[Gate-users] voxellized phantom attenuation problem

[Richard Taschereau]

Hi Ahmet,

Could you send your script file and your phantom please ? I¹ll try to
reproduce the problem.

(Sebastien what is that patch in 3.1.2 ?)

Richard


On 2/27/08 3:38 PM, "ayanas at mail.med.upenn.edu" <ayanas at mail.med.upenn.edu>
wrote:

> 
> Dear Gate'rs
> 
> I am observing a problem with a voxelized phantom (using compressed voxel)
> with gate-3.1.1.
> Here is what happens:
> I load a voxellized MCAT phantom as the attenuating medium.
> The source is a simple point source at the center of the phantom.
> 
> I am recording the un-scattered photons (140 keV) making out
> of the MCAT torso.
> 
> Obervations:
> 1) When I make the material definitions of the all voxels as "Bone",
> (a uniform material made of bone) I get a sensible number of photons
> un-scattered. This is fine..
> 
> 2) When I make the material definitions of the all voxels as, "Lung"
> I, again,  get a sensible number of photons un-scattered. This is also fine..
> 
> 3) However, When I make the original MCAT definition, that is with
> Body (muscle),  Lung, Bone etc, I get a number of
> un-scattered photons much higher than the "All Bone" case
> making out of the MCAT torso;
> while I would expect to get a number between "All Bone" and "All Lung" case,
> (the densest material is the Bone, and the least dense is Lung).
> 
> Has anybody observed such a behaviour?
> Any ideas/suggestions as to what my problem might be?
> 
> I also saw a patch for gate 3.1.2 (patch_v3.1.2.tar.bin) with a mention
> to "compressed voxel capabilities". Does (Should) this patch apply
> also to gate 3.1.1 ?
> 
> Thank you very much,
> ahmet.


-- 
Richard Taschereau, Ph.D.
Crump Institute for Molecular Imaging
University of California Los Angeles
700 Westwood Plaza, A222
Los Angeles, CA 90095-1770
Phone: (310) 825-0697
Fax:     (310) 206-8975
email: RTaschereau at mednet.ucla.edu



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