[Gate-users] [ no subject ]

[Chen, Yu]

Thanks Jasmine for all you did.

See below my comments after **.

Yu Chen, Ph.D.
University of Massachusetts Medical School
Division of Nuclear Medicine
55 Lake Avenue North
Worcester, MA 01655-0243
Phone:  (508) 856-6123
Fax:    (508) 856-4572



-----Original Message-----
From: Jasmine Schirmer [mailto:jasmine.schirmer at tum.de]
Sent: Thu 12/20/2007 4:39 AM
To: Chen, Yu; gate-users at lists.healthgrid.org
Subject: Re: RE: RE: [Gate-users] [ no subject ]
 
Dear Yu Chen,

Thank-you for all your suggestions. First, we have attached the results of the PET benchmark from our two versions of GATE. They appear identical.

** 
When you say "They appear identical", have you compare those single's energy spectra? You can plot two benchmarkPET.root coincidence energy1 (or energy2) in LOG for comparison. If they are really same, the problem (higher energy in new GATE) could be "readout" module related.
**

As for the readout depth, we have intentionally set this to 5 because we are simulating a small animal PET scanner which indeed has individual crystal electronic readout. This has never given problems with the old version of GATE. The intercrystal coincidences are still expected to be
zero at 400 keV low energy threshold (independent of the readout depth) because it cannot be
that the same annihilation photon (511 keV) deposits twice 400 keV (=800
keV). At lower "low energy thresholds" (below 255 keV for an ideal
detector, no blurring in energy), our system can detect intercrystal
coincidences due to the individual crystal readout, which is simulated as readout
depth 5. We have checked now for you, and both versions of GATE are running the same single layer macro (i.e. the same readout depth 5). We do not believe that the problem lies here because we have also tested the ECAT simulation as well and it also gives the strange energy spectra when using the newest version of GATE (please see our plots in the November 29th email).

** 
I know that even you set depth 5 you should still get no energy for single above 511 keV (if no blurring). This strange thing is like a physical
pileup effect due to high activity when I first looked into it. That is why I suggest a low activity simulation. Now I am worried By MJ's normal results that it could be just a C++ technical problem and not a physics problem in Geant4 or GATE. I am not a real C++ expert. My guess is:

When multiple pulses are needed for one incident photon, the array to hold those pulses is not correctly zeroed.

Now you can do the following in changing your single_layer.mac to check:

1) set depth 1 -> is it normal?
2) set depth 5 -> how many more singles you get using the same time and activity as those in 1)?
                  can you plot different singles in different layers separately for those intercrystal coincident events? what do they look like? 
**


We have performed the energy blurring test you recommmended and in our GATE3.1.2 set the energy blurring resolution to 0.01. The attached figure (Gate312_energy_singles_1percent_blurr.ps) shows the result and the output of the simulation for a 400keV low energy threshold is:

There are: => 868148 singles
=> 35080 coincidences
=> 4097 intercrystal coincidences
=> 9900 randoms
=> 2313 intercrystal randoms

We welcome your thoughts!

Jasmine and Irene

Original Message:

I see.
<br />
<br />I downloaded your single_layer.mac and found the problem:
<br />
<br />You set your module *readout* depth as 5!
<br />while benchmarkPET is 1.
<br />
<br />Remember in cylindricalPET system:
<br />
<br />Level 1: rsector
<br />Level 2: module
<br />Level 3: submodule
<br />Level 4: crystal
<br />Level 5: layer
<br />
<br />What the depth 5 means that you have electronics readout for each layer crystal!
<br />If you have a penetration or scatter in different crystals for one incident photon,
<br />you will get multiple pulses there for multiple singles for the same photon.
<br />That's why you get many intercrystal coincidences.
<br />
<br />Now problem is:
<br />
<br />1) are you sure you used the same macro for both GATE version (setDepth 5)?
<br />If yes, that means for some reason that readout (setDepth) module does not work well in old
<br />GATE.
<br />
<br />2) did MJ use the exact same single_layer.mac (setDepth 5)?
<br />
<br />No matter what, setDepth 5 is wrong unless you really want to simulate penetration effect.
<br />
<br />Please change it to setDepth 1 (or 2 if you have a PMT for each module) and see what you get. 
<br />
<br />
<br />Yu Chen, Ph.D.
<br />University of Massachusetts Medical School
<br />Division of Nuclear Medicine
<br />55 Lake Avenue North
<br />Worcester, MA 01655-0243
<br />Phone:  (508) 856-6123
<br />Fax:    (508) 856-4572
<br />
<br />
<br />
<br />-----Original Message-----
<br />From: i.torres at lrz.tu-muenchen.de [mailto:i.torres at lrz.tu-muenchen.de]
<br />Sent: Wed 12/19/2007 2:06 PM
<br />To: Chen, Yu
<br />Subject: RE: RE: [Gate-users] [ no subject ]
<br /> 
<br />Hi Yu Chen,
<br />
<br />> Do you have the energy plot from single_layer?
<br />
<br />I do not have it here. But I send you the results from another GATE user
<br />that has the same problems. I posted the emails from this GATE user (he
<br />could not do it), but I am waiting for the administrator approval. You
<br />will see his emails soon. But in advanced I send you the plots of the
<br />enery spectra.
<br />
<br />> I tend to agree with MJ now that problem may not from GATE.
<br />
<br />I do not know where is the problem, but we have the recommended versions
<br />for CLHEP, Geant, gcc..., the benchmark is fine, but the results from the
<br />ECAT and single_layer macros are not right... puzzling.
<br />
<br />Thank you for you time and help.
<br />
<br />Bye,
<br />
<br />Irene and Jasmine
<br />
<br />

-- 

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.opengatecollaboration.org/mailman/private/gate-users/attachments/20071220/ae0705ae/attachment.htm>