[Gate-users] Z-grid spacing problem

kangh at mskcc.org kangh at mskcc.org
Fri May 2 16:32:29 CEST 2008

Hello Kris,

I am having a problem with z grid spacing for using STIR.  I read
through STIR-user messages but it is not clear to me what I have to
change to make my current interfile work for STIR.  When I tried to run
STIR with my current .hv file I have gotten the following message

WARNING: BinNormalisationFromAttenuationImage:
        attenuation image data are supposed to be in units cm^-1
        Reference: water has mu .096 cm^-1
        Max in attenuation image: 0.096

ERROR: DataSymmetriesForBins_PET_CartesianGrid can currently only
support z-grid spacing equal to the ring spacing of the scanner divided
by an integer. Sorry

I found out that the cause of the error is incorrect scaling factor for
the z direction.  
The following lines are from my .hv file.

!matrix size [3] := 21
scaling factor (mm/pixel) [3] := 1.27999

I was told that changing the value of scaling factor (mm/pixel) [3] from
1.27999 to 4.25 should work. I tried and actually I did not get the
error message.  I was going to recalculate the matrix size to be 6 or 7
to make scaling factor to be 4.25 (21*1.27999/4.25). However, there
seems to be certain ways to assign those parameters according to the
messages about z-grid in the user message instead of simply fixing the
value of scaling factor (mm/pixel) [3] to be 4.25.  

Could you clarify this?

Thank you in advance,


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