1. GATE ( G eant4A pplication forT omographicE mission): 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 vivophysiologic analysis

• Spatial distribution (andevolution! ) of radio nuclides in the body (pharmacokinetics, metabolism)We see the organduring its activity

• Quantitative analysis (concentrations)

PET:

• Biological moleculestaggedwith radioactive isotopes withshortlife-time( 15 O T 1/2 ~2 min,11 C 20 min)

• Resolution down to a few mm 3

SPECT:

• Longer decay times( 99m Tc 6 h,123 I 13 h ,133 Xe 5 d)

• • no need for accelerator facilities

• Poorer sensitivity (and resolution)

Multimodality

• Due to low resolutionrecently often associated to other modalities of scanning (MRI, CT)

3. Simulations in Nuclear Medicine

Wide rangeof applications

• scanner design, image reconstruction, scatter correction, protocol optimization,

Analyticalcomputations

Since a couple of decades: accurateMonte Carlo simulationsare widely usedin parallelto 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)

4. Two approaches

Dedicatedsimulation programs (PETsim, SimSET, Eidolon, )

• Simple geometry, limited number of requirements

• Fast development

• Optimized on application

• Limits in the physics description

• Maintenance, upgrades?

General purposesimulation codes (Geant4, EGS4, MCNP)

• Wide community of developers and users

• code and physics validation

• documentation and support

• Complexity

• Speed

GATE 5. GATE

Based onGeant4

• Physicsdescription

• Long termavailability

• Upgrades ,documentation&support

• Object Oriented Analysis & Design

Extensionsto build a simulation platform forPET/SPECT

• Ease of usefor non C++ programmers

• • scripting almost everywhere, geometry included

• Typical Nuclear Medicine optionsincluded

• • material database, sources, readout,

AND MORE !

• Time management

• Movements

6. How it works

3 different layers

Developerlevel

• Frameworkandapplicationclasses

• C++ programming

Userlevel

• Simulationparameters

• • Geometry

• • Sources

• Scriptingonly

User Interface Application classes Framework Geant4 7. GATE detailed structure Geometry mgr Specific I/O Source scripting Source mgr Time mgr Analysis mgr I/O mgr Geometry scripting I/O choice scripting Specific source type Specific source Geant4 Specific analysis Analysis scripting Timing scripting Specific volume User Interface 8. Geometry scripting world D.StrulUni Lausanne Source Body Head Scanner Rsector Crystal LSO BGO 9. Geometry examples SPECT S. Staelens, Univ. Ghent PET Collimator detail 10. Source management

Multiple sources

• Controlled bysource manager

• Inserted viascripting

• Complex geometries: customizedGPS

Optimized decay

• Customized G4Radioactive Decay Module(RDM)

• PET-specificsources

An example:

• Dual isotope scan

• Simulation forindependent time frames

• • 0-2 and 14-16 min

11. Timing

Simulation time

• Aclockmodels the passing of time during experiments

• Theuserdefines the experiment timing

Time-dependent objects

• Updated when time changes

• Allows programming ofmovement, tracer kinetics...

0s 20s 40s 60s 12. Sensitive volumes and digitisation

Pre-programmedcomponents

• Sensitive detectors

• Trajectory analyser

Digitizer

• Linearsignal processing chain

• Modular : set-up via scripting

Hits Energy response Spatial response Centroid readout Threshold Electronics Digis 13. Data output

Pluggable output modules

• Multiple parallel output channels ROOT, ASCII

• Include features for real-time display

Output management ASCII ROOT Binary format GATE 14. Validation

SeveralSPECT/gamma cameraprojects

• Clermont-Ferrand

• Ghent

PETvalidation work to start soon

• Lausanne, .

D. Lazaro, LPC-IN2P3, Clermont-Ferrand IASAgamma camera 15. Toward parallel computation

Computation speed is essential

• Simple geometry

• But: voxels, huge number of events,

Projects

• LAN parallelisation

• Implementation on DATAGRID (W.I.P.)

Inputfile Data basefile Input file exploding Output file merging Grid-GATE output file Output result file GATE on the Grid Database file D. Lazaro, LPC-IN2P3, Clermont-Ferrand 16. OpenGATE collaboration

Shareddevelopment

• Optimal use of manpower and skills

• Long-termmaintenance and support

• Coordination of efforts

• Multipledevelopment 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

• Aspokesman

• Steering committee(one delegate/member)

• Technical meetings

17. Summary

On-going project

• Develop a versatilesimulation platformfor PET/SPECT

• Build a shared-developmentcollaboration

• Development and validationwork on their way

For more info

• http://www-iphe.unil.ch/~PET/research/gate/

The End