Compton camera tutorial
Pedro Arce
GAMOS tutorial
Compton Camera
Exercises
http://fismed.ciemat.es/GAMOS
Introducción a GEANT4 1
Compton Camera Simulation Exercises
Ex. 1: Define Compton camera geometry
Ex. 2: Obtain information about what is happening in the simulation
Ex. 3: Apply Detector effects
The exercises are sequential
Use the commands of the previous exercise (only change what is indicated)
Pedro Arce Introducción a GEANT4 2
Compon Camera Exercise 1a: Compton geometry
Scatterer: 0.5 cm X 0.5 cm X 1 cm Si crystal
Absorber: 0.5 cm X 0.5 cm X 2 cm CZT crystal
12 x 12 crystals in 1 block in each ring
2 cm separation between scatterer ring and absorber ring
Source of 141 keV photons at (0,0,0) towards the X axis, 5 cm from scatterer ring
Pedro Arce Introducción a GEANT4 3
Compton Camera Exercise 1b: use gamma source in water
Place gamma source homogeneously distributed in a water sphere
Activity: 1 milliCurie
Energy: 141 keV
Pedro Arce Introducción a GEANT4 4
Compton Camera Exercise 2a: obtain information
Make info about the physics processes that occur
Make the crystal sensitive detector and produce signals
(hits)
Obtain histograms about hits quantities (energy, position, …)
Get detailed info about Compton and Photoelectric effect in crystals
Pedro Arce Introducción a GEANT4 5
Compton Camera Exercise 2b: standard physics
Use GEANT4 standard electromagnetic package, instead of low energy electromagnetic package
Observe differences in energy distribution
Observe differences in processes occurring
Observe differences in CPU time
Pedro Arce Introducción a GEANT4 6
Compton Camera Exercise 2c: Classify events as Compton Imaging events
A Compton imaging event is defined as one that has at least one signal in at least one scatterer crystal and one absorber crystal, with a summed energy approximately equal to the source energy
Classification is done looking at the reconstructed hits
Define a RecHitBuilder that builds hits for each crystal and defines the position as the centre of the pixel
Count % of Compton imaging events
How many are true single single events?
How many have more than 2 reconstructed hits?
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Compton Camera Exercise 3a: Energy resolution
Set the photopeak energy gate as 1%
Observe differences in number of Compton imaging events
Pedro Arce Introducción a GEANT4 8
Compton Camera Exercise 3ai: Energy resolution
Set the photopeak energy gate as 1%
Set the scatterer detector energy resolution as 1%
Observe differences in number of Compton imaging events
Observe differences in hits energy
Pedro Arce Introducción a GEANT4 9
Compton Camera Exercise 3aii: Energy resolution
Set the photopeak energy gate as 1%
Set the absorber detector energy resolution as 5%
Observe differences in number of Compton imaging events
Observe differences in hits energy
Pedro Arce Introducción a GEANT4 10
Compton Camera Exercise 3aiii: Energy resolution
Set the photopeak energy gate as 1%
Set the scatterer detector energy resolution as 1% AND the absorber detector energy resolution as 5%
Observe differences in number of Compton imaging events
Observe differences in hits energy
Pedro Arce Introducción a GEANT4 11
Compton Camera Exercise 3bi: Dead time
Set the dead time of scatter detector crystals as 1 microseconds
When a crystal takes signal, the full 12x12 crystal array becomes dead for a time
Observe differences in number of Compton imaging events
Pedro Arce Introducción a GEANT4 12
Compton Camera Exercise 3bii: Dead time
Set the dead time of absorber detector crystals as 1 microseconds
When a crystal takes signal, the full 12x12 crystal array becomes dead for a time
Observe differences in number of Compton imaging events
Pedro Arce Introducción a GEANT4 13
Compton Camera Exercise 3biii: Dead time
Set the dead time of scatterer and absorber detector crystals as 1 microseconds
When a crystal takes signal, the full 12x12 becomes dead for a time
Observe differences in number of Compton imaging events
Pedro Arce Introducción a GEANT4 14
Compton Camera Exercise 3ci:
Measuring time
Set the measuring time of the scatterer detector crystals as 1 microseconds
Two signals in a crystal cannot be distinguised if they differe less than a given amount
Observe differences in number of Compton imaging events
Pedro Arce Introducción a GEANT4 15
Compton Camera Exercise 3cii:
Measuring time
Set the measuring time of the absorber detector crystals as 1 microseconds
Two signals in a crystal cannot be distinguised if they differe less than a given amount
Observe differences in number of Compton imaging events
Pedro Arce Introducción a GEANT4 16
Compton Camera Exercise 3cii:
Measuring time
Set the measuring time of the scatterer and absorber detector crystals as 1 microseconds
Two signals in a crystal cannot be distinguised if they differe less than a given amount
Observe differences in number of Compton imaging events
Pedro Arce Introducción a GEANT4 17
Compton Camera Exercise 2c: Using events with multiple interactions
Compton imaging is done on 2 detector events, so when there are multiple interactions within a detector event it is necessary to identify the position and energy of the interaction of interest, to reduce to one interaction in each detector
This can be achieved via “Identifying Compton
Interactions” using various algorithms
It may be appropriate to use the interaction energy, position or separations to identify the 1st interaction.
Pedro Arce Introducción a GEANT4 18
Compton Camera Exercise 3a: Using events with multiple interactions
Set the ComptonRecHitDist for the scatterer and absorber to 0 mm.
/gamos/setParam CC:EvtClass:ComptRecHitDistScat 0.*mm
/gamos/setParam CC:EvtClass:ComptRecHitDistAbs 0.*mm
Use the NM1stHitByEnergy Algorithm
Only single/singles will be identified
Write out singles using
/gamos/setParam CC:EvtClass:DumpSingles 1
/gamos/setParam CC:EvtClass:DumpMultiples 0
Observe number of Compton imaging events
Pedro Arce Introducción a GEANT4 19
Compton Camera Exercise 3b: Using events with multiple interactions
Set the ComptonRecHitDist for the scatterer to 6 mm and absorber to 0 mm.
/gamos/setParam CC:EvtClass:ComptRecHitDistScat 6.*mm
/gamos/setParam CC:EvtClass:ComptRecHitDistAbs 0.*mm
Use the NM1stHitByEnergy Algorithm
Only multiples/singles and singles/multiples will be identified
Write out only the multiples using
/gamos/setParam CC:EvtClass:DumpSingles 0
/gamos/setParam CC:EvtClass:DumpMultiples 1
Observe number of Compton imaging events
Pedro Arce Introducción a GEANT4 20
Compton Camera Exercise 3c: Using events with multiple interactions
Set the ComptonRecHitDist for the scatterer to 0 mm and absorber to 6 mm.
/gamos/setParam CC:EvtClass:ComptRecHitDistScat 0.*mm
/gamos/setParam CC:EvtClass:ComptRecHitDistAbs 6.*mm
Use the NM1stHitByEnergy Algorithm
Only singles/multiples and singles/multiples will be identified
Write out only the multiples using
/gamos/setParam CC:EvtClass:DumpSingles 0
/gamos/setParam CC:EvtClass:DumpMultiples 1
Observe number of Compton imaging events
Pedro Arce Introducción a GEANT4 21
Compton Camera Exercise 3d: Using events with multiple interactions
Set the ComptonRecHitDist for the scatterer to 6 mm and absorber to 6 mm.
/gamos/setParam CC:EvtClass:ComptRecHitDistScat 6.*mm
/gamos/setParam CC:EvtClass:ComptRecHitDistAbs 6.*mm
Use the NM1stHitByEnergy Algorithm
Multiples/multiples, singles/multiples, multiples/singles and singles/multiples will be identified
Write out only the multiples using
/gamos/setParam CC:EvtClass:DumpSingles 0
/gamos/setParam CC:EvtClass:DumpMultiples 1
Observe number of Compton imaging events
Pedro Arce Introducción a GEANT4 22
Compton Camera Exercise 3d: Using events with multiple interactions
Set the ComptonRecHitDist for the scatterer to 0 mm and absorber to 6 mm.
/gamos/setParam CC:EvtClass:ComptRecHitDistScat 0.*mm
/gamos/setParam CC:EvtClass:ComptRecHitDistAbs 6.*mm
Use the NM1stHitByXYZPos Algorithm singles/multiples will be identified
Write out only the multiples using
/gamos/setParam CC:EvtClass:DumpSingles 0
/gamos/setParam CC:EvtClass:DumpMultiples 1
Observe number of Compton imaging events
Pedro Arce Introducción a GEANT4 23
