[Gate-users] How to find the relation between different hits?

[Uwe Pietrzyk]

Dear Rebecca, dear Astrid,

let me briefly add to what already was explained: The eventID is unique only
for each time slice / run. For each runID you will find increasing eventID numbers.
For example, if you simulate for 30 sec with a time slice of 1 sec, the runID will
have 30 different increasing values and for each runID, you will find the
respective eventIDs. In your root-module, you should check for the runID
to be the same, then for the eventID and finally for this eventID you can
extract further information from the Hits branch.
For coincidences, this is even more complicated, as you will find
labels 1 and 2 for the two legs of the annihilation event.
Please also note, that the event handling and numbering (to my
understanding) tightly relates to the GEANT4 rules, as do for
example the particle IDs.

I hope this helps.

Kind regards, Uwe

On 06.11.2009, at 15:18, Rebecca Gregory wrote:

Dear Astrid,

Isn't there also a crystalID, there is in my version 3.1.2. But I simulate a PET system maybe it is different.

I agree it is difficult to work out what the contents of the root file means. There is in the documentation a description of the columns of the ascii output which should be similar I eventually worked out the contents of some of the root file from there.

Then looking at the nature of the data I worked out the rest I hope. Clearly all events with the same eventID originate from the same emission. Then as these photons interact creating further particles/photons these are tracked with new track IDs. The Procees name says what type of interaction occurs. edep is the energy deposited in the crystal and crystal ID shows which crystal. In PET the photon ID is 1 for the first photon and 2 for the second. I found the parent ID was 0 if the photon originated from the nucleas, rather than an interation (annihilation). Maybe the parent ID is 1 if the photon was generated?
I haven't looked into the primary ID.

If the root output hasn't changed ( i hope it hasn't) I think you can get all the info you want.
Becky


Rebecca Gregory
The Joint Department of Physics,
Royal Marsden NHS Foundation Trust
and Institute of Cancer Research,
Downs Road, Sutton,
Surrey SM2 5PT, UK
Astrid Velroyen <astrid at velroyen.de<mailto:astrid at velroyen.de>> 11/05/09 11:20 AM >>>
Dear GATE users,

I have got a question about how to analyze a GATE Hits simulation with
.root-Output. I'd like to be able to identify which hits belong to the
same incident gamma quantum. That means, that I want to keep track of of
each photon and find out which way it has gone, if it has left energy in
different crystals and so on.
I'm not sure which of the histogrammed data in the root output can
provide this information, the User's Guide does not give any detailed
information and I already looked up the GateCrystalHit.hh, where the
comments do not more than repeat the variable names.
Can anyone clarify what means trackID, parentID, photonID, primaryID,
eventID, and runID? Can anything of these data be used to follow the
ways of one gamma quantum coming out of my gamma beam source?
I tried to get the meaning of each of these histograms by looking how
many bins I have for a Hits list with about 1,000,000 entries:
TrackID is something between 1-7, parentID between 1-5.
PhotonID is always 1; I guess it just distinguishes between the two
annihilation photons, which I don't have, because I defined a simple
gamma beam source.
PrimaryID is also always 1.
EventID has 300*10^3 bins, maybe this is what I am looking for?
runID is always 1.

Has anyone of you experience with analyzing a hits output and can give
me some advice? Thanks.

regards,

Astrid

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Prof. Dr. Uwe Pietrzyk
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