[Gate-users] Digitizer modules for Gamma-Cameras/SPECT
Träuble, Korbinian Linus
korbinian.traeuble at tum.de
Thu Sep 15 13:21:01 CEST 2022
Dear Dimitris,
Thanks for the explanation.
With my initial example, my count rates are too high, because I think quantum efficiency of the Photodetector and the crystal is not taken into account yet.
When I use the old energy blurring and insert crystal blurring on top but with just setCrystalQE set to 1.0 (no resolutionmin/max), I get circa 10% of the counts as without the module inserted.
Would for example
/gate/digitizer/Singles/insert crystalblurring
/gate/digitizer/Singles/crystalblurring/setCrystalResolutionMin 0.099
/gate/digitizer/Singles/crystalblurring/setCrystalResolutionMax 0.099
/gate/digitizer/Singles/crystalblurring/setCrystalQE 0.5
/gate/digitizer/Singles/crystalblurring/setCrystalEnergyOfReference 140.5 keV
be valid to implement a 9.9% energy blurring with a 50% QE? Or which modules would you suggest if I want to include the 9.9% energy blurring and QE of 50%?
Maybe my count rates were too low, because I was applying energy blurring twice (once with blurring and once with crystal blurring), and broadening the photo peak, so less hits are inside the energy window (?)
I’m using a mono energetic 140.5keV source since I was doing experiments on the real gamma camera with tc99m pertechnetate. The real gamma camera also used the 126 - 154 keV energy window. I compare the gate simulations with the measurements.
Cheers,
Korbinian
Am 15.09.2022 um 13:05 schrieb Dimitrios Thanasas <dthanas at uoa.gr<mailto:dthanas at uoa.gr>>:
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><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><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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