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

Dimitrios Thanasas dthanas at uoa.gr
Thu Sep 15 13:05:53 CEST 2022 

Dear Korbinian,

Crystalblurring module is similar to (energy) blurring module.
It does not affect the count rate. It affects the energy spectrum as it is
the "error" of the energy of each photon detected by the system.
This means that a photon of 140.5 keV will be detected with
140.5+/-(0.15-0.35)*140.5 keV (randomly).
CrystalQE 0.9 means that the 90% of the detected photons are recorded by
the system so it downgrades your count rate.

I think it is easier to use blurring as you have at your initial example:
> /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
(a photon of 140.5 keV will be detected with 140.5+/-(0.099)*140.5 keV).

The "thresholder" module is one of the modules that affects your count rate
> /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

The above energies are more or less the photopeak of 99mTc.

What energies do you use in your simulation?

Best regards,
Dimitris



> Hi,
>
> Thank you very much for your reply!
> I’ve read your preprint and implemented the modules dead time and pileup.
>
> However, I’m having trouble implementing the „Efficiency" module.
> The closest module I could find in the docs was the crystal blurring
> module which has a setCrystalQE parameter.
>
> But I don’t really understand the module. I don’t understand what the
> setCrystalResolution and setCrystalEnergyOfReference parameters are for.
> I tried all kind of combinations by commenting out parts of the crystal
> blurring to compare the result. But all the time, the count rates were
> very low.
> Even when I put setCrystalQE to 1.0 (so 100%) and did not use the
> CrystalResolution parameters, the count rate was still maybe 10% what the
> count rate is without the crystal blurring module inserted.
>
> Can anybody help with this module or is there another Efficiency module in
> the digitizer?
>
> Cheers,
> Korbinian
>
> Code of the module:
> /gate/digitizer/Singles/insert crystalblurring
> /gate/digitizer/Singles/crystalblurring/setCrystalResolutionMin 0.15 #I
> don’t understand those parameters
> /gate/digitizer/Singles/crystalblurring/setCrystalResolutionMax 0.35 #I
> don’t understand those parameters
> /gate/digitizer/Singles/crystalblurring/setCrystalQE 0.9
> /gate/digitizer/Singles/crystalblurring/setCrystalEnergyOfReference 140.5
> keV #I don’t understand those parameters
>
>
> Am 07.09.2022 um 15:32 schrieb Matthew Strugari
> <matthew.strugari at dal.ca<mailto:matthew.strugari at dal.ca>>:
>
> 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<mailto: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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