# OSEM reconstruction for SPECT using SIMIND

**URL:** <https://pytomography.discourse.group/t/osem-reconstruction-for-spect-using-simind/64>\
**Category:** Usage Questions\
**Created:** [September 11, 2024, 2:54am UTC](https://pytomography.discourse.group/t/osem-reconstruction-for-spect-using-simind/64 "2024-09-11T02:54:34Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Haruki](https://avatars.discourse-cdn.com/v4/letter/h/c89c15/32.png) [@Haruki](https://pytomography.discourse.group/u/Haruki)\
**Post date:** [September 11, 2024, 2:54am UTC](https://pytomography.discourse.group/t/osem-reconstruction-for-spect-using-simind/64/1 "2024-09-11T02:54:34Z")

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Hello, everyone.  
I have a trouble, about OSEM reconstruction.  
I was doing OSEM with pytomography, but the image after reconstruction dose not work. I was using a cylindrical homogeneous phantom with a diameter of 18cm, but the image is smaller when reconstructed.  
I also do scatter correction and attenuation correction using CT images.

What are the possible causes of this and what is the solution?  
Please help me.

![SIMIND_image_bold](https://global.discourse-cdn.com/free1/uploads/pytomography/original/1X/718fcfcd161dfecb9c65dc3fd2257245a454474e.png)  
Projection image

![Rec_image_bold](https://global.discourse-cdn.com/free1/uploads/pytomography/original/1X/f31606a8b51135fc21b94e38f4934d6067ca9f49.png)  
Reconstruction image

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**Author:** ![lukepolson](https://avatars.discourse-cdn.com/v4/letter/l/e9a140/32.png) [@lukepolson](https://pytomography.discourse.group/u/lukepolson)\
**Post date:** [September 27, 2024, 5:01am UTC](https://pytomography.discourse.group/t/osem-reconstruction-for-spect-using-simind/64/2 "2024-09-27T05:01:17Z")

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@Haruki which version of SIMIND are you using? There’s an issue in SIMIND v8.0 (where collimator dimensions are now expressed in mm instead of cm) that messes with PyTomography

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**Author:** ![Haruki](https://avatars.discourse-cdn.com/v4/letter/h/c89c15/32.png) [@Haruki](https://pytomography.discourse.group/u/Haruki)\
**Post date:** [September 27, 2024, 6:29am UTC](https://pytomography.discourse.group/t/osem-reconstruction-for-spect-using-simind/64/3 "2024-09-27T06:29:40Z")

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Dear Luke.

Thank you for your reaction.  
This was exactly the problem And I was able to resolve it.

One question: what do the units mean after reconstruction?  
Is it [counts/MBq/sec] as in projection data?