[Gate-users] ideal PET system

[Matthew Lewis]

is there anyway to model an ideal PET system where the (x,y,z) coordinates
in the detector crystals have no variance? that is, each coincidence event
contains two points where the connecting line passes through the source up
to round-off error

i tried to do this with the following:
# setup simple physics - turn off scattering - this is horribly inefficient
since it now requires 2 simultaneous PE at 511 keV to generate coincidence,
but i get about 5000 in 1M primaries
/gate/physics/addProcess PhotoElectric
/gate/physics/processes/PhotoElectric/setModel StandardModel
#/gate/physics/addProcess Compton
#/gate/physics/processes/Compton/setModel StandardModel
#/gate/physics/addProcess RayleighScattering
#/gate/physics/processes/RayleighScattering/setModel PenelopeModel
/gate/physics/addProcess ElectronIonisation
/gate/physics/processes/ElectronIonisation/setModel StandardModel e-
/gate/physics/processes/ElectronIonisation/setModel StandardModel e+
/gate/physics/processList Enabled
/gate/physics/processList Initialized

#disable adder and blurring
#/gate/digitizer/Singles/insert adder
/gate/digitizer/Singles/insert readout
/gate/digitizer/Singles/readout/setDepth 1
#/gate/digitizer/Singles/insert blurring
#/gate/digitizer/Singles/blurring/setResolution 0.01
#/gate/digitizer/Singles/blurring/setEnergyOfReference 511. keV
/gate/digitizer/Singles/insert thresholder
/gate/digitizer/Singles/thresholder/setThreshold 350. keV
/gate/digitizer/Singles/insert upholder
/gate/digitizer/Singles/upholder/setUphold 650. keV
/gate/digitizer/Coincidences/setWindow 10. ns
/gate/digitizer/Coincidences/minSectorDifference 1
/gate/digitizer/name delay
/gate/digitizer/insert coincidenceSorter
/gate/digitizer/delay/setWindow 10. ns
/gate/digitizer/delay/setOffset 500. ns

source is backtoback gamma 0.511 MeV at 0 0 0

If I look at the coincidence events (globalPosX1, etc.), I was hoping the
LORs would all go through the origin.
the mean of all the intercepts is close to 0, but there is a residual 0.2
mm PSF.
Can anyone tell me where this is coming from? something in the digitizer?

mlewis
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