# SPECT Butterfly effect

**URL:** <https://castor-project.discourse.group/t/spect-butterfly-effect/23>\
**Category:** General Discussions\
**Created:** [May 8, 2017, 8:10am UTC](https://castor-project.discourse.group/t/spect-butterfly-effect/23 "2017-05-08T08:10:57Z")\
**Posts on this page:** 2\
**Page:** 1

<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:** [May 8, 2017, 8:10am UTC](https://castor-project.discourse.group/t/spect-butterfly-effect/23/1 "2017-05-08T08:10:57Z")

</div>

Dear users and developers,

I am trying to use CASToR for image reconstruction on SPECT. I have simulate 2 cylinders, 1 big + 1 small with activity. I have also slightly modify castor-GATERootToCastor in order that I can manually insert the parameters required (for example: number of pixels, distance from scanner etc.).

I am attaching the images from the root file and the reconstructed ones. Does anyone know what have gone wrong?

Thank you in advance,

Konstantinos

![rootxy.png](https://global.discourse-cdn.com/free1/uploads/castor_project/original/1X/120c726019bd4d2bb3fb53221844b4f99d92f56e.png)

![rootxz.png](https://global.discourse-cdn.com/free1/uploads/castor_project/original/1X/933c300170e8a34e8218f1f76ab89c6ad9edaa74.png)

 ![castor_xy+xz.png](https://global.discourse-cdn.com/free1/uploads/castor_project/original/1X/e2f50f71f3f58b73b35e610a9acb6ed15c1687ff.png)

---

<div class="post-metadata">

**Author:** ![STUTE\_Simon](https://avatars.discourse-cdn.com/v4/letter/s/b3f665/32.png) [@STUTE\_Simon](https://castor-project.discourse.group/u/STUTE_Simon)\
**Post date:** [May 9, 2017, 1:03pm UTC](https://castor-project.discourse.group/t/spect-butterfly-effect/23/2 "2017-05-09T13:03:18Z")

</div>

Dear Konstantinos,

Maybe a guess: Seeing the sourcePos from ROOT, you have a ring of activity around the two cylinders, however, in the reconstructed image, it seems that the reconstructed field-of-view is not large enaugh to include this ring. If this is the case, then the artifacts can come from that (with iterative algorithms, the whole activity distribution has to be included in the image space).

Cheers  
Simon