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GATE a simulation platform for nuclear medicine based on GEANT4

G eant4 A pplication for T omographic E mission. GATE a simulation platform for nuclear medicine based on GEANT4. D. Lazaro, V. Breton For the OpenGATE Collaboration. SPECT Single photon emitters ( 99m Tc  6 h) Resolution down to 7 mm Poor sensitivity. PET

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GATE a simulation platform for nuclear medicine based on GEANT4

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  1. Geant4 Application for Tomographic Emission GATEa simulation platform for nuclear medicine based on GEANT4 D. Lazaro, V. Breton For the OpenGATE Collaboration

  2. SPECT • Single photon emitters (99mTc  6 h) • Resolution down to 7 mm • Poor sensitivity • PET • Positron emitters (18FDG  2 h) • Resolution down to 2 mm • Multimodality • Combined imaging modalities (e.g PET/CT) • Resolution improved Imaging 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)

  3. Why simulations in Nuclear Medicine? ImageReconstruction Scannerdesign Simulation Dataanalysis Protocoloptimization Algorithmtesting Scattercorrection Quantificationrecovery

  4. 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. PET/SPECT dedicated tools GEANT4 core potentialities Simulation requirements GATE • 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

  6. GATE A generic simulation platform for PET/SPECT applications • 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. User interface Application classes Framework Geant4 GATE 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

  8. Scanner Source Body Head Rsector Crystal LSO BGO Geometry construction by scripting commands world • A specific mechanism has been developed to help the user construct easily a geometry • scripting commands • geometry = combination of geometric volumes, like ‘russian dolls’ D.Strul Uni Lausanne

  9. Multi-ring PET Triple-head gamma camera D. Strul IPHE Lausanne S. Staelens Uni Ghent Geometry examples of GATE applications

  10. 15O 11C Source 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

  11. Timing • 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. PHOTONS ELECTRONS Physical processes • Choices of processes via scripting commands: low energy, standard or inactive • Cut settings LE photoelectric effect Standard photoelectric effect LE Compton scattering Standard Compton scattering LE Rayleigh scattering Standard Gamma conversion LE Gamma conversion Standard Ionisation LE Ionisation StandardBremsstrahlung LEBremsstrahlung

  13. sensitivity (%) Relative difference (%) crystal thickness (mm) crystal thickness (mm) Photons: Standard or low energy processes ? NaI(Tl) crystal sensitivity : comparison between values computed with different versions of GEANT4 and NIST values

  14. Stopping power in NaI(Tl) in GEANT4 and NIST values Stopping power in water in GEANT4 and NIST values Relative difference (%) Relative difference (%) energy (keV) energy (keV) Electrons: Standard or low energy processes ?

  15. Sensitive detector / Digitizer Hits • Pre-programmed components • Sensitive detectors • Trajectory analyser • Digitizer • Linear signal processing chain • Modular: set-up via scripting Digis Energyresponse Spatialresponse Centroidreadout ThresholdElectronics

  16. Data 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. The 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. Current 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. PSPMT Lead shielding CsI(Tl) crystal array LEHR collimator source crystal array Validation of GATE against experiment • Simulation of a small animal imaging gamma camera • CsI(Tl) crystal array coupled to a PSPMT • Small animal imaging (study of new radiopharmaceuticals)

  20. Input file Input file exploding Database file Database file GATE on the GRID GATE output result file GRID-GATE output file Output file merging GATE deployment on DataGRID • 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. 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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