[Castor-users] Visualisation of a Line of the System Matrix

[M.R Teimoori]

Hello Simon,

Thank you for your replies to my two emails.

I've attached a file of a CASToR-formatted crystal lookup table for an
arbitrary PET scanner called "aSamplePETScanner.lut" with its header
"aSamplePETScanner.hscan". Let's assume that I'd like to visualize a sample
line of the system matrix that corresponds to a coincidence between
crystalIDs 6000 and 6142. The XYZ coordinates of the centroids of the
crystals, as defined by CASToR's coordinates system, are [-161.4  -11.0
 -15.8] and [156.4  37.4  -12.6]. I've made a sample binary coincidence
data file that has the information of this coincidence and set the time of
the event to 1 ms. This file is called "aSampleLOR.Cdf" and is attached
along with its header "aSampleLOR.Cdh". No
attenuation/scatter/random/normalization
coefficient is defined in this overly simplified case.

I usually find visualizing a single row of the system matrix extremely
helpful if I want to learn the effects of various reconstructions
parameters on image quality. Today in my investigations, I learned that it
actually is possible to see this coincidence only if *no convolution* is
used. I've attached a 2D superimposed image of all image slices for the
mentioned event to this email. Once I introduce a convolution (i.e. -conv
...... ), the images turn to be blank. So, I'm wondering how one can have
the images of a single coincidence with some convolution parameters
introduced.

Also, here are some side notes about what I observed about this discussion.
They may be useful for other CASToR users too, if you use one or only a few
coincidences:

- You probably see uniform images in iteration 1 and 2 and see your LOR(s)
only after the 2nd iteration which puzzles me a bit,
- Enabling multi-threading when only a few events are used directs the
reconstruction code to an infinite loop.

Thank you,

Cheers,
Reza

On Tue, May 2, 2017 at 10:47 AM, Simon Stute <simon.stute at cea.fr> wrote:

> Hi again !
>
> Could you send the geometry description of your scanner along with your
> tiny list-mode please ?
> I will be able to test it quickly and find why you do not see nothing.
>
> Cheers
> Simon
>
>
> Le 28/04/2017 à 19:06, M.R Teimoori a écrit :
>
> Hi All,
>
> I would like to visualize a sample line of the system matrix using CASToR.
> If I am not wrong, this should be feasible when you input a single
> coincidence data (corresponding to the desire line of the system matrix)
> and reconstruct an image using listmode EM with 1 iteration. However,
> CASToR returns a uniform image if the input has only the data for one
> coincidence. Why is this not possible? If anybody knows a workaround,
> please let me know.
>
> Thank you for your help,
>
> Cheers,
> Reza
>
>
>
>
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