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

[Simon Stute]

Hi Wei,

Few questions:

1. What version of Gate are you using ?

2. What navigator are you using ?

  Typically if regularMatrix, be careful with the skipVoxelBoundaries flag
(try to turn it off).
  If fictitiousVoxelMap, are you forcing the fictitious energy, or the
gamma-discard energy ?

3. Could you give the numbers ? is it a big difference ?

Also, happy new year to all !

Cheers,
Simon


On Mon, Dec 16, 2013 at 4:47 AM, Wei ZHAO <zhihuaigu at 163.com> wrote:

>
> 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 :=
>
> -------------------------------------------------------------------------------------------------------------------------
>
>
>
>
>
> _______________________________________________
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> Gate-users at lists.opengatecollaboration.org
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>
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