[Castor-users] CASToR TOF reconstruction

[Xinjie Cao]

Hi Maxime,

Could you remember the name of the paper you mentioned? I am interested in
that paper. Thanks!

Best,
Xinjie

On Fri, Apr 23, 2021 at 2:05 PM Maxime Toussaint <
Maxime.Toussaint at usherbrooke.ca> wrote:

> 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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-- 
*....................................................*
*Xinjie Cao*
*M.Eng. / Ph.D. Candidate*
*Research Project Assistant*
*Department of Electrical and Computer Engineering & Radiology *
*Novel Medical Imaging Technologies Lab*
*Health Science Center Level 8*
*Stony Brook, NY 11794-8460 *
*Tel: +1 (631)202-9445*
you.stonybrook.edu/goldan/people/
*email: **xinjie.cao at stonybroo*k.edu <xinjie.cao at stonybrook.edu>


*....................................................*
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