forward projection

General Discussions
1

Dear CASTOR users and developers
I need to forward project an image and I reed a previous email in the castor mailing list that there is a piece of code for this process. Does anyone work with this code and is it possible to receive this code?
any help would be appreciated.
Best
Hadi

2

Hi Hadi,

Sure, I’ll send it to you in a separate email.

Best,
Thibaut

3

Hi Thibaut,

Would it be possible for you to share the same code with me?
I am working on forward projecting an image as well and would really appreciate it if you could share the code with me.

I have also requested access to the GitLab repo for “CASToR collaboration”. If you can grant me access to the repo I would highly appreciate it.

Thanks,
Mohammad Syed

5

Hi Thibaut,

Just wanted to follow up on my last post from last week.
I would really appreciate it if you could share the code with me and provide me access to the CASToR GitLab repo. Looking forward to your response.

Thanks,
Mohammad Syed

6

Hi Mohammad,
Sorry for the delay, I granted you access.
Regarding the forward projection tool, the branch castor-proj-asim contains a way more improved version in comparison with the original code. It is still work-in-progress but most of the features are already available. You can have a look in its documentation or the embedded help (castor-proj -h) for more information.

Best,
Thibaut

7

Thank you for your help.
I really appreciate it.

Thanks,
Mohammad Syed

8

Hi,

I tried the CASToR forward projection and I am running into a few issues. I am listing the process I used below please let me know if you find any issues here.
I have a LM file from a Siemens mCT for a cardiac scan scanner that I converted into CASToR format using the data converter. Reconstruction was done using MLEM with 3 iterations and 21 subsets. I ignored the scatter, normalization, attenuation, and randoms correction during the reconstruction.
This was followed by forward projection of the reconstructed image using the “castor-proj” from the “castor-proj-asim” branch. I used the following parameters for the forward projection
-PET_maxAxialDiffmm 196
-PET_isotope Rb-82
-sc PET_SIEMENS_BIOGRAPH_MCT
-img list-mode_OSEM_it3.hdr

I think the “maxAxialDiffmm” is the max ring difference which for the mCT is 49x4mm please correct me if I am wrong here. I did not include TOF information for the forward projection. I performed a reconstruction for the forward projected image as well.

Comparing the two reconstructed images (1. from castor converter, 2. from forward projected data) I noticed there is alot of difference around the edges of the images in the intensity. For example the max intensity for the castor converted file is 6978778.5 while for the forward projected image max is 29940064.0. However if I only focus on the Left ventricle then the max is 2073318.5 for the castor converted image and its 2145377.5 for the forward projected image.

The images themselves look OK but the intensity is different. Please let me know if you have any insight into why this could be or if this is expected.

Thanks,
Mohammad Syed

9

Hi Mohammad,

Apparently, you are the very first to post a discussion about the “castor-proj-asim” branch, a work in progress branch not yet released.

First, I would not expect exactly the same images, even if you do not add Poisson noise. Then, it is difficult to perform a comparison based on the maximum intensity value. It would be easier if you can share both images as well as the full commands used for the reconstructions and the simulation.

Your PET_maxAxialDiffmm looks correct.

Best,

Claude COMTAT
BioMaps
Service Hospitalier Frédéric Joliot
91401 Orsay, France
www.biomaps.universite-paris-saclay.fr