[Gate-users] PET Randoms high

[Hunor Kertesz]

Dear GATE users,

I am simulating the Siemens Biograph mMR system (based on these 
publications: Aklan et al 2015 
http://iopscience.iop.org/article/10.1088/0031-9155/60/12/4731/meta, 
Delso et al 2011  https://www.ncbi.nlm.nih.gov/pubmed/22080447), I am 
working on the count rate simulations as I mentioned in my previous 
e-mail.

The number of randoms I obtain is much higher. When I simulated an 
activity of 675 MBq (only 0.001 s for testing) using the scatter 
phantom. In the coincidence window I obtain: 17743 prompts (737 trues, 
16538 random, 468 scatter), delayed coincidence window: 18397, final 
coincidence window: 9010 prompts (212 trues, 8652 randoms, 146 scatter).

I ran some tests (0.01 s), changing the coincidence window from 5.9 ns 
(I obtained 179835 prompts(7333 trues, 167826 randoms, 4676 scatter)) to 
2.95 ns (123373 prompts (8217 trues, 109643 randoms, 5513 scatter)).

Can somebody give me a hint on what am I doing wrong or what is the 
issue?

My digitizer for the coincidence window is:

/gate/digitizer/Coincidences/setWindow 5.9 ns
/gate/digitizer/Coincidences/setOffset 0. ns
/gate/digitizer/Coincidences/MultiplesPolicy takeWinnerIfIsGood
/gate/digitizer/Coincidences/describe

/gate/digitizer/name delay
/gate/digitizer/insert coincidenceSorter
/gate/digitizer/delay/setWindow 5.9 ns
/gate/digitizer/delay/setOffset 50. ns
/gate/digitizer/delay/MultiplesPolicy takeWinnerIfIsGood
/gate/digitizer/delay/describe

/gate/digitizer/name finalCoinc
/gate/digitizer/insert coincidenceChain
/gate/digitizer/finalCoinc/addInputName delay
/gate/digitizer/finalCoinc/addInputName Coincidences
/gate/digitizer/finalCoinc/usePriority true

/gate/digitizer/finalCoinc/insert deadtime
/gate/digitizer/finalCoinc/deadtime/setDeadTime 100 ns
/gate/digitizer/finalCoinc/deadtime/setMode nonparalysable
/gate/digitizer/finalCoinc/describe

/gate/digitizer/finalCoinc/insert buffer
/gate/digitizer/finalCoinc/buffer/setBufferSize 64 B
/gate/digitizer/finalCoinc/buffer/setReadFrequency 12 MHz
/gate/digitizer/finalCoinc/buffer/setMode 1

Other parts of the digitizer:

/gate/distributions/name energy_distrib
/gate/distributions/insert Gaussian
/gate/distributions/energy_distrib/setMean 511 keV
/gate/distributions/energy_distrib/setSigma 1 keV
/gate/distributions/name dt_distrib
/gate/distributions/insert Exponential
/gate/distributions/dt_distrib/setLambda 7.57 us

/gate/digitizer/Singles/insert adder
/gate/digitizer/Singles/insert readout
/gate/digitizer/Singles/readout/setDepth 2

/gate/digitizer/Singles/insert timeResolution
/gate/digitizer/Singles/timeResolution/setTimeResolution 2.93 ns

/gate/digitizer/Singles/insert crystalblurring
/gate/digitizer/Singles/crystalblurring/setCrystalResolutionMin 0.15
/gate/digitizer/Singles/crystalblurring/setCrystalResolutionMax 0.35
/gate/digitizer/Singles/crystalblurring/setCrystalQE 0.80
/gate/digitizer/Singles/crystalblurring/setCrystalEnergyOfReference 511 
keV

/gate/digitizer/Singles/insert blurring
/gate/digitizer/Singles/blurring/setResolution 0.15
/gate/digitizer/Singles/blurring/setEnergyOfReference 511 keV

/gate/digitizer/Singles/insert deadtime
/gate/digitizer/Singles/deadtime/setDeadTime 355.0 ns
/gate/digitizer/Singles/deadtime/setMode nonparalysable
/gate/digitizer/Singles/deadtime/chooseDTVolume module

/gate/digitizer/Singles/insert noise
/gate/digitizer/Singles/noise/setDeltaTDistribution dt_distrib
/gate/digitizer/Singles/noise/setEnergyDistribution energy_distrib

Best regards,
Hunor