G.Santin (ESA-ESTEC & Trieste University) D.Strul, C.Morel (Lausanne University)

1. GATE(Geant4 Application for Tomographic Emission):a PET/SPECT general-purpose simulation platform G.Santin (ESA-ESTEC & Trieste University) D.Strul, C.Morel (Lausanne University) (for the OpenGATE Collaboration)

2. Imaging in Nuclear Medicine • Anatomical imaging • X-rays, MRI scanners, CAT, ultrasound • Detailed info about the tissue structure and composition • Functional imaging • In vivo physiologic analysis • Spatial distribution (and evolution!) of radio nuclides in the body (pharmacokinetics, metabolism)  We see the organ during its activity • Quantitative analysis (concentrations) • PET: • Biological molecules tagged with radioactive isotopes with short life-time (15OT1/2~2 min, 11C20 min) • Resolution down to a few mm3 • SPECT: • Longer decay times (99mTc6 h, 123I13 h , 133Xe5 d) • no need for accelerator facilities • Poorer sensitivity (and resolution) G.Santin GATE • Multimodality • Due to low resolution  recently often associated to other modalities of scanning (MRI, CT)

3. Simulations in Nuclear Medicine • Wide range of applications • scanner design, image reconstruction, scatter correction, protocol optimization,… • Analytical computations • Since a couple of decades: accurate Monte Carlo simulations are widely used in parallel to analytical computations or experimental studies for a large range of PET and SPECT applications • PETsim, SimSET, EIDOLON, SIMIND, SimSPECT, SORTEO, MCMATV, PET-EGS, … • Non exaustive list • Computation time • Is still a concern • ( see later) G.Santin GATE

4. Two approaches… • Dedicated simulation programs (PETsim, SimSET, Eidolon,… ) • Simple geometry, limited number of requirements • Fast development • Optimized on application • Limits in the physics description • Maintenance, upgrades? • General purpose simulation codes (Geant4, EGS4, MCNP) • Wide community of developers and users • code and physics validation • documentation and support • Complexity • Speed GATE G.Santin GATE

5. GATE • Based on Geant4 • Physics description • Long term availability • Upgrades, documentation & support • Object Oriented Analysis & Design • Extensions to build a simulation platform for PET/SPECT • Ease of use for non C++ programmers • scripting almost everywhere, geometry included… • Typical Nuclear Medicine options included • material database, sources, readout,… G.Santin GATE • AND MORE ! • Time management • Movements

6. How it works • 3 different layers • Developer level • Framework and application classes • C++ programming • User level • Simulation parameters • Geometry • Sources • … • Scripting only User Interface Application classes Framework G.Santin GATE Geant4

7. GATE detailed structure Analysis scripting Timing scripting I/O choice scripting Source scripting Specific source type Specific source Specific I/O Geometry scripting Specific analysis Time mgr Analysis mgr Source mgr Specific volume G.Santin GATE I/O mgr Geometry mgr Geant4 User Interface

8. Scanner Source Body Head Rsector Crystal LSO BGO Geometry scripting world G.Santin GATE D.Strul Uni Lausanne

9. Collimator detail Geometry examples PET SPECT S. Staelens, Univ. Ghent G.Santin GATE

10. 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 • An example: • Dual isotope scan • Simulation for independent time frames • 0-2 and 14-16 min G.Santin GATE

11. 0s 20s 40s 60s Timing • Simulation time • A clock models the passing of time during experiments • The user defines the experiment timing • Time-dependent objects • Updated when time changes • Allows programming of movement, tracer kinetics... G.Santin GATE

12. Sensitive volumes and digitisation • Pre-programmed components • Sensitive detectors • Trajectory analyser • Digitizer • Linear signal processing chain • Modular: set-up via scripting Hits Digis Energyresponse Spatialresponse Centroidreadout ThresholdElectronics G.Santin GATE

13. Data output • Pluggable output modules • Multiple parallel output channels ROOT, ASCII… • Include features for real-time display GATE G.Santin GATE Output management ASCII ROOT Binary format

14. IASA gamma camera D. Lazaro, LPC-IN2P3, Clermont-Ferrand Validation • Several SPECT/gamma camera projects • Clermont-Ferrand • Ghent • … • PET validation work to start soon • Lausanne, …. G.Santin GATE

15. Input file Input file exploding Data basefile Database file GATE on the Grid Output result file Grid-GATEoutput file Output file merging D. Lazaro, LPC-IN2P3, Clermont-Ferrand Toward parallel computation • Computation speed is essential • “Simple” geometry • But: voxels, huge number of events, … • Projects • LAN parallelisation • Implementation on DATAGRID (W.I.P.) G.Santin GATE

16. OpenGATE collaboration • Shared development • Optimal use of manpower and skills • Long-term maintenance and support • Coordination of efforts • Multiple development axes: tool implementation, validation, … • Current composition • 10 groups • Fields: SPECT, PET, PET • Application: design, validation • All members contribute • According to their interests and know-how • On a best-effort basis • Coordination • A spokesman • Steering committee (one delegate/member) • Technical meetings G.Santin GATE

17. Summary • On-going project • Develop a versatile simulation platform for PET/SPECT • Build a shared-development collaboration • Development and validation work on their way • For more info http://www-iphe.unil.ch/~PET/research/gate/ The End G.Santin GATE