Compton camera tutorial

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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?

Pedro Arce Introducción a GEANT4 7

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

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