03 AM Maxime Toussaint <
Maxime.Toussaint at usherbrooke.ca> wrote:

> 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> de la
> part de COMTAT Claude <claude.comtat at cea.fr>
> *Envoyé :* 24 avril 2021 10:05
> *À :* castor-users at lists.castor-project.org <
> 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%7C3d4c00a746ae4287bd8808d9072a0979%7C3a5a8744593545f99423b32c3a5de082%7C0%7C0%7C637548699406188273%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=zL17d21iQOYDLuGLX5ql%2BDI2eqbZmdZD44GZwtZzJNc%3D&reserved=0>
>
> [image: BIOMAPS]
>
>
>
> *De :* Castor-users <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
> *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> de la
> part de Philip Kalaitzidis <kalaitzidis.philip at gmail.com>
> *Envoyé :* 23 avril 2021 12:54
> *À :* castor-users at lists.castor-project.org <
> 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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