[Gate-users] Noise module clarification

[Matthew Strugari]

Hi all,

I am in need of assistance with implementing the noise module in my digitizer for SPECT applications. I have attempted to implement this in the past with no success, but I have decided to give it another go. The lines below are implemented in my digitizer. Please inform me if you see any apparent issues because I cannot determine why I do not have any noise in my acquisitions.


/gate/distributions/name energy_distrib
/gate/distributions/insert File
/gate/distributions/energy_distrib/setUnitX keV
/gate/distributions/energy_distrib/setColumnX 0
/gate/distributions/energy_distrib/setColumnY 1
/gate/distributions/energy_distrib/setFileName NoiseSpectrum.txt # energy in first column, counts in second column
/gate/distributions/energy_distrib/read

/gate/distributions/name dt_distrib
/gate/distributions/insert Exponential
/gate/distributions/dt_distrib/setLambda 25.13 ms

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


An experimental 10 minute acquisition without a radioactive source produced the energy distribution below, which I have written to NoiseSpectrum.txt for import with energy_distrib. Importing the noise spectrum appears to be successful since I can getRandom values which appear to follow the distribution and provide units of keV. One question I have here is: do I need to specify units for column Y?
[Chart, histogram  Description automatically generated]

To configure my deltaT distribution, I calculated the time difference between subsequent background noise events and filled a histogram to verify the exponential relation. Is it correct to define lambda as the mean time difference (deltaT) between subsequent noise events, i.e. 0.025 s as indicated by the vertical line in the plot below? Configuration of the DeltaT distribution appears to be successful since I can also getRandom values which appear follow the distribution and provide units of ms.
[Chart, histogram  Description automatically generated]

To test the implemented noise module, a 10 minute simulation with a 0 MBq source does not produce any counts in the ROOT output, and a simulation with a negligible activity does not produce any counts with event_ID == -2. How can I implement noise in my projection data? Is there something that I am missing, or perhaps a bug? Could someone also please clarify the functionality of the noise module? How are noise events actually inserted into the ROOT output? It does not seem to be based on the start and stop times of a simulation but rather the events produced by source particles.

Regards,
Matthew

--
Matthew Strugari
PhD Candidate at Biomedical Translational Imaging Centre - BIOTIC,
5890 University Ave, Halifax, NS, B3K 6R8
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