# Question

**URL:** <https://castor-project.discourse.group/t/question/220>\
**Category:** General Discussions\
**Created:** [June 10, 2021, 10:15pm UTC](https://castor-project.discourse.group/t/question/220 "2021-06-10T22:15:23Z")\
**Posts on this page:** 5\
**Page:** 1

<div class="post-metadata">

**Author:** ![Hamid\_Nezampour](https://avatars.discourse-cdn.com/v4/letter/h/bb73d2/32.png) [@Hamid\_Nezampour](https://castor-project.discourse.group/u/Hamid_Nezampour)\
**Post date:** [June 10, 2021, 10:15pm UTC](https://castor-project.discourse.group/t/question/220/1 "2021-06-10T22:15:23Z")

</div>

Hello

We designed a partial PET scanner based on a cylinder PET scanner but we could not reconstruct the exact image. Is there a limit to the Castor application that cannot reconstruct a dual PET scanner?

Thanks,

---

<div class="post-metadata">

**Author:** ![sstute](https://avatars.discourse-cdn.com/v4/letter/s/8c91f0/32.png) [@sstute](https://castor-project.discourse.group/u/sstute)\
**Post date:** [June 11, 2021, 6:49am UTC](https://castor-project.discourse.group/t/question/220/2 "2021-06-11T06:49:20Z")

</div>

Hello,

The limit is not in CASToR but is mathematical. If you cannot record enough projection angles of your object, the problem is under-determined and you cannot recover the exact object.

Simon

---

<div class="post-metadata">

**Author:** ![Konstantinos\_P\_Chatz](https://avatars.discourse-cdn.com/v4/letter/k/ac8455/32.png) [@Konstantinos\_P\_Chatz](https://castor-project.discourse.group/u/Konstantinos_P_Chatz)\
**Post date:** [June 11, 2021, 8:12am UTC](https://castor-project.discourse.group/t/question/220/3 "2021-06-11T08:12:40Z")

</div>

Hello,

As a user of CASToR, I have extensively use it for 2-head PET reconstruction for experimental and simulation data. But there are many parameters that could go wrong. It needs caution.

Konstantinos

---

<div class="post-metadata">

**Author:** ![Gabriel\_Canizares\_Le](https://avatars.discourse-cdn.com/v4/letter/g/d9b06d/32.png) [@Gabriel\_Canizares\_Le](https://castor-project.discourse.group/u/Gabriel_Canizares_Le)\
**Post date:** [June 17, 2021, 4:12pm UTC](https://castor-project.discourse.group/t/question/220/4 "2021-06-17T16:12:26Z")

</div>

Dear CASToR users

I have been using this platform some months with iterative algorithms. Nowadays, I am trying to reconstruct some small spherical sources with FBP2D algorithm. Is there any possibility to achieve this goal with CASToR? I read time ago that this algorithm is not implemented, but just to be sure

Regards

Gabriel

---

<div class="post-metadata">

**Author:** ![sstute](https://avatars.discourse-cdn.com/v4/letter/s/8c91f0/32.png) [@sstute](https://castor-project.discourse.group/u/sstute)\
**Post date:** [June 18, 2021, 8:27am UTC](https://castor-project.discourse.group/t/question/220/5 "2021-06-18T08:27:53Z")

</div>

Hi Gabriel,

Indeed, it is not implemented has it requires a sinogram representation of the data with invariant sinogram bin size.

In some future, there will be a “sinogram scanner” in CASToR so that any type of PET, SPECT or CT data from a real scanner could be rebinned into a user’s specified sinogram representation.

For the moment, you will have to look somewhere else for FBP2D.

Best

Simon