[Gate-users] Digitizer modules for Gamma-Cameras/SPECT

[Matthew Strugari]

Hi Korbinian,

You might be interested in talking a look at my preprint (https://assets.researchsquare.com/files/rs-1946160/v1_covered.pdf?c=1660749461) in which I validated a GATE model of a preclinical SPECT system. The examples you refer to are somewhat outdated and are not intended to be a thorough demonstration of a complete system. My preprint introduces the digitizer modules and methods I used for tuning the parameters to the best of my ability. For my study, count rates were matched with the efficiency, dead time, and pileup modules, and blurring parameters were set to yield simulation observables that matched measurement, i.e., simply setting the measured value for a blurring module may not produce an identical result in simulation, but that depends on the accuracy you desire.

You will need to explicitly define each digitizer module that you would like to use to obtain their effects. I would recommend starting with a simple working case and then build on one module at a time from there.

Best,
Matthew

On Sep 7, 2022, at 9:19 AM, Träuble, Korbinian Linus <korbinian.traeuble at tum.de> wrote:


CAUTION: The Sender of this email is not from within Dalhousie.
Dear all,

I’m having trouble understanding the digitizer modules for SPECT/gamma cameras. According to the SPECT examples I’ve found only the adder, readout, blurring, spblurring and thresholds modules are used.
But modules such as lightyield, transfer efficiency, quantum efficiency, crystal blurring are not yet taken into account in all of those examples.
Are the former already covered by the definition of the crystal material (in my case, NaI(Tl) crystal) and blurring (in my case 10% @ 140keV)?
Or do I need to define them additionally to the ones in my code to get realistic images?
Also I don’t really understand based on the documentation how to apply the digitizer modules which are not part of my code yet, because it always throws a segmentation violations error.

Based on my code the pictures look good qualitatively, but the count rates don’t match with real measurements.

Would be glad to get some feedback.

Cheers,
Korbinian


Code:

###CAMERA model
/gate/world/daughters/name SPECThead
/gate/world/daughters/insert box
/gate/SPECThead/geometry/setXLength             300 mm     #
/gate/SPECThead/geometry/setYLength             76.5 mm
/gate/SPECThead/geometry/setZLength             300 mm     #
/gate/SPECThead/placement/setTranslation        0 -20 0 mm
/gate/SPECThead/setMaterial                     Air

/gate/SPECThead/daughters/name crystal
/gate/SPECThead/daughters/insert box
/gate/crystal/geometry/setXLength             230 mm
/gate/crystal/geometry/setYLength             6.5   mm
/gate/crystal/geometry/setZLength             210 mm
/gate/crystal/placement/setTranslation        0. -6. 0. mm
/gate/crystal/setMaterial                     NaITl

/control/execute mac/Collimator/collimator_for_{isotope}/hexagon_clinicV2.mac



###DIGITIZER
/gate/digitizer/Singles/insert adder

/gate/digitizer/Singles/insert readout
#/gate/digitizer/Singles/readout/setPolicy TakeEnergyCentroid #this does not work somehow, but I thought might be better bcs my camera uses PMTs
/gate/digitizer/Singles/readout/setDepth 1

/gate/digitizer/Singles/insert blurring
/gate/digitizer/Singles/blurring/setLaw inverseSquare
/gate/digitizer/Singles/blurring/inverseSquare/setResolution 0.099
/gate/digitizer/Singles/blurring/inverseSquare/setEnergyOfReference 140.5 keV

#spatialblurring
/gate/digitizer/Singles/insert spblurring
/gate/digitizer/Singles/spblurring/setSpresolution 3.2 mm
/gate/digitizer/Singles/spblurring/verbose 0

/gate/digitizer/Singles/insert thresholder
/gate/digitizer/Singles/thresholder/setThreshold 126.45 keV
/gate/digitizer/Singles/insert upholder
/gate/digitizer/Singles/upholder/setUphold 154.55 keV
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