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ppt

  1. 1. 1 GATEGATE a simulation platform for nucleara simulation platform for nuclear medicine based on GEANT4medicine based on GEANT4 D. Lazaro, V. Breton For the OpenGATE Collaboration GGeant4 AApplication for TTomographic EEmission
  2. 2. 2 Imaging in nuclear medicineImaging in nuclear medicine Two imaging modalities:  morphological imaging (MRI, scanner, X-rays…) detailed informations about the patient anatomy  Functional imaging (scintigraphic imaging: SPECT, PET) non-invasive method: a radioactive drug is injected to the patient and naturally evacuated from the organism spatial distribution of the radiopharmaceutical in the body  study of the functional activity of an organ or a specific tissue (e.g tumor)PETPET  Positron emitters (18 FDG ≈ 2 h)  Resolution down to 2 mm SPECTSPECT  Single photon emitters (99m Tc ≈ 6 h)  Resolution down to 7 mm  Poor sensitivityMultimodalityMultimodality  Combined imaging modalities (e.g PET/CT)  Resolution improved
  3. 3. 3 Why simulations in NuclearWhy simulations in Nuclear Medicine?Medicine? Scanner design Protocol optimization Algorithm testing Scatter correction Quantification recovery Data analysis Image Reconstruction Simulation
  4. 4. 4 Two approaches…Two approaches… General purpose simulation codes (GEANT4, EGS4, MCNP…)  wide range of physics  wide community of developers and users  documentation, maintenance and support  complexity  speed Dedicated simulation codes (PETsim, SimSET, Eidolon,…)  optimized for nuclear medical imaging applications (geometry, physics...)  ease of use and fast development  maintenance, upgrades
  5. 5. 5 Simulation requirementsSimulation requirements Realistic modelisation of PET/SPECT experiments  modelisation of detectors, sources, patient  movement (detector, patient)  time-dependent processes (radioactive decay, movement management, biological kinetics) Ease-of-use Fast Long-term availability, support and training PET/SPECT dedicated tools GEANT4 core potentialities GATEGATE
  6. 6. 6 GATEGATE A generic simulation platform for PET/SPECTA generic simulation platform for PET/SPECT applicationsapplications Based on GEANT4  object Oriented Analysis & Design  wide range of physics models  long term availability  upgrades, documentation & support Specific developments regarding to Nuclear medical imaging needs  material database, sources, readout  time and movement management Ease-of-use for non C++ programmers  scripting commands to define all paramaters of the simulation (construction of the geometry, specification of the physical processes involved, of the sources...)
  7. 7. 7 GATE structureGATE structure 3 different levels GEANT4 core Developer level  framework and application classes  C++ programming User level  sequence of scripting commands  geometry construction  physical processes involved  sources (geometry, activity)  movement (type, speed…)  duration of the acquisition User interface Application classes Framework Geant 4
  8. 8. 8 Geometry construction byGeometry construction by scripting commandsscripting commands A specific mechanism has been developed to help the user construct easily a geometry  scripting commands  geometry = combination of geometric volumes, like ‘russian dolls’ world Sourc e Body Head Scanner Rsector Crystal LSO BG O D.Strul Uni Lausanne
  9. 9. 9 Geometry examples of GATEGeometry examples of GATE applicationsapplications Multi-ring PET D. Strul IPHE Lausanne Triple-head gamma camera S. Staelens Uni Ghent
  10. 10. 10 Source managementSource management Multiple sources  controlled by source manager  inserted via scripting  complex geometries: customized GPS Optimized decay  customized G4 Radioactive Decay Module (RDM)  PET-specific sources 15 O 11 C
  11. 11. 11 TimingTiming Simulation time – a clock models the passing of time during experiments – the user defines the experiment timing Time-dependant objects – updated when time changes – allows programming of movement, tracer kinetics...
  12. 12. 12 Physical processesPhysical processes PHOTONS ELECTRON S Standard photoelectric effect LE Compton scattering Standard Gamma conversion Standard Ionisation Standard Bremsstrahlung LE photoelectric effect Standard Compton scattering LE Rayleigh scattering LE Gamma conversion LE Ionisation LE Bremsstrahlung Choices of processes via scripting commands: low energy, standard or inactive Cut settings
  13. 13. 13 Photons:Photons: Standard or low energy processes ?Standard or low energy processes ? NaI(Tl) crystal sensitivity : comparison between values computed with different versions of GEANT4 and NIST values 0 2 4 6 8 10 12 14 0 1 2 3 4 5 6 7 8 9 10 11 (NIST - G4.2.0 std)/NIST (NIST - G4.2.0 low)/NIST (NIST - G4.4.0 std)/NIST (NIST - G4.4.0 low)/NIST (NIST - GEANT3)/NIST crystal thickness (mm) Relativedifference(%)30 40 50 60 70 80 90 100 0 1 2 3 4 5 6 7 8 9 10 11 GEANT4.2.0 std GEANT4.2.0 low E GEANT4.4.0 std GEANT4.4.0 low E GEANT3 XCOM (NIST) sensitivity(%) crystal thickness (mm)
  14. 14. 14 Electrons:Electrons: Standard or low energy processes ?Standard or low energy processes ? 0 2 4 6 8 10 12 14 16 18 20 0 20 40 60 80 100 120 140 160 (NIST-Geant4.2.0 Std)/NIST (NIST-Geant4.2.0 LowE)/NIST (NIST-Geant4.4.0 Std)/NIST (NIST-Geant4.4.0 LowE)/NIST energy (keV) Relativedifference(%) Stopping power in NaI(Tl) in GEANT4 and NIST values 0 2 4 6 8 10 12 14 0 20 40 60 80 100 120 140 160 (NIST-Geant4.2.0 Std)/NIST (NIST-Geant4.2.0 LowE)/NIST (NIST-Geant4.4.0 Std)/NIST (NIST-Geant4.4.0 LowE)/NIST energy (keV) Relativedifference(%) Stopping power in water in GEANT4 and NIST values
  15. 15. 15 Sensitive detector / DigitizerSensitive detector / Digitizer Hits Digis Energy response Spatial response Centroid readout Threshold Electronics  Pre-programmed components – Sensitive detectors – Trajectory analyser  Digitizer – Linear signal processing chain – Modular: set-up via scripting
  16. 16. 16 Data outputData output Multiple parallel output channels:  ROOT (real-time display, storage in ROOT files for further analysis)  ASCII files  Binary files  Specific scanner formats (e.g Crystal Clear LMF…) GATE simulation Sinogram Reconstructed image
  17. 17. 17 The OpenGATE CollaborationThe OpenGATE Collaboration GATE under development since Autumn 2001 Objectives of the collaboration Develop a reliable generic simulation platform for nuclear medicine  shared development  share results and know-how  allow multiple work axes: development, validation… Current status: 10 groups Fields: planar scintigraphy, SPECT, PET, microPET Organization  Steering committee (one representative / group)  Technical meeting every two months
  18. 18. 18 Current efforts of developmentCurrent efforts of development Improvement of the detection models Use of voxelised geometries (sources): under development Validation work, against experimental data  Small animal imaging gamma camera (LPC – IASA Athens)  Dual-headed gamma camera (University of Ghent) Strategies to improve computation speed  Parallel computation  Use of computing grids
  19. 19. 19 Validation of GATEValidation of GATE against experimentagainst experiment  Simulation of a small animal imaging gamma camera – CsI(Tl) crystal array coupled to a PSPMT – Small animal imaging (study of new radiopharmaceuticals) Lead shielding PSPMT LEHR collimator source CsI(Tl) crystal array crystal array
  20. 20. 20 GATE deploymentGATE deployment on DataGRIDon DataGRID Input file Database file Input file exploding Output file merging GRID- GATE output file GATE output result file GATE on the GRID Databas e file Computation speed becomes (too!) large in case of  voxelised geometry  huge number of events Potential solution under study at LPC: deployment of GATE on DataGRID (first tests successful in July 2001)
  21. 21. 21 For more informations…For more informations… GATE web site http://www-iphe.unil.ch/~PET/research/gate/ Technical Coordinator: Daniel Strul, IPHE Lausanne daniel.strul@iphe.unil.ch Spokesman: Christian Morel, IPHE Lausanne christian.morel@iphe.unil.ch

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