GAMOS tutorial PET Exercises Pedro Arce Dubois CIEMAT http://fismed.ciemat.es/GAMOS Pedro Arce Introducción a GEANT4

PET simulation Exercises Ex. 1: Define PET geometry Ex. 2: Obtain information about what is happening in a PET Ex. 3: Detector effects The exercises are sequential Use the commands of the previous exercise (only change what indicated Pedro Arce Introducción a GEANT4

PET Exercise 1a: PET geometry 2 cm X 2 cm X 10 cm LSO crystals LSO: Lu 76.4016%, Si 6.1328%, O 17.4656% Block of 8X8 crystals 20 blocks in a ring of radius 60 cm Pace 5 rings blocks along Z separated 10 cm Water sphere of radius 2 cm at the centre of the rings Source of 511 keV photons at (0,0,0) towards the X axis Pedro Arce Introducción a GEANT4

PET Exercise 1b: use F18 as source Place F18 homogeneously distributed in the water sphere Activity: 1 milliCurie Pedro Arce Introducción a GEANT4

PET 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

PET 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

PET Exercise 2c: Classify events as PET events A PET event is the one that has two signals of energy about 511 keV in the crystals Classification is done looking at the reconstructed hits Define a RecHitBuilder that sums all the energy of the crystals in a block of 8X8, and assign the position as the centre of the crystal with biggest energy Count % of PET events How many are false coincidences In how many the line joining the two crystals passes too far from the F18 positron creation Pedro Arce Introducción a GEANT4

PET Exercise 3a: Energy resolution Set crystal energy resolution as 20% Observe differences in hits energy Observe differences in number of PET events Pedro Arce Introducción a GEANT4

PET Exercise 3b: Dead time Set the dead time of crystals as 1 microseconds When a crystal takes signal, full block of 8X8 crystal becomes dead for a time Observe differences in number of PET events Pedro Arce Introducción a GEANT4

PET Exercise 3c: Measuring time Set the measuring time of 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 PET events Observe differences in recontructed hits Pedro Arce Introducción a GEANT4