[Gate-users] backprojection of coincidences

[Chen, Yu]

What about positron range?
Which positron have you simulated?

Can positron range and scatter account for 25%?

You should be able to look at list file to figure out
different kinds of events in your recorded coincidences. 

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: gate-users-bounces at lists.healthgrid.org on behalf of Angela Foudray
Sent: Thu 9/13/2007 12:36 PM
To: Peter Bloomfield
Cc: gate-users at lists.healthgrid.org
Subject: Re: [Gate-users] backprojection of coincidences
 
Yep, sounds like scatter to me.  Some fraction of the photons are
scattering in your water medium, some of those at small enough angles
that they would still be included in your energy window, but large
enough to move the line or response away from its original line.

Ange

On Thu, 2007-09-13 at 11:49 -0400, Peter Bloomfield wrote:
> On Thursday 13 September 2007 11:08, Marlen Priegnitz wrote:
> > Dear Gate-Users,
> >
> > I found some strange result for the backprojection of coincidences and
> > cannot find any explanation for it. Maybe somebody can help me with this?
> > This is what I did:
> > I was simulating a PETscanner and saving the coincidences in an ASCII-File.
> > My source is a voxelized cylinder (diameter 180 mm) of water with some
> > background activity (0.01 Bq per voxel) and inside there are some
> > spheres (water) with activity 0.04 Bq per voxel.
> > I have chosen this low activity to get in principle no randoms.
> > I'm simulating Positrons.
> > When I do the backprojection of the registered coincidences, then I
> > found, that approx. 25 % of the registered coincidences lie outside of
> > the source. (Also if I set the background activity to zero and have only
> > the hot spheres, I get this result)
> > How can this be? I don't believe that this are randoms, because when I
> > simulate a delayed time window, then I got nearly no coincidences.
> > Can anybody help me with this?
> > Did anybody observed something similar?
> > I'm grateful for each hint.
> > Thanks in advance.
> >
> > Marlen
> 
> Scatter?
> 
> Peter
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