[Gate-users] 3-D image reconstruction using STIR from GATE Results

[Claude Comtat]

Hi Guifen,

I do not know if this helps, but in a ecat7 sinogram, the center of the
sinogram along the radial direction is offset by the half of the bin
size. This is due to the fact that the number of radial bins is even.
For example, if you have 4 radial bins, numbered from 0 to 3, bin 2 will
be at the center. I would imagine that the reconstruction algorithm
should know that (at least, the ecat7 based reconstruction algorithms).

Claude

Guifen Lin wrote:

> Hi 
> simulate a point source (x=0,y=0) in the file PET_Ecat.mac.I 
> reconstructe the image in two mwthod:
> 1.Method one
> <1>.
> cd /usr/local/gate/gate_v3.0.0/examples/my_example/PET
> source /usr/local/gate/gate_v3.0.0/env_gate.csh
> /usr/local/gate/g4work/bin/Linux-g++/Gate PET_Ecat.mac
> ......
> 
> <2>.
> [root at localhost ~]# cd /usr/local/gate/STIR/my_test
> [root at localhost my_test]# /usr/local/gate/STIR/bin/ifheaders_for_ecat7 
> MySinogramFile.S
> Attempt all data-sets (Y) or single data-set (N) [Y/N D:Y]:
> Data number ? [0,8 D:0]:
> WARNING: ECAT7 IO: Bin size from header.x_resolution (2.2471) does not 
> agree with expected value 2.25
> for scanner ECAT 962. Using bin size from header...
> 
> <3>.
> [root at localhost my_test]# /usr/local/gate/STIR/bin/display_projdata 
> MySinogramFile_S_f1g1d0b0.hs
>  
> The sinogram shows a clear discontinuity in the line and the 
> reconstructing image shows  horseshoe shape . A friend said that this 
> horseshoe shape is usually a result of an offset of 1 pixel along the 
> x-axis in the sinogram.this 
> means I need to shift my sinogram by n pixels in the +x or -x 
> direction.How I can shift my sinogram by n pixels in the +x 
> or -x direction.Do I modify STIR's program?
> I'm looking forward to your help.
> Thank you in advance!
> guifen
>  
> 
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-- 
Claude Comtat						
Laboratoire d'Imagerie Moléculaire Expérimentale	
CEA/DSV/I2BM/SHFJ