[Gate-users] scatter extract from voxelized phantom with different voxel size

[Wei ZHAO]

Dear GATE user,
 
I have imported a thorax 3D data set using voxelized phantom format and want to investigate influence of the phantom downsampling on the extracted scatter signal. The scatter events were extracted with VOXELPHANTOMSD. The voxelized phantoms are 32x32x16, 64x64x16,128x128x16,256x256x16 grids with 8.8x8.8x11.2mm^3, 4.4x4.4x11.2mm^3,2.2x2.2x11.2mm^3,1.1x1.1x11.2mm^3 voxel size respectively. Since the phantom size is the same (with different voxel size), the extract scatter shouldn't change significantly. However, the final scatter have dramatic change. This may related to HOW GATE RETRIEVAL SCATTER USING VOXELPHANTOMSD? Does this dependent on voxel size? I have used the ROOT output.
 
I have used the below command to record scatter events.
 /gate/thorax_phantom/attachVoxelPhantomSD
the result is the smaller voxel size is, the smaller scatter signal I got.
 Can anyone help me sort this out? Any suggestion will be appreciated.
 
Thank you very much!
Best regards
Wei
 
below is my interfile  for 64x64x16 and 32x32x16 voxelized phantom :
--------------------------64x64x16------------------------------------------------------------
!number of images/energy window := 16
!process status := Reconstructed
!matrix size [1] := 64
!matrix size [2] := 64
!number format := unsigned integer
!number of bytes per pixel := 2
scaling factor (mm/pixel) [1] := +4.400000e+00
scaling factor (mm/pixel) [2] := +4.400000e+00
!number of projections := 16
!extent of rotation :=
!time per projection (sec) := 0
study duration (sec) := 0
!maximum pixel count := +2.000000e+02
patient orientation := head_in
patient rotation := supine
;
!SPECT STUDY (reconstructed data) :=
method of reconstruction := Unknown
!number of slices := 16
number of reference frame := 0
slice orientation := Transverse
slice thickness (pixels) := +11.200000e+00
centre-centre slice separation (pixels) := +11.200000e+00
filter name := Unknown
filter parameters := Cutoff
method of attenuation correction := measured
scatter corrected := N
oblique reconstruction := N
!END OF INTERFILE :=
------------------------------------------------------------------------------------------------------
---------------------------------------32x32x16--------------------------------------------------
!number of images/energy window := 16
!process status := Reconstructed
!matrix size [1] := 32
!matrix size [2] := 32
!number format := unsigned integer
!number of bytes per pixel := 2
scaling factor (mm/pixel) [1] := +8.800000e+00
scaling factor (mm/pixel) [2] := +8.800000e+00
!number of projections := 16
!extent of rotation :=
!time per projection (sec) := 0
study duration (sec) := 0
!maximum pixel count := +2.000000e+02
patient orientation := head_in
patient rotation := supine
;
!SPECT STUDY (reconstructed data) :=
method of reconstruction := Unknown
!number of slices := 16
number of reference frame := 0
slice orientation := Transverse
slice thickness (pixels) := +11.200000e+00
centre-centre slice separation (pixels) := +11.200000e+00
filter name := Unknown
filter parameters := Cutoff
method of attenuation correction := measured
scatter corrected := N
oblique reconstruction := N
!END OF INTERFILE :=
-------------------------------------------------------------------------------------------------------------------------

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.opengatecollaboration.org/mailman/private/gate-users/attachments/20131216/212e6258/attachment-0001.html>